Promoters exhibiting endothelial cell specificity and methods of using same

[0001] This application is a Continuation-In-Part of PCT/IL01/01059, filed Nov. 15, 2001 and published in English under PCT Article 21 (2), which claims priority from U.S. Provisional Patent Application No. 60/248,582, filed Nov. 17, 2000, the specifications of which are hereby incorporated by reference.

[0002] The present invention relates to isolated polynucleotide sequences exhibiting endothelial cell specific promoter activity, and methods of use thereof and, more particularly, to a modified-preproendothelin-1 (PPE-1) promoter which exhibits increased activity and specificity in endothelial cells. The invention further relates to modifications of the PPE promoter, which enhance its expression in response to physiological conditions including hypoxia and angiogenesis.

[0003] Angiogenesis, the process of formation of new blood vessels, plays an important role in physiological processes such as embryonic and postnatal development as well as in wound repair. Formation of blood vessels can also be induced by pathological processes involving inflammation (e.g., diabetic retinopathy and arthritis) or neoplasia (e.g., cancer) (Folkman, 1985, Perspect, Biol. Med., 29, 10).

[0004] Angiogenesis occurs under conditions of low oxygen concentration (ischemia and tumor metastases etc.) and thus may be an important environmental factor in neovascularization. The expression of several genes including erythropoietin, transferrin and its receptor, most of glucose transport and glycolytic pathway genes, LDH, PDGF-BB, endothelin-1 (ET-1), VEGF and VEGF receptors is induced under hypoxic conditions by the specific binding of the Hypoxia Inducible Factor (HIF-1) to the Hypoxic Response Element (HRE) regulating the transcription of these genes. Expression of these genes in response to hypoxic conditions enables the cell to function under low oxygen conditions.

[0005] The angiogenic process is regulated by angiogenic growth factors secreted by tumor or normal cells as well as the composition of the extracellular matrix and by the activity of endothelial enzymes (Nicosia and Ottinetti, 1990, Lab. Invest., 63, 115). During the initial stages of angiogenesis, endothelial cell sprouts appear through gaps in the basement membrane of pre-existing blood vessels (Nicosia and Ottinetti, 1990, supra; Schoefl, 1963, Virehous Arch, Pathol. Anat. 337, 97-141; Ausprunk and Folkman, 1977, Microvasc. Res. 14, 53-65; Paku and Paweletz, 1991, Lab Invest. 63, 334-346). As new vessels form, their basement membrane undergoes complex structural and compositional changes that are believed to affect the angiogenic response (Nicosia, et. al., 1994, Exp Biology. 164, 197-206).

[0006] Unbalanced angiogenesis typifies various pathological conditions and often sustains progression of the pathological state. For example, in solid tumors, vascular endothelial cells divide about 35 times more rapidly than those in normal tissues (Denekamp and Hobson, 1982 Br. J. Cancer 46:711-20). Such abnormal proliferation is necessary for tumor growth and metastasis (Folkman, 1986 Cancer Res. 46:467-73).

[0007] Vascular endothelial cell proliferation is also important in chronic inflammatory diseases such as rheumatoid arthritis, psoriasis and synovitis, where these cells proliferate in response to growth factors released within the inflammatory site (Brown & Weiss, 1988, Ann. Rheum. Dis. 47:881-5).

[0008] In atherosclerosis, formation of an arteriosclerotic plaque is triggered by a monoclonal expansion of endothelial cells in blood vessels (Alpern-Elran 1989, J. Neurosurg. 70:942-5). Furthermore, in diabetic retinopathy, blindness is thought to be caused by basement membrane changes in the eye, which stimulate uncontrolled angiogenesis and consumption of the retina (West and Kumar, 1988, Lancet 1:715-6).

[0009] Endothelial cells are also involved in graft rejection. In allograft rejection episodes, endothelial cells express pro-adhesive determinants that direct leukocyte traffic to the site of the graft. It is believed that the induction of leukocyte adhesion molecules on the endothelial cells in the graft may be induced by locally-released cytokines, as is known to occur in an inflammatory lesion.

[0010] Abrogated angiogenesis, on the other hand, is also a major factor in disease development, such as in atherosclerosis induced coronary artery blockage (e.g., angina pectoris), in necrotic damage following accidental injury or surgery, or in gastrointestinal lesions such as ulcers.

[0011] Hence, regulating or modifying the angiogenic process can have an important therapeutic role in limiting the contributions of this process to pathological progression of an underlying disease state as well as providing a valuable means of studying their etiology.

[0012] Recently a significant progress in the development of endothelial regulating agents, whether designed to be inhibitory or stimulatory, has been made. For example, administration of αFGF protein, within a collagen-coated matrix, placed in the peritoneal cavity of adult rats, resulted in a well vascularized and normally perfused structure (Thompson, et al., PNAS 86:7928-7932, 1989). Injection of βFGF protein into adult canine coronary arteries during coronary occlusion reportedly led to decreased myocardial dysfunction, smaller myocardial infarctions, and increased vascularity (Yanagisawa-Miwa, et al., Science 257:1401-1403, 1992). Similar results have been reported in animal models of myocardial ischemia using βFGF protein (Harada, et al., J Clin Invest 94:623-630, 1994, Unger, et al., Am J Physiol 266:H1588-H1595, 1994).

[0013] However, for mass formation of long lasting functional blood vessel there is a need for repeated or long term delivery of he above described protein factors, thus limiting their use in clinical settings. Furthermore, in addition to the high costs associated with the production of angiogenesis-regulating factors, efficient delivery of these factors requires the use of catheters to be placed in the coronary arteries, which further increases the expense and difficulty of treatment.

[0014] With the identification of new genes that regulate the angiogenic process, somatic gene therapy has been attempted to overcome these limitations. Although, great efforts have been directed towards developing methods for gene therapy of cancer, cardiovascular and peripheral vascular diseases, there is still major obstacles to effective and specific gene delivery. In general, the main limiting factor of gene therapy with a gene of interest using a recombinant viral vector as a shuttle is the ability to specifically direct the gene of interest to the target tissue. Indeed, non-specific gene targeting, results in systemic expression of the transgene which leads to several problems. For example, systemic expression of VEGF, a key regulator of the angiogenic process has been tested in animal models of ischemia and in clinical trials [Hammond, H. K. and McKirnan, M. D. Cardiovasc Res 49, 561-7. (2001); Gowdak, L. H. et al. Circulation 102, 565-71. (2000); Rosengart, T. K. et al. Ann. Surg. 230, 466-70; discussion 470-2. (1999). Simovic, D et al. Arch Neurol 58, 761-8. (2001)]. However, due to the systemic nature of expression, all modalities of treatment faced the problems of facilitated atherogenesis [Dulak J. (2001) J Am Coll Cardiol 38:2137-8 and Celletti F L et al. (2001) J Am Coll Cardiol 2126-30] and edema [Harrigan M R et al. (2002) Neurosurgery 50:589-598; Funatsu H et al. (2002) Am J Opthalmol 133:70-7; Thicket D R (2001) Am J Respir Crit Care Med 164:1601-5], vessel immaturity, hyper permeability and regression [Benjamin, L. E et al (1999) J Clin Invest 103:159-65; Alon, T et al. Nat Med 1:1024-8. (1995); Benjamin, L. E. et al. (1997) Proc Natl Acad Sci USA 94:8761-6].

[0015] Hence, regulation of the angiogenic process by targeted gene therapy to the vascular endothelium can be tremendously important in inducing efficient therapy for these diseases.

[0016] Several endothelial cell specific promoters have been described in the prior art. For example, Aird et al., [Proc. Natl. Acad. Sci. (1995) 92:7567-571] isolated 5′ and 3′ regulatory sequences of human von Willebrand factor gene that may confer tissue specific expression in-vivo. However, these sequences could mediate only a heterogeneous pattern of reporter transgene expression. Bacterial LacZ reporter gene placed under the regulation of von Willebrand regulatory elements in transgenic mice revealed transgene expression in a subpopulation of endothelial cells in the yolk sac and adult brain. However, no expression was detected in the vascular beds of the spleen, lung liver, kidney, heart, testes and aorta as well as in the thrombomodulin locus.

[0017] Korhonen J et al [Blood (1995) 96:1828-35] isolated the human and mouse TIE gene promoter which contributed to a homogeneous expression of a transgene throughout the vascular system of mouse embryos. However, expression in adult was limited to the vessels of the lung and kidney and no expression was detected in the heart brain, liver. Similar results were obtained by Schlaeger M et al. who isolated a 1.2 kb 5′ flanking region of the TIE-2 promoter, and showed transgene expression limited to endothelial cells of embryonic mice [Schlaeger T M et al. (1995) Development 121:1089-1098].

[0018] Thus, none of these sequences work uniformly in all endothelial cells of all developmental stages or in the adult animal. Furthermore, some of these sequences were not restricted to the endothelium.

[0019] U.S. Pat. No. 5,747,340 teaches use of the murine PPE-1 promoter and portions thereof. However, this patent contains no hint or suggestion that an endothelial-specific enhancer can be employed to increase the level of expression achieved with the PPE promoter while preserving endothelial specificity. Further, this patent does not teach that the PPE-1 promoter is induced to higher levels of transcription under hypoxic conditions.

[0020] An autonomous endothelial-specific enhancer in the first intron of the mouse TIE-2 gene was recently described. Combination of the TIE-2 promoter with an intron fragment containing this enhancer allowed it to target reporter gene expression specifically and uniformly to all vascular endothelial cells throughout embryogenesis and adulthood [Schlaeger T M (1997) Proc. Natl. Acad. Sci. 94:3058-3063]. Though, promising until today no expression of angiogenic transgenes have been described in conjugation with this regulatory element.

[0021] While reducing the present invention to practice, the present inventors have constructed and employed a novel configuration of the PPE-1 promoter which exhibits unexpected and highly specific activity in endothelial cells participating in angiogenesis.

[0022] Due to its capability to direct high expression of exogenous genes in an endothelial cell specific manner, the PPE-1 promoter of the present invention, which is designated as PPE-1-3× herein, enables regulating endothelial-specific processes. Thus, angiogenesis-regulating factors placed under the modified promoters of the present invention can serve as powerful in-vivo pro-angiogenic or anti-angiogenic tools in basic research and in clinical applications, such as of the cardiovascular system.

[0023] According to one aspect of the present invention there is provided an isolated polynucleotide functional as a promoter in eukaryotic cells. The isolated polynucleotide includes an enhancer element including at least two copies of the sequence set forth in SEQ ID NO:6.

[0024] According to another aspect of the present invention there is provided a method of expressing a nucleic acid sequence of interest, encoding an active RNA molecule or a protein such as an enzyme, reporter molecule and the like in endothelial cells. The method includes administering to a subject a construct, which includes the nucleic acid sequence of interest positioned under the regulatory control of a promoter functional in eukaryotic cells. The construct further includes an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:6.

[0025] According to yet another aspect of the present invention there is provided a method of regulating angiogenesis in a tissue. The method includes administering a nucleic acid construct including: (a) an endothelial cell specific promoter; (b) at least one copy of a hypoxia response element set forth in SEQ ID NO:5; and (c) a nucleic acid sequence encoding an angiogenesis regulator, the nucleic acid sequence being under regulatory control of the promoter and to the hypoxia response element.

[0026] According to still another aspect of the present invention there is provided an isolated polynucleotide functional as a promoter in eukaryotic cells. The isolated polynucleotide includes an enhancer element including the sequence set forth in SEQ ID NO: 7.

[0027] According to an additional aspect of the present invention there is provided a method of regulating angiogenesis in a tissue. The method includes administering a nucleic acid construct including: (a) an endothelial cell specific promoter; (b) an enhancer element including the sequence set forth in SEQ ID NO: 7; (c) at least one copy of a hypoxia response element set forth in SEQ ID NO:5; and (d) a nucleic acid sequence encoding an angiogenesis regulator, the nucleic acid sequence being under regulatory control of the promoter, the enhancer element and the hypoxia response element.

[0028] According to still a further aspect of the present invention there is provided isolated polynucleotide functional as a promoter in eukaryotic cells, the isolated polynucleotide includes an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:8.

[0029] According to still a further aspect of the present invention there is provided a method of expressing a nucleic acid sequence of interest in endothelial cells, the method includes administering to a subject a construct, the construct includes the nucleic acid sequence of interest positioned under the regulatory control of a promoter functional in eukaryotic cells, and an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:8.

[0030] According to still another further aspect of the present invention there is provided isolated polynucleotide functional as a promoter in eukaryotic cells, the isolated polynucleotide includes an enhancer element including the sequence set forth in SEQ ID NO: 8.

[0031] According to further features in preferred embodiments of the invention described below, the enhancer element includes three copies of the sequence set forth in SEQ ID NO:6.

[0032] According to still further features in preferred embodiments of the invention the at least two copies of the sequence set forth in SEQ ID NO:6 are contiguous.

[0033] According to still further features in preferred embodiments of the invention the isolated polynucleotide further includes an endothelial specific promoter element.

[0034] According to still further features in preferred embodiments of the invention the endothelial specific promoter element includes at least one copy of the PPE-1 promoter.

[0035] According to still further features in preferred embodiments of the invention the isolated polynucleotide further includes a hypoxia response element.

[0036] According to still further features in preferred embodiments of the invention the hypoxia response element includes at least one copy of the sequence set forth in SEQ ID NO: 5.

[0037] According to still further features in preferred embodiments of the invention the enhancer element is as set forth in SEQ ID NO: 7.

[0038] According to still further features in preferred embodiments of the invention there is provided a nucleic acid construct including a claimed isolated polynucleotide and a nucleic acid sequence of interest, the nucleic acid sequence of interest being under regulatory control of the isolated polynucleotide.

[0039] According to still further features in preferred embodiments of the invention the nucleic acid sequence of interest is selected from the group consisting of VEGF, p55 and PDGF-BB and other growth factors, proangiogenic factors or cytokines.

[0040] According to still further features in preferred embodiments of the invention there is provided a mammalian cell transformed with a claimed isolated polynucleotide.

[0041] According to still further features in preferred embodiments of the invention the promoter exhibits endothelial cell specificity.

[0042] According to still further features in preferred embodiments of the invention the promoter is the PPE-1 promoter as set forth in SEQ ID NO: 1.

[0043] According to still further features in preferred embodiments of the invention administering is effected by a method selected from the group consisting of: (i) systemic in-vivo administration; (ii) ex-vivo administration to cells removed from a body of a subject and subsequent reintroduction of the cells into the body of the subject; and (iii) local in-vivo administration.

[0044] According to still further features in preferred embodiments of the invention the nucleic acid construct further includes an enhancer element including at least two copies of the sequence set forth in SEQ ID NO:6.

[0045] According to still further features in preferred embodiments of the invention the endothelial cell specific promoter includes at least one copy of the PPE-1 promoter.

[0046] According to still further features in preferred embodiments of the invention there is provided a nucleic acid construct including a claimed isolated polynucleotide and a nucleic acid sequence of interest, the nucleic acid sequence of interest being under regulatory control of the isolated polynucleotide.

[0047] According to still further features in the described preferred embodiments the enhancer element further includes at least one copy of the sequence set forth in SEQ ID NO:6.

[0048] According to still further features in the described preferred embodiments the enhancer element includes one copy of the sequence set forth in SEQ ID NO:8 and at least two copies of the sequence set forth in SEQ ID NO:6.

[0049] According to still further features in the described preferred embodiments the enhancer element further includes at least one copy of the sequence set forth in SEQ ID NO:6.

[0050] According to still further features in the described preferred embodiments the at least one copy includes two copies.

[0051] According to still further features in the described preferred embodiments the nucleic acid construct further includes an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:8.

[0052] According to yet another further aspect of the present invention there is provided method of regulating angiogenesis in a tissue, the method comprising administering a nucleic acid construct including: (a) an endothelial cell specific promoter, (b) an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:8; and (c) a nucleic acid sequence encoding an angiogenesis regulator, the nucleic acid sequence being under regulatory control of the promoter and the enhancer element.

[0053] According to still further features in the described preferred embodiments the enhancer element further includes at least one copy of the sequence set forth in SEQ ID NO:6.

[0054] According to still further features in the described preferred embodiments the enhancer element includes one copy of the sequence set forth in SEQ ID NO:8 and at least two copies of the sequence set forth in SEQ ID NO:6.

[0055] The present invention successfully addresses the shortcomings of the presently known configurations by providing improved isolated polynucleotide sequences with endothelial cell specificity, and methods of use thereof. The improvements in the sequence make feasible methods of treating a variety of diseases, disorders and conditions which were previously considered infeasible. Specifically, the improvements relate to increased specificity to endothelial cells, increased levels of expression of a sequence of interest and enhanced induction by conditions including ischemia and angiogenesis.

[0106] The present invention is of an improved endothelial cell-specific promoter which can be employed to reliably direct high-level expression of a sequence of interest to endothelial cells and in particular endothelial cells participating in angiogenesis.

[0107] The principles and use of the present invention may be better understood with reference to the drawings and accompanying descriptions.

[0108] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the examples and drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0109] Although endothelial specific promoters have been previously described (e.g. U.S. Pat. No. 5,747,340) these promoters have typically been inefficient at directing expression to endothelial cells or have not been demonstrated as being specific to endothelial cells in-vivo.

[0110] Enhancer elements specific to endothelial cells have also been described. Bu et al. (J. Biol Chem. (1997) 272(19): 32613-32622) have demonstrated that three copies (3×) of the 1× enhancer element of PPE-1 (containing elements ETE-C, ETE-D, and ETE-E) endows promoter sequences with endothelial cell specificity in-vitro, however such specificity has not been demonstrated in-vivo.

[0111] As is well known in the art, in-vitro experiments cannot reliably predict in-vivo results. As such, the results presented by Bu et al., although suggestive of endothelial cell specificity, do not provide sufficient evidence as to the utility of 3× enhancer element in-vivo.

[0112] The lack of in-vivo studies also brings into question the endothelial cell specificity of the 3× enhancer element in whole organisms. Lack of tis data implies that therapeutic application of this element is questionable, because when employed in-vivo, and in particular when employed for regulating angiogenesis, it is imperative that expression of an angiogenesis regulator (e.g., cell toxin) be directed specifically to endothelial cells, preferably in a specific subset of endothelial cells which are involved in angiogenesis.

[0113] As is illustrated in the examples section which follows, the present inventors, through laborious experimentation, have provided, for the first time, conclusive evidence as to the in-vivo activity of the 3× enhancer element. Such evidence identifies the 3× element and its sequence derivatives (e.g., SEQ ID NO:7) as highly suitable for use in therapeutic applications.

[0114] In addition, in reducing tie present invention to practice, it was discovered that a novel configuration of the PPE-1 enhancer sequence of the present invention endows promoter sequences with an unexpected and highly specific activity in endothelial cells participating in angiogenesis.

[0115] Thus, according to one aspect of the present invention there is provided an isolated polynucleotide functional as an endothelial cell specific promoter in a mammal such as a human being.

[0116] The isolated polynucleotide includes an enhancer element including one or more copies of the sequence set forth in SEQ ID NO:6 and preferably one or more copies of the sequence set forth in SEQ ID NO:8, which as is illustrated in the Examples section which follows, plays an important role in regulating expression in endothelial cells participating in angiogenesis.

[0117] One specific and novel sequence configuration of an enhancer element utilizable by the present invention is illustrated in SEQ ID NO:7.

[0118] For purposes of this specification and the accompanying claims, the term “enhancer” refers to any polynucleotide sequence, which increases the transcriptional efficiency of a promoter.

[0119] According to some embodiments of the invention, the isolated polynucleotide includes contiguous copies of SEQ ID Nos:6 and/or 8. Such sequences are preferably positioned in a head-to-tail orientation, although, the enhancer element of the present invention can also include one or more copies of a specific portion of the sequence of SEQ ID NO:6 or 8, in an inverted orientation, e.g., by using sequences complementary to SEQ ID NO:6 or 8 in construction of the enhancer element.

[0120] Preferably the isolated polynucleotide further includes an endothelial cell-specific promoter sequence element. For purposes of this specification and the accompanying claims, the term “promoter” refers to any polynucleotide sequence capable of mediating RNA transcription of a downstream sequence of interest. The endothelial specific promoter element may include, for example, at least one copy of the PPE-1 promoter.

[0121] Preferably, the isolated polynucleotide further includes a hypoxia response element, for example at least one copy of the sequence set forth in SEQ ID NO: 5.

[0122] Thus, according to this aspect of the present invention, an endothelial cell specific promoter which includes various enhancer element configurations is provided.

[0123] It will be appreciated that the enhancer element sequences can be positioned within the promoter sequence used, upstream of the promoter, between the promoter and a downstream sequence of interest or within the sequence of interest (e.g., intron).

[0124] The isolated nucleic acid sequence of the present invention can be used to regulate gene expression in eukaryotic tissue, and in particular, in proliferating endothelial cells, for example endothelial cells involved in angiogenesis.

[0125] Thus, the isolated polynucleotide sequence of the present invention may be provided, in some cases, as part of a nucleic acid construct further including a nucleic acid sequence of interest which is positioned under the regulatory control of the isolated polynucleotide of the present invention. It will be appreciated that such a nucleic acid construct can further include any additional polynucleotide sequences such as for example, sequences encoding selection markers, origin of replication in bacteria, or sequences encoding reporter polypeptides. Such a nucleic acid construct is preferably configured for mammalian cell expression and can be of viral origin. Numerous examples of nucleic acid constructs suitable for mammalian expression are known in the art; the Examples section which follows provides further detail of several such constructs.

[0126] For purposes of this specification and the accompanying claims, the phrase “sequence of interests” refers to any polynucleotide sequence that has the capacity to be transcribed by an RNA polymerase. This definition includes coding sequences translatable into polypeptides, as well as sequence for antisense RNA, RNA which binds DNA, ribozymes and other molecular moieties which are not destined to undergo translation. Examples of nucleic acid sequence of interest which may be used by the construct according to the present invention are provided hereinbelow and in the Examples section which follows.

[0127] Examples presented hereinbelow illustrate that the improved endothelial cell specific promoters of the present invention can reliably direct expression of a reporter gene to endothelial tissue following systemic in-vivo administration. These examples further show, for the first time, that the isolated polynucleotide of the present invention can be used to preferentially express a reporter protein (GFP) in ischemic and/or angiogenic tissue, thus providing for the first time direct evidence as to the importance of the PPE-1 enhancer element and its derivative in therapeutic applications.

[0128] While use of a reporter protein, such as GFP, may have utility in detection of early stages of metastatic tumor growth, especially in animal models, or for non-invasive imaging of metastases (Yang, M. et al., Proc. Nat. Acad. of Sci. (2001) 27:2616-2621) such a use is only a small portion of the projected utility of the claimed invention. It is believed, for example, that AdPPE-1GFP can be used in a combination with AdPPE1tk, AdPPE-1p55 and/or other anti-angiogenic treatments, in order to follow and treat angiogenesis by a relatively non-invasive method.

[0129] Replacement of the GFP reporter gene with an apoptosis inducing factor (e.g. p55; GenBank accession M75866) in a construct of, for example AdPPE-1-3×-p55 is predicted to reliably target apoptosis to rapidly proliferating endothelial cells in angiogenic blood vessels of a growing tumor. Because such a vector may be administered systemically, it can be employed to effectively induce apoptosis in developing metastatic foci, without discovering the location of those foci. Such a use represents a significant improvement in comparison to prior art practice. By inducing apoptosis specifically in developing vasculature, it is feasible to eliminate angiogenesis.

[0130] An opposite approach may be used to re-vascularize tissue, for example in atherosclerotic patients or in patients that have suffered significant impairment of peripheral circulation as a result of disease or injury. In this case, a construct of the type AdPPE-1-3×-GF, where GF is a growth factor (e.g., cytokine) or modificants thereof (e.g., AdPPE-1-SEQ ID NO:7-GF), can be employed. Suitable growth factors for use in this context include, but are not limited to, VEGF (GenBank accession M95200) and rat PDGF-BB (GenBank accession; 99% identity to mus-AF162784) and EGR-1 (GenBank accession M22326) FGFs (including, but not limited to, GenBank accession XM 003306) and combinations thereof.

[0131] It will be appreciated that the use of more than one angiogenic factor may be preferable according to this aspect of the present invention to avoid problems of vessel immaturity and blood vessel regression which have been shown to be associated with administration of VEGF alone (for further details see Example 22 and 26 of the Examples section). Combined therapy can mimic the first stage of endothelial channel sprouting and subsequently recruitment of smooth muscle cells to stable the nascent vessels [Richardson D M et al. (2001) Nat. Biotechnol. 19-1029-1034]. Combined therapy according to this aspect of the present invention may be practiced by cloning the polynucleotides of interest on the same nucleic acid construct each of which being under the regulation of the isolated nucleic acid of the present invention. Alternatively, or preferably, each of the polynucleotides of interest may be separately cloned into the nucleic acid constructs of the present invention, thereby enabling a more tight regulation on the induced angiogenic process.

[0132] Incorporation of a hypoxia response element (e.g. SEQ D NO: 5) within the promoter sequence of the present invention can also be used with the present invention in order to further enhance expression selectivity to ischemic tissues, thus leading to neo-vascularization of selected tissues. As the blood supply improves, ischemia is relieved, the hypoxia response element ceases to be induced, GF levels decline and the neo-vascularization process is halted.

[0133] The promoter sequences generated according to the teachings of the present invention are particularly useful in regulating angiogenesis in a tissue. As illustrated in the Examples section which follows, the modified 3× (SEQ. ID. NO:7) containing promoter sequence of the present invention and the unmodified PPE-1 promoter are both expressed in metastatic foci of the LLC model. However example 22 clearly illustrates that the modified 3× sequence is specifically responsible for both a decrease in expression levels of the reporter gene in normal lung and a dramatic increase in expression of the reporter gene in metastatic foci. There is neither a hint nor a suggestion in the prior art that such a result could be achieved. Thus, use of a construct including the 3× element in a gene therapy context can be expected to maximize delivery to tumors while minimizing toxic effects on surrounding normal tissue. Significantly, this is true even if the surrounding tissue contains an endothelial component, as illustrated in FIG. 37. This is because, as demonstrated in Example 11, the 3× sequence greatly increases the level of expression in rapidly proliferating endothelial tissue, even in the context of the PPE-1 promoter.

[0134] For example, the p55 gene might be used in conjunction with a promoter of the present invention containing a hypoxia response element in order to specifically induce apoptosis in growing tumors. Such a strategy is deemed feasible because a growing tumor mass tends toward ischemia as tumor growth often exceeds the angiogenic capacity of the surrounding tissue. Other expressible cell toxins which can be used along with the promoter sequence of the present invention in order to specifically reduce a tumor mass include but are not limited to, other pro-apoptotic genes, the Herpes simplex thymidine kinase gene (HSV-tk; included in the pORF-HSV1tk expression vector available from InvivoGen, San Diego, Calif.) angiostatin (Genbank accession number X05199), endostatin (Genbank accession number M33272) and angiostatin-endostatin chimera (included in the pORF-HSV1tk expression vector available from InvivoGen, San Diego, Calif.).

[0135] Alternately, or additionally, angiostatin or endostatin genes might be used in conjunction with a promoter of the present invention in order to specifically block angiogenesis without inducing apoptosis.

[0136] Thus, according to alternate preferred embodiments, angiogenesis may be stimulated or blocked. This flexibility will allow varied uses of the invention including, but not limited to reduction of tumor mass and re-vascularization of atherosclerotic regions of the heart or neo-vascularization of peripheral tissues with an inadequate blood supply. One relevant clinical scenario is use of a promoter according to the present invention to generate new blood vessels to increase the blood supply in limbs of diabetic patients.

[0137] The nucleic acid construct according to the present invention can be administered to a subject (mammals, preferably humans) per se or in a pharmaceutical composition where it is mixed with suitable carriers or excipients.

[0138] As used herein a “pharmaceutical composition” refers to a preparation of one or more of the active ingredients described herein with other chemical components such as physiologically suitable carriers and excipients. The purpose of a pharmaceutical composition is to facilitate administration of a compound to an organism.

[0139] Herein the term “active ingredient” refers to the nucleic acid construct accountable for the biological effect.

[0140] Hereinafter, the phrases “physiologically acceptable carrier” and “pharmaceutically acceptable carrier” which may be interchangeably used refer to a carrier or a diluent that does not cause significant irritation to an organism and does not abrogate the biological activity and properties of the administered compound. An adjuvant is included under these phrases.

[0141] Herein the term “excipient” refers to an inert substance added to a pharmaceutical composition to further facilitate administration of an active ingredient. Examples, without limitation, of excipients include calcium carbonate, calcium phosphates various sugars and types of starch, cellulose derivatives, gelatin, vegetable oils and polyethylene glycols.

[0142] Techniques for formulation and administration of drugs may be found in “Remington's Pharmaceutical Sciences,” Mack Publishing Co., Easton, Pa., latest edition, which is incorporated herein by reference.

[0143] Pharmaceutical compositions of the present invention may be manufactured by processes well known in the art, e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or lyophilizing processes.

[0144] Pharmaceutical compositions for use in accordance with the present invention thus may be formulated in conventional manner using one or more physiologically acceptable carriers comprising excipients and auxiliaries, which facilitate processing of the active ingredients into preparations which, can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen.

[0145] For injection, the active ingredients of the pharmaceutical composition may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hank's solution, Ringer's solution, or physiological salt buffer. For transmucosal administration, penetrants appropriate to the barrier to be permeated are used in the formulations. Such penetrants are generally known in the art.

[0146] It will be appreciated that the isolated polynucleotide of the present invention has been isolated based on its capacity to promote or enhance transcription in eukaryotic cells of an endothelial lineage. Therefore a mammalian cell transformed with a claimed isolated polynucleotide is an additional embodiment of the invention. Numerous examples of such transformed cells are provided in examples recited herein below.

[0147] While the examples provided hereinbelow deal specifically with the use of the 3× sequence in conjunction with the PPE-1 promoter, it is anticipated that the enhancer sequence of the present invention will also exert its cell specific effect when used with other eukaryotic promoter sequences.

[0148] Such anticipation is based on prior art findings which show that enhancer elements are often portable, i.e., they can be transferred from one promoter sequence to another, unrelated, promoter sequence and still maintain activity. For examples, see D. Jones et al. (Dev. Biol. (1995) 171(1):60-72); N. S. Yew et al, (Mol. Ther. (2001) 4:75-820) and L. Wu. et al. (Gene Ther. (2001) 8;1416-26). Indeed, the earlier work of Bu et al. (J. Biol Chem. (1997) 272(19): 32613-32622) strongly suggests that enhancer elements related to those of the present invention, for example enhancers including SEQ ID NO: 6 may be used with constitutive promoters, for example the SV-40 promoter. As such, constructs containing, methods employing and isolated polynucleotides including a eukaryotic promoter modified to include the enhancer sequence of the present invention are well within the scope of the claimed invention.

[0149] Thus, it is postulated that a minimal configuration of an enhancer element according to the present invention is an isolated polynucleotide as set forth in SEQ ID NO:8. This enhancer is anticipated to function with a wide variety of promoters, including but not limited to endothelial specific promoters (e.g. PPE-1; SEQ ID NO.: 1) and constitutive promoters, for example viral promoters such as those derived from CMV and SV-40. This enhancer should be capable of imparting endothelial specificity to a wide variety of promoters. The enhancer element may be augmented, for example by addition of one or more copies of the sequence set forth in SEQ ID NO:6. These additional sequences may be added contiguously or non-contiguously to the sequence of SEQ ID NO.: 8.

[0150] The present invention further includes a method of expressing a nucleic acid sequence of interest in endothelial cells employing a construct which relies upon an enhancer element including at least one copy of the sequence set forth in SEQ ID NO:8 and a promoter to direct high level expression of the sequence of interest specifically to endothelial cells.

[0151] As used herein “ex-vivo administration to cells removed from a body of a subject and subsequent reintroduction of the cells into the body of the subject” specifically includes use of stem cells as described in (Lyden et al. (2001) Nature Medicine 7:1194-1201).

[0152] While adenoviruses are employed in the experiments described in examples presented hereinbelow, the construct of the present invention could be easily adapted by those of ordinary skill in the art to other viral delivery systems.

[0153] The viral vectors, containing the endothelial cell specific promoters, can also be used in combination with other approaches to enhance targeting of the viral vectors. Such approaches include short peptide ligands and/or bispecific or bifunctional molecule or diabodies (Nettelbeck et al. Molecular Therapy 3:882;2001).

[0154] Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

[0155] Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non-limiting fashion.

[0156] Generally, the nomenclature used herein and the laboratory procedures utilized in the present invention include molecular, biochemical, microbiological and recombinant DNA techniques. Such techniques are thoroughly explained in the literature. See, for example, “Molecular Cloning: A laboratory Manual” Sambrook et al., (1989); “Current Protocols in Molecular Biology” Volumes I-III Ausubel, R. M., ed. (1994); Ausubel et al., “Current Protocols in Molecular Biology”, John Wiley and Sons, Baltimore, Md. (1989); Perbal, “A Practical Guide to Molecular Cloning”, John Wiley & Sons, New York (1988); Watson et al., “Recombinant DNA”, Scientific American Books, New York; Birren et al. (eds) “Genome Analysis: A Laboratory Manual Series”, Vols. 1-4, Cold Spring Harbor Laboratory Press, New York (1998); methodologies set forth in U.S. Pat. Nos. 4,666,828; 4,683,202; 4,801,531; 5,192,659 and 5,272,057; “Cell Biology: A Laboratory Handbook”, Volumes I-III Cellis, J. E., ed. (1994); “Current Protocols in Immunology” Volumes I-III Coligan J. E., ed. (1994); Stites et al. (ads), “Basic and Clinical Immunology” (8th Edition), Appleton & Lange, Norwalk, Conn. (1994); Mishell and Shiigi (eds), “Selected Methods in Cellular Immunology”, W. H. Freeman and Co., New York (1980); available immunoassays are extensively described in the patent and scientific literature, see, for example, U.S. Pat. Nos. 3,791,932; 3,839,153; 3,850,752; 3,850,578; 3,853,987; 3,867,517; 3,879,262; 3,901,654; 3,935,074; 3,984,533; 3,996,345; 4,034,074; 4,098,876; 4,879,219; 5,011,771 and 5,281,521; “Oligonucleotide Synthesis” Gait, M. J., ed. (1984); “Nucleic Acid Hybridization” Hames, B. D., and Higgins S. J., eds. (1985); “Transcription and Translation” Hames, B. D., and Higgins S. J., eds. (1984); “Animal Cell Culture” Freshney, R. I., ed. (1986); “Immobilized Cells and Enzymes” IRL Press, (1986); “A Practical Guide to Molecular Cloning” Perbal, B., (1984) and “Methods in Enzymology” Vol. 1-317, Academic Press; “PCR Protocols: A Guide To Methods And Applications”, Academic Press, San Diego, Calif. (1990); Marshak et al., “Strategies for Protein Purification and Characterization—A Laboratory Course Manual” CSHL Press (1996); all of which are incorporated by reference as if fully set forth herein. Other general references are provided throughout this document. The procedures therein are believed to be well known in the art and are provided for the convenience of the reader. All the information contained therein is incorporated herein by reference.

[0157] Specifically, experiments conducted in conjunction with the examples recited hereinbelow employed the following methods and materials:

[0158] Cell Culture

[0159] Lewis Lung Carcinoma—(D122-96), Human Embryonic Kidney (293) and HeLa cells were grown in 4.5 gr/l DMEM, supplemented with 10% fetal calf serum (FCS), 50 U/ml penicillin, 50 μg/ml streptomycine and 2 mM glutamine (Biological industries, Beit-Haemek, Israel). Bovine Aortic Endothelial Cells—BAEC, Normal Skin Fibroblasts—NSF, HepG2 and Human Umbilical Endothelial Cells—HUVEC-304 (ATCC, USA) were grown in 1.0 gr/l DMEM (Biological industries, Beit-Haemek, Israel), supplemented with 5% FCS, 50 U/ml penicillin, 50 μg/ml streptomycine and 2 mM glutamine. The BAEC cells were supplemented with complete fibroblast growth factor (Sigma, St. Louis, Mo.). RINr1046-38 (RIN-38) were grown in 199 Earle's salts (5.5 mM glucose) medium supplemented with 5% FCS (Biological Industries, Beit-Haemek, Israel), 50U penicillin/ml, 50 μg streptomycine/ml and 2 mM glutamine.

[0160] “HepG2” as used herein refers to ATCC-HB-8065.

[0161] “HeLa” as used herein refers to ATCC-CCL-2.

[0162] “Human Bronchial Epithelial cells” and “B2B” as used herein refers to ATCC-CRL-9609.

[0163] “HUVEC” and “Human Umbilical Vein Endothelial Cells” as used herein refers to ATCC-CRL-1730.

[0164] “CHO” and “Chinese Hamster Ovary” as used herein refers to ΛTCC-61.

[0165] Hypoxia Induction

Twenty six hours post transfection or transduction cells were incubated in an isolated chamber which was washed for 30 minutes by a gas flow containing 0.5% O₂, 5% CO₂, balance by N₂. The isolated chamber was placed in humidified 5% C₂, 37° C. incubator.

[0166] Luciferase Activity in Cells and Tissues

[0167] To assay the PPE-1 promoter activity quantitatively in-vitro and in-vivo, a Luciferase gene expression system kit was employed (Promega Corp., Madison, Wis.). Forty eight hours post transfection or transduction the cells were washed and 200 μl lysis buffer was added for 15 minutes. Cells lysates were collected and centrifuged for 15 minutes (14,000 rpm) at 4° C. Subsequently, 10 μl of the supernatant was added to 50 μl Luciferase assay buffer. The activity was measured in Luminometer over a 20 second period.

[0168] To assay Luciferase activity in solid tissue a 20 mg sample was excised and homogenized in 1 ml of the homogenization solution and centrifuged for 15 minutes (14,000 rpm) at 4° C., and 10 ml of the supernatant were assayed for Luciferase activity, as described above. Results were expressed as Luciferase light units per 1 μg protein. Protein was measured using the Bradford assay with bovine serum albumin (BSA) as a standard.

[0169] GFP Activity In-Vitro and In-Vivo

[0170] To test GFP expression in-vitro, cells were washed twice with PBS and were fixed for 30 minutes with freshly made 4% paraformaldehyde in PBS. Following fixation, examination by fluorescent microscopy was conducted.

[0171] In order to test the cellular distribution of the delivered gene in-vivo, tissues were fixed in freshly made 4% paraformaldehyde in 0.1 M phosphate buffer for 6 hours at 4° C., soaked overnight in 30% sucrose at 4° C. and frozen in OCT compound (Sakura, USA). The tissue blocks were sliced by a cryostat at 10 μm thickness and observed directly under fluorescence microscopy (FITC filter).

[0172] Proliferating and Quiescent Cells

[0173] In order to compare the PPE-1 promoter activity in proliferating and quiescent BAEC, the cells were divided into two groups: 1. proliferating cells—growing and infecting in 10% FCS media. 2. quiescent cells—growing and infected in serum free media started in 72 hours prior to the transduction. All cells were grown in humidified incubator, 5% CO₂, 37° C.

[0174] Preparation of Recombinant Replication Deficient Adenoviruses

[0175] Several recombinant replication deficient adenoviruses (type 5) were constructed. An expression cassette including the murine preproendothelin-1 (PPE-1) promoter (SEQ ID NO:1) located upstream to the Luciferase gene (originated from pGL2-basic GenBank Accession number X65323) and the SV40 polyA site (originated from pGL2-basic GenBank Accession number X65323) was ligated into the BamHI restriction site of pPAC.p1pA (promoter-less construct). The GFP gene (originated from pEGFP, GenBank accession number AAB02572) was ligated to the PPE-1 promoter at the NotI restriction site. The replication deficient recombinant adenoviruses termed Ad5PPE-1Luc or Ad5PPE-1GFP were prepared by co-transfection of pPACPPE-1Luc or Ad5PPE-1GFP with adenovirus plasmid pJM17 as described by Becker, T. C. et al. (Methods Cell biol. 43, Roth M. (ed). New York, Academic Press, 1994, pp. 161-189) followed by harvest of recombinant virions.

[0176] Viruses were prepared for large-scale production. The viral stocks were stored at 4° C. at concentration of 10⁹-10¹² plaque-forming units/ml (pfu/ml). The viruses Ad5CMV-Luc and Ad5CMV-GFP (Quantum biotechnologies, Carlsbad, Canada) containing the cytomegalovirus (CMV) immediate early promoter (GenBank Accession number U47119) were prepared for large scale preparation as described for the PPE-1 viral vectors and were used as a non-tissue specific control.

[0177] Modifications of the PPE Promoter

[0178] The modified murine PPE-1 promoter was developed by inserting three copies of the positive transcription element discovered by Bu et al (J. Biol Chem. (1997) 272(19): 32613-32622) into the NheI restriction enzyme site located downstream (−286 bp) to the 43 base pairs endogenous positive element (−364 to −320 bp).

[0179] The enhancer fragment termed herein “3×” is a triplicate copy of an endogenous sequence element (nucleotide coordinates 407-452 of SEQ ID NO:1) present in the murine PPE-1 promoter. It has been previously shown that induction of PPE-1 promoter activity in vascular endothelial cells depends on the presence of this element Bu et al (J. Biol Chem. (1997) 272(19): 32613-32622). The 3× fragment was synthesized by using two complementary single stranded DNA strands 96 base pares in length (BioTechnology industries; Nes Tziona, Israel), (SEQ ID NO: 2 and 3). The two single stranded DNA fragment were annealed and filled using Klenow fragment (NEB); the resulting double stranded DNA was 145 base pairs long and included Nhe-1 restriction sites (SEQ ID NO: 4)

[0180] The 3× fragment was ligated into the murine PPE-1 promoter down stream of endogenous Nhe-1 site using T4 Ligase. The resulting construct was propagated in DH5α compatent cells and a large-scale plasmid preparation was produced using the maxi-prep Qiagene kit.

[0181] Wild Type PPE-1 Promoter

[0182] The PPE-1-Luciferase cassette (5249 bp) containing 1.4 kb of the murine preproendothelin-1 (PPE-1) promoter, the Luciferase gene with an SV40 polyA signal (GenBank Accession number X 65323) site and the fist intron of the murine ET-1 gene is originated from the pEL8 plasmid (8848 bp) used by Harats et al (J. Clin Inv. (1995) 95: 1335-1344). The PPE-1-Luciferase cassette was extracted from the pEL8 plasmid by using the BamHI restriction enzyme, following by extraction of the DNA fragment from a 1% agarose gel using an extraction kit (Qiagen, Hilden, Germany).

[0183] The Promoter-Less pPAC.plpA Plasmid

[0184] The promoter-less pPAC.p1pA plasmid (7594 bp) containing sequences of the adenovirus type 5 was originated from the pPACCMV.pLpA (8800 bp). The CMV promoter, the multiple cloning site and the SV40 polyadenylation site (1206 bp) were eliminated by NotI restriction enzyme. The fragmented DNA was extracted from 1% agarose gel. The linear plasmid (7594 bp) was filled-in by Klenow fragment and BamHI linker was ligated by rapid DNA ligation kit to both cohesive ends. The linear plasmid was re-ligated by T4 DNA ligase and transformed into DH5α competent cells, in order to amplify the pPAC.plpA with the BamHI restriction sites. The plasmid was prepared for large-scale preparation and purified by maxi prep DNA purification kit.

[0185] pPACPPE-1Luciferase Plasmid

[0186] The pPACPPE-1Luciferase plasmid was constructed by inserting the PPE-1-Luciferase cassette into the BamHI restriction site or the pPAC.plpA plasmid, by using T4 DNA ligase. The plasmid was subsequently used to transform DH5α competent cells. The plasmid (12843 bp) was prepared for large-scale preparation and purified by maxi prep DNA purification kit.

[0187] pPACPPE-1GFP Plasmid

[0188] The pPACPPE-1GFP plasmid was constructed by sub-cloning the GFP gene (originated from pEGFP, GenBank accession number AAB02572) downstream to the PPH-1 promoter into the NotI restriction site, by T4 DNA ligase.

[0189] The plasmid was subsequently used to transform DH5α competent cells. The plasmid (11,801 bp) was prepared for large-scale preparation and purified by maxi prep DNA purification kit.

[0190] pACPPE-13×Luciferase and pACPPE-13× GFP Plasmids

[0191] The pPACPPE-1-3×Luciferase and pPACPPE-1-3×GFP were constructed by inserting the PPE-1-3×Luc or PPE-1-3×GFP cassette digested by BamHI restriction enzyme from pEL8-3× (FIG. 26B) containing Luc or GFP into the BamHI restriction site of the pPAC.p1pA plasmid. pEL8-3× contains the modified murine PPE-1 promoter (1.55 kb) (red)—located between BamHI and NotI fat contains the triplicate endothelial specific enhancer 3× (as set forth in SEQ D NO.: 7) located between two NheI site. The promoter, the Luciferase or GFP gene, the SV40 poly A sites and the first intron of the endothelin-1 gene, all termed the PPE-1 modified promoter cassette was digested and extracted by BamHI restriction enzyme as described in materials and methods. The plasmids (12843 bp) were prepared for large-scale preparation and purified by maxi prep DNA purification kit.

[0192] In-vitro experiment, DNA transduction—Cells were plated in 24 or 96 well dishes 24 hours prior to transduction. Subconfluent cells were counted in a sample well. Thereafter, growth media was aspirated from each well, and the indicated viral vectors, at the indicated multiplicity of infection (MOI), were diluted in infection media (DMEM or RPMI 1640, 2% FBS) and added to the monolayers. Cells were incubated for 4 h at room temperature. Subsequently, complete medium was added, and the cells were incubated at 37° C., 5% CO₂ for 72 h.

[0193] Animals

[0194] All animal procedures were approved by the “Animal Care and Use Committee” of Sheba Medical Center, Tel-Hashomer.

[0195] Different mouse strains were used:

• • [0196] (i) Male, 3 months old, wild type C57BL/6 mice (Harlan farms, Jerusalem, Israel).
  • [0197] (ii) Male 3 month old BALB/C mice (Harlan farms, Jerusalem, Israel).
  • [0198] (iii) Male and female 6 month old ApoE gene deficient mice hybrids of C57BL/6×SJ129 mice (Plump A S. et al. Cell (1991) 71:343-353).
  • [0199] (iv) Male and female 3 month old over-expressing the Luciferase gene under the control of murine PPE-1 promoter (5.9 Kb), generated by Harats et al. (J. Clin. Inv. (1995) 95: 1335-1344).

[0200] All mice were grown in the Lipids and Atherosclerosis Research Institute.

[0201] Tissue Gene Expression in Normal Mice

[0202] To assay the efficiency and tissue specificity, 10¹⁰ pfu/ml of Ad5PPE1Luc or Ad5CMVLuc (as non-tissue-specific control), were suspended in 100 μl of physiological saline and injected into the tail vein of mice as described hereinabove. Luciferase activity was assayed 1, 5, 14, 30 and 90 days post-injection. To localize cellular distribution of the expressed reporter genes, Ad5PPE-1GFP or Ad5CMVGFP (10¹⁰ pfu/ml in 100 μl physiological saline) were injected into the tail vein of normal 3 month old, male C57BL/6 mice. GFP expression was detected five days post-injection. All mice appeared healthy and no toxicity or inflammation was noted in the liver or other tissue.

[0203] GFP Activity in Tissues

[0204] To test the cellular distribution of the delivered gene in-vivo, tissue samples from injected mice were fixed in freshly made 4% paraformaldehyde in 0.1 M phosphate buffer for 6 hours at 4° C., soaked overnight in 30% sucrose at 4° C. and frozen in OCT compound (Sakura, Calif., USA). The tissue blocks were sliced at 10 μm thickness and observed directly under fluorescence microscopy (FITC filter).

[0205] Tumor Implantation

[0206] Lewis Lung Carcinoma cells (LLC) were harvested with trypsin/EDTA, washed 3 times with PBS and counted with 0.1% trypan blue (Biological industries, Beit-Haemek, Israel) to assess their viability. In order to test the level of activity of the PPE-1 promoter activity in tumor angiogenesis in mice, two different tumor models were used.

[0207] In the primary tumor model, the cells (1×10⁶ cells/ml in 100 μl physiological saline) were subcutaneously injected to the mice backs (n=17). Twenty-one days post injection Ad5PPE-1, Ad5PPE-1GFP, Ad5CMV, or Ad5CMVGFP (10¹⁰ pfu/ml) were injected into the tumor tissue (IT) or intravenously and their activity was detected as described above.

[0208] In the metastatic tumor model, the cells (5×10⁵ cells/ml in 50 μl physiological saline) were injected to the mice foot-pad (n=12). When the tumor tissue reached a size of 0.7 mm in diameter, the foot pad (with the primary tumor) was resected under anaesthetic and sterile conditions. Fourteen days post surgery the viruses (Ad5PPE-1, Ad5PPE-1GFP, Ad5CMVLuc or Ad5CMVGFP) were injected to the mouse tail vein.

[0209] In both tumor experimental models mice were sacrificed 5 days post viral injection, their tissues were excised and tested for Luciferase or GFP activities.

[0210] Wound Healing Model

[0211] Male 3 month old C57BL/6 mice were anaesthetized by subcutaneous injection of sodium pentobarbital (6 mg/kg). Their backs were shaved and 5 cm of straight incisions was made. The incisions were immediately sutured by 4/0 sterile silk thread. The angiogenic process in the healing wound was examined every two days by H&E and anti von-Willibrand antibody immuno-histochemistry staining.
Ten days post incisions 10¹⁰ pfu/ml of Ad5PPE-1Luc or Ad5CMVLuc were systemically injected to the tail vein. Five days post injections the mice were sacrificed and Luciferase activity was assayed as described above in the skin of the incision site and in the normal contra lateral site as a control.

[0212] Histological examination—In order to evaluate the extent of angiogenesis in tumor and metastasized tissue, the tissues were sliced into 5 μm sections and stained with Haematoxylin and Eosin (H&E). Anti CD31 (rat anti mouse CD31 monoclonal Ab. Pharminogen, N.J., USA) antibodies were used for analyses of neo-vascularization in the tumor models.

[0213] Plasmids and adenoviral vectors for VEGF and PDGF-B transgenic expression—Recombinant replication-deficient adenoviruses serotype 5 were constructed as described in Varda-Bloom, N. et al. [Tissue-specific gene therapy directed to tumor angiogenesis. (2001) Gene Ther 8, 819-27]. Briefly, pACCMV.pLpA plasmid was modified to include either the cDNA for murine VEGF₁₆₅ (GenBank Accession number M95200) or rat PDGF-B (GenBank Accession number AF162784), under the regulation of the cytomegalovirus (CMV) immediate early promoter. The pACPPE-1-3× plasmids, in which the CMV promoter was replaced by the modified murine preproendothelin-1 (PPE-1-3×) promoter, were constructed with the same cDNA sequences. Each of the plasmids was co-transfected with pJM17 plasmid into HEK293 cells, to generate the various recombinant adenoviruses. The viruses were propagated in HEK293 cells and reduced to a concentration of 10¹⁰ PFUs/ml. Control vectors were generated similarly.

[0214] Mouse model of hind limb ischemia and gene therapy—Male and female C57B16 mice (Harlan Laboratories Ltd., Israel), at least 12 weeks of age, were maintained in accordance with guidelines of the Animal Care and Use Committee of Sheba Medical Center. Hind limb ischemia was induced based on previously described protocol [Couffinhal, T. et al. Mouse model of angiogenesis. Am J Pathol 152, 1667-79. (1998)], In brief, animals were anesthetized with pentobarbital sodium (40 mg/kg, IP). Following shaving of the limb fur the right femoral artery was ligated, proximal to the bifurcation of the saphenous and popliteal arteries. Five days following ligation, 10⁹ PFUs of the various adenoviral vectors were I.V. administrated.

[0215] Ultrasonic imaging—Ultrasonic imaging was performed at 7 days intervals following ligation using Synergy ultrasound system (General Electric, USA) at 7.5 MHz in angiographic mode. Animals were awake and restrained while imaging. Animals were accommodated under conventional conditions for up to 90 days.

[0216] Immunohistochemistry—Skeletal muscles from both hind limbs and liver tissue of sacrificed ischemic mice were frozen in OCT compound and cryo-sectioned. Endothelial cells were immunostained using rat monoclonal anti-CD31 antibodies (PharMingen, San Diego, Calif.). Smooth muscle cells were immunostained using mouse polyclonal anti-α-SMactin antibodies (SIGMA, St. Louis, Mo.). Background was stained with hematoxylin,

[0217] In-situ hybridization—5 μm skeletal muscle sections were prepared from both hind limbs of ischemic animals. In-situ hybridization with either sense or antisense DIG-labeled probes to VEGF₁₆₅ or PDGF-B was performed, and digoxigenin (DIG) was detected by anti-DIG-AP conjugate (Roche Molecular Biochemicals, Mannheim, Germany). Background was stained with methyl green.

[0218] Image processing—Ultrasonic images were processed using the Image-Pro Plus software tools (Media Cybernetics, Silver Spring, Md.). Number of colored pixels indicating the most intensive perfusion was calculated for each image.

[0219] Statistical Analysis

Analysis between groups for statistically significant differences was performed with the use of t-test ANOVA, or the Mann-Whitney Rank test. Data are shown as mean+SE.

[0220] In order to analyze the activity of the PPE-1-3×, comparison of reporter gene expression in the PPE-1-3× promoter plasmid and the unmodified PPE-1 promoter plasmid was undertaken. Reporter gene plasmids containing either the PPE-1-3× fragment or the unmodified PPE-1 fragment and the reporter gene Luciferase were transfected into endothelial and non-endothelial cell lines as well as to a bronchial epithelium cell line (B2B) which express the PPE-1 promoter (see materials and methods above). The B2B cell line was chosen to provide an indication of the 3× element's capacity to reduce expression in non-endothelial cell lines relative to the PPE-1 promoter. Transfection was accomplished using lipofectamine (Promega Corp., Madison, Wis.). A βgal-neo plasmid was employed as an indicator of the transfection efficiency in each case according to accepted molecular biology practice.

[0221] Forty-eight hours post transfection, the cells were harvested using lysis buffer (Promega Corp., Madison, Wis.) and Luciferase activity was analyzed by a luminometer (Th20e—Turner Designs, Sunnyvale, Calif.). In parallel, βgal activity was analyzed in order to standardize for different transformation efficiencies. The results are summarized in FIG. 1 and Table 1. Luciferase activity under the control of PPE-3× is 15-20 times higher than Luciferase activity under the control of the unmodified PPE-1. In non-endothelial cell lines minimal expression was detected using both the PPE-1 and PPE-1-3×. This demonstrates that PPE-3× is a promising candidate for delivery of a gene specifically into endothelial cells in-vivo.

[0222]

TABLE 1
Luciferase activity in cells transfected will, PPE-1 and PPE-1-3X
Luciferase constructs
	Laciferase activity in:
	endothelial cell lines	non endothelial cell lines
	Plasmid	HUVAC	BAEC	RIN
	PPE-1	135.12	1121.3	0.73
	PPE-1-3X	768	18331.7	0.32

[0223] The PPE-1/Luciferase, PPE-1-3×/Luciferase, PPE-1/GFP and PPE-1-3×/GFP were also ligated into the Ad5 plasmid to produce Ad5PPE-1/Luc and Ad5PPE-1-3×/luc, Ad5PPE-1/GFP and Ad5PPE-1-3×/GFP (Varda-Bloom et al., (2001) Gene therapy 8:819-827). These constructs were assayed separately as detailed hereinbelow.

[0224] In order to test the activity of the Ad5PPE-1/luc, transfections of B2B (Human bronchial epithelial), BAEC (Bovine Aortic Endothelial Cells) and to HUVEC (Human Umbilical Vein Endothelial Cells) were undertaken. These three cell lines express the endothelin gene and were chosen to indicate levels of expression of the tested construct in an endothelial cell. The RIN (Rat Insulinoma) cell line, which does not express endothelin, was employed as a negative control and transfected with the same construct. Ad5CMVLuc (Luciferase under the control of CMV promoter) was used as non-endothelial-specific control in all cell lines.

[0225] FIG. 2 clearly illustrates that higher Luciferase expression was achieved in endothelial BAEC and HUVEC cell lines with the PPE-1 promoter than with the CMV promoter. In the RIN cells, which are not of endothelial origin, the CMV promoter produced more Luciferase activity than the PPE-1 promoter. These results demonstrate the endothelial specificity of the un-modified PPE-1 promoter.

[0226] The Ad5PPE-3×/Luciferase and Ad5PPE-3×/GFP constructs were used to transfect the cell lines described hereinabove in Example 2 in order to ascertain the impact of the 3× element on specificity and expression levels. As in example 2, Ad5CMVLuc was used as a non-endothelial-specific control. Higher Luciferase expression in BAEC and HUVEC cell lines was detected under the control of the PPE-3× promoter as compared to the CMV promoter.

[0227] FIG. 3A is a photomicrograph illustrating GFP expression under the control of Ad5PPE-1-3× in the BAEC cell line. FIG. 3B is a photomicrograph illustrating GFP expression of Ad5CMV in the BAEC line. As is clearly shown by these Figures, the PPE-1-3× promoter is more active in endothelial cells. These results clearly indicate that the 3× element does not detract from the endothelial specificity of the PPE-1 promoter. Relative activities of the PPE-1 and PPE-1-3× promoters in cell culture are presented in example 6 hereinbelow.

[0228] Following sub cloning of P55 (TNFR1, GenBank accession number M75866) into PACPPE3× (containing the PPE-1-3× promoter), and into PACCMV, co-transfection of these plasmids and GFP (pEGFP-C1 vector; CLONTECH, Palo Alto, Calif.). was performed as described hereinabove, Briefly, the gene was subcloned downstream to the PPE-1 promoter (instead of the luciferase gene) into the NotI restriction site, by T4 DNA ligase, following by transforming it into DH5α competent cells. Twenty four hours post-transfection, small and rounded apoptotic cells were visually discernible from normal cells. Electron microscopy of cells transfected with the pro-apoptotic plasmids showed typical appearance of apoptosis, confirming the visual evaluation.

[0229] Under the control of the PPE-1-3× promoter, apoptosis was induced by p55 only in endothelial cells (FIG. 4), whereas the CMV promoter did not show any cell specific activity. Luciferase under the control of PPE-1-3× did not induce apoptosis in any tested cell lines. These results indicate that by employing the PPE-1-3× promoter, it is feasible to induce apoptosis specifically in endothelial cells.

[0230] Hypoxia is an important regulator of blood vessels' tone and structure. It has also been shown to be a potent stimulus of angiogenesis (in both ischemic heart diseases and cancer (Semenza, G. L. et al. (2000) Adv Exp Med Biol.; 475:123-30; Williams, K. J. (2001) Breast Cancer Res. 2001: 3;328-31 and Shimo, T. (2001) Cancer Lett. 174;57-64). Further, hypoxia has been reported to regulate the expression of many genes including erythropoietin, VEGF, glycolytic enzymes and ET-1. These genes are controlled by a common oxygen-sensing pathway, an inducible transcription complex termed hypoxia inducible factor-1 (HIF-1). The HIF-1 complex mediates transcriptional responses to hypoxia by binding the cis acting hypoxia responsive element (HRE) of target genes. The HRE is a conserved sequence located in the promoters of few genes that respond to hypoxia including: VEGF, Nitric Oxide Syntase-2, erytropoietin arid others including endothelin-1, ET-1. The ET-1 promoter contains an inverted hypoxia response element at position—118 bp upstream of the transcription start site, the element contain 7 base pairs and is located between the GATA-2 and AP1 sites 5′ GCACGTT 3′—50 base-pairs. (SEQ ID NO: 5.)

[0231] The preproendothelin-1 (PPE-1) promoter contains an hypoxia responsive element (HRE) that has the potential to increase its expression in the hypoxic microenvironment of tumor or ischemic tissues, thus making it “tumoral tissue specific” and/or “ischemic tissue specific”. In order evaluate the actual function of this HRE, assays of the PPE-1 promoter and PPE-1-3× promoter in conjunction with a Luciferase or GFP reporter gene and delivered by an adenoviral vector were undertaken.

[0232] Luciferase activity under the control of the PPE-1 promoter or the PPE-1-3× promoter was compared in BAEC cells under normoxic and hypoxic conditions (0.5% O₂ for 16 h). The Luciferase activity under the control of PPE-1 promoter was 5 times higher when exposed to hypoxia (FIGS. 5 and 6). Further, the Luciferase activity under the control of PPE-1-3× promoter was 2.5 times higher under hypoxic conditions. In summary, introduction of the 3× element into the PPE 1 promoter is till capable of increasing expression levels of a downstream gene in response to hypoxia, even though the normoxic levels of expression with the PPE-1-3× gene are higher than those observed with the unmodified PPE-1 promoter.

[0233] FIG. 7 summarizes the results from B2B, HUVEC and BAEC transfection experiments using pPPE-1/Luciferase and pPPE-1-3×/Luciferase. Higher Luciferase expression (30, 8.5 and 1.5 times more) was observed under the control of the PPE-1-3× promoter than under the PPE-1 promoter in B2B, HUVEC and BAEC, respectively. These results confirm those presented hereinabove and serve to establish that PPE-1-3× is well suited to directing high level expression specifically to endothelial cells. In the context of future in-vivo delivery, the higher levels of expression achieved with the PPE-1-3× construct translate into administration of smaller amounts of DNA. This, in turn, will serve to increase specificity even further.

[0234] In order to confirm that the endothelial specificity of expression observed in examples 2 through 6 was not an artifact of cell culture, the Ad5PPE-1/Luciferase construct was injected into C57BL/6 mice as described hereinabove in “Tissue gene expression in normal mice”. As in the in-vitro studies, Ad5CMV/Luciferase was employed as a negative control.

[0235] Following injection of adenoviral vectors, the specific activity and stability of Luciferase in vascularized and non-vascularized tissues was assayed. Results are summarized in FIG. 8 (Luciferase expression relative to expression in liver) and Table 2 (Luciferase expression as a percentage of total expression in the body). As expected, in Ad5CMV/Luciferase treated mice most of the Luciferase activity (>80% of the total body expression) was found in the liver. Luciferase activity controlled by the PPE-1 promoter was lower in the liver (37-54% of the total body expression). The PPE-1 derived expression was much higher in the aorta (23-33% of the total body expression 5 and 14 days post injection, respectively), compared to Ad5CMV/Luciferase, treated mice (up to 1.8% of total body expression; Table 2). These results confirm the endothelial specificity observed in cell culture. It should he remembered that the liver is a highly vascularized organ. Therefore examination of cellular expression within organs was undertaken, as detailed hereinbelow.

[0236]

TABLE 2
Luciferase expression in organs 5 and 14 days post injection of
PPE-1 and CMV based constructs
	Day post injection
	5	14
	Light units/μg protein	Light units/μg protein
Organ	PPE-1	CMV	PPE-1	CMV
Aorta	13.0 ± 2.9	1.4 ± 0.5	10.6 ± 2.4	1.3 ± 0.3
	(32.7%)	(0.56%)	(12.6%)	(1.1%)
Heart	0.2 ± 0.1	1 ± 0.6	1.5 ± 0.3	1.8 ± 0.6
	(0.5%)	(0.4%)	(1.7%)	(1.6%)
liver	22.7 ± 4.5	219 ± 111.5	34.9 ± 7.8	52.8 ± 10.6
	(57%)	(88.6%)	(41.6%)	(46.8%)
lung	0.2 ± 0.1	2.3 ± 1.0	3.6 ± 0.8	2.0 ± 0.9
	(0.5%)	(0.9%)	(4.3%)	(1.8%)
muscle	0.3 ± 0.1	0.8 ± 0.2	1.2 ± 0.3	1.5 ± 0.5
	(0.7%)	(0.3%)	(1.4%)	(1.3%)
spleen	1.3 ± 0.8	1.6 ± 0.9	2.0 ± 0.4	2.3 ± 0.9
	(3.2%)	(0.6%)	(2.4%)	(2.0%)
pancreas	2 ± 0.6	20.1 ± 6.8	26.4 ± 5.9	45.2 ± 24.5
	(5.0%)	(8.1%)	(31.5%)	(40.1%)
kidney	0.1 ± 0	0.9 ± 0.6	0.6 ± 0.1	0.8 ± 0.3
	(0.25%)	(0.4%)	(0.71%)	(0.7%)

[0237] FIGS. 30A and 30B demonstrate the absolute Luciferase activity (light units/μg protein) in the aortas (A) and livers (B) of the 110 injected mice. Luciferase activity was measured 1 (n=13), 5 (n=34), 14 (n=32), 30 (n=20) and 90 (n=11)days post injection. The results in the aorta represent the promoters (PPE-1 or CMV) activity mostly in endothelial cells, while the results in the livers represent their activity mostly in hepatocytes.

[0238] The experiments of example 7 were repeated in 12 week old BALB/C mice (n=10 for each group) in order to demonstrate that the observed results were not an artifact of a particular strain of animals.

[0239] Because Absolute results with the adenoviral vectors were lower in BALB/C mice than in C57BL/6 mice, the Luciferase expression is expressed as percentage of the total Luciferase activity in all tissues.

[0240] The highest relative Luciferase expression 5 days post injection was observed in the spleens of Ad5PPE-1 (90.9%), and in the livers of Ad5CMV (86.2%) injected mice. A significant increase in the relative Luciferase activity in the aortas of Ad5PPE-1 injected mice 14 days post injection (32.9%), compared to its activity five days post injection (1.75%) was also observed (FIGS. 31A and 31B; Ad5PPE-1Luc—open bars; Ad5CMVLuc-black bars).

[0241] These results confirm that regardless of mouse strain, the tissue specificity of the PPE-1 promoter is sufficiently strong to effectively eliminate hepatocyte expression, despite preferential uptake of injected DNA by hepatocytes.

[0242] In order to ascertain cellular expression sites of the gene expressed by PPE-1 in-vivo, Green Fluorescent Protein (GFP) delivered by the adenoviral vector Ad5PPE-1-GFP was used. Ad5CMVGFP (Quantum, Canada) was used as non-endothelial-cell-specific negative control. Five days post-intravenous injection the mice were sacrificed and their tissues wore analyzed by fluorescent microscopy.

[0243] In the mice injected with Ad5CMVGFP vector, most of the expression was detected in the hepatocytes, and no expression was detected in endothelial cell in the liver (FIG. 9A). In sharp contrast, Ad5PPE-1-GFP injected mice (FIG. 9B), showed no expression in hepatocytes, but significant expression in endothelial cells in the blood vessels of the liver. Similar results were obtained in other tissues where practically all the PPE-1 derived expression was detected in the endothelium, while none of the CMV derived expression was endothelial. These results indicate endothelial specificity is preserved even within an own containing endothelial and non-endothelial cells. This finding has important implications for prevention of angiogenesis in growing tumors.

[0244] In order to determine the relative efficacy of Ad5PPE-1 and Ad5PPE-1-3× in driving expression of the reporter genes Luciferase and green fluorescent protein (GFP) in cells, specific activity in endothelial cells was tested in-vitro using cell lines described hereinabove. Ad5CMVLuc and Ad5CMVGFP were employed as non-tissue specific controls. Ad5PPE-1Luc and Ad5PPE-1GFP were employed to ascertain the relative change in expression level caused by addition of the 3× sequence.

[0245] Results, summarized in FIGS. 10 and 11, indicate that Luciferase activities under the control of the PPE-1-3× promoter were 5-10 times higher in EC lines (Bovine Aortic Endothelial Cells—BAEC) compared to activity in non-endothelial cells—Rat Insulinoma—RIN, HeLA, HePG2 and normal skin fibroblasts (NSF) (FIGS. 10 and 11).

[0246] FIG. 10 shows Luciferase activity as light units/μg protein in B2B, BAEC and RIN cells transduced by Ad5PPE-1Luc, Ad5PPE-1-3×Luc, and

[0247] Ad5CMVLuc Highest Luciferase expression was observed in RIN cells transduced by Ad5CMVLuc, however this construct was poorly expressed in BAEC and B2B cells. The next highest level of Luciferase expression was observed in BAEC cells transduced by Ad5PPE-1-3×Luc. Ad5PPE-1Luc was expressed at lower levels in BAEC cells. In the B2B cell line Ad5PPE-1Luc and Ad5PPE-1-3×Luc were expressed at nearly identical levels.

[0248] Overall, Luciferase activity in the endothelial cell lines under the control of PPE-1-3× promoter was 23 times higher than under the control of PPE-1 promoter and 23-47 times higher than under the control of the CMV promoter to at the same infection conditions (moi=10). This is despite the fact that Luciferase expression in non-endothelial RIN cells was 3000 times higher under the control of the CMV promoter (FIG. 10).

[0249] In order to establish that PPE-1 and PPE-1-3× are inactive in other non-endothelial cell lineages HeLA, HepG2, NSF cell lines were transduced. BAEC was employed as an endothelial control. FIG. 11 shows Luciferase activity as light units/μg protein in HeLA, HepG2, NSF and BAEC cells transduced by Ad5PPE-1Luc, Ad5PPE-1-3×Luc and Ad5CMVLuc. Transduction with Ad5CMVLuc caused high levels of Luciferase expression in HeLA HepG2 and NSF cells. These cell lines failed to express Luciferase under the control of PPE-1 and expressed Luciferase at low levels with the PPE-1-3× promoter. As expected, BAEC cells transduced with Ad5PPE-1Luc or Ad5PPE-1-3×Luc exhibited high Luciferase expression.

[0250] Taken together these results indicate that introduction of the 3× sequence into the PPE-1 promoter caused higher levels of expression in endothelial cell lines while preventing unwanted expression in non-endothelial cells.

[0251] Addition of the 3× sequence to the PPE-1 promoter also increased levels of Green fluorescent protein expression in EC lines (Bovine Aortic Endothelial Cells—BAEC) as indicated in FIGS. 12A-C which depicts GFP expression in BAEC transduced by moi=1. No expression of GFP was observed using a CMV promoter in this experiment.

[0252] In FIG. 12, panel A indicates Ad5PPE-1-3×GFP transduced cells, panel B indicates Ad5PPE-1GFP transduced cells and panel C indicates Ad5CMVGFP. Again, introduction of the 3× sequence into the PPE-1 promoter significantly increased expression of the reporter gene. This result indicates that the ability of the 3× sequence to function as an endothelial specific enhancer is not a function of the downstream gene being transcribed.

[0253] Moreover, Ad5PPE-1-3×-GFP and Ad5PPE-1GFP transduction resulted in no GFP expression in non-endothelial cells SMC, HeLa, HePG2 and normal skin fibroblasts (NSF) compared to the high expression under the CMV promoter as summarized in FIGS. 13-16.

[0254] FIG. 13 shows GFP expression in SMC transduced by moi=1 of either Ad5PPE-1-3×GFP (panel A) or Ad5CMVGFP (panel B). While high level GFP expression resulted from Ad5CMVGFP transduction, no GFP expression resulted from transduction with Ad5PPE-1-3×GFP transduction.

[0255] FIG. 14 shows results of a similar experiment conducted in HeLa cells. As in the previous Figure, panel A indicates cells transduced with Ad5PPE-1-3×GFP and panel B indicates cells transduced with AD5CMVGFP. Again, while high level GFP expression resulted from Ad5CMVGFP transduction, no GFP expression resulted from transduction with Ad5PPE-1-3×GFP transduction.

[0256] FIG. 15 shows results of a similar experiment conducted in HepG2 cells. As in the previous Figure, panel A indicates cells transduced with Ad5PPE-1(3×)GFP and panel B indicates cells transduced with Ad5CMVGFP. Again, while high level GFP expression resulted from Ad5CMVGFP transduction, no GFP expression resulted from transduction with Ad5PPE-1-3×GFP.

[0257] FIG. 16 shows results of a similar experiment conducted in NSF cells. As in the previous figure, panel A indicates cells transduced with Ad5PPE-1-3×GFP and panel B indicates cells transduced with Ad5CMVGFP. Again, while high level GFP expression resulted from Ad5CMVGFP transduction, very low GFP expression resulted from transduction with Ad5PPE-1-3×GFP.

[0258] These results, taken together, indicate a high level of endothelial specificity and a high level of endothelial expression is obtained by using a modified PPE-1 promoter containing the 3× sequence of SEQ ID NO.: 7.

[0259] In order to determine the cellular localization pattern of a reporter gene expressed under the control of the PPE-1-3× promoter in-vivo, Ad5PPE-1-3×GFP and Ad5PPE-1GFP were injected into mice as described hereinabove. Five days post-intravenous injection, the mice were sacrificed and their tissues were analyzed by a fluorescent microscopy.

[0260] Significantly higher GFP activity was observed in the endothelial cells of the liver, kidney and spleen blood vessels of Ad5PPE-1-3×GFP injected mice compared to the Ad5PPE-1GFP injected mice. FIGS. 17A-B show representative results.

[0261] FIG. 17A shows low level GFP expression in endothelial cells lining a blood vessel of a mouse injected with the Ad5PPE-1GFP. FIG. 17B shows the much higher level of GFP expression resulting from addition of the 3× sequence to the construct.

[0262] Despite the high expression in the lining of the blood vessels, no expression was detected in the hepatocytes, glomerulii, epithelial cells and splenocytes (FIGS. 18 and 19).

[0263] FIG. 18 shows representative results from kidney tissue of injected mice. Ad5CMVGFP injected mice (FIG. 18A), Ad5PPE-1GFP (FIG. 18b) and Ad5PPE-1-3×GFP (FIG. 18C) injected mice all exhibited low GFP activity in kidney cells. In FIG. 18B, slightly higher GFP expression is visible in the blood vessel wall (indicated by arrow).

[0264] FIG. 19 shows representative results from spleen tissue of injected mice. Ad5CMVGFP injected mice(FIG. 19A), Ad5PPE-1GFP injected mice (FIG. 19B) and Ad5PPE-1-3×GFP injected mice (FIG. 19C) all exhibited low level GFP activity in cells of the spleen. Higher GFP activity is visible in the blood vessels of Ad5PPE-1-3×GFP injected mice (indicated by arrow).

[0265] These results confirmed that both the PPE-1 and the PPE-1-3× promoter are endothelial cell specific in-vivo. They further suggest that activity of both promoters was limited in non-proliferating endothelial tissue (i.e. blood vessels of healthy organs. Therefore, assays in a tumor angiogenic model were undertaken.

[0266] In order to ascertain the ability of AD5PPE to specifically direct expression of a reporter gene to angiogenic blood vessels in a tumor, the murine LLC model (described hereinabove in materials and methods) was employed. In a one experiment, Luciferase expression in tumor neovascularization was tested five days post systemic injections of Ad5PPE-1Luc or Ad5CMVLuc (10¹⁰ pfu/ml each).

[0267] In this experiment, systemic injection of Ad5CMVLuc to both primary and metastatic tumor models resulted in minimal expression in the primary tumor or in the metastatic lung. This level of expression was similar to the minimal expression of Luciferase directed by CMV in naive normal lungs (FIG. 35; black bars; n=12). In sharp contrast, under the control of PPE-1 promoter (FIG. 35; open bars; n=9), the highly angiogenic lung metastases were associated Luciferase activity which was about 200 times higher than the Luciferase activity in the poorly-vascularized primary tumor and the naive lungs.

[0268] The Luciferase expression in non-metastatic tissues such as the liver, kidney, heart and pancreas was minimal. The expression level in the aorta was about 30% of the levels in the metastatic lungs.

[0269] In an additional experiment in the LLC model Ad5PPE-1GFP and Ad5CMVGFP constructs were employed to localize reporter gene expression in the primary tumor and metastatic lungs.

[0270] Ad5PPE-1GFP injected mice, showed high levels of GFP specific expression in the blood vessels of the primary tumor (FIG. 36C), although no expression was detected in the tumor cells themselves. This observation is consistent with the results of the LLC cell culture model presented in example 20. In lung metastases, high levels of GFP expression were detected in both big arteries and small angiogenic vessels of the metastatic foci (FIG. 36A). No expression was detected in the normal lung tissue. The endothelial cell localization was demonstrated by co-localization of the GFP expression (FIG. 16A) and the CD31 antibody immunostaining (FIG. 16B). In striking contrast, in Ad5CMVGFP injected mice, no GFP activity was detectable in both the primary tumor and lung metastasis.

[0271] FIG. 36C illustrates GFP expression in blood vessels of a primary tumor following intra tumoral injection of Ad5PPE-1GFP. FIG. 36D is a phase contrast image of the same filed as panel C illustrating the tumor and its blood vessels.

[0272] These results indicate that while PPE-1 does not drive high level expression in tumor cells per se, the promoter does drive high level expression in vascular endothelia within the tumor, especially in rapidly proliferating angiogenic vessels.

[0273] Intra-tumor injection of Ad5CMV into primary subcutaneous tumor model resulted in high Luciferase expression in the tumor tissue and moderately levels of expression liver (10% of the amount expressed in the tumor; FIG. 42). No expression was detected in the metastatic lungs. On the other hand, when injected intra-tumoral, Luciferase expression under the control PPE-1 promoter resulted in similar Luciferase levels of expression in the primary tumor and the metastatic lungs and no expression was detected in the liver.

[0274] In order to assay the efficiency of Ad5PPE-1 and Ad5CMV to drive Luciferase expression in cancerous cells, the D122-96 Lewis Lung Carcinoma cell line was employed.

[0275] In-vitro transduction at varying multiplicities of infection (moi) was performed. The results indicate that both adenoviral vectors are able to transduced the Luciferase gene to these cells (Table 3). Nevertheless, Luciferase activity directed by the PPE-1 promoter was much lower in the LLC cells than the activity de d in endothelial cells, 50 vs. 1000-2500 light units/μg protein, respectively.

[0276]

TABLE 3
In-vitro transduction of Lewis lung carcinoma cell line (D122-96)
with Ad5PPE-1Luc and Ad5CMVLuc.
	MOI = 1	MOI = 5	MOI = 10
	Ad5PPE-1	8.1 ± 0.06	33.95 ± 7.0	50.7 ± 5.0
	Ad5CMV	9.3 ± 1.1	47.3 ± 4.0	88.13 ± 10.1

[0277] In order to ascertain the effect of the 3× sequence on the PPE-1 promoter in angiogenic blood vessels, the Lewis Lung Carcinoma (LLC) metastases model (described hereinabove in material and methods) was employed. Five days post IV injection of 10¹⁰ infectious units of Ad5PPE-1GFP, Ad5PPE-1-3×GFP or Ad5CMVGFP, the mice were sacrificed and their tissues were analyzed as described in material and methods.

[0278] FIGS. 20A-D summarize the GFP expression in metastatic lungs of control mice injected with Saline (FIG. 20A), mice injected with Ad5CMVGFP (FIG. 20B),.mice injected with Ad5PPE-1GFP (FIG. 20C) and mice injected with Ad5PPE-1-3×GFP (FIG. 20D). Anti-CD31 immunostaining FIGS. 20C′ to 20D′) confirm the location of the GFP expression in each metastatic tissue. The results show that while no GFP expression was detected in control—saline injected mice (FIG. 20A), there was a slight expression around the epithelial bronchi of the CMV injected mice, but not in the angiogenic blood vessels of the metastatic lung of these mice (FIG. 20B). Low GFP expression was observed in metastatic lungs of Ad5PPE-1GFP injected mice (FIGS. 20C and 20C′), while high and specific expression was observed in the new blood vessels of Ad5PPE-1-3×GFP injected mice (FIGS. 20D and 20D′).

[0279] These results explain the apparent disparity between the in-vivo results of example 10 and the in-vitro results of examples 2, 3 and 6. Both the PPE-1 and the PPE-1-3× promoter are endothelial specific. However, the 3× sequence greatly increases the level of expression in rapidly proliferating endothelial tissue, such as newly forming blood vessels in a growing tumor.

[0280] In order to study the effect of the 3× element of the present invention on efficacy and specific activity of the PPE-1 promoter in tumor angiogenic blood vessels, the LLC metastases model was employed. Five days post i.v. injection of 10¹⁰ pfu/ml of Ad5PPE-1Luc, Ad5PPE-1-3×Luc, Ad5CMVLuc, Ad5PPE-1GFP, Ad5PPE-1-3×-GFP or Ad5CMVGFP, the mice were sacrificed and their tissues were analyzed for Luciferase or GFP expression as described hereinabove.

[0281] FIG. 37 is a histogram comparing Luciferase expression in normal lungs versus that in metastatic lungs following systemic injection of Ad5PPE-1-3×luc, Ad5PPE-1Luc or Ad5CMVLuc. Experimental groups were Ad5CMVLuc (n=7; black bars), Ad5PPE-1Luc (n=6 ;gray bars) and A5PPE-1-3×Luc (n=13; brown bars). Activity is expressed as light units/μg protein.

[0282] Luciferase expression under the control of the PPE-1-3× promoter was 35 fold greater in the metastatic lungs relative to its activity in normal lungs and 3.5 fold higher than expression driven by the PPE-1 promoter without the 3× element (p<0.001). Very low Luciferase activity was detected in other tissues of mice injected with Ad5PPE-1-3×Luc. Calculating the Luciferase expression in the lungs as percentage from the liver of each injected animal revealed that the activity increased 10 fold in the metastatic lung compared to the activity in normal lung (FIG. 38).

[0283] In order to localize reporter gene expression to specific cell types, GFP constructs were employed. FIG. 39A-B show the GFP expression (FIG. 39A) in metastatic lungs of Ad5PPE-1-3×GFP injected mice. Immunostaining by CD31 antibody (FIG. 39B) confirm the location of the GFP expression in the new blood vessels. No GFP expression was detected in control—saline injected mice. Low level expression around the epithelial bronchi of the CMV injected mice, but not in the angiogenic blood vessels of the metastatic lung.

[0284] In summary, these results indicate that large increases in expression level resulted from introduction of a 3× element into Ad5PPE-1 constructs and that this increased expression was specific to the angiogenic blood vessels of tumors. Potentially, the observed effect may he coupled with the hypoxia response described hereinabove to further boost expression levels of a sequence of interest.

[0285] In order to further characterize the effect of hypoxia on the murine PPE-1 promoter activity, bovine aortic endothelial cells (BAEC) were transfected by a DNA plasmid (pEL8; FIG. 26A). The pEL8 plasmid contains the murine PPE-1 promoter (1.4 kb) (red) the luciferase gene (1842 bp), the SV40 poly A sites and the first intron of the endothelin-1 gene, all termed the PPE-1 promoter cassette was digested and extracted by BamHI restriction enzyme as described in material and methods. Following transfection, cells were subjected to hypoxic conditions.

[0286] Luciferase expression in transfected BEAC subjected to 18 hours of hypoxia (0.5% O2) was eight times higher than Luciferase expression in cells grown in a normoxic environment (FIG. 21). FIG. 21 shows that Luciferase activity (light units/μg protein) in BAEC transfected by a plasmid containing the murine PPE-1 promoter was significantly higher when transfected cells were incubated in a hypoxic environment. Equivalent transfection efficiencies were confirmed by co-transfection with a β-galactosidase reporter vector and assays of LacZ activity.

[0287] In order to determine whether murine PPE-1 promoter delivered by adenoviral vector is also up-regulated by hypoxia, BAEC were transduced by Ad5PPE-1Luc. Ad5CMVLuc was used a non specific control in this experiment. Results are summarized in FIG. 22. Hypoxia Luciferase activity in BAEC transduced by Ad5PPE-1Luc. In stark contrast, no significant difference between normoxia and hypoxia was detected in the Ad5CMV transduced cells (FIG. 22).

[0288] To understand whether the enhancement of the PPE-1 promoter activity is specific to endothelial cells, different cell lines (BAEC, B2B, CHO, RIN and Cardiac Myocytes) were transduced by Ad5PPE-1 (moi=10) and were subjected to hypoxia (0.5% O2) or normoxia environment. Results are summarized in FIG. 23. Luciferase expression was slightly increased in B2B cells and significantly increased in BAEC cells cultured in a hypoxic environment Luciferase expression in other cell lines was reduced by the hypoxic environment compared to normoxia. These results confirm that hypoxic induction of the PPE-1 promoter occurs primarily in endothelial cell lineages.

[0289] In order to ascertain the effect of the 3× sequence on the PPE-1 hypoxia response, BAEC were transduced by Ad5PPE-1Luc and Ad5PPE-1(3×)Luc. Following transduction the BAEC cells were incubated either in a hypoxic or a normoxic environment as detailed hereinabove. Results are summarized in FIG. 24. Luciferase expression using the Ad5PPE-1Luc construct significantly increased (seven folds) in response to hypoxia (2578 in hypoxia and 322.1 in normoxia). In contrasts the Ad5PPE-1(3×)Luc construct exhibited only 1.5 fold increase in response to hypoxia (from 2874.5 in normoxia to 4315 in hypoxia conditions). These results indicate that the high normoxic level of expression observed when the 3× sequence is added to the PPE-1 promoter serves to mask the hypoxic response to some extent.

[0290] In order to examine the murine PPE-1 promoter activity in tissues subjected to regional hypoxia/ischemia, mPPE-1-Luc transgenic mice, described hereinabove in materials and methods, were employed. The mice were induced to regional hind limb ischemia as previously described (Couffinhal T. et al. (1998) Am. J. Pathol. 152;1667-1679). In brief, animals were anesthetized with pentobarbital sodium (40 mg/kg, IP). Unilateral ischemia of the hind limb was induced by ligation of the right femoral artery, approx 2 mm proximal to the bifurcation of the saphenous and popliteal arteries. To verily the induction of functional change in perfusion, ultrasonic imaging was performed on days 4 and 14 by Synergy ultrasound system (GE) equipped with a 7.5 MHz transducer and angiographic software. Animals were housed under conventional conditions for up to 18 days.

[0291] Luciferase expression was assayed 2, 5, 10 and 18 days post ligation in the ischemic muscle, in the normal non-ligated muscle, in the liver, lung, and aorta.

[0292] Results, summarized in FIG. 25, show that while no significant difference was detected in the liver, lung and aorta during the days post ligation, Luciferase gene expression increased following the femoral ligation in both in the normal non-ligated and in the ischemic muscle. While peak Luciferase expression in the ischemic muscle was detected five days post ligation, peak Luciferase expression in the non-ligated muscle was detected ten days post femoral artery ligation. This indicates that the hypoxic response of the PPE-1 promoter is functional in an in-vivo system. Luciferase expression in the non-ischemic muscle did not change during the days tested, compared to its expression in the control non-operated tissue (day=0). In contrast, Luciferase expression in the ischemic muscle was significantly higher on day 5 than at other time points.

[0293] On day 5, PPE-1 driven expression of Luciferase was 2.5 times higher than in control non-operated mice and compared to the ischemic muscle in days 10 and 18 (FIG. 40).

[0294] Expression of Luciferase in other non-ischemic tissues including liver, lungs and aorta of the transgenic mice subjected to regional ischemia revealed no significant changes within 18 days post ischemic induction in the Luciferase expression in these tissues (FIG. 41).

[0295] Further, these results confirm that Luciferase expression was higher in tissues containing a high percentage of endothelial tissue (lung and aorta) than in those tissues containing a low percentage of endothelial tissue (liver and non-ischemic muscle).

[0296] In order to ascertain the effect of level of cellular proliferation on efficiency and specific activity of Ad5PPE-1Luc, an angiogenic model of endothelial cells (BAEC), was tested in-vitro. Transduced BAEC were either induced to quiescence by serum deprivation or grown in 10% FCS for normal proliferation. Briefly, cells were transduced for 48 hours either as quiescent cells—72 hours post serum deprivation or as proliferating cells—in normal media (10% FCS). Luciferase activity is expressed as light unit/μg protein, to normalize for the difference in cell amount. The results presented we an average of triplicate test from four representative independent experiments.

[0297] Luciferase expression under the control of PPE-1 promoter (open bars; FIG. 28) was 4 times higher in normal proliferating BAEC than in quiescent cells, and 25 times higher in normal proliferating BAEC than Luciferase expression under control of the CMV promoter (Black bars; FIG. 28). Further, in proliferating cells, the activity under the control of PPE-1 promoter was 10 times higher an that under the CMV promoter control.

[0298] In order to simulate angiogenic conditions in-vitro, Ad5PPE-1Luc activity was tested in BAEC induced to rapid proliferation by addition of 40 ng/ml vascular endothelial growth factor (VEGF). Activity under these conditions was compared activity in normal proliferating cells and quiescent cells as described hereinabove. Luciferase expression in BAEC induced to cell proliferation with VEGF was 44 times higher than in normal proliferating cells and 83 times higher than in quiescent cells (FIG. 29).

[0299] Together, these experiments indicate that the level of activity of a sequence of interest under transcriptional control of the PPE-1 Promoter is a function of the level of cellular proliferation, with rapid proliferation causing higher levels of expression.

In order to test the efficiency and specificity of tie Ad5PPE-1 vector in atherosclerotic blood vessels, 10¹⁰ pfu/ml of the viral vectors were systemically injected to 6 month old ApoE deficient mice (Plump, A. S. et al. Cell; 1991; 71:343-353).

[0300] As ApoE deficient mice age, they develop high cholesterol values and extensive atherogenic plaques with no induction of lipid reach diet FIG. 32 is a picture of an aorta dissected from an ApoE deficient mouse colored by Sudan—IV. Note that the thoracic aorta contains less red stained atherosclerotic lesions while the abdominal region is highly atherosclerotic. (FIG. 32 adapted from Imaging of Aortic atherosclerotic lesions by 125I-HDL and 125I-BSA. A. Shaish et al, Pathobiology—submitted for publication).

[0301] FIG. 33 summarizes Luciferase expression observed 5 days post systemic injections of Ad5PPE-1Luc (open bars n=12) and Ad5CMVLuc (black bars; n=12) to ApoE deficient mice. Results are presented as absolute Luciferase expression in the thoracic area that contains less atherosclerotic lesion, and the abdominal aorta that is rich atherosclerotic lesion.

[0302] Luciferase expression controlled by the PPE-1 promoter was 6 fold higher in the highly atherosclerotic abdominal, and 1.6 fold higher in the slightly atherosclerotic thoracic aorta as compared to expression under the control CMV promoter.

[0303] No significant difference was observed between the two aorta regions in the Ad5PPE-1Luc injected mice, while higher Luciferase expression was observed in thoracic aorta of the Ad5CMVLuc injected group compared to low expression in the abdominal aorta that contain lesion.

[0304] These results indicate that while a constitutive promoter (CMV) has a tendency to shut down in areas where atherosclerosis is most severe, the PPE-1 promoter is relatively unaffected by disease progression.

[0305] In order to test the Ad5PPE-1 constructs efficiency and specific activity in directing Luciferase expression to healing wound blood vessels, a murine wound healing as described hereinabove in Material and Methods was employed.

[0306] As in other experiments, Ad5CMVLuc was used as a non-tissue specific control. Luciferase activity under the PPE-1 promoter (FIG. 34; open bars) control was higher both in the normal (6.8±3.2) and in healing wound region (5±1.6) compared to the activity observed under the CMV control (FIG. 34; black bars).

[0307] Because both the CMV and PPE-1 promoter exhibited reduced expression levels in the healing wound, these results are difficult to interpret. Despite this unexpected observation, it is clear that the PPE-1 promoter drives higher levels of expression than the CMV promoter in both normal and healing tissue. The presence of necrotic scar tissue may account for the reduced expression levels observed with both promoters in the healing wound.

[0308] In-vivo induction of angiogenesis oftentimes results in a primitive vessel network consisting of endothelial cells. These nascent vessels rupture easily, prone to regression and leakiness and poorly perfused. To overcome these limitations localized, timed and dose-controlled delivery of various angiogenic factors, capable of recruiting endothelial cells as well as periendothelial cells (i.e., pericytes in small vessels or smooth muscle cells in larger vessels) is desired.

[0309] The modified preproendothelin-1 promoter, PPE-1-3× was used to express in the endothelium of ischemic limb muscles either VEGF or PDGF-B, an endothelial secreted factor which recruits smooth muscle cells towards the origin of secretion thereby preventing hyper permeability of newly formed vessels.

[0310] To determine expression of VEGF and PDGF-B in ischemic tissues, in-situ hybridization was performed. As shown in FIGS. 43A-C, while a significant expression of VEGF mRNA could be detected in ischemic muscle sections from Ad5PPE-1-3×VEGF treated mice, essentially no signal could be seen in muscle sections of Ad5CMVVEGF or saline-treated mice. Similarly, the presence of mRNA of PDGF-B was detected in ischemic limb muscles of mice treated with Ad5PPE-1-3×PDGF-B, but not in Ad5CMVPDF-B or saline-treated mice (FIGS. 43E-G). Interestingly, the pattern of the signal in FIGS. 1A and 1E resembled vascular structure. Notably, representative liver sections from the various treatment groups demonstrated massive expression of VEGF or PDGF-B in Ad5CMV treated animals (FIGS. 43D and 43D), while no expression was detected in the livers of Ad5PPE-1-3× vectors treated mice (data not shown).

[0311] Altogether, the assay indicates that the Ad5PPE-1-3× vectors mediate measurable expression of angiogenic factors in a target organ, while the constitutive Ad5CMV vectors expressed their transgene almost exclusively in hepatic tissues.

[0312] The therapeutic effect of Ad5PPE-1-3×VEGF was compared to that of previously reported Ad5CMVVEGF. 10⁹ PFUs of either therapeutic vectors, as well as reporter vector Ad5CMVluciferase and equivalent volume of saline as control were systemically administered to mice, 5 days following femoral artery ligation. Ultrasonic (US) images of the medial aspect of both limbs were taken in angiographic mode. As shown in FIGS. 27A-D, 21 days following ligation, the signal of perfusion was diminished and truncated in the control animals; however, continuous, enhanced signal was seen in the US images of both Ad5PPE-1-3×VEGF and Ad5CMVVEGF treated mice. The mean intensity of perfusion on the 21^st day in the two VEGF treatment groups was over 3 times higher than that of the control group (p<0.01), and similar to that recorded from the normal, contralateral limbs of the animals (FIG. 27E). Immunohistochemistry analysis done 21 days following femoral artery ligation and using anti CD-31, an endothelial specific marker, showed a mean of 546 CD31+ cells/mm² in the ischemic muscle sections of Ad5PPE-1-3×VEGF treated mice, comparing to 585 and 485 CD31+ cells/mm² in the Ad5CMVVEGF and control groups, respectively (FIG. 27F). This data shows that in the short term treatment with Ad5PPE-1-3×VEGF is as effective as the treatment with the potent CMV promoter of Ad5CMVVEGF. Furthermore, liver sections of the mice stained in H&E showed no indications for hepatitis or other pathological chronic changes (data not shown), thereby ruling out adenovirus tropic effect on hepatocytes.

[0313] Tissue specific expression versus constitutive expression of pro-angiogenic factors was addressed with respect to the induction of angiogenesis. The effects of PPE-regulated and CMV-regulated VEGF expression on perfusion and angiogenesis were tested in 70 days long experiments. Mice with ischemic limb were treated as above (see Example 23). US imaging revealed significant improvement in perfusion in both treatment groups beginning 1-2 weeks following virus administration, while minor changes were detected in the control group (data not shown). The long-term effect of the Ad5PPE-1-3×VEGF treatment was detected 50 and 60 days following femoral artery ligation. Perfusion was significantly increased in the Ad5PPE-1-3×VEGF treated mice, as compared to Ad5CMVVEGF or saline-treated mice. The difference in perfusion between Ad5CMVVEGF and control treated animals decreased over that time interval. On the 50^th day, mean intensity of perfusion in the Ad5PPE-1-3×VEGF treated group was about 50% higher than in the Ad5CMVVEGF or saline treated mice, and similar to that of the contralateral normal limb (p<0.01, FIG. 44A). Upon sacrifice of the animals on the 70^th day, the capillary density in the muscle sections of Ad5PPE-1-3×VEGF treated mice was 747 CD31+ cells/mm², which is 57% and 117% higher than in the Ad5CMVVEGF (474 CD31+ cells/mm²) and control (342 CD31+ cells/mm²) groups, respectively p<0.01, FIG. 44B).

[0314] PDGF-B is a paracrine endothelial secreted factor, which has been shown to be involved in vessel maturation by recruitment of smooth muscle cells, and probably also in angiogenesis [Edelberg, J. M et al. Circulation 105, 608-13. (2002); Hsu et al. J Cell Physiol 165, 239-45. (1995); Koyama, N. et al. J Cell Physiol 159, 1-6. (1994)]. It has also been shown that PDGF-B is involved in intimal thickening [Sano, H. et al. Circulation 103, 2955-60. (2001); Kaiser, M., et al. Arthritis Rheum 41, 623-33. (1998)] and in fibroblast proliferation [Nesbit, M. et al. Lab Invest 81, 1263-74. (2001); Kim, W. J. et al. Invest Ophthalmol Vis Sci 40, 1364-72. (1999).]. The ability of PDGF-B to induce angiogenesis under endothelial specific regulation was tested in vitro and in-vivo.

[0315] Ad5PPE-1-3×PDGF-B vector induced angiogenic changes in endothelial cells in-vitro, like Ad5PPE-1-3×VEGF (data not shown). Transduction of endothelial cells cultured on fibrin coated cultureware with 10 MOI of Ad5PPE-1-3×PDGF-B resulted in the formation of 2-dimensional circular structures and fibrin degradation.

[0316] For in-vivo effect, mice were systemically treated with 10⁹ PFUs of Ad5PPE-1-3×PDGF-B, 5 days following femoral artery ligation. 30 days following ligation the mean intensity of perfusion in the Ad5PPE-1-3×PDGF-B treated mice was about 90% higher than that in the control group (FIG. 45A). 80 days following ligation the intensity of perfusion in the Ad5PPE-1-3×PDGF-B treated group was 60% higher than in the control group (FIG. 45B)

[0317] Capillary density was measured 35 and 90 days following ligation. In the short time interval, the mean capillary density in ischemic muscle sections of the Ad5PPE-1-3×PDGF-B treated mice was 516 CD31+ cells/mm², while in the saline-treated group it was 439 (FIG. 45C). 90 days following ligation the mean capillary density in Ad5PPE-1-3×PDGF-B treated mice increased slightly to 566 CD31+ cells/mm², while a moderate decrease was detected in the control group (378 CD31+ cells/mm² FIG. 45D)

[0318] The results indicate that Ad5PPE-1-3×PDGF-B vector by itself is a potent angiogenic treatment, which not only induces angiogenesis in the short term following administration, but is capable of retaining a therapeutic effect for a long period of time. No chronic changes were detected in the livers of the mice treated with Ad5PPE-1-3×PDGF-B.

[0319] The assumption that further enhancement of angiogenesis and maturation of vasculature can be achieved by utilizing both VEGF and PDGF-B in a combination therapy was tested using two modalities of treatment: (i) single administration of 10⁹ PFUs of Ad5PPE-1-3×VEGF and of Ad5PPE-1-3×PDGF-B, (ii) administration of similar dose of Ad5PPE-1-3×PDGF-B 5 days following administration of Ad5PPE-1-3×VEGF. Both modalities yielded the same results, and therefore are referred to as one. 90 days following ligation, both the combination therapy and the Ad5PPE-1-3×VEGF treated mice exhibited significantly higher capillary density as compared to the control, Ad5PPE-1-3×GFP treated mice, but there was no significant difference among the various therapeutic groups (FIG. 46B). However, the mean intensity of perfusion in US imaging in the combination therapy group was up to 42% higher than the Ad5PPE-1-3×VEGF treated group (FIG. 46A). This can be explained by maturation of small vessels in the ischemic muscles of the combination therapy groups and Ad5PPE-1-3×PDGF-B treated mice. Significant staining for vascular smooth muscle cells was seen in muscle sections from mice treated with the combination therapy or Ad5PPE-1-3×PDGF-B, immunostained for α-SMactin (FIGS. 46C-D), Sparse staining could be seen in control and Ad5PPE-1-3×VEGF treated mice (FIGS. 46E-F) In the normal limb muscles there was prominent staining around larger arterioles and venules (FIG. 46G). Similar results were obtained as early as 35 days following ligation in mice treated with Ad5PPE-1-3×PDGF-B (data not shown). No chronic changes were apparent in liver sections of treated mice 35 days following ligation.

[0320] These results were further substantiated in a separate experiment, which addressed the effect of PDGF-B alone and in combination therapy on blood perfusion 50 days following ligation. As shown in FIG. 47, 50 days following ligation, blood perfusion intensity in the combination therapy group resembled completely that of normal limb. This effect was PPE-3× dependent, as constitutive expression (CMV promoter) of both growth factors resulted in only half perfusion capacity. Interestingly, PPE-3× dependent expression of PDGF-B alone could mediate nearly the sane perfusion (i.e., 77%) as induced by the combination therapy. However, such results were not apparent using a constitutive promoter.

[0321] These results corroborate that the PPE-1-3× promoter is capable of strong enough activation of the therapeutic genes, in spite of the systemic administration, without compromising the preferential expression in angiogenic endothelial cells. Furthermore, these results substantiate PDGF-B as a pro-angiogenic factor which can mediate its angiogenic action without further addition of well established angiogenic growth factors, such as VEGF.

[0322] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications aid variations that fall within the spirit and broad scope of the appended claims. All publications, patents, patent applications and sequences identified by their accession numbers mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent, patent application or sequence identified by their accession number was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.