Bombesin-Related Peptides

The present invention relates generally to the manipulation of genetic materials, and, more particularly, to recombinant DNA procedures which make possible the identification of DNA sequences encoding novel peptides.

Bombssin, a tetradecapeptide amide first isolated from the skin of the frog Bombina bombina, is a potent mitogen for mouse Swiss 3T3 fibroblast cells. It also stimulates secretion for guinea pig pancreatic acini. Bombssin-like peptides are produced and secreted by human small cell lung cancer cells and exogenously added bombssin-like peptides can stimulate the growth of human SCLC cells in vitro. Two examples of bombssin-like peptides are gastrin releasing peptide ("GRP") and Neuromedin B ("NMB").

GRP is a 27 amino acid peptide amide first isolated from the porcine gut. The C-terminal amino acid sequence of GRP is almost identical to that of bombssin. Neuromedin B is a decapeptide amide, the structure of which is almost identical to the last ten amino acids in the C-terminal region of GRP. Both GRP and Neuromedin B share amino acid sequence homology with bombssin and possess bombssin-like properties. Other bombesin-like peptides include litorin and Neuromedin C.

Recent structure-function and DNA cloning studies demonstrate that at least two classes of receptors mediate the action of bombesin-related peptides. One class, the GRP preferring subtype (GRP receptor), has a high affinity for GRP and a low affinity for NMB, whereas the other class, the NMB-preferring subtype (NMB receptor), has a high affinity for NMB and lower affinity for GRP. Both classes of receptors are widely present both in the central nervous system and in the gastrointestinal tract.

The present invention features a pure DNA encoding a peptide which is a bombssin-related peptide and identified herein as SEQ ID NO: 1 (BIM-26337) or SEQ ID NO: 2 (BIM-26336). Preferably, the DNA of this invention consists essentially of a nucleotide sequence identified herein as SEQ ID NO: 3 or SEQ ID NO: 4.

Also within this invention is a vector or a cell containing one of the above-described DNA sequences. Preferably, in a cell which contains the DNA sequence of the invention, the DNA is introduced into the cell in a manner allowing the cell to express the peptide, e.g., by transforming or transfecting the cell with a vector containing the DNA sequence.

The present invention further features a pure peptide identified herein as SEQ ID NO: 1 or SEQ ID NO: 2.

It is a further feature of the present invention to prepare one of the above-described peptides by a DNA recombinant method which includes the steps of (i) introducing a DNA encoding the peptide into cells in a manner allowing the cells to express the peptide; (ii) culturing the cells in a medium; and (iii) recovering the expressed peptide.

What is meant by "pure DNA" herein is DNA that is not immediately contiguous with both of the coding sequences with which it is immediately contiguous (i.e., one at the 5' end and one at the 3' end) in the naturally-occurring genome of the organism from which the DNA of the invention is derived. The term therefore includes, for example, a recombinant DNA which is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule (e.g., a cDNA or a genomic DNA fragment produced by the polymerase chain reaction technique or restriction endonuclease treatment) independent of other DNA sequences. It also includes a recombinant DNA which is part of a hybrid gene encoding additional polypeptide sequence.

A pure peptide, on the other hand, is a peptide free or substantially free of the components with which it is naturally associated.

The peptides of this invention can be provided in the form of pharmaceutically acceptable salts. Examples of preferred salts are those with therapeutically acceptable organic acids (e.g, acetic, lactic, maleic, citric, malic, ascorbic, succinic, benzoic, methanesulfonic, toluenesulfonic, or pamoic acid), as well as polymeric acids (e.g., tannic acid or carboxymethyl cellulose), and salts with inorganic acids as the hydrohalic acids (e.g., hydrochloric acid, sulfuric acid, or phosphoric acid).

In other preferred embodiments, a therapeutically effective amount of a peptide of this invention and a pharmaceutically acceptable carrier substance (e.g., magnesium carbonate, lactose, or a phospholipid with which the therapeutic compound can form a micelle) together form a therapeutic composition (e.g., a pill, tablet, capsule, or liquid) for administration (e.g., intravenously, subcutaneously, nasally, vaginally, or iontorphoretially) to a subject in need of the peptide. The pill, tablet, or capsule can be coated with a substance capable of protecting the composition from the gastric acid and intestinal enzymes in the subject's stomach for a period of time sufficient to allow the composition to pass undigested into the subject's small intestine. The therapeutic composition can also be in the form of a biodegradable or nonbiodegradable sustained release formulation for intramuscular administration (e.g., U.S. Pat. Nos. 4,675,189 and 4,767,628, hereby incorporated by reference). For maximum efficacy, zero order release is desired, and can be obtained using an implantable or external pump (e.g., INFUSAID.TM. pump) to administer the therapeutic composition.

Also within the scope of this invention are methods of using a peptide of this invention to treat diseases or disorders. Such utilities are well known to a person of ordinary skill in the art. For example, see U.S. Pat. No. 5,217,955, PCT WO 94/02018 and PCT WO 92/20363, all of which are hereby incorporated by reference.

The effective amount of the peptide of this invention to be used varies depending upon the manner of administration and the condition of the subject to be treated, and ultimately will be decided by the attending physician or veterinarian.

Other features and advantages of the invention will be apparent from the following description and from the claims.

The drawings are first briefly described.

FIG. 1 is the sequence and translation of a cDNA encoding peptides of this invention, i.e., BIM-26336 and BIM-26337.

FIG. 2 is a graph showing the effect of BIM-26336 and BIM-26337 on the inhibition of [.sup.125 I] NMB binding.

FIG. 3 is a graph showing the effect of BIM-26336 and BIM-26337 on the inhibition of [.sup.125 I-Tyr4] bombesin binding.

FIG. 4 is a graph showing the effect of BIM-26336 and BIM-26337 on calcium uptake in xenopus oocytes expressing the human NMB receptor.

FIG. 5 is a graph showing the effect of BIM-26336 and BIM-26337 on calcium uptake in xenopus oocytes expressing the human GRP receptor.

FIG. 6 is a graph showing the effect of BIM-26336 and BIM-26337 on thymidine uptake in 3T3 cells ("BN" stands for bombesin).

Structure

We discovered that the peptides [Phe.sup.8 ]phyllolitorin and [Leu.sup.8 ] phyllolitorin are encoded in frogs of the sphilomedusa genus by two nearly identical DNA sequences which differ by only a single nucleotide. This finding suggested that highly similar DNA sequences might also encode multiple bombesin-like peptides in other species of frogs.

Skin, brain, and extracts of Bombina orientalis, a frog species that produces bombesin, were examined for the existence of multiple bombesin-like peptides by the following protocol:

Total RNA was prepared by homogenization of frog tissues in guanidine thiocyanate followed by centrifugation through CsCl. 5 .mu.g total RNA was reverse transcribed with 25 pmole oligo(dT.sup.18), 200 units of M-MLV reverse transcriptase (BRL), 5X Buffer (250 mM Tris-HCL, pH 8.3; 375 mM KCl, 15 nM MgCl.sub.2, 50 mM DTT, 2.5 mM dNTP's) in 20 .mu.l total volume at 37.degree. C. for one hour. The entire reverse transcription was used in a 100 .mu.l PCR reaction using 100 pmoles of a 5' primer ATTCCTCTGAACAGGATC and 100 pmoles of a 3' primer AAGTCCCATATCTCAGGC. These primers correspond, respectively, to positions 68-83 and 458-475 of the Bombina orientalis cDNA reported in Spindel, et al., Proc. Natl. Acad. Sci. USA 87:9813-17 (1990), which is hereby incorproated by reference.

PCR conditions were as follows: one cycle of 92.degree. C..times.1 min, 50.degree. C..times.2 min, 72.degree. C..times.5 min for a second strand synthesis followed by 35 cycles of 92.degree. C..times.2 min, 55.degree. C..times.1 min, 72.degree. C..times.2 min. 20 .mu.l of the reaction was separated on a 1% agarose gel, blotted and hybridized to a .sup.32 P-end labeled internal oligonucleotide probe CATGGAGTTCGTTGAAGA. The hybridizing product was subcloned into PGEM-T vector (Promega) and sequenced according to standard procedures. See Negalla, et al., J. Biol. Chem. 267:6916-6922, which is hereby incorporated by reference.

The nucleotide sequence of a frog cDNA thus obtained, as well as the deduced amino acid sequence, is shown in FIG. 1. A new bombesin-related peptide revealed by the deduced amino acid sequence, i e., [Ser.sup.3, Arg.sup.10, Phe.sup.13 ] bombesin, is designated herein as "SAP bombesin." SAP bombesin-14 ("BIM-26337"): H-pGlu-Gln-Ser-Leu-Gly-Asn-Gln-Trp-Ala-Arg-Gly-His-Phe-Met-NH.sub.2 (SEQ ID NO: 1 )

All abbreviations of amino acids in this disclosure, with the exception of pGlu, stand for a residue with structure of --NH--CH(R)--CO--, wherein R is a side chain. The abbreviation pGlu stands for ##STR1##

In FIG. 1, the sequence encoding SAP bombesin-14 and the glycine for the carboxy-terminal amide are boxed. The N-terminal Gln provides the amino-terminal pyroglutamyl residue of SAP bombesin-14. See Spindel et al., Proc. Natl. Acad. Sci. USA 87:9813 (1990). The C-terminal glycine serves as the amide donor for the C-terminal methionyl-amide reside of SAP bombesin-14. Bradbury et al., Nature 298:686 (1982). The three prohormone processing points, Ser-Leu, Ser-Leu and Lys-Lys, are double overlined. Douglas et al. Annu. Rev. Biochem., 53:665 (1984).

Because bombesin is cleaved from its precursor following the amino acids Ser-Leu, which are double overlined in FIG. 1, this dictates that SAP bombesin-14 is internally cleaved after the Ser-Leu to yield the following peptide:

SAP Bombesin-10 ("BIM-26336"): Gly-Asn-Gln-Trp-Ala-Arg-Gly-His-Phe-Met-NH.sub.2 (SEQ ID NO: 2)

SAP bombesin-10 possesses homology to human NMB. That is, it differs from the human NMB by two amino acid residues: Gln vs. Leu at position 3 and Arg vso Thr at position 6.

SAP bombesin-14 and SAP bombesin-10 are encoded by the following segments in the cDNA sequence shown in FIG. 1, respectively: ##STR2##

Insertion of a bombesin-encoding sequence into an expression vector and introduction of the recombinant vector into a host cell are desirable. For example, an SAP bombesin can be produced by such a host cell. The techniques involved in recombinant production of peptides are well known to a person of ordinary skill in the art and in any event can be found in the literature, e.g., Sambrook, et al. Molecular Cloning, A Laboratory Manual, 2nd Ed. Cold Spring Harbor Laboratory Press, New York (1989), hereby incorporated by reference.

Function

I. Binding to Receptors

A. NMB Receptor

Membranes of the NMB receptor used in the binding assay were obtained by homogenizing rat olfactory bulb tissue (Polytron, setting 6, 15 sec) in ice-cold 50 mM Tris-HC1 (Buffer A) and centrifuging twice as 39,000 x g (10 min), with an intermediate resuspension in fresh buffer. The final pellets were resuspended in the 50 mM Tris-HCl, containing 0.1 mg/ml bacitracin, and 0.1% BSA (Buffer B), and held on ice for the receptor binding assay. For the assay, aliquots (0.4 ml) were incubated with 0.05 ml [.sup.125 I] NMB (-2200 Ci/mmol, New England Nuclear) and Buffer B, with and without 0.05 ml of unlabeled competing peptides. The experiment was performed with BIM-26336, BIM-23337, GRP, and NMB as competing peptides.

After a 30 min incubation (4.degree. C.), the bound [.sup.125 I]NMB was separated from the free by rapid filtration through GF/B filters which had been previously soaked in 0.3% polyethyleneimine. The filters were then washed three times with 5 ml aliquots of ice-cold Buffer A. Specific binding was defined as the total [125I] NMB bound minus that bound in the presence of 1 .mu.M unlabeled NMB.

The results of this experiment are presented on FIG. 2. BIM-26336 has a Ki value of 15.1 nM, while BIM26337 has a Ki value of 610 nM.

B. GRP Receptor

Membranes of the GRP receptor used in the binding assay were obtained by homogenizing cultured AR42J cells (Polytron, setting 6, 15 sec) in ice-cold 50 mM Tris-HC1 (Buffer A) and centrifuging twice as 39,000 x g (10 min), with an intermediate resuspension in fresh buffer. The final pellets were resuspended in the 50 mM Tris-HCl, containing 0.1 mg/ml bacitracin, and 0.1% BSA (Buffer B), and held on ice for the receptor binding assay. For the assay, aliquots (0.4 ml) were incubated with 0.05 ml [.sup.125 I-Tyr.sup.4 ] bombesin (.about.2200 Ci/mmol, New England Nuclear) and Buffer B, with and without 0.05 ml of unlabeled competing peptides. The experiment was performed with BIM-26336, BIM-23337, GRP, and NMB as competing peptides.

After a 30 min incubation (4.degree. C.), the bound [.sup.125 I]-Tyr.sup.4 ] bombesin was separated from the free by rapid filtration through GF/B filters which had been previously soaked in 0.3% polyethyleneimine. The filters were then washed three times with 5-ml aliquots of ice-cold Buffer A. Specific binding was defined as the total [.sup.125 I-Tyr.sup.4 ] bombesin bound minus that bound in the presence of 1 .mu.M unlabeled bombesin.

The results of this experiment are presented on FIG. 3. BIM-26336 has a Ki value of 6.6 nM, while BIM-26337 has a Ki value of 6.4 nM. BIM-26336, thus, effectively binds to both NMB and GRP receptors, while BIM-26337 possesses a more selective binding of GRP than NMB receptors.

II. Calcium Uptake Assay

The ability of BIM-26336 and BIM-26337 to activate both the GRP and NMB receptors were analyzed using a calcium uptake functional assay.

A. NMB Receptor

Xenopus oocytes, a frog egg naturally deprived of any receptors, were coinjected with both NMB receptor RNA and calcium photoprotein aequorin. The ability of SAP bombesins to induce change in intracellular calcium levels within the cells were measured luminometrically. See Spindel, et al., Recent Progress in Hormone Research 48:365 (1993); Corjay, et al., J. Biol. Chem. 266:18771 (1991); and Giladi et al., BioTechniques 10:744 (1991), all of which are hereby incorporated by reference.

The ability of bombesin, NMB, SAP bombesin-14, and SAP bombesin-10 to agonize the receptor was tested. FIG. 4 demonstrates the effect of these peptides on the level of intracellular calcium. The y-axis of the graph shows the relative luminometric response to the peptide while the xaxis depicts time elapsed in seconds. These results indicates that SAP bombesin-10 has nearly the same potency as NMB at the NMB receptor. The potency of SAP bombesin-14 and bombesin are approximately two log units less than that of NMB.

B. GRP Receptor

Xenopus oocytes were coinjected with both GRP receptor RNA and calcium photoprotein aequorin. The ability of SAP bombesins to induce change in intracellular calcium levels within the cells can be measured luminometrically.

The ability of bombesin, NMB, SAP bombesin-14, and SAP bombesin-10 to agonize the receptor was tested. FIG. 5 demonstrates the effect of these peptides on the level of intracellular calcium. The y-axis of the graph shows the relative luminometric response to the peptide while the x-axis depicts time elapsed in seconds. These results indicates that SAP bombesin-14 has a significantly greater potency than SAP bombesin-10 at the GRP receptor.

III. Thymidine Uptake Assay

Swiss 3T3/1R mouse embryo fibroblast cells were plated in 24 well tissue culture plates at a density of 2.times.10.sup.4 cells in 1 ml of Dublbecco's modified eagles medium (DMEM) supplemented with 40 mM glutamine (Gln) in 10% fetal bovine serum. Cells were incubated 3 or 4 days at 37% in a humidified atmosphere at 95% air/5% CO.sub.2 before replacing the growth medium with DMEM/Gln and 250 .mu.g/ml gentamicin. On the following day, 1 .mu.Ci thymidine was added to all wells, and activity was addressed by addition of test peptides alone or in the presence on 3 nM bombesin, respectively. After 24 h, the cells were rinsed with icecold isotonic saline and treated with ice-cold 5% trichloroacetic acid for 30 min. Cells were then rinsed with 95% ethanol and incubated with 0.1 N NaOH overnight at room temperature. One ml aliquots of neutralized samples were counted in a Packard Tri-Carb liquid scintillation analyzer. Test sample activity was measured in 2 independent experiments performed in quadruplicate.

This experiment was performed using 5 test samples: (1) bombesin (3 nM); (2) BIM-26336; (3) BIM-26337; (4) bombesin (3 nM) and BIM-26336; and (5) bombesin (3 nM)+BIM-26337. The results of these experiments are depicted on FIG. 6, wherein the x-axis depicts concentration of the respective SAP bombesin and the y-axis depicts disintegration per minute. The graph thus shows that both BIM-26336 and BIM-26337 induce thymidine uptake. Surprisingly, this effect is also substantially enhanced with the addition of a slight concentration of bombesin (3 nM).

The invention includes any peptide which is substantially homologous (i.e., 80% or greater) to SAP bombesins identified above as SEQ ID NO: 1 and SEQ ID NO: 2. "Homologous" refers to the sequence similarity between two peptides. When a position in both of the two compared sequences is occupied by identical amino acid monomeric subunits, it is homologous at that position. The homology between two sequences is a function of the number of matching or homologous positions shared by the two sequences. For example, if 8 of 10 of the positions in two sequences are occupied by identical amino acids then the two sequences are 80% homologous.

Other SAP bombesins which are also included in this invention are allelic variations, mammalian analogs, natural mutants, induced mutants, peptides encoded by DNA that hybridizes under high or low stringency conditions (see below) to SEQ ID NO: 3 or SEQ ID NO: 4, and peptides specifically bound by antisera to SEQ ID NO: 1 or SEQ ID NO: 2.

The invention also includes a pure DNA characterized as including a sequence which hybridizes under highly stringent conditions (e.g., as described in Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1989, hereby incorporated by reference) to a nucleic acid probe which includes at least a six-nucleotide segment (preferably at least 10 nucleotides) of SEQ ID NO: 3 or SEQ ID NO: 4. Alternatively, the DNA of the invention may be characterized as being capable of hybridizing under low-stringency conditions to a nucleic acid probe which includes the coding sequence of SEQ ID NO: 3 or SEQ ID NO: 4. An example of such low-stringency conditions is as follows: prehybridization in 50% formamide, 5X SSC, 25 mM potassium phosphate buffer (pH 7.4), 5X Denhardt's, and 50 .mu.g/ml denatured salmon sperm DNA for 4-12 hours at 20.degree. C.; hybridization for 12-24 hours at 20.degree. C.; and washing in 5X SSC containing 0.1 % SDS, at 20.degree. C.

The invention also includes any biologically active analog of SEQ ID NO: 1 or SEQ ID NO: 2. By "biologically active" is meant possessing at least 75% of the activity of bombesin or neuromedin.

Analogs can differ from naturally occurring SAP bombesins in amino acid sequence or can be modified in ways that do not involve the sequence, or both. Alterations in primary sequence include genetic variants, both natural and induced. Also included are analogs that include residues other than naturally occurring L-amino acids.

Other embodiments are also within the following claims.