US 5,672,501 AGrant
Base-Modified Enzymatic Nucleic Acid
Issue Date:1997-09-30
•16 Claims
•36 Drawing Sheets
Abstract
An enzymatic nucleic acid having a modification selected from pyridin-4-one, pyridin-2-one, phenyl, pseudouracil, 2, 4, 6-trimethoxy benzene, 3-methyluracil, dihydrouracil, naphthyl, 6-methyl-uracil and aminophenyl.
Metadata
Assignee
- Ribozyme Pharmaceuticals, Inc.
Inventors
- Jasenka Matulic-Adamic
- Leonid Beigelman
- Nassim Usman
- Alex Karpeisky
- Alex Burgin
Application Information
Application Number:US 5413656
Filing Date:1995-10-05
Priority Date:1994-12-23
Art Unit:189
Classifications
IPC:
C07H 2100C12N 506C12N 1500C12P 1934
Field of Search:
4355145366;91;91.31;91.5;172.3;240.1;240.2;172.14423.1;24.1;24.5
Patent Drawings (36 sheets)
Description
BACKGROUND OF THE INVENTION
This invention relates to enzymatic RNA molecules or ribozymes having a modified nucleotide base sequence.
Ribozymes are nucleic acid molecules having an enzymatic activity which is able to repeatedly cleave other separate RNA molecules in a nucleotide base sequence specific manner. Such enzymatic RNA molecules can be targeted to virtually any RNA transcript, and efficient cleavage achieved in vitro. Kim et al., 84 Proc. Natl. Acad. Sci. USA 8788, 1987; Haseloff and Gerlach, 334 Nature 585, 1988; Cech, 260 JAMA 3030, 1988; and Jefferies et al., 17 Nucleic Acids Research 1371, 1989.
Ribozymes act by first binding to a target RNA. Such binding occurs through the target RNA binding portion of a ribozyme which is held in close proximity to an enzymatic portion of the RNA which acts to cleave the target RNA. Thus, the ribozyme first recognizes and then binds a target RNA through complementary base-pairing, and once bound to the correct site, acts enzymatically to cut the target RNA. Strategic cleavage of such a target RNA will destroy its ability to direct synthesis of an encoded protein. After a ribozyme has bound and cleaved its RNA target it is released from that RNA to search for another target and can repeatedly bind and cleave new targets.
By "complementarity" is meant a nucleic acid that can form hydrogen bond(s) with other RNA sequence by either traditional Watson-Crick or other non-traditional types (for example, Hoogsteen type) of base-paired interactions.
Six basic varieties of naturally-occurring enzymatic RNAs are known presently. Each can catalyze the hydrolysis of RNA phosphodiester bonds in trans (and thus can cleave other RNA molecules) under physiological conditions. Table I summarizes some of the characteristics of these ribozymes. In general, enzymatic nucleic acids act by first binding to a target RNA. Such binding occurs through the target binding portion of a enzymatic nucleic acid which is held in close proximity to an enzymatic portion of the molecule that acts to cleave the target RNA. Thus, the enzymatic nucleic acid first recognizes and then binds a target RNA through complementary base-pairing, and once bound to the correct site, acts enzymatically to cut the target RNA. Strategic cleavage of such a target RNA will destroy its ability to direct synthesis of an encoded protein. After an enzymatic nucleic acid has bound and cleaved its RNA target, it is released from that RNA to search for another target and can repeatedly bind and cleave new targets.
The enzymatic nature of a ribozyme is advantageous over other technologies, such as antisense technology (where a nucleic acid molecule simply binds to a nucleic acid target to block its translation) since the effective concentration of ribozyme necessary to effect a therapeutic treatment is lower than that of an antisense oligonucleotide. This advantage reflects the ability of the ribozyme to act enzymatically. Thus, a single ribozyme molecule is able to cleave many molecules of target RNA. In addition, the ribozyme is a highly specific inhibitor, with the specificity of inhibition depending not only on the base pairing mechanism of binding, but also on the mechanism by which the molecule inhibits the expression of the RNA to which it binds. That is, the inhibition is caused by cleavage of the RNA target and so specificity is defined as the ratio of the rate of cleavage of the targeted RNA over the rate of cleavage of non-targeted RNA. This cleavage mechanism is dependent upon factors additional to those involved in base pairing. Thus, it is thought that the specificity of action of a ribozyme is greater than that of antisense oligonucleotide binding the same RNA site.
The following discussion of relevant art is dependent on the diagram shown in FIG. 1, in which the numbering of various nucleotides in a hammerhead ribozyme is provided. This is not to be taken as an indication that the Figure is prior art to the pending claims, or that the art discussed is prior art to those claims.
Odai et al., FEBS 1990, 267:150, state that substitution of guanosine (G) at position 5 of a hammerhead ribozyme for inosine greatly reduces catalytic activity, suggesting "the importance of the 2-amino group of this guanosine for catalytic activity."
Fu and McLaughlin, Proc. Natl. Acad. Sci. (USA) 1992, 89:3985, state that deletion of the 2-amino group of the guanosine at position 5 of a hammerhead ribozyme, or deletion of either of the 2'-hydroxyl groups at position 5 or 8, resulted in ribozymes having a decrease in cleavage efficiency.
Fu and McLaughlin, Biochemistry 1992, 31:10941, state that substitution of 7-deazaadenosine for adenosine residues in a hammerhead ribozyme can cause reduction in cleavage efficiency. They state that the "results suggest that the N.sup.7 -nitrogen of the adenosine (A) at position 6 in the hammerhead ribozyme/substrate complex is critical for efficient cleavage activity." They go on to indicate that there are five critical functional groups located within the tetrameric sequence GAUG in the hammerhead ribozyme.
Slim and Gait, 1992, BBRC 183, 605, state that the substitution of guanosine at position 12, in the core of a hammerhead ribozyme, with inosine inactivates the ribozyme.
Tuschl et al., 1993 Biochemistry 32, 11658, state that substitution of guanosine residues at positions 5, 8 and 12, in the catalytic core of a hammerhead, with inosine, 2-aminopurine, xanthosine, isoguanosine or deoxyguanosine cause significant reduction in the catalytic efficiency of a hammerhead ribozyme.
Fu et al., 1993 Biochemistry 32, 10629, state that deletion of guanine N.sup.7, guanine N.sup.2 or the adenine N.sup.6 -nitrogen within the core of a hammerhead ribozyme causes significant reduction in the catalytic efficiency of a hammerhead ribozyme.
Grasby et al., 1993 Nucleic Acids Res. 21, 4444, state that substitution of guanosine at positions 5, 8 and 12 positions within the core of a hammerhead ribozyme with O.sup.6 -methylguanosine results in an approximately 75-fold reduction in k.sub.cat.
Seela et al., 1993 Helvetica Chimica Acta 76, 1809, state that substitution of adenine at positions 13, 14 and 15, within the core of a hammerhead ribozyme, with 7-deazaadenosine does not significantly decrease the catalytic efficiency of a hammerhead ribozyme.
Adams et al., 1994 Tetrahedron Letters 35, 765, state that substitution of uracil at position 17 within the hammerhead ribozyme.cndot.substrate complex with 4-thiouridine results in a reduction in the catalytic efficiency of the ribozyme by 50 percent.
Ng et al., 1994 Biochemistry 33, 12119, state that substitution of adenine at positions 6, 9 and 13 within the catalytic core of a hammerhead ribozyme with isoguanosine, significantly decreases the catalytic activity of the ribozyme.
Jennings et al., U.S. Pat. No. 5,298,612, indicate that nucleotides within a "minizyme" can be modified. They state--
"Nucleotides comprise a base, sugar and a monophosphate group. Accordingly, nucleotide derivatives or modifications may be made at the level of the base, sugar or monophosphate groupings . . . . Bases may be substituted with various groups, such as halogen, hydroxy, amine, alkyl, azido, nitro, phenyl and the like."
WO93/23569, WO95/06731, WO95/04818, and WO95/133178 describe various modifications that can be introduced into ribozyme structures.
SUMMARY OF THE INVENTION
This invention relates to production of enzymatic RNA molecules or ribozymes having enhanced or reduced binding affinity and enhanced enzymatic activity for their target nucleic acid substrate by inclusion of one or more modified nucleotides in the substrate binding portion of a ribozyme such as a hammerhead, hairpin, VS ribozyme or hepatitis delta virus derived ribozyme. Applicant has recognized that only small changes in the extent of base-pairing or hydrogen bonding between the ribozyme and substrate can have significant effect on the enzymatic activity of the ribozyme on that substrate. Thus, applicant has recognized that a subtle alteration in the extent of hydrogen bonding along a substrate binding arm of a ribozyme can be used to improve the ribozyme activity compared to an unaltered ribozyme containing no such altered nucleotide. Thus, for example, a guanosine base may be replaced with an inosine to produce a weaker interaction between a ribozyme and its substrate, or a uracil may be replaced with a bromouracil (BrU) to increase the hydrogen bonding interaction with an adenosine. Other examples of alterations of the four standard ribonucleotide bases are shown in FIGS. 6a-d with weaker or stronger hydrogen bonding abilities shown in each figure.
In addition, applicant has determined that base modification within some catalytic core nucleotides maintains or enhances enzymatic activity compared to an unmodified molecule. Such nucleotides are noted in FIG. 7. Specifically, referring to FIG. 7, the preferred sequence of a hammerhead ribozyme in a 5' to 3' direction of the catalytic core is CUG ANG A G.cndot.C GAA A, wherein N can be any base or may lack a base (abasic); G.cndot.C is a base-pair. The nature of the base-paired stem II (FIGS. 1, 2 and 7) and the recognition arms of stems I and III are variable. In this invention, the use of base-modified nucleotides in those regions that maintain or enhance the catalytic activity and/or the nuclease resistance of the hammerhead ribozyme are described. (Bases which can be modified include those shown in capital letters).
Examples of base-substitutions useful in this invention are shown in FIGS. 6, 8-14 and 27B. In preferred embodiments cytidine residues are substituted with 5-alkylcytidines (e.g., 5-methylcytidine, FIG. 8, R.dbd.CH.sub.3, 9), and uridine residues with 5-alkyluridines (e.g., ribothymidine (FIG. 8, R.dbd.CH.sub.3, 4) or 5-halouridine (e.g., 5-bromouridine, FIG. 8, X.dbd.Br, 13) or 6-azapyrimidines (FIG. 8, 17) or 6-alkyluridine (FIG. 14). Guanosine or adenosine residues may be replaced by diaminopurine residues (FIG. 8, 22) in either the core or stems. In those bases where none of the functional groups are important in the complexing of magnesium or other functions of a ribozyme, they are optionally replaced with a purine ribonucleoside (FIG. 8, 23), which significantly reduces the complexity of chemical synthesis of ribozymes, as no base-protecting group is required during chemical incorporation of the purine nucleus. Furthermore, as discussed above, base-modified nucleotides may be used to enhance the specificity or strength of binding of the recognition arms with similar modifications. Base-modified nucleotides, in general, may also be used to enhance the nuclease resistance of the catalytic nucleic acids in which they are incorporated. These modifications within the hammerhead ribozyme motif are meant to be non-limiting example. Those skilled in the art will recognize that other ribozyme motifs with similar modifications can be readily synthesized and are within the scope of this invention.
Substitutions of sugar moieties as described in the art cited above, may also be made to enhance catalytic activity and/or nuclease stability.
Thus, in a first aspect, the invention features a modified ribozyme having one or more substrate binding arms including one or more modified nucleotide bases; and in a related aspect, the invention features a method for production of a more active modified ribozyme (compared to an unmodified ribozyme) by inclusion of one or more of such modified nucleotide bases in a substrate binding arm.
The invention provides ribozymes having increased enzymatic activity in vitro and in vivo as can be measured by standard kinetic assays. Thus, the kinetic features of the ribozyme are enhanced by selection of appropriate modified bases in the substrate binding arms. Applicant recognizes that while strong binding to a substrate by a ribozyme enhances specificity, it may also prevent separation of the ribozyme from the cleaved substrate. Thus, applicant provides means by which optimization of the base pairing can be achieved. Specifically, the invention features ribozymes with modified bases with enzymatic activity at least 1.5 fold (preferably 2 or 3 fold) or greater than the unmodified corresponding ribozyme. The invention also features a method for optimizing the kinetic activity of a ribozyme by introduction of modified bases into a ribozyme and screening for those with higher enzymatic activity. Such selection may be in vitro or in vivo. By enhanced activity is meant to include activity measured in vivo where the activity is a reflection of both catalytic activity and ribozyme stability. In this invention, the product of these properties in increased or not significantly (less that 10 fold) decreased in vivo compared to an all RNA ribozyme.
By "enzymatic portion" is meant that part of the ribozyme essential for cleavage of an RNA substrate.
By "substrate binding arm" is meant that portion of a ribozyme which is complementary to (i.e., able to base-pair with) a portion of its substrate. Generally, such complementarity is 100%, but can be less if desired. For example, as few as 10 bases out of 14 may be base-paired. Such arms are shown generally in FIGS. 1-3 as discussed below. That is, these arms contain sequences within a ribozyme which are intended to bring ribozyme and target RNA together through complementary base-pairing interactions; e.g., ribozyme sequences within stems I and III of a standard hammerhead ribozyme make up the substrate-binding domain (see FIG. 1).
By "unmodified nucleotide base" is meant one of the bases adenine, cytosine, guanosine, uracil joined to the 1' carbon of .beta.-D-ribo-furanose. The sugar also has a phosphate bound to the 5' carbon. These nucleotides are bound by a phosphodiester between the 3' carbon of one nucleotide and the 5' carbon of the next nucleotide to form RNA.
By "modified nucleotide base" is meant any nucleotide base which contains a modification in the chemical structure of an unmodified nucleotide base which has an effect on the ability of that base to hydrogen bond with its normal complementary base, either by increasing the strength of the hydrogen bonding or by decreasing it (e.g., as exemplified above for inosine and bromouracil). Other examples of modified bases include those shown in FIGS. 6a-d and other modifications well known in the art, including heterocyclic derivatives and the like.
In preferred embodiments the modified ribozyme is a hammerhead, hairpin VS ribozyme or hepatitis delta virus derived ribozyme, and the hammerhead ribozyme includes between 32 and 40 nucleotide bases. The selection of modified bases is most preferably chosen to enhance the enzymatic activity (as observed in standard kinetic assays designed to measure the kinetics of cleavage) of the selected ribozyme, i.e., to enhance the rate or extent of cleavage of a substrate by the ribozyme, compared to a ribozyme having an identical nucleotide base sequence without any modified base.
By "enzymatic nucleic acid molecule" it is meant a nucleic acid molecule which has complementarity in a substrate binding region to a specified gene target, and also has an enzymatic activity which is active to specifically cleave RNA in that target. That is, the enzymatic nucleic acid molecule is able to inter-molecularly cleave RNA and thereby inactivate a target RNA molecule. This complementarity functions to allow sufficient hybridization of the enzymatic nucleic acid molecule to the target RNA to allow the cleavage to occur. One hundred percent complementarity is preferred, but complementarity as low as 50-75% may also be useful in this invention.
In preferred embodiments of this invention, the enzymatic nucleic acid molecule is formed in a hammerhead or hairpin motif, but may also be formed in the motif of a hepatitis delta virus, group I intron or RNaseP RNA (in association with an RNA guide sequence) or Neurospora VS RNA. Examples of such hammerhead motifs are described by Rossi et al., 1992, Aids Research and Human Retroviruses 8, 183, of hairpin motifs by Hampel et al., EP0360257, Hampel and Tritz, 1989 Biochemistry 28, 4929, and Hampel et al., 1990 Nucleic Acids Res. 18, 299, and an example of the hepatitis delta virus motif is described by Perrotta and Been, 1992 Biochemistry 31, 16; of the RNaseP motif by Guerrier-Takada et al., 1983 Cell 35, 849, Neurospora VS RNA ribozyme motif is described by Collins (Saville and Collins, 1990 Cell 61, 685-696; Saville and Collins, 1991 Proc. Natl. Acad. Sci. USA 88, 8826-8830; Collins and Olive, 1993 Biochemistry 32, 2795-2799) and of the Group I intron by Cech et al., U.S. Pat. No. 4,987,071. These specific motifs are not limiting in the invention and those skilled in the art will recognize that all that is important in an enzymatic nucleic acid molecule of this invention is that it has a specific substrate binding site which is complementary to one or more of the target gene RNA regions, and that it have nucleotide sequences within or surrounding that substrate binding site which impart an RNA cleaving activity to the molecule.
In a preferred embodiment the invention provides a method for producing a class of enzymatic cleaving agents which exhibit a high degree of specificity for the RNA of a desired target. The enzymatic nucleic acid molecule is preferably targeted to a highly conserved sequence region of a target RNAs such that specific treatment of a disease or condition can be provided with either one or several enzymatic nucleic acids. Such enzymatic nucleic acid molecules can be delivered exogenously to specific cells as required.
By "kinetic assays" or "kinetics of cleavage" is meant an experiment in which the rate of cleavage of target RNA is determined. Often a series of assays are performed in which the concentrations of either ribozyme or substrate are varied from one assay to the next in order to determine the influence of that parameter on the rate of cleavage.
By "rate of cleavage" is meant a measure of the amount of target RNA cleaved as a function of time.
In a second aspect, enzymatic nucleic acid having a hammerhead configuration and modified bases which maintain or enhance enzymatic activity is provided. Such nucleic acid is also generally more resistant to nucleases than unmodified nucleic acid. By "modified bases" in this aspect is meant those shown in FIGS. 6 A-D, and 8, 14, AND 27B or their equivalents; such bases may be used within the catalytic core of the enzyme as well as in the substrate-binding regions. In particular, the invention features modified ribozymes having a base substitution selected from pyridin-4-one, pyridin-2-one, phenyl, pseudouracil, 2, 4, 6-trimethoxy benzene, 3-methyluracil, dihydrouracil, naphthyl, 6-methyl-uracil and aminophenyl. As noted above, substitution in the core may decrease in vitro activity but enhances stability. Thus, in vivo the activity may not be significantly lowered. As exemplified herein such ribozymes are useful in vivo even if active over all is reduced 10 fold. Such ribozymes herein are said to "maintain" the enzymatic activity on all RNA ribozyme.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawings will first briefly be described.
Drawings
FIG. 1 is a diagrammatic representation of the hammerhead ribozyme domain known in the art. Stem II can be .gtoreq.2 base-pair long. Each N is independently any base or non-nucleotide as used herein.
FIG. 2a is a diagrammatic representation of the hammerhead ribozyme domain known in the art; FIG. 2b is a diagrammatic representation of the hammerhead ribozyme as divided by Uhlenbeck (1987, Nature, 327, 596-600) into a substrate and enzyme portion; FIG. 2c is a similar diagram showing the hammerhead divided by Haseloff and Gerlach (1988, Nature, 334, 585-591) into two portions; and FIG. 2d is a similar diagram showing the hammerhead divided by Jeffries and Symons (1989, Nucl. Acids. Res., 17, 1371-1371) into two portions.
FIG. 3 is a diagrammatic representation of the general structure of a hairpin ribozyme. Helix 2 (H2) is provided with a least 4 base pairs (i.e., n is 1, 2, 3 or 4) and helix 5 can be optionally provided of length 2 or more bases (preferably 3-20 bases, i.e., m is from 1-20 or more). Helix 2 and helix 5 may be covalently linked by one or more bases (i.e., r is .gtoreq.1 base). Helix 1, 4 or 5 may also be extended by 2 or more base pairs (e.g., 4-20 base pairs) to stabilize the ribozyme structure, and preferably is a protein binding site. In each instance, each N and N' independently is any normal or modified base and each dash represents a potential base-pairing interaction. These nucleotides may be modified at the sugar, base or phosphate. Complete base-pairing is not required in the helices, but is preferred. Helix 1 and 4 can be of any size (i.e., o and p is each independently from 0 to any number, e.g., 20) as long as some base-pairing is maintained. Essential bases are shown as specific bases in the structure, but those in the art will recognize that one or more may be modified chemically (abasic, base, sugar and/or phosphate modifications) or replaced with another base without significant effect. Helix 4 can be formed from two separate molecules, i.e., without a connecting loop. The connecting loop when present may be a ribonucleotide with or without modifications to its base, sugar or phosphate. "q" is .gtoreq.2 bases. The connecting loop can also be replaced with a non-nucleotide linker molecule. H, refers to bases A, U or C. Y refers to pyrimidine bases. "- - - - - " refers to a chemical bond.
FIG. 4 is a representation of the general structure of the hepatitis delta virus ribozyme domain known in the art.
FIG. 5 is a representation of the general structure of the self-cleaving VS RNA ribozyme domain.
FIGS. 6a-d are diagrammatic representations of standard base modifications for adenine, guanine, cytosine and uracil, respectively.
FIG. 7 is a diagrammatic representation of a position numbered hammerhead ribozyme (according to Hertel et al., Nucleic Acids Res. 1992, 20:3252) showing specific substitutions in the catalytic core and substrate binding arms. Compounds 4, 9, 13, 17, 22, 23 are described in FIG. 8.
FIG. 8 is a diagrammatic representation of various nucleotides that can be substituted in the catalytic core of a hammerhead ribozyme.
FIG. 9 is a diagrammatic representation of the synthesis of a ribothymidine phosphoramidite.
FIG. 10 is a diagrammatic representation of the synthesis of a 5-methylcytidine phosphoramidite.
FIG. 11 is a diagrammatic representation of the synthesis of 5-bromouridine phosphoramidite.
FIG. 12 is a diagrammatic representation of the synthesis of 6-azauridine phosphoramidite.
FIG. 13 is a diagrammatic representation of the synthesis of 2,6-diaminopurine phosphoramidite.
FIG. 14 is a diagrammatic representation of the synthesis of a 6-methyluridine phosphoramidite.
FIG. 15 is a representation of a hammerhead ribozyme targeted to site A (HHA). Site of 6-methyl U substitution is indicated.
FIG. 16 shows RNA cleavage reaction catalyzed by HHA ribozyme containing 6-methyl U-substitution (6-methyl-U4). U4, represents a HHA ribozyme containing no 6-methyl-U substitution.
FIG. 17 is a representation of a hammerhead ribozyme targeted to site B (HHB). Sites of 6-methyl U substitution are indicated.
FIG. 18 shows RNA cleavage reaction catalyzed by HHB ribozyme containing 6-methyl U-substitutions at U4 and U7 positions (6-methyl-U4). U4, represents a HHB ribozyme containing no 6-methyl-U substitution.
FIG. 19 is a representation of a hammerhead ribozyme targeted to site C (HHC). Sites of 6-methyl U substitution are indicated.
FIG. 20 shows RNA cleavage reaction catalyzed by HHC ribozyme containing 6-methyl U-substitutions at U4 and U7 positions (6-methyl-U4). U4, represents a HHC ribozyme containing no 6-methyl-U substitution.
FIG. 21 shows 6-methyl-U-substituted HHA ribozyme-mediated inhibition of rat smooth muscle cell proliferation.
FIG. 22 shows 6-methyl-U-substituted HHC ribozyme-mediated inhibition of stromelysin protein production in human synovial fibroblast cells.
FIG. 23 is a diagrammatic representation of the synthesis of pyridin-2-one nucleoside and pyridin-4-one nucleoside phosphoramidite.
FIG. 24 is a diagrammatic representation of the synthesis of 2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopr opylphosphoramidite)-1-deoxy-1-phenyl-b-D-ribofuranose phosphoramidite.
FIG. 25 is a diagrammatic representation of the synthesis of pseudouridine, 2,4,6-trimethoxy benzene nucleoside and 3-methyluridine phosphoramidite.
FIG. 26 is a diagrammatic representation of the synthesis of dihydrouridine phosphoramidite.
FIG. 27 A) is diagrammatic representation of a hammerhead ribozyme targeted to site B. B) shows RNA cleavage reaction catalyzed by hammerhead ribozyme with modified base substitutions at either position 4 or position 7.
FIGS. 28(A) and 28(B) and 28(C) show further kinetic characterization of RNA cleavage reactions catalyzed by HH-B ribozyme (A); HH-B with pyridin-4-one substitution at position 7 (B); and HH-B with phenyl substitution at position 7(C).
FIG. 29 is a diagrammatic representation of the synthesis of 2-O-t-Butyldimethylsilyl-5-O-Dimethoxytrityl-3-O-(2-Cyanoethyl-N,N-diisopr opylphosphoramidite)-1-Deoxy-1-Naphthyl-.beta.-D-Ribofuranose.
FIG. 30 is a diagrammatic representation of the synthesis of Synthesis of 2-O-t-Butyldimethylsilyl-5-O-Dimethoxytrityl-3-O-(2-Cyanoethyl-N,N-diisopr opylphosphoramidite)-1-Deoxy-1-(p-Aminophenyl)-.beta.-D-Ribofuranose.
MODIFIED RIBOZYMES
There is a narrow range of binding free-energies between a ribozyme and its substrate that will produce maximal ribozyme activity. Such binding energy can be optimized by making ribozymes with G to I and U to BrU substitutions (or equivalent substitutions) in the substrate-binding arms. This allows manipulation of the binding free-energy without actually changing the target recognition sequence, the length of the two substrate-binding arms, or the enzymatic portion of the ribozyme. The shape of the free-energy vs. ribozyme activity curve can be readily determined using data from experiments in which each base (or several bases) is modified or unmodified, and without the complication of changing the size of the ribozyme/substrate interaction.
Such experiments will indicate the most active ribozyme structure. It is likely that only one or two modifications are necessary since a very small change in binding free energy (even one base-pair interaction) can dramatically affect ribozyme activity; the use of modified bases thus permits "fine tuning" of the binding free energy to assure maximal ribozyme activity. In addition, replacement of such bases, e.g., I for G, may permit a higher level of substrate specificity when cleavage of non-target RNA is a problem.
Method
Modified substrate binding arms can be synthesized using standard methodology. For example, phosphoramidites of inosine and 5-bromouracil can be used. Generally, a target site that has been optimized for stem I and III lengths (in a hammerhead ribozyme--other ribozymes can be treated in a similar manner), and that has G and/or U in the ribozyme portion of stem I and III, is selected. Modified ribozymes are made by replacing various G and U residues with I and BrU, respectively, during synthesis of the ribozyme. The modified ribozymes are then tested to determine kinetic parameters using standard procedures (see Draper et al., International PCT Publication No. WO 93/23569, hereby incorporated by reference herein). The binding affinities for the ribozymes can also be determined by standard procedures, e.g., by T-melt, gel-binding, or by competition kinetics assays. By comparison of binding affinity and ribozyme activity the optimum binding affinity of a ribozyme can then be found. Other combinations of G, I, U BrU, and other bases can then be tested with nearly identical binding free energy, but different base sequence, to determine whether factors other than simple binding free-energy play a role.
It is preferred to perform routine experiments of this type to select a desired ribozyme substrate binding sequence by use of an unmodified ribozyme with a modified substrate (which contains the modified bases). That is, the reverse experiment to that described above is performed. Such an experiment is more readily performed since the substrate is generally shorter than the ribozyme, and can be readily synthesized without concern about its secondary structure. Thus, a single ribozyme can be tested against a plurality of modified substrates in order to define which of the substrates provides better kinetic results. Once a preferred substrate is identified, the ribozyme can then be modified in a way which mirrors the selected substrate, and then tested against an unmodified substrate.
Such experiments will define useful ribozymes of this invention in which one or more modified bases are provided in the substrate binding arms with greater enzymatic activity in vitro and in vivo than comparable unmodified ribozymes. Such modifications may also be advantageous if they increase the resistance of a ribozyme to enzymatic degradation in vivo.
Synthesis of Ribozymes
Synthesis of nucleic acids greater than 100 nucleotides in length is difficult using automated methods, and the therapeutic cost of such molecules is prohibitive. In this invention, small enzymatic nucleic acid motifs (e.g., of the hammerhead or the hairpin structure) are used for exogenous delivery. The simple structure of these molecules increases the ability of the enzymatic nucleic acid to invade targeted regions of the mRNA structure.
The ribozymes are chemically synthesized. The method of synthesis used follows the procedure for normal RNA synthesis as described in Usman et al., 1987 J. Am. Chem. Soc., 109, 7845; Scaringe et al., 1990 Nucleic Acids Res., 18, 5433; and Wincott et al., 1995 Nucleic Acids Res. 23, 2677-2684 and makes use of common nucleic acid protecting and coupling groups, such as dimethoxytrityl at the 5'-end, and phosphoramidites at the 3'-end. Small scale synthesis were conducted on a 394 Applied Biosystems, Inc. synthesizer using a modified 2.5 .mu.mol scale protocol with a 5 min coupling step for alkylsilyl protected nucleotides and 2.5 min coupling step for 2'-O-methylated nucleotides. Table II outlines the amounts, and the contact times, of the reagents used in the synthesis cycle. A 6.5-fold excess (163 .mu.L of 0.1M=16.3 .mu.mol) of phosphoramidite and a 24-fold excess of S-ethyl tetrazole (238 .mu.L of 0.25M=59.5 .mu.mol) relative to polymer-bound 5'-hydroxyl was used in each coupling cycle. Average coupling yields on the 394 Applied Biosystems, Inc. synthesizer, determined by colorimetric quantitation of the trityl fractions, were 97.5-99%. Other oligonucleotide synthesis reagents for the 394 Applied Biosystems, Inc. synthesizer: detritylation solution was 2% TCA in methylene chloride (ABI); capping was performed with 16% N-methyl imidazole in THF (ABI) and 10% acetic anhydrides/10% 2,6-lutidine in THF (ABI); oxidation solution was 16.9 mM I.sub.2, 49 mM pyridine, 9% water in THF (Millipore). B & J Synthesis Grade acetonitrile was used directly from the reagent bottle. S-Ethyl tetrazole solution (0.25M in acetonitrile) was made up from the solid obtained from American International Chemical, Inc.
Deprotection of the RNA was performed as follows. The polymer-bound oligoribonucleotide, trityl-off, was transferred from the synthesis column to a 4 mL glass screw top vial and suspended in a solution of methylamine (MA) at 65.degree. C. for 10 min. After cooling to -20.degree. C., the supernatant was removed from the polymer support. The support was washed three times with 1.0 mL of EtOH:MeCN:H.sub.2 O/3:1:1, vortexed and the supernatant was then added to the first supernatant. The combined supernatants, containing the oligoribonucleotide, were dried to a white powder.
The base-deprotected oligoribonucleotide was resuspended in anhydrous TEA.cndot.HF/NMP solution (250 .mu.L of a solution of 1.5 mL N-methylpyrrolidinone, 750 .mu.L TEA and 1.0 mL TEA.cndot.3HF to provide a 1.4M HF concentration) and heated to 65.degree. C. for 1.5 h. The resulting, fully deprotected, oligomer was quenched with 50 mM TEAB (9 mL) prior to anion exchange desalting.
For anion exchange desalting of the deprotected oligomer, the TEAB solution was loaded onto a Qiagen 500.RTM. anion exchange cartridge (Qiagen Inc.) that was prewashed with 50 mM TEAB (10 mL). After washing the loaded cartridge with 50 mM TEAB (10 mL), the RNA was eluted with 2M TEAB (10 mL) and dried down to a white powder.
Inactive hammerhead ribozymes were synthesized by substituting a U for G.sub.5 and a U for A.sub.14 (numbering from (Hertel, K. J., et al., 1992, Nucleic Acids Res., 20, 3252)).
The average stepwise coupling yields were >98% (Wincott et al., 1995 Nucleic Acids Res. 23, 2677-2684).
Hairpin ribozymes are synthesized either as one part or in two parts and annealed to reconstruct the active ribozyme (Chowrira and Burke, 1992 Nucleic Acids Res., 20, 2835-2840).
Ribozymes are purified by gel electrophoresis using general methods or are purified by high pressure liquid chromatography (HPLC; See Stinchcomb et al., International PCT Publication No. WO 95/23225, the totality of which is hereby incorporated herein by reference) and are resuspended in water.
Various modifications to ribozyme structure can be made to enhance the utility of ribozymes. Such modifications will enhance shelf-life, half-life in vitro, stability, and ease of introduction of such ribozymes to the target site, e.g., to enhance penetration of cellular membranes, and confer the ability to recognize and bind to targeted cells.
Optimizing Ribozyme Activity
Ribozyme activity can be optimized as described by Stinchcomb et al., supra. The details will not be repeated here, but include altering the length of the ribozyme binding arms (stems I and III, see FIG. 2c), or chemically synthesizing ribozymes with modifications that prevent their degradation by serum ribonucleases (see e.g., Eckstein et al., International Publication No. WO 92/07065; Perrault et al., 1990 Nature 344, 565; Pieken et al., 1991 Science 253, 314; Usman and Cedergren, 1992 Trends in Biochem. Sci. 17, 334; Usman et al., International Publication No. WO 93/15187; Rossi et al., International Publication No. WO 91/03162; as well as Sproat, U.S. Pat. No. 5,334,711 which describe various chemical modifications that can be made to the sugar moieties of enzymatic RNA molecules). Modifications which enhance their efficacy in cells, and removal of stem II bases to shorten RNA synthesis times and reduce chemical requirements are desired. (All these publications are hereby incorporated by reference herein).
Administration of Ribozyme
Sullivan et al., PCT WO 94/02595, describes the general methods for delivery of enzymatic RNA molecules. Ribozymes may be administered to cells by a variety of methods known to those familiar to the art, including, but not restricted to, encapsulation in liposomes, by iontophoresis, or by incorporation into other vehicles, such as hydrogels, cyclodextrins, biodegradable nanocapsules, and bioadhesive microspheres. For some indications, ribozymes may be directly delivered ex vivo to cells or tissues with or without the aforementioned vehicles. Alternatively, the RNA/vehicle combination is locally delivered by direct injection or by use of a catheter, infusion pump or stent. Other routes of delivery include, but are not limited to, intravascular, intramuscular, subcutaneous or joint injection, aerosol inhalation, oral (tablet or pill form), topical, systemic, ocular, intraperitoneal and/or intrathecal delivery. More detailed descriptions of ribozyme delivery and administration are provided in Sullivan et al., supra and Draper et al., PCT WO93/23569 which have been incorporated by reference herein.
EXAMPLES
The following are non-limiting examples showing the synthesis and activity of base-modified catalytic nucleic acids.
Example 1: Synthesis of Hammerhead Ribozymes Containing Base-Modified Nucleotides
The method of synthesis used follows the procedure for normal RNA synthesis as described in Usman et al., J. Am. Chem. Soc. 1987, 109, 7845-7854; Scaringe et al., Nucleic Acids Res. 1990, 18, 5433-5441 and Wincott et al., 1995 Nucleic Acids Res. 23, 2677-2684 and makes use of common nucleic acid protecting and coupling groups, such as dimethoxytrityl at the 5'-end, and phosphoramidites at the 3'-end (compounds 4, 9, 13, 17, 22, 23). The average stepwise coupling yields were >98%. These base-modified nucleotides may be incorporated not only into hammerhead ribozymes, but also into hairpin, VS ribozymes, hepatitis delta virus, or Group I or Group II introns. They are, therefore, of general use as replacement motifs in any nucleic acid structure.
In the case of the hammerhead ribozyme the following specific substitutions may be used:
Referring to FIG. 7, in the catalytic core (numbered nucleotides), the pyrimidine C3 may be replaced by the cytosine analogs shown in FIG. 6c and compound 9 in FIG. 8.
Referring to FIG. 7, in the catalytic core (numbered nucleotides), the pyrimidines U4 and N7 may be replaced by the cytosine analogs shown in FIG. 4c, the uridine analogs shown in FIG. 6d and compounds 4,9,13 and 17 in FIG. 8 and FIG. 14.
Referring to FIG. 7, in the catalytic core (numbered nucleotides), the purines G5, G8 and G12 may be replaced by the guanine analogs shown in FIG. 6b and compounds 22 and 23 in FIG. 8.
Referring to FIG. 7, in the catalytic core (numbered nucleotides), the purines A6, A9, A13 and A14 may be replaced by the adenine analogs shown in FIG. 6a and compounds 22 and 23 in FIG. 8.
Referring to FIGS. 1 and 5, in stems I, II and III any of the pyrimidines may be replaced by the pyrimidine analogs shown in FIGS. 6c and 6d and compounds 4,9,13 and 17 in FIG. 8 and FIG. 14 as long as base-pairing is maintained in the stems.
Referring to FIGS. 1 2 and 7, in stems I, II and III any of the purines may be replaced by the purine analogs shown in FIGS. 6a and 6b and compounds 22 and 23 in FIG. 8 as long as base-pairing is maintained in the stems.
Referring to FIGS. 1 2 and 7, in loop II (denoted as loop II in FIG. 7) any nucleotide may be replaced by the pyrimidine analogs shown in FIGS. 6c and 6d, the purine analogs shown in FIGS. 6a and 6b and compounds 4,9,13, 17, 22 and 23 in FIG. 8 and FIG. 14.
Example 2: Synthesis of Ribothymidine Phosphoramidite 4
Referring to FIG. 9, ribothymidine 1 was prepared according to Vorbruggen et al., Chem. Ber. 1981, 114:1234, and tritylated to yield DMT derivative 2. 2 was silylated to yield 2'-O-TBDMS derivative 3. The phosphoramidite 4 was prepared according to Scaringe et al., Nucleic Acids Res. 1990, 18:5433.
Example 3: Synthesis of 5-Methylcytidine Phosphoramidite 9
Referring to FIG. 10, Ribothymidine 1 (4 g, 15.5 mmol) was co-evaporated with dry pyridine (2.times.100 ml) and redissolved in dry pyridine (100 ml). To the resulting solution 4,4'-DMT-Cl (6.3 g, 18.6 mmol) was added and the reaction mixture was left at room temperature (about 20.degree.-25.degree. C. for 16 hours. The reaction mixture was quenched with methanol (25 ml) and evaporated to dryness. The residue was partitioned between chloroform and 5% sodium bicarbonate. The organic layer was washed with 5% sodium bicarbonate and brine, then dried over sodium sulfate and evaporated. The residue was additionally dried by co-evaporation with dry pyridine (2.times.50 ml) then redissolved in dry pyridine (100 ml) and acetic anhydride (4.4 ml, 46.5 mmol) was added to the resulting solution. The reaction mixture was left at room temperature overnight, then quenched with methanol (25 ml), evaporated and worked-up as outlined above. The crude 5'-O-dimethoxytrityl-2',3',-di-O-acetyl-ribo-thymidine 5 was purified by flash chromatography on silica gel, (hexanes:ethylacetate:triethylamine/45:45:10 to give 6.86 g (68.7%) of 5 as a yellowish foam.
Triethylamine (14.72 ml, 105.6 mmol) was added dropwise to a stirred ice-cooled mixture of triazole (6.56 g, 95.04 mmol) and phosphorous oxychloride (2 ml, 21.2 mmol) in 100 ml of dry acetonitrile. A solution of nucleoside 5 (6.89, 10.56 mmol) in 50 ml of dry acetonitrile was added dropwise to the resulting suspension and the reaction mixture was stirred at room temperature for 4 hours. The reaction was concentrated, dissolved in chloroform and washed with a saturated aqueous solution of sodium bicarbonate, water, dried over sodium sulfate and evaporated to dryness. To a solution of the residue (7.24 g) in dioxane (120 ml) was added 40 ml of 29% aqueous NH.sub.4 OH and the resulting solution was left overnight, then evaporated to dryness to yield 6.86 g of crude cytidine derivative 6 which was used without purification.
To a solution of 6 (3.5 g, 6.25 mmol) in dry pyridine (100 ml) was added 3.97 ml of trimethylchlorosilane to transiently protect free sugar hydroxyls. The reaction mixture was then treated with isobutyryl chloride (0.98 ml, 9.375 mmol) for 5 hours. The resulting mixture was quenched with 10 ml of methanol, then 10 ml of water was added and after 10 minutes 10 ml of 29% aq. ammonia was added and the reaction mixture was stirred for 2 hours and evaporated to dryness. The resulting residue was worked-up as outlined above for the compound 5 and purified by flash chromatography on silica gel (ethylacetate:hexanes/1:3) to yield 2.37 g (60%) of the nucleoside 7.
To a solution of compound 7 (1.3 g, 2.06 mmol) in dry pyridine 0.97 g (5.72 mmol) of silver nitrate was added followed by 2.86 ml of a 1M solution of tert-butyldimethyl chloride in THF. The reaction mixture was left for 8 hours, evaporated, and dissolved in chloroform. The silver salt precipitate was filtered off and the reaction solution was washed with 5% aq. sodium bicarbonate and brine, dried over sodium sulfate and evaporated. The mixture of 2'- and 3'-isomers was separated by flash chromatography on silica gel (hexanes:ethylacetate/4:1) to yield 0.62 g (40%) of 2'-isomer 8, which was converted to the phosphoramidite 9 by the general method described in Scaringe et al., Nucleic Acids Res. 1990, 18:5433.
Example 4: Synthesis of 5-Bromouridine Phosphoramidite 13 (See, Talbat et al., Nucl. Acids Res. 18:3521-21, 1990)
Referring to FIG. 11, 5-Bromouridine 10 (1.615 g, 5 mmol) was co-evaporated with dry pyridine and redissolved in dry pyridine. To the resulting solution 2.03 g (6 mmol) of DMT-Cl was added and the reaction mixture was left overnight. After work-up and purification by flash chromatography on silica gel (chloroform:methanol/95:5) 2.5 g (80%) of the dimethoxytritylated compound 11 was obtained.
To a solution of 11 (2 g) in dry pyridine was added 1.5 eq. of TBDMS-Cl for 2 days. The reaction mixture was evaporated, dissolved in chloroform, washed with 5% aq. sodium bicarbonate and brine. The organic layer was dried over sodium sulfate, evaporated and purified by flash chromatography on silica gel (ethylacetate:hexanes/1:2) to yield 1.4 g (60%) of 2'-isomer 12, which was converted to the phosphoramidite 13 by the general method described in Scaringe et al., Nucleic Acids Res. 1990, 18:5433.
Example 5: Synthesis of 6-Azauridine Phosphoramidite 17
Referring to FIG. 12, 6-Azauridine (4.9 g, 20 mmol) was evaporated with dry pyridine (2.times.100 ml) and dissolved in dry pyridine (100 ml) and, after addition of 4,4'-DMT-Cl (7.45 g, 22 mmol) left for 16 hours at room temperature. The reaction mixture was diluted with dry MeOH (50 ml), evaporated to dryness, co-evaporated with toluene (2.times.100 ml), the residue dissolved in CHCl.sub.3 (500 ml) and washed with 5% NaHCO.sub.3 (100 ml), brine (100 ml), dried, and purified by flash chromatography (a gradient CHCl.sub.3 to 5% EtOH/CHCl.sub.3 to yield 1 g (92.2%) of intermediate) 15.
To a solution of 15 (3.23 g, 5.9 mmol) in 100 ml of dry THF, AgNO.sub.3 (7.08 mmol) and dry pyridine (2.1 ml, 4.4 mmol) were added. The reaction mixture was stirred at room temperature until full dissolution of AgNO.sub.3 (about 1 hour) occurred. Then 7 ml of a 1M solution of TBDMS-Cl in THF was added and the reaction mixture stirred for 16 hours at room temperature. The reaction mixture was filtered and the filtrate evaporated to dryness. The resulting residue was dissolved in CHCl.sub.3 (300 ml) and washed with 5% NaHCO.sub.3 (100 ml), brine (100 ml), dried, and purified by flash chromatography (gradient of hexanes to hexanes:ethyl acetate/1:1) to yield 3.71 g (62%) of 2'-TBDMS-isomer 16 which was converted to the phosphoramidite 17 by the general method described in Scaringe et al., Nucleic Acids Res. 1990, 18:5433.
Example 6: Synthesis of 2,6-Diaminopurine Phosphoramidite 22
Referring to FIG. 13, phosphoramidite 22 was prepared by the general method described in Scaringe et al., Nucleic Acids Res. 1990, 18:5433. Specifically, guanosine (11.32 g, 40 mmol) was dried by coevaporation with dry pyridine and redissolved in dry pyridine. Chlorotrimethylsilane (26.4 ml, 208 mmol) was added under stirring to the above solution and the reaction mixture was stirred overnight. To the resulting persilylated guanosine derivative phenylacetylchloride (12.7 ml, 96 mmol) was added dropwise and the reaction mixture was stirred for 12 hours. The reaction was quenched with 50 ml of methanol and 50 ml of water and stirred for 15 minutes, then 50 ml of 29% ammonia was added and the reaction mixture left for an additional 2 hours. Solvents were removed in vacuo, and the resulting oil was partitioned between ethyl acetate and water. The separated water layer was washed with ethyl acetate and was precipitated at 4.degree. C. The resulting solid was filtered off to give 8 g of N.sup.2 -phenylacetylguanosine 18. The mother liquor was concentrated to give additional crop (4 g). Overall yield .about.12 g (75%).
N.sup.2 Phenylacetylguanosine 18 (2.3 g, 5.73 mmol) was dried by coevaporation (3 times) with dry pyridine and dissolved in 50 ml of dry pyridine. To the resulting solution dimethoxytritylchloride (2.33 g, 6.88 mmol) was added and the reaction mixture was left at room temperature for 5 hours. The reaction was quenched with 25 ml of methanol and evaporated to dryness. The residue was dissolved in dichloromethane, washed with 5% aq. sodium bicarbonate and brine, dried over sodium sulfate and evaporated. The resulting oil was further dried by coevaporation with dry pyridine, dissolved in pyridine and treated with acetic anhydride (1.4 ml) for 4 hours at room temperature. The reaction mixture was quenched and worked-up as described above. The crude final compound was purified by flash chromatography on silica gel using dichloromethane:methanol/98:2 mixture as eluent. The desired fractions were collected and evaporated to give 3.5 g (77%) of 5'-O-dimethoxytrityl-2',3'-di-O-acetyl-N.sup.2 -phenylacetylguanosine 19 as a yellowish foam.
To a solution of compound 19 (3.5 g, 4.45 mmol) in 50 ml of dry dichloromethane, containing 3.11 ml of diisopropylethylamine, was added mesitylenesulfonyl chloride (1.9 g, 8.9 mmol) and dimethylaminopyridine (0.28 g). The reaction mixture was stirred for 30 minutes, evaporated and purified by flash chromatography on silica gel using dichloromethane (1 l) followed by 2% Methanol in dichloromethane (0.7 l) to give 2.8 g (64%) of O.sup.6 -mesitylene intermediate 20. To a solution of 20 in 40 ml of dry tetrahydrofuran lithium disulfide (0.3 g, 6.8 mmol) was added and the reaction mixture was stirred for 20 hours. The resulting clear solution was evaporated and worked-up as described above. The residue was purified by flash chromatography on silica gel in 1% Methanol in dichloromethane to give 1.1 g (31%) of 5'-O-dimethoxytrityl-2',3'-di-O-acetyl-N.sup.2 phenylacetyl-6-thioguanosine 21.
To an ice-cooled (0.degree. C.) solution of 5'-O-dimethoxytrityl-2',3'-di-O-acetyl-N.sup.2 phenylacetyl-6-thioguanosine 21 (1 g) in pyridine:methanol/20 ml:2.6 ml, 2.4 ml of 1M aq. sodium hydroxide were added and the reaction mixture was allowed to stay at 0.degree. C. for 20 minutes. The solution was neutralized with Dowex 2x8 (Pyr.sup.+) to pH 7. The resin was filtered off and washed with aq. pyridine. The combined filtrate and washings were evaporated and dried in vacuo to give quantitatively 5'-O-dimethoxytrityl-N.sup.2 phenylacetyl-6-thioguanosine.
To a stirred suspension of 5'-O-dimethoxytrityl-N.sup.2 phenylacetyl-6-thioguanosine (1.13 g, 1.57 mmol) in dry acetonitrile (35 ml) and triethylamine (1 ml) was added dinitrofluorobenzene (0.34 g, 1.88 mmol) and the reaction mixture was stirred under anhydrous conditions for 2 hours. The reaction was evaporated and worked-up as described for compound 20 and purified by flash chromatography on silica gel in 1% methanol in chloroform (containing 1% triethylamine) as an eluent to give 0.93 g (67%) of 5'-O-dimethoxytrityl-N.sup.2 phenylacetyl-6-S-dinitrophenyl guanosine.
To a solution of 5'-O-dimethoxytrityl-N.sup.2 phenylacetyl-6-S-dinitrophenyl guanosine (0.9 g, 1 mmol) in dry pyridine t-butyldimethylsilylchloride (0.46 g, 3 mmol) and tetrabutylammonium nitrate (3 mmol) were added and the reaction mixture was left for 50 hours. TLC (hexane:ethyl acetate/3:1) showed disappearance of the starting material and formation of two new compounds with a predominance of a lower R.sub.f (3'-O-silyl isomer according to .sup.1 H-NMR). The desired 2'-isomer (70 mg) was obtained after evaporation and work-up and separation by flash chromatography on silica gel using hexane:ethyl acetate/4:1 as eluent. The remaining mixture was rearranged in methanol with 2 drops of triethylamine and separated as above. This rearrangement procedure was repeated twice to finally give 250 mg of the desired 2'-isomer. 5'-O-dimethoxytrityl-2'-O-t-butyldimethylsilyl-N.sup.2 phenylacetyl-6-S-dinitrophenyl guanosine.
5'-O-Dimethoxytrityl-2'-O-t-butyldimethylsilyl-N.sup.2 phenylacetyl-6-S-dinitrophenyl guanosine (0.18 g, 0.18 mmol) was dissolved in dry tetrahydrofuran under dry argon. N-Methylimidazole (0.01 ml, 0.09 mmol) and sym-collidine (0.178 ml, 1.35 mmol) were added and the solution was ice-cooled. 2-Cyanoethyl N,N'-diisopropylchlorophosphoramidite (0.083 ml, 0.36 mmol) was added dropwise and stirring was continued for 3 hours at room temperature. The reaction mixture was again ice-cooled and quenched with 6 ml of dry degassed ethyl acetate. After 5 min stirring the mixture was concentrated in vacuo (40.degree. C.), dissolved in chloroform, washed with 5% aq sodium bicarbonate, then with brine and evaporated. The residue was purified by flash chromatography on silica gel using ethyl acetate:hexane/:3 containing 2% triethylamine as an eluent to yield 0.14 g (64%) 5'-O-dimethoxytrityl-2'-O-t-butyldimethylsilyl-N.sup.2 phenylacetyl-6-S-dinitrophenylguanosine-3'-(2-cyanoethyl N,N-diisopropylphosphoramidite) 22 as a yellow foam.
Example 7: Synthesis of 6-Methyl-uridine Phosphoramidite
Referring to FIG. 14, the suspension of 6-methyl-uracil (2.77 g, 21.96 mmol) in the mixture of hexamethyldisilazane (50 mL) and dry pyridine (50 mL) was refluxed for three hours. The resulting clear solution of trimethylsilyl derivative of 6-methyl uracyl was evaporated to dryness and coevaporated 2 times with dry toluene to remove traces of pyridine. To the solution of the resulting clear oil, in dry acetonitrile, 1-O-acetyl-2',3',5'-tri-O-benzoyl-b-D-ribose (10.1 g, 20 mmol) was added and the reaction mixture was cooled to 0.degree. C. To the above stirred solution, trimethylsilyl trifluoromethanesulfonate (4.35 mL, 24 mmol) was added dropwise and the reaction mixture was stirred for 1.5 h at 0.degree. C. and then 1 h at room temperature. After that the reaction mixture was diluted with dichloromethane washed with saturated sodium bicarbonate and brine. The organic layer was evaporated and the residue was purified by flash chromatography on silica gel with ethylacetate-hexane (2:1) mixture as an eluent to give 9.5 g (83%) of the compound 2 and 0.8 g of the corresponding N.sup.1,N.sup.3 -bis-derivative.
To the cooled (-10.degree. C.) solution of the compound (4.2 g, 7.36 mmol) in the mixture of pyridine (60 mL) and methanol (10 mL) ice-cooled 2M aqueous solution of sodium hydroxide (16 mL) was added with constant stirring. The reaction mixture was stirred at -10.degree. C. for additional 30 minutes and then neutralized to pH 7 with Dowex 50 (Py.sup.+). The resin was filtered off and washed with a 200 mL mixture of H.sub.2 O--Pyridine (4:1). The combined "mother liquor" and the washings were evaporated to dryness and dried by multiple coevaporation with dry pyridine. The residue was redissolved in dry pyridine and then mixed with dimethoxytrityl chloride (2.99 g, 8.03 mmol). The reaction mixture was left overnight at room temperature. Reaction was quenched with methanol (25 mL) and the mixture was evaporated. The residue was dissolved in dichloromethane, washed with saturated aqueous sodium bicarbonate and brine. The organic layer was dried over sodium sulfate and evaporated. The residue was purified by flash chromatography on silica gel using linear gradient of MeOH (2% to 5%) in CH.sub.2 Cl.sub.2 as eluent to give 3.4 g (83%) of the compound 6.
Example 8: Synthesis of 6-Methyl-cytidine Phosphoramidite
Triethylamine (13.4 ml, 100 mmol) was added dropwise to a stirred ice-cooled mixture of 1,2,4-triazole (6.22 g, 90 mmol) and phosphorous oxychloride (1.89 ml, 20 mmol) in 50 ml of anhydrous acetonitrile. To the resulting suspension the solution of 2',3',5'-tri-O-Benzoyl-6-methyl uridine (5.7 g, 10 mmol) in 30 ml of acetonitrile was added dropwise and the reaction mixture was stirred for 4 hours at room temperature. Then it was concentrated in vacuo to minimal volume (not to dryness). The residue was dissolved in chloroform and washed with water, saturated aq sodium bicarbonate and brine. The organic layer was dried over sodium sulfate and the solvent was removed in vacuo. The residue was dissolved in 100 ml of 1,4-dioxane and treated with 50 mL of 29% aq NH.sub.4 OH overnight. The solvents were removed in vacuo. The residue was dissolved in the in the mixture of pyridine (60 mL) and methanol (10 mL), cooled to -15.degree. C. and ice-cooled 2M aq solution of sodium hydroxide was added under stirring. The reaction mixture was stirred at -10.degree. to -15.degree. C. for additional 30 minutes and then neutralized to pH 7 with Dowex 50 (Py.sup.+). The resin was filtered off and washed with 200 mL of the mixture H.sub.2 O --Py (4:1). The combined mother liquor and washings were evaporated to dryness. The residue was crystallized from aq methanol to give 1.6 g (62%) of 6-methyl cytidine.
To the solution of 6-methyl cytidine (1.4 g, 5.44 mmol) in dry pyridine 3.11 mL of trimethylchlorosilane was added and the reaction mixture was stirred for 2 hours at room temperature. Then acetic anhydride (0.51 mL, 5.44 mmol) was added and the reaction mixture was stirred for additional 3 hours at room temperature. TLC showed disappearance of the starting material and the reaction was quenched with MeOH (20 mL), ice-cooled and treated with water (20 mL, 1 hour). The solvents wee removed in vacuo and the residue was dried by four coevaporations with dry pyridine. Finally it was redissolved in dry pyridine and dimethoxytrityl chloride (2.2 g, 6.52 mmol) was added. The reaction mixture was stirred overnight at room temperature and quenched with MeOH (20 mL). The solvents were removed in vacuo. The remaining oil was dissolved in methylene chloride, washed with saturated sodium bicarbonate and brine. The organic layer was separated and evaporated and the residue was purified by flash chromatography on silica gel with the gradient of MeOH in methylene chloride (3% to 5%) to give 2.4 g (74%) of the compound (4).
Example 9: Synthesis of 6-Aza-uridine and 6-Aza-cytidine
To the solution of 6-aza uridine (5 g, 20.39 mmol) in dry pyridine dimethoxytrityl chloride (8.29 g, 24.47 mmol) was added and the reaction mixture was left overnight at room temperature. Then it was quenched with methanol (50 mL) and the solvents were removed in vacuo. The remaining oil was dissolved in methylene chloride and washed with saturated aq sodium bicarbonate and brine. The organic layer was separated and evaporated to dryness. The residue was additionally dried by multiple coevaporations with dry pyridine and finally dissolved in dry pyridine. Acetic anhydride (4.43 mL, 46.7 mmol) was added to the above solution and the reaction mixture was left for 3 hours at room temperature. Then it was quenched with methanol and worked-up as above. The residue was purified by flash chromatography on silics gel using mixture of 2% of MeOH in methylene chloride as an eluent to give 9.6 g (75%) of the compound.
Triethylamine (23.7 ml, 170.4 mmol) was added dropwise to a stirred ice-cooled mixture of 1,2,4-triazole (10.6 g, 153.36 mmol) and phosphorous oxychloride (3.22 ml, 34.08 mmol) in 100 ml of anhydrous acetonitrile. To the resulting suspension the solution of 2',3'-di-O-Acetyl-5'-O-Dimethoxytrityl-6-aza Uridine (7.13 g, 11.36 mmol) in 40 ml of acetonitrile was added dropwise and the reaction mixture was stirred for 6 hours at room temperature. Then it was concentrated in vacuo to minimal volume (not to dryness). The residue was dissolved in chloroform and washed with water, saturated aq sodium bicarbonate and brine. The organic layer was dried over sodium sulfate and the solvent was removed in vacuo. The residue was dissolved in 150 ml of 1,4-dioxane and treated with 50 mL of 29% aq NH.sub.4 OH for 20 hours at room temperature. The solvents were removed in vacuo. The residue was purified by flash chromatigraphy on silica gel using linear gradient of MeOH (4% to 10%) in methylene chloride as an eluent to give 3.1 g (50%) of azacytidine.
To the stirred solution of 5'-O-Dimethoxytrityl-6-aza cytidine (3 g, 5.53 mmol) in anhydrous pyridine trimethylchloro silane (2.41 mL, 19 mmol) was added and the reaction mixture was left for 4 hours at room temperature. Then acetic anhydride (0.63 mL, 6.64 mmol) was added and the reaction mixture was stirred for additional 3 hours at room temperature. After that it was quenched with MeOH (15 mL) and the solvents were removed in vacuo. The residue was treated with 1M solution of tetrabutylammonium fluoride in THF (20.degree., 30 min) and evaporated to dryness. The remaining oil was dissolved in methylene chloride, washed with saturated aq sodium bicarbonate and water. The separated organic layer was dried over sodium sulfate and evaporated to dryness. The residue was purified by flash chromatography on silica gel using 4% MeOH in methylene chloride as an eluent to give 2.9 g (89.8%) of the compound.
General Procedure for the Introducing of the TBDMS-Group: To the stirred solution of the protected nucleoside in 50 mL of dry THF and pyridine (4 eq) AgNO.sub.3 (2.4 eq) was added. After 10 minutes tert-butyldimethylsilyl chloride (1.5 eq) was added and the reaction mixture was stirred at room temperature for 12 hours. The resulted suspension was filtered into 100 mL of 5% aq NaHCO.sub.3. The solution was extracted with dichloromethane (2.times.100 mL). The combined organic layer was washed with brine, dried over Na.sub.2 SO.sub.4 and evaporated. The residue was purified by flash chromatography on silica gel with hexanes-ethylacetate (3:2) mixture as eluent.
General Procedure for Phosphitylation: To the ice-cooled stirred solution of protected nucleoside (1 mmol) in dry dichloromethane (20 mL) under argon blanket was added dropwise via syringe the premixed solution of N,N-diisopropylethylamine (2.5 eq) and 2-cyanoethyl N'N-diisopropylchlorophosphoramidite (1.2 eq) in dichloromethane (3 mL). Simultaneously via another syringe N-methylimidazole (1 eq) was added and stirring was continued for 2 hours at room temperature. After that the reaction mixture was again ice-cooled and quenched with 15 ml of dry methanol. After 5 min stirring, the mixture was concentrated in vacuo (<40.degree. C.) and purified by flash chromatography on silica gel using hexanes-ethylacetate mixture contained 1% triethylamine as an eluent to give corresponding phosphoroamidite as white foam.
Example 10: RNA Cleavage Activity of HHA Ribozyme Substituted with 6-Methyl-Uridine
Hammerhead ribozymes targeted to site A (see FIG. 15) were synthesized using solid-phase synthesis, as described above. U4 position was modified with 6-methyl-uridine.
RNA cleavage assay in vitro:
Substrate RNA is 5' end-labeled using .gamma.-.sup.32 P! ATP and T4 polynucleotide kinase (US Biochemicals). Cleavage reactions were carried out under ribozyme "excess" conditions. Trace amount (.ltoreq.1 nM) of 5' end-labeled substrate and 40 nM unlabeled ribozyme are denatured and renatured separately by heating to 90.degree. C. for 2 min and snap-cooling on ice for 10-15 min. The ribozyme and substrate are incubated, separately, at 37.degree. C. for 10 min in a buffer containing 50 mM Tris-HCl and 10 mM MgCl.sub.2. The reaction is initiated by mixing the ribozyme and substrate solutions and incubating at 37.degree. C. Aliquots of 5 .mu.l are taken at regular intervals of time and the reaction is quenched by mixing with equal volume of 2.times. formamide stop mix. The samples are resolved on 20% denaturing polyacrylamide gels. The results are quantified and percentage of target RNA cleaved is plotted as a function of time.
Referring to FIG. 16, hammerhead ribozymes containing 6-methyl-uridine modification at U4 position cleave the target RNA efficiently.
Example 11: RNA Cleavage Activity of HHB Ribozyme Substituted with 6-Methyl-Uridine
Hammerhead ribozymes targeted to site B (see FIG. 17) were synthesized using solid-phase synthesis, as described above. U4 and U7 positions were modified with 6-methyl-uridine.
RNA cleavage reactions were carried out as described above. Referring to FIG. 18, hammerhead ribozymes containing 6-methyl-uridine modification at U4 and U7 positions cleave the target RNA efficiently.
Example 12: RNA Cleavage Activity of HHC Ribozyme Substituted with 6-Methyl-Uridine
Hammerhead ribozymes targeted to site C (see FIG. 19) were synthesized using solid-phase synthesis, as described above. U4 and U7 positions were modified with 6-methyl-uridine.
RNA cleavage reactions were carried out as described above. Referring to FIG. 20, hammerhead ribozymes containing 6-methyl-uridine modification at U4 positions cleave the target RNA efficiently.
Sequences listed in FIGS. 7, 15, 17, 19, and others and the modifications described in these figures are meant to be non-limiting examples. Those skilled in the art will recognize that variants (base-substitutions, deletions, insertions, mutations, chemical modifications) of the ribozyme and RNA containing other 2'-hydroxyl group modifications, including but not limited to amino acids, peptides and cholesterol, can be readily generated using techniques known in the art, and are within the scope of the present invention.
Example 13: Inhibition of Rat Smooth Muscle Cell Proliferation by 6-Methyl-U Substituted Ribozyme HHA
Hammerhead ribozyme (HHA) is targeted to a unique site (site A) within c-myb mRNA. Expression of c-myb protein has been shown to be essential for the proliferation of rat smooth muscle cell (Brown et al., 1992 J. Biol. Chem. 267, 4625).
The ribozymes that cleaved site A within c-myb RNA described above were assayed for their effect on smooth muscle cell proliferation. Rat vascular smooth muscle cells were isolated and cultured as described (Stinchcomb et al., supra). HHA ribozymes were complexed with lipids and delivered into rat smooth muscle cells. Serum-starved cells were stimulated as described by Stinchcomb et al., supra. Briefly, serum-starved smooth muscle cells were washed twice with PBS, and the RNA/lipid complex was added. The plates were incubated for 4 hours at 37.degree. C. The medium was then removed and DMEM containing 10% FBS, additives and 10 .mu.M bromodeoxyuridine (BrdU) was added. In some wells, FBS was omitted to determine the baseline of unstimulated proliferation. The plates were incubated at 37.degree. C. for 20-24 hours, fixed with 0.3% H.sub.2 O.sub.2 in 100% methanol, and stained for BrdU incorporation by standard methods. In this procedure, cells that have proliferated and incorporated BrdU stain brown; non-proliferating cells are counter-stained a light purple. Both BrdU positive and BrdU negative cells were counted under the microscope. 300-600 total cells per well were counted. In the following experiments, the percentage of the total cells that have incorporated BrdU (% cell proliferation) is presented. Errors represent the range of duplicate wells. Percent inhibition then is calculated from the % cell proliferation values as follows: % inhibition=100--100 (Ribozyme--0% serum)/(Control--0% serum).
Referring to FIG. 21, active ribozymes substituted with 6-methyl-U at position 4 of HHA were successful in inhibiting rat smooth muscle cell proliferation. A catalytically inactive ribozyme (inactive HHA), which has two base substitutions within the core (these mutations inactivate a hammerhead ribozyme; Stinchcomb et al., supra), does not significantly inhibit rat smooth muscle cell proliferation.
Example 14: Inhibition of Stromelysin Production in Human Synovial Fibroblast Cells by 6-Methyl-U Substituted Ribozyme HHC
Hammerhead ribozyme (HHC) is targeted to a unique site (site C) within stromelysin mRNA.
The general assay was as described (Draper et al., supra). Briefly, fibroblasts, which produce stromelysin, are serum-starved overnight and ribozymes or controls are offered to the cells the next day. Cells were maintained in serum-free media. The ribozyme were applied to the cells as free ribozyme, or in association with various delivery vehicles such as cationic lipids (including Transfectam.TM., Lipofectin.TM. and Lipofectamine.TM.), conventional liposomes, non-phospholipid liposomes or biodegradable polymers. At the time of ribozyme addition, or up to 3 hours later, Interleukin-1.alpha. (typically 20 units/ml) can be added to the cells to induce a large increase in stromelysin expression. The production of stromelysin can then be monitored over a time course, usually up to 24 hours.
Supernatants were harvested 16 hours after IL-1 induction and assayed for stromelysin expression by ELISA. Polyclonal antibody against Matrix Metalloproteinase 3 (Biogenesis, NH) was used as the detecting antibody and anti-stromelysin monoclonal antibody was used as the capturing antibody in the sandwich ELISA (Maniatis et al., supra) to measure stromelysin expression.
Referring to FIG. 22, HHC ribozyme containing 6-methyl-U modification, caused a significant reduction in the level of stromelysin protein production. Catalytically inactive HHC had no significant effect on the protein level.
Example 15: Synthesis of Pyridin-2(4)-one Nucleoside 3'-Phosphoramidites
General procedure for the preparation of 1-(2,3,5-tri-O-benzoyl-.beta.-D-ribofuranosyl)-2(4)-pyridones (3) and (9)
Referring to FIG. 23, 2- or 4-hydroxypyridine (1) or (8) (2.09 g, 22 mmol), 1-O-acetyl-2,3,5-tri-O-benzoyl- .beta.-D-ribofuranose (2) (10.08 g, 20 mmol) and BSA (5.5 ml, 22 mmol) were dissolved in dry acetonitrile (100 ml) under argon at 70.degree. C. (oil bath) and the mixture stirred for 10 min. Trimethylsilyl trifluoromethanesulfonate (TMSTfl) (5.5 ml, 28.5 mmol) was added and the mixture was stirred for an additional hour for 1 or four hours for 8. The mixture was then cooled to room temperature (RT) followed by dilution, with CHCl.sub.3 (200 ml), and extraction, with sat. aq. NaHCO.sub.3 solution. The organic layer was washed with brine, dried (Na.sub.2 SO.sub.4) and evaporated to dryness in vacuo. The residue was chromatographed on the column of silica gel; 1-5% gradient of methanol in dichloromethane was used for purification of 3 (98% yield) and 2-10% gradient of methanol in dichloromethane for purification of 9 (84% yield).
1-(.beta.-D-Ribofuranosyl)-2(4)-pyridones (4) and (10)
3 or 9 (18 mmol) was dissolved in 0.3M NaOCH.sub.3 (150 ml) and the solution was stirred at RT for 1 hour. The mixture was then neutralized, with Dowex 50WX8 (Py.sup.+), the ion-exchanger was filtered off and the filtrate was concentrated to a syrup in vacuo. The residue was dissolved in water (100 ml) and the solution was washed with chloroform (2.times.50 ml) and ether (2.times.50 ml). The aqueous layer was evaporated to dryness and the residue was then crystallized from ethyl acetate (3.9 g, 91% 4; Niedballa et al., Nucleic Acid Chemistry, Part 1, Townsend, L. B. and Tipson, R. S., Ed.; J. Wiley & Sons, Inc.; New York, 1978, p 481-484); 10 (Niedballa and Vorbruggen, J. Org. Chem. 1974, 39, 3668-3671) was crystallized from ethanol (3.6 g, 84%).
1-(2-O-TBDMSi-5-O-DMT-.beta.-D-ribofuranosyl)-2(4)-pyridones
4 or 10 was 5'-O-dimethoxytritylated according to the standard procedure (see Oligonucleotide Synthesis: A Practical Approach, M. J. Gait Ed.; IRL Press, Oxford, 1984, p 27) to yield 5 in 76% yield and pyridin-4-one derivative in 67% yield in the form of yellowish foams after silica gel column chromatography (0.5-10% gradient of methanol in dichloromethane). These compounds were treated with t-butyldimethylsilyl chloride under the conditions described by Hakimelahi et al., Can. J. Chem. 1982, 60, 1106-1113, and the reaction mixtures were purified by the silica gel column chromatography (20-50% gradient of ethyl acetate in hexanes) to enable faster moving 2'-O-TBDMSi isomers (68.5% and 55%, respectively) as colorless foams.
1-2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diiso propylphosphoramidite!-2(4)-pyridones (7) and (11)
1-(2-O-TBDMS-5-O-DMT-.beta.-D-ribofuranosyl)-2(4)-pyridones were phosphitylated under conditions described by Tuschl et al., Biochemistry 1993, 32, 11658-11668, and the products were isolated by silica gel column chromatography using 15-50% gradient of ethyl acetate in hexanes (1% Et.sub.3 N) for 7 (89% yield) and dichloromethane (1% Et.sub.3 N) for 11 (94% yield).
Phosphoramidites 7 and 11 were incorporated into ribozymes and substrates using the method of synthesis, deprotection, purification and testing previously described (Wincott et al., 1995 supra). The average stepwise coupling yields were .about.98%.
Example 16: Synthesis of 2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopr opylphosphoramidite)-1-deoxy-1-phenyl-.beta.-D-ribofuranose (8) Phosphoramidites
5-O-t-Butyldiphenylsilyl-2,3-O-isopropylidene-1-deoxy-1-phenyl-.beta.-D-rib ofuranose (3)
Referring to FIG. 24, compound 3 was prepared using the procedure analogous to that described by Czernecki and Ville, J. Org. Chem. 1989, 54, 610-612. Contrary to their result, we succeeded in obtaining the title compound, by using the more acid resistant t-butyldiphenylsilyl group for 5-O-protection, instead of t-butyldimethylsilyl.
1-Deoxy-1-phenyl-.beta.-D-ribofuranose (5)
Compound 3 (1 g, 2.05 mmol) was dissolved in THF (20 ml) and the solution was mixed with 1M TBAF in THF (3 ml, 3 mmol). The reaction mixture was stirred at RT for 30 min followed by evaporation into a syrup. The residue was applied on to a silica gel column and eluted with hexanes followed by 5-70% gradient of ethyl acetate in hexanes. The 5-O-desilylated product was obtained as a colorless foam (0.62 g, 88% yield). This material was dissolved in 70% acetic acid and heated at 100.degree. C. (oil bath) for 30 min. Evaporation to dryness under reduced pressure and crystallization of the residual syrup from toluene resulted in 5 (0.49 g, 94% yield), mp 120.degree.-121.degree. C.
2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-1-deoxy-1-phenyl-.beta.-D-ribo furanose (7)
Compound 5 (770 mg, 3.66 mmol) was 5-O-dimethoxytritylated according to the standard procedure (Oligonucleotide Synthesis: A Practical Approach, M. J. Gait Ed.; IRL Press, Oxford, 1984, p 27) to yield 1.4 g (75% yield) of 5-O-dimethoxytrityl derivative as a yellowish foam, following silica gel column chromatography (0.5-2% gradient of methanol in dichloromethane). This material was treated with t-butyldimethylsilyl chloride under the conditions described by Hakimelahi et al., Can. J. Chem. 1982, 60, 1106-1113, and the reaction mixture was purified by silica gel column chromatography (2-10% gradient of ethyl acetate in hexanes) to afford a slower moving 2'-O-TBDMSi isomer 7 (0.6 g, 35% yield) as a colorless foam. The faster migrating 3'-O-TBDMSi isomer 6 was also isolated (0.55 g, 32% yield).
2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopro pylphosphoramidite)-1-deoxy-1-phenyl-.beta.-D-ribofuranose (8)
Compound 7 (0.87 g, 1.39 mmol) was phosphitylated under conditions described by Tuschl et al., supra and the product was isolated by silica gel column chromatography using 0.5% ethyl acetate in toluene (1% Et.sub.3 N) for elution (0.85 g, 74% yield).
Example 17: Synthesis of Pseudouridine, 3-Methyluridine and 2,4,6-Trimethoxy Benzene Nucleoside Phosphoramidites
Starting with a pseudo uridine, 3-methyluridine or 2,4,6-trimethoxy benzene nucleoside (Gasparutto et al., Nucleic Acid Res. 1992 20, 5159-5166; Kalvoda and Farkas, Nucleic Acid Chemistry, Part 1, Townsend, L. B. and Tipson, R. S., Ed.; J. Wiley & Sons, Inc.; New York, 1978, p 481-484), phosphoramidites can be prepared by standard protocols described below.
General Procedure for the Introducing of the TBDMS-Group: To the stirred solution of the protected nucleoside in 50 mL of dry THF and pyridine (4 eq) AgNO.sub.3 (2.4 eq) was added. After 10 minutes tert-butyldimethylsilyl chloride (1.5 eq) was added and the reaction mixture was stirred at room temperature for 12 hours. The resulted suspension was filtered into 100 mL of 5% aq NaHCO.sub.3. The solution was extracted with dichloromethane (2.times.100 mL). The combined organic layer was washed with brine, dried over Na.sub.2 SO.sub.4 and evaporated. The residue was purified by flash chromatography on silica gel with hexanes-ethylacetate (3:2) mixture as eluent.
General Procedure for Phosphitylation: To the ice-cooled stirred solution of protected nucleoside (1 mmol) in dry dichloromethane (20 mL) under argon blanket was added dropwise via syringe the premixed solution of N,N-diisopropylethylamine (2.5 eq) and 2-cyanoethyl N'N-diisopropylchlorophosphoramidite (1.2 eq) in dichloromethane (3 mL). Simultaneously via another syringe N-methylimidazole (1 eq) was added and stirring was continued for 2 hours at room temperature. After that the reaction mixture was again ice-cooled and quenched with 15 ml of dry methanol. After 5 min stirring, the mixture was concentrated in vacuo (<40.degree. C.) and purified by flash chromatography on silica gel using hexanes-ethylacetate mixture contained 1% triethylamine as an eluent to give corresponding phosphoroamidite as white foam.
Pseudouridine, 3-methyluridine or 2,4,6-trimethoxy benzene phosphoramidites were incorporated into ribozymes using solid phase synthesis as described by Wincott et al., 1995 supra. The ribozymes were deprotected using the standard protocol described above with the exception of ribozymes with pseudouridine. Pseudouridine-modified ribozymes were deprotected first by incubation at room temperature, instead of at 55.degree. C., for 24 hours in a mixture of ethanolic ammonia (3:1).
Example 18: Synthesis of Dihydrouridine Phosphoramidites
Referring to FIG. 26, dihydrouridine phosphoramidite was synthesized base on the method described in Chaix et al., 1989 Nucleic Acid Res. 17, 7381-7393:
i. Uridine (1; 10 g, 41 mmoles) was dissolved in 200 ml distilled water and to the solution 2 g of Rh (10% on alumina) was added. The slurry was brought to 60 psi of hydrogen, and hydrogenation was continued for 16 hrs. Reaction was monitored by disappearance of UV absorbing material. All of starting material was converted to dihdrouridine (DHU) and tetrahydrouridine (2:1 based on NMR). Tetrahydrouridine was not removed at this step.
ii. Dihydrouridine (2; 10 g, 41 mmoles) was dissolved in 400 ml dry pyridine; dimethylaminopyridine (0.244 g,2 mmoles), triethylamine (7.93 ml, 56 mmoles), and dimethoxytritylchloride (16.3 g, 48 mmoles) were added and stirred under argon overnight. The reaction was quenched with 50 ml methanol, extracted with 400 ml 5% sodium bicarbonate, and then 400 ml brine. The organic phase was dried over sodium sulphate, filtered, and then dried to a foam. 5'-DMT-DHU (3) was purified by silica gel chromatography (dichloromethane with 0.5-5% gradient of methanol; final yield=9 g; 16.4 mmoles).
iii. 5'-DMT-DHU (3; 9.0 g, 16.4 mmoles) was dissolved in 150 ml dry THF. Pyridine (4.9 ml, 60 mmoles) and silver nitrate (3.35 g, 19.7 mmoles) were added at room temperature and stirred under argon for 10 min., then tert-butyldimethylsilylchloride (tBDMS-Cl; 3.0 g, 19.7 mmoles) was added and the slurry was stirred under argon overnight. The reaction was filtered over celite into 500 ml aqueous 5% sodium bicarbonate and then extracted with 200 ml chloroform. The organic phase was washed with 250 ml brine, dried over sodium sulfate, and then evaporated to a yellow foam. 2'-tBDMS, 5'-DMT-DHU (4) was purified by silica gel chromatography (hexanes with 10-50% gradient ether; final yield=5.1 g; 7.7 mmoles), dried over sodium sulfate, filtered, and then dried to a white powder. The product was kept under high vacuum for 48 hrs.
iv. 5'-DMT, 2'-tBDMS-DHU (4; 2.10 g, 3.17 mmoles) was dissolved in 40 ml anhydrous dichloromethane. NN-dimethylaminopyridine (2.21 ml, 12.7 mmoles), N-methylimidizole (1.27 ml, 1.59 mmoles), and chloro-diisopropylcyanoethylphosphoramidite (1.2 ml, 5.22 mmoles) were added and the reaction was stirred under argon for 3 hrs. The reaction was quenched with 4 ml anhydrous methanol and then evaporated to an oil. Final product (5) was purified by silica gel chromatography (dichloromethane with 0-1% ethanol; 1% triethylamine; final yield=2.2 g; 2.5 mmoles).
The dihydrouridine was incorporated into ribozymes using solid phase synthesis as described by Wincott et al., 1995 supra. The ribozyme containing dihydrouridine substitution was deprotected using the standard protocol described above with a minor modification: ribozyme was incubated at room temperature, instead of at 55.degree. C., for 24 hours in a mixture of ethanolic ammonia (3:1).
Example 19: Synthesis of 2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopr opylphosphoramidite)-1-deoxy-1-naphthyl-.beta.-D-ribofuranose (7) Phosphoramidites
1-Deoxy-1-naphthyl-.beta.-D-ribofuranose (4)
Referring to FIG. 29, the title compound was synthesized from naphthalene 1 and tetra-O-acetyl-.beta.-D-ribofuranose 2 according to the procedure of Ohrui et al., Agr. Biol. Chem. 1972, 36, 1651-1653.
2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopro pylphosphoramidite)-1-deoxy-1-naphthyl-.beta.-D-ribofuranose (7)
7 was synthesized in three steps from 4: a) 5'-O-dimethoxytritylation using 4,4'-dimethoxytrityl triflate, followed by chromatographic separation of .alpha. and .beta. anomer, respectively; b) 2'-O-silylation was carried out as described by Hakimelahi et al., 1982 supra (32% yield); c) 3'-O-phosphitylation was carried out essentially as described by Tuschl et al., 1993 supra (85% yield).
This phosphoramidite is incorporated into ribozymes using solid phase synthesis as described by Wincott et al., 1995 supra. The ribozyme containing naphthyl substitution was deprotected using the standard protocol described above.
Example 19: Synthesis of 2-O-t-Butyldimethylsilyl-5-O-Dimethoxytrityl-3-O-(2-Cyanoethyl-N,N-diisopr opylphosphoramidite)-1-Deoxy-1-(p-Aminophenyl)-.beta.-D-Ribofuranose Phosphoramidites
5-O-t-Butyldiphenylsilyl-2,3-O-isopropylidene-1-deoxy-1-(p-bromophenyl)-.be ta.-D-ribofuranose (3)
Referring to FIG. 30, 3 was prepared from 4-bromo-1-lithiobenzene and t-butyldiphenylsilyl-2,3-O-isopropylidene-D-ribono-1,4-lactone using the procedure analogous to that described by Czernecki and Ville, J. Org. Chem. 1989, 54, 610-612. Contrary to their result, we succeeded in obtaining the title compound, by using instead of t-butyldimethylsilyl the more acid resistant t-butyldiphenylsilyl group for 5-O-protection.
5-O-t-Butyldiphenylsilyl-2,3-O-isopropylidene-1-deoxy-1-(p-aminophenyl)-.be ta.-D-ribofuranose (5)
Compound 3 was aminated using liquid ammonia and CuI as described by Piccirilli et al. Helv. Chim. Acta 1991, 74, 397-406 to give the title compound in 63% yield.
5-O-t-Butyldiphenylsilyl-2,3-O-isopropylidene-1-deoxy-1-p-(N-TFA) aminophenyl!-.beta.-D-ribofuranose (6)
5 (1.2 g, 2.88 mmol) in dry pyridine (20 ml) was treated with trifluoroacetic anhydrides (0.5 ml, 3.6 mmol) for 1 hour at 0.degree. C. The reaction mixture was then quenched with methanol (5 ml) and evaporated to a syrup. The syrup was partitioned between 5% aq. NaHCO.sub.3 and dichloromethane, organic layer was dried (Na.sub.2 SO.sub.4) and evaporated to dryness under reduced pressure. This material was used without further purification in the next step.
1-Deoxy-1-p-(N-TFA)aminophenyl!-.beta.-D-ribofuranose (7)
The title compound was prepared from 6 in an identical manner as for the synthesis of deblocked phenyl analog; (82% overall yield for 5'-O-desilylation and the cleavage of 2',3'-O-isopropylidene group).
2-O-t-Butyldimethylsilyl-5-O-dimethoxytrityl-3-O-(2-cyanoethyl-N,N-diisopro pylphosphoramidite)-1-deoxy-1-p-(N-TFA) aminophenyl!-.beta.-D-ribofuranose (10)
Using the same three step sequence as for the phenyl analog, 10 was prepared from 7 in 32% overall yield.
This phosphoramidite is incorporated into ribozymes using solid phase synthesis as described by Wincott et al., 1995 supra. The ribozyme containing aminophenyl substitution was deprotected using the standard protocol described above.
Example 21: RNA Cleavage Reactions Catalyzed by HH-B Substituted with Modified Bases
Hammerhead ribozymes targeted to site B (see FIG. 27A) were synthesized using solid-phase synthesis, as described above. U4 and U7 positions were substituted with various base-modifications shown in FIG. 27B.
RNA cleavage reactions were carried out as described above. Referring to FIG. 27B, hammerhead ribozymes containing base modifications at positions 4 or 7 cleave the target RNA to varying degrees of efficiency. Some of the base modifications at position 7 appear to enhance the catalytic efficiency of the hammerhead ribozymes compared to a standard base at that position (see FIG. 27B, pyridin-4-one, phenyl and 3-methyl U modifications).
HH-B ribozymes with either pyridin-4-one or phenyl substitution at position 7 were further characterized (FIG. 28). It appears that HH-B ribozyme with pyridin-4-one modification at position 7 cleaves RNA with a 10 fold higher k.sub.cat when compared to a ribozyme with a U at position 7 (compare FIG. 28 A with 28 B). HH-B ribozyme with a phenyl group at position 7 cleaves RNA with a 3 fold higher k.sub.cat when compared to a hammerhead ribozyme with U at position 7 (see FIG. 28C).
Sequences listed in FIGS. 7, 15, 17, 19, 27 and the modifications described in these figures are meant to be non-limiting examples. Those skilled in the art will recognize that variants (base-substitutions, deletions, insertions, mutations, chemical modifications) of the ribozyme and RNA containing other 2'-hydroxyl group modifications, including but not limited to amino acids, peptides and cholesterol, can be readily generated using techniques known in the art, and are within the scope of the present invention.
Other embodiments are within the following claims.
TABLE I
Characteristics of Ribozymes
Group I Introns
Size: .about.200 to >1000 nucleotides.
Requires a U in the target sequence immediately 5' of the cleavage site.
Binds 4-6 nucleotides at 5' side of cleavage site.
Over 75 known members of this class. Found in Tetrahymena thermophila rRNA, fungal mitochondria, chloroplasts, phage T4, blue-green algae, and others.
RNAseP RNA (M1 RNA)
Size: .about.290 to 400 nucleotides.
RNA portion of a ribonucleoprotein enzyme. Cleaves tRNA precursors to form mature tRNA.
Roughly 10 known members of this group all are bacterial in origin.
Hammerhead Ribozyme
Size: .about.13 to 40 nucleotides.
Requires the target sequence UH immediately 5' of the cleavage site.
Binds a variable number nucleotides on both sides of the cleavage site.
14 known members of this class. Found in a number of plant pathogens (virusoids) that use RNA as the infectious agent (FIG. 1)
Hairpin Ribozyme
Size: .about.50 nucleotides.
Requires the target sequence GUC immediately 3' of the cleavage site.
Binds 4-6 nucleotides at 5' side of the cleavage site and a variable number to the 3' side of the cleavage site.
Only 3 known member of this class. Found in three plant pathogen (satellite RNAs of the tobacco ringspot virus, arabis mosaic virus and chicory yellow mottle virus) which uses RNA as the infectious agent (FIG. 3).
Hepatitis Delta Virus (HDV) Ribozyme
Size: 50-60 nucleotides (at present).
Cleavage of target RNAs recently demonstrated.
Sequence requirements not fully determined.
Binding sites and structural requirements not fully determined, although no sequences 5' of cleavage site are required.
Only 1 known member of this class. Found in human HDV (FIG. 4).
Neurospora VS RNA Ribozyme
Size: .about.144 nucleotides (at present)
Cleavage of target RNAs recently demonstrated.
Sequence requirements not fully determined.
Binding sites and structural requirements not fully determined. Only 1 known member of this class. Found in Neurospora VS RNA (FIG. 5).
Claims
We claim:
1. An enzymatic nucleic acid molecule comprising at least one modified nucleotide base substitution, wherein the base portion of said nucleotide is selected from the group consisting of pyridin-4-one, pyridin-2-one, phenyl, pseudouracil, 2, 4, 6-trimethoxy benzene, 3-methyluracil, dihydrouracil, naphthyl, and aminophenyl.
2. An enzymatic nucleic acid molecule comprising at least two modified nucleotide base substitutions, wherein the base portion of said nucleotide is selected from the group consisting of pyridin-4-one, pyridin-2-one, phenyl, pseudouracil, 2, 4, 6-trimethoxy benzene, 3-methyluracil, dihydrouracil, naphthyl, and aminophenyl, wherein said nucleotide base substitution is same or different.
3. The enzymatic nucleic acid molecule of claim 1 or 2, wherein said nucleic acid molecule is in a hammerhead configuration.
4. A mammalian cell in vitro comprising an enzymatic nucleic acid molecule of claim 1 or 2.
5. The enzymatic nucleic acid molecule of claim 3, wherein said hammerhead nucleic acid molecule includes said modified nucleotide base substitutions at position 4 or at position 7.
6. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is pyridin-4-one.
7. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is phenyl.
8. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is pyridin-2-one.
9. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is pseudouracil.
10. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is 2, 4, 6-trimethoxy benzene.
11. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is dihydrouracil.
12. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is 3-methyluracil.
13. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is naphthyl.
14. The enzymatic nucleic acid molecule of claim 5, wherein said substitution is aminophenyl.
15. The enzymatic nucleic acid molecule of claim 1, wherein said nucleic acid molecule is in a hairpin configuration.
16. The enzymatic nucleic acid molecule of claim 3, wherein said hammerhead nucleic acid molecule includes said modified nucleotide base substitutions at one or more positions in the Loop II region.
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