Patent Application
20110207197
The subject of the present invention is a method to inhibit ribonuclease Dicer, ribonuclease Dicer inhibitor, and use of RNA aptamers to inhibit ribonuclease Dicer. More specifically, this solution relates to using RNA aptamers as competitive ribonuclease Dicer inhibitors, use of RNA aptamers as allosteric ribonuclease Dicer inhibitors, and use of RNA aptamers as selective inhibitors of emergence of the selected miRNAs.
Aptamers are relatively short RNA or DNA molecules, which bind with a strictly defined molecule with high affinity and specificity. The word “aptamer” comes from Latin “aptus”, i.e. “match” [Tuerk, C. and L. Gold, Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase. Science, 1990. 249(4968): p. 505-10; Ellington, A. D. and J. W. Szostak, In vitro selection of RNA molecules that bind specific ligands. Nature, 1990. 346(6287): p. 818-22]. One can say that the aptamer is a ligand capable of binding some specific molecule e.g. a protein, sugar, amino acid, nucleotide, antibiotic, or vitamin. Up till now, a substantial number of various aptamers has been obtained. They were selected as a ligands binding a wide spectrum of individuals, from small inorganic molecules to single-cell organisms [Blank, M. and M. Blind, Aptamers as tools for target validation. Curr Opin Chem Biol, 2005. 9(4): p. 336-42; Nimjee, S. M., C. P. Rusconi, and B. A. Sullenger, Aptamers: an emerging class of therapeutics. Arum Rev Med, 2005. 56: p. 555-83; Yan, A. C., et al., Aptamers: prospects in therapeutics and biomedicine. Front Biosci, 2005. 10: p. 1802-27; Proske, D., et al., Aptamers—basic research, drug development, and clinical applications. Appl Microbiol Biotechnol, 2005. 69(4): p. 367-74]. Specificity and high binding force (dissociation constant amounting to nano- or picomoles) results in aptamers being often compared to antibodies. Aptamer molecular mass is 10-15 kDa on average, i.e. about 10 times less than the mass of a single antibody [White, R. R., B. A. Sullenger, and C. P. Rusconi, Developing aptamers into therapeutics. J Clin Invest, 2000. 106(8): p. 929-34], which makes it easier for them to be spread within the organism and to be promptly removed from the blood circulation system.
Aptamers are usually obtained by in vitro selection that is called the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) method. The method makes it possible to identify the molecules that possess a desired property, e.g. strong binding with a selected molecule (target molecule—TM), from the input pool of many RNA or DNA molecules (molecules with an undefined sequence, i.e. random sequence). The input pool of RNA or DNA molecules is called a combinatorial library. It is a set of all oligonucleotides with definite length n that are possible to be synthesised. In practice, the oligonucleotides being selected, beside the centrally situated random sequence, also contain the so-called flanking regions with known sequences. They are used to amplify and clone the identified molecules. The number of oligonucleotides that create the full combinatorial library (complete input pool) depends on random sequence's length. In each of its positions, one of the four nucleotides: A, G, C, or T/U can occur. Therefore, in case of n-nt random sequence, it is possible to synthesise 4n of various oligonucleotides.
Typical RNA aptamer selection takes place according to the following scheme. Initially, a possibly high number of single-strand DNA molecules that contain n-nt random sequence is obtained by chemical synthesis. These molecules are then converted to the double-strand DNA, which serves as a template to synthesise a combinatorial library of single-strand RNA molecules, by the in vitro transcription method. The RNA obtained is incubated with a selected target molecule (TM). Then, all non-bound RNA molecules are removed. At the next stage, molecules bound with TM are isolated. The RNAs thus obtained are converted to the double-strand DNA by the RT-PCR method involving starters that are complementary to flanking sequences. The product obtained serves as a template to synthesise the narrowed RNA pool by in vitro transcription. The molecules obtained then undergo the selection process again. Upon having conducted the planned number of selection cycles, dsDNA is ligated into the plasmid and cloned in bacterial cells. Finally, individual clones are sequenced. In this way, the sequences of RNA molecules that bind with TM are identified.
To read out the information that is stored in genomes of living organisms is one of the most important tasks faced by contemporary molecular biology and bioinformatics. It was proved that a single gene could be a source of more than one type of transcript. What is more, many different mRNAs may arise from a single type of transcript. No observation was made that there existed any simple correlation between genome size and complexity of the organism. Only in bacteria and simple animal or plant organisms, most of the genome encodes proteins. In higher organisms, protein-encoding sequences constitute only a small part of the genetic material (less than 5% in humans). Due to the fact that the human genome's full sequence had been identified, it was acknowledged that, contrary to what had been expected earlier, it did not contain 150 thousand, but only about 25 thousand genes, i.e. more or less the same amount as can be found in the simple model plant, Arabidopsis thaliana. Nevertheless, a real turning point in research concerning mechanisms that govern the expression of genetic information has taken place only recently, chiefly due to an unexpected discovery of the phenomenon called RNA interference (RNAi) and of short regulatory RNAs, including micro RNAs (miRNAs) [Fire, A., et al., Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature, 1998. 391(6669): p. 806-11]. It was found that sequences that encode regulatory RNA molecules, the so-called miRNAs, are present in genomes of eukaryotic organisms, and thus in the human genome too. Such sequences may both occur within protein coding genes (often in introns), and create independent genes that do not encode proteins but only RNA miRNA containing transcripts are called pri-miRNA. In their structures, there usually occur about 50-80 nucleotide long, not fully complementary double-strand regions, which, due to their shape, are referred to as the hairpin type structures. It was observed that miRNAs arise both in plants and animals, but their maturing process is different in both types of organisms. In case of human cells, three basic stages of miRNA biogenesis can be distinguished [Bartel, D. P., MicroRNAs: genomics, biogenesis, mechanism, and function. Cell, 2004. 116(2): p. 281-97]. At the first one, the enzyme called Drosha cuts a double-strand fragment (hairpin structure) out of the pri-miRNA. At the second stage, the newly emerged 50-80 nucleotide (nt) molecule—pre-miRNA is transported from nucleus to cytoplasm by exportin 5. At the third stage, pre-miRNA is recognised by ribonuclease Dicer, which cuts a 20-23 nt duplex out of it. Then, the duplex is conveyed into another protein complex RISC (RNA-induced silencing complex). At the next stage, RISC is activated. This process consists in removing one strand of the duplex, whereas the other one, called miRNA, remains within the complex, and serves as a probe that makes it possible to specifically recognize fully or partially complementary RNA molecules [Nykanen, A., B. Haley, and P. D. Zamore, ATP requirements and small interfering RNA structure in the RNA interference pathway. Cell, 2001. 107(3): p. 309-21; Hammond, S. M., et al., An RNA-directed nuclease mediates post-transcriptional gene silencing in Drosophila cells. Nature, 2000. 404(6775): p. 293-6]. The active RISC complex can bind with mRNA. If mRNA is fully complementary to the miRNA that is present in the RISC complex, then it is cut (more or less in the middle of the mRNA/siRNA duplex) [Haley, B. and P. D. Zamore, Kinetic analysis of the RNAi enzyme complex. Nat Struct Mol Biol, 2004. 11(7): p. 599-606]. As a consequence, within a relatively short time, the whole mRNA pool becomes degraded, and the so-called posttranscriptional gene silencing (PTGS), takes place. However, if mRNA is only partially complementary to the miRNA that is present in the RISC complex, then it is not degraded, but remains bound with the protein complex, and thus it cannot serve as a template for protein synthesis. As a result, the gene is silenced at the level of translation (TR—translational repression).
It was proved that miRNAs perform some very important roles both in many physiological processes (e.g. developmental processes: cell differentiation, apoptosis, maintaining the line of maternal cells or brain morphogenesis) and pathological processes (cancerous transformation, neurodegenerative processes, etc.) [Mattick, J. S. and I. V. Makunin, Small regulatory RNAs in mammals. Hum Mol Genet, 2005. 14 Spec No 1: p. R121-32; Croce, C. M. and G. A. Calin, miRNAs, cancer, and stem cell division. Cell, 2005. 122(1): p. 6-7; Giraldez, A. J., et al., MicroRNAs regulate brain morphogenesis in zebrafish. Science, 2005. 308(5723): p. 833-8]. Results of some of the most resent research indicate that about 30-40% of all human genes are controlled by miRNA.
Ribonuclease Dicer is a member of the RNase III family, i.e. those endoribonucleases that specifically cut double-strand RNA molecules. All enzymes that belong to this family are characterised by the presence of one or two ribonuclease domains, called the RNase III domain. As a result of dsRNA digesting by RNases III, short duplexes are generated. They possess the phosphate group at the 5′ ends, and two non-paired nucleotides at the 3′ ends. RNases III differ in size, and they may have 200 to 2000 amino acids. The data that has been collected so far suggests that only one Dicer nuclease is encoded in the human genome. In case of miRNA biogenesis, ribonuclease Dicer is responsible for cutting 20-23 nt miRNA—containing duplexes, out of precursor pre-miRNAs. Based on biochemical data, it has been found out that human ribonuclease Dicer and bacterial RNase III contains only one active centre, in which both of the RNA strands are cut [Zhang, K. and A. W. Nicholson, Regulation of ribonuclease III processing by double-helical sequence antideterminants. Proc Natl Acad Sci USA, 1997. 94(25): p. 13437-41; Macrae, I. J., et al., Structural basis for double-stranded RNA processing by Dicer. Science, 2006. 311(5758): p. 195-8]. It was also proved, however, that in case of human Dicer, two RNase III domains, which make it up, act independently from each other (i.e. each of them cuts only one of the strands) [Macrae, I. J., et al.].
There are many examples that indicate that RNA aptamers may be successfully used as regulators of processes that take place in living organisms. Some of them have already been introduced as medicines into the market, for instance in the therapy of the disease called AMD (Age Macular Degeneration). The main factor that causes blood vessel hypertrophy and effusions in the AMD disease is one of the isoforms of the vascular endothelial growth factor—VEGF165 [Ferrara, N., H. P. Gerber, and J. LeCouter, The biology of VEGF and its receptors. Nat Med, 2003. 9(6): p. 669-76]. RNA aptamer selection was conducted on VEGF165, and 3 molecules were obtained, which bound themselves specifically with VEGF165 (Kd+49-130 pM) [Rudman, J., et al., 2′-Fluoropyrimidine RNA-based aptamers to the 165-amino acid form of vascular endothelial growth factor (VEGF165). Inhibition of receptor binding and VEGF-induced vascular permeability through interactions requiring the exon 7-encoded domain. J Biol Chem, 1998. 273(32): p. 20556-67]. One of these aptamers, 27 nt NX-1838, is a strong angiogenesis inhibitor, and it has been used to produce the medicine called Macugen® [Siddiqui, M. A. and G. M. Keating, Pegaptanib: in exudative age-related macular degeneration. Drugs, 2005. 65(11): p. 1571-7; discussion 1578-9; Cunningham, E. T., Jr., et al., A phase II randomized double-masked trial of pegaptanib, an anti-vascular endothelial growth factor aptamer, for diabetic macular edema. Ophthalmology, 2005. 112(10): p. 1747-57; Ng, E. W. and A. P. Adamis, Targeting angiogenesis, the underlying disorder in neovascular age-related macular degeneration. Can J Ophthalmol, 2005. 40(3): p. 352-68; Bell, C., et al., Oligonucleotide NX1838 inhibits VEGF165-mediated cellular responses in vitro. In Vitro Cell Dev Biol Anim, 1999. 35(9): p. 533-42]. It prevents VEGF from being bound by VEGFR1 and VEGFR2 receptors. Based upon clinical research, improvement of vision was noticed with 80% of patients within 3 months after the aptamer had been administered. In 2004, Macugen® was approved by FDA as a medicine for patients with Age Macular Degeneration [http://www.centerwatch.com/patient/drugs/area13.html].
Also, impact of the NX-1838 upon Wilms tumour development was tested in the organism of a mouse. An 84% reduction in cancerous mass was noted as compared to the control. Furthermore, lower occurrence of lung metastasis (20%) was observed as compared to the control (60%) [Huang, J., et al., Highly specific antiangiogenic therapy is effective in suppressing growth of experimental Wilms tumors. J Pediatr Surg, 2001. 36(2): p. 357-61], coupled with 53% inhibition of neuroblastoma growth [Kim, E. S., et al., Potent VEGF blockade causes regression of coopted vessels in a model of neuroblastoma. Proc Natl Acad Sci USA, 2002. 99(17): p. 11399-404].
Also, some attempts were described to use aptamers in thrombosis treatments. Thrombosis is a disease that is connected with distortions in the blood-clotting process. It can lead to some serious damages of the heart and other organs. One of the factors that induce the blood-clotting process is thrombin. Therefore, DNA aptamers were obtained with a high degree of affinity towards thrombin (Kd between 2 and 200 nM). One of them extended blood-clotting time from 25 to 169 seconds. Furthermore, it was observed that this aptamer inhibited both the free thrombin and the one that caused blood to clot. It stops to be active shortly after having been administered into the organism, which prevents from the necessity to use antidote [Bock, L. C., et al., Selection of single-stranded DNA molecules that bind and inhibit human thrombin. Nature, 1992. 355(6360): p. 564-6].
Also, an RNA aptamer (called 9.3t) was obtained, which specifically binds factor IX (Kd below 3 nM) that is a serine protease which takes part in thrombin creation from prothrombin. It was proved that the 9.3t significantly extended the blood-clotting time both in vitro and in vivo. Based on the 9.3t sequence, an antisense oligonucleotide (5-2C) was designed in such a way as to bind with the 9.3t and to block its activity. It was proved that when the 5-2C was added, the aptamer's anticoagulation activity would get promptly inhibited [Rusconi, C. P., et al., RNA aptamers as reversible antagonists of coagulation factor IXa. Nature, 2002. 419(6902): p. 90-4; Rusconi, C. P., et al., Antidote-mediated control of an anticoagulant aptamer in vivo. Nat Biotechnol, 2004. 22(11): p. 1423-8]. Tests were made to find out if the pair 9.3t aptamer—5-2C antidote could be used during heart surgeries (with cardiopulmonary bypass) as a substitute for heparin and protoamine. To this aim, heparin (300 IU/kg) and 9.3tC aptamer (0.5 mg/kg) were administered to pigs, and upon restoring systemic blood circulation (after 60 minutes), respectively, protamine (1 mg/100 IU of heparin) or 5-2C (5 mg/kg) was administered in order to inhibit anticoagulation action of heparin or aptamer. It was proved that the aptamer could effectively substitute heparin, no blood clot emergence was observed; the 5-2C antidote administered was well tolerated by the organism, and, furthermore, it reversed the aptamer-caused anticoagulation effect promptly and effectively [Nimjee, S. M., et al., A novel antidote-controlled anticoagulant reduces thrombin generation and inflammation and improves cardiac function in cardiopulmonary bypass surgery. Mol Ther, 2006. 14(3): p. 408-15].
Aptamers that bind tenascine-C (TN-C) were also identified. TN-C is a protein that occurs in the extracellular matrix. The gene that encodes it is expressed during foetal development, wound healing, regeneration of organs, and in pathological conditions [Erickson, H. P. and M. A. Bourdon, Tenascin: an extracellular matrix protein prominent in specialized embryonic tissues and tumors. Annu Rev Cell Biol, 1989. 5: p. 71-92; Drtkiewicz K, W. E., Rolle K, Nowak S, Zukiel L, Barciszewski J, Rola tenascyny-C w patogenezie. Neuroskop, 2005. 7: p. 19-26]. A high level of TN-C gene expression was observed in malicious cancers. In vitro selection was conducted on whole U251 glioblastomy cells with TN-C expression, and on purified TN-C protein. As a result, aptamer of the length of 39 nt, called TTA1, was obtained, with dissociation constant of 5 nM [Hicke, B. J., et al., Tenascin-C aptamers are generated using tumor cells and purified protein. J Biol Chem, 2001. 276(52): p. 48644-54]. It was found out that TTA1 binds to TN-C fibrinogen-like domain. Possibilities were also tested to deliver radioactive isotopes and cytotoxic medicines to cancerous cells using the TTA1. To this aim, several different cancers were examined, i.e.: breast cancer, lung cancer, colon cancer, and glioblastomy cancer (while the TTA1 labelled was administered intravenously). It was found out that fast intake and removal of TTA1 from blood and tissues made it possible to clearly visualise cancers [Hicke, B. J., et al., Tumor targeting by an aptamer. J Nucl Med, 2006. 47(4): p. 668-78].
In prostate cancers, increased accumulation of Prostate-Specific Membrane Antigen (PSMA) was observed. It was proved that its concentration increased together with progress of the disease (prostate cancer), whereas the highest PSMA level occurred in case of cancers that are resistant to hormonal treatment and in case of metastatic cancers. PSMA emergence was also observed outside prostate, during blood vessel creation in various solid tumours [Bostwick, D. G., et al., Prostate specific membrane antigen expression in prostatic intraepithelial neoplasia and adenocarcinoma: a study of 184 cases. Cancer, 1998. 82(11): p. 2256-61; Gregorakis, A. K., E. H. Holmes, and G. P. Murphy, Prostate-specific membrane antigen: current and future utility. Semin Urol Oncol, 1998. 16(1): p. 2-12; Chang, S. S., et al., Five different anti-prostate-specific membrane antigen (PSMA) antibodies confirm PSMA expression in tumor-associated neovasculature. Cancer Res, 1999. 59(13): p. 3192-8; Silver, D. A., et al., Prostate-specific membrane antigen expression in normal and malignant human tissues. Clin Cancer Res, 1997. 3(1): p. 81-5; Nielsen G K, S. K., Trumbull K, Spaulding B, Welcher R., Immunohistochemical characterization of prostate specific membrane antigen expression in the vasculature of normal and neoplastic tissues. Modern Path, 2004. 17: p. 326A]. In vitro selection was conducted on the extracellular PSMA-xPSM component. After six selection rounds, two aptamers were obtained that did not manifest any common sequential motifs, called xPSM-A9 and xPSM-A10 o Kd=11.9 nM [Lupold, S. E., et al., Identification and characterization of nuclease-stabilized RNA molecules that bind human prostate cancer cells via the prostate-specific membrane antigen. Cancer Res, 2002. 62(14): p. 4029-33].
Also, prion-binding aptamer (PrP) selection was carried out. The PrP is a protein, which may occur in two alternative spatial forms: normal PrPC (which contains about 40% α-helix and just a few β-folds) and pathogenic PrPSc (which is built of approx. 30% α-helix and 45% β-folds) [Pan, K. M., et al., Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins. Proc Natl Acad Sci USA, 1993. 90(23): p. 10962-6]. PrPSc proteins are able to aggregate and deposit in the brain, which, in effect, leads to functioning distortions in cells and their death [Prusiner, S. B., et al., Prion protein biology. Cell, 1998. 93(3): p. 337-48; Prusiner, S. B., Prions. Proc Natl Acad Sci USA, 1998. 95(23): p. 13363-83]. As a result of aptamer selection, RNA molecules were obtained that specifically recognised PrPSc and PrPC prion proteins in mouse, hamster, and cattle brain homogenates [Rhie, A., et al., Characterization of 2′-fluoro-RNA aptamers that bind preferentially to disease-associated conformations of prion protein and inhibit conversion. J Biol Chem, 2003. 278(41): p. 39697-705].
As early as at the beginning of the 90s of the 20th century, the SELEX method was used to obtain aptamers binding to reverse transcriptase of the HIV-1 virus. It was found out that one of them (called 1.1) significantly lowered the HIV-1 RT polymerase activity, but it did not affect remaining RT activities nor reverse transcriptase of other retroviruses [Tuerk, C., S. MacDougal, and L. Gold, RNA pseudoknots that inhibit human immunodeficiency virus type 1 reverse transcriptase. Proc Natl Acad Sci USA, 1992. 89(15): p. 6988-92]. Aptamers were also selected on nsP10 protein of the SARS (Severe Acute Respiratory Syndrome) virus. The molecules obtained efficiently inhibited nsP10 helicase activity [fang, K. J., Lee, N. R., Yeo, W. S., Jeong, Y. J., Kim, D. E., Isolation of inhibitory RNA aptamers against severe acute respiratory syndrome (SARS) coronavirus NTPase/Helicase. Biochem Biophys Res Commun. 2007 Dec. 17].
The patent application WO2007043784 (publ. Apr. 19, 2007) relates to RNA aptamers and uses thereof, more precisely RNA aptamers interfering the interaction of TCF with other proteins by binding specifically to ss-catenin, RNA aptamers binding specifically to HMG domains of TCF-I proteins and uses of the same. The RNA aptamer of the present invention can be effectively used for the development of an anticancer agent since it binds specifically to TCF-I to interrupt the interaction of TCF with ss-catenin involved in tumorigenesis and metastasis and the transcriptional activity of TCF-I in relation to oncogenes.
The patent application U.S. Pat. No. 6,995,249 (publ. Feb. 2, 2006) relates to a novel nucleic acid (aptamer) which binds specifically to the target protein of Ras, more particularly, a novel RNA aptamer which binds specifically to Raf-1; a method for screening an RNA capable of binding specifically to the target protein of Ras which comprises selecting an RNA capable of binding to the target protein of Ras from a pool of RNAs having various base sequences; a method for regulating the signal transduction causing the proliferation or differentiation of cells by using the above-described nucleic acid; and medicinal compositions with the use of the same.
The patent application US2005202423 (publ. Sep. 15, 2005) disclosed a method for identifying compounds (lead structures) which specifically bind to (a) desired RNA target motif and can inhibit or eliminate the function thereof or (b) suppress a compound associated with a desired RNA target motif and can thereby inhibit or eliminate the function thereof. The inventive method is based on the attachment of a ligand (=a compound to be identified) to a RNA target motif which is coupled to a modified ribozyme so that the ribozyme is transformed into an active or inactive conformation resulting in the cleaving of a signal-giving ribozyme substrate. The identified compounds enabling modification of the cellular function of the RNA target motifs enable specific medicaments to be produced. The invention also relates to a polynucleotide comprising a hammerhead ribozyme and an aptamer for a target molecule. The base pairing model of the polynucleotide, when the target molecule binds to the aptamer, is different from the base pairing model of the polynucleotide when the target molecule does not bind to the aptamer.
The patent application US2005239061 (publ. 2005-10-27) relates to the construction of an allosteric control module in which a catalytic RNA forms a part of or is linked to an effector-binding RNA domain or aptamer. These constructs place the activity of the catalytic RNA under the control of the effector and require the presence of an appropriate effector for activation or inactivation. The present invention provides means to identify useful effector molecules as well as their use to evolve cognate aptamers. The invention involves both the evolution of RNA sequences which bind the effector and a selection process in which the allosteric control modules are identified by their catalytic function in the presence and absence of the effector. The resulting regulatable catalytic RNAs may be used to alter the expression of a target RNA molecule in a controlled fashion.
As has been mentioned earlier, miRNAs play an extraordinarily significant role in regulating gene expression, especially in such processes as cell differentiation and proliferation, maturing, apoptosis, or cancerous transformation. Although the general miRNA functioning principles have already been recognised, we still have no methods that would allow us to actively influence their emergence or functioning. Working out some molecular tools that would allow us e.g. to control the enzymes that take part in miRNA biogenesis may thus be crucial for such areas as medicine (especially treatment of cancer diseases) or biotechnology.
The aim of this invention was to select RNA aptamers that specifically bind human ribonuclease Dicer, which is one of the main enzymes that take part in miRNA biogenesis and the biogenesis of other short regulatory RNAs, and then to find out if pre-selected molecules affect enzyme activity. Other aims of this solution include: (i) using RNA aptamers as ribonuclease Dicer competitive inhibitors; (ii) using RNA aptamers that are allosteric ribonuclease Dicer inhibitors, (iii) identifying RNA aptamers that are selective inhibitors of emergence of selected miRNAs.
This invention fulfils the aims described as above, and solves problems related with the possibility to use RNA aptamers as ribonuclease Dicer competitive inhibitors and as allosteric ribonuclease Dicer inhibitors, as well as selective inhibitors of emergence of the selected miRNAs.
The subject matter of this invention is the method to inhibit ribonuclease Dicer, wherein ribonuclease Dicer is inhibited by means of RNA aptamer, whereas it includes the selection process of RNA aptamers that specifically bind ribonuclease Dicer, checking the influence of preselected aptamers upon enzyme activity, and using pre-selected aptamers to inhibit Dicer activity ribonuclease, whereas each preselected RNA aptamer contains two flanking sequences each and a centrally situated random sequence.
Preferably, pre-miRNA cutting efficiency decreases together with increase in RNA aptamer concentration, whereas the scope of the aptamer's molar excess as compared to Dicer is contained within range from 1 to 100. Preferably, flanking sequences of pre-selected RNA aptamers contain from 10 to 30 nucleotides, while the centrally situated random sequence contains from 10 to 30 nucleotides. Preferably, ribonuclease Dicer is inhibited by means of the aptamer that acts upon the competition basis. Preferably, ribonuclease Dicer is inhibited by means of the RNA aptamer, which is an allosteric inhibitor. Preferably, ribonuclease Dicer is inhibited by means of the aptamer that acts as a selective or non-selective inhibitor of emergence of the selected miRNAs. Preferably, mammalian, preferably human ribonuclease Dicer, is inhibited.
The next subject matter of this invention is a ribonuclease Dicer inhibitor, wherein the inhibitor is an RNA aptamer, which has been obtained in the way of in vitro selection, and which binds ribonuclease Dicer, and it contains two flanking sequences and a centrally situated random sequence.
Preferably, flanking sequences contain from 10 to 30 nucleotides, while the central random sequence contains from 10 to 30 nucleotides. Preferably, inhibitor acts upon the competition basis. Preferably, the inhibitor is an allosteric inhibitor. Preferably, inhibitor selectively or non-selectively inhibits emergence of the selected miRNAs.
The next subject matter of this invention is use of RNA aptamers, in which RNA aptamers are obtained in the way of in vitro selection, and contain two flanking sequences each and the centrally situated random sequence, to inhibit ribonuclease Dicer.
Preferably, pre-miRNA cutting efficiency decreases together with increase in aptamer concentration, whereas the scope of the aptamer's molar excess as compared to Dicer is contained within range from 1 to 100. Preferably, flanking sequences of preselected RNA aptamers contain from 10 to 30 nucleotides, while the centrally situated random sequence contains from 10 to 30 nucleotides. Preferably, ribonuclease Dicer is inhibited by means of the aptamer that acts upon the competition basis. Preferably, ribonuclease Dicer is inhibited by means of the RNA aptamer that is an allosteric inhibitor. Preferably, ribonuclease Dicer is inhibited by means of aptamer that acts as selective or non-selective inhibitor of emergence of the selected miRNAs. Preferably, mammalian, preferably human ribonuclease Dicer, is inhibited.
Drawings enclosed at the end of this study facilitate better understanding of the discussed issues, and illustrate the subject matters of this invention.
A. Influence of ATD15.52 upon pre-hsa-miR33a cutting.
B. Influence of ATD15.52 upon pre-hsa-miR210 cutting.
In reactions marked with number 1, the aptamer:Dicer molar relation was 1:1, in reactions marked with number 2 it was 10:1, and in reactions marked with number 3 it was 100:1. Additionally, two control reactions were always carried out, i.e.: K+—standard reaction with no aptamer addition and K− standard reaction with no enzyme.
C. Cutting efficiency determined for both of these substrates by Dicer (average from three independent experiments).
A. Influence of ATD13.6 upon pre-hsa-miR33a cutting.
B. Influence of ATD13.6 upon pre-hsa-miR210 cutting.
In reactions marked with number 1, the aptamer:Dicer molar relation was 1:1, in reactions marked with number 2 it was 10:1, and in reactions marked with number 3 it was 100:1. Additionally, two control reactions were conducted in each case, i.e.—K+—standard reaction with no aptamer addition and K− standard reaction with no enzyme.
C. Cutting efficiency determined for both of these substrates by Dicer (average from three independent experiments).
Lanes, for which reaction mixtures were incubated for 10′, 1 h, 2 h, 5 h and 16 h were labelled as 1, 2, 3, 4 and 5, respectively.
T1—aptamer cut by ribonuclease T1, F—aptamer that underwent formamide hydrolysis. K0—control reaction with no enzyme, K16—control reaction with no enzyme after 16 h incubation.
Presented below are example embodiments of the present invention defined above.
Ribonuclease Dicer is one of the key enzymes that take part in both miRNA biogenesis and biogenesis of other short regulatory RNAs. It cuts functional miRNA molecules out of double-strand pre-miRNA precursors. Therefore, a question was raised if activity of the enzyme that is responsible for generating short regulatory RNAs, including miRNAs, can be controlled by other RNA molecules. In order to solve this problem, we decided to conduct selection of RNA aptamers that specifically bind human ribonuclease Dicer, and then to check if pre-selected molecules affect this enzyme's activity.
At first, a combinatorial library of single-strand DNAs (ssDNAs) was obtained (as shown in
1Reaction buffer: 75 mM Tris-HCl (pH 8.8 at 25° C.), 20 mM (NH4)2SO4, 0.01% (v/v) Tween 20
2In order to ensure proper PCR conditions, the reaction mixture was divided into eight parts at least, so that a single test-tube contained maximum 50 μl of the mixture.
The dsDNAs obtained served as a template to synthesise the combinatorial library of single-strand RNAs (ssRNAs) by the in vitro transcription method. The transcription was carried out in the volume of 50 μl, and the reaction mixture with composition as given in Table 3 was incubated for 4 hours at 37° C. After this time, RNase-free DNase was added into the reaction mixture in order to remove the DNA template.
After transcription, the RNA was purified in 12% denaturating polyacrylamide gel according to the following procedure:
1Kinase buffer: 70 mM Tris-HCl ph 7.6, 10 mM MgCl2, 5 mM DTT.
The reaction was carried out in the volume of 100 μl in mixture which composition is presented in Table 5; 10-times molar RNA excess was used as compared to protein.
In order to conduct the next selection cycle, the ssRNA obtained was converted into single- and then double-strand DNA by the RT-PCR method. To this end, 6 μl of water solution of the AT3 starter (25 pmole/μl) was added to the RNA sample that had been obtained in the former selection cycle (dissolved in 20 μl of water), the whole was incubated for 3 min. at 65° C., and cooled down for 10 min. at 4° C. Then, the reaction mixture which composition is presented in Table 6 was prepared. 35 μl of the mixture was added to the RNA sample that included the AT3 starter. The whole was incubated for 1.5 h at 42° C.
The reverse transcription reaction product obtained was amplified by PCR using ATD2 and ATD3 starters. The PCR reaction was conducted in the Biometra® apparatus. Reaction products were then analysed by electrophoresis in a 12% polyacrylamide gel in denaturating conditions. Concentration of the DNA obtained was determined by measuring UV light absorption for λ=260 nm. The dsDNA obtained constituted a template to synthesise the narrowed RNA pool (by in vitro transcription), which underwent the selection process at the successive cycle.
As soon as the 15th selection cycle was over, the obtained RT-PCR product was not converted to RNA, but was cloned into the plasmid in line with methods being generally used. Then, single clones were sequenced. As a result, 50 sequences were identified that corresponded to RNA molecules, which bound with Dicer.
After a thorough bioinformatic analysis of pre-selected RNA's primary and secondary structures, the following 4 aptamers were selected for further examinations:
Impact of the obtained aptamers upon Dicer activity was tested in vitro. To this aim, some standard reactions of human pre-miRNA digestion by Dicer were conducted. Within a single experiment that was carried out at least three times for each aptamer, 4 reactions were conducted: one control reaction (with no aptamer addition) and three reactions with the addition of various aptamer volumes (Dicer:aptamer molar relation was respectively 1:1, 1:10, and 1:100 in these reactions). The two pre-miRNAs previously characterised, i.e. pre-hsa-miR-33a and pre-hsa-miR-210, were selected as substrates (http://microma.sanger.ac.uk/cgi-bin/sequences).
Reactions were conducted in the volume of 10 μl in a commercial ribonuclease Dicer buffer. The pre-miRNA, which was labelled at the 5′ end using radioactive phosphorus, was used in this reaction (the labelling was done according to procedure described above). At first, renaturation of aptamers and labelled substrates was carried out separately (by heating them up to 95° C., and then slowly cooling them down to ambient temperature).
At the next stage, Dicer was pre-incubated with a various amounts of the aptamer for 10 min. at 37° C. (Dicer:aptamer molar ratio was changing as follow: 1:1, 1:10, and 1:100). Then, the pre-miRNA was added. The digestion reaction was conducted for 10 min. at 37° C. Each reaction was repeated three times for each aptamer. In case of the ATD15.52 aptamer, an analogous series of reactions was additionally carried out, but without pre-incubation.
As soon as the reaction was over, the products obtained were denaturated by heating them up to 95° C. for 5 minutes and rapidly cooling them down on ice, and then they were analysed by electrophoresis in a 15% denaturating polyacrylamide gel. The electrophoretic separation was carried out in the following conditions:
After the electrophoretic separation, the products were analysed using a scanner for radioisotopically labelled materials (Phosphorimager, Typhoon 8600).
Experiments carried out indicated that the ATD15.14 and ATD15.26 aptamers inhibited Dicer activity only in a small degree (by about 30 and 40% respectively, when Dicer:aptamer molar ratio was 1; 100).
Based upon these experiments, it was found out that ATD15.52 significantly inhibited the pre-hsa-miR-210 cutting process (when Dicer: aptamer molar ratio was 1; 100, only 16% of the substrate was digested), and that it inhibited the pre-hsa-miR33a cutting (when Dicer:aptamer molar ratio was 1; 100, 70% of the substrate was digested) (
It was noticed that together with the increase in aptamer concentration, the pre-hsa-miR-210 cutting efficiency was falling. This inhibitory effect was already observed at aptamer:enzyme molar relation of 1:1, where the number of cutting products tended to fall by 19%. With ten-times molar aptamer excess as compared to the enzyme, about 50% inhibition was observed, and 84% inhibition for 100-times excess. The inhibitor effect was much lower for the pre-miR-33a substrate, reaching 30% inhibition for 100-times excess of ATD15.52.
Similar results were obtained while examining the impact of the ATD13.6 aptamer upon
Dicer activity (
In the next experiments, it was proved that the ATD15.52 aptamer was cut by Dicer, whereas the ATD13.6 was not a substrate for this ribonuclease [compare
| Number | Date | Country | Kind |
|---|---|---|---|
| 384455 | Feb 2008 | PL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/PL09/00013 | 2/9/2009 | WO | 00 | 10/5/2010 |
