R-7128

R-7128 is a selective nucleoside analog inhibitor of the hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase.

Hepatitis C virus (HCV) is an enveloped (+)-single stranded RNA virus, and the viral RNA is replicated in host cell via HCV's RNA-dependent RNA polymerase, which is the cause of hepatitis C and some cancer lymphomas.

R-7128 is a nucleotide triphosphate analog which is the substrate for HCV polymerase NS5B. Incorporation of R-7128 into nascent HCV RNA strongly decreased the efficiency of RNA elongation by RNA polymerase NS5B, leading to the termination of the nascent RNA product. It has been shown that R-7128 is able to inhibit the RNA synthesis of HCV in vitro [1].

32 patient infected with HCV genotype-1 was treated with R-7128 for 14 days with 750-mg or 1500-mg administered once (QD) or twice daily (BID), and the HCV RNA level was frequently measured. Initial decline of HCV RNA was generally slower than treatment with interferon-alpha or protease inhibitors but 12 patients showed a novel pattern of HCV RNA kinetics that the effectiveness in inhibiting viral production gradually increased over time to reach its final value. The final value was high with BID dose (mean 750-mg and 1500-mg: 98.0% and 99.8%, P=0.018) and significantly higher than in patients treated QD (mean QD vs BID: 90% vs 99%, P<10^-7) [2].

References:
[1] Ma H et al. , Characterization of the metabolic activation of Hepatitis C virus nucleoside inhibitor β-D-2′-Deoxy-2′-fluoro-2′-C-methylcytidine (PSI-6130) and identification of a novel active 5′-Triphosphate species. J Biol Chem. 2007, 282(41): 29812-20.
[2] Guedj J et al. , Hepatitis C viral kinetics with the nucleoside polymerase inhibitor mericitabine (RG7128). Hepatology. 2012, 55(4): 1030-1037.

[Inhibitors of hepatitis C virus--current standards and status of investigations].[Pubmed:21473060]

Przegl Epidemiol. 2010;64(4):473-8.

The current standard of chronic hepatitis C therapy is the combined use of pegylated IFN-alpha 2a (PegIFN-alpha) and rybavirin (RBV). The new form of interferon, IFN-alpha 2b, was also introduced with no better results. Overall, the effectiveness of therapy with the use of the above scheme is not satisfactory. Thus the search for new therapeutic agents for hepatitis C is ongoing. These studies have the goal to find new preparations inhibiting the replication cycle of HCV. The new analogue of RBV, eg. tarybavirin was introduced, with lesser side effects, but the same effectiveness. The activity of new agents relies upon the inhibition of the most important enzymes of the HCV replication cycle: RNA polymerase, protease and helicase. Polymerase NS5 inhibitors are divided into nucleoside (R-7128) and nonnucleoside (ANA-598, GS 9190, VCH-759, VX-222). The intensive studies on the R-7128 analogue are ongoing. The effects of action of particular compounds in the I and II studies were summarized. The promised prodrug is nonnucleoside polymerase inhibitor, ANA-598 which when administrated to patients, gave 75% SVR. The combined administration of the newly described agents is the basis of specifically targeted antiviral therapies for HCV (STAT-C). These therapies allow to achieve better effectiveness of treatment, its shortening, the diminishment and limitation of side effects.

Mericitabine (RG 7128; R-7128) is a nucleoside inhibitor of the HCV NS5B polymerase that acts as an RNA chain terminator and prevents elongation of RNA transcripts during replication.

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