16th International HIV Drug Resistance Workshop 12-16 June 2007, Barbados

ANTI-HCV ACTIVITY AND CELLULAR PHARMACOLOGY OF 2′-METHYLCYTIDINE ALONE AND IN COMBINATION WITH NON-TOXIC CONCENTRATIONS OF RIBAVIRIN IN THE HCV REPLICON SYSTEM

Antivir Ther. 2007; 12:S28 (abstract no. 26)

BI Hernandez-Santiago, L Bassit, J Grier and RF Schinazi
Department of Pediatrics, Laboratory of Biochemical Pharmacology, Emory School of Medicine/Veterans Affair Medical Center, Decatur, GA, USA

BACKGROUND: Combined chemotherapeutic modalities are essential to reduce or prevent the development of resistant viruses. Valopicitabine (NM283), the prodrug of NM107 (2′-MeC), is currently in Phase II clinical trials for HCV. NM283 in combination with peg IFN-α has been shown to markedly suppress viraemia in treatment-naïve HCV-infected persons. The interaction of NM107 in combination with RBV (an IMPDH inhibitor) was determined in liver cells at the level of triphosphate production and mitochondrial toxicity. The anti-HCV activity of RBV alone or in combination with NM107 in Huh-7 cells was determined in a HCV replicon (Clone B).

METHODS: NM107 (1 or 10 µM) and RBV (0.1–100 µM) were incubated for 4 hr in Huh-7 or Huh-6 cells and levels of NM107-TP were determined. For the antiviral assay, the interaction of NM107 in combination with RBV at a ratio of 1:5 (NM107:RBV) was determined. Ribosomal and HCV RNA levels were quantified using a multiplex RT-PCR assay. Data analyses were performed using CalcuSyn program.

RESULTS: In Huh-7 or Huh-6 cells, NM107 was rapidly converted to similar levels of NM107-TP. Combination of NM107 (10 µM) with RBV (1–100 µM) resulted in reduction of NM107-TP levels at ratio of 1:1 and 1:10 (NM107:RBV), but not at 10:1. However, even at the 1:10 ratio, the levels of NM107-TP (about 2.6 µM) were higher than the IC₅₀ of NM107-TP (0.24 µM) against the HCV polymerase. NM107 was not toxic up to 100 µM, whereas RBV was cytotoxic at >30 µM in replicon cells. RBV at >30 µM demonstrated significant mitochondrial toxicity in Huh-6 and Huh-7 cells. The antiviral combination of NM107 with RBV at a ratio of 1:5 had a weighted average combination index of 1.5 indicating additive antiviral effects with no apparent cytotoxicity.

CONCLUSIONS: NM107-TP levels in liver cells in the presence of non-toxic concentrations of RBV were 10- fold higher than the levels that inhibit HCV polymerase. Combination between NM107 and RBV at clinically relevant ratios resulted in additivity. These results suggest that NM107 (and NM283) can be used in combination with RBV for the treatment of HCV.

2007-06-12
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