Substituted imidazopyridines as potent inhibitors of HCV replication

Abstract

Background/aims: Following lead optimization, a set of substituted imidazopyridines was identified as potent and selective inhibitors of in vitro HCV replication. The particular characteristics of one of the most potent compounds in this series (5-[[3-(4-chlorophenyl)-5-isoxazolyl]methyl]-2-(2,3-difluorophenyl)-5H-imidazo[4,5-c]pyridine or GS-327073), were studied.

Methods: Antiviral activity of GS-327073 was evaluated in HCV subgenomic replicons (genotypes 1b, 1a and 2a), in the JFH1 (genotype 2a) infectious system and against replicons resistant to various selective HCV inhibitors. Combination studies of GS-327073 with other selective HCV inhibitors were performed.

Results: Fifty percent effective concentrations for inhibition of HCV subgenomic 1b replicon replication ranged between 2 and 50 nM and were 100-fold higher for HCV genotype 2a virus. The 50% cytostatic concentrations were > or = 17 microM, thus resulting in selectivity indices of > or = 340. GS-327073 retained wild-type activity against HCV replicons that were resistant to either HCV protease inhibitors or several polymerase inhibitors. GS-327073, when combined with either interferon alpha, ribavirin, a nucleoside polymerase or a protease inhibitor resulted in overall additive antiviral activity. Combinations containing GS-327073 proved highly effective in clearing hepatoma cells from HCV.

Conclusions: GS-327073 is a potent in vitro inhibitor of HCV replication either alone or in combination with other selective HCV inhibitors.

Fig. 1

Structural formulae and an overview of some of the major steps in the lead optimization towards GS-327073.

Fig. 2

Dose–response curves for inhibition of HCV replicon replication in (A) Huh 9-13, (B) Huh 5-2 and (C) HuH6 cells by GS-327073.

Fig. 3

Anti-HCV activity of the combination of GS-327073 with either (A) 2′-C-MeCyt, (B) VX-950, (C) IFNα 2b or (D) ribavirin. Values between −20% and 0% below expected are labelled in purple. Values between 0% and 20% above expected are labelled in orange. Values between 20% and 40% above expected values are labelled in blue.

Fig. 4

Clearance of HCV RNA from replicon-containing Huh 9-13 cells following treatment with (A–C) 5 × EC₅₀ of VX-950 (violet diamond), 5 × EC₅₀ GS-327073 (pink square) or the combination of 5 × EC₅₀ GS-327073 and 5 × EC₅₀ VX-950 (green–blue ball); (D–F) 20 × EC₅₀ of IFNα 2b (green diamond), 20 × EC₅₀ GS-327073 (pink square) or the combination of 20 × EC₅₀ GS-327073 and 20 × EC₅₀ IFNα 2b (orange ball); (G–I) 20 × EC₅₀ 2′-C-MeCyt (blue diamond), 20 × EC₅₀ GS-327073 (pink square) or the combination of 20 × EC₅₀ GS327073 and 20 × EC₅₀ 2′-C-MeCyt (purple ball) or 10 × EC₅₀ GS327073 and 10 × EC₅₀ 2′-C-MeCyt (orange triangle). Clearance capacities after one passage in the presence of drug(s) depicted are in graphs A, D and G; after two passages in the presence of drug(s) are depicted in graphs B, E and H; after three passages in the presence of drug(s) are depicted in graphs C, F and I.