17th International HIV Drug Resistance Workshop 10-14 June 2008, Sitges, Spain

HOW HEPATITIS C VIRUS NS3-4A PROTEASE R155K/T STRAINS CAN DISCRIMINATE VX-950 AND ITMN-191 BUT AFFECT DIFFERENTIALLY SCH-503034

Antivir Ther. 2008; 13(Suppl. 3):A43 (abstract no. 38)

J Courcambeck¹, M Bouzidi¹, G Roche¹, G Pèpe² and P Halfon^1
1GenoScience, Marseille, France; ²CINaM UPR-CNRS 3118 Parc Scientifique de Luminy, Marseille, France

BACKGROUND: During the selection of hepatitis C virus (HCV) NS3-4A protease mutations under the drug pressure of HCV protease inhibitor (PI) VX-950, mutation R155K/T was selected in patients undergoing treatment, but not in vitro. ITMN-191 shows a reduced susceptibility to HCV NS3-4A^R155K strain by 89-fold. Furthermore, it is noteworthy that R155K exhibits similar replication capacity to the wild type and shows selective advantage. Even though mutation R155K is not described in vitro with ITMN-191, mutation R155K has all viral features (replication capacity and high fold resistance) to be selected in vivo. Interestingly, SCH-503034 does not share the same R155K/T resistance profile (FR^R155K: 4). The aim of this study is to describe the molecular and structural basis of this different resistance profile between VX-950, ITMN-191 and SCH-503034 against NS3-4A^R155K.

METHODS: Structures of drug-resistant HCV NS3-4A protease were obtained from the wild-type structure by mutation of Arg155 to Lys. The resulting ternary complexes formed between HCV NS3-4A protease and each drug were optimized using GenMol software (www.genosciencepharma.com).

RESULTS: The molecular mechanism of HCV NS34A^{R155K/ T} resistance to VX-950 does not involve only the loss of hydrophobic interactions between its bicyclic P2 and the side chain of residue 155. Indeed, this is not consistent with the SCH-503034 resistance profile. Arg155 participates in the orientation of the VX-950 P4 cyclohexyl towards the Val158 S4 binding pocket. Mutation R155K/T induces the loss of Arg155 orientation function and VX-950 undergoes a destabilization, which occurs during the VX-950 recognition and covalent steps. SCH503034 undergoes, like VX-950, just minor modifications in the P2–S2 interaction area and SCH-503034 is not strongly affected by the loss of Arg155 P4 orientation function. The molecular mechanism of ITMN-191 resistance against HCV NS3-4A^R155K involves a direct resistance mechanism through the modification of the interactions between P2 and S2 binding pocket. Moreover, R155K induces the loss of a key salt bridge between Asp168 and Arg123. Asp168 takes another conformation decreasing indirectly the hydrophobic P4–S4 interactions.

CONCLUSIONS: These data provide new insights into the understanding of the molecular mechanisms of HCV drug escape, potential virological breakthrough and bring predictive potential cross-resistance phenomena with future PIs.

2008-06-10
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