Resistance of hepatitis C virus to NS3-4A protease inhibitors: mechanisms of drug resistance induced by R155Q, A156T, D168A and D168V mutations.

BACKGROUND/AIMS: One of the main issues in the development of antiviral therapy is the emergence of drug-resistant viruses. In the case of hepatitis C virus (HCV), selection of drug-resistant mutants was evidenced by in vitro studies on protease inhibitors (PIs); for example, BILN-2061, VX-950 and SCH-6. Four mutations in the HCV protease (R155Q, A156T, D168A and D168V) have been identified in vitro in the HCV replicon system that confer resistance to BILN-2061 (a reference inhibitor). However, the molecular mechanism of drug resistance is still unknown. The aim of this study is to unravel, using an molecular modelling strategy, the structural basis of such molecular mechanism of HCV resistance to PIs. We focused on protease mutations conferring HCV resistance to BILN-2061 and described for the first time such mechanism at a molecular level. METHODS: The structures of drug-resistant NS3 proteases were obtained by mutation of selected residues (R155Q, A156T, D168A and D168V) and the ternary complexes formed between NS3-4A and BILN-2061 were optimized using GenMol software (www.3dgenoscience.com; Genoscience, Marseille, France). RESULTS: Two mechanisms were evidenced for viral resistance to BILN-2061. A 'direct' resistance mechanism is based on contacts between the mutated R155Q and A156T protease residues and its inhibitor. In the 'indirect' resistance mechanism, the mutated D168A/V residue is not in close contact with the drug itself but interacts with other residues connected to the drug. CONCLUSIONS: These data provide new insights in the understanding of the mechanisms of HCV drug escape, and may allow predicting potential cross-resistance phenomenon with other PIs. This approach can be used as a basis for future rational PI drug design candidates.

Detection of IL28B SNP DNA from buccal epithelial cells, small amounts of serum, and dried blood spots.

BACKGROUND & AIMS: Point mutations in the coding region of the interleukin 28 gene (rs12979860) have recently been identified for predicting the outcome of treatment of hepatitis C virus infection. This polymorphism detection was based on whole blood DNA extraction. Alternatively, DNA for genetic diagnosis has been derived from buccal epithelial cells (BEC), dried blood spots (DBS), and genomic DNA from serum. The aim of the study was to investigate the reliability and accuracy of alternative routes of testing for single nucleotide polymorphism allele rs12979860CC. METHODS: Blood, plasma, and sera samples from 200 patients were extracted (400 µL). Buccal smears were tested using an FTA card. To simulate postal delay, we tested the influence of storage at ambient temperature on the different sources of DNA at five time points (baseline, 48 h, 6 days, 9 days, and 12 days). RESULTS: There was 100% concordance between blood, plasma, sera, and BEC, validating the use of DNA extracted from BEC collected on cytology brushes for genetic testing. Genetic variations in HPTR1 gene were detected using smear technique in blood smear (3620 copies) as well as in buccal smears (5870 copies). These results are similar to those for whole blood diluted at 1/10. A minimum of 0.04 µL, 4 µL, and 40 µL was necessary to obtain exploitable results respectively for whole blood, sera, and plasma. No significant variation between each time point was observed for the different sources of DNA. IL28B SNPs analysis at these different time points showed the same results using the four sources of DNA. CONCLUSION: We demonstrated that genomic DNA extraction from buccal cells, small amounts of serum, and dried blood spots is an alternative to DNA extracted from peripheral blood cells and is helpful in retrospective and prospective studies for multiple genetic markers, specifically in hard-to-reach individuals.