Specifically-targeted antiviral therapies for hepatitis C virus (HCV) (STAT-C) currently represent a great hope for therapeutic management of individuals chronically infected with HCV-genotype 1 strains. Promising results in a phase 1 clinical trial on efficiency of telaprevir, an HCV protease inhibitor that blocks the nonstructural protein 3 (NS3)-protease dependent cleavage of the HCV polyprotein, have been recently highlighted in HEPATOLOGY.1, 2 However, the high level of HCV variability and diversity is an ongoing challenge for STAT-C. Thus, the emergence of amino acid (aa) substitutions within HCV NS3-protease that confer low-level resistance to telaprevir have been observed during the first 15 days of therapy.1 We describe here, for the first time to our knowledge, a case of natural presence of the arginine-to-lysine substitution at residue 155 (R155K) in HCV NS3 sequences from a patient chronically infected with HCV, but who never received any anti-HCV drug.
A 39-year-old human immunodeficiency virus (HIV)-–seronegative man was admitted to our center in June 2007 for decompensated liver cirrhosis related to chronic HCV infection of presumed old evolution but diagnosed 4 months earlier. Serum HCV RNA was 5.04 log10 international units (IU)/mL (as determined by Cobas TaqMan assay, Roche). Liver transplantation was performed in August 2007, and HCV recurrence was diagnosed 1 month later (HCV RNA, 7.8 log10 IU/mL). No anti-HCV therapy has been introduced either before liver graft or thereafter. The HCV genotype was 1a, as determined by phylogenetic analysis of the NS3-protease coding region sequence using in-house protocols with primers that were chosen using the SVARAP program.3 Outer primers were MarsNS3F2: 5′-ATCACsTGGGGrGCrGAyAC/MarsNS3R1: 5 ′-AAyTTGCCrTAkGTGGAGTAyGT; inner primers were MarsNS3F3: 5′-ACsGCrGCrTGygGGGACAT/MarsNS3R2: 5′-GTGCTCTTrCCGCTrCCrGT. Surprisingly, aa Lysine-155 (codon AAA) was found within NS3-protease and confirmed on another serum collected 2 months later (1 month after liver transplantation). Clonal analysis, performed as described,4 revealed that codon 155-AAA was harbored by 100% of 15 clonal sequences. In addition, after selecting the 100 BLAST hits with the highest score on sequences from our patient (www.ncbi.nlm.nih.gov/BLAST/), we did not find any other NS3-protease sequence that harbors this codon.
Substitution R155K has been recently identified in 14-day telaprevir phase 1 clinical studies, and its selection was associated with virological rebound.1, 5 It is located in the HCV NS3-protease catalytic domain and was found to confer low-level resistance to telaprevir.1, 6 Although no R155K mutation was observed at treatment baseline, it was detected as early as day 4 at low levels (5%-20%) by using a highly sensitive sequencing assay that detects minor HCV populations representing at least 5% of global populations. However, this does not exclude that a small minority of drug-resistant viral variants might have been present prior to antiviral initiation, as previously observed in the setting of HIV infection.7
It is noteworthy that in the study by Kieffer et al. and in our case1 R155K-HCV variants have only been observed in patients infected with HCV genotype 1a.1 This might be explained by the fact that 2 nucleotide mutations are required for the Arg-to-Lys (AAA or AAG) substitution in HCV genotype 1b in comparison with 1 mutation in genotype 1a (http://hcv.lanl.gov/content/hcv-db/GET_ALIGNMENTS/alignments.html).1, 6
Further studies are needed to confirm and assess the extent of primary resistance to telaprevir, which would represent a concern for its future use.