NS5A Sequence Heterogeneity and Mechanisms of Daclatasvir Resistance in Hepatitis C Virus Genotype 4 Infection

Hepatitis C virus (HCV) is genetically diverse, with 7 recognized genotypes[1]. HCV genotype4 represents approximately 8% of chronic HCV infections worldwide; it is most prevalent in the Middle Eastand Northand Central Africa, representing the most common HCV genotypein many countries in these areas [2–4]. Recently, genotype4 prevalence has increased in Europe and has been reported in Asia and North and South America [2, 4–6]. Genotype4 is highly heterogeneous, with 17 recognized subtypes and other subtypes awaiting assignment. The relative prevalence of genotype4 subtypes varies geographically [7]. The introduction of direct-acting antiviral (DAA) agents has markedly improved therapeutic outcomes for patients with chronic HCV infection [8]. However, most studies of new HCV therapies have focused on genotype1, in part because of its predominance in North America, eastern Asia, and most European countries [2]. Despite its substantial global prevalence, genotype4 has received limited attention with respect to basic virologic and therapeutic research. Recently, several DAA-based regimens have been evaluated in genotype4 infection, including combinations of a DAA with pegylated interferonalfa and ribavirin (pegIFN/RBV) [9–12] and more recently, all-oral, pegIFN-free regimens [13–16]. Consistent with results in genotype1 infection, DAA-based regimens have demonstrated greater antiviral efficacy than pegIFN/RBV in genotype4 infection. With genotype1 infection, there is extensive evidence that genotype1 subtype (1a or 1b) influences the efficacy and barrier to resistance of some DAAs and DAA-based HCV therapeutic regimens [11, 17–20]. However, the potential influence of genotype4 subtype on the efficacy and resistance profiles of DAA-based therapeutic regimens has not been reported. Owing to the heterogeneity of genotype4 and the marked geographic differences in the prevalence of genotype4 subtypes, the potential impact of these differences on antiviral therapies needs to be evaluated because they may affect treatment strategies for patients with genotype4 infection. Daclatasvir(DCV) is a potent, pan- genotypicinhibitor of the HCV NS5Aprotein [21]. DCV has been evaluated in multiple clinical studies and has demonstrated robust antiviral responses and a good safety and tolerability profile in combination with other agents [22]. Studies in patients with genotype4 infection have investigated DCV combined with pegIFN/RBV, as well as the all-oral combination of DCV with the NS3protease inhibitor asunaprevirand the nonnucleoside NS5Bpolymerase inhibitor beclabuvir[11, 15]. The objective of this study was to investigate the prevalence and geographic distribution of genotype4 subtypes with which patients were infected, preexisting polymorphisms at NS5Aamino acid positions associated with DCV resistance (28, 30, 31, or 93) in relation to genotype4 subtype, the effect of these polymorphisms on DCV susceptibility in vitro, the relationship of baseline polymorphisms to therapeutic outcome, and resistance polymorphisms that emerged in patients who experienced virologic failure.