For two Group A GT1b-infected patients, no viral breakthrough occurred during 24 RG-7388 weeks of treatment and neither patient experienced

relapse during the 48-week follow-up period. For patients in Group A, trough plasma concentrations of daclatasvir 24 hours postdose on Day 14 ranged from 187-617 nM in Group A. Range in plasma concentrations of asunaprevir 12 hours postdose on Day 14 ranged from 32-501 nM. No correlation was observed between these trough plasma concentrations of daclatasvir and asunaprevir and virologic breakthrough (Table 1). In vitro resistance phenotypes (EC90 values in transient and stable replicon cell line assays) of emergent predominant resistance variants, however, were higher than observed drug exposures VX-770 in plasma for daclatasvir and asunaprevir. Review of manual pill counts and dosing diaries suggested excellent adherence to treatment except for Patient 1, who admitted to several missed asunaprevir doses within the first 2 weeks of treatment. Patient 1 (GT1a) had early viral

breakthrough with detectable drug-resistant variants as early as Week 2 (Fig. 2) and started treatment intensification with peginterferon alfa-2a and ribavirin at Week 4. Emergent NS5A-Y93N conferred 19,267-fold reduced susceptibility to daclatasvir in vitro, and persisted through posttreatment Week 48. NS3-D168Y and NS3-D168A also emerged at virologic breakthrough and conferred 93-fold and 29-fold reduced susceptibilities to asunaprevir (Table 3) with 0.23 and 0.01-fold relative replication capacities (Fig. 2), respectively, versus a GT1a (H77c) reference replicon. NS3-D168T emerged 上海皓元 as a minor variant (10%; 4/40 clones), determined by clonal analysis, at Week 12 (8 weeks into treatment intensification) conferring 205-fold reduced susceptibility to asunaprevir (Table 3) and 1.6-fold relative replication

capacity when compared to GT1a (H77c) (Fig. 2). This became the predominant variant from Week 24 (20 weeks after treatment intensification) through posttreatment Week 36. D168T may have emerged from D168A based on synonymous codon usage. The low relative replication capacity of D168A was improved by changing to D168T (see comparison of in vitro replication capacities, Fig. 2). D168T was no longer detected by clonal analysis at posttreatment Week 48 due to outgrowth of wild-type virus. It should be noted that D168G (13-fold reduced susceptibility to asunaprevir) was detected in one sequenced colony at this timepoint. The time course of HCV viral load for Patient 2 (GT1a) indicated early viral breakthrough at Week 4 followed by viral suppression during treatment intensification with peginterferon alfa-2a and ribavirin for approximately 41 weeks and viral relapse within 4 weeks of treatment discontinuation (Fig. 3).