According to literature RASs V

According to literature, RASs V36M, T54S, Q80K and R155K are considered primary resistance mutations to different PIs. RASs V36M and R155K can reduce susceptibility to recently approved PIs simeprevir, paritaprevir and grazoprevir [18], [31], [32]. T54S is associated to resistance for first-wave telaprevir [33]. Q80K is highly associated with resistance to simeprevir [34]. The presence of RAS V36M in HCV strains could be related with therapeutic failure experimented by four patients in a previous treatment with telaprevir. The identification of this substitution in one patient from group 2 suggested a primary infection with a drug-resistant viral variant, an observation that warns for the circulation of resistant strains that could impact the effectiveness of DAAs in the near future. For all five patients with RAS V36M, combined therapy with new generation PIs should not be considered since V36M is associated with resistance to the majority of approved NS3 DAAs. Indeed, since it was already available in Brazil, treatment with sofosbuvir combined with daclatasvir was chosen and all five patients had similar treatment outcome which was undetectable HCV RNA after 12 weeks post-treatment. A study conducted a retrospective analysis to determine the prevalence of resistance mutations among telaprevir-treated patients [33] and V36M methylphenidate hcl was identified in 28/232 (12%) patients which failed telaprevir therapy, thus demonstrating its importance as a mutation indicative of resistance whose poor prognosis does not reveal reliability in the use of first-generation PI. Barnard et al. [35] identified resistance mutations in non-responders to triple therapy with boceprevir/peg-IFN/RBV infected with subtype 1a and concluded that V36M can be a major cause of therapeutic failure with the use of first-wave PIs. Results from the present study demonstrated that mutations at position 36 were found in both DAA-experienced and non-experienced patients included in the study, which indicated that treatment with DAAs other than PI should be considered in order to minimize risk of resistance and achieve SVR in these patients. Among RASs observed in patients from group 2, RAS T54S was identified in one patient infected with subtype 1b. This mutation had been shown to cause resistance to boceprevir and telaprevir, but not to simeprevir [36]. This was confirmed here since this patient achieved SVR after 12 weeks of treatment with simeprevir. The low prevalence of RAS T54S (4.6%) in patients not treated with DAAs was also reported in previous Brazilian studies [30], [37]. In the present study, RAS Q80K was not observed in isolates of subtype 1a and was only detected in one subtype 1b sample from a group 2 patient with compensated hepatic cirrhosis, type 2 diabetes mellitus and systemic arterial hypertension. In 2016, this patient was asymptomatic and decided not to continue with other available DAA therapeutic options. Q80K is most frequently observed in subtype 1a isolates and is rarely detected in HCV subtype 1b [20]. Studies had reported the high prevalence of Q80K mutation in USA (37–47%) [38], [39]. Sarrazin et al. [40] evaluated NS3 baseline RASs from 467 patients and results for Q80 polymorphisms demonstrated high prevalence for PI treatment-experienced patients (110/265; 41.5%) and PI treatment-naive patients (93/202; 46%). In contrast to data from other countries, Q80K prevalence in Brazil is low [30], [37], [41]. Therefore, due to low prevalence of this mutation in Brazilian strains reported in previous studies and corroborated here, there is no need to incorporate pretreatment resistance tests for infected patients with subtypes 1a and 1b of HCV in Brazil. Even with the identification of this variant, the use of other PIs is not limited since there is no evidence with resistance. RAS R155K is related to resistance to first and second-wave PIs. A study reported a higher frequency of treatment failure for subtype 1a due to low genetic barrier to viral resistance when compared to subtype 1b [13]. Sarrazin et al. [36] described that combination of substitutions V36M + R155K induces high resistance to telaprevir and may inhibit drug action. In the present study, combination of mutations at loci 36 (V36M) and 155 (R155K) was identified in one telaprevir-experienced patient infected with HCV subtype 1a. After 12 weeks of therapy with telaprevir, viral load was 4.74 log10 IU/mL and it was decided to suspend the treatment. RAS R155K confers resistance to all available PIs for subtype 1a strains and new therapeutic options for this patient should target other non-structural HCV proteins. Indeed, in this case, a rescue therapy with NS5B and NS5A inhibitors was selected and HCV RNA was undetectable after 4 weeks.