In the 24 months following the initiation of the Telaprevir in Genotype 3 (TIG3) hepatitis C trial, there have been significant advances in the treatment of hepatitis C. Following patient recruitment onto the TIG3 trial compassionate use of sofosbuvir with ledipasvir and daclatasvir was commenced in 2014 for patients with decompensated liver disease due to hepatitis C in the UK. The ALLY 3 trial had demonstrated that sofosbuvir and daclatasvir for 12 weeks only achieved SVR rates of 63% in patients with genotype 3 HCV and liver cirrhosis173. A subsequent trial evaluating sofosbuvir,
daclatasvir and ribavirin for 12 or 16 weeks in patients with liver cirrhosis achieved SVR rates of 83- 89%174. Real world data from the expanded access programme in the UK175demonstrated that while
the overall rate for SVR was high (for this cohort of patients with predominantly decompensated liver disease), there was a marked difference between outcomes for genotype 1 HCV and genotype 3. The SVR rates for genotype 1 patients treated on the early access programme was 91% compared to 69% for genotype 3 patients. In particular, the SVR rate for patients with genotype 3 hepatitis C treated with sofosbuvir and ledipasvir was only 62% compared to 73% for those treated with sofosbuvir and daclatasvir.
While the early access programme was underway, second generation NS5A inhibitors were being evaluated in clinical trials. The ASTRAL-3176trial used sofosbuvir and velpatasvir (a second generation
NS5A inhibitor) for 12 weeks achieving SVR rates of 97% in patients with genotype 3 HCV without cirrhosis, with a modest decrease in patients with compensated cirrhosis (91%). The ASTRAL-4177
study also used velpatasvir and sofosbuvir, but demonstrated that patients with genotype 3 hepatitis C and decompensated liver disease had lower SVR rates than their genotype 1 counterparts (SVR 50% for 12 or 24 weeks sofosbuvir and velpatasvir, SVR 85% for 12 weeks sofosbuvir, velpatasvir and ribavirin compared to 88%, 93%, and 94% for the equivalent genotype 1a groups). So, although direct acting antiviral drugs had significantly improved outcome for genotype 3 patients with
advanced liver disease (with a further small improvement by adding ribavirin) there remained a significant minority of patients with genotype 3 HCV who did not achieve an SVR.
In order to investigate this variation and to understand the mechanism by which treatment failed for the small proportion of patients that didn’t achieve an SVR, next generation sequencing of patient HCV was undertaken as part of the clinical trials evaluating newer direct acting antivirals. It was noted that particular resistance associated substitutions, especially in the NS5A sequence, resulted in a decreased SVR12 rate. A30K, L31F/M and Y93H were especially implicated in resistance to NS5A inhibitors, while the following resistance associated substitutions were noted in NS5B: N142T, L159F, E237G, L320I, S282 and V321A/IS96T176. Despite the presence of NS5A resistance associated
substitutions in 28% of patients (using a sequencing cut off of 15% of sequencing reads) in the POLARIS studies using sofosbuvir and velpatasvir, SVR rates of 97-100% were achieved in genotypes 1,2,4,5 or 6. For genotype 3 however, 12% of patients had NS5A resistance associated substitutions at baseline. In patients with NS5A resistance associated substitutions the SVR rates were lower, 93% compared to those without those substitutions at baseline (98%). In patients with genotype 3 hepatitis C and the Y93H substitution in the NS5A sequence the SVR12 rate dropped further to 86%178, whilst patients in the ALLY-3 trial (who received 12 weeks of sofosbuvir and daclatasvir) with
the Y93H substitution only achieved an SVR12 of 54%173.
Whilst the NS5A/NS5B combinations achieved excellent SVR rates, in particular for patients with genotype 1 hepatitis C even with previous treatment failure or advanced liver disease (where SVR rates still remained above 95%), in genotype 3 hepatitis C the data from the ALLY-3 and POLARIS studies along with real world data from the expanded access programme demonstrated that an unmet treatment need still existed for patients with genotype 3 hepatitis C and advanced liver disease or Y93 resistance associated substitutions.
Fortunately, additional treatment regimens were also in development at the time, including some which contained second generation protease inhibitors. Elbasvir (NS5A inhibitor) and grazoprevir (NS3 inhibitor) were evaluated in the treatment of genotype 3 hepatitis C (in treatment naïve non- cirrhotic patients). This combination only achieved SVR rates of 45% with 12 weeks of treatment or 57% with 16 weeks of treatment166. Analysis undertaken to determine whether resistance associated
substitutions accounted for virological failure only identified NS3 substitutions (which conferred a >5 fold change in sensitivity) in only 35% of patients with virological failure. NS5A resistance associated substitutions however occurred more frequently, with the Y93H substitution occurring in 76% of patients who experienced virological breakthrough. The C-ISLE study evaluated grazoprevir, elbasvir and sofosbuvir (with or without ribavirin) in the treatment of patients with genotype 3 hepatitis C and cirrhosis. Treatment naïve patients treated with elbasvir/grazoprevir, sofosbuvir and ribavirin for eight weeks achieved an SVR of 91%, whilst treatment with elbasvir/grazoprevir and sofosbuvir for 12 weeks achieved an SVR12 of 96%. In patients who had been treated with interferon and ribavirin previously, treatment with elbasvir/grazoprevir and sofosbuvir for 12 or 16 weeks resulted in SVR12 rates of 94%. In both the trials above, a high proportion of patients had baseline NS3 resistance associated substitutions but these were not necessarily associated with clinical outcome. In the C- ISLE study, despite 50% of patients having detectable NS5A RAS at baseline, the SVR rate was 98% in participants with or without RAS179.
Another regimen that has subsequently become the standard of care treatment for genotype 3 hepatitis C in the United Kingdom is glecaprevir and pibrentasvir. Glecaprevir (ABT-493) is a pan genotypic NS3 inhibitor which maintained activity even against substitutions at 155 and 168 (which conferred resistance against previous generations of NS3 inhibitors). Pibrentasvir (ABT-530) is a NS5A inhibitor with an improved resistance profile to RAS at M28T, A30K and Y93H. The Surveyor II study evaluated this combination in patients with genotype 3 HCV and compensated cirrhosis, achieving SVR rates of 95% in treatment naïve patients following 12 weeks of treatment. In
achieved an SVR12 (75%). The combination of ABT-493/ABT-530 and ribavirin achieved an SVR12 of 100% in patients with genotype 3 HCV and cirrhosis (irrespective of prior treatment status)167. In the
third phase of the Surveyor II trial, larger numbers of patients were treated with glecaprevir and pibrentasvir. Treatment naïve cirrhotic genotype 3 patients achieved an SVR12 of 98% following 12 weeks of treatment. Treatment experienced non-cirrhotic genotype 3 patients achieved SVR12 of 91% and 95% with 12 and 16 weeks of treatment respectively. An SVR12 of 96% was achieved in treatment experienced genotype 3 patients with cirrhosis following 16 weeks of treatment. Patients with previous sofosbuvir experience achieved an SVR12 of 98%180.
Initial trials evaluating treatment duration with sofosbuvir/velpatasvir and voxilaprevir (a pan genotypic NS3 inhibitor) achieved SVR12 rates of 94% following eight weeks of treatment in treatment naïve genotype 3 HCV patients with cirrhosis. Treatment experienced genotype 3 HCV patients with cirrhosis were given 12 weeks of treatment and also achieved SVR rates of 94%181.
Subsequent trials evaluated this combination for 12 weeks in NS5A experienced patients (POLARIS- 1), and also in patients exposed to any DAA except NS5A inhibitors (POLARIS-4). In POLARIS-1 genotype 3 NS5A experienced patients achieved an SVR12 of 95%, with an SVR12 rate of 93% in patients with cirrhosis. In POLARIS-4 an SVR rate of 96% was achieved in genotype 3 patients treated with a non-NS5A DAA regimen (predominantly sofosbuvir based treatment)182. In POLARIS-3 SVR12
rates of 96% were achieved with both 12 weeks of sofosbuvir/velpatasvir and eight weeks of sofosbuvir/velpatasvir and voxilaprevir in DAA naive patients with genotype 3 hepatitis C and liver cirrhosis168.
As these newer, pangenotypic (and better tolerated) protease inhibitors became available, first generation protease inhibitors were superseded and therefore withdrawn from usage. As a result telaprevir was withdrawn from use in Europe in September 2016. Some of the challenges faced in the Telaprevir in Genotype 3 clinical trial still remain, however. The limited efficacy of
confer benefit in a proportion of patients. Interestingly, there were no significant NS3 RAS that were identified that conferred resistance to treatment in patients with genotype 3 HCV. This contrasts with the NS5A resistance associated substitutions which are well documented with both initial NS5A inhibitors (daclatasvir, ledipasvir and elbasvir) along with newer NS5A inhibitors (velpatasvir and pibrentasvir). With the most recent NS3 containing regimens, the high efficacy of treatment results in a small number of patients who have virological failure or relapse post treatment. Subsequently, predicting patients who may fail treatment or identifying combinations of RAS that confer resistance is challenging. As the sequencing data from the telaprevir in genotype 3 trial demonstrated, in a small cohort of samples the likelihood of identifying RAS which confer NS3 resistance in genotype 3 is limited. Whilst there may be certain RAS which appear to correlate with clinical outcome, it is difficult to extrapolate firm conclusions when other variables may be present (such as sensitivity to additional drugs in a treatment regimen, pharmacokinetic variables and treatment adherence). This highlights the need for an effective in vitro system to enable accurate phenotyping of patient derived genotype 3 HCV to direct acting antiviral drugs. This data then allows a greater number of samples to be tested and may improve the ability to detect RAS which confer resistance to a single DAA (which may not be apparent when patients are treated with multi-DAA combinations).