Monday, June 17, 2013

Telaprevir - Analysis of Genotype 2/3 Hepatitis C Virus Variants

Analysis of Genotype 2 and 3 Hepatitis C Virus Variants in Patients Treated With Telaprevir Demonstrates a Consistent Resistance Profile Across Genotypes

Abstract and Introduction
Study C209 evaluated the activity of telaprevir in treatment-naïve patients with genotypes 2 or 3 (G2, G3) hepatitis C virus (HCV) infection. Telaprevir monotherapy showed potent activity against HCV G2, but limited activity against G3. This analysis was performed to characterize HCV viral variants emerging during telaprevir-based treatment of G2/G3 HCV-infected patients. Patients were randomized to receive 2 weeks of treatment with telaprevir (telaprevir monotherapy), telaprevir plus peginterferon alfa-2a and ribavirin (triple therapy), or placebo plus peginterferon alfa-2a and ribavirin (control), followed by 22–24 weeks of peginterferon/ribavirin alone. Viral breakthrough was defined as an increase >1 log10 in HCV RNA from nadir, or HCV RNA >100 IU/mL in patients previously reaching <25 IU/mL. Twenty-three patients (47%) had G2 and 26 (53%) had G3 HCV. Viral breakthrough occurred during the initial 2-week treatment phase in six G2 patients (66.7%; subtypes 2, 2a and 2b) and three G3 patients (37.5%; all subtype 3a), all in the telaprevir monotherapy arm. Four breakthrough patients (three G2, one G3) subsequently achieved sustained virologic response (SVR). In all patients with breakthrough and available sequence data, mutations associated with reduced susceptibility to telaprevir in genotype 1 (G1) HCV were observed. No novel G2/G3-specific mutations were associated with telaprevir resistance. The telaprevir resistance profile appeared consistent across HCV genotypes 1, 2 and 3. Although viral breakthrough with resistance occurred in patients receiving telaprevir monotherapy, half of these patients achieved an SVR upon addition of peginterferon/ribavirin highlighting the importance of combination therapy.

Discussion Only
Full text available @ Medscape

In treatment-naïve patients, telaprevir monotherapy had significant antiviral activity against G2 HCV but little or no activity against G3 HCV.[14] All vBTs occurred during telaprevir monotherapy, and most NS3 mutations emerging during breakthrough occurred at amino acid positions previously reported to be associated with reduced telaprevir susceptibility in G1 HCV. The finding that telaprevir monotherapy is associated with a high rate of vBT in G2/G3 HCV is similar to previous observations in G1 HCV,[15,16] and highlights the importance of combining telaprevir with peginterferon/ribavirin to control the emergence of resistant variants that remain susceptible to these agents.

In the telaprevir monotherapy arms, vBT was reported in six of nine patients with G2 HCV and three of eight patients with G3 HCV. Seven of these nine patients with vBT had undetectable HCV RNA at the end of subsequent treatment with peginterferon/ribavirin, and four achieved an SVR. The fact that G2 and G3 HCV variants with reduced telaprevir susceptibility remained sensitive to, and can be eradicated by, peginterferon/ribavirin extends similar observations with G1 HCV.[15]
Three mutations associated with reduced telaprevir susceptibility in G1 HCV (R155K, T54A, A156S) were seen in G2 HCV patients with vBT; two (R155K and T54A) were seen in G3 HCV patients with vBT. As in G1a HCV,[16] all emergent mutations required only a single nucleotide change from baseline. Several additional mutations were identified by the present analyses, but these did not occur consistently across patients and were not previously reported for other HCV protease inhibitors.[2,15,17] Moreover, none of these additional mutations occurred with significantly higher frequency than in HCV samples from patients not exposed to telaprevir. However, small sample sizes and a restricted diversity of subtypes limited the robustness of our findings and, for G2, statistical analyses could not be performed.

Furthermore, in samples with these additional mutations, resistance could be explained by known telaprevir-resistant mutations using site-directed mutagenesis, although we had not formally introduced the additional mutations into baseline samples to determine their impact on telaprevir susceptibility. In spite of this, our data suggest a lack of G2- or G3-specific mutations for telaprevir resistance. Therefore, the resistance profile appears consistent across G1, G2 and G3.

The NS3 region of HCV shows some differences between genotypes. For example, position 36 of the NS3 region, identified as a site for telaprevir-resistant G1 mutations, contains leucine (L) in patients with G2 and G3 HCV, but valine (V) in G1 HCV. The impact of this amino acid change, if any, on telaprevir susceptibility is not fully understood and may be genotype and subtype dependent. For example, some G2 NS3 proteins carrying an 'L' at position 36 exhibited telaprevir FC values similar to those observed with G1 proteins carrying a 'V' at position 36 (Janssen Infectious Diseases BVBA, data on file). G3 NS3 proteins carrying an 'L' at position 36 exhibited on average higher FC values, although changes at other amino acid positions could have caused this decrease in susceptibility. This type of finding may underlie the differences observed in this study between G2 and G3 in baseline telaprevir FC, as well as the differences in viral activity of telaprevir against the two genotypes.

G2-infected patients with vBT during telaprevir therapy had subtype 2b, 2a or an unknown subtype, but none had 2c. Although patient numbers were small, this suggests that vBT may be less common with subtype 2c. All G3-infected patients with vBT had subtype 3a. The lack of vBT among subtype 3b patients could relate to the lack of telaprevir activity. The R155K mutation only emerged in G2-infected patients with subtype 2b; in G2a viruses, the emergence of a 'K' at position 155 would require a double nucleotide change. The R155K mutation was dominant in G3a HCV patients with vBT.

For patients with G2 HCV in the telaprevir monotherapy arm, the greatest HCV RNA decline from baseline to day 3 was observed in those with the highest telaprevir susceptibility at baseline. Conversely, in G3 patients, the greatest HCV RNA decline from baseline to day 3 was in those with the lowest baseline telaprevir susceptibility. Patient numbers were small, and the phenotype data were obtained with a biochemical assay, which is less reliable than a cell-based assay. However, this inverse correlation might relate to the low efficacy of telaprevir monotherapy in G3 patients. As previously observed in G1 HCV, emergence of the R155K mutation at vBT was associated with a high FC increase, and site-directed mutagenesis confirmed that R155K is associated with reduced susceptibility to telaprevir in G2/G3 patients. In addition, the A156S mutation was associated with reduced telaprevir susceptibility in G2 HCV.

Clonal sequence analysis confirmed that in most instances of vBT in patients with G2/G3 HCV, mutations associated with reduced telaprevir susceptibility in G1 HCV emerged and became the dominant quasispecies. In two patients, a mutation associated with reduced telaprevir susceptibility was detected at baseline in one clone. However, a mutation found in one clone of 22–27 clones can be the result of a PCR amplification error and not a true mutation present in the clonal population.
In addition to the limitations already mentioned for this study, the sample size was small, and a proportion of patients were unfortunately lost to follow-up. Small samples, however, are a common characteristic of proof-of-principle studies exploring the intrinsic activity of an antiviral agent.

In summary, telaprevir showed activity against G2 HCV in treatment-naïve patients, but limited or no activity against G3 HCV. The resistance profile of telaprevir in G2 and G3 HCV appears to involve similar amino acid substitutions as previously observed in G1 HCV. All cases of vBT occurred in the telaprevir monotherapy arms, highlighting the importance of combining telaprevir with peginterferon/ribavirin to avoid the emergence of resistant variants. A high proportion of patients who experienced vBT with telaprevir monotherapy still achieved an SVR after peginterferon/ribavirin treatment, indicating that the emergence of variants with reduced susceptibility to telaprevir can be controlled with these agents

Abstract and Introduction
  • Materials and Methods
  • Results
  • Discussion

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