New therapeutic strategies in HCV: second-generation protease inhibitors
Virginia C. Clark,
Joy A. Peter,
David R. Nelson*
Article first published online: 3 JAN 2013
Telaprevir and boceprevir are the first direct-acting antiviral agents approved for use in HCV treatment and represent a significant advance in HCV therapy. However, these first-generation drugs also have significant limitations related to thrice-daily dosing, clinically challenging side-effect profiles, low barriers to resistance and a lack of pan-genotype activity. A second wave of protease inhibitors are in phase II and III trials and promise to provide a drug regimen with a better dosing schedule and improved tolerance. These second-wave protease inhibitors will probably be approved in combination with PEG-IFN and Ribavirin (RBV), as well as future all-oral regimens. The true second-generation protease inhibitors are in earlier stages of development and efficacy data are anxiously awaited as they may provide pan-genotypic antiviral activity and a high genetic barrier to resistance.
AEs adverse effects
cEVR complete early virological response
PIs NS3-4A protease inhibitors
RVR rapid virological response
SVR sustained viral response
A large number of NS3-4A protease inhibitors (PIs) have reached clinical development, including two drugs, telaprevir and boceprevir, that have already been approved for use in combination with pegylated IFN-α (PEG-IFN) and ribavirin (RBV) in patients infected with genotype 1 hepatitis C virus. Telaprevir and boceprevir significantly improve virological outcomes in both treatment-naїve [1, 2] and -experienced genotype 1 patients [3, 4]. However, the clinical utility of these first-generation PIs is limited by a thrice-daily dosing schedule (with food), increased rates of adverse effects (AEs) (anaemia and rash), a low genetic barrier to resistance and extensive drug–drug interactions. These limitations highlight the opportunities for improvement in protease inhibitors. This review will discuss the newer protease inhibitors under late-stage development, which should be more potent, with higher barriers to viral resistance, and improved dosing regimens.
Second-wave protease inhibitors
|Simeprevir||Phase 3||Second wave|
|BI1335||Phase 3||Second wave|
|Asunaprevir||Phase 3 (all oral)||Second wave|
|Danoprevir/r||Phase 2||Second wave|
|Sovaprevir||Phase 2||Second wave|
|ABT450/r||Phase 2||Second wave|
|MK 5172||Phase 2||Second generation|
|ACH 2684||Phase 2||Second generation|
Simeprevir (TMC435; Tibotec, Beerse, Belgium; Medivir Pharmaceuticals, Stockholm, Sweden; Janssen, Beerse, Belgium) is a once-a day-oral NS3/4A protease inhibitor currently in phase III clinical development for the treatment of HCV infection. Phase I and II trials have demonstrated that TMC435 is generally well tolerated, has a pharmacokinetic profile that supports once-a-day dosing, and demonstrates potent antiviral activity and efficacy . The final results of two phase IIb trials of TMC435 with PEG-IFN/RBV in naïve and treatment-experienced populations have been completed . PILLAR study enrolled 368 treatment-naïve subjects with genotype 1 and compared two different doses (75mg vs 150 mg) and durations (12 weeks vs 24 weeks) of simeprevir therapy in combination with PEG-IFN/RBV for either 24 or 48 weeks. A sustained viral response (SVR) was achieved in 68–76% of patients with this triple therapy regimen and approximately 80% of subjects were eligible to receive shortened 24 weeks of therapy with very high SVR (93–96%). Adverse effects were similar to standard therapy, and the lowest rate of relapse was found in the study arm receiving 150 mg daily TMC435 in addition to PEG-IFN/RBV for 24 weeks (8%). In addition, SVR rates in the 150-mg dosing arms did not differ according to HCV subtype (1a vs 1b), but as expected, SVR was highest in the IL28B CC genotype.
BI201335 (Boehringer Ingelheim Pharmaceuticals, Ingelheim, Germany) is another NS3/4A protease inhibitor with once-a-day dosing that has completed phase 2 testing. SILEN-C1 study reported the efficacy data from a randomized phase II trial with 429 genotype 1 treatment-naïve patients . The treatment regimen included BI201335 in addition to PEG-IFN/RBV for 24 weeks at doses of 120 and 240 mg, followed by another 24 weeks of standard therapy. Response-guided therapy was evaluated and achievement of an eRVR (HCV-RNA negative at week 4 and week 12) resulted in randomization to stop therapy at week 24 or continue with PEG-IFN/RBV for a total of 48 weeks. The overall SVR rate was 83% for the 240-mg dose (lower for the 120-mg dose), and 92% of the patients with an eRVR achieved a SVR regardless of the subsequent duration of PEG-IFN/RBV. Adverse events (mostly gastrointestinal) resulted in drug discontinuation in 7.3% of subjects. SILEN-C2 study evaluated 288 partial or non-responders and evaluated the 240-mg dose, either once or twice daily in combination with PEG-IFN/RBV for 24 weeks . The highest SVR was achieved in the once-a-day dosing groups: it was 50% in partial responders and 35% in non-responders. It should be noted that patients with cirrhosis were not included in this study. Both SILEN-C1 and C2 tested the efficacy of a 3-day lead-in with PEG-IFN/RBV. The expectation was that the lead-in would limit the development of resistance by providing better antiviral drug coverage when the PI was introduced. For unknown reasons, the lead-in arms in both trials showed a significant decrease in efficacy, and this strategy to limit resistance has been abandoned. SILEN-C3 evaluated treatment-naïve, genotype 1 patients and randomized them to either 12 or 24 weeks of once-a-day 120 mg BI 201335. Both groups received PEG-IFN/RBV for 24 weeks and patients who did not achieve an eRVR continued PEG-IFN/RBV until week 48. SVR rates were similar for both durations, 65% vs 73% overall and 82% vs 81% in those with eRVR respectively. Through all of the SILEN-C phase 2 trials, the adverse-event profile of BI 201335 appeared to be mild rash and photosensitivity along with some GI toxicity (nausea, diarrhoea and vomiting). As with a few other PIs under development, BI 201335 is associated with a transient rise in indirect or unconjugated bilirubin that is related to inhibition of the bilirubin transporter (inhibition of hepatic uptake of uridine diphosphate glucuronosyl transferase 1 family polypeptide A1, UGT1A1). The once-per-day dosing regimen that is moving forwards into phase 3 trials has fewer adverse events than the twice-per-day dosing regimen.
Danoprevir/r (RG7277; Roche, Basle, Switzerland; Intermune Pharmaceuticals, Brisband, CA) is a twice-a-day, ritonavir-boosted HCV protease inhibitor with good antiviral activity against genotypes 1, 4 and 6. Of note, the early hepatotoxicity signals of the drug were virtually eliminated by the addition of ritonovir boosting, which leads to strong inhibition of CYP3A and increased through concentrations of the PI. DAUPHINE is a large phase 2 trial in naïve patients that evaluated three different doses (50, 100 and 200 mg danoprevir, boosted with 100 mg ritonavir, twice daily) and response-guided therapy in combination with PEG-IFN/RBV . Twelve weeks after stopping therapy, antiviral negativity (SVR12) was 93% in the 200-mg dosing arm, 83% in the 100-mg arm and 67% in the 50-mg arm. At the 200-mg dose, the response was not influenced by either HCV subtype (1a vs 1b) or IL28B genotype (CC vs non-CC), suggesting that this regimen leads to potent viral suppression. Of note, genotype 4 patients had a 100% SVR 12 across all dosing arms. Danoprevir is also being evaluated in IFN-free regimens combined with the nucleoside inhibitor, Mercitabine (RG7128) .
Second-generation protease inhibitors
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