New protease inhibitors for HCV – Help is on the way
Authors: Dahlene N. Fusco, Raymond T. Chung
Journal: Journal of Hepatology (2011)

HCV infects an estimated 170 million people and is the leading indication for liver transplantation. For patients harboring infection with HCV-1, the predominant genotype worldwide, treatment with peginterferon and ribavirin produces sustained virologic response (SVR) in only 45% of patients and is limited by substantial side effects [[1]Modi A.A. Liang T.J. Hepatitis C virus: a clinical review.Oral Dis. 2008; 14: 10-14Crossref PubMed Scopus (61) Google Scholar]. In the coming months, HCV therapy will enter a new era with the introduction of direct acting antiviral agents (DAAs) [2Jacobson I. Emerging and novel therapies for hepatitis C.Gastroenterol Hepatol. 2010; 6: 623-627Google Scholar, 3McGovern B. Abu Dayyeh B. Chung R.T. Avoiding therapeutic pitfalls: the rational use of specifically targeted agents against hepatitis C infection.Hepatology. 2008; 48: 1700-1712Crossref PubMed Scopus (27) Google Scholar, 4Kwong A. McNair L. Jacobson I. George S. Recent Progress in the development of selected hepatitis C virus NS3–4A protease and NS5B polymerase inhibitors.Curr Opin Pharmacol. 2008; 8: 522-531Crossref PubMed Scopus (99) Google Scholar, 5Vermehren J, Sarrazin C. New HCV Therapies on the Horizon. Clin Microbiol Infect. 2010 Nov 18.Google Scholar]. The most advanced HCV DAAs in the development pipeline include inhibitors of the viral NS3/4A protease and the viral NS5B RNA-dependent RNA polymerase [[2]Jacobson I. Emerging and novel therapies for hepatitis C.Gastroenterol Hepatol. 2010; 6: 623-627Google Scholar]. Inhibitors of the NS3/4A protease are particularly attractive, since these drugs may have the double-edged action of not only directly inhibiting HCV replication, but also abrogating HCV NS3/4A’s subversion of the innate immune response [[6]Gale M. Foy E. Evasion of intracellular host defence by hepatitis C virus.Nature. 2005; 436PubMed Google Scholar]. The NS3/4A compounds currently furthest along in development, the linear protease inhibitors (PIs) boceprevir (Merck) and telaprevir (VX 950, Vertex), have shown that they can substantially improve SVR when used in combination with peginterferon and ribavirin, and may also permit truncation of therapy [7McHutchison J.G. Everson G.T. Gordon S.C. PROVE1 Study Team et al.Telaprevir with peginterferon and ribaviron for chronic HCV genotype 1 infection.N Engl J Med. 2009; 360: 1827-1838Crossref PubMed Scopus (994) Google Scholar, 8Hézode C. Forestier N. Dusheiko G. PROVE2 Study Team et al.Telaprevir and peginterferon with or without ribaviron for chronic HCV infection.N Engl J Med. 2009; 360: 1839-1850Crossref PubMed Scopus (967) Google Scholar, 9Kwo P.Y. Lawitz E.J. McCone J. et al.Efficacy of boceprevir, an NS3 protease inhibitor, in combination with peginterferon alfa-2b and ribavirin in treatment naive patients with genotype 1 hepatitis C infection (SPRINT-1): an open-label, randomised, multicentre phase 2 trial.Lancet. 2010; 376: 705-716Abstract Full Text Full Text PDF PubMed Scopus (616) Google Scholar]. Phase 3 trials of these PIs have been recently completed [[2]Jacobson I. Emerging and novel therapies for hepatitis C.Gastroenterol Hepatol. 2010; 6: 623-627Google Scholar], and their results are anxiously awaited by patients and HCV providers alike. The arrival of these drugs heralds a major advance for HCV therapy, though they are associated with important limitations. Both agents require thrice daily dosing; telaprevir has also been associated with skin reactions, and boceprevir with anemia and dysgeusia. As DAAs, both drugs are associated with rapid development of resistance mutations when given as monotherapy [7McHutchison J.G. Everson G.T. Gordon S.C. PROVE1 Study Team et al.Telaprevir with peginterferon and ribaviron for chronic HCV genotype 1 infection.N Engl J Med. 2009; 360: 1827-1838Crossref PubMed Scopus (994) Google Scholar, 8Hézode C. Forestier N. Dusheiko G. PROVE2 Study Team et al.Telaprevir and peginterferon with or without ribaviron for chronic HCV infection.N Engl J Med. 2009; 360: 1839-1850Crossref PubMed Scopus (967) Google Scholar, 9Kwo P.Y. Lawitz E.J. McCone J. et al.Efficacy of boceprevir, an NS3 protease inhibitor, in combination with peginterferon alfa-2b and ribavirin in treatment naive patients with genotype 1 hepatitis C infection (SPRINT-1): an open-label, randomised, multicentre phase 2 trial.Lancet. 2010; 376: 705-716Abstract Full Text Full Text PDF PubMed Scopus (616) Google Scholar] (Table 1).Table 1Comparison of 1st and 2nd generation HCV NS3/4A protease inhibitors.∗∗Seiwert et al. Antimicrobial Agents and Chemotherapeutics 2008. % Susser et al. Hepatology 2009.?4,5,6 indicates that there may be danoprevir activity vs HCV genotypes 4,5,6 based on preclinical data but no clinical trials have examined this yet. Open table in a new tab ∗∗Seiwert et al. Antimicrobial Agents and Chemotherapeutics 2008. % Susser et al. Hepatology 2009. ?4,5,6 indicates that there may be danoprevir activity vs HCV genotypes 4,5,6 based on preclinical data but no clinical trials have examined this yet. Two phase 1b studies of new NS3/4A protease inhibitors published in this issue of the Journal of Hepatology [10Forestier N. Larrey D. Guyader D. Marcellin P. Rouzier R. Patat A. et al.Treatment of chronic hepatitis C patients with the NS3/4A protease inhibitor danoprevir (ITMN-191-RG7227) leads to robust reductions in viral RNA: Phase 1b multiple ascending dose study.J Hepatol. 2011; 54: 1130-1136Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar, 11Manns M. Bourliere M. Benhamou Y. Pol S. Bonacini M. Trepo C. et al.Potency, safety and pharmacokinetics of the NS3/4A protease inhibitor BI201335 in patients with chronic HCV genotype-1 infection.J Hepatol. 2011; 54: 1114-1122Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar] provide promising evidence that HCV treatment options will continue to improve. Forestier et al. present phase 1b study results for the NS3/4A protease inhibitor danoprevir (ITMN 191/RG7227). Danoprevir is a macrocyclic PI notable for its high specificity [12Rajagopalan R. Misialek S. Stevens S. Myszka D. Brandhuber B. Ballard J. et al.Inhibition and binding kinetics of the hepatitis C virus NS3 protease inhibitor ITMN-191 reveals tight binding and slow dissociative behavior.Biochemistry. 2009; 48: 2559-2568Crossref PubMed Scopus (60) Google Scholar, 13Seiwert S. Andrews S. Jiang Y. Serebyany V. Tan H. Kossen K. et al.Preclinical characteristics of the hepatitis C virus NS3/4 protease inhibitors ITMN-191 (RG7227).Antimicrob Agents Chemother. 2008; 52: 4432-4441Crossref PubMed Scopus (168) Google Scholar] and high hepatic concentrations [[13]Seiwert S. Andrews S. Jiang Y. Serebyany V. Tan H. Kossen K. et al.Preclinical characteristics of the hepatitis C virus NS3/4 protease inhibitors ITMN-191 (RG7227).Antimicrob Agents Chemother. 2008; 52: 4432-4441Crossref PubMed Scopus (168) Google Scholar]. Their study evaluated safety, pharmacokinetics, and antiviral activity of 14 days of danoprevir monotherapy administered two or three times daily in multiple ascending doses versus placebo in two groups: 40 treatment naïve genotype 1 infected patients (TNs) and 10 peginterferon and ribavirin non-responders (NRs). Subjects were predominantly male, non-obese, and non-cirrhotic. Danoprevir monotherapy was safe and well tolerated in both groups, with limited side effects. HCV RNA declines occurred in all treatment groups and were dose dependent, with median maximal declines ranging from 1.8 to 3.9 logs. Viral kinetics revealed that, overall, 27% of patients experienced viral rebound, 35% plateau, and 38% continuous viral decline, including 3/8 prior non-responders, although the nonresponse category (e.g., null versus partial versus relapser) was not specified. As anticipated, resistance mutations were detected. All patients with virologic rebound, including GT1b patients, selected R155K mutations; another two also had D168V/E/T mutations. Half of the patients who experienced virologic plateau selected for R155K or D168V/E/T mutations. Not surprisingly, GT1a patients exhibited rebound more often and selected for a higher frequency of R155K mutations, likely since 1a virus requires only one nucleotide substitution to generate this mutant, whereas 1b requires two substitutions [[14]Susser S. Welsch C. Wang Y. Zettler M. Domingues F. Karey U. et al.Characterization of resistance to the protease inhibitor Boceprevir in hepatitis C virus-infected patients.Hepatology. 2009; 50: 1709-1718Crossref PubMed Scopus (275) Google Scholar]. Of note, R155K mutants, which may confer cross class resistance [[15]He Y. King M. Kempf D. Lu L. Lim H. Krishnan P. et al.Relative replication capacity and selective advantage profiles of protease inhibitor-resistant hepatitis C virus NS3 protease mutants in the HCV genotype 1b replicon system.Antimicrob Agents Chemother. 2008; 52: 1101-1110Crossref PubMed Scopus (93) Google Scholar], persisted following treatment cessation. This finding is consistent with the report that these mutants may display fitness resembling that of wild type HCV [[15]He Y. King M. Kempf D. Lu L. Lim H. Krishnan P. et al.Relative replication capacity and selective advantage profiles of protease inhibitor-resistant hepatitis C virus NS3 protease mutants in the HCV genotype 1b replicon system.Antimicrob Agents Chemother. 2008; 52: 1101-1110Crossref PubMed Scopus (93) Google Scholar]. Conversely, D168 mutations may lead to macrocyclic PI resistance but may actually increase susceptibility to linear PIs [[15]He Y. King M. Kempf D. Lu L. Lim H. Krishnan P. et al.Relative replication capacity and selective advantage profiles of protease inhibitor-resistant hepatitis C virus NS3 protease mutants in the HCV genotype 1b replicon system.Antimicrob Agents Chemother. 2008; 52: 1101-1110Crossref PubMed Scopus (93) Google Scholar]. These patterns will need to be confirmed with longer term follow-up. Finally, Forestier et al. observed an inferior virologic response in NRs versus TNs, despite equal to higher drug exposure in NRs. This phenomenon suggests an important role for the innate immune response, which is likely to be impaired in most peginterferon and ribavirin non-responders, and may still be critical even in the setting of monotherapy with DAAs. NS3/4A inhibitors may unmask an innate immune response ordinarily suppressed by the NS3/4A protein [[6]Gale M. Foy E. Evasion of intracellular host defence by hepatitis C virus.Nature. 2005; 436PubMed Google Scholar]. This liberated immune response may vary significantly from patient to patient, and may or may not correlate with the IL28B genotype [[16]Ge D, Fellay J, Thompson AJ, Simon JS, Shianna KV, Urban TJ, Heinzen EL, Qiu P, Bertelsen AH, Muir AJ, Sulkowski M, McHutchison JG, Goldstein DB. Genetic variation in IL28B predicts hepatitis C treatment-induced viral clearance. Nature. 2009 Sep 17;461(7262):399–401. Epub 2009 Aug 16.Google Scholar]. While it will be important to track the results of ongoing phase 2b studies of new generation PIs combined with standards of care, the greatest focus will and should be placed on efforts to combine these agents with other DAA classes, particularly nucleoside HCV NS5b polymerase inhibitors, a DAA class that offers an exceptionally high barrier to resistance [17Gane E. Roberts S. Stedman C. Angus P. Ritchie B. Elston R. et al.Combination therapy with a nucleoside polymerase (RG7128) and protease (RG7227/ITMN-191) inhibitor in HCV: safety, pharmacokinetics and virologic results from INFORM-1.Hepatology. 2009; 50: 394A-395AGoogle Scholar, 18Gane E. Roberts S. Stedman C. Angus P. Elston R. et al.Final in-man demonstration of potent antiviral activity with a nucleoside polymerase (R7128) and protease (R7227/ITMN-191) inhibitor combination in HCV: safety, pharmacokinetics, and virologic results from INFORM-1.J Hepatol. 2009; 50: S380Abstract Full Text PDF Google Scholar]. Also in this issue, Manns et al. present a phase 1b multiple ascending dose study of a second generation NS3/4A inhibitor, BI201335, in 34 treatment naïve patients and 19 treatment experienced patients with genotype 1 HCV [[11]Manns M. Bourliere M. Benhamou Y. Pol S. Bonacini M. Trepo C. et al.Potency, safety and pharmacokinetics of the NS3/4A protease inhibitor BI201335 in patients with chronic HCV genotype-1 infection.J Hepatol. 2011; 54: 1114-1122Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar]. Patients were middle aged, non-obese Caucasians and Asians. One major advantage of BI201335 is its once daily dosing schedule. In contrast to the study of Forestier, which was confined to study of monotherapy, Manns et al. evaluated monotherapy followed by combination therapy (BI201335/pegylated interferon/ribavirin) in treatment of naïve patients with >=1 log HCV decline after 14 days of DAA. Treatment experienced patients only received combined therapy, with no monotherapy phase. Ninety-six percent of patients receiving BI120335 monotherapy achieved a >=2 log HCV RNA decline at some point, though, as with danoprevir, monotherapy was associated with the frequent selection of resistance mutations, including R155K and D168V/E. In contrast to danoprevir, however, B1201335 resistance mutations stratified almost completely by HCV subtype (1a developed R155, 1b developed D168V/E), again consistent with a lower barrier to selection of R155K in 1a infection [[14]Susser S. Welsch C. Wang Y. Zettler M. Domingues F. Karey U. et al.Characterization of resistance to the protease inhibitor Boceprevir in hepatitis C virus-infected patients.Hepatology. 2009; 50: 1709-1718Crossref PubMed Scopus (275) Google Scholar]. Side effects were mild, although a rash was reported in 4/34 patients on DAA with SOC, and the authors cite a slightly increased frequency of rash in ongoing phase II trials. In addition, indirect hyperbilirubinemia was detected in patients on high dose mono- and combination therapy; the mechanism underlying this phenomenon is currently under investigation [[11]Manns M. Bourliere M. Benhamou Y. Pol S. Bonacini M. Trepo C. et al.Potency, safety and pharmacokinetics of the NS3/4A protease inhibitor BI201335 in patients with chronic HCV genotype-1 infection.J Hepatol. 2011; 54: 1114-1122Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar]. Overall, these two DAA studies represent an important step forward toward the eradication of HCV [[19]Pawlotsky JM. HCV: from discovery to eradication in 40 years? Clin Microbiol Infect. 2010 Nov 18. [Epub ahead of print].Google Scholar]. Their major contributions include potent antiviral effects with a lower pill burden and manageable side effect profiles. The major drawback of these drugs, as expected, is selection of resistant variants during monotherapy. While monotherapy studies are important for the evaluation of safety, it is clear that monotherapy is not a viable long term strategy, and that DAAs will for now need to be added onto a backbone of peginterferon and ribavirin. For the particular case of prior null responders, added caution will be required, since retreatment with a single DAA added to SOC may amount to the functional equivalent of DAA monotherapy. Indeed, phase 2 and 3 data in null responder populations have shown high rates of residual viremia enriched for NS3/4A mutations. The success rates of about 30% SVR for prior null responders treated with PEG/RBV and telaprevir suggests that only those null responders with more advanced histologic disease should be offered the combination of PEG/RBV/PI therapy [[20]McHutchison J.G. Manns M.P. Muir A.J. PROVE3 Study Team et al.Telaprevir for previously treated chronic HCV infection.N Engl J Med. 2010; 362: 1292-1303Crossref PubMed Scopus (655) Google Scholar]. For prior null responders, referral to a clinical trial including at least two DAA agents with PEG and RBV may need to be considered. While sequencing studies have suggested the gradual regression of most PI-resistant variants to wildtype virus over time [[14]Susser S. Welsch C. Wang Y. Zettler M. Domingues F. Karey U. et al.Characterization of resistance to the protease inhibitor Boceprevir in hepatitis C virus-infected patients.Hepatology. 2009; 50: 1709-1718Crossref PubMed Scopus (275) Google Scholar], the long term implications of these findings is unclear. For instance, it is unknown how quickly PI-resistant virus will be selected with re-exposure to PI-containing regimens. The clonal sequencing of viral populations using sensitive measures such as ultradeep pyrosequencing will help to clarify the correlates of rapid re-selection of resistance. The additional finding that some PI-resistant variants may retain fitness comparable to wildtype virus [[15]He Y. King M. Kempf D. Lu L. Lim H. Krishnan P. et al.Relative replication capacity and selective advantage profiles of protease inhibitor-resistant hepatitis C virus NS3 protease mutants in the HCV genotype 1b replicon system.Antimicrob Agents Chemother. 2008; 52: 1101-1110Crossref PubMed Scopus (93) Google Scholar] bolsters the argument that monotherapy, even for a short time, could limit future treatment options for patients enrolled in clinical trials. In summary, the two studies that have been described provide further welcome news that HCV protease inhibitors with improved side effect profiles and decreased dose frequency are on the horizon, just behind the first generation of PIs. We can anticipate that these agents will eventually supplant first generation PIs not only in combination with PEG and RBV, but, more importantly, as cardinal components of future IFN-sparing DAA cocktails. These considerations place a premium on both adherence and tolerability. In 2011 and beyond, HCV providers must now rise to the challenge of quickly assimilating and carefully applying DAA data as it unfolds. Great care will be necessary to counsel against unnecessary therapy in persons who have a low likelihood of responding to PEG/RBV and a PI, including those persons with prior null response to PEG/RBV, and limited hepatic fibrosis. We will therefore likely require a substantial re-education campaign for providers in the coming years. The future appears bright, provided we proceed with an appropriate measure of circumspection. The authors declared a relationship with the manufacturers of the drugs involved. Tibotec-Advisory Board 2009. Roche-Clinical Trial. Potency, safety, and pharmacokinetics of the NS3/4A protease inhibitor BI201335 in patients with chronic HCV genotype-1 infectionJournal of HepatologyVol. 54Issue 6PreviewBI201335 is a highly specific and potent HCV protease inhibitor. This multiple rising dose trial evaluated antiviral activity and safety in chronic HCV genotype-1 patients. Full-Text PDF Treatment of chronic hepatitis C patients with the NS3/4A protease inhibitor danoprevir (ITMN-191/RG7227) leads to robust reductions in viral RNA: A phase 1b multiple ascending dose studyJournal of HepatologyVol. 54Issue 6PreviewDanoprevir is a potent and selective inhibitor of the hepatitis C virus (HCV) NS3/4A serine protease. The present study assessed the safety, pharmacokinetics, and antiviral activity of danoprevir in a randomized, placebo-controlled, 14-day multiple ascending dose study in patients with chronic HCV genotype 1 infection. Full-Text PDF Corrigendum to ‘‘New protease inhibitors for HCV – Help is on the way’’ [J Hepatol 2011;54:1087–1089]Journal of HepatologyVol. 55Issue 4PreviewIn the above named article, Table 1 contained errors. The table is correctly represented below. Full-Text PDF