SCH 503034, a mechanism-based inhibitor of hepatitis C virus NS3 protease, suppresses polyprotein maturation and enhances the antiviral activity of alpha interferon in replicon cells

In vitro assessment of drug-drug interaction potential of boceprevir associated with drug metabolizing enzymes and transporters

The inhibitory effect of boceprevir (BOC), an inhibitor of hepatitis C virus nonstructural protein 3 protease was evaluated in vitro against a panel of drug-metabolizing enzymes and transporters. BOC, a known substrate for cytochrome P450 (P450) CYP3A and aldo-ketoreductases, was a reversible time-dependent inhibitor (k(inact) = 0.12 minute(-1), K(I) = 6.1 µM) of CYP3A4/5 but not an inhibitor of other major P450s, nor of UDP-glucuronosyltransferases 1A1 and 2B7. BOC showed weak to no inhibition of breast cancer resistance protein (BCRP), P-glycoprotein (Pgp), or multidrug resistance protein 2. It was a moderate inhibitor of organic anion transporting polypeptide (OATP) 1B1 and 1B3, with an IC(50) of 18 and 4.9 µM, respectively. In human hepatocytes, BOC inhibited CYP3A-mediated metabolism of midazolam, OATP1B-mediated hepatic uptake of pitavastatin, and both the uptake and metabolism of atorvastatin. The inhibitory potency of BOC was lower than known inhibitors of CYP3A (ketoconazole), OATP1B (rifampin), or both (telaprevir). BOC was a substrate for Pgp and BCRP but not for OATP1B1, OATP1B3, OATP2B1, organic cation transporter, or sodium/taurocholate cotransporting peptide. Overall, our data suggest that BOC has the potential to cause pharmacokinetic interactions via inhibition of CYP3A and CYP3A/OATP1B interplay, with the interaction magnitude lower than those observed with known potent inhibitors. Conversely, pharmacokinetic interactions of BOC, either as a perpetrator or victim, via other major P450s and transporters tested are less likely to be of clinical significance. The results from clinical drug-drug interaction studies conducted thus far are generally supportive of these conclusions.

Hepatitis C viral kinetics: the past, present, and future

Mathematical modeling of hepatitis C viral kinetics has been an important tool in understanding hepatitis C virus (HCV) infection dynamics and in estimating crucial in vivo parameters characterizing the effectiveness of HCV therapy. Because of the introduction of direct-acting antiviral agents, there is a need to extend previous models so as to understand, characterize, and compare various new HCV treatment regimens. Here we review recent modeling efforts in this direction.

Molecular mechanism by which a potent hepatitis C virus NS3-NS4A protease inhibitor overcomes emergence of resistance

Although optimizing the resistance profile of an inhibitor can be challenging, it is potentially important for improving the long term effectiveness of antiviral therapy. This work describes our rational approach toward the identification of a macrocyclic acylsulfonamide that is a potent inhibitor of the NS3-NS4A proteases of all hepatitis C virus genotypes and of a panel of genotype 1-resistant variants. The enhanced potency of this compound versus variants D168V and R155K facilitated x-ray determination of the inhibitor-variant complexes. In turn, these structural studies revealed a complex molecular basis of resistance and rationalized how such compounds are able to circumvent these mechanisms.

Single-dose pharmacokinetics of boceprevir in subjects with impaired hepatic or renal function

BACKGROUND AND OBJECTIVE

Boceprevir is a novel inhibitor of the hepatitis C virus NS3 protease and was recently approved for the treatment of patients with chronic hepatitis C infection. The objective of this study was to evaluate the impact of impaired hepatic or renal function on boceprevir pharmacokinetics and safety/tolerability.

METHODS

We conducted two open-label, single-dose, parallel-group studies comparing the safety and pharmacokinetics of boceprevir in patients with varying degrees of hepatic impairment compared with healthy controls in one study and patients with end-stage renal disease (ESRD) on haemodialysis with healthy controls in the other. Patients with hepatic impairment (mild [n = 6], moderate [n = 6], severe [n = 6] and healthy controls [n = 6]) received a single dose of boceprevir (400 mg) on day 1, and whole blood was collected at selected timepoints up to 72 hours postdose to measure plasma drug concentrations. Patients with ESRD and healthy subjects received a single dose of boceprevir 800 mg orally on days 1 and 4, with samples for pharmacokinetic analyses collected at selected timepoints up to 48 hours postdose on both days. In addition, 4 hours after dosing on day 4, patients with ESRD underwent haemodialysis with arterial and venous blood samples collected up to 8 hours postdose.

RESULTS

In the hepatic impairment study, there was a trend toward increased mean maximum (peak) plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC) of boceprevir with increasing severity of liver impairment. Point estimates for the geometric mean ratio for C(max) ranged from 100% in patients with mild hepatic impairment to 161% in patients with severe hepatic impairment, with the geometric mean ratio for AUC ranging from 91% in patients with mild hepatic impairment to 149% for patients with severe hepatic impairment, relative to healthy subjects. The mean elimination half-life (t(1/2;)) and median time to C(max) (t(max)) values of boceprevir were similar in healthy subjects and patients with hepatic impairment. In the renal impairment study, mean boceprevir C(max) and AUC values were comparable in patients with ESRD and in healthy subjects, with point estimates for the geometric mean ratio of 81% and 90%, respectively, compared with healthy subjects. Mean t(1/2;), median t(max) and mean apparent oral total clearance (CL/F) values were similar in healthy subjects and patients with ESRD. Boceprevir exposure was also similar in patients with ESRD on day 1 (no dialysis) and day 4 (dialysis beginning 4 hours postdose), with point estimates for the geometric mean ratio of C(max) and AUC to the last measurable sampling time (AUC(last)) on day 1 compared with day 4 of 88% and 98%, respectively. Treatment-emergent adverse events were reported in one patient with severe hepatic impairment (mild vomiting) and two patients with ESRD (moderate ventricular extrasystoles, flatulence and catheter thrombosis).

CONCLUSION

In the present studies, the pharmacokinetic properties of boceprevir were not altered to a clinically meaningful extent in patients with impaired liver or renal function. These data indicate that boceprevir dose adjustment is not warranted in patients with impaired hepatic function or ESRD, including those receiving dialysis. Boceprevir is not removed by haemodialysis.

Single-dose pharmacokinetics of boceprevir in subjects with impaired hepatic or renal function

BACKGROUND AND OBJECTIVE

Boceprevir is a novel inhibitor of the hepatitis C virus NS3 protease and was recently approved for the treatment of patients with chronic hepatitis C infection. The objective of this study was to evaluate the impact of impaired hepatic or renal function on boceprevir pharmacokinetics and safety/tolerability.

METHODS

We conducted two open-label, single-dose, parallel-group studies comparing the safety and pharmacokinetics of boceprevir in patients with varying degrees of hepatic impairment compared with healthy controls in one study and patients with end-stage renal disease (ESRD) on haemodialysis with healthy controls in the other. Patients with hepatic impairment (mild [n = 6], moderate [n = 6], severe [n = 6] and healthy controls [n = 6]) received a single dose of boceprevir (400 mg) on day 1, and whole blood was collected at selected timepoints up to 72 hours postdose to measure plasma drug concentrations. Patients with ESRD and healthy subjects received a single dose of boceprevir 800 mg orally on days 1 and 4, with samples for pharmacokinetic analyses collected at selected timepoints up to 48 hours postdose on both days. In addition, 4 hours after dosing on day 4, patients with ESRD underwent haemodialysis with arterial and venous blood samples collected up to 8 hours postdose.

RESULTS

In the hepatic impairment study, there was a trend toward increased mean maximum (peak) plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC) of boceprevir with increasing severity of liver impairment. Point estimates for the geometric mean ratio for C(max) ranged from 100% in patients with mild hepatic impairment to 161% in patients with severe hepatic impairment, with the geometric mean ratio for AUC ranging from 91% in patients with mild hepatic impairment to 149% for patients with severe hepatic impairment, relative to healthy subjects. The mean elimination half-life (t(1/2;)) and median time to C(max) (t(max)) values of boceprevir were similar in healthy subjects and patients with hepatic impairment. In the renal impairment study, mean boceprevir C(max) and AUC values were comparable in patients with ESRD and in healthy subjects, with point estimates for the geometric mean ratio of 81% and 90%, respectively, compared with healthy subjects. Mean t(1/2;), median t(max) and mean apparent oral total clearance (CL/F) values were similar in healthy subjects and patients with ESRD. Boceprevir exposure was also similar in patients with ESRD on day 1 (no dialysis) and day 4 (dialysis beginning 4 hours postdose), with point estimates for the geometric mean ratio of C(max) and AUC to the last measurable sampling time (AUC(last)) on day 1 compared with day 4 of 88% and 98%, respectively. Treatment-emergent adverse events were reported in one patient with severe hepatic impairment (mild vomiting) and two patients with ESRD (moderate ventricular extrasystoles, flatulence and catheter thrombosis).

CONCLUSION

In the present studies, the pharmacokinetic properties of boceprevir were not altered to a clinically meaningful extent in patients with impaired liver or renal function. These data indicate that boceprevir dose adjustment is not warranted in patients with impaired hepatic function or ESRD, including those receiving dialysis. Boceprevir is not removed by haemodialysis.

Telaprevir/boceprevir era: From bench to bed and back

Hepatitis C virus (HCV) infects approximately 200 million people worldwide. Interferon-based therapies have dominated over the past two decades. However, the overall response rates remain suboptimal. Thanks to the tremendous effort from both academia and industry, two serine protease inhibitors telaprevir and boceprevir for treating chronic hepatitis C have finally reached the clinic. Although these compounds are only approved for combination use with interferon and ribavirin in genotype 1 HCV infected chronic patients, the management of HCV patients however is now evolving incredibly. Here, we overviewed a series of landmark studies, regarding the clinical development of telaprevir and boceprevir. We discussed the mechanism-of-action of telaprevir/boceprevir and their potential application in HCV-positive liver transplantation patients. We further emphasized some emerging concerns with perspective of further development in this field.

Inhibition of both protease and helicase activities of hepatitis C virus NS3 by an ethyl acetate extract of marine sponge Amphimedon sp

Combination therapy with ribavirin, interferon, and viral protease inhibitors could be expected to elicit a high level of sustained virologic response in patients infected with hepatitis C virus (HCV). However, several severe side effects of this combination therapy have been encountered in clinical trials. In order to develop more effective and safer anti-HCV compounds, we employed the replicon systems derived from several strains of HCV to screen 84 extracts from 54 organisms that were gathered from the sea surrounding Okinawa Prefecture, Japan. The ethyl acetate-soluble extract that was prepared from marine sponge Amphimedon sp. showed the highest inhibitory effect on viral replication, with EC₅₀ values of 1.5 and 24.9 µg/ml in sub-genomic replicon cell lines derived from genotypes 1b and 2a, respectively. But the extract had no effect on interferon-inducing signaling or cytotoxicity. Treatment with the extract inhibited virus production by 30% relative to the control in the JFH1-Huh7 cell culture system. The in vitro enzymological assays revealed that treatment with the extract suppressed both helicase and protease activities of NS3 with IC₅₀ values of 18.9 and 10.9 µg/ml, respectively. Treatment with the extract of Amphimedon sp. inhibited RNA-binding ability but not ATPase activity. These results suggest that the novel compound(s) included in Amphimedon sp. can target the protease and helicase activities of HCV NS3.

Pharmacokinetics of new oral hepatitis C antiviral drugs

INTRODUCTION

Approximately 175 million people worldwide are chronically infected with the hepatitis C virus (HCV), representing 3% of the total world population. Until recently, the only available therapeutic option for these patients was the combination of pegylated IFN-α plus ribavirin that overall resulted in HCV eradication in less than a half of cases. The development of new therapies with greater efficacy has been eagerly awaited but new challenges have emerged, with drug interactions being among the most challenging.

AREAS COVERED

This review updates the main pharmacokinetic and pharmacodynamic characteristics of the most promising new oral direct-acting antivirals (DAA) for hepatitis C. Given that a large proportion of chronic hepatitis C patients receive other medications, drug interactions are further discussed.

EXPERT OPINION

The recent approval of the first HCV genotype 1 protease inhibitors is a landmark step in the fight against the HCV pandemic. The benefit of higher rates of response along with shorter duration of treatment is counterbalanced by significant drug interactions and unprecedented complexities in the use of these drugs and management of their side effects. The knowledge of key pharmacologic parameters of distinct DAA is important for care providers in charge of chronic hepatitis C patients as it will avoid the danger of unexpected drug interactions. This concern must be particularly emphasized in special group populations, such as in HIV-HCV coinfected individuals and transplant patients, in whom interactions between DAA and antiretrovirals or immunosuppressants, respectively, are frequent.

Boceprevir: a novel NS3/4 protease inhibitor for the treatment of hepatitis C

Hepatitis C virus (HCV) infection affects over 170 million people worldwide and is the most common blood-borne infection in the United States. Standard treatment with peginterferon alfa-ribavirin results in low sustained virologic response (SVR) rates in many patients, especially those who are African-American, are coinfected with human immunodeficiency virus (HIV), or have liver cirrhosis. Because of suboptimal SVR rates, new direct-acting antiviral agents that target HCV viral replication steps are in development. Boceprevir is one of the novel NS3/4A protease inhibitors that was recently approved by the U.S. Food and Drug Administration. We evaluated the literature regarding boceprevir by performing a MEDLINE search (January 1996-July 2011) to identify relevant clinical trials. Abstracts and poster and oral presentations from hepatology and HIV conferences were also reviewed. Potent anti-HCV activity was seen in clinical trials with boceprevir when it was studied in HCV genotype 1-infected patients who were naïve to or had experience with HCV therapy. Data with boceprevir in HIV-HCV-coinfected patients are currently lacking; however, initial data on drug-drug interactions between boceprevir and antiretrovirals have become available. Resistance to boceprevir has been evaluated in trials as well, although more data are needed in this area. The most common adverse events with boceprevir included anemia and dysgeusia. Based on available data, boceprevir is one of the promising novel direct-acting antiviral agents that will likely reshape the treatment of patients with HCV infection.

Boceprevir and personalized medicine in hepatitis C virus infection

Boceprevir was the first agent, along with telaprevir, of a novel class of direct-acting antivirals that entered clinical practice for the treatment of chronic hepatitis C. Boceprevir is an antiprotease that directly blocks hepatitis C virus (HCV) replication. Two studies in patients with HCV genotype 1 infection have shown that addition of boceprevir to the standard of care, ie, pegylated interferon-alfa (PEG-IFN-α) and ribavirin, markedly increased the rate of sustained virological response. A sustained virological response was obtained in about 70% of patients who had never been treated, as well as in 69%-75% and 40% of previous relapsers and nonresponders to PEG-IFN-α-ribavirin, respectively. Side effects were observed in almost all treated patients. Anemia, the most frequent adverse event related to administration of boceprevir, occurred in about 50% of patients. The decision to add boceprevir to the standard of care is made on an individual basis, and takes into account the prognosis of the liver disease, the efficacy of therapy, as it could be at best predicted, and the side effects that may arise, taking into account the comorbidities of the patient. Ultimately, the treatment must be accepted by the patient, who should fully understand the benefits and risks. Boceprevir trials were designed with the concept of individualized and response-guided therapy which establishes treatment decisions on how rapidly patients respond to treatment. Individualized therapy for chronic hepatitis C is based on patient and viral characteristics to make the best choice about whether a person will benefit from therapy and to evaluate on-treatment predictors of response to shorten therapy in patients with a rapid response as well as in patients who did not respond sufficiently to expect HCV eradication. This review focuses on the main results obtained so far, their impact on the treatment of patients with chronic hepatitis C, and potential therapeutic perspectives.

MK-5172, a selective inhibitor of hepatitis C virus NS3/4a protease with broad activity across genotypes and resistant variants

HCV NS3/4a protease inhibitors are proven therapeutic agents against chronic hepatitis C virus infection, with boceprevir and telaprevir having recently received regulatory approval as add-on therapy to pegylated interferon/ribavirin for patients harboring genotype 1 infections. Overcoming antiviral resistance, broad genotype coverage, and a convenient dosing regimen are important attributes for future agents to be used in combinations without interferon. In this communication, we report the preclinical profile of MK-5172, a novel P2-P4 quinoxaline macrocyclic NS3/4a protease inhibitor currently in clinical development. The compound demonstrates subnanomolar activity against a broad enzyme panel encompassing major hepatitis C virus (HCV) genotypes as well as variants resistant to earlier protease inhibitors. In replicon selections, MK-5172 exerted high selective pressure, which yielded few resistant colonies. In both rat and dog, MK-5172 demonstrates good plasma and liver exposures, with 24-h liver levels suggestive of once-daily dosing. When administered to HCV-infected chimpanzees harboring chronic gt1a or gt1b infections, MK-5172 suppressed viral load between 4 to 5 logs at a dose of 1 mg/kg of body weight twice daily (b.i.d.) for 7 days. Based on its preclinical profile, MK-5172 is anticipated to be broadly active against multiple HCV genotypes and clinically important resistance variants and highly suited for incorporation into newer all-oral regimens.

The molecular basis of drug resistance against hepatitis C virus NS3/4A protease inhibitors

Hepatitis C virus (HCV) infects over 170 million people worldwide and is the leading cause of chronic liver diseases, including cirrhosis, liver failure, and liver cancer. Available antiviral therapies cause severe side effects and are effective only for a subset of patients, though treatment outcomes have recently been improved by the combination therapy now including boceprevir and telaprevir, which inhibit the viral NS3/4A protease. Despite extensive efforts to develop more potent next-generation protease inhibitors, however, the long-term efficacy of this drug class is challenged by the rapid emergence of resistance. Single-site mutations at protease residues R155, A156 and D168 confer resistance to nearly all inhibitors in clinical development. Thus, developing the next-generation of drugs that retain activity against a broader spectrum of resistant viral variants requires a comprehensive understanding of the molecular basis of drug resistance. In this study, 16 high-resolution crystal structures of four representative protease inhibitors – telaprevir, danoprevir, vaniprevir and MK-5172 – in complex with the wild-type protease and three major drug-resistant variants R155K, A156T and D168A, reveal unique molecular underpinnings of resistance to each drug. The drugs exhibit differential susceptibilities to these protease variants in both enzymatic and antiviral assays. Telaprevir, danoprevir and vaniprevir interact directly with sites that confer resistance upon mutation, while MK-5172 interacts in a unique conformation with the catalytic triad. This novel mode of MK-5172 binding explains its retained potency against two multi-drug-resistant variants, R155K and D168A. These findings define the molecular basis of HCV N3/4A protease inhibitor resistance and provide potential strategies for designing robust therapies against this rapidly evolving virus.

Hepatitis C virus (HCV) infects over 170 million people worldwide and is the leading cause of chronic liver diseases, including cirrhosis, liver failure, and liver cancer. New classes of directly-acting antiviral agents that target various HCV enzymes are being developed. Two such drugs that target the essential HCV NS3/4A protease are approved by the FDA and several others are at various stages of clinical development. These drugs, when used in combination with pegylated interferon and ribavirin, significantly improve treatment outcomes. However HCV evolves very quickly and drug resistance develops against directly-acting antiviral agents. Thus, despite the therapeutic success of NS3/4A protease inhibitors, their long-term effectiveness is challenged by drug resistance. Our study explains in atomic detail how and why drug resistance occurs for four chemically representative protease inhibitors –telaprevir, danoprevir, vaniprevir and MK-5172. Potentially with this knowledge, new drugs could be developed that are less susceptible to drug resistance. More generally, understanding the underlying mechanisms by which drug resistance occurs can be incorporated in drug development to many quickly evolving diseases.

Probing of exosites leads to novel inhibitor scaffolds of HCV NS3/4A proteinase

BACKGROUND

Hepatitis C is a treatment-resistant disease affecting millions of people worldwide. The hepatitis C virus (HCV) genome is a single-stranded RNA molecule. After infection of the host cell, viral RNA is translated into a polyprotein that is cleaved by host and viral proteinases into functional, structural and non-structural, viral proteins. Cleavage of the polyprotein involves the viral NS3/4A proteinase, a proven drug target. HCV mutates as it replicates and, as a result, multiple emerging quasispecies become rapidly resistant to anti-virals, including NS3/4A inhibitors.

METHODOLOGY/PRINCIPAL FINDINGS

To circumvent drug resistance and complement the existing anti-virals, NS3/4A inhibitors, which are additional and distinct from the FDA-approved telaprevir and boceprevir α-ketoamide inhibitors, are required. To test potential new avenues for inhibitor development, we have probed several distinct exosites of NS3/4A which are either outside of or partially overlapping with the active site groove of the proteinase. For this purpose, we employed virtual ligand screening using the 275,000 compound library of the Developmental Therapeutics Program (NCI/NIH) and the X-ray crystal structure of NS3/4A as a ligand source and a target, respectively. As a result, we identified several novel, previously uncharacterized, nanomolar range inhibitory scaffolds, which suppressed of the NS3/4A activity in vitro and replication of a sub-genomic HCV RNA replicon with a luciferase reporter in human hepatocarcinoma cells. The binding sites of these novel inhibitors do not significantly overlap with those of α-ketoamides. As a result, the most common resistant mutations, including V36M, R155K, A156T, D168A and V170A, did not considerably diminish the inhibitory potency of certain novel inhibitor scaffolds we identified.

CONCLUSIONS/SIGNIFICANCE

Overall, the further optimization of both the in silico strategy and software platform we developed and lead compounds we identified may lead to advances in novel anti-virals.

Boceprevir: an oral protease inhibitor for the treatment of chronic HCV infection

Chronic hepatitis C (CHC) virus infection affects more than 170 million people globally. The aim of treatment of CHC is to affect sustained elimination of the virus (a sustained virological response [SVR]). The success and duration of therapy with interferon is dependent on HCV genotype. The current standard of care comprises combined treatment with pegylated interferon and ribavirin. Rates of SVR in patients with genotype 1 infection, the least responsive group, are less than 50%. Boceprevir is a ketoamide protease inhibitor that binds reversibly to the HCV nonstructural NS3 protease active site inhibiting intracellular viral replication. Phase III clinical studies have demonstrated that, in combination with the current standard of care, boceprevir significantly increases the SVR rate in both treatment-naive and previously treated patients with genotype 1 CHC. Both the US FDA and EMA have approved boceprevir for the treatment of genotype 1 CHC: the first directly-acting antiviral drug to be licensed for this indication. This article will review the pharmacology and pharmacodynamics of boceprevir, the efficacy and safety of the drug, and explore possible future developments in the management of CHC.

C-6 aryl substituted 4-quinolone-3-carboxylic acids as inhibitors of hepatitis C virus

Quinolone-3-carboxylic acid represents a highly privileged chemotype in medicinal chemistry and has been extensively explored as antibiotics and antivirals targeting human immunodeficiency virus (HIV) integrase (IN). Herein we describe the synthesis and anti-hepatitis C virus (HCV) profile of a series of C-6 aryl substituted 4-quinlone-3-carboxylic acid analogues. Significant inhibition was observed with a few analogues at low micromolar range against HCV replicon in cell culture and a reduction in replicon RNA was confirmed through an RT-qPCR assay. Interestingly, evaluation of analogues as inhibitors of NS5B in a biochemical assay yielded only modest inhibitory activities, suggesting that a different mechanism of action could operate in cell culture.

Boceprevir: a novel nonstructural 3 (NS3) protease inhibitor for the treatment of chronic hepatitis C infection

Chronic hepatitis C infection is a leading cause of morbidity and mortality worldwide, with hepatitis C related cirrhosis being the most common indication for transplant and a major cause for the increase in hepatocellular carcinoma worldwide. Treatment for hepatitis C has consisted of nonspecific immunomodulatory therapies that stimulate the immune system and inhibit hepatitis C replication. Pegylated (peg-)interferon and ribavirin have been the standard of care with an overall sustained response rate of 40-50% in patients with genotype 1 infection, and 80% in genotype 2 or 3. Recently, direct-acting antiviral agents, including boceprevir, have demonstrated improved sustained response rates in patients with genotype 1 infection when given in combination with interferon and ribavirin. Boceprevir is a structurally novel hepatitis C virus (HCV) nonstructural 3 (NS3) protease inhibitor that has demonstrated robust antiviral activity in HCV replicons. Clinically, in phase II and III trials, boceprevir 800 mg three times daily with peginterferon and ribavirin has led to improved sustained response rates in genotype 1 infection treatment-naive patients, relapsers, partial responders, and null responders. Phase II data have demonstrated that ribavirin is essential for optimal boceprevir response. Moreover, phase II data have suggested that a 4-week peginterferon or ribavirin lead-in strategy may reduce relapse rates and provide crucial on-treatment data for treatment response with boceprevir addition. Side effects of boceprevir when added to peginterferon and ribavirin are similar to peginterferon and ribavirin, though higher rates of anemia have been noted, with an incremental increase in erythropoietin use. The addition of boceprevir represents a major advance in patients with genotype 1 infection who are treatment naïve.

New developments in small molecular compounds for anti-hepatitis C virus (HCV) therapy

Infection with hepatitis C virus (HCV) affects approximately 170 million people worldwide. However, no vaccine or immunoglobulin is currently available for the prevention of HCV infection. The standard of care (SOC) involving pegylated interferon-α (PEG-IFN α) plus ribavirin (RBV) for 48 weeks results in a sustained virologic response in less than 50% of patients with chronic hepatitis C genotype 1, the most prevalent type of HCV in North America and Europe. Recently, reliable in vitro culture systems have been developed for accelerating antiviral therapy research, and many new specifically targeted antiviral therapies for hepatitis C (STAT-C) and treatment strategies are being evaluated in clinical trials. These new antiviral agents are expected to improve present treatment significantly and may potentially shorten treatment duration. The aim of this review is to summarize the current developments in new anti-HCV drugs.

Discovery of MK-5172, a Macrocyclic Hepatitis C Virus NS3/4a Protease Inhibitor

A new class of HCV NS3/4a protease inhibitors containing a P2 to P4 macrocyclic constraint was designed using a molecular modeling-derived strategy. Building on the profile of previous clinical compounds and exploring the P2 and linker regions of the series allowed for optimization of broad genotype and mutant enzyme potency, cellular activity, and rat liver exposure following oral dosing. These studies led to the identification of clinical candidate 15 (MK-5172), which is active against genotype 1-3 NS3/4a and clinically relevant mutant enzymes and has good plasma exposure and excellent liver exposure in multiple species.

Genotype and subtype profiling of PSI-7977 as a nucleotide inhibitor of hepatitis C virus

PSI-7977, a prodrug of 2'-F-2'-C-methyluridine monophosphate, is the purified diastereoisomer of PSI-7851 and is currently being investigated in phase 3 clinical trials for the treatment of hepatitis C. In this study, we profiled the activity of PSI-7977 and its ability to select for resistance using a number of different replicon cells. Results showed that PSI-7977 was active against genotype (GT) 1a, 1b, and 2a (strain JFH-1) replicons and chimeric replicons containing GT 2a (strain J6), 2b, and 3a NS5B polymerase. Cross-resistance studies using GT 1b replicons confirmed that the S282T change conferred resistance to PSI-7977. Subsequently, we evaluated the ability of PSI-7977 to select for resistance using GT 1a, 1b, and 2a (JFH-1) replicon cells. S282T was the common mutation selected among all three genotypes, but while it conferred resistance to PSI-7977 in GT 1a and 1b, JFH-1 GT 2a S282T showed only a very modest shift in 50% effective concentration (EC(50)) for PSI-7977. Sequence analysis of the JFH-1 NS5B region indicated that additional amino acid changes were selected both prior to and after the emergence of S282T. These include T179A, M289L, I293L, M434T, and H479P. Residues 179, 289, and 293 are located within the finger and palm domains, while 434 and 479 are located on the surface of the thumb domain. Data from the JFH-1 replicon variants showed that amino acid changes within the finger and palm domains together with S282T were required to confer resistance to PSI-7977, while the mutations on the thumb domain serve to enhance the replication capacity of the S282T replicons.

Current status and future directions in the management of chronic hepatitis C

Hepatitis C virus (HCV) is endemic worldwide, and it causes cirrhosis and other complications that often lead to death; nevertheless, our knowledge of the disease and its mechanisms is limited. HCV is most common in underdeveloped nations, including many in Africa and Asia. The virus is usually transmitted by parenteral routes, but sexual, perinatal, and other types of transfer have been known to occur. Approximately 80% of individuals who contract hepatitis C develop a chronic infection, and very few are able to spontaneously clear the virus. Because hepatitis C is asymptomatic in the majority of patients, the presence of HCV RNA in the serum is the best diagnostic tool. Although serious complications from hepatitis C may not occur for 20 years, 1/5 of chronic patients eventually develop life - threatening cirrhosis. More research is needed on the different therapy options for the disease, and many factors, most importantly the genotype of the virus, must be taken into account before beginning any treatment. As there is no vaccine against HCV at present, the most effective and recommended therapy is pegylated-interferon-α-2a plus ribavirin. While interferon is marginally effective as a monotherapy, both adding the moiety and combining it with ribavirin have been shown to dramatically increase its potency. While there are numerous alternative and complementary medicines available for patients with hepatitis C, their efficacy is questionable. Currently, research is being done to investigate other possible treatments for hepatitis C, and progress is being made to develop a vaccine against HCV, despite the many challenges the virus presents. Until such a vaccination is available, prevention and control methods are important in containing and impeding the spread of the virus and mitigating its deleterious effects on the health of people and communities worldwide.

Peptidomimetic escape mechanisms arise via genetic diversity in the ligand-binding site of the hepatitis C virus NS3/4A serine protease

BACKGROUND & AIMS

It is a challenge to develop direct-acting antiviral agents that target the nonstructural protein 3/4A protease of hepatitis C virus because resistant variants develop. Ketoamide compounds, designed to mimic the natural protease substrate, have been developed as inhibitors. However, clinical trials have revealed rapid selection of resistant mutants, most of which are considered to be pre-existing variants.

METHODS

We identified residues near the ketoamide-binding site in x-ray structures of the genotype 1a protease, co-crystallized with boceprevir or a telaprevir-like ligand, and then identified variants at these positions in 219 genotype-1 sequences from a public database. We used side-chain modeling to assess the potential effects of these variants on the interaction between ketoamide and the protease, and compared these results with the phenotypic effects on ketoamide resistance, RNA replication capacity, and infectious virus yields in a cell culture model of infection.

RESULTS

Thirteen natural binding-site variants with potential for ketoamide resistance were identified at 10 residues in the protease, near the ketoamide binding site. Rotamer analysis of amino acid side-chain conformations indicated that 2 variants (R155K and D168G) could affect binding of telaprevir more than boceprevir. Measurements of antiviral susceptibility in cell-culture studies were consistent with this observation. Four variants (ie, Q41H, I132V, R155K, and D168G) caused low-to-moderate levels of ketoamide resistance; 3 of these were highly fit (Q41H, I132V, and R155K).

CONCLUSIONS

Using a comprehensive sequence and structure-based analysis, we showed how natural variation in the hepatitis C virus protease nonstructural protein 3/4A sequences might affect susceptibility to first-generation direct-acting antiviral agents. These findings increase our understanding of the molecular basis of ketoamide resistance among naturally existing viral variants.

Advances in the treatment of hepatitis C virus infection

Therapy for chronic hepatitis C virus (HCV) infection with pegylated interferon α and ribavirin leads to suboptimal rates of viral eradication in patients with genotype 1 HCV, the most common viral strain in the United States and many other countries. Recent advances in the study of viral kinetics, host factors that predict response to antiviral therapy, and viral protein structure have established the foundation of a new era in the treatment of HCV infection. The HCV NS3/4A protease inhibitors boceprevir and telaprevir, the first 2 agents in a new and promising generation of direct-acting antiviral agents to have completed phase III studies, were approved by the US Food and Drug Administration in May 2011. The addition of these HCV protease inhibitors to standard therapy has been demonstrated to dramatically improve sustained virologic response rates, both in treatment-naïve patients and in prior relapsers and nonresponders. These novel agents represent only the beginning of a revolution in HCV therapy, which will include additional protease inhibitors as well as other classes of drugs currently under investigation, such as polymerase inhibitors, NS5A inhibitors, and host factor inhibitors such as cyclophilin antagonists. The future of HCV therapy holds promise for significantly higher sustained virologic response rates with shorter treatment durations, as well as the intriguing potential to achieve virologic cure with interferon-free combination therapy regimens.

Discovery of GS-9451: an acid inhibitor of the hepatitis C virus NS3/4A protease

The discovery of GS-9451 is reported. Modification of the P3 cap and P2 quinoline with a series of solubilizing groups led to the identification of potent HCV NS3 protease inhibitors with greatly improved pharmacokinetic properties in rats, dogs and monkeys.

Impact of HCV genetic differences on pathobiology of disease

Multiple HCV genotypes have been isolated worldwide. Genotype seems to be involved in the main pathological aspects of HCV infection. Insulin resistance, steatosis and progression toward cirrhosis, fibrosis and hepatocellular carcinoma establish and develop following genotype-specific mechanisms. Moreover genotype influences pharmacological treatment in term of dose and duration. Pathways involved in cell proliferation, apoptosis, lipid metabolism, insulin and interferon signaling are impaired to a different extent among genotypes, leading to distinct pathological settings. Genotype 1 is associated with a more aggressive disease with increased insulin resistance, worst response to therapy, higher risk of cirrhosis and hepatocellular carcinoma development, while genotype 3 is associated with increased steatosis and fibrosis. The identification and characterization of HCV types and subtypes provides insight into the different outcome of HCV infection and responsiveness to therapy. In the present article, we focused on the pathogenicity of HCV genotypes and their effect on disease progression and treatment.

Discovery of GS-9256: a novel phosphinic acid derived inhibitor of the hepatitis C virus NS3/4A protease with potent clinical activity

A potent and novel class of phosphinic acid derived product-like inhibitors of the HCV NS3/4A protease was discovered previously. Modification of the phosphinic acid and quinoline heterocycle led to GS-9256 with potent cell-based activity and favorable pharmacokinetic parameters. Based on these attributes, GS-9256 was advanced to human clinical trial as a treatment for chronic infection with genotype 1 HCV.

Antiviral activity of the new DAAs for the treatment of hepatitis C virus infection: virology and resistance

The treatment of chronic hepatitis C virus (HCV) infection has substantially evolved over the past decade, following the Consensus Conference organized by the European Association for the Study of the Liver in 1999. Since then, the standard of care (SoC) for patients with chronic hepatitis C has been the combination of pegylated interferon (pegIFN) alpha-2a or -2b and ribavirin. In patients infected with HCV genotype 1, by far the most frequent HCV genotype worldwide, such treatment leads to a cure of infection in only 40-50% of cases. After a decade in which pegIFN alpha and ribavirin therapy was the only available option, triple therapy with HCV protease inhibitors (PIs; boceprevir and telaprevir) in combination with pegIFN alpha and ribavirin has become the new SoC for genotype-1-infected patients. With PI therapy, higher cure rates can be achieved, but specific issues are also raised, such as the emergence of resistance to PIs. For this reason, the present report examines the antiviral activity of PIs and what is currently known about resistance to them, while focusing on telaprevir and boceprevir, two HCV PIs recently licensed for the treatment of treatment-naïve and treatment-experienced genotype-1 patients with chronic hepatitis C. The clinical relevance of resistance testing is also discussed.

The therapeutic approaches for hepatitis C virus: protease inhibitors and polymerase inhibitors

The current standard of care for hepatitis C infection is peginterferon/ribavirin (PegIFN/RBV). We are entering the era where direct-acting antiviral agents (DAAs) will be added to PegIFN/RBV, leading to higher sustained response rates in genotype 1 infected individuals. Currently DAAs are directed toward specific proteins involved in hepatitis C replication with NS3/NS4A protease inhibitors furthest in development. Telaprevir and boceprevir are both NS3/NS4a inhibitors that significantly improve sustained response when added to PegIFN and RBV. The hepatitis C virus (HCV) polymerase inhibitors are another promising DAA class. These molecules are divided into nucleoside/nucleotide polymerase inhibitors and nonnucleotide/nucleoside polymerase inhibitors. Nucleoside/nucleotide polymerase inhibitors have a high barrier to resistance and appear to be effective across a broad range of genotypes. Nonnucleoside polymerase inhibitors have a lower barrier of resistance and appear to be genotype specific. Preliminary data with these compounds are also promising. A third class, NS5A inhibitors, has also shown potent HCV RNA suppression in preliminary studies as monotherapy and with PegIFN and RBV. Combinations of these agents are also entering clinical trials and indeed a preliminary report has demonstrated that the combination of an NS3/4A protease inhibitor and NS5B polymerase inhibitor can effectively suppress virus in genotype 1 individuals. Future studies will concentrate on combinations of direct-acting antiviral agents without and with PegIFN and RBV. Clinicians will need to be familiar with managing side effects as well as resistance as we enter this new era.

The design, synthesis and biological evaluations of C-6 or C-7 substituted 2-hydroxyisoquinoline-1,3-diones as inhibitors of hepatitis C virus

C7-Substituted 2-hydroxyisoquinoline-1,3-diones inhibit the strand transfer of HIV integrase (IN) and the reverse-transcriptase-associated ribonuclease H (RNH). Hepatitis C virus (HCV) NS5B polymerase shares a similar active site fold to RNH and IN, suggesting that N-hydroxyimides could be useful inhibitor scaffolds of HCV via targeting the NS5B. Herein we describe the design, chemical synthesis, replicon and biochemical assays, and molecular docking of C-6 or C-7 aryl substituted 2-hydroxyisoquinoline-1,3-diones as novel HCV inhibitors. The synthesis involved an improved and clean cyclization method, which allowed the convenient preparation of various analogs. Biological studies revealed that the C-6 analogs, a previously unknown chemotype, consistently inhibit both HCV replicon and recombinant NS5B at low micromolar range. Molecular modeling studies suggest that these inhibitors may bind to the NS5B active site.

Boceprevir: a protease inhibitor for the treatment of chronic hepatitis C

OBJECTIVE

To review the pharmacology, pharmacokinetics, safety, and efficacy of boceprevir, a novel oral hepatitis C virus (HCV) nonstructural 3 (NS3) protease inhibitor for the treatment of chronic HCV infection, specifically, genotype 1.

DATA SOURCES

A literature search was conducted through MEDLINE and EMBASE (1966-May 2011) using the terms boceprevir and SCH 503034. Data from the package insert, abstracts obtained from conferences, and unpublished Phase 2-3 clinical trials, obtained through clinicaltrials.gov, were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles identified from the data sources were evaluated. References from selected articles were used to identify other pertinent citations. Article selection focused on pharmacology, clinical trials, safety analyses, and resistance. Preference was given to human data.

DATA SYNTHESIS

Boceprevir is an oral protease inhibitor that binds to the NS3 protein of HCV, ultimately inhibiting viral intracellular replication. Boceprevir displays linear pharmacokinetics and is rapidly absorbed upon oral administration. In clinical studies of treatment-naïve and treatment-experienced patients, boceprevir, in combination with standard of care (pegylated interferon [Peg-IFN]-α-2b with or without ribavirin) achieved greater sustained viral response (SVR) rates compared to standard of care. Safety analyses showed an increased incidence of adverse effects when boceprevir was used with Peg-IFN-α-2b and ribavirin. The most common adverse events reported include fatigue, headache, nausea, dysguesia, and anemia; the incidence of the latter 2 adverse effects may be increased if boceprevir is added to standard therapy. Additional Phase 2 and 3 studies are currently enrolling participants.

CONCLUSIONS

Boceprevir should be used in combination with Peg-IFN-α-2b and ribavirin in the treatment of chronic HCV genotype 1 infection. The improved response rates achieved with that combination will make boceprevir a viable option compared with other developing and approved NS3 protease inhibitors for treatment-naïve and treatment-experienced nonresponders/relapsers. Additional data are needed to clarify the potential for resistance and drug interactions.

Boceprevir: a user's guide

Given its essential role in the process of hepatitis C virus (HCV) replication, the viral NS3/4A serine protease is arguably the most thoroughly characterized HCV enzyme and the most intensively pursued anti-HCV target for drug development thus far. Recent data have demonstrated promise for the NS3 protease inhibitor boceprevir, which, when added to the standard of care peginterferon and ribavirin, improves sustained virological response while shortening duration of therapy in genotype-1-infected individuals. This review discusses the mechanism of action of boceprevir, its effects on HCV, and its viral resistance.

New treatments for chronic hepatitis C virus infection

The treatment of hepatitis C virus infection (HCV) by a combination of pegylated interferon and ribavirin, according to early viral kinetics, leads to a sustained virological response (SVR) in more than 50% of patients with chronic infection. This SVR is a complete recovery of the infection but more than 50% of genotype 1-infected patients do not achieve SVR. A better understanding of the viral cycle, and the characterization of viral enzymes which are potential targets, resulted in the development of new molecules, direct acting antivirals (DAA) targeted against HCV, either specific of genotype 1 (protease inhibitors NS3/NS4A and polymerase inhibitors NS5B) or with a wider spectrum (NS5A or entry inhibitors), and non-specific antivirals (new interferons, cyclophilin inhibitors). We describe the results of phase II and III trials which clearly demonstrated a 20 to 30% increase in the SVR rate of genotype 1-infected patients, either naïve or treatment experienced. These new drugs should be approved by the end of 2011, after a temporary approval for compassionate use in cirrhotic patients with previous relapse or partial response to the combination therapy. In the future, the main limitations of triple therapy will be safety (cutaneous rash or anemia which may be controlled), cost, compliance, viral resistance, and drug interactions that must be avoided by educating patients and physicians.

Directly acting antivirals against hepatitis C virus

The approval of directly acting antivirals (DAA) for the treatment of chronic hepatitis C virus (HCV) infection will represent a major breakthrough for the 180 million persons infected worldwide. Paradoxically, hepatitis C is the only human chronic viral disease that can be cured, as all other pathogenic viruses infecting humans either display self-limited courses or establish non-eradicable persistent infections. Until now, treatment of chronic hepatitis C consisted of the combination of peginterferon-α plus ribavirin, which provided limited rates of cure and was associated with frequent side effects. Several DAA have been identified that inhibit the NS3 protease, the NS5B polymerase or the NS5A replication complex, and have entered the final steps of clinical development. These molecules, coupled with significant progress made in the recognition of more potent and safe interferon forms (e.g. interferon-λ) and host protein targets (e.g. alisporivir), are opening a new era in hepatitis C therapeutics. The expectations are so great that, to some extent, it is reminiscent of what happened in 1996 in the HIV field when the introduction of the first protease inhibitors as part of triple combinations revolutionized antiretroviral therapy. To maximize treatment success and reduce the likelihood of drug resistance selection, a proper individualization of hepatitis C therapy will be required, choosing the most convenient drugs and strategies according to distinct viral and host profiles. The complexity of HCV therapeutics has reached a point that presumably will lead to the birth of a new specialist, the HCV doctor.

Estimation of inhibitory quotient using a comparative equilibrium dialysis assay for prediction of viral response to hepatitis C virus inhibitors

The relationship of inhibitory quotient (IQ) with the virologic response to specific inhibitors of human hepatitis C virus (HCV) and the best method to correct for serum protein binding in calculating IQ have not been addressed. A common method is to determine a fold shift by comparing the EC(50) values determined in cell culture in the absence and presence of human serum (fold shift in EC(50) ), but this method has a number of disadvantages. In the present study, the fold shifts in drug concentrations between 100% human plasma (HP) and cell culture medium (CCM) were directly measured using a modified comparative equilibrium dialysis (CED) assay for three HCV protease inhibitors (PIs) and for a novel HCV inhibitor GS-9132. The fold shift values in drug concentration between the HP and CCM (CED ratio) were ∼1 for SCH-503034, VX-950 and GS-9132 and 13 for BILN-2061. These values were ∼3-10-fold lower than the fold shift values calculated from the EC(50) assay for all inhibitors except BILN-2061. Using the CED values, a consistent pharmacokinetic and pharmacodynamic relationship was observed for the four HCV inhibitors analysed. Specifically, an approximate 1 log(10) reduction in HCV RNA was achieved with an IQ close to 1, while 2-3 and greater log(10) reductions in HCV RNA were achieved with IQ values of 3-5 and greater, respectively. Thus, use of CED to define IQ provides a predictive and quantitative approach for the assessment of the in vivo potency of HCV PIs and GS-9132. This method provides a framework for the evaluation of other classes of drugs that are bound by serum proteins but require the presence of serum for in vitro evaluation.

Characterization of human liver enzymes involved in the biotransformation of boceprevir, a hepatitis C virus protease inhibitor

Boceprevir (SCH 503034), a protease inhibitor, is under clinical development for the treatment of human hepatitis C virus infections. In human liver microsomes, formation of oxidative metabolites after incubations with [(14)C]boceprevir was catalyzed by CYP3A4 and CYP3A5. In addition, the highest turnover was observed in recombinant CYP3A4 and CYP3A5. After a single radiolabeled dose to human, boceprevir was subjected to two distinct pathways, namely cytochrome P450-mediated oxidation and ketone reduction. Therefore, attempts were made to identify the enzymes responsible for the formation of carbonyl-reduced metabolites. Human liver S9 and cytosol converted ∼ 28 and ∼ 68% of boceprevir to M28, respectively, in the presence of an NADPH-generating system. Screening of boceprevir with recombinant human aldo-keto reductases (AKRs) revealed that AKR1C2 and AKR1C3 exhibited catalytic activity with respect to the formation of M+2 metabolites (M28 and M31). The formation of M28 was inhibited by 100 μM flufenamic acid (80.3%), 200 μM mefenamic acid (83.7%), and 100 μM phenolphthalein (86.1%), known inhibitors of AKRs, suggesting its formation through carbonyl reduction pathway. Formation of M28 was also inhibited by 100 μM diazepam (75.1%), 1 mM ibuprofen (70%), and 200 μM diflunisal (89.4%). These data demonstrated that CYP3A4 and CYP3A5 are primarily responsible for the formation of oxidative metabolites and the formation of M28 and M31, the keto-reduced metabolites, are most likely mediated by AKR1C2 and AKR1C3. Because the biotransformation and clearance of boceprevir involves two different enzymatic pathways, boceprevir is less likely to be a victim of significant drug-drug interaction with concomitant medication affecting either of these pathways.

An assessment of the use of chimpanzees in hepatitis C research past, present and future: 1. Validity of the chimpanzee model

The USA is the only significant user of chimpanzees in biomedical research in the world, since many countries have banned or limited the practice due to substantial ethical, economic and scientific concerns. Advocates of chimpanzee use cite hepatitis C research as a major reason for its necessity and continuation, in spite of supporting evidence that is scant and often anecdotal. This paper examines the scientific and ethical issues surrounding chimpanzee hepatitis C research, and concludes that claims of the necessity of chimpanzees in historical and future hepatitis C research are exaggerated and unjustifiable, respectively. The chimpanzee model has several major scientific, ethical, economic and practical caveats. It has made a relatively negligible contribution to knowledge of, and tangible progress against, the hepatitis C virus compared to non-chimpanzee research, and must be considered scientifically redundant, given the array of alternative methods of inquiry now available. The continuation of chimpanzee use in hepatitis C research adversely affects scientific progress, as well as chimpanzees and humans in need of treatment. Unfounded claims of its necessity should not discourage changes in public policy regarding the use of chimpanzees in US laboratories.

Pyridine Carboxamides: Potent Palm Site Inhibitors of HCV NS5B Polymerase

Pyridine carboxamide-based inhibitors of the hepatitis C virus (HCV) NS5B polymerase were diversified and optimized to a variety of topologically related scaffolds. In particular, the 2-methyl nicotinic acid scaffold was developed into inhibitors with improved biochemical (IC50-GT1b = 0.014 μM) and cell-based HCV replicon potency (EC50-GT1b = 0.7 μM). Biophysical and biochemical characterization identified this novel series of compounds as palm site binders to HCV polymerase.

Discovery of (7R)-14-cyclohexyl-7-{[2-(dimethylamino)ethyl](methyl) amino}-7,8-dihydro-6H-indolo[1,2-e][1,5]benzoxazocine-11-carboxylic acid (MK-3281), a potent and orally bioavailable finger-loop inhibitor of the hepatitis C virus NS5B polymerase

Infections caused by hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. The polymerase of HCV is responsible for the replication of viral genome and has been a prime target for drug discovery efforts. Here, we report on the further development of tetracyclic indole inhibitors, binding to an allosteric site on the thumb domain. Structure-activity relationship (SAR) studies around an indolo-benzoxazocine scaffold led to the identification of compound 33 (MK-3281), an inhibitor with good potency in the HCV subgenomic replication assay and attractive molecular properties suitable for a clinical candidate. The compound caused a consistent decrease in viremia in vivo using the chimeric mouse model of HCV infection.

Antiviral activity of narlaprevir combined with ritonavir and pegylated interferon in chronic hepatitis C patients

Narlaprevir (SCH 900518) is a potent inhibitor of the hepatitis C virus (HCV) nonstructural protein 3 serine protease that is primarily metabolized by the cytochrome P450-3A4 system. In order to explore the use of ritonavir-based pharmacokinetic enhancement of an HCV protease inhibitor, this study investigated the safety, tolerability, pharmacokinetics, and antiviral activity of narlaprevir (with or without ritonavir) administered as monotherapy and as combination therapy with pegylated interferon-α-2b (PEG-IFN-α-2b) to HCV genotype 1-infected patients. This was a randomized, placebo-controlled, two-period, blinded study in 40 HCV genotype 1-infected patients (naïve and treatment-experienced). In period 1, narlaprevir was administered for 7 days as 800 mg three times daily without ritonavir or 400 mg twice daily with 200 mg ritonavir twice daily. In period 2, after a 4-week washout, the same dose and regimen of narlaprevir was administered in combination with PEG-IFN-α-2b for 14 days. Upon completion of period 2, all patients initiated PEG-IFN-α-2b and ribavirin treatment. A rapid and persistent decline in plasma HCV-RNA was observed in both treatment-experienced and treatment-naïve patients during period 1, with a mean viral load decline of at least 4 log₁₀ in all treatment groups. A high percentage of both treatment-experienced (50%) and treatment-naïve (≥ 60%) patients had undetectable HCV-RNA (< 25 IU/mL) after period 2. Standard of care resulted in sustained virological response (SVR) rates of 38% and 81% in treatment-experienced and treatment-naïve patients, respectively. Narlaprevir (with or without ritonavir) alone or in combination with PEG-IFN-α-2b was safe and well tolerated.

CONCLUSION

Narlaprevir administration resulted in a robust HCV-RNA decline and high SVR rates when followed by standard of care in both treatment-experienced and treatment-naïve HCV genotype 1-infected patients.