Hepatitis C virus (HCV) nonstructural protein (NS) 3/4A protease

For the HCV encoded polyprotein (intomature forms of NS3, NS4A, NS4B, NS5A, and NS5B proteins) to be cleaved by protease and subsequently for viral replication, NS3/4A protease is required[1]. utilizing isogenic NS4A peptide cofactors supplied in trans and recombinant NS3 protease domains in enzymatic assays. Voxilaprevir has Ki values of 0.038 nM and 0.066 nM, respectively, against the NS3 proteases of HCV genotypes 1b and 3a[1].in stable cell lines that express HCV replicons that encode renilla luciferase (Huh-7-Lunet or Huh7-1C cells). Across genotypes 1 through 6, vitilaprevir demonstrates strong pangenotypic antiviral activity, with an EC50 ranging from 0.33 to 6.6 nM. Voxilaprevir has IC50 values of 0.33 nM, 3.9 nM, 3.3 nM, 3.7 nM, 4.5 nM, 1.8 nM, and 6.6 nM, 1.9 nM against HCV replicon strains DQ314805, H77, Con1, JFH-1, J6, J8 (full length), and HM568433, SA13 (NS3 Chimera), respectively[1].

In this study, the safety, tolerability, antiviral activity and pharmacokinetics (PK) of Voxilaprevir/GS-9857 were evaluated in patients with chronic HCV genotype 1–4 infection. Patients with genotype 1–4 infection received placebo or once-daily GS-9857 at doses ranging from 50 to 300 mg for 3 days under fasting conditions. GS-9857 was well tolerated; all reported adverse events (AEs) were mild or moderate in severity. Diarrhoea and headache were the most commonly reported AEs. Grade 3 or 4 laboratory abnormalities were observed in 17% of patients receiving GS-9857; there were no Grade 3 or 4 abnormalities in alanine aminotransferase, aspartate aminotransferase or alkaline phosphatase levels. GS-9857 demonstrated potent antiviral activity in patients with chronic HCV infection, achieving mean and median maximum reductions in HCV RNA of ≥3 log10 IU/mL following administration of a 100-mg dose in patients with HCV genotype 1a, 1b, 2, 3 or 4 infection. The antiviral activity of GS-9857 was unaffected by the presence of pretreatment NS3 RAVs. In patients with genotype 1–4 infection, GS-9857 exhibited linear PK and was associated with a median half-life of 29–42 h, supporting once-daily dosing. Thus, the tolerability, efficacy and pharmacokinetic profile of GS-9857 support its further evaluation for treatment of patients with chronic HCV infection. [2]

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Among treatment-naive patients without cirrhosis, rates of SVR12 were 71% (24 of 34; 95% CI, 53–85) in patients receiving 6 weeks of treatment, and 100% (36 of 36; 95% CI, 90–100) in patients receiving 8 weeks of treatment (Table 2). Among treatment-naive patients with cirrhosis, rates of SVR12 were 94% (31 of 33; 95% CI, 80–99) in patients receiving 8 weeks of sofosbuvir-velpatasvir plus Voxilaprevir/GS-9857 and 81% (25 of 31; 95% CI, 63–93) in patients receiving 8 weeks of sofosbuvir-velpatasvir plus GS-9857 with ribavirin (Table 2). Among patients previously treated with DAA-containing regimen(s), rates of SVR12 were 100% (31 of 31; 95% CI, 89–100) in patients without cirrhosis receiving 12 weeks of treatment, and 100% (32 of 32; 95% CI, 89–100) in patients with cirrhosis receiving 12 weeks of treatment. Across the groups, no significant differences in SVR12 rates were observed based on baseline differences (Appendix). Eighteen patients with virologic failure relapsed after the end of treatment; no patient had a virologic breakthrough during treatment (Appendix).

Table 3 shows the SVR rates for patients without RASs and with single and multiclass NS3, NS5A, and NS5B RASs with a 1% sequencing cut-off level. In treatment-naive patients, 8 weeks of treatment with sofosbuvir-velpatasvir plus Voxilaprevir/GS-9857 without ribavirin led to SVR12 in 96% (23 of 24) and 98% (44 of 45) of patients without and with baseline RASs, respectively. Use of a 15% sequencing cut-off level led to a similar result (Supplementary Material). All DAA-experienced patients, regardless of the presence of single or multiclass RASs, achieved SVR12 after 12 weeks of treatment with sofosbuvir-velpatasvir plus GS-9857. There were 12 DAA-experienced patients with the NS5A RAS Y93H/N at baseline, all of whom achieved SVR12.

In a phase 2 open-label trial, we found 8 weeks of treatment with sofosbuvir-velpatasvir plus Voxilaprevir/GS-9857 to be safe and effective in treatment-naive patients; 12 weeks was safe and effective in patients previously treated with DAAs. The combination was safe and effective in patients with or without compensated cirrhosis. Clinicaltrials.gov no: NCT02378935 [3].

This was a double-blind, multicentre, randomized, placebo-controlled study evaluating the safety, tolerability, antiviral activity and PK of Voxilaprevir/GS-9857 in patients with chronic HCV infection (NCT02185794) (Fig. 1). The approved study protocol allowed for up to 10 unique dosing cohorts, of which the first three cohorts were placebo-controlled and dosed in a fasted state, while the remaining, adaptive cohorts did not include a placebo control and could be dosed in either a fasted or a fed state. The final study included seven cohorts; results from the five cohorts that received GS-9857 under fasting conditions are included here, while results from the two cohorts that received GS-9857 treatment under fed conditions will be reported separately. [2]

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\n\nPatients were screened within 30 days prior to the first study drug dose administration. Patients satisfying study criteria were randomized and admitted to the study facility on day−1 to commence dosing on baseline/day 1. Following treatment with the study drug once daily for 3 days (days 1, 2 and 3), patients were discharged from the study facility on day 4. Short-term follow-up occurred on days 5, 6, 7, 8 and 10, and long-term follow-up visits were scheduled for weeks 12, 24 and 48. [2]
\n\nPatients with HCV genotype 1a, HCV genotype 2 and HCV genotype 3 received double-blinded Voxilaprevir/GS-9857 (50, 100 or 300 mg for patients with HCV genotype 1a and 3, and 100 mg for patients with HCV genotype 2) or placebo once daily under fasting conditions for 3 days (Fig. 1). GS-9857 100 mg was administered once daily for 3 days under fasting conditions to patients with HCV genotype 1b and HCV genotype 4. [2]

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\n\nTo evaluate Voxilaprevir/GS-9857 antiviral activity against HCV in patients with genotype 1–4 HCV infection, the primary efficacy endpoint, the change in HCV RNA from baseline to each postdose assessment, was determined. Plasma samples were collected at screening; at predose on day 1; at 2, 4, 6, 8, 12, 16, 24 (predose on day 2), 36, 48 (predose on day 3), 54, 60, 72 and 96 h following administration of the first dose; and on the mornings of days 6, 7, 8 and 10, and at weeks 12, 24 and 48 of the follow-up period. HCV RNA viral load was measured using COBAS TaqMan HCV Test v2.0 for use with the High Pure System (Roche Molecular Diagnostics, Pleasanton, CA, USA). The lower limit of quantification (LLOQ) of the assay was 15 IU/mL. Viral genotype and subtype at screening were determined using the VERSANT HCV Genotype INNO-line probe assay (LiPA) 2.0 Assay (Siemens Medical Solutions USA, Inc., Malvern, PA, USA). Secondary efficacy endpoints included absolute value of HCV RNA levels at each assessment; categorical decline from baseline for patients with a <1, ≥1 and <2, ≥2 and <3, or ≥3 log10 IU/mL decrease in HCV RNA from baseline to each postdose assessment up to day 10 by treatment and cohort; and the number and percentage of patients with HCV RNA \n\nFor pharmacokinetic evaluation, blood samples were collected after the administration of the first and the third dose at the following time points: predose, and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16 and 24 h postdose. Additionally, samples were collected at approximately 48, 72, 96, 120 and 168 h following the third dose. Plasma concentration of Voxilaprevir/GS-9857 was determined using validated high performance liquid chromatography tandem mass spectroscopy (LC/MS/MS) bioanalytical methods. The assays were performed by inVentiv Health Clinical Lab, Inc. (Princeton, NJ, USA), for GS-9857. Pharmacokinetic parameters were estimated using WinNonlin software (Certara, NJ, USA) with standard noncompartmental methods. [2]

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\n\nThe pharmacokinetic parameters calculated included area under the plasma concentration vs time curve from zero to the last quantifiable concentration (AUClast), area under the plasma concentration vs time curve extrapolated to infinity (AUCinf), area under the plasma concentration vs time curve up to 24 h (AUC0–24), maximum plasma concentration (Cmax), observed plasma concentration at 24 h postdose (C24), last observed quantifiable plasma drug concentration (Clast), time of maximum plasma concentration (Tmax), time of last observed quantifiable plasma drug concentration (Tlast), elimination half-life (t1/2), terminal elimination rate constant (λz) and apparent oral clearance of drug following administration (CL/F). Dose proportionality was evaluated based on AUC0–24, C24 and Cmax on days 1 and 3 using both the power model and the analysis of variance method. Accumulation indices for Voxilaprevir/GS-9857 were summarized by comparing day 3 to day 1 for AUC0–24, C24 and Cmax. [2] \n\n

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\n\nCohort 1 [3]
\nAt the time the study was initiated, 2 groups of treatment-naive patients were enrolled in cohort 1: a group of patients without cirrhosis, who received sofosbuvir-velpatasvir plus Voxilaprevir/GS-9857 for 6 weeks, and a group of patients with cirrhosis, who received sofosbuvir-velpatasvir plus GS-9857 for 8 weeks. The protocol specified that if the rate of relapse among patients with cirrhosis who received 8 weeks of treatment was 10% or less, there was an option that another group could be enrolled to receive 6 weeks of treatment. This option was not exercised. Instead, preliminary results from these first 2 groups prompted us to amend the protocol to add 2 groups to this cohort: a group of patients without cirrhosis, who received 8 weeks of sofosbuvir-velpatasvir plus GS-9857, and a group of patients with cirrhosis, who received 8 weeks of sofosbuvir-velpatasvir plus GS-9857 with ribavirin.

\nCohort 2 [3]
\nTwo groups of DAA-experienced patients—those with and without cirrhosis—were enrolled in cohort 2. Both groups received 12 weeks of sofosbuvir-velpatasvir plus Voxilaprevir/GS-9857. The protocol specified that if the rate of relapse in either group was 10% or less, there was an option that another group of patients could be enrolled to receive 8 weeks of treatment. This option was not exercised.\n

\nAll patients received a fixed-dose combination tablet of sofosbuvir 400 mg and velpatasvir 100 mg once daily, along with a 100-mg tablet of Voxilaprevir/GS-9857 once daily, taken with food. Ribavirin was administered 1000–1200 mg/day (1000 mg for patients weighing <75 kg and 1200 mg for patients weighing ≥75 kg) in a divided daily dose. This was an open-label study, in which patients were enrolled by investigators at the study centers. No participants or study personnel were blinded to treatment assignments at any time during the study.

Absorption, Distribution and Excretion When used in combination with [DB08934] and [DB11613] at a fixed dose, voxiprevir reaches its maximum plasma concentration (Cmax) of 192 ng/mL 4 hours after administration.
Voxprevir is mainly excreted via bile.

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Metabolism/MetabolitesVoxprevir is mainly metabolized by cytochrome P450 3A4 (CYP3A4), with a small amount metabolized by CYP2C8 and CYP1A2.

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Biological Half-Life33 hours

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Voxprevir[1]
Voxprevir(VOX) is rapidly absorbed into the systemic circulation and reaches its maximum plasma concentration 4 hours after administration. 2-5 hours after administration. The median steady-state half-life of VOX was 28–41 hours across multiple doses tested. The drug is >99% bound to plasma proteins and is metabolized by CYP3A4. Therefore, drug concentrations may vary when co-administered with CYP3A4 inhibitors/inducers. The drug is eliminated via the biliary route with a terminal elimination half-life of 33 hours. Approximately 95% of the drug (40% of which is unchanged) is excreted in feces [1]. Sofosbuvir/velpatasvir/voxiprevir [1] The AUC0-24 and Cmax of SOF were similar in healthy adults and patients with active HCV. Compared with healthy subjects (N = 137), the AUC0-24 and Cmax of VEL in HCV-infected individuals were reduced by 41% and 39%, respectively. In patients with hepatitis C virus infection, VOX had an AUC0–24 and Cmax that were 260% higher than those in healthy subjects (N = 63). Safety [1] In the POLARIS-2 and POLARIS-3 studies, no patients in the SOF/VOX/VEL group discontinued treatment due to serious adverse events. In the POLARIS-2 study, adverse events occurred in 72% of patients in the SOF/VOX/VEL group, and serious adverse events occurred in 3% of patients. Only one patient experienced a serious adverse event. In the POLARIS-2 study, pyelonephritis was the only serious adverse event observed in either treatment group. Other adverse events observed in the SOF/VOX/VEL treatment group included headache (27%), fatigue (20%), diarrhea (18%), and nausea (16%), while the corresponding adverse event rates in the SOF/VEL treatment group were headache (23%), fatigue (21%), diarrhea (7%), and nausea (9%), respectively. In the POLARIS-3 study, adverse events occurred in 75% of patients treated with SOF/VOX/VEL. Of the 110 patients, 2 experienced 4 serious adverse events. The incidence of adverse events in the SOF/VOX/VEL treatment group was comparable to that in the 12-week SOF/VEL treatment group, but the incidence of mild nausea and diarrhea in the SOF/VOX/VEL treatment group was similar to the incidence of adverse events associated with prior NS3/4A protease inhibitors.
It has been reported that HBV reactivation may occur in patients co-infected with HCV and hepatitis B virus (HBV) who have received or completed direct-acting antiviral (DAA) therapy for HCV. Cases of fulminant hepatitis, liver failure, and death have been reported. The risk of HCV reactivation may be increased in patients receiving HCV DAA therapy who are concurrently taking certain immunosuppressants or chemotherapy drugs, or who are HBsAg positive, or who have serological evidence of HBV clearance.

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Pharmacokinetic Results[2]
Except for one patient who received 100 mg voxiprevir/GS-9857, plasma drug concentrations were detectable within 24 hours after single or multiple doses in all patients. Plasma concentration-time curves for GS-9857 were similar after 1 or 3 days of administration, regardless of HCV genotype. Administration of 50–300 mg GS-9857 resulted in dose-proportional increases in Cmax and AUC0–24. Median Tmax ranged from 1.3 to 4.0 hours after the first dose and from 1.8 to 5.0 hours after three doses (Table S2). The median t1/2 on day 3 ranged from approximately 29 to 42 hours in all cohorts. Consistent with the half-life of GS-9857, significant drug accumulation was observed at all assessed dose levels.

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Exposure-Response Relationship[2]
In patients infected with genotypes 1a, 1b, 2, or 4, anti-HCV activity was independent of the dose of 50, 100, or 300 mg of Voxilaprevir/GS-9857; while in patients infected with genotype 3, the median antiviral response was related to the GS-9857 dose. This exposure-response relationship can be adequately described using a simple maximum anti-HCV activity (Emax) model using AUC0-24 on day 3 of treatment. Similar exposure-response relationships were also provided using similar models using GS-9857 Cmax or C24.

Effects During Pregnancy and Lactation
◉ Overview of Drug Use During Lactation
No studies have been conducted on voxiprevir in breastfeeding women undergoing treatment for hepatitis C. Because it binds to maternal plasma proteins at a rate exceeding 99%, its concentration in breast milk is likely to be very low. Some sources suggest that breastfeeding should be avoided when voxiprevir is used in combination with ribavirin.
Hepatitis C is not transmitted through breast milk, and breast milk has been shown to inactivate the hepatitis C virus (HCV). However, the U.S. Centers for Disease Control and Prevention (CDC) recommends that breastfeeding should be considered if the mother has cracked or bleeding nipples. It is unclear whether this warning applies to mothers undergoing treatment for hepatitis C.
Infants born to HCV-infected mothers should be tested for HCV infection; nucleic acid testing is recommended because maternal antibodies are present in the infant for the first 18 months after birth and before the infant develops an immune response.
◉ Impact on Breastfed Infants
No published information was found as of the revision date.
◉ Effects on lactation and breast milk
As of the revision date, no relevant published information was found.

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Protein binding
Vocirevi binds to human plasma proteins in more than 99%.

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Tolerability[1]
In the POLARIS-2 and POLARIS-3 studies, none of the patients who received SOF/VOX/VEL for 8 weeks discontinued treatment due to serious adverse events; in contrast, 0.5% of the patients who received SOF/VEL for 12 weeks discontinued treatment due to serious adverse events in the POLARIS-2 study. In the POLARIS-4 study, none of the patients in the SOF/VOX/VEL treatment group discontinued treatment due to treatment interruption within 12 weeks, while one patient in the SOF/VEL treatment group discontinued treatment due to treatment interruption within 12 weeks. No dose adjustment of SOF/VOX/VEL is required for patients with mild or moderate renal impairment. Therefore, this therapy is well tolerated in patients.

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Safety[2]
Table 2 lists the adverse events that occurred in patients in each treatment group during treatment. Overall, 11 patients (16.4%) experienced adverse events, of whom 9 received Voxilaprevir/GS-9857 (9/59; 15.3%) and 2 received placebo (2/8; 25.0%). The incidence of treatment-related adverse events was 6.8% (4/59) in patients receiving GS-9857 and 12.5% (1/8) in patients receiving placebo. No serious adverse events, adverse events leading to discontinuation of the study drug, or death occurred during the study. All adverse events were mild or moderate. The most common adverse event was diarrhea, occurring in 5.1% (3/59) of the GS-9857 group and 12.5% (1/8) of the placebo group; the most common adverse event was headache, occurring in 1.7% (1/59) of the GS-9857 group and 25.0% (2/8) of the placebo group. The incidence of adverse events was not related to the study drug dose. In patients treated with Voxilaprevir/GS-9857, 15.3% (9/59) experienced grade 3 laboratory abnormalities and 1.7% (1/59) experienced grade 4 laboratory abnormalities (Table S1). No grade 3 or 4 abnormalities were observed in laboratory tests in the placebo group. The incidence of grade 3 and 4 laboratory abnormalities was not related to the GS-9857 dose, nor was the dose related to adverse events. Analysis of vital signs and physical examination results by treatment group or by individual patient revealed no clinically significant changes relative to baseline during the study period.

[1]. Expert Opin Pharmacother.2018 May;19(7):749-757.

[2]. J Viral Hepat. 2016 Aug;23(8):614-22.

[3]. Gastroenterology. 2016 Nov;151(5):893-901.e1.

Pharmacodynamics
Voxilaprevir is a direct-acting antiviral drug that targets the viral NS3/4A protein, reducing serum HCV RNA levels. It blocks HCV replication by specifically inhibiting the key function of the NS3/4A protein in the replication complex. Even at doses up to nine times the maximum recommended dose, it does not appear to prolong the QT interval. Voxilaprevir is a direct-acting antiviral (DAA) used in combination therapy for chronic hepatitis C. Chronic hepatitis C is an infectious liver disease caused by infection with the hepatitis C virus (HCV). HCV is a single-stranded RNA virus with nine different genotypes, of which genotype 1 is the most common in the United States, affecting 72% of patients with chronic HCV. Voxilaprevir exerts its antiviral effect by reversibly binding to and inhibiting the NS3/4A serine protease of hepatitis C virus (HCV). After HCV virus replicates its genetic material and translates it into a single polypeptide chain, non-structural protein 3 (NS3) and its activating cofactor non-structural protein 4A (NS4A) are responsible for cleaving the genetic material into the following structural and non-structural proteins, which are essential for mature viral assembly: NS3, NS4A, NS4B, NS5A, and NS5B. Vosevi inhibits viral proteases NS3/4A, thereby preventing viral replication and function. Since 2011, significant progress has been made in treatment options for chronic hepatitis C with the development of direct-acting antiviral agents (DAAs) such as vosevi. Since July 2017, vosevi has been marketed as a fixed-dose combination of sofosbuvir and velpatasvir under the brand name Vosevi. Vosevi is approved for the treatment of adult patients with chronic hepatitis C virus (HCV) infection of genotypes 1, 2, 3, 4, 5, or 6. It is worth noting that Vosevi is approved for patients with genotypes 1-6 who have previously received NS5A inhibitor therapy, or patients with genotypes 1a or 3 who have previously received sofosbuvir HCV therapy without NS5A inhibitors. Prior to the market launch of Vosevi, there were no approved retreatment options for chronic HCV-infected patients who had failed prior treatment with NS5A inhibitors. Vosevi is a hepatitis C virus NS3/4A protease inhibitor. Its mechanism of action is as an inhibitor of hepatitis C virus (HCV) NS3/4A protease, a P-glycoprotein, a breast cancer resistance protein, an organic anion transporter 1B1, and an organic anion transporter 1B3. Vosevi is an orally bioavailable hepatitis C virus (HCV) nonstructural protein 3/nonstructural protein 4A (NS3/NS4A) serine protease with antiviral activity. After administration, vorasilapvir binds to the HCV NS3/NS4A serine protease, preventing NS3/NS4A protease-mediated maturation of the polyprotein. This disrupts viral protein processing and the formation of the viral replication complex, thereby inhibiting viral replication and function. NS3 is a serine protease crucial for proteolytic cleavage at multiple sites within the HCV polyprotein and plays a key role in HCV RNA replication. NS4A is an activator of NS3. HCV is a small, enveloped, single-stranded RNA virus belonging to the Flaviviridae family; HCV infection is closely associated with the development of hepatocellular carcinoma (HCC). Hepatitis C is a major global disease. In recent years, the treatment of this disease has undergone revolutionary changes. With the approval of second-generation direct-acting antiviral drugs, the treatment of hepatitis C has fundamentally changed, and current drugs for treating hepatitis C are significantly more effective and safer than previously approved drugs. For patients who have failed direct-acting antiviral therapy, treatment options have always been complex and difficult to implement, but the approval of sofosbuvir/velpatasvir/voxiprevir has brought new treatment options to these patients. This article will introduce sofosbuvir/velpatasvir/voxiprevir, a recently approved combination therapy for the treatment of hepatitis C. This article reviews the relevant studies on the approval of this combination therapy and analyzes its efficacy and safety. Expert opinion: Sofosbuvir/velpatasvir/voxiprevir fills a previous gap in the treatment of hepatitis C, namely for patients who have failed treatment due to drug-resistant viral infection. With this gap being filled, the pace of new therapy development seems to have slowed down in general. While understandable, the reduction in the development of new drugs for hepatitis C poses a considerable risk in the long run. [1] Conclusion The SOF/VOX/VEL combination therapy is a well-tolerated and effective treatment option for patients who have failed other hepatitis C drug treatments. In addition, it is effective against all major hepatitis C virus genotypes. Although the drug has some side effects, it is generally well-tolerated. In the Phase III clinical trial, only one patient discontinued SOF/VOX/VEL due to an adverse reaction. In particular, compared to previous generations of hepatitis C treatments, the observed side effects were often milder. Even patients who failed other treatments showed a high SVR rate with SOF/VOX/VEL, ensuring that SOF/VOX/VEL will remain an important supplement to HCV treatment for the next few years.
Expert Opinion
The revolutionary changes in HCV drug approval and treatment over the past seven years have completely altered the landscape of anti-HCV drugs, to the point that many drugs approved in 2011 are now obsolete. With these significant changes, the pace of approval and development of new anti-HCV drugs has slowed. In fact, for all major HCV genotypes, many areas of HCV treatment appear to have been taken over by effective and well-tolerated treatments. While approved drugs can be used to treat patients who have failed DAA regimens, treatment options were limited for patients who had failed novel DAAs prior to the approval of SOF/VOX/VEL. In this area, SOF/VOX/VEL holds promise as a key drug for HCV treatment and represents an important new combination therapy for drug-resistant HCV. A comprehensive evaluation of the efficacy of SOF/VOX/VEL in patients who have failed novel regimens, including SOF/VEL and glecaprevir/pibrentasvir, is also crucial. Although the drug has not yet been approved in the US for treatment-naïve patients due to the results of the POLARIS-2 trial, there is an urgent need for effective treatments for patients who have failed first-line therapy. Even in HCV-infected individuals who have developed resistance to approved direct-acting antiviral agents (DAAs), the SOF/VOX/VEL regimen maintains a high sustained virological response rate (SVR), which is likely to ensure its key role in future HCV treatment. Because the SOF/VOX/VEL regimen includes three major classes of DAAs, treatment success is still possible even with partial resistance to one of the drugs. We believe that given the high SVR rates of most approved treatment regimens for treatment-naïve patients, especially those requiring only 8 weeks, differences in treatment cost and health insurance coverage are likely major factors influencing treatment regimen selection. The recently approved gliclazvir/pirentavir regimen is also suitable for treatment-naïve patients, requiring only 8 weeks, with a high SVR rate and relatively low cost. If the SOF/VOX/VEL regimen is ultimately approved in the US for treatment-naïve patients, the gliclazvir/pirentavir regimen may limit its use in this indication. A noteworthy development in hepatitis C treatment is the significant improvement in treatment duration and side effects over time. Even with newer direct-acting antiviral (DAAs), many regimens have shortened their treatment duration from 12 weeks to 8 weeks. However, the effectiveness of shorter treatment durations remains an open question. A 2016 study investigated a 6-week course of ledipasvir/SOF treatment for hepatitis C genotype 1 infection, showing a high sustained virological response (SVR) rate. This contrasts sharply with previous results from other direct-acting antiviral (DAA) trials, which indicated lower efficacy with a 6-week course. Whether this efficacy can be generalized to other genotypes or other treatment options remains an important question. The rapid pace of new DAA development also reflects how market demand for anti-HCV drugs is being met. Many pharmaceutical companies have shifted their R&D focus from hepatitis C to hepatitis B virus (HBV) and other diseases. Currently, it appears that the next major step in combating hepatitis C virus (HCV) will be vaccine development, rather than other drug interventions. From an economic perspective, shifting the focus of R&D from new anti-HCV drugs to other diseases is understandable, but it is not without risk. While currently used drugs are highly effective and have a relatively low risk of resistance, most direct-acting antiviral (DAAs) drugs can still develop resistance, with some reported resistance rates between 10% and 15%. As with antimicrobial drugs, even these newer drugs can develop resistance over time. The risk of resistance to these drugs increases as new DAAs are developed more slowly. [1]

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In this randomized phase 1b study, researchers evaluated the safety, antiviral efficacy, and pharmacokinetics of voxilaprevir/GS-9857 in patients with chronic genotype 1–4 HCV infection at doses ranging from 50 to 300 mg. GS-9857 was generally well tolerated in patients with chronic hepatitis C virus (HCV) infection, administered once daily for 3 consecutive days. All adverse events (AEs) were mild or moderate, with diarrhea and headache being the most common. Although some protease inhibitor-based treatment regimens have been previously reported to increase the incidence of rash, pruritus, nausea, and anemia^7–10, no such events were observed in this study. Among patients treated with GS-9857, 16.9% experienced grade 3 or 4 laboratory abnormalities, unrelated to GS-9857 dose or adverse events. Notably, assessment of ALT, AST, and alkaline phosphatase levels revealed no grade 3 or 4 abnormalities, indicating that GS-9857 administration did not cause significant changes in liver function. Physical examination and electrocardiographic evaluation revealed no clinically significant findings. Following treatment with 100 mg or 300 mg doses of GS-9857, viral load decreased by >3 log10 IU/mL from baseline in all genotypes (including genotype 3), demonstrating potent antiviral activity of GS-9857 in HCV-infected patients. This observation is consistent with in vitro data showing pan-genotypic activity of GS-9857 against genotypes 1 through 6, with a half-maximal effective concentration (MCD) range of 1.5 to 6.6 nM. Except for patients with genotype 3a infection treated with <100 mg GS-9857, HCV RNA levels decreased rapidly and persistently in all patients, maintaining this level until day 10. For patients with genotype 3a infection treated with 50 mg GS-9857, the rate of HCV RNA level decline was slower. This study characterized amino acid substitutions at positions 36, 41, 43, 54, 55, 80, 122, 155, 156, 168, and 170, which have been reported to be associated with resistance to NS3/4A protease inhibitors^11-17. Before initiating GS-9857 treatment, 22.4% of patients who underwent sequencing carried NS3 resistance-associated variants (RAV). After GS-9857 treatment, the mean maximum viral load reduction was similar regardless of whether patients carried NS3 RAVs, indicating that the antiviral efficacy of GS-9857 can be maintained even in the presence of mutations typically associated with resistance. In patients who underwent sequencing 3 days after GS-9857 treatment, the majority (73.6%) did not develop new NS3 RAVs, nor did they develop new NS3 RAVs in patients with genotype 2 or 4 infection. A156V or A156T are the most common mutations in patients with genotype 1a or 1b infection. In vitro data indicate that GS-9857 is potent against the most common genotype 1 RAVs other than A156T. This substitution was associated with high levels of resistance (>100-fold) but low viral fitness (only 1.5% compared to wild-type 1a genotype replicons). The overall low incidence of NS3 resistance-associated variants (RAVs) suggests that GS-9857 has a relatively high resistance barrier compared to other first-generation protease inhibitors, which may be a significant advantage for retreatment in patients who have failed previous DAA regimens.
Under fasting conditions, GS-9857 exposure increased proportionally with dose, with doses ranging from 50 to 300 mg. The median half-life for each cohort was approximately 29–42 hours, supporting once-daily dosing. Consistent with its relatively long median half-life, significant cumulative exposure to GS-9857 was observed. The plasma pharmacokinetics of GS-9857 were similar in patients with HCV infection of genotypes 1a, 1b, 2, 3, or 4.
This preliminary study excluded patients with cirrhosis or chronic liver disease. Therefore, the lack of significant safety concerns observed may be due to the low incidence of adverse events in the study population. Further evaluation of GS-9857 in patients with more severe disease or other complications is needed to confirm the results of this study.
In conclusion, repeated administration of GS-9857 was well tolerated and significantly reduced HCV RNA levels in patients with HCV infection of genotypes 1–4. It is noteworthy that GS-9857 maintains its potent antiviral activity even with the presence of common NS3 mutations associated with protease inhibitor resistance. GS-9857 exhibits linear pharmacokinetic characteristics when administered at doses of 50 to 300 mg on an empty stomach. The median half-life of GS-9857 is 29 to 42 hours, making it suitable for once-daily dosing. In addition, in vitro studies have shown that GS-9857 has additive antiviral activity when used in combination with sofosbuvir or velpatasvir. In summary, these data support further development of once-daily GS-9857 in combination with other direct-acting antiviral agents (DAAs) for the treatment of patients with chronic hepatitis C virus (HCV) infection. [2]

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An unexpected result in our trial was that, for treatment-naïve patients with cirrhosis, the addition of ribavirin to sofosbuvir-velpatasvir in combination with voxiprevir/GS-9857 did not appear to be beneficial. Although the SVR12 rate in the ribavirin-treated group was numerically lower than that in the treatment-naïve cirrhosis group treated with sofosbuvir-velpatasvir plus GS-9857 (ribavirin-free) (81% vs 94%), the confidence intervals overlapped, which may reflect the smaller sample size. Factors limiting the interpretation of these results include the small sample size and the non-controlled, open-label design. Although this trial only included patients with genotype 1 HCV, another similarly designed trial has been conducted to evaluate the efficacy of this combination regimen in non-genotype 1 HCV patients. In conclusion, 12 weeks of sofosbuvir-velpatasvir plus GS-9857 resulted in a 100% SVR12 rate in patients with no other treatment options (including both compensated and uncompensated cirrhosis patients who had previously received NS5A inhibitor-containing regimens but did not achieve SVR) and was well-tolerated. In treatment-naïve patients, sofosbuvir-velpatasvir combined with GS-9857 showed good safety and effectively shortened the treatment duration to 8 weeks while maintaining a high SVR12 rate. These three potent pan-genotypic DAAs have been co-formulated into a fixed-dose combination tablet. A phase 3 clinical trial will evaluate the efficacy of this fixed-dose combination in treatment-naïve patients for 8 weeks and in patients who have previously received DAA treatment (including those who have previously received NS5A inhibitors) for 12 weeks. [3]

C40H52F4N6O9S

868.94

868.345

C, 55.29; H, 6.03; F, 8.75; N, 9.67; O, 16.57; S, 3.69

1535212-07-7

89921642

White to off-white solid powder

1.4±0.1 g/cm3

1.596

3.83

3

15

9

60

1780

8

S(C1(C)CC1)(NC([C@]1(C[C@H]1C(F)F)NC([C@@H]1[C@H](CC)[C@@H]2CN1C([C@H](C(C)(C)C)NC(=O)O[C@@H]1C[C@H]1CCCCC(C1C(=NC3C=C(C=CC=3N=1)OC)O2)(F)F)=O)=O)=O)(=O)=O

MZBLZLWXUBZHSL-FZNJKFJKSA-N

InChI=1S/C40H52F4N6O9S/c1-7-22-27-19-50(28(22)32(51)48-39(18-23(39)31(41)42)35(53)49-60(55,56)38(5)14-15-38)34(52)30(37(2,3)4)47-36(54)59-26-16-20(26)10-8-9-13-40(43,44)29-33(58-27)46-25-17-21(57-6)11-12-24(25)45-29/h11-12,17,20,22-23,26-28,30-31H,7-10,13-16,18-19H2,1-6H3,(H,47,54)(H,48,51)(H,49,53)/t20-,22-,23+,26-,27+,28+,30-,39-/m1/s1

(33R,34S,35S,91R,92R,5S)-5-(tert-butyl)-N-((1R,2R)-2-(difluoromethyl)-1-(((1-methylcyclopropyl) sulfonyl)carbamoyl)cyclopropyl)-34-ethyl-14,14-difluoro-17-methoxy-4,7-dioxo-2,8-dioxa-6-aza-1(2,3)-quinoxalina-3(3,1)-pyrrolidina-9(1,2)-cyclopropanacyclotetradecaphane-35-carboxamide

GS-9857; GS 9857; Voxilaprevir; 1535212-07-7; Voxilaprevir [INN]; Voxilaprevir [USAN:INN]; VOXILAPREVIR [MI]; (1R,18R,20R,24S,27S,28S)-24-tert-butyl-N-[(1R,2R)-2-(difluoromethyl)-1-[(1-methylcyclopropyl)sulfonylcarbamoyl]cyclopropyl]-28-ethyl-13,13-difluoro-7-methoxy-22,25-dioxo-2,21-dioxa-4,11,23,26-tetrazapentacyclo[24.2.1.03,12.05,10.018,20]nonacosa-3,5(10),6,8,11-pentaene-27-carboxamide; GS9857; trade name: Vosevi

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 100 mg/mL (~115.08 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (2.88 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)