Article 3

Background and Introduction to Hepatitis C Virus (HCV) Treatment

• Current State of HCV Treatment: The majority of patients chronically infected with hepatitis C virus (HCV) can be successfully treated with direct-acting antiviral agents (DAAs) that target viral replication. Combination regimens provides sustained virologic response (SVR) rates exceeding $90\%$, irrespective of genotype, disease stage, or treatment history.
• Infected Population Scale: Estimates indicate up to $150\text{ million}$ people are infected worldwide. Even with high success rates, the absolute number of patients who do not achieve SVR is substantial and expected to grow.
• Retreatment Challenges: There are currently no approved retreatment options for patients who have failed a regimen containing an NS5A inhibitor. This group is of particular concern because NS5A inhibitors select for resistance-associated substitutions (RASs) that maintain viral fitness long after treatment failure.

Profiles of the Combination Therapeutic Agents

• Sofosbuvir (SOF): A nucleotide analogue HCV NS5B polymerase inhibitor. It is approved for use in combination with other DAAs for all HCV genotypes.
• Velpatasvir (VEL): An HCV NS5A inhibitor with pangenotypic potency.
• Voxilaprevir (VOX): Formerly known as GS-9857 (Gilead Sciences), this is a pangenotypic inhibitor of the HCV NS3–NS4A protease.
• Fixed-Dose Tablet: The treatment evaluated is a single tablet containing $400\,mg$ of sofosbuvir, $100\,mg$ of velpatasvir, and $100\,mg$ of voxilaprevir.

Trial Design and Methodology of POLARIS-1 and POLARIS-4

• Oversight and Ethics: Both trials were phase 3, international studies approved by institutional review boards and conducted according to the Declaration of Helsinki and Good Clinical Practice guidelines. Gilead Sciences designed the protocols and performed statistical analyses.
• POLARIS-1 Design:     * Population: Patients with HCV genotype 1 who previously failed an NS5A inhibitor-containing regimen.     * Randomization: Randomized $1:1$ to receive sofosbuvir–velpatasvir–voxilaprevir or a matching placebo for $12\text{ weeks}$.     * Stratification: Based on the presence or absence of cirrhosis.     * Other Genotypes: Patients with non-genotype 1 (genotypes 2, 3, 4, 5, or 6) were enrolled directly into the active-treatment group (non-randomized).
• POLARIS-4 Design:     * Population: Patients with HCV genotypes 1, 2, or 3 who previously failed a DAA regimen that did not include an NS5A inhibitor.     * Randomization: Randomized $1:1$ to receive sofosbuvir–velpatasvir–voxilaprevir or sofosbuvir–velpatasvir for $12\text{ weeks}$.     * Inclusion Criteria Exceptions: Patients previously treated only with a protease inhibitor plus peginterferon and ribavirin were excluded because they already have approved retreatment options.     * Stratification: Based on HCV genotype and cirrhosis status.
• Sites: POLARIS-1 used $108\text{ sites}$ and POLARIS-4 used $101\text{ sites}$ across the United States, Canada, New Zealand, Australia, France, Germany, and the United Kingdom.

Patient Eligibility and Screening Assessments

• HCV RNA Measurement: Serum levels were measured using the COBAS AmpliPrep/COBAS TaqMan HCV Quantitative Test, version $2.0$. The lower limit of quantification (LLOQ) was $15\,IU/mL$.
• Genotyping: IL28B genotype was determined by PCR amplification of the single-nucleotide polymorphism rs12979860. Initial HCV genotyping used the Abbott RealTime HCV genotype II assay, followed by deep sequencing of NS3, NS5A, and NS5B regions using BLAST for final analysis.
• Exclusion/Inclusion Criteria: Patients must have had virologic failure after at least $4\text{ weeks}$ of previous treatment. Those who discontinued treatment due to adverse events or nonadherence were excluded.

Primary and Secondary End Points and Statistics

• Primary Efficacy End Point: Sustained virologic response ($SVR12$), defined as HCV RNA below $15\,IU/mL$ at $12\text{ weeks}$ after the end of treatment.
• Primary Safety End Point: Proportion of patients who discontinued treatment prematurely due to adverse events (AEs).
• Secondary End Points: SVR at $4$ and $24\text{ weeks}$ post-treatment, virologic failure rates, and the emergence of viral resistance.
• Statistical Analysis:     * Superiority Test: Compared SVR rates against a performance goal of $85\%$.     * Significance Levels: $0.05$ for POLARIS-1 and $0.025$ for POLARIS-4 (Bonferroni adjustment).     * Power: Planned enrollment provided >90\% power to detect a $10\text{ percentage point}$ advantage over the $85\%$ goal.

Baseline Demographic and Clinical Characteristics

• Cirrhosis Prevalence: In all three active-treatment groups, the percentage of patients with compensated cirrhosis was exactly $46\%$.
• POLARIS-1 Previous Treatments: The most common NS5A inhibitors used in failed regimens were ledipasvir ($55\%$), daclatasvir ($23\%$), and ombitasvir ($13\%$).
• POLARIS-4 Previous Treatments: $85\%$ of patients had previously received sofosbuvir.
• General Demographics:     * Mean Age: Ranged from $57$ to $59\text{ years}$.     * Sex: Predominantly male ($75\%$ to $80\%$).     * Race: Predominantly White ($80\%$ to $88\%$), with Black participants comprising $9\%$ to $14\%$.     * Mean HCV RNA: Consistency across groups at approximately $6.3\,log_{10}\,IU/mL$.

Efficacy Results: Sustained Virologic Response (SVR)

• POLARIS-1 (NS5A-Inhibitor Experienced):     * Overall SVR: $96\%$ ($253$ of $263$ patients; $95\%\,CI$, $93\%$ to $98\%$; P < 0.001).     * Placebo Group: $0\%$ SVR.     * Genotype-Specific SVR:         * Genotype 1a: $96\%$         * Genotype 1b: $100\%$         * Genotype 2: $100\%$         * Genotype 3: $95\%$         * Genotype 4: $91\%$     * Cirrhosis Impact: SVR was $99\%$ in patients without cirrhosis and $93\%$ in those with cirrhosis.
• POLARIS-4 (Non-NS5A-Inhibitor DAA Experienced):     * SOF-VEL-VOX Group: $98\%$ SVR ($178$ of $182$ patients; $95\%\,CI$, $95\%$ to $99\%$; P < 0.001).     * SOF-VEL Group: $90\%$ SVR ($136$ of $151$ patients; $95\%\,CI$, $84\%$ to $94\%$; $P = 0.09$).     * Cirrhosis Impact in SOF-VEL-VOX: $98\%$ SVR in both cirrhotic and non-cirrhotic patients.     * Cirrhosis Impact in SOF-VEL: $94\%$ SVR in non-cirrhotic vs. $86\%$ in cirrhotic patients.
• Virologic Failure Details:     * POLARIS-1: $1$ patient had virologic breakthrough (likely nonadherence based on low drug metabolite levels); $6$ had relapse.     * POLARIS-4: In the SOF-VEL-VOX group, $1$ relapse. In the SOF-VEL group, $14$ relapses ($8$ of which were genotype 3a).

Viral Resistance Analysis

• Baseline Resistance:     * In POLARIS-1, $83\%$ of patients had baseline RASs for NS3 or NS5A inhibitors. SVR was $97\%$ in these patients compared to $98\%$ in those without RASs.     * In POLARIS-4, $49\%$ had baseline RASs. For the SOF-VEL-VOX group, SVR was $100\%$ with RASs vs. $99\%$ without RASs.
• Emergent Resistance: Only $1$ patient (POLARIS-1, Genotype 4) who relapsed developed a new RAS ($NS5A\,Y93H$). The single relapser in the POLARIS-4 triple-therapy group had no RASs at baseline or relapse.

Safety and Tolerability

• Treatment Discontinuation: Extremely low across active groups ($\le 1\%$).     * In POLARIS-1, one active-treatment patient ($59\text{-year-old woman}$) stopped due to angioedema after starting ramipril on day 11.     * In POLARIS-4, one SOF-VEL patient stopped due to worsening headache.
• Most Common Adverse Events (SOF-VEL-VOX):     * Headache: $25\%$ to $27\%$     * Fatigue: $21\%$ to $24\%$     * Diarrhea: $18\%$ to $20\%$     * Nausea: $12\%$ to $14\%$
• Severity of Events: Diarrhea was mostly mild; Grade 2 diarrhea occurred in only $1$ to $3\%$. There were no Grade 3 or 4 diarrhea events.
• Laboratory Abnormalities: Grade 3 laboratory abnormalities (e.g., lipase or creatine kinase elevations) were not accompanied by clinical pancreatitis or myopathy. One transient Grade 3 bilirubin elevation occurred in a patient with Grade 2 elevation at baseline.
• Deaths: One participant in POLARIS-4 (SOF-VEL-VOX) died of an illicit drug overdose $2\text{ days}$ after completing treatment; this was not considered treatment-related.

Discussion and Final Conclusions

• Clinical Significance: The combination of sofosbuvir–velpatasvir–voxilaprevir is highly effective for patients who previously failed DAA regimens, including those with NS5A inhibitor failures and compensated cirrhosis.
• RAS Impact: Unlike other regimens, the triple therapy was not affected by the presence of baseline resistance-associated substitutions.
• Limitations:     * Small sample sizes for certain subpopulations (e.g., genotype 3 with cirrhosis).     * Limited data on participants who failed the most recent DAA regimens (e.g., those containing elbasvir or velpatasvir).     * Non-generalizablilty to patients with HBV/HIV coinfection or decompensated cirrhosis.
• Summary Conclusion: A $12\text{-week}$ course of the single-tablet SOF-VEL-VOX regimen provides a potent retreatment option across all HCV genotypes.