Gilead Sciences, Inc. announced data from the Phase 2b MYR204 open-label study assessing the efficacy and safety of the first-in-class entry inhibitor bulevirtide as monotherapy and in combination with pegylated interferon alfa-2a (PegIFN), in adults living with compensated chronic hepatitis delta virus (HDV) infection. Published in the New England Journal of Medicine (NEJM), the data demonstrate that the investigational combination of bulevirtide 10 mg with PegIFN was superior to investigational bulevirtide 10 mg monotherapy in achieving undetectable HDV RNA (lower limit of quantification (LLOQ), target not detected) at Week 24 after the end of treatment (EOT). The end of study data presented at the European Association for the Study of the Liver (EASL) Congress 2024, demonstrate that treatment with bulevirtide 10 mg in combination with PegIFN maintained a 46% rate of undetectable HDV RNA at Week 48 after EOT, confirming its potential as a finite therapy for adults living with chronic HDV.

HDV affects an estimated 5% of people living with chronic hepatitis B (HBV), with a global prevalence of more than 12 million people. Bulevirtide 2 mg remains the only approved treatment for adults with chronic HDV and compensated liver disease in the European Economic Area (EEA), Great Britain and Switzerland and is not approved in the U.S. Bulevirtide 10 mg is an investigational product and is not approved anywhere. Data published in NEJM demonstrate that at Week 24 after EOT, undetectable HDV RNA was achieved by 32% and 46% of patients taking bulevirtide 2 mg in combination with PegIFN and bulevirtide 10 mg in combination with PegIFN, respectively.

In the monotherapy groups, PegIFN monotherapy and bulevirtide 10 mg monotherapy, undetectable HDV RNA was achieved by 17% and 12%, respectively. The safety profiles of bulevirtide in combination with PegIFN were consistent with those of the individual components. The most frequent adverse events were leukopenia, neutropenia and thrombocytopenia, and most were mild to moderate.

Data presented at EASL (GS-002) demonstrate that at Week 48 after EOT, undetectable HDV RNA was achieved by 26% and 46% of patients taking bulevirtide 2 mg in combination with PegIFN and bulevirtide 10 mg in combination with PegIFN, respectively. In the monotherapy groups, PegIFN monotherapy and bulevirtide 10 mg monotherapy, undetectable HDV RNA was achieved by 25% and 12%, respectively. Also at EASL, late-breaking data (LB-309) on the pivotal Phase 3 MYR301 study evaluating bulevirtide as monotherapy for the treatment of adults with chronic HDV infection were also presented and reinforced bulevirtide as an efficacious and generally well-tolerated long-term treatment option.

Patients had similar rates of combined response (virologic response and ALT normalization) at Week 144 compared to Week 96, with 57% and 54%, respectively, among those receiving bulevirtide 2 mg or 10 mg. This is consistent with and builds on the data shared at EASL 2023. Bulevirtide continued to be generally well-tolerated through Week 144, and the safety profile was similar between the bulevirtide 2 mg and 10 mg treatment arms, with the study investigators attributing no serious adverse events to bulevirtide treatment.

Through 144 weeks of treatment, dose-dependent increases in bile acids remained asymptomatic, were not associated with any clinical sequelae and did not result in any discontinuations or treatment interruption. The MYR204 study was a randomized, open-label, controlled, parallel-group, multicenter, Phase 2b trial, in which a total of 174 patients were randomized and received PegIFN alone for 48 weeks; bulevirtide 2 mg with PegIFN for 48 weeks, followed by bulevirtide 2 mg alone for 48 weeks; bulevirtide 10 mg with PegIFN for 48 weeks, followed by bulevirtide 10 mg alone for 48 weeks; or bulevirtide 10 mg alone for 96 weeks. All patients were followed for an additional 48 weeks after EOT.

The primary endpoint of MYR204 was undetectable HDV RNA at 24 weeks after EOT. Secondary efficacy endpoints included undetectable HDV RNA at Week 48 (all groups) during treatment, undetectable HDV RNA at Week 96 (all bulevirtide groups) during treatment, and undetectable HDV RNA at Week 48 after EOT (all groups). MYR301 is an ongoing, Phase 3 clinical trial evaluating the long-term efficacy and safety of bulevirtide in 150 people living with chronic HDV randomly allocated to treatment with bulevirtide 2 mg once daily (n=49), 10 mg once daily (n=50) or no antiviral treatment (delayed treatment, n=51).

Primary efficacy and safety data were assessed at Week 48. After Week 48, patients in the delayed treatment group of the study were switched to bulevirtide 10 mg once daily for an additional 96 weeks. The total duration of treatment across all groups in the study is 144 weeks.

The primary endpoint, combined response, is defined as an undetectable HDV RNA or = 2log10 IU/ml decline from baseline and ALT normalization at Week 48. Secondary endpoints at Week 48 include undetectable HDV RNA (key secondary endpoint), ALT normalization, and a change from baseline in liver stiffness measured by transient elastography.