GSK, Ionis unveil data for hepatitis B drug touted as ‘functional cure’

GSK and Ionis' Bepirovirsen Achieves Functional Cure in Phase 3 Hepatitis B Trials

GSK and Ionis Pharmaceuticals announced positive Phase 3 trial results for their RNA-based shot, bepirovirsen, for chronic hepatitis B. Published in the New England Journal of Medicine, the B-Well 1 and B-Well 2 trials showed that approximately one-fifth of patients (20% and 19% respectively) achieved a "functional cure," a significant improvement over current oral antivirals which achieve less than 1%. The drug, an antisense oligonucleotide, is already under FDA review with Fast Track and Breakthrough Therapy designations, and an approval decision is anticipated by October 26. Analysts project bepirovirsen could generate over $2 billion in peak sales.

• In the B-Well 1 (n=981) and B-Well 2 (n=857) Phase 3 trials, bepirovirsen achieved a functional cure in 20% and 19% of recipients, respectively, compared to 0% in placebo arms. This represents a substantial advance for chronic hepatitis B patients, as current oral antivirals rarely achieve this outcome. Higher cure rates (25-28%) were observed in patients who entered the trial with lower baseline levels of a key viral protein.
• Bepirovirsen is an antisense oligonucleotide that not only prevents viral replication but also stimulates an immune response, a dual mechanism designed to help the body clear infected cells. This approach offers the potential for a longer-term "functional cure," differentiating it from existing antiviral therapies like Gilead Sciences’ Vemlidy, which only stop replication and require lifelong administration.
• The Food and Drug Administration (FDA) has granted bepirovirsen Fast Track and Breakthrough Therapy designations, accelerating its review process. An approval decision is expected by October 26. GSK has identified bepirovirsen as one of 15 drugs with potential to generate over $2 billion in peak sales, positioning it as a key backbone for future combination strategies in hepatitis B treatment.

Addressing the Unmet Need for a Functional Cure in Chronic Hepatitis B

Current treatment approaches for chronic hepatitis B face significant limitations that prevent achieving a functional cure in most patients. The primary challenge stems from the inability to eliminate the covalently closed circular DNA (cccDNA) pool, which serves as a persistent reservoir for viral replication even under effective antiviral suppression.

• Persistence of viral reservoirs: The cccDNA pool remains intact during treatment, and HBV-DNA integration into the host genome creates permanent viral reservoirs that current therapies cannot eliminate, necessitating lifelong treatment to prevent viral rebound

• Limited efficacy of existing therapies: Nucleos(t)ide analogues effectively suppress viral replication but have minimal impact on hepatitis B surface antigen (HBsAg) levels, while interferon-based immune modulation shows efficacy in only a small subpopulation of patients and carries significant tolerability concerns

• Compromised immune responses: Chronic HBV infection is characterized by immune dysfunction that impedes viral clearance, with current direct antiviral therapies unable to restore adequate HBV-specific immune responses necessary for sustained viral control

• Treatment duration uncertainty: Current therapies require lifelong administration due to frequent viral rebound upon cessation, with unclear optimal treatment duration guidelines despite established criteria for treatment initiation

• Drug resistance emergence: Long-term treatment with nucleoside/nucleotide analogues faces the challenge of resistance development, particularly problematic given the requirement for extended therapy duration

• Healthcare access barriers: High costs of antiviral drugs and inadequate reimbursement systems create significant obstacles to treatment adherence, particularly in high-burden regions, compounded by insufficient disease awareness among patients and healthcare providers

• Genotype-specific treatment challenges: Certain HBV genotypes, particularly genotype C, demonstrate greater refractoriness to standard antiviral therapies compared to genotypes A and B, requiring tailored therapeutic approaches

Bepirovirsen's Phase 3 Trials: Design, Endpoints, and Efficacy for CHB

Recent evidence demonstrates that chronic hepatitis B (CHB) clinical trials have evolved toward standardized endpoints focused on achieving functional cure, defined as sustained HBsAg loss and undetectable HBV DNA. Phase II/III trials increasingly employ finite treatment regimens with off-treatment follow-up periods to assess durability of response, while incorporating novel biomarkers and patient-focused outcomes.

Bepirovirsen: Ushering in a New Era for Chronic HBV Cure

The recent positive Phase 3 results for bepirovirsen mark a significant turning point in the management of chronic hepatitis B (CHB). For decades, the goal of CHB therapy has largely been viral suppression, a lifelong commitment for most patients with limited rates of functional cure. Bepirovirsen, an antisense oligonucleotide (ASO), now offers a tangible path toward a functional cure for a substantial proportion of patients, with reported rates around 20% in clinical trials. This represents a dramatic improvement over the less than 1% achieved with current oral antivirals, fundamentally shifting the treatment paradigm from management to eradication.

This breakthrough not only offers renewed hope for millions living with CHB but also underscores the growing maturity of ASO technology in tackling complex viral diseases. Bepirovirsen's mechanism of action is multifaceted, involving direct degradation of HBV messenger RNAs and potentially stimulating the innate immune system to clear infected hepatocytes. This dual approach may explain its superior efficacy compared to previous generations of therapies.

However, as with any novel therapy, important considerations remain. The durability of these functional cures and the potential for post-treatment relapse will be critical to assess in ongoing Phase 3 studies, particularly given that even sequential therapy with pegylated interferon-α-2a has shown varied response rates. Furthermore, the drug's optimal efficacy appears to be concentrated in specific patient populations, notably those with lower baseline HBsAg levels. While generally well-tolerated, clinicians will need to monitor for common adverse events such as injection site reactions and transient ALT flares, which, while potentially a sign of therapeutic immune activity, require careful management. Despite these considerations, bepirovirsen's potential to deliver a functional cure positions it as a transformative agent, paving the way for future combination therapies and accelerating the global effort towards CHB elimination.