Arbutus Biopharma secures FDA Fast Track designation for imdusiran, an RNAi therapy showing functional cure potential in Phase 2a trials for chronic hepatitis B.
Written By: Samiksha Jadhav, BPharm
Reviewed By: Pharmacally Editorial Team
Arbutus Biopharma Corporation has secured Fast Track designation from the U.S. Food and Drug Administration for its investigational RNA interference (RNAi) therapy, imdusiran, showing advancement in chronic hepatitis B treatment.
The designation enables more frequent engagement with the FDA and may allow eligibility for expedited pathways such as Priority Review, Accelerated Approval, or Rolling Review.
Clinical Progress and Early Outcomes
Imdusiran (AB-729) is designed to suppress hepatitis B viral proteins, including hepatitis B surface antigen (HBsAg), a key factor believed to inhibit immune control of the virus. By reducing these antigens, the therapy aims to restore immune responsiveness in affected patients.
In Phase 2a clinical trials including IM-PROVE I (NCT04980482) and IM-PROVE II (NCT06245291) Arbutus reported that 10 patients have achieved what is defined as a “functional cure,” characterized by sustained clearance of HBsAg and undetectable viral DNA after discontinuation of treatment. Among these, a majority have maintained this response for more than two years.
Additionally, 41 patients were able to remain off standard nucleos(t)ide analogue therapy for at least 48 weeks following treatment with imdusiran-based combinations. The therapy has also demonstrated a favorable safety and tolerability profile, alongside meaningful reductions in viral markers.
Mechanism and Delivery Approach
Imdusiran uses RNAi technology to silence viral gene expression across all hepatitis B antigens. It is delivered subcutaneously and targets liver cells (hepatocytes) using a proprietary N-Acetylgalactosamine (GalNAc) conjugation platform, enhancing uptake and specificity.
Company Perspective
Lindsay Androski, President and CEO of Arbutus, emphasized the clinical potential observed so far, noting that imdusiran has enabled functional cure in a subset of patients and allowed others to discontinue ongoing therapy. She described the FDA’s Fast Track designation as validation of the drug candidate’s importance and indicated the company’s intent to work closely with regulators through the remaining development stages.
Disease Burden and Unmet Need
Chronic hepatitis B remains a major global health challenge. The condition can progress to cirrhosis and liver cancer, contributing to significant mortality. According to global estimates, more than 250 million individuals live with chronic infection worldwide, with approximately 1.1 million deaths annually linked to its complications.
Despite the availability of vaccines and antiviral treatments, current therapies rarely achieve functional cure, underscoring the need for novel approaches such as RNAi-based interventions.
References
About the Writer
Samiksha Vikram Jadhav is a B.Pharm graduate with a strong academic foundation in pharmaceutical sciences, pharmacology, and drug development. She has a keen interest in healthcare advancements, clinical research, medical writing, and emerging therapies. Her work focuses on presenting developments in the pharmaceutical and healthcare sectors through clear and accurate scientific communication.