Recently, Gilead Sciences officially relinquished its development rights to ABI-4334 , a novel antiviral drug candidate for hepatitis B that is currently in Phase 1 clinical trials , returning all rights to the original developer, Assembly Biosciences.

The development of ABI-4334 began at Assembly Biosciences. It is a next-generation capsid assembly regulator whose core mechanism of action is to inhibit the capsidation of hepatitis B virus pregenomic RNA and disrupt the capsid that enters hepatocytes, thereby preventing the formation of covalently closed circular DNA (cccDNA).

Gilead's collaboration with Assembly began in October 2023, when Gilead paid a $100 million upfront payment for priority access to all of Assembly's existing and future projects, with a 12-year cooperation period . Subsequently, in December 2023, the two companies further deepened their collaboration, with Gilead acquiring two of Assembly's recurrent genital herpes (HSV) treatment products for $35 million. ABI-4334, as a key hepatitis B research project under Assembly, was naturally included in the collaboration, and Assembly advanced it to Phase Ib clinical trials in 2024.

Based on the published Phase Ib clinical data, ABI-4334 demonstrated good safety and potent antiviral activity . Assembly Biosciences released a statement on June 25, 2025, through GLOBE NEWSWIRE, disclosing the positive top-line results of the drug's clinical trials.

Significant decreases in HBV DNA were observed during the 28-day treatment period in both the 150 mg and 400 mg daily oral dose cohorts, with a mean decrease of 2.9 log10 IU/mL in the 150 mg dose group and a mean decrease of 3.2 log10 IU/mL in the 400 mg dose group. The treatment was well-tolerated, with no serious adverse events reported and no discontinuation of treatment due to treatment-related adverse events. Pharmacokinetic data also supported once-daily oral administration.

Furthermore, detailed clinical data presented at the 2025 American Association for the Study of Liver Diseases (AASLD) Annual Meeting showed that ABI-4334 demonstrated stable efficacy in different populations , with significant reductions in viral load in both HBeAg-negative and HBeAg-positive subjects. Moreover, the drug exposure in the 400 mg dose group far exceeded the target level required to inhibit cccDNA formation, indicating its potential for further development into a combination therapy.

Despite positive clinical data, Gilead chose to relinquish the development rights to ABI-4334, likely due to a shift in the company's R&D strategy . As a global leader in antiviral drugs, Gilead's approach to hepatitis B has recently focused on " core competencies and pipeline optimization ." Currently, Gilead has the marketed hepatitis B drug Vemlidy (tenofovir alafenamide, TAF), which is projected to generate approximately $1 billion in global sales in 2024, making it a crucial pillar of the company's liver disease business.

Meanwhile, Gilead has not withdrawn from the hepatitis B field, but has shifted its research and development focus to other paths . For example, through a long-term collaboration with Hookipa Pharma, it is advancing the Phase Ia/Ib clinical trial of HB-400, an HBV therapeutic vaccine based on the arenavirus platform, and will pay $10 million in 2025 to acquire the rights to the relevant project.

In conclusion , Gilead's decision to abandon ABI-4334 is a microcosm of the "survival of the fittest" phenomenon in the biopharmaceutical industry. Even in popular treatment areas, positive early data does not guarantee commercial success. For the long race to cure hepatitis B, setbacks may simply be necessary detours on the way to the finish line. The turning point in ABI-4334's fate may be a new starting point for it to find a more suitable development path.

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