Assembly Biosciences Falls Short with Hepatitis B Drug in Phase 2 Study


Assembly Biosciences, Inc. provided an update on Nov. 5 of its ongoing Phase 2 extension study, Study 211, examining vebicorvir (VBR, or ABI-H0731) in patients with hepatitis B virus infection. Study 211 is one of the first of its kind to look at whether sustained virologic response (SVR) can be achieved after discontinuing therapy in virologically-suppressed patients who receive at least 12 to 18 months of combination treatment with VBR and a nucleos(t)ide analogue reverse transcriptase inhibitor (NrtI).

According to the company, 22 out of 23 patients who have discontinued treatment with HBeAg negative HBV have relapsed. Sixteen of these individuals relapsed at post-treatment Week 4, three at post-treatment Week 12, and three at post-treatment Week 16. Among the HBeAg positive patients, 17 of 18 relapsed at post-treatment Week 4.

“With the addition of our first-generation core inhibitor, vebicorvir, to NrtI, we were able to drive viral suppression deeper in patients with chronic HBV infection to levels below the limits of our highly sensitive assays for six months or more,” said John McHutchison, AO, MD, Chief Executive Officer and President of Assembly Biosciences. “Patients like these normally face a lifetime of therapy, so we took the pioneering step to test whether their virologic response could be sustained off treatment. As we had previously indicated, we believe an SVR24 rate of at least 15% would have marked a meaningful first advance in HBV finite therapy, but preliminary results have shown that we will fall short of that mark. While we are just beginning to analyze the data and this is not the outcome we were hoping for, we firmly believe it was the right experiment to conduct, and the learnings will inform the field and our ongoing development programs.”

The company’s other two Phase 2 trials, Study 201 and 202, showed that the addition of VBR to NrtI therapy achieved a quicker, deeper level of viral suppression than with NrtI alone.

However, Assembly Biosciences is exploring other use cases for ABI-H0731. In August, the company announced that it had entered a clinical collaboration agreement with Arbutus Biopharma Corporation to evaluate the product, in combination with Arbutus’ proprietary GalNAc delivered RNAi therapeutic AB-729 and NrtI therapy, for the treatment of chronic hepatitis B virus infection.

The companies planned to initiate a randomized, multi-center, open-label Phase 2 clinical trial that explores the safety, pharmacokinetics, and antiviral activity of ABI-H0731, RNAi therapeutic AB-729 and an NrtI. They will be compared to the double combinations of ABI-H0731 with an NrtI and AB-729 with an NrtI.

“Arbutus is focused on discovering and developing a cure for chronic hepatitis B,” said William Collier, President and Chief Executive Officer of Arbutus, at the time of the announcement. “We maintain this can best be accomplished through a combination of agents with different mechanisms of action that target distinct parts of the virus lifecycle. To this end, we are advancing a proprietary portfolio of compounds at various stages of clinical and preclinical development that have the potential to lead to a functional cure with a finite treatment duration.”

ABI-H0731 is a first-generation core inhibitor that is typically administered with NrtI therapy. It has been shown to be well-tolerated and statistically superior in antiviral activity in hepatitis B virus DNA suppression, compared to NrtI therapy alone. 

AB-729 is an RNA interference (RNAi) therapeutic. It targets hepatocytes using Arbutus’ novel covalently conjugated N-acetylgalactosamine (GalNAc) delivery technology. In a Phase 1a/1b clinical trial, AB-729 demonstrated positive preliminary safety and tolerability data.

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