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Hepatitis B: can GSK’s bepirovirsen deliver functional cure?
GSK’s antisense oligonucleotide is looking to further prove its value in disrupting viral replication via a Phase III test.
By Urtė Fultinavičiūtė
Last month, GSK provided an early look at positive Phase IIb data that got the hepatitis B field excited. Results show that bepirovirsen could potentially lead to functional cure, which means that the candidate lowered hepatitis B surface antigen (HBsAg) to undetectable levels.
The Phase IIb data is a “major breakthrough,” says Dr Pietro Lampertico, professor of gastroenterology at the University of Milan. This is the first time in a decade whereby a new candidate was able to show lowered HBsAg to undetectable levels after weeks of treatment, Lampertico explains.
With GSK gearing to initiate a Phase III bepirovirsen trial in the first half of 2023, this is the first time an antisense oligonucleotide candidate would be investigated at this stage. It’s also been years since a new hepatitis B agent would be studied at Phase III, notes Dr Jordan Feld, senior scientist at Toronto General Hospital Research Institute.
As such, all eyes are on GSK on how it will design its forthcoming study, and if the asset’s efficacy profile sustains in the next development stage.
While there is initial positive Phase IIb data, more results from this study are needed. Experts say there are still questions about the candidate’s potential for durable efficacy, as well as concerns around liver inflammation. There are also doubts if bepirovirsen, by itself, would deliver functional cure for many.
Phase IIb hepatitis B data has caveats
GSK, formerly GlaxoSmithKline, presented positive interim analysis at this year’s EASL Liver Congress from the Phase IIb B-clear trial (NCT04449029) investigating bepirovirsen in treatment-naïve patients and ones already taking nucleotide analogues (NA). In the trial’s secondary endpoint, 28% of patients on NA (n=68) and 29% of treatment-naïve participants (n=70) experienced lowered HBsAg and hepatitis B virus (HBV) levels with 300mg bepirovirsen at the end of the 24-week treatment. NAs suppress HBV to undetectable levels but must be taken long term, if not indefinitely.
Final B-clear data is expected later this year. Phase IIb investigator Dr Man-Fung Yuen notes the asset’s potential for durable efficacy at 48 weeks after the first dose, which is the trial’s primary endpoint, will be a key efficacy indicator.
Dr Man-Fung Yuen, hepatology professor at the University of Hong Kong and B-clear trial principal investigator
Bepirovirsen is likely to have some lingering efficacy impact after the therapy is stopped, notes Yuen, who is also a hepatology professor at the University of Hong Kong. “I would be comfortable to say that the sustained effects would last for at least six months after stopping the therapy,” he says.
In a Phase IIa trial (NCT03020745), declined HBsAg levels rebounded after two weeks but participants received a lower dose than in the Phase IIb. The best performing Phase IIa cohort in terms of durability was given the drug once weekly at 120mg for 12 weeks. In Phase IIb, the positive data was from patients given a 300mg weekly dose at 24 weeks.
Even if B-clear durability data is positive, it would still be too early for efficacy conclusions, says Dr Way-Kay Seto, clinical professor, School of Clinical Medicine, at the University of Hong Kong. The Phase IIb data is too small, he adds. While the Phase IIb had 457 patients, it had multiple arms investigating different doses.
There are also side-effect questions that need to be addressed. Phase IIb data shows an increase in alanine aminotransferase (ALT), which is a marker for liver inflammation. ALT flares can occur due to drug-induced injury or the immune system attacking the virus in the liver, Yuen explains. In the latter, the larger the HBsAg drop, the higher chance of an ALT flare, he adds. Regardless of what causes the flare, liver damage is still a risk, and thus patients need extensive monitoring, he notes.
A GSK spokesperson says, in the Phase IIb, treatment-related serious adverse events (AEs) were observed in less than 1% of patients receiving NA and 1% of treatment-naïve patients, with no clinically meaningful differences in AEs across treatment arms. |
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