GSK reports 19% functional cure rate for near-approval hepatitis B drug

The placebo-controlled trials assessed the ability of bepirovirsen, an antisense oligonucleotide targeting hepatitis B transcripts, to cause functional cures in adults with noncirrhotic chronic infections. Across the two studies, GSK randomized more than 1,800 people to receive subcutaneous bepirovirsen or placebo weekly for 24 weeks.

After 72 weeks, 19% of patients who received bepirovirsen across the two trials met the functional cure criteria, compared to 0% of people on placebo. With cure rates of 19% and 20% in the two studies, both trials met their primary endpoints. GSK reported hits on the primary endpoints in January, but deferred the release of the data until the European Association for the Study of the Liver (EASL) Congress. 

The results compare favorably to expectations, with the cure rate exceeding the 16% seen in a similar population of patients in a Phase II trial. The company was targeting a 15% to 20% functional cure rate in Phase III, Tony Wood, GSK’s chief scientific officer, said at the J.P. Morgan Healthcare Conference in January. 

Commercial prospects

A survey of 29 physicians by Guggenheim Securities analysts suggests the cure rate is high enough to fuel bepirovirsen sales. In a note posted in January, the analysts said 86% of physicians would prescribe the molecule to at least 26% of their eligible patients if it achieved a cure rate of 16% to 25% in the Phase III program. More than 30% of physicians said they would prescribe the drug to at least half their patients.

The analysts estimate about 40% of chronic hepatitis B patients could be eligible for treatment with the antisense oligonucleotide. Currently, physicians use nucleoside or nucleotide analog therapy and pegylated interferon to suppress replication of the virus and reduce the risk of cirrhosis and liver cancer. However, the drugs fail to eradicate the virus or the risk of liver cancer. 

Earlier this month, the analysts forecast £1.3 billion (€1.5 billion) in risk-adjusted 2033 bepirovirsen sales, compared to the £500 million consensus estimate of their peers. The analysts were waiting on the EASL data to validate their forecast. GSK has forecast non-risk adjusted peak year sales of more than £2 billion.

The FDA has accepted a filing for approval of bepirovirsen for review, positioning GSK to secure clearance to launch the drug in the US in late October. GSK licensed the drug candidate from Ionis Pharmaceuticals for $25 million upfront in 2019. The deal is worth up to $260 million, including milestones. GSK recently paid Ionis $15 million because the European Medicines Agency accepted bepirovirsen for review.