Assembly Biosciences’ shares were dragged down more than 20% Wednesday evening after the biotech was forced to toss out a midstage hepatitis B treatment due to safety concerns.
The biotech will now stop work on the experimental treatment, known as ABI-H2158, after it increased liver toxicity in a phase 2 trial that was focused on previously untreated patients with HBeAg-positive or HBeAg-negative chronic hepatitis B (HBV) infection without liver scarring.
Assembly said in a statement that “elevated ALT levels consistent with drug-induced hepatotoxicity” were seen in the test. Two patients on the med saw Grade 4 elevations in ALT, a biomarker that can show liver damage, leading them to stop taking the drug.
two patients saw Grade 3 ALT elevations. “No alternate causes for the ALT elevations have been identified, and these four patients continue to be closely monitored,” the biotech said. The study has been voluntarily stopped and Assembly has told the FDA, with the agency swiftly slapping a clinical hold on it anyway.
“Patient safety is always our priority, which is why we have elected to discontinue the development of 2158,” said John McHutchison, M.D., chief and president of Assembly.
This comes 10 months after Assembly saw a flop for another midstage HBV hopeful vebicorvir. The therapy failed to hit sustained virologic response in an open-label phase 2 trial in chronic HBV patients in combination with an older med, missing the primary endpoint.
Assembly had touted the drug as a possible cure for HBV in a combo setting but had to rethink those plans. Vebicorvir is now being considered as a chronic rather than curative treatment. New data from that med are expected next year, with the biotech funneling more cash into that drug and other pipeline assets, from the now defunct ‘2158 program.
“We remain committed to our pursuit of developing finite and curative therapies for individuals with chronic hepatitis B, and our strategy remains unchanged,” McHutchison said. “We will continue to evaluate our core inhibitor portfolio, to ultimately choose the best and safest candidate to take forward into later stage clinical trials as we believe this mechanism will be an important and key component of future curative regimens.”
Analysts at Jefferies said, “in our view, [the dropping of the drug] has no read across to the rest of the pipeline including lead drug vebicorvir.”
Shares in the company opened down 21% in premarket trading Thursday morning.