RAPT Faces 'Unfortunate and Unexpected' Clinical Hold After Liver Failure in Atopic Dermatitis Trial

Rapt Therapeutics is reeling from an “unfortunate and unexpected” clinical hold after a patient in a phase 2 immunology trial experienced liver failure that may be related to the study drug. 

That’s how CEO Brian Wong, M.D., Ph.D., described the turn of events in Tuesday’s press release, adding that Rapt is working to learn more about what happened: “Patient safety is our top priority and we will work with the FDA to resolve this as quickly as possible.”

The serious adverse event occurred in a phase 2b atopic dermatitis trial. The cause remains unknown but Rapt said the event may be “potentially related to zelnecirnon.”

The FDA notified Rapt of the clinical hold on both the phase 2b atopic dermatitis trial and a phase 2a study in asthma. 

Rapt noted that roughly 350 patients have been treated with the drug across three trials and no signs of liver toxicity had been reported before now and there has been no evidence of potential liver toxicity in clinical trials. At the end of November, Rapt published phase 1 data of zelnecirnon which found that the drug was “generally well-tolerated” with no serious adverse events and that all reported side effects were mild-to-moderate. 

Rapt implied that there may be more variables at play with the individual patient beyond just receiving the study drug. The South San Francisco biotech says that the person had a drug allergy to Dupixent, an autoimmune disease requiring thyroid hormone replacement therapy, contracted COVID-19 during the trial and used “an herbal supplement known to be associated with liver failure.” 

That meant little to investors, with the company’s share price nosediving after the markets opened Tuesday, down 64% from $25.97 to $9.25.

Rapt is supposedly just a few months away from reporting interim data, saying in a third-quarter earnings report that initial atopic dermatitis data was expected by the middle of the year. 

With the inflammation program on hold for now, all attention turns to Rapt's phase 2 oncology med, tivumecirnon, which is being tested alone and in a combo with Merck & Co.'s Keytruda.

Rapt reported $184.8 million in cash on hand at the end of September, enough to last into the middle of 2025.