RAPT Therapeutics' stock plunges as FDA halts two clinical trials

By Eleanor Laise

Liver failure in trial participant prompts regulator's intervention

RAPT Therapeutics Inc. shares (RAPT) dropped more than 60% premarket on Tuesday after the company said regulators have hit pause on two clinical trials of its experimental inflammation treatment due to liver failure in a trial participant.

The U.S. Food and Drug Administration has verbally notified RAPT that a clinical hold has been placed on two trials of zelnecirnon, one in atopic dermatitis and the other in asthma, the company said in a release Tuesday. RAPT said it expects to receive a formal clinical hold letter from the FDA, meaning the company must pause the trials.

The regulator's decision was based on "a serious adverse event" of liver failure in one patient participating in the atopic dermatitis trial, RAPT said. The cause of the liver failure is not known, but it "has been characterized as potentially related to zelnecirnon," the company said. There has been no evidence of liver toxicity in any other trial participants, the company said.

"RAPT is undertaking a thorough investigation of this case," the company said, which involved a patient with a complex medical history. Dosing of zelnecirnon and enrollment of new participants has been halted in both trials, the company said.

"Patient safety is our top priority and we will work with the FDA to resolve this as quickly as possible," Dr. Brian Wong, president and chief executive of RAPT, said in a statement.

Zelnecirnon is one of two lead assets for RAPT, which is also developing an experimental cancer treatment.

The experimental inflammation drug was seen as having "pipeline-in-a-product" potential, Goldman Sachs analysts wrote in a report late last year, meaning it could be effective in treating a range of conditions. But RAPT would need a partner to help develop zelnecirnon and move it to phase 3 trials, the analysts wrote.

RAPT shares are down 12.2% in the past 12 months, while the S&P 500 SPX has gained 22.7%.

-Eleanor Laise

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02-20-24 0836ET

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