FDA Puts Clinical Hold on RAPT Therapeutics’ Lead Candidate in Two Trials

FDA sign_iStock, JHVEPhoto

Pictured: FDA sign at agency's headquarters/iStock, JHVEPhoto

RAPT Therapeutics announced Tuesday that the FDA has placed a clinical hold on a Phase IIb trial of its drug zelnecirnon in atopic dermatitis as well as a Phase IIa trial in asthma.

The regulator’s clinical hold comes after a single patient had a case of liver failure in the atopic dermatitis trial, the cause of which is unknown, according to the company. RAPT said in its announcement that while it expects to receive a formal clinical hold letter from the FDA, the cause “has been characterized as potentially related to zelnecirnon.”

The immunology-based company’s stock price sharply declined Tuesday morning, dropping over 67%.

RAPT said that around 350 patients are enrolled across three trials investigating zelnecirnon and that “no evidence” of liver toxicity was witnessed in any other trial participant or nonclinical studies. Dosing and enrollment have been stopped in the two clinical trials, but the hold does not apply to RAPT’s ongoing trial of tivumecirnon in oncology.

“Patient safety is our top priority, and we plan to work closely with the agency to resolve this as quickly as possible. We expect a formal letter from the FDA with more details, including information needed to lift the hold. This formal feedback will be critical to direct our investigation and identify the best path forward. We are undertaking a thorough investigation of this case,” RAPT CEO Brian Wong said in a Tuesday conference call.

Wong noted on the call that the patient in question had a “particularly complex” medical history, which included having the autoimmune disease Hashimoto’s disease and requiring hormone replacement therapy. He also said the patient had a history of taking a particular herbal supplement, which has been associated with liver failure, while also having an active COVID-19 infection at the time of the event. Wong added that the patient received a liver transplant and is recovering.

“We continue to diligently investigate the matter and work with the agency to resolve the hold as quickly as possible,” Wong said.

Before the clinical hold was announced, analysts were bullish on RAPT.

According to BNN, Wolfe Research last week initiated coverage on RAPT with an “outperform” rating and saw a positive future for the biotech as it anticipated results from a Phase IIb trial. Last week, Seeking Alpha likewise reported that Evercore ISI started coverage with an outperform rating, citing upcoming Phase IIb data.

In November 2023, the Phase Ia/Ib results for zelnecirnon in atopic dermatitis showed that the drug was well tolerated and no serious adverse events were reported.

Tyler Patchen is a staff writer at BioSpace. You can reach him at tyler.patchen@biospace.com. Follow him on LinkedIn.

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