Why Is Inflammatory Disease/Oncology-Focused RAPT Therapeutics Shares Tumbling Today?

Tuesday, the FDA verbally notified RAPT Therapeutics Inc RAPT that a clinical hold has been placed on the company’s Phase 2b trial of zelnecirnon (RPT193) in atopic dermatitis and its Phase 2a trial in asthma. 

RAPT Therapeutics anticipated reporting top-line data from the Phase 2b trial of zelnecirnon in atopic dermatitis in mid-2024.

The company expects to receive a formal clinical hold letter from the FDA. 

The clinical hold determination was based on a serious adverse event of liver failure in one patient in the atopic dermatitis trial, the cause of which is currently unknown but has been characterized as potentially related to zelnecirnon. 

Dosing of zelnecirnon has been halted in both clinical trials, as has enrollment of new trial participants. 

The clinical hold does not apply to RAPT’s ongoing trial of tivumecirnon (FLX475) in oncology.

Approximately 350 patients have been enrolled across three trials evaluating zelnecirnon – the two Phase 2 trials and an earlier Phase 1a/1b study. 

The company says that no evidence of liver toxicity has been observed with any other trial participant. Additionally, no evidence of liver toxicity was observed in nonclinical studies.

RAPT is undertaking a thorough investigation of this case, which involved a patient with a complex medical history, including a history of drug allergy to dupilumab, an autoimmune disease resulting in thyroid hormone replacement therapy and use of an herbal supplement known to be associated with liver failure, as well as a reported COVID-19 infection during the time of the event.

Price Action: RAPT shares are down 65.7% at $8.9 on the last check Tuesday.