Rapt Therapeutics, Inc. (RAPT) saw its stock plummet by over 46% on Monday after the company announced the termination of its zelnecirnon (RPT193) program due to a serious adverse event (SAE) of liver injury. The program was being investigated in two Phase 2 clinical trials for asthma and atopic dermatitis, but both trials were placed on FDA clinical hold in February 2024. This decision followed a liver injury requiring a transplant in a patient participating in the atopic dermatitis trial. The company subsequently closed both studies and discontinued the zelnecirnon program, highlighting the challenges faced in drug development due to safety concerns. Rapt Therapeutics is now focusing on developing next-generation CCR4 compounds with improved safety profiles.