RAPT Therapeutics’ CEO Brian Wong said there was no “viable path forward” for the compound. Image credit: Shutterstock/Andrii Yalanskyi.

RAPT Therapeutics has called it quits on a clinical programme evaluating zelnecirnon (RPT193) in inflammatory disorders following feedback with the US Food and Drug Administration (FDA).

The agency previously placed two trials using the drug on clinical hold in February this year due to a serious adverse event (SAE), which required a patient to undergo a liver transplant following injury to the organ. RAPT Therapeutics stated that following feedback recently received from the FDA, it has stopped the programme.

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“In light of the agency’s feedback, we do not see a viable path forward for zelnecirnon,” the immunology company’s CEO Brian Wong said in a statement.

Shares in the Nasdaq-listed company were down 48% at market open on 11 November compared to a pre-announcement market close. RAPT has a market cap of $54.3m.

RAPT announced plans to shelve the two Phase II clinical trials in May, three months after the clinical hold. The Phase IIa (NCT05935332) and Phase IIb trial (NCT05399368), which were evaluating the CCR4 antagonist in patients with asthma and atopic dermatitis respectively, have now been formally terminated as part of the programme’s end.

CCR4 is expressed by several immune cells such as T helper 2 (TH2) cells, regulatory T cells (Tregs), mast cells, and skin-homing lymphocyte Ag–positive T cells. Inhibiting the protein results in a dampened inflammatory response in patients with inflammatory disorders, though its exact functional pathway is unknown.

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Wong added that RAPT believes CCR4 remains a promising target for an oral therapeutic option across multiple inflammatory diseases. The company highlighted that no liver toxicity nor other treatment-related SAEs were reported in any other trial participant taking zelnecirnon.

“We plan to continue advancing our next generation CCR4 compounds with improved safety margins for inflammatory disease and expect to identify a new candidate in the first half of 2025,” Wong said.

Zelnecirnon falling by the wayside means the biotech’s sole remaining clinical-stage asset is tivumecirnon (FLX475), also a CCR4 antagonist. The therapy is being tested alone and in combination with MSD’s blockbuster cancer treatment Keytruda (pembrolizumab). Earlier this year, RAPT shared results from 32 patients enrolled in the Phase II trial (NCT03674567), demonstrating an objective response rate (ORR) of 15.6%.

Wong added: “We continue to actively pursue in-licensing opportunities for clinical-stage assets.”