Merck’s IBD Drug from $10.8B Prometheus Deal Claims First Phase 3 Win

Merck has scored its first Phase 3 win for its inflammatory bowel disease (IBD) drug stemming from its $10.8 billion acquisition of Prometheus Biosciences in 2023.

The anti–TL1A biologic, now called tulisokibart (formerly PRA023/MK-7240), met its primary endpoint of clinical remission at 12 weeks in the Phase 3 ATLAS‑UC induction study in patients with moderately to severely active ulcerative colitis (UC).

All key secondary endpoints were also met, and the safety profile was consistent with earlier Phase 2 data, which showed 26% of patients on the drug achieving clinical remission versus 1% on placebo.

Merck describes these as the first positive Phase 3 induction results for an anti‑TL1A biologic, giving it a first‑mover edge in a competitive IBD class also targeted by rivals such as Roivant Sciences.

This win comes from the pipeline assets acquired in the Prometheus deal, where PRA023 was already considered a late‑stage, Phase 3‑ready candidate for UC and Crohn’s disease.