Phase 2 bowel disease data fire Prometheus' stock up 170% and set bar for Pfizer, Roivant

Prometheus Biosciences has laid down a major marker in the anti-TL1A space. Days after Pfizer offloaded its rival candidate to Roivant, Prometheus has reported midphase data in ulcerative colitis and Crohn’s disease that sent its stock up 170% in premarket trading.

Evidence that TL1A modulates the location and severity of inflammation and fibrosis led researchers to identify the protein as a way to treat inflammatory bowel disease. Prometheus and Pfizer are leading the push to validate that idea in the clinic. And, as the pair has moved in parallel toward midphase data, the biotech has maintained that its asset has an edge in terms of target engagement and bioavailability. 

Now, Prometheus has data to support its claims. The update covers two trials, ARTEMIS-UC in ulcerative colitis and APOLLO-CD in Crohn’s. Both studies met their primary endpoints—and by an extent that sent Prometheus’ stock spiraling upward. 

In the ulcerative colitis trial, 26.5% of recipients of the anti-TL1A antibody PRA023 went into clinical remission by Week 12 compared to 1.5% of their peers on placebo. The study also met all of its ranked secondary goals, linking PRA023 to improvements in clinical, endoscopic, histologic and patient-reported outcome measures. Almost 37% of patients had endoscopic improvement, versus 6% in the placebo arm.

The Crohn’s trial lacked a control arm but provides early evidence that PRA023 can improve outcomes in patients with endoscopically active disease failed by existing therapies. Around one-quarter, 26%, of patients had endoscopic response, and 49% entered clinical remission. Prometheus compared the data favorably to historical placebo endoscopic and clinical remission rates of 12% and 16%, respectively.

Exactly how good the results are will become clearer when Pfizer and Roivant show their hand. Pfizer has completed the induction period of the midphase TUSCANY-2 study of its rival antibody PF-06480605 but is yet to share data. Roivant has formed a new subsidiary for further development of the Pfizer prospect. 

Durability will be important for both programs, but for now, Prometheus, armed with its efficacy data and a fairly clean safety profile, can bask in the success of the induction studies. Shares in the biotech rose more than 200% at points during premarket trading. At the time of writing, the stock is up around 170% at close to $100. 

The data emboldened Prometheus to set out plans to move PRA023 into phase 3 clinical trials in Crohn’s and ulcerative colitis next year following talks with regulators about the designs of the studies.