PRA023 Showing Promise in Both Crohn’s Disease, Ulcerative Colitis

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Prometheus Biosciences is expected to begin phase 3 trials for the treatment in 2023.

New topline data shows PRA023 had strong efficacy and favorable safety data in patients with ulcerative colitis and Crohn’s disease.

Prometheus Biosciences announced the results from the ARTEMIS-UC phase 2 and APOLLO-CD phase 2a studies testing the treatment and will not be moving forward with phase 3 studies in 2023.


The ARTEMIS-UC trial was a 12-week, double-blind, placebo-controlled randomized study evaluating the efficacy and safety of PRA023 in patients with moderate-to-severely active ulcerative colitis who failed conventional or advanced therapy.

The treatment met all primary and ranked secondary endpoints, including clinical, endoscopic, histologic, and patient-reported outcome measures in the initial cohort.

In the trial, all 68 patients treated with PRA023 completed the cohort 1 study, compared to 89.6% (n = 60) in the placebo group.

Of this group, 26.5% reached clinical remission in the PRA023 group, compared to 1.5% of the placebo group.This resulted in a placebo-adjusted clinical remission rate of 25% (P <0.0001).

For secondary endpoints, 36.8% of patients treated with PRA023 achieved endoscopic improvement, compared to 6% of the placebo cohort. This resulted in a placebo-adjusted endoscopic improvement rate of 30.8% on the secondary endpoint (P <0.0001).

The treatment was well-tolerated in the first cohort, with no treatment-emergent serious adverse events, adverse events that led to treatment discontinuation, severe adverse events, opportunistic infections, or infusion reactions in the treatment group.

The only adverse event that occurred in more than 2 patients and was higher in the PRA023 group was COVID-19 infections (n = 5; 7.4% vs. n = 3; 4.5%).


In the 12-week open-label APOLLO-CD study, the investigators examined 55 patients with moderate-to-severely active Crohn’s disease with endoscopically active disease who had failed conventional or biologic therapy.

The patients included were highly refractory with 70.9% of patients previously treated with at least 1 biologic therapy and 52.7% treated with 2 or more biologic therapies.

The results show 26% of patients treated with PRA023 achieved an endoscopic response (P = 0.002) compared to 12% prespecified historical placebo rate.

In addition, 49.1% of patients achieved clinical remission in the PRA023 group (P <0.001) compared to 16% prespecified historical placebo rate.

Once again, the treatment was well-tolerated with no treatment-emergent serious adverse events, adverse events leading to disconsolation, or severe adverse events. There were also no opportunistic infections or infusion reactions reported.

COVID-19, urinary tract infections, Crohn’s disease, anemia, nasopharyngitis, and fatigue occurred in more than 2 patients.

There was also a reduction in the markers of inflammation and fibrosis found between pre-treatment and post-treatment with PRA023, measured by circulating cytokine levels, immunohistochemistry, and gene expression in disease tissue.

“PRA023 has clearly demonstrated clinical proof-of-concept in CD and remarkable efficacy for the treatment of UC,” said Allison Luo, MD, Chief Medical Officer, in a statement. “We are grateful to all of our investigators and patients for their participation and look forward to further evaluating PRA023 in Phase 3 studies with the goal of bringing this promising candidate to the market.”