Proof of Concept Study Evaluating the Efficacy and Safety of ATH-063 Treatment in Patients With Relapsed/Refractory Moderately to Severely Active Ulcerative Colitis (UC)

The trial will consist of a 4-week screening period, a 12-week double-blind treatment period, and an open-label extension. Following completion of the 12-week double-blind period, participants who wish to continue into the open-label extension will be unblinded. Participants who do not wish to continue into the extension will remain blinded and proceed to posttreatment follow-up at Weeks 16 and 24 (via telephone calls). Unblinded participants who are revealed to have been randomized to receive ATH-063 will also proceed to posttreatment follow-up at Weeks 16 and 24 (via telephone calls). Unblinded participants revealed to have been randomized to receive placebo will receive open-label ATH-063 150 mg as three 50 mg capsules once daily (QD) from Week 12 to Week 24 with visits at Weeks 16, 20, and 24. At the end of the open-label treatment, these participants will proceed to posttreatment follow-up at Weeks 28 and 36.