This Phase IIa, multicenter, single-arm trial evaluates the efficacy, safety, tolerability, and pharmacokinetics of PTT-621 tablets in adults (18-70 years) with moderate-to-severe active ulcerative colitis (UC) who have inadequate response/intolerance to standard therapies. Participants receive PTT-621 for 12 weeks. The primary endpoint is the proportion of participants achieving endoscopic improvement at Week 12. Secondary endpoints include safety, clinical remission, clinical response, symptom response, pharmacokinetics, and inflammatory biomarkers. The study is sponsored by Pyrotech Therapeutics, with ethical approval from Renji Hospital's IRB.
1. Male or female participants aged 18-70 years inclusive at screening. 2. Diagnosed with ulcerative colitis (UC) at least 60 days prior to the first dose of IP.
1. A current diagnosis of Crohn's disease (CD), indeterminate colitis, infectious colitis, or any other colitis/enteritis that could interfere with efficacy evaluation； 2. Has UC complications (e.g., fulminant colitis, toxic megacolon, prior total or partial colectomy, or other conditions requiring surgery)； 3. Prior or current gastrointestinal dysplasia； 4. History of gastrointestinal malignancy, or any current evidence of gastrointestinal cancer.