Alpha-0261 Tablets for Moderate-to-Severe Ulcerative Colitis

Inclusion Criteria: * Aged 18 to 75 years (inclusive), male or female. * Diagnosed with ulcerative colitis at least 3 months prior to screening; this diagnosis must be confirmed by endoscopy or histology. * Patients must have moderate-to-severe active ulcerative colitis, as defined by an mMS score of 4 to 9 (blood in stool subscore ≥ 1, frequency of bowel ovements subscore ≥ 1, and colonoscopy subscore ≥ 2 \[as confirmed by the study site's image reviewer\]; the sum of these three subscores must be at least 4). * The investigator determines that the participant has had an inadequate response to or is intolerant of at least one conventional therapy aminosalicylates, corticosteroids, or immunosuppressants) or a biologic agent (anti-TNF-α, anti-α4β7 integrin, or anti-IL-12/23 antibodies, etc.). * Voluntarily sign the informed consent form and be willing to comply with the study procedures and complete the trial in accordance with the protocol. Exclusion Criteria: * Has a diagnosis of Crohn's Disease (CD) or indeterminate colitis (inflammatory bowel disease (IBD)-undefined) or other types of colitis or enteritis that may confound efficacy assessment * Has a current diagnosis of fulminant colitis and/or toxic megacolon * Has UC limited to the rectum * Has a history of or is anticipated to require surgical intervention for ulcerative colitis during the study, including but not limited to ostomy, ileal pouch-anal anastomosis, and intestinal resection. * Has any active infection as specified in the protocol * Is known to be infected with hepatitis B virus (HBV), hepatitis C virus (HCV), or human immunodeficiency virus (HIV) * Has evidence of active tuberculosis (TB) or meets TB exclusionary parameters * Has a history of cancer (except fully treated nonmelanoma skin cell cancers or cervical carcinoma in situ after complete surgical removal) and is disease free for \<5 years before Randomization * Has had major surgery within 4 weeks before Screening or has a major surgery (ie, surgical procedure requiring general anesthesia) planned during the study * Has received protocol-specified prohibited medications