Phase 2a Evaluation of Safety, Tolerability, and Pharmacokinetics of PLN-74809 in Patients With Primary Sclerosing Cholangitis (PSC)

Inclusion Criteria: * Established clinical diagnosis of large duct PSC based on an abnormal cholangiography as assessed by magnetic resonance cholangiopancreatography (MRCP), endoscopic retrograde cholangiopancreatography (ERCP), and/or percutaneous transhepatic cholangiopancreatography (PTC) in the context of cholestatic liver chemistry * Suspected liver fibrosis, as defined by liver stiffness measurement (LSM), assessed by ultrasound-based transient elastography (TE, FibroScan®) OR Enhanced Liver Fibrosis (ELF) Score OR Historical liver biopsy showing fibrosis without cirrhosis (by any scoring system) OR Magnetic resonance elastography (MRE) * Serum ALP concentration within normal limits or \> 1 times the upper limit of normal (ULN) * Participants receiving treatment for IBD are allowed, if on a stable dose from screening and expected to remain stable for the duration of the study * Serum AST and ALT concentration ≤ 5 times the upper limit of normal * If receiving treatment with UDCA, therapy is at a dose of \< 25 mg/kg/day, has been stable for at least 3 months before screening. Exclusion Criteria: * Other causes of liver disease, including secondary sclerosing cholangitis or viral, metabolic, or alcoholic liver disease, as assessed clinically * Known or suspected overlapping clinical and histologic diagnosis of autoimmune hepatitis * Small duct PSC with no evidence of large duct involvement (evidence of PSC on historical liver histology, with normal bile ducts on cholangiography) * Presence of liver cirrhosis as assessed by liver histology, ultrasound-based liver stiffness measurement, ELF score, MRE, and/or signs and symptoms of hepatic decompensation (including but not limited to, jaundice, ascites, variceal hemorrhage, and/or hepatic encephalopathy. * Serum ALP concentration \> 10 times the upper limit of normal.