A Study to Assess the Efficacy and Safety of XP23829 in Subjects With Moderate-to-Severe Chronic Plaque-Type Psoriasis

Study Design : This is a , multi-center, double blind, placebo-controlled, phase 2 (dose-finding) efficacy and safety study in which subjects with moderate-to- severe chronic plaque-type psoriasis will be randomized in a 1:1:1:1 allocation ratio to 1 of 3 active doses of XP23829 or placebo. Approximately 50 subjects will be enrolled into each treatment group. Study Periods: The study includes a 4-week screening phase, a 12-week treatment phase (with 9 weeks of XP23829 or placebo at the maintenance dose), and a 4-week observational post-treatment follow-up phase. A treatment-free follow-up period is designed to evaluate safety and disease relapse and rebound. Specifically, the study periods are as follows: 1. Screening Phase: Weeks -4 through 0 2. Treatment phase included: 1. Titration Phase: Weeks 1 through 3 2. Double-Blind Maintenance Phase: Weeks 4 through 12 3. Post-treatment follow-up: Weeks 13 through 16 Efficacy assessments will be performed in the clinic at Baseline (Visit 2) and at the end of Weeks 2, 4, 8, 12, 14, and 16. Patient-reported outcome measures will be assessed in the clinic at Baseline and at Week 12. Blood samples for pharmacodynamic (PD) assessments will be collected at Baseline and at Weeks 4, 8, 12 and 16. PD assessments will be conducted in all subjects, with the intent of evaluating psoriasis-associated inflammatory markers.