A Study to Assess the Safety and Effectiveness of COL-5671-PRO Capsules in Adults With Moderate-to-Severe Plaque Psoriasis

Prior treatment

• Participant had a major surgery within 8 weeks prior to the first dose or has a major surgery planned during the trial.

Other illness

• Participant has a positive result for hepatitis B virus (HBV) (positive for hepatitis B surface antigen \[HBsAg\] or detectable hepatitis B virus core antibody (HBcAb\]; participants having a negative HBsAg and a positive HBcAb result may enroll if they have a positive hepatitis B virus surface antibody \[HBsAb\] demonstrating natural immunity), or for hepatitis C virus (HCV) (positive for HCV antibody \[Ab\] and positive confirmatory polymerase chain reaction test for HCV; however, a participant with documented proof of cure from HCV may be enrolled).
• Participant has a history of human immunodeficiency virus (HIV) Ab positivity, or tests positive for HIV at screening.
• Participant has a history of or current immunosuppressive condition.
• Participant meets 1 of the following tuberculosis (TB) criteria at screening:
  • A history of active or currently active TB (regardless of treatment).
  • A positive QuantiFERON®-TB Gold Plus In-tube test at screening unless the investigator assesses this is due to a documented history of adequately treated latent TB infection (LTBI).
• Participant has evidence of skin conditions other than psoriasis (e.g. eczema) at the time of screening or baseline visit that would interfere with the evaluation of psoriasis, per investigator judgement.
• Participant has a history of malignancy within the past 5 years prior to screening with the exception of excised and curatively treated non-metastatic basal cell carcinoma or squamous cell carcinoma of the skin or in situ uterine cervical carcinoma which is considered cured with minimal risk of recurrence.

Lab values

• Candidate has current drug-induced psoriasis (e.g. a new onset of psoriasis or an exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium).
• Participant has a history or presence of clinically significant abnormalities detected on 12-lead ECG at screening or either rhythm or conduction, e.g. known long QT syndrome, or a QT interval corrected for heart rate using Fridericia's formula (QTcF) \>450 ms for male participants or \>470 ms for female participants detected on the 12-lead ECG.

Other

• Candidate has non-plaque form of psoriasis (e.g. erythrodermic, guttate, or pustular psoriasis).

• Participant must be able and willing to comply with the clinical trial protocol requirements and must sign and date the informed consent form(s) as approved by the IEC/IRB prior to any screening evaluation and, if applicable, prior to participating in the optional skin biopsy subtrial.
• Diagnosed with plaque psoriasis, with stable psoriatic arthritis or without psoriatic arthritis, ≥6 months prior to screening.
• Participant has had stable plaque psoriasis ≥3 months before screening
• Screening and baseline PASI score ≥12 (moderate to severe) with affected BSA ≥10% and sPGA score ≥3.
• Candidate for phototherapy or systemic treatment for plaque psoriasis.
• Participant must have a Body Mass Index of ≥18 and ≤39 kg/m\^2.
• Participant must be able and willing to comply with restrictions on prior and concomitant medication.
• Participant must be able and willing to adhere to the lifestyle restrictions as described in the protocol.
• Participant with plaque psoriasis, that according to the investigator's judgement is not adequately controlled with his/her current therapy.
• Participant must be otherwise stable on the basis of medical history, physical examination, vital signs, and 12-lead Electrocardiogram (ECG) performed at screening.