A Study to Evaluate the Efficacy and Safety of DC-806 in Participants With Moderate to Severe Plaque Psoriasis

Key Inclusion Criteria:

• Male or female, 18 to 70 years of age
• Body mass index (BMI) of 18 to 40 kg/m2
• All of the following psoriasis criteria:

• Clinical diagnosis of plaque psoriasis for ≥6 months before the Baseline visit
• Stable moderate to severe chronic plaque psoriasis, defined as ≥10% BSA psoriasis involvement, sPGA score of ≥3, and PASI score ≥12 at the Screening and Baseline visits
• Candidate for phototherapy or systemic therapy, as assessed by the Investigator
• Women of childbearing potential (WOCBP) and men who are sexually active with WOCBP must be willing to use a highly effective method of contraception during the study and for ≥30 days after the last dose of study drug
• Willing to discontinue topical and/or systemic therapies for psoriasis before the first dose of study drug

Key Exclusion Criteria:

• Have had a clinically significant flare of psoriasis during the 12 weeks before the Baseline visit, as assessed by the Investigator
• History of erythrodermic psoriasis, generalized or localized pustular psoriasis, predominantly guttate psoriasis, medication-induced or medication-exacerbated psoriasis
• History of chronic infections including human immunodeficiency virus (HIV) or viral hepatitis (hepatitis B virus [HBV], hepatitis C virus [HCV])
• History of active tuberculosis (TB)
• History or evidence of active infection (including but not limited to coronavirus disease 2019 [COVID-19] infection) and/or febrile illness within 7 days, serious infections leading to hospitalization and intravenous antibiotic treatment within 90 days, or serious infection requiring antibiotic treatment within 30 days before the first dose of study drug
• History of malignancy or lymphoproliferative disease except resected cutaneous squamous cell or basal cell carcinoma that has been treated without recurrence
• Presence of active suicidal ideation, or positive suicide behavior using the "Baseline/Screening" version of the Columbia Suicide Severity Rating Scale (C-SSRS) and with either of the following criteria:

• History of suicide attempt (including an actual attempt, interrupted attempt, or aborted attempt) within 5 years before the Screening visit
• Suicidal ideation in the past month before the Screening visit as indicated by a positive response ("Yes") to either Question 4 or Question 5 of the "Baseline/Screening" version of the C-SSRS
• Participant has experienced primary failure (no response at approved doses after ≥3 months of therapy) to one or more therapeutic agents targeted to IL-17 (including but not limited to secukinumab, ixekizumab, brodalumab, bimekizumab)
• Systemic use of known strong and moderate cytochrome P450 (CYP)3A4 inhibitors or strong CYP3A4 inducers from Screening through the end of the study
• A 12-lead electrocardiogram (ECG) at Screening that demonstrates clinically significant abnormalities or criteria associated with QT interval abnormalities including prolongation of QT interval corrected for heart rate using Fridericia's formula (QTcF) (>500 msec)
• Laboratory values meeting the following criteria within the screening period before the first dose of study drug:

• Serum aspartate transaminase ≥2× upper limit of normal (ULN)
• Serum alanine transaminase ≥2×ULN
• Serum total, direct, or indirect bilirubin ≥2.0 mg/dL; except for participants with isolated elevation of indirect bilirubin relating to a confirmed diagnosis of Gilbert syndrome
• Estimated glomerular filtration rate (GFR) by simplified 4-variable Modification of Diet in Renal Disease (MDRD) formula <45 mL/min/1.73m2
• Total white blood cell count <3000/μL
• Absolute neutrophil count <1500/μL
• Platelet count <100,000/μL
• Hemoglobin <9 g/dL
• In the opinion of the Investigator or Sponsor, have any uncontrolled clinically significant laboratory abnormality that would affect interpretation of study data or the participant's enrollment in the study