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

Prior treatment

• Have had a clinically significant flare of psoriasis during the 12 weeks before the Baseline visit, as assessed by the Investigator
• 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
• 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
• Systemic use of known strong and moderate cytochrome P450 (CYP)3A4 inhibitors or strong CYP3A4 inducers from Screening through the end of the study

Other illness

• 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 of malignancy or lymphoproliferative disease except resected cutaneous squamous cell or basal cell carcinoma that has been treated without recurrence
• 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)

Lab values

• 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

• 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