A Phase 1/1b Study to Evaluate Safety, Tolerability and Pharmacokinetics of ZL-1503 in Healthy Volunteers and Participants With Moderate to Severe Atopic Dermatitis

Inclusion criteria

• Part A:
• Healthy male and female volunteers, 18-65 years of age
• Body mass index (BMI) between ≥ 18.5 and \< 32.5 kg/m2
• Negative pregnancy tests for women of childbearing potential.
• Part B:
• 18-65 years of age;
• BMI between ≥18.5 and \<40.0 kg/m2
• Have a diagnosis of AD at least 12 months prior to Day 1;
• Moderate-to-severe AD at Screening and Baseline visit, defined as:
• Eczema Area and Severity Index (EASI) score ≥ 16;
• Affected Body Surface Area (BSA)≥ 10%;
• vIGA-AD™ score ≥ 3
• History of an inadequate response to treatment with topical medications
• Average peak pruritus numeric rating scale (PP-NRS) score ≥4 in the 7 days before randomization.
• Negative pregnancy tests for women of childbearing potential.

Exclusion criteria

• Part A and B:
• Significant health issues, such as positive tests for human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B surface antigen (HBsAg), active tuberculosis, immunodeficiencies or autoimmune diseases.
• History of major metabolic, liver, kidney, hematologic or other significant disorders.
• Abnormal Electrocardiogram (ECG) findings
• Clinically relevant abnormal lab results, including low blood counts, or abnormal liver and kidney function.
• History of drug abuse or addiction within 6 months prior to screening
• Current smoker or use of any nicotine or tobacco containing products within the last 6 months prior to dosing.
• Donated \>500mL blood within 2 months of dosing.
• For Part B only:
• Presence of dermatologic conditions and/or comorbidities that might confound the diagnosis of AD and/or might interfere with study assessments.
• Uncontrolled chronic disease that might require bursts of oral corticosteroids.
• Any other sound medical, psychiatric, and/or social reason as determined by the investigator.