Ph 1a/1b Single Ascending Dose and Multiple Ascending Dose Study of ARQ-234

This is a first-in-human, Phase 1, double-blind, randomized, placebo-controlled, dose-escalation study evaluating ARQ-234. The study is designed to assess the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of ARQ-234 in two populations: healthy volunteers and participants with moderate to severe atopic dermatitis (AD). Healthy volunteers will participate in Single Ascending Dose (SAD) Cohorts 1-5. Participants with moderate to severe AD will be enrolled in SAD Cohorts 6-7, Multiple Ascending Dose (MAD) Cohorts, and a Proof-of-Concept (POC) expansion cohort.