The purpose of this study is to evaluate the study drug, SYX-5219, in a multi-part First-in-Human (FiH) study to be conducted in healthy volunteers and participants with Atopic Dermatitis (AD). The objectives of this study are to determine the safety, tolerability and levels of SYX-5219 in the blood and urine when SYX-5219 is given in each part of the study (SAD, MAD, Food Effect and Participants with AD).
The study will be split into up to 3 parts as follows:
* Part 1 - Single Ascending Dose (SAD) and Food Effect in healthy volunteers
* Part 2 - Multiple Ascending Dose (MAD) in healthy volunteers
* Part 3 - Multiple Dose in Participants with AD - enrolling up to 45 males and females with a confirmed diagnosis of AD of at least 6 months, evaluating multiple dose administrations of SYX-5219 or placebo daily over a period of 42 days.