This is a phase I, randomized, double-blind, placebo-controlled, single and multiple ascending dose study to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, food effect of ASC50 tablets in healthy adult participants and adult participants with mild to moderate plaque psoriasis.

Inclusion Criteria:

1. Male and female participants between 18 to 65 years of age inclusive, at the time of screening.
2. Willing and able to give informed consent prior to any study specific procedures being performed.
3. Have venous access sufficient to allow for blood sampling

Exclusion Criteria:

1. Female participants who are pregnant, breastfeeding or plan to be pregnant during the study period and 3 months after last dose.
2. History or presence of any clinically relevant acute or chronic medical or psychiatric condition that could interfere with the subject's safety during the clinical study or expose the subject to undue risk as judged by the Investigator.
3. Have received systemic immunosuppressive therapy (MTX, apremilast, azathioprine, cyclosporine, 6-thioguanine, mercaptopurine, mycophenolate mofetil, hydroxyurea, and tacrolimus) within 4 weeks of first administration of study drug.
4. Have any other conditions, which, in the opinion of the investigator or sponsor, would make the participant unsuitable for inclusion or could interfere with the participant participating in or completing the study.