A Phase 1 Study of SSS17 in Healthy Subjects.

The study will enroll healthy volunteers from a single academic medical center in China. All participants will be informed about the study and potential risks and required to provide written informed consent prior to undergoing study-related procedures.The study will be divided into 3 parts. Part 1: Subjects will be allocated 2:8 to receive placebo or SSS17（it was only 2:2 in 5mg dose group）,which will be administered by oral route with single dose. At each dose, tolerability, safety, PK and PD characteristics will be investigated. Part 2: Subjects will be allocated 2:8 to receive placebo or SSS17, which will be administered by oral route with multiple dose. At each cohort，tolerability, safety, PK and PD characteristics will be investigated. Part 3: The subjects will receive two cycles of treatment, one is given on an empty stomach, the other is given after a high-fat meal, with an interval of 15 days.