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.
This study will investigate the efficacy, safety, pharmacokinetics and pharmacodynamics of single oral administration of 5 mg, 15 mg, 20 mg and 25 mg of SSS17 compared with placebo, and evaluate the efficacy, safety, tolerance, pharmacokinetics and pharmacodynamics of multiple oral administration of 15 mg and 20 mg of SSS17 compared with placebo. In addition, the study will assess the effect of food on the pharmacokinetics of SSS17.