• To quantitatively analyze the total radioactivity (TRA) in excrement after a single oral dose of [14C] D-1553 in healthy subjects, and obtain radioactivity recovery and primary excretion pathways in humans;
• To obtain radioactive metabolite profiles of human plasma, urine and feces , identify major metabolites of D-1553 and determine the major metabolic pathways and elimination pathways;
• To quantitatively analyze the TRA in whole blood and plasma and obtain PK parameters of plasma TRA and investigate whole blood/plasma ratio for TRA.

Primary Objectives:

• To quantitatively analyze the total radioactivity (TRA) in excrement after a single oral dose of [14C] D-1553 in healthy subjects, and obtain radioactivity recovery and primary excretion pathways in humans;
• To obtain radioactive metabolite profiles of human plasma, urine and feces after a single oral dose of [14C] D-1553 in healthy subjects, identify major metabolites of D-1553 and determine the major metabolic pathways and elimination pathways;
• To quantitatively analyze the TRA in whole blood and plasma after a single oral dose of [14C] D-1553 in subjects, and obtain PK parameters of plasma TRA and investigate whole blood/plasma ratio for TRA.

Secondary Objectives:

• To observe the safety of a single oral dose of [14C] D-1553 in healthy subjects;
• To quantitatively analyze the concentration of D-1553 and its metabolites (if applicable) in plasma using the validated LC-MS (liquid chromatography-mass spectrometry)/MS method and obtain the pharmacokinetic (PK) parameters of D-1553 and its metabolites (if applicable) in plasma.

Inclusion Criteria:

• Subjects who volunteer to participate in this clinical trial, understand the study procedures and sign the Informed Consent Form (ICF) in writing.
• Healthy Chinese adult male subjects aged 19-55 years (inclusive) at the time of signing the ICF.
• Body weight ≥ 50.0 kg, 19 kg/m2 ≤ body mass index (BMI) ≤ 26.0 kg/m2, and BMI = body weight (kg)/body height2 (m2) at screening.
• Subjects with normal test results or with abnormal but not clinically significant results as judged by the clinician for vital signs, physical examination, 12-lead ECG, chest radiograph (PA view), abdominal color Doppler ultrasound (liver, gallbladder, pancreas, spleen, and kidneys), ophthalmological examination, and laboratory tests (including hematology, blood chemistry, coagulation function, urinalysis, thyroid function, screening for infectious diseases, stool routine test + occult blood) during screening.
• Subjects who agree to abstain, are surgically sterilized, or agree to use an effective contraceptive method from the time of signing the ICF and for the duration of study participation to 180 days after administration of the study drug.

Exclusion Criteria:

• Subjects with any medical history of disorders of the central nervous system, cardiovascular system, blood and lymphatic system, immune system, urinary system, digestive system, respiratory system, and metabolic and skeletal system, etc., other acute or chronic diseases or mental diseases, which are abnormal and clinically significant at the discretion of the investigator.
• Subjects who are positive for hepatitis B surface antigen (HBsAg), hepatitis C antibody, treponema pallidum antibody (TPA), or HIV antigen/antibody combination test (preliminary screening).
• Subjects who have smoked more than 5 cigarettes or 1 pipe per day (or equivalent of nicotine products) on average within 3 months prior to screening, or who are unable to stop using any tobacco products during the trial.
• Subjects with hemorrhoids with hematochezia or perianal disease with regular/ongoing hematochezia, or with severe nausea, vomiting, constipation or diarrhea within one week prior to screening; or with positive test results for fecal occult blood.
• Subjects with a history of blood or needle phobia.
• Subjects who have undergone a major surgery that affects the absorption or metabolism of the study drug within 6 months prior to the first dose.
• Subjects who have participated in clinical trials of other study drugs within 3 months before the first dose; if the half-life of that other investigational drug is long, the time period is limited to 5 half-lives of the drug.
• Subjects unwilling or unable to follow the life restrictions described in the study protocol (such as dietary restrictions, activity and contraceptive requirements, etc.).
• Subjects who have lost blood or donated blood, or received blood transfusions or used blood products within 1 month before administration.
• Subjects who are exposed to radioactive work conditions for a long time, or have significant radiation exposure (≥ 2 chest/abdominal CTs, or ≥ 3 other types of X-ray examinations) within 1 year before the first dose, or have participated in a radiopharmaceutical labeled trial.
• Subjects who are unsuitable for the study participation for other reasons at the discretion of the investigator.

Healthy Chinese adult male subjects aged 19-55 years (inclusive) at the time of signing the ICF.