The primary objectives of the study are:

• To determine the absolute bioavailability of SK-1404
• To assess the mass balance recovery after a single oral (PO) dose of carbon-14 (14C)-SK-1404
• To provide plasma, urine and faecal samples for metabolite profiling and structural identification

The secondary objectives of the study are:

• To determine the routes and rates of elimination of [14C]-SK-1404
• To identify the chemical structure of each metabolite with an exposure (AUC) of more than 10% of circulating total radioactivity
• To explore the intravenous (IV) pharmacokinetics (PK) of [14C]-SK-1404
• To further explore the PO PK of SK-1404
• To provide additional safety and tolerability information for SK-1404

This is a single-centre, 2-part, open-label, non-randomised, sequential, single dose study in healthy male subjects. It is planned to enrol a single cohort of 6 healthy male subjects who will participate in Parts 1 and Part 2 of the study.

In Part 1, each subject will receive a single PO dose of SK-1404 followed by an IV microtracer dose of [14C]-SK-1404.

In Part 2, each subject will receive a single PO dose of [14C]-SK-1404.

Inclusion Criteria:

1. Healthy males
2. Age 30 to 65 years of age
3. Body mass index of 18.0 to 35.0 kg/m2 or, if outside the range, considered not clinically significant by the investigator
4. Must be willing and able to communicate and participate in the whole study
5. Must provide written informed consent
6. Must have regular bowel movements (ie average stool production of ≥1 and ≤3 stools per day)
7. Must agree to use an adequate method of contraception

Exclusion Criteria:

1. Males with pregnant partners
2. Participation in a clinical research study within the 3 months prior to IMP dose
3. Subjects who are study site employees, or immediate family members of a study site or sponsor employee
4. Subjects who have previously been enrolled in this study
5. Subjects who have previously been dosed with SK-1404
6. History of any drug or alcohol abuse in the past 2 years
7. Regular alcohol consumption in males >21 units per week (1 unit = ½ pint beer, 25 mL of 40% spirit or a 125 mL glass of wine) in the past year
8. Current smokers and those who have smoked within the last 12 months; this includes cigarettes, e-cigarettes and nicotine replacement products. A breath carbon monoxide reading of greater than 10 ppm at screening or admission
9. Radiation exposure, including that from the present study, excluding background radiation but including diagnostic x-rays and other medical exposures, exceeding 5 mSv in the last 12 months or 10 mSv in the last 5 years. No occupationally exposed worker, as defined in the Ionising Radiation Regulations 1999, shall participate in the study
10. Subjects who have been enrolled in an ADME study in the last 12 months
11. Subjects who do not have suitable veins for multiple venepunctures/cannulation as assessed by the investigator at screening
12. Clinically significant abnormal biochemistry, haematology or urinalysis as judged by the investigator (laboratory parameters are listed in Appendix 1)
13. Aspartate aminotransferase, alanine aminotransferase or alkaline phosphatase >1.5 × upper limit of normal confirmed by repeat testing
14. Serum sodium below the lower limit of normal