The primary objective is to confirm the target receptor occupancy of SK-1405 and to correlate receptor occupancy with SK-1405 dose and plasma concentration.

The secondary objective is to assess the safety and tolerability of SK-1405 in healthy, Caucasian, male subjects.

Inclusion Criteria:

• Able and willing to provide written informed consent to participate in this study, as confirmed by signing the informed consent document(s).
• Adult Caucasian male aged ≥20 and ≤50 years.
• Body Mass Index (BMI) of ≥ 20 and ≤ 30 kg/m2.
• Height ≤ 190 cm.
• Subject is a non-smoker or has not smoked in the past 6 months.
• Subject is considered to be in good health in the opinion of the investigator.
• Subject's pre-study clinical laboratory findings are within normal range.
• Subject must be willing and able to comply with all protocol requirements.

Exclusion Criteria:

• Use of prohibited medications as described in the study protocol.
• Current known or suspected history of drug/solvent abuse.
• Current known or suspected history of alcohol abuse or currently drinks in excess of 21 units per week.
• Subjects who have consumed caffeine containing products within 24 hours prior to baseline PET-CT.
• Any concurrent medical, surgical, or psychiatric condition that may affect the subject's ability to meet all protocol requirements during the study duration and/or any significant illness in the investigator's opinion in the 4 weeks before screening.
• Participation in any other clinical study with an investigational drug/device within three months prior to the first day of dosing and after enrolment in the current study.
• Subject has a positive result of HIV screen, hepatitis B screen or hepatitis C screen.
• Subject has had a serious adverse reaction or significant hypersensitivity to any drug.
• Subject has donated 500 mL or more of blood within the three months prior to screening.
• History of neurological conditions.
• Participation in a research study or other radiation exposure which in conjunction with this study would result in additional ionisation radiation exposure exceeding 10 mSv within the last year.
• A contraindication for MRI, including but not limited to, MRI-incompatible pacemakers, recent metallic implants, foreign body in the eye, or other indications as assessed by a standard pre-MRI questionnaire, that preclude the subject undergoing MRI scans.
• Subject has claustrophobia.
• Subjects who have consumed Saint John's wort, red wine, Seville oranges, grapefruit or grapefruit juice within 7 days prior to dosing.
• Subject has a partner who is either pregnant or breastfeeding for the duration of the study.