A Study to Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Single Ascending Doses of ACT-1004-1239 in Healthy Male Subjects

Inclusion Criteria: * Signed informed consent in a language understandable to the subject prior to any study-mandated procedure. * Healthy male subjects aged between 18 and 55 years (inclusive) at Screening. * No sperm donation from (first) study treatment administration up to at least 90 days after (last) study treatment administration. * Sexual abstinence or use of condoms from (first) treatment administration up to at least 90 days after (last) study treatment administration. Moreover, the female partner of childbearing potential must use a highly effective method of contraception. Exclusion Criteria: * Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol. * Any previous and/or ongoing relevant immune-related disorder or any evidence for immune dysfunction based on medical history and laboratory tests at Screening * Any cardiac condition or illness (including clinically relevant 12-lead ECG abnormalities) with a potential to increase the cardiac risk of the subject based on medical history and 12-lead ECG measured at Screening. * QT interval corrected with Fridericia's formula (QTcF) \> 430 ms, respectively, QRS interval \> 110 ms, PR interval \> 200 ms, or heart rate (HR) \> 90 bpm on 12-lead ECG at Screening and Day 1 pre-dose (of the first period when applicable). * Treatment with another investigational treatment within the 2 months prior to Screening or participation in more than 3 investigational treatment studies within the year prior to Screening. * History or clinical evidence of any disease and/or existence of any surgical or medical condition that might interfere with the ADME of the study treatment (e.g., appendectomy and herniotomy allowed, cholecystectomy not allowed). * Previous treatment with any prescribed medications (including vaccines and strong CYP3A4 inhibitors/inducers) or over-the-counter (OTC) medications (including homeopathic preparations, herbal medicines, vitamins, and minerals) within the 2 weeks or 5 terminal half-lives (t½; whichever is longer) prior to (first) study treatment administration.