The aim of the study is to examine the safety and tolerability of GLPG3121-modified release formulation when given to healthy male subjects once as a single dose or multiple times over a period of 14 days in fasting condition or after a standard breakfast.

The study will evaluate how the body absorbs and breaks down GLPG3121, and how GLPG3121 and the major breakdown product of GLPG3121 are eliminated from the body. In addition, the study will investigate the effect of food (high-fat) after a single oral dose of GLPG3121 as modified release tablet.

Inclusion Criteria:

• Male between 18 and 55 years of age (extremes included), on the date of signing the informed consent form (ICF).
• A body mass index (BMI) between 18.0 and 30.0 kg/m2, inclusive.
• Judged to be in good health by the investigator based upon the results of a medical history, physical examination, vital signs, 12-lead electrocardiogram (ECG), and fasting clinical laboratory safety tests, available at screening and prior to randomization. Hemoglobin, neutrophil, lymphocyte, and platelet counts must be above the lower limit of normal range. Total bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and serum creatinine must be no greater than the upper limit of normal (ULN). Other clinical laboratory safety test results must be within the reference ranges or test results that are outside the reference ranges need to be considered not clinically significant in the opinion of the investigator.
• Subject must be able and willing to comply with restrictions on prior and concomitant medication.
• Negative screen for drugs (amphetamines, barbiturates, benzodiazepines, cannabis, cocaine, opiates, methadone, tricyclic antidepressants) and alcohol.

This list only contains the key inclusion criteria.

Exclusion Criteria:

• Known hypersensitivity to investigational product (IP) ingredients or history of a significant allergic reaction to IP ingredients as determined by the investigator.
• Positive serology for hepatitis B virus surface antigen (HBsAg) or hepatitis C virus (HCV) or history of hepatitis from any cause with the exception of hepatitis A that was resolved at least 3 months prior to first dosing of the IP.
• History of or a current immunosuppressive condition (e.g. human immunodeficiency virus [HIV] infection).
• Having any illness, judged by the investigator as clinically significant, in the 3 months prior to first dosing of the IP.
• Presence or sequelae of gastrointestinal, liver, kidney (estimated glomerular filtration rate [eGFR] <=90 mL/min/1.73 m2, using the Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI] formula) or other conditions known to interfere with the absorption, distribution, metabolism, or excretion of drugs.

This list only contains the key exclusion criteria.