Drug-drug Interaction Study with GLPG3970 and Sulfasalazine in Adult, Healthy Subjects

Inclusion Criteria: * Male or female between 18 and 55 years of age (extremes included), on the date of signing the informed consent form (ICF). Females should be of non-childbearing potential. * A body mass index (BMI) between 18.0 to 30.0 kg/m2, inclusive. * A breast cancer resistance protein (BCRP) c421C/C genotype. * 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 the first sulfasalazine administration. Bilirubin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) must be no greater than 1.5x upper limit of normal range (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. This list only contains the key inclusion criteria. Exclusion Criteria: * Known hypersensitivity to the investigational product (IP) (GLPG3970), or sulfasalazine, or sulfa drugs, or to their ingredients, or history of a significant allergic reaction to IP or sulfasalazine 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 sulfasalazine. * 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 sulfasalazine. * 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. * Subjects with an N-acetyltransferase 2 (NAT2) slow acetylator genotype. This list only contains the key exclusion criteria.