The study was early terminated due to lack of efficacy.

This is an exploratory, randomized, double-blind, placebo-controlled, parallel group, multicenter, proof of concept study (Phase 2a), evaluating orally administered GLPG2737 for a double-blind (DB) treatment period of 52 weeks and 4 weeks of follow up as well as an open-label extension (OLE) treatment period of 52 weeks and 4 weeks of follow-up, in participants with rapidly progressing ADPKD.

Key Inclusion Criteria for the double-blind period of the study:

• Documented diagnosis of typical ADPKD, using the Ravine criteria (Ravine, et al., 1994).

• Rapidly progressive disease, defined as presence of all of the following:

  • Total Kidney Volume (TKV) >750 mL, as determined on imaging not older than 5 years before screening. If historical imaging is not available or older than 5 years, imaging can be performed during the screening period according to local clinical practice (that is, echography, magnetic resonance imaging [MRI])
  • Mayo ADPKD Classification Classes 1C to 1E.

• eGFR at screening between 30 to 90 milliliters per minute per 1.73 square meter (mL/min/1.73 m^2) for participants aged 18 to 40 years (inclusive), and between 30 to 60 mL/min/1.73 m^2 for participants aged 40 to 50 years.

• Blood pressure ≤ 150/90 millimeters of mercury (mmHg). In case a participant is treated for hypertension, she/he should be on a stable treatment regimen of antihypertensive therapy for at least 8 weeks prior to the screening visit, and during the screening period.

Key Inclusion Criteria for the OLE period of the study:

• Male and female participants who completed the 52-week double-blind treatment period on investigational product (IP).
• Participant, according to the investigator's judgment, may benefit from long-term treatment with GLPG2737.

Key Exclusion Criteria for the double-blind period of the study:

• Congenital absence of 1 kidney, or participant had a previous nephrectomy or has a transplanted kidney or a transplantation is planned in the foreseeable future.
• Administration of polycystic kidney disease-modifying agents (for example, tolvaptan, somatostatin analogues) or interventions (such as cyst aspiration or cyst fenestration) within 12 weeks prior to the screening visit and during the screening period. In case tolvaptan is not being administered, this should be because of e.g. non-availability, intolerance, or physician's clinical judgment.
• Any condition or circumstances that, in the opinion of the investigator, may make a participant unlikely or unable to complete the study or comply with study procedures and requirements (for example, unable to undergo magnetic resonance imaging (MRI) due to participant's weight exceeds the weight capacity of the MRI, ferromagnetic metal prostheses, aneurysm clips, severe claustrophobia, etc.).

Key exclusion criteria for the OLE period of the study:

• Clinically significant abnormalities detected on 12-lead electrocardiogram (ECG) of either rhythm or conduction, QTcF >450 ms, or long QT syndrome.

Note: Other protocol-defined Inclusion/Exclusion criteria may apply.