Study of Lunresertib Alone or in Combination With RP-3500 or Debio 0123 in Patients With Advanced Solid Tumors

The primary purpose of this study is to assess the safety and tolerability of lunresertib alone and in combination with RP-3500 or in combination with Debio 0123 in patients with eligible advanced solid tumors, determine the maximum tolerated dose (MTD) and assess preliminary anti-tumor activity.

Phase 1/1b, multi-center, open-label, dose-escalation study to: * Evaluate the safety profile and MTD of lunresertib alone and in combination with RP-3500 or in combination with Debio 0123 when administered orally to establish the recommended Phase 2 dose and schedule * Characterize the PK and pharmacodynamics of lunresertib alone and in combination with RP-3500 or in combination with Debio 0123 * Assess preliminary anti-tumor activity associated with lunresertib alone and in combination with RP-3500 or in combination with Debio 0123 This study was previously posted by Repare Therapeutics. In September 2025, sponsorship of the trial was transferred to Debiopharm International S.A Expanded Access Status: There is no expanded access program available for the investigational products in this study at this time.

Inclusion Criteria: * Male or female and ≥12 years-of-age at the time of informed consent. * Lansky performance status ≥50% for patients ≤16 years of age, or ECOG score of 0, 1, (or 2 for module 1) for patients \>16 years of age. * Locally advanced or metastatic resistant or refractory solid tumors. * Patients \<18 years of age must weigh at least 40 kg. * Submission of available tumor tissue at screening or willingness to have a biopsy performed if safe and feasible * Next generation sequencing (NGS) report obtained in a CLIA-certified or equivalent laboratory demonstrating eligible tumor biomarker. * CCNE1 amplification (non-equivocal) as determined by either a tumor or plasma NGS test, or FISH * FBXW7 deleterious mutations identified by either a tumor or plasma NGS test * PPP2R1A deleterious mutations identified by either a tumor or plasma NGS test * Measurable disease as per RECIST v1.1. For certain modules, patients with prostate cancer or ovarian cancer that have non-measurable disease but have elevated tumor markers (PSA or CA-125, respectively) can also be eligible * Ability to swallow and retain oral medications. * Acceptable hematologic and organ function at screening. * Negative pregnancy test (serum) for women of childbearing potential (WOCBP) at Screening. * Resolution of all toxicities of prior therapy or surgical procedures. * Any prior radiation must have been completed at least 7 days prior to the start of study drugs, and patients must have recovered from any acute adverse effects prior to the start of study treatment. Exclusion Criteria: * Chemotherapy or small molecule antineoplastic agent given within 21 days or \<5 half-lives, whichever is shorter, prior to first dose of study drug. * History or current condition, therapy, or laboratory abnormality that might confound the study results or interfere with the patient's participation for the full duration of the study treatment. * Patients who are pregnant or breastfeeding. * Life-threatening illness, medical condition, active uncontrolled infection, or organ system dysfunction or other reasons which, in the investigator's opinion, could compromise the participating patient's safety. * Major surgery within 4 weeks prior to first dose of lunresertib. * Uncontrolled, symptomatic brain metastases. * Uncontrolled hypertension. * Certain prior anti-cancer therapy * Psychological, familial, sociological, or geographical conditions that do not permit compliance with the protocol and/or follow-up procedures outlined in the protocol.