ABSTRACT Radiation therapy effectively treats prostate cancer, but tumor recurrence remains a clinical challenge, highlighting the need for strategies to enhance radiosensitivity. In this study, we developed a simple, high‐throughput drug repurposing screening platform to find radiosensitizers from compounds approved by the U.S. Food and Drug Administration. A library of 1134 compounds was systematically screened at two concentrations (0.2 and 2 μM) using LNCaP cells stably expressing Metridia luciferase, allowing highly sensitive and quantitative assessment of cell viability through luciferase activity in culture supernatants. In the primary screening, 8 and 12 candidate radiosensitizers were identified at 0.2 μM and 2 μM, respectively. In the secondary screening, 19 compounds were evaluated at two radiation doses (4 Gy and 6 Gy) and six drug concentrations, identifying 5 radiation‐sensitizing candidate compounds. Through this stepwise screening approach, cladribine was identified as the most potent radiosensitizer. Cladribine increased radiation‐induced cytotoxicity in multiple prostate cancer cell lines (22Rv1, DU145, and PC3), with dose‐modifying factors of 1.46, 1.55, and 1.43, respectively, based on the radiation dose needed to achieve 90% cell death. Mechanistically, cladribine prevented the repair of radiation‐induced DNA double‐strand breaks, shown by increased γH2AX levels. Importantly, its radiosensitizing effect was further confirmed in vivo using 22Rv1 and DU145 xenograft models. This study demonstrates that a luciferase‐based high‐throughput drug repurposing platform is useful for identifying clinically relevant radiosensitizers, revealing that cladribine is a promising candidate for further translational research in prostate cancer radiotherapy.
Oka et al. (2026) studied this question.