NU7441 (KU-57788) is a potent and selective inhibitor of DNA-dependent protein kinase (DNA-PK), a key enzyme involved in the repair of DNA double-strand breaks through the non-homologous end joining (NHEJ) pathway. Its primary application lies in cancer research, particularly in enhancing the effectiveness of DNA-damaging therapies such as ionizing radiation and certain chemotherapeutic agents. By inhibiting DNA-PK, NU7441 prevents cancer cells from efficiently repairing radiation- or chemotherapy-induced DNA damage, leading to increased cell death and improved treatment outcomes in preclinical models. It is widely used in studies exploring radiosensitization and chemosensitization, especially in tumors that rely heavily on the NHEJ pathway for DNA repair. NU7441 has shown promise in combination with radiotherapy in various cancer types, including glioblastoma, lung, and breast cancers, where it amplifies the cytotoxic effects of radiation without significantly increasing damage to normal tissues when used under controlled conditions. Additionally, it serves as a valuable tool compound for investigating DNA repair mechanisms and validating DNA-PK as a therapeutic target in oncology.