RI-1 is a small molecule inhibitor that targets the RAD51 protein, which plays a key role in DNA repair through homologous recombination. Its primary application is in cancer research, particularly in studies focused on sensitizing tumor cells to DNA-damaging treatments such as chemotherapy and radiation. By inhibiting RAD51, RI-1 disrupts the repair of DNA double-strand breaks, making cancer cells more vulnerable to these therapies. It is especially studied in cancers with defects in other DNA repair pathways, such as BRCA-mutated tumors, where targeting backup repair mechanisms can lead to synthetic lethality. RI-1 serves as a valuable tool compound for exploring the role of homologous recombination in cellular responses to genotoxic stress and for developing new combination treatment strategies in oncology.