A RAD51 inhibitor (IC50 = 27.4 μM in a FRET-based DNA strand exchange assay); selective for RAD51 over RecA and RAD54 at concentrations up to 250 and 200 μM, respectively; inhibits irradiation-induced RAD51 foci formation in HEK293 cells at a concentration of 50 μM; increases sensitivity to cisplatin in vitro and in an MDA-MB-231 mouse xenograft model when used at a dose of 50 mg/kg