ri-1 (chemical) ri-1 (chemical) ri-1 is a selective inhibitor of rad51, which is a central gene molecule of homologous recombination, with ic50 ranging from 5 to 30 μm. ri-1 names preferred iupac name 3-chloro-1-(3,4-dichlorophenyl)-4-(morpholin-4-yl)-1h-pyrrole-2,5-dione identifiers cas number 415713-60-9 3d model (jsmol) interactive image pubchem cid 1074953 unii s8wg8zrq99 y comptox dashboard (epa) dtxsid30360083 smiles c1coccn1c2=c(c(=o)n(c2=o)c3=cc(=c(c=c3)cl)cl)cl properties chemical formula c14h11cl3n2o3 molar mass 361.60 g·mol−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references antitumor mechanism rad51 is a eukaryote gene, encoding rad51 protein that participates in dna damage induction and complex signal pathway of cell cycle checkpoint of homologous recombination in cells. however, over-expression of rad51 may lead the occurrence and development progress of tumours and besides, the insensitivity of tumours to chemoradiotherapy. at present, over-expression of rad51 has been found in many kinds of human cancers, such as breast cancer, lung cancer and ovarian cancer. ri-1 inhibits the over-expression of rad51 in cancer cells by bonding covalently to the surface of rad51 protein at cys 319 and irreversibly loosen a protein-protein interface that is essential for filament formation and recombinase activity. targeted drugs to rad51 has the prospect to be a new generation of oncologic drugs, like ri-1. it is also a unique tool for mechanism studies of dna repair.