A Small Molecule Inhibitor of Human RAD51 Potentiates Breast Cancer Cell Killing by Therapeutic Agents in Mouse Xenografts

Abstract

The homologous recombination pathway is responsible for the repair of DNA double strand breaks. RAD51, a key homologous recombination protein, promotes the search for homology and DNA strand exchange between homologous DNA molecules. RAD51 is overexpressed in a variety of cancer cells. Downregulation of RAD51 by siRNA increases radio- or chemo-sensitivity of cancer cells. We recently developed a specific RAD51 small molecule inhibitor, B02, which inhibits DNA strand exchange activity of RAD51 in vitro. In this study, we used human breast cancer cells MDA-MB-231 to investigate the ability of B02 to inhibit RAD51 and to potentiate an anti-cancer effect of chemotherapeutic agents including doxorubicin, etoposide, topotecan, and cisplatin. We found that the combination of B02 with cisplatin has the strongest killing effect on the cancer cells. We then tested the effect of B02 and cisplatin on the MDA-MB-231 cell proliferation in mouse xenografts. Our results showed that B02 significantly enhances the therapeutic effect of cisplatin on tumor cells in vivo. Our current data demonstrate that use of RAD51-specific small molecule inhibitor represents a feasible strategy of a combination anti-cancer therapy.

Quinazolinone derivatives as inhibitors of homologous recombinase RAD51

“…Depending on the availability of the building blocks, the cinnamide analogues (B) were also constructed by Heck coupling of the corresponding aromatic bromide with acrylamide C. After introducing motif 1 as an amine through amide coupling (D to E), the intermediates were cyclized under mild dehydration conditions with iodine and hexamethyldisilazine 18 to give the desired quinazolinone products (F). In this way, one series of compounds incorporated alkyl and cycloalkyl substituents (1)(2)(3)(4)(5)(6)(7)(8), and another series contained substituted aromatics with a variable spacer -(CH 2 )n-(n =0-2, 9-27). The latter series was designed to optimally target residues F195 and Y191 through piinteractions.…”

“…A D-loop assay confirmed B02 specificity for human RAD51 over its bacterial homologue RecA and other human HR proteins 15 . In vitro, B02 inhibited irradiation-induced RAD51 foci formation, HR repair of dsDNA breaks 7 and sensitized cells to a panel of chemotherapy drugs 5,7 . In vivo B02 significantly enhanced the therapeutic effect of cisplatin in a TNBC xenograft model 5 .…”

“…In vitro, B02 inhibited irradiation-induced RAD51 foci formation, HR repair of dsDNA breaks 7 and sensitized cells to a panel of chemotherapy drugs 5,7 . In vivo B02 significantly enhanced the therapeutic effect of cisplatin in a TNBC xenograft model 5 . The structure of B02 involves three chemically distinct components, which could be constructed and optimised through parallel approaches.…”

“…RAD51 has been recognized as a potential oncotarget due to its critical role in HR, and contributes to an aggressive cellular phenotype and resistance to therapeutics. Several small molecule RAD51 inhibitors have been discovered by high-throughput screening of compound libraries, notably B02 [5][6][7] , the RI series [8][9][10] and the IBR2 series 11,12 ( Figure 1). Alternatively, a fragmentbased screening approach at Cambridge identified another series of compounds 13,14 ( Figure 1).…”

The tales of two organic cation transporters, OCT-1 and OCT-2, in C. elegans

“…In human cells, B02 has been shown to interfere with the DNA strand exchange and the nuclear foci formation catalyzed by the DNA repair protein RAD51. RAD51 is required to repair DNA double strand breaks during meiosis and in response to DNA damaging agents [53][54][55]. Examination of the pharmacological effect of B02 in C. elegans revealed that this inhibitor caused sterility in the oct-1 null mutant.…”