A high-throughput pharmaceutical screen identifies compounds with specific toxicity against BRCA2-deficient tumors.
OBJECTIVE
Hereditary breast cancer is partly explained by germline mutations in BRCA1 and BRCA2. Although patients carry heterozygous mutations, their tumors have typically lost the remaining wild-type allele. Selectively targeting BRCA deficiency may therefore constitute an important therapeutic approach. Clinical trials applying this principle are underway, but it is unknown whether the compounds tested are optimal. It is therefore important to identify alternative compounds that specifically target BRCA deficiency and to test new combination therapies to establish optimal treatment strategies.


METHODS
We did a high-throughput pharmaceutical screen on BRCA2-deficient mouse mammary tumor cells and isogenic controls with restored BRCA2 function. Subsequently, we validated positive hits in vitro and in vivo using mice carrying BRCA2-deficient mammary tumors.


RESULTS
Three alkylators-chlorambucil, melphalan, and nimustine-displayed strong and specific toxicity against BRCA2-deficient cells. In vivo, these showed heterogeneous but generally strong BRCA2-deficient antitumor activity, with melphalan and nimustine doing better than cisplatin and the poly-(ADP-ribose)-polymerase inhibitor olaparib (AZD2281) in this small study. In vitro drug combination experiments showed synergistic interactions between the alkylators and olaparib. Tumor intervention studies combining nimustine and olaparib resulted in recurrence-free survival exceeding 330 days in 3 of 5 animals tested.


CONCLUSIONS
We generated and validated a platform for identification of compounds with specific activity against BRCA2-deficient cells that translates well to the preclinical setting. Our data call for the re-evaluation of alkylators, especially melphalan and nimustine, alone or in combination with the poly-(ADP-ribose)-polymerase inhibitors, for the treatment of breast cancers with a defective BRCA pathway.
Evers
Bastiaan
B
Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
Schut
Eva
E
van der Burg
Eline
E
Braumuller
Tanya M
TM
Egan
David A
DA
Holstege
Henne
H
Edser
Pauline
P
Adams
David J
DJ
Wade-Martins
Richard
R
Bouwman
Peter
P
Jonkers
Jos
J
D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D024682:BRCA2 Protein / Q000172:deficiency*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000627:therapeutic use*; D016503:Drug Delivery Systems; D004357:Drug Synergism; D005260:Female; D015674:Mammary Neoplasms, Animal / Q000178:diet therapy* / Q000188:drug therapy / Q000235:genetics; D051379:Mice; D009154:Mutation; D010793:Phthalazines / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays
D018906:Antineoplastic Agents, Alkylating; D024682:BRCA2 Protein; D010793:Phthalazines; D010879:Piperazines; D002945:Cisplatin; C531550:olaparib