Abstract 3314: Sensitization of human tumor cells to chemotherapy drugs by antisense downregulation of BRCA2 and thymidylate synthase (TS): Induction of synthetic lethality by targeting DNA repair.
Authors: Ferguson Peter J. , Rytelewski Mateusz , Vincent Mark D. , Figueredo René , Koropatnick James 
Published: August 2014

Abstract
Although genomic instability contributes to tumor progression and development of drug resistance, molecular events underlying instability could also lead to selective sensitivity of tumor cells to certain treatments. Deficiencies in specific mechanisms of DNA repair, with resultant dependence on other repair pathways, have been exploited in therapeutic strategies. For example, BRCA1 and BRCA2, which are involved in homologous recombination repair, have been implicated in hereditary and sporadic carcinomas of the breast, ovary, and other sites. Notably, individuals with BRCA2 mutations respond more favourably to conventional chemotherapy. It is hypothesized that in the absence of functional BRCA2 protein, tumor cells are unable to efficiently repair DNA damage induced by anticancer agents. This "synthetic lethality" can be exploited to selectively kill BRCA1- or BRCA2-deficient tumor cells both in vitro (Nature 434: 913, and 917, 2005) and in patients (NEJM 361: 123, 2009). To advance the utility of this phenomenon to selectively kill cancer cells, it may be possible to use antisense technology to create synthetic lethal situations in tumors. siRNA knockdown of BRCA2 in human A549 non-small cell lung cancer cells inhibited proliferation and induced sensitization to cisplatin (DNA cross-linker), melphalan (alkylating agent), the poly(ADP-ribose) polymerase inhibitor olaparib, and the thymidylate synthase (TS)-targeting agent 5-fluorodeoxyuridine. Three novel oligodeoxynucleotides (ODNs) were synthesized to target the BRCA2 mRNA, 2 against the coding region (ODNs BR1 and BR2) and the other in the 3′-untranslated region (BR3). All three ODNs sensitized A549 cells to cisplatin by up to 80%, and BR1 synergistically inhibited proliferation in combination with an antisense ODN targeting TS, SARI-083. A combination of siRNA treatments that knocked down both BRCA2 and TS sensitized cells to a combination of alkylating agents (cisplatin or melphalan) and a TS-targeting drug (5-FUdR). This combination was more effective at inhibiting proliferation than would be predicted by knockdown of TS and BRCA2 followed by treatment with any single drug (5-FUdR, cisplatin, or melphalan). These data suggest that: (1) targeting BRCA2 is a viable strategy to increase the effectiveness of common chemotherapeutic drugs; and (2) it is possible to use antisense-mediated targeting of both TS and a DNA repair protein to sensitize the same cell to two different drugs, and thus potentiate overall therapeutic effectiveness. This is progressing towards human trials. Supported by a grant from the Canadian Institutes of Health Research (CIHR) to JK and MDV. MR is a scholar of the CIHR Strategic Training Program in Cancer Research and Technology Transfer (CaRTT) and a recipient of the Queen Elizabeth II Scholarship in Science and Technology.
Citation Format: Peter J. Ferguson, Mateusz Rytelewski, Mark D. Vincent, René Figueredo, James Koropatnick. Sensitization of human tumor cells to chemotherapy drugs by antisense downregulation of BRCA2 and thymidylate synthase (TS): Induction of synthetic lethality by targeting DNA repair. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3314. doi:10.1158/1538-7445.AM2013-3314