Synthetic Lethality Screening Reveals Atr As Responsible For Oxaliplatin Resistance In Colorectal Cancer Cells

Despite the recent advances achieved in the treatment of colon cancer, tumor resistance is a frequent cause of chemotherapy failure. Our work was aimed to determine the molecular mechanisms involved in the resistance to oxaliplatin, an anticancer agent widely used in colorectal cancer treatment. To this end, we establish an oxaliplatin-resistant cellular model from the colon adenocarcinoma cell line HCT-116. Among cellular clones obtained, we used one displaying mild resistance (10 fold called HCT116-R1) to perform short hairpin RNA-based loss of function genetic screen in order to identify genes that can modulate the cellular response to oxaliplatin by revealing genes the silencing of which causes drug sensitivity (synthetic lethal interactions with the drug). Using this screen, we have identified ATR (Ataxia-telangiectasia mutated and rad3 related), a protein that plays a key role in the repair of DNA double-strand breaks induced by various DNA damaging agents, including platinum derivatives. We further validated ATR implication in oxaliplatin resistance by showing that (i) shRNA-mediated repression of ATR in HCT116-R1 oxaliplatin-resistant CRC cells sensitizes such cells to the drug; (ii) co-incubation with the ATR inhibitor VE-822 (or VX-970) and oxaliplatin led to a dramatic synergistic effect in six different CRC cell lines (two oxaliplatin-sensitives: HCT116 and SW48; and four oxaliplatin-resistant: HCT116-R1, HCT116-R2, SW48-R1 and SW48-R2) using 2D and 3D cell growth inhibition assays and in vivo. The synergistic effect was evaluated using dose matrix data (an algorithm that was implemented in our group); (iii) the synergistic effect of oxaliplatin and VE-822 was accompanied by an increase of ssDNA, DNA double-strand breaks, growth arrest and apoptosis induction. In conclusion, our preliminary data confirm the results of our screen by demonstrating for the first time the functional role of ATR in the sensitivity to oxaliplatin. Citation Format: Eve Combes, Augusto Faria-Andrade, Diego Tosi, Pierre Martineau, Maguy Del Rio, Roderick Beijersbergen, Nadia Vie, Celine Gongora. Synthetic lethality screening reveals ATR as responsible for oxaliplatin resistance in colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1187. doi:10.1158/1538-7445.AM2017-1187