Abstract
Today, treatments for metastatic colorectal cancer have evolved through the combination of conventional chemotherapy 5-FU, oxaliplatin and / or Irinotecan and targeted therapies directed against the EGF receptor or VEGF. Despite an improved survival rate through the combination of these drugs, innate and acquired resistance to treatment is a common cause of therapeutic failure.In order to discover new therapeutic targets we carried out several phenotypic screenings using cellular resistance models acquired to chemotherapies (oxaliplatin and irinotecan) generated in the laboratory as well as the HCT116 line which exhibits an innate resistance to anti-EGFR therapies (cetuximab , panitumumab, Erlotinib). The ultimate goal of this project is to reveal genes, whose inhibition restores sensitivity to one of these treatments, thus displaying a lethal interaction with the drug.Once the kinases potentially involved in resistance to CCR therapies identified, specific inhibition by shRNA and / or a specific inhibitor was performed to confirm the potential therapeutic targets and / or biomarkers for response to treatments. The most promising target, identified as a determinant of resistance to oxaliplatin is the ATR protein (Ataxia-telangiectasia mutated and rad3 related). A protein that plays a key role in DNA repair and is activated in response to the presence of persistent single stranded DNA (ssDNA) or replicative stress, which can be generated by certain anti-cancer therapies.The inhibition of ATR via its pharmacological inhibitor VE-822 (VX-970) combined with oxaliplatin was then studied by the use of cytotoxic tests supplemented by an additivity study. Thus, we demonstrated that the inhibition of ATR combined with oxaliplatin leads to a strong synergy in the HCT116-R1 cell line in both 2D and 3D. This effect is also found in other oxaliplatin resistant clonal lines (HCT116-R2, SW48-R) as well as in the cell lines originating from them (HCT116, SW48).We have also shown that the synergistic effect of oxaliplatin and VE-822 in the HCT116-R1 line is accompanied by an increase in the presence of single-stranded DNA followed by numerous double-stranded DNA breaks, stopping proliferation and inducing apoptosis. The occurrence of this damage to DNA is also correlated with activation of the ATM pathway, p53 and inhibition of CDK2 activity. Moreover, in vitro the double treatment causes an induction of the molecular signals triggering the immunogenic cell death equivalent or superior to the treatments by oxaliplatin alone.Finally, the combination of oxaliplatin + VE-822 is also effective in vivo in immunodeficient mice xenografted with HCT116-R1 cells as well as in immunologically competent mice with a higher synergistic effect indicating that immune death (ICD ) is part of the mechanism of this combination of drugs.In conclusion, all these data confirm the interest of phenotypic screening in the discovery of new therapeutic targets by demonstrating for the first time the functional role of ATR in sensitivity to oxaliplatin.