Abstract
Pancreatic Ductal Adenocarcinoma (PDAC) is an extremely aggressive disease. There is a clear need of new strategies and newresearches to treat and diagnose these patients. Regarding treatments, surgery is possible in only 20% of cases, and thechemotherapeutic molecule Gemcitabine is unfortunately lacking a good response rate. Recently, a new polychemotherapyoxaliplatin-based (FOLFIRINOX), which is a combination of 4 drugs: oxaliplatin, irinotecan, fluorouracil and leucovorin, has beenapproved. It has showed a significant increase of the overall survival in patients compared to gemcitabine, but associated with moretoxicity and still limited efficiency. Most of the drugs induce their toxicity by provoking DNA damages and replication stress, leadingto the activation of DNA repair pathways. In this context, our research project proposes to find a synergistic association ofFOLFIRINOX with specific inhibitors of DNA damage repair - Ataxia Telangiectasia and Rad3 related inhibitor (ATRi) – to increase theefficiency of the chemotherapy while reducing its toxicity. The resistance to chemotherapy can come from the stroma thatrepresents up to 80% of the tumor mass. The impact of the chemotherapies on the microenvironment can be a key to increase theefficiency of these treatments. That’s why in this project, we studied co-culture models to look at the effect of this newpolychemotherapy on tumor cells and its microenvironment, in particular Cancer- Associated Fibroblasts (CAFs). Viability matrix in2D & 3D in vitro co-culture of tumor cells with primary CAFs were carried out. DNA damage and proteins from the DNA damagerepair pathways were analysed after treatments. Cell death and autophagy pathways were studied. In vivo, immunodeficient micexenografted with ATCC and Patient Derived Xenograft models were treated with FOLFIRINOX and ATRi to evaluate the effect ontumor progression. Finally, orthotopic graft of KPC cell line in immunocompetent mice was carried. A synergistic effect of theassociation was demonstrated in vitro independently of the KRAS, ATM, TP53, BRCA1/2 mutation statuts in several pancreaticmodels (ATCC and derived from PDX) and in co-culture with CAFs. A higher apoptosis and DNA damages were observed in tumorcells treated with FOLFIRINOX combined with ATRi. These results were associated with a decrease of DNA damage repair pathwaysleading to more apoptosis compared to the chemotherapy alone and an inhibition of the autophagy flux. Also, a phenotypic changein the cells was found after treating with ATRi and with an increase of this particular phenotype when the chemotherapy was added.A protective effect of the CAFs on tumor cells was observed and CAF secretome was analysed. In vivo, in immunodeficient andimmunocompetent mice, the association FOLFIRINOX with ATRi inhibits significantly the tumor growth compared to each treatmentalone. More collagen was observed in immunodeficient mice, which correlates in the literature with good prognostic and OS in miceand patients. Also, more immune infiltration was observed with FOLFIRINOX+ATRi compared to FOLFIRINOX in immunocompetentmice. Precise identification of immune populations is now required, in order to confirm the therapeutic potential of this newtreatment for PDAC.