Tu1685 Loss of Cohesin is a Common Early Event in Colorectal Cancer: Potential Mediator of Chromosomal Instability

G A A b st ra ct s in presence or not of FOLFOX (50 μM of 5-FU and 1.25, 2.5 or 5 μM of oxaliplatin; 50 μM of 5-FU/2.5 μM of oxaliplatin being considered as the circulating blood concentration of patients treated by FOLFOX) (luminescence viability assay). ABCG2 mRNA expression in 2D vs. 3D HT29 cultures (HT29 being more resistant than HCT116; see results) was also studied (Q-PCR). FOLFOX significantly decreased HT29 and HCT116 viability without any dose-dependency. HCT116 cells were more affected than HT29 cells (e.g. 20±2% vs 43±2% for FOLFOX 50/2.5; p<0.05). Using 3D cultures, FOLFOX decreased dose-dependently HCT116 viability but at a lesser extent than in 2D (72±1% for FOLFOX 50/2.5; p<0.01). By contrast, viability of HT29 colonospheres was not affected, these cells cultured in 3D therefore appearing as completly resistant to FOLFOX. CFE was significantly decreased both in HCT116 and HT29 cells. In HT29 cells, basal expression of ABCG2 mRNA was significantly higher in 2D vs. 3D cultures (p=0.001). However, as FOLFOX increased twotimes ABCG2 mRNA expression in 2D HT29 cultures, it increases by 6-fold ABCG2 mRNA expression in HT29 colonospheres (p<0.01 compared to untreated colonospheres). In conclusion, HCT116 and at a much greater level HT29 cells cultured in 3D are significantly more resistant to FOLFOX than in 2D cultures, suggesting that 3D culture is more appropriate to study in vitro resistance to anticancer drugs in CC. This chemoresistance seems to be at least partly explained by increased expression of ABCG2 drug transporter. Acknowlegments: F.P was supported by an academic grant from the French Research Ministery (Annee Recherche). This work was also supported by grants from Alsace contre le Cancer and from Association Coeur-Cancer from the Departement de la Manche, France.