Inhibition von TCF7L2 mittels RNA-Interferenz sensibilisiert kolorektale Krebszellen für Bestrahlung

Abstract

The clinical response of locally advanced rectal cancers to preoperative chemoradiotherapy is very heterogeneous. To determine the molecular characteristics associated with this heterogeneity, we recently profiled a series of responsive and resistant rectal adenocarcinomas using gene expression microarrays, and identified a set of differentially expressed genes. One gene that was significantly overexpressed in the resistant tumors was TCF7L2, the main downstream effector of the Wnt signaling pathway. The aim of this study was to evaluate if RNAi-mediated silencing of TCF7L2 sensitizes tumor cells to radiation therapy. We therefore transfected the colorectal cancer cell line SW480, which expresses TCF7L2, with two different shRNA-vectors targeting TCF7L2 and a non-silencing control, and subsequently established stable single cell clones. Protein levels after RNAi-mediated gene silencing were analyzed by Western blotting. For each vector, single cell clones were plated and irradiated at 2, 4, 6 and 8 Gy. Colonies were counted after 10 days, and survival fractions were subsequently calculated. The TCF7L2 protein levels were reduced to ~ 34 % (shRNA_1) and ~ 29 % (shRNA_2) of the non-silencing control. RNAi-mediated silencing of TCF7L2 led to a ~ 1.6-fold growth inhibition (plating efficiency) compared to the non-silencing control, and, importantly, significantly reduced colony-formation after radiation: We observed dose reduction factors of ~ 1.45 and ~ 1.65 at 37 % survival for shRNA_1 and shRNA_2, respectively. In summary, TCF7L2 was found to be overexpressed in resistant rectal carcinomas, and its RNAi-mediated silencing caused a significant growth inhibition and radiosensitization of colorectal cancer cells. Thus, TCF7L2 might represent a potential molecular target to sensitize a priori resistant tumor cells.