Abstract 3946: Wnt/ß-catenin signaling mediates resistance of colorectal cancer cells to chemoradiotherapy

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Preoperative chemoradiotherapy represents the standard treatment for patients with rectal cancer. However, the clinical response of individual tumors to multimodal treatment is not uniform, and ranges from complete response to complete resistance. Therefore, the identification of novel therapeutic targets whose modification could be harnessed to sensitize a priori resistant tumors is exceedingly important. In this context, we have previously demonstrated that the Wnt transcription factor TCF4 was over-expressed in rectal cancers that were resistant to chemoradiotherapy. The aim of this study was to explore the functional relevance of TCF4 and Wnt/β-catenin signaling for mediating treatment resistance. Methods: Colorectal cancer cell lines SW837, SW480, and HT-29 were transfected with shRNAs targeting TCF4. After establishing stable single-cell clone (SCC) populations, selected clones were irradiated at 0, 1, 2, 4, 6 and 8 Gy of X-rays. To assess the putative Wnt/β-catenin dependency, β-catenin was inhibited in cancer cell lines using siRNAs, the tankyrase inhibitors XAV939 / JW55 and the porcupine inhibitor LGK 974. Furthermore Wnt/β-catenin signaling activity was stimulated in normal retinal pigment epithelial (RPE) cells through incubation with Wnt3a. Results: RNAi-mediated silencing of TCF4 led to a significant radiosensitization in SW837 and SW480, two cell lines with a high basal TCF4-activity, whereas no effect was observed in HT-29 a cell line with low activity. Inhibition of β-catenin similarly caused a pronounced sensitization of CRC cells to clinically relevant doses of X-rays. Finally, exogenous stimulation of canonical Wnt signaling with Wnt3a resulted in a significantly decreased sensitivity of RPE cells to radiotherapy, i.e. induced radioresistance. Conclusion: We have uncovered a novel role of Wnt/β-catenin signaling in mediating resistance to chemoradiotherapy. Moreover, these data suggest that targeting key components of this pathway may represent a potential therapeutic strategy to increase the proportion of patients that respond to chemoradiotherapy, with considerable clinical implications. Citation Format: Georg Emons, Melanie Spitzner, Sebastian Reineke, Janneke Moller, Emil Kendziorra, Tim Beissbarth, Margret Rave-Fraenk, Jochen Gaedcke, Thomas Ried, Michael Ghadimi, Marian Grade. Wnt/s-catenin signaling mediates resistance of colorectal cancer cells to chemoradiotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3946. doi:10.1158/1538-7445.AM2014-3946