Abstract 4760: Wnt/β-catenin signaling mediates resistance of colorectal cancer cell lines to chemoradiotherapy
Authors: Emons Georg , Spitzner Melanie , Reineke Sebastian , Auslander Noam , Kramer Frank , Rave-Fraenk Margret , Gaedcke Jochen , Ghadimi Michael , Ried Thomas , Grade Marian 
Published: July 2017

Abstract
Background: Activation of Wnt/β-catenin signaling plays a central role in the development and progression of colorectal cancer (CRC). Previously, we demonstrated that the Wnt transcription factor TCF7L2 was overexpressed in primary rectal cancers that were resistant to chemoradiotherapy (CRT), and that TCF7L2 functionally mediates resistance of CRC to clinically relevant doses of CRT. However, it remained unclear whether the resistance was mediated by a TCF7L2 inherent mechanism or Wnt/β-catenin signaling in general.
Methods: We silenced another key-component of canonical Wnt-signaling, CTNNB1 (β-catenin) in rectal cancer cell lines LS1034, SW480, and SW837 by RNAi. Afterwards cells were exposed to varying doses of irradiation (+/- 5 FU) to assess the influence of β-catenin on radiation response. Activation of Wnt-signaling in “normal” epithelial cells (retina pigment epithelial cells RPE) was achieved either by stimulation with Wnt-3A, or stable overexpression of non-degradable β-catenin (S33Y-mutated) and confirmed by a dual luciferase reporter assay. Changes in radio-(chemo-) sensitivity were analyzed again by a colony formation assay. SW1463 were repeatedly irradiated (68Gy) to establish an isogenic radio-resistant cell line. Gene-expression profiles, without or 6h after a single dose of 4Gy, of RPE cells expressing a control vector or overexpressing β-catenin and radioresistant or wildtype SW1463 cells were established using micro Arrays.
Results: Silencing of CTNNB1 resulted in (chemo-) radiation-sensitization of all three CRC-cell lines. To further investigate the potential role of Wnt/β-catenin signaling in controlling therapeutic responsiveness, non-tumorigenic RPE cells were stimulated with Wnt-3A, which significantly increased resistance to CRT. This effect could be recapitulated by overexpression of β-catenin (S33Y-mut.), resulting in a significantly increased resistance to CRT. The effect could be rescued by siRNA mediated knockdown of β-catenin. Consistent with these findings, we observed higher expression levels of active (unphosphorylated) β-catenin as well as increased TCF reporter activity in SW1463 cells that were rendered radiation-resistant due to repeated IR treatment. Gene expression profiling of radioresistant and wildtype SW1463 as well as RPE cells overexpressing β-catenin or a control vector revealed significant transcriptomal changes. Most interestingly the resistant cells (radioresistant SW1463 and RPE overexpressing β-catenin) reacted with differential activation of metabolic, inflammatory, cell survival and cell cycle pathways to irradiation.
Conclusion: Together, these findings strongly support the interpretation that Wnt/β-catenin signaling plays a central role in mediating resistance of CRC cells to CRT by deregulating essential pathways. Hence, pathway inhibition may represent a promising strategy to increase therapeutic responsiveness to CRT.
Citation Format: Georg Emons, Melanie Spitzner, Sebastian Reineke, Noam Auslander, Frank Kramer, Margret Rave-Fraenk, Jochen Gaedcke, Michael Ghadimi, Thomas Ried, Marian Grade. Wnt/β-catenin signaling mediates resistance of colorectal cancer cell lines to chemoradiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4760. doi:10.1158/1538-7445.AM2017-4760