Abstract 2515: Pharmacological WNT-inhibition acts synergistically with chemo- and radiotherapy by overcoming treatment-resistance in glioma stem cells

Abstract

Abstract Objective: Glioma Stem Cells (GSCs) are considered to be responsible for Glioblastoma's (GBM’s) dismal prognosis. WNT signaling is one of the major players in GSCs that promotes their radio- and chemoresistance. In this study we tested whether LGK974, an inhibitor of both canonical and non-canonical WNT signaling, might sensitize GBM cells to chemotherapeutics and irradiation and determined possible mechanisms causing treatment-resistance in GBM. Methods: At first we analyzed MGMT promoter methylation status of several GBM cell lines in order to define cells resistant to the standard chemotherapeutic drug Temozolomide (TMZ). For further investigations we chose two cell lines resistant or sensitive to TMZ, respectively. IC50 concentrations of TMZ and LGK974 as well as IC50 dose of γ-irradiation were tested via Titer Blue cell viability assay. Effectiveness of different concentration of each single therapy and its combination with LGK974 was determined to create a drug-response-curve due to the computerized simulation of synergism and antagonism in drug combination studies (Chou, 2006). A reporter assay for canonical WNT/β-catenin signaling was used to quantify the effect of TMZ and irradiation alone and in combination with LGK974 on the canonical and non-canonical WNT pathway. Western Blot and qPCR were applied to analyze the effects of combinatory therapy on protein and gene expression concerning WNT pathway activation. Results: We observed a significant synergy of combined irradiation/TMZ with LGK974 in all cell lines. There was no difference in effectiveness between cell lines resistant or sensitive to TMZ. Interestingly, following TMZ treatment or irradiation cells showed slightly decreased canonical WNT pathway activity. Furthermore, non-canonical target genes and receptors were upregulated under chemo- and radiotherapy, suggesting a reciprocal activation of the non-canonical branch of WNT signaling pathway. This phenomenon might possibly be responsible for the development of resistance against standard chemo- and radiotherapy. Conclusions: We propose that GSCs undergo a shift from canonical to non-canonical WNT signaling to become treatment-resistant under standard chemo- and radiotherapy. Treatment with LGK974 results in therapeutic synergy at least in part via suppressing the therapy-induced activation of non-canonical WNT signaling. Our results confirm the potential benefit of combining TMZ or irradiation with the WNT inhibitor LGK974 to overcome therapy-resistance in GBM. Citation Format: Abigail K. Suwala, Ulf D. Kahlert, Jaroslaw Maciaczyk. Pharmacological WNT-inhibition acts synergistically with chemo- and radiotherapy by overcoming treatment-resistance in glioma stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2515.