Abstract 1712: Estrogen receptor beta signaling sensitizes glioblastoma cells to chemo and radiation therapy
Authors: Pratap Uday P. , Sareddy Gangadhara Reddy , Li Mengxing , Luo Yiliao , Zhou Mei , Viswanadhapalli Suryavathi , Tekmal Rajeshwar Rao , Brenner Andrew , Vadlamudi Ratna K. 
Published: August 2019

Current treatment options for glioblastoma (GBM) are poor, the mortality rates are very high and therapy resistance is a major clinical problem. Standard treatment consists of surgical resection, external beam radiation therapy, adjuvant chemotherapy with temozolomide (TMZ), and tumor treating fields. Nonetheless, despite a heavy investment in therapy, all patients eventually succumb to their disease. Recent studies suggest that estrogen receptor beta (ERβ) may function as a tumor suppressor in GBM. However, the mechanism(s) by which ERβ contributes to chemo- and radiation therapy response remains unknown. The objective of this study is to examine whether ERβ sensitizes GBM to chemo- and radiation therapy and to understand the mechanistic insights of ERβ mediated tumor suppression in GBM.

Methods: To study the functions of endogenous ERβ in GBM cells, we have utilized multiple ERβ overexpressing GBM model (GBM- ERβ) cells using lentiviral transduction. As a second model we have also generated ERβ knockout (ERβKO) cells using CRISPR/Cas9 system, and as a third model we used lentiviral-ERβshRNA transfected primary GBM cells (ERβKD). We then examined the effect of TMZ and radiation on the expression of ERβ using qRT-PCR. The effect of TMZ and radiation on ERβ overexpression and knockout models was examined using MTT cell viability assays. Mechanistic studies were conducted using RNA-seq, HR reporter gene assays, confocal microscopy, western blot, and qRT-PCR analysis. The in vivo role of ERβ on chemo sensitivity of TMZ was studied using orthotopic models of GBM and mouse survival was determined using Kaplan-Meier survival curves.

Results: Cell viability and survival assays using multiple established and primary GBM cells demonstrated that ERβ sensitizes GBM cells to DNA damaging agents including TMZ and radiation therapy. qRT-PCR analysis demonstrated that ERβ expression was decreased following chemo- and radiation treatment. Combination analysis of RNA-seq studies using ERβ overexpression, and ERKO models, revealed an alteration in the number of genes involved in DNA recombination and repair, ATM signaling, and cell cycle check point control. Mechanistic studies showed that ERβ plays a significant role in homologous recombination (HR) mediated repair; and ERβ reduced expression and activation of ATM upon DNA damage. Generation of optimal γH2AX foci following TMZ treatment is dependent on the status of ERβ. More importantly, GBM cells expressing ERβ had increased survival when compared to control GBM cells in orthotopic GBM models. ERβ overexpression further enhanced the survival of mice to TMZ therapy in both TMZ sensitive and TMZ resistant GBM models.

Conclusion: Our results provided evidence that ERβ is required for optimal chemo- and radiation- induced DNA damage response in GBM cells.

Citation Format: Uday P. Pratap, Gangadhara Reddy Sareddy, Mengxing Li, Yiliao Luo, Mei Zhou, Suryavathi Viswanadhapalli, Rajeshwar Rao Tekmal, Andrew Brenner, Ratna K. Vadlamudi. Estrogen receptor beta signaling sensitizes glioblastoma cells to chemo and radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1712.