Abstract 4764: Activation of estrogen receptor beta signaling reduces stemness and promotes differentiation of glioma stem cells
Authors: Sareddy Gangadhara Reddy , Liu Jinyou , Viswanadhapalli Suryavathi , Tekmal Rajeshwar R. , Brenner Andrew , Vadlamudi Ratna K. 
Published: July 2017

Glioblastoma (GBM) are the most common and deadliest tumors of the central nervous system. GBM have poor prognosis due to tumor recurrence and resistance to current therapies. Glioma Stem Cells (GSCs) are implicated in the tumor initiation and therapy resistance of GBM. Agents that can specifically reduce stemness of GSCs are urgently needed for the effective treatment of GBM. Estrogen play a crucial role during brain development, differentiation and in neuroprotection. However, its role in promoting differentiation of GSCs remain unknown. Estrogen effects are mediated by two estrogen receptors (ESR1 and ESR2) and ESR2 functions as a tissue-specific tumor suppressor. Our recent studies discovered that GSCs preferably express ESR2 with low or undetectable levels of ESR1. The objective of this study is to test whether ESR2 agonists modulate stemness of GSCs and to determine their mechanism(s) of action. We have tested the hypothesis using GSCs isolated from established and patient derived GBM cells using stem cell markers CD133 and CD15. Knockout of ESR2 using CRISPR/Cas9 system increased the CD133 positive GSCs and overexpression of ESR2 reduces the CD133-positive population in GBM cells. Treatment of GSCs with ESR2 agonists (Liquiritigenin and LY500307) significantly inhibited the neurosphere formation, self-renewal ability and proliferation. Further ESR2 agonist treatment resulted in the loss of stemness and induction of differentiation and apoptosis of GSCs. Western blot analysis and RT-qPCR analysis revealed reduced expression of stemness markers such as Nestin and Sox-2 and increased expression of differentiation markers GFAP and tuj-1 in GSCs. RNA sequencing analysis of ESR2 agonist treated and untreated GSCs revealed modulation of pathways related to apoptosis, cell cycle, stemness and differentiation. Further, ESR2 agonists treatment significantly reduced the GSCs mediated tumor growth in orthotopic models and improved the mice overall survival. Immunohistochemical studies demonstrated that ESR2 agonists reduces the expression of proliferation of marker Ki67 and induced the apoptosis in tumors. Together, our results established ESR2 agonists liquiritigenin and LY500307 as novel therapeutic agents for elimination of GSCs. Since ESR2 agonists has good blood-brain barrier permeability and less neuronal toxicity, they can be readily transferred to clinical use with current radiation and chemotherapies, thereby providing an additional tool for enhancing survival in GBM patients.

Citation Format: Gangadhara Reddy Sareddy, Jinyou Liu, Suryavathi Viswanadhapalli, Rajeshwar R. Tekmal, Andrew Brenner, Ratna K. Vadlamudi. Activation of estrogen receptor beta signaling reduces stemness and promotes differentiation of glioma stem cells [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 4764. doi:10.1158/1538-7445.AM2017-4764