Abstract 1718: Development of potent estrogen receptor beta agonists for treating glioblastoma
Authors: Pratap Uday P. , Tidwell Michael , Balinda Henriette U. , Viswanadhapalli Suryavathi , Sareddy Gangadhara Reddy , McHardy Stanton , Brenner Andrew , Vadlamudi Ratna K. 
Published: June 2023

Abstract
Background: Glioblastoma (GBM) is the most prevalent and aggressive type of adult brain cancers with low 5-year overall survival rates. Epidemiologic data suggest estrogen may decrease brain tumor growth. The lack of powerful, selective brain permeable estrogen receptor beta (ERβ) ligands to promote its anticancer action is limiting the therapeutic promise of ERβ. The goal of this project is to create a new class of brain permeable ERβ agonists for the treatment of GBM.
Method: We have used four different assays to identify potent leads. (1) ERβ and estrogen receptor alpha (ERα) reporter assays, (2) Polar Screen Estrogen Receptor (ER) Competitive Binding Assays, (3) Cell viability assays using GBM cells, and (4) Activity in WT and ERβ-KO GBM cells. CellTiter-Glo Cell Viability and colony formation assays were used to test the efficacy of ERβ agonists. Invasion was measured by matrigel invasion chamber assays and apoptosis was measured by Caspase-Glo® 3/7 and Annexin V assays. Flow cytometry was used to evaluate the cell cycle. Western blotting, RNA-Seq, RT-qPCR, and ERβ KO cells were used in the mechanistic studies. Both orthotopic patient-derived xenografts and GBM cell line-derived (CDX) xenografts were used to test the ERβ agonist's activity in vivo.
Results: Indanone and tetralone-oximes or keto-oximes have been hypothesized, produced, and evaluated as new ER agonists. Due to its high action in ERβ reporter assays, specific binding to ERβ in polar screen assays (EC50 91 nM), and potent growth inhibitory activity (IC50 7.4) in GBM cells, CIDD-97 was discovered as a possible hit by screening a library of ~60 compounds. CIDD-97 is significantly more selective for ERβ than ERα (40-fold). Treatment with CIDD-97 markedly reduced U251 cell viability while having little to no effect on U251-ER-KO cells and normal human astrocytes. Further, CIDD-97 treatment decreased the expression of stemness markers in patient derived GSC lines and promoted apoptosis. Additionally, CIDD-ERβ agonist improved TMZ's ability to reduce GBM cell survival. The activation of ERβ target genes in cells treated with CIDD-97 was verified by using RNA-Seq and RTqPCR. PK studies confirmed that CIDD-0149897 has systemic exposure, was found in the brain, and its maximal detectable levels suggested that it has good BBB permeability. Mice tolerated daily intraperitoneal treatment of CIDD-0149897 (50 mg/kg) with a 7-day repeat dosage with no evidence of toxicity. Additionally, when compared to vehicle CIDD-97 (50 mg/kg/i.p.) treatment significantly decreased tumor growth in xenograft models and extended the survival of tumor-bearing mice in orthotopic GSC models.
Conclusion: Collectively, these findings pointed to CIDD-97 as a possible ERβ agonist and is easily adaptable to clinical use alongside current chemo- and radiation-therapy regimens, offering GBM patients an additional means of improving survival.
Citation Format: Uday P. Pratap, Michael Tidwell, Henriette U. Balinda, Suryavathi Viswanadhapalli, Gangadhara Reddy Sareddy, Stanton McHardy, Andrew Brenner, Ratna K. Vadlamudi. Development of potent estrogen receptor beta agonists for treating glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1718.