Abstract 1141: The CoREST complex as a novel target to disrupt AT/RT’s abnormal epigenetic landscape
Authors: Geethadevi Anupa , Collard Marianne , Vaidya Nikhil , Findlay Tyler , Malebranche Kristen , Eberhart Charles , Raabe Eric , Cole Philip , Alani Rhoda , Rubens Jeffrey 
Published: April 2023

Abstract
Atypical teratoid/rhabdoid tumors (AT/RT) are deadly infantile brain tumors. Their aggressive phenotype results from a single recurring biallelic loss-of-function mutation in genes encoding components of the SWI/SNF chromatin-remodeling complex - SMARCB1 in the majority of tumors and SMARCA4 in remaining tumors. Residual SWI/SNF activity continues to inhibit EZH2 methyltransferase except at gene promoter regions where EZH2 co-localizes with the REST complex. At these sites, EZH2 increases repressive H3K27me3 marks. EZH2 co-localizes with REST on neuronal differentiation and tumor suppressor genes. As a result, this epigenetic abnormality helps maintain AT/RT in a stem cell-like state, driving its aggressive growth and therapy resistance. We study the consequences of disrupting SWI/SNF inhibition at sites of EZH2/REST co-localization to target AT/RT precisely. While there are no known interactions between the REST complex and SWI/SNF, there are interactions between REST’s primary co-factor CoREST and SWI/SNF. The CoREST complex consists of LSD1, HDAC1, and the scaffolding protein RCOR. We disrupted the CoREST complex with lentiviral knockdown of RCOR2 (kdRCOR2). KdRCOR2 reversed AT/RT’s stem cell-like state, driving neuronal differentiation and slowing AT/RT growth. Interestingly, kdRCOR1 had no impact on cell differentiation (microscopy and qRT-PCR) and had a modest impact on cell growth (MUSE cell viability assay). We next used Corin to pharmacologically target the CoREST complex in 3 AT/RT cell lines (CHLA05, CHLA06, and BT37). Corin is a bi-functional inhibitor of LSD1 and HDAC1/2, the component enzymes of the CoREST complex. Similar to kdRCOR2, Corin induced neuronal differentiation in AT/RT with increased adherence to plastic and new axonal development (microscopy). Cells also increased expression of neuronal differentiation markers identified by immunofluorescence (MAP2) and qRT-PCR (CEND1, and NEUROD2, t-test p&lt;0.05), and decreased expression of stem cell markers (western blot SOX2 and LIN28). In addition, Corin reduced AT/RT cell viability and proliferation (MUSE Cell viability assay p&lt;0.05; MUSE BrdU assay p&lt;0.05) and increased apoptosis (MUSE Annexin V assay, p&lt;0.05). In mice bearing orthotopic CHLA06 tumors, convection-enhanced delivery of a single dose of Corin increased H3K27me3 and H3K27ac, demonstrating that Corin engaged its target in vivo and induced apoptosis (western blot, PARP). These studies demonstrate that targeting the CoREST complex disrupts AT/RT epigenetic abnormalities, reversing their stem cell-like state, slowing tumor cell growth, and inducing apoptosis. Targeting the CoREST complex with Corin is a promising new strategy that may translate into the clinical setting to help improve AT/RT’s dismal survival.
Citation Format: Anupa Geethadevi, Marianne Collard, Nikhil Vaidya, Tyler Findlay, Kristen Malebranche, Charles Eberhart, Eric Raabe, Philip Cole, Rhoda Alani, Jeffrey Rubens. The CoREST complex as a novel target to disrupt AT/RT’s abnormal epigenetic landscape [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 1141.