LAUSR

The histone methyltransferase Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex 2 (PRC2). Its overexpression in triple-negative breast cancer (TNBC) correlates with aggressive, poorly differentiated phenotypes and poor prognosis. EZH2 methylates histone 3 at lysine 9/27 and controls the transcription of many genes, such as cyclin D1, Cyclin E and MMP9, which are involved in tumor survival, proliferation, migration, invasion, and angiogenesis. EZH2 also promotes breast tumor-initiating cell expansion (BITC) through impairment of the DNA repair process and the favoring of oncogenes. Small-molecule EZH2 inhibitors, including Tazmetostat (TAZVERIK), mainly inhibit the SET domain methylase activity which may not completely abrogate the actions of EZH2. Recently, TAZVERIK was FDA approved for follicular lymphoma and is in clinical trials for other solid tumors including the breast. The PI3K-AKT pathway in TNBC plays a pivotal role in metastasis and tumorigenesis, and it associates and interacts with other proteins and pathways. Post translational modifications of EZH2 lead to its role in cancer progression, and importantly, AKT phosphorylates EZH2 and promotes oncogenesis independent of PRC2-mediated gene transcriptional silencing. Docking studies using PyRx 0.8 software revealed AKT inhibitor MK2206 interact with EZH2. We hypothesize that enhancing EZH2 inhibition by combining Tazmetostat with an Akt inhibitor will be highly effective in suppressing progression and metastasis in TNBC. The in-silico analysis revealed MK2206 actively interacts with the CXC (Cystein rich region) an integral part of the catalytic site of EZH2. The binding affinity of MK2206 was observed to be -6.9 kcal/mol, which is -1.3 kcal/mol less than the affinity of Tazmetostat (-8.2Kcal/mol). Tazmetostat binds to the SET domain, inhibiting methyltransferase activity, while MK2206 binds towards the CXC region. Tazmetostat by itself effectively inhibit cell growth (IC50: 20.3 μM) but combining with MK2206 caused a synergistic inhibition of cell viability. The combination of 8µM Tazmetostat and 5μM MK2206 significantly suppressed EZH2 activity and migration. Additionally, we investigated the Protein-Protein interaction STRING between AKT and EZH2 in humans, which revealed interactions with proteins involved in regulation of cell cycle progression (CDK2), RING -type E3 Ubiquitin Transferase (TTC3), and the triggering of histone H3-k27 methylation (EED). The combination of Tazmetostat and MK2206 significantly inhibits TNBC proliferation, invasion and migration by disrupting the catalytic activity by preventing EZH2-DNA interactions, abrogating methylation and inhibiting the EZH2-Akt interaction in the TNBC phenotype. (Work supported by DOD: W81XWH2010065, for Eswar Shankar). Citation Format: Gowripriya Thirumugam, Gautham Sarathy, Shiv Verma, Shivani Dhekne, Balamurugan Krishnaswamy, Sanjay Gupta, Bhuvaneswari Ramaswamy, Eswar Shankar. Computational drug repositioning identifies Akt inhibitor MK2206 binding to EZH2 as enhancer of Tazmetostat efficacy in inhibition of triple negative breast cancer proliferation [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 2561.