Abstract 2786: Seizure related 6 homolog (SEZ6), a cancer stem cell-specific secreted protein, is a novel GBM therapeutic target

Abstract

Abstract Cancer Stem Cells (CSCs) are known to initiate a tumor, resist chemotherapy and radiotherapy, and also cause tumor recurrence. A deeper understanding of CSC biology is needed for a more effective therapeutic response. An integrative study of regulated transcriptome of human patient-derived Glioma Stem-like Cells (GSCs) using Gene Ontology (GO) analysis and Gene Set Enrichment Analysis (GSEA) identified a potential role for GSC in tumor angiogenesis. We chose Seizure Related 6 Homolog (SEZ6), one of the Wnt target genes, for further study, as its downregulation inhibited the potential of GSCs to induce angiogenesis without impacting GSC growth. SEZ6, a transmembrane protein, is shed upon cleavage by Beta-site APP cleaving enzyme 1 (BACE 1) and is known to be involved in normal neuronal functions; however, its role in cancer has not been studied yet. SEZ6 silencing inhibited GSC-initiated tumor growth in an intracranial orthotopic mouse model due to reduced tumor angiogenesis and increased the mouse survival. Pre-treatment with a pharmacological inhibitor of BACE1 (BACE1i) prevented SEZ6 shedding from GSCs and inhibited the ability of the GSC-secretome to induce angiogenesis. Further investigations are ongoing to establish the use of BACE1i or BACE1-silencing as a novel therapeutic strategy to inhibit SEZ6-mediated tumor angiogenesis. We also carried out a protein array-based investigation, which revealed that SEZ6 induced IL8 in endothelial cells to induce angiogenesis. Additional investigation showed that SEZ6 activated the TGFβ pathway in endothelial cells to induce IL8. SEZ6 interacted with TGFβRII as seen by confocal microscopy and co-immunoprecipitation. Generation of various deletion mutants of SEZ6 revealed that three Sushi [also known as complement control protein (CCP) module or the short consensus repeat (SCR)] domains, 3, 4, and 5, interacted with TGFβRII. Molecular docking and dynamic simulation studies identified Sushi-3 domain as the mediator of the interaction between SEZ6 and TGFβRII extracellular domain. Based on the above results, experiments are underway to design specific inhibitors of this interaction. We are also developing an improved BACE1 inhibitor that would inhibit the shedding of SEZ6 into the extracellular milieu to inhibit SEZ6 functions. Thus, this study establishes that GSC-secreted SEZ6 activates the TGFβ pathway in endothelial cells to induce tumor angiogenesis and proposes a novel therapeutic target. Citation Format: Arani Mukherjee, Shreoshi Sengupta, Abhishek Chowdhury, Anand Srivastava, Kumar Somasundaram. Seizure related 6 homolog (SEZ6), a cancer stem cell-specific secreted protein, is a novel GBM therapeutic target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2786.