SMARCA5 Inhibition as a Therapeutic Target for Glioblastoma

About This Grant

PROJECT SUMMARY Glioblastoma (GBM) is an aggressive form of primary brain tumor, characterized by high malignancy and genetic heterogeneity, and standard treatment for GBM has remained unchanged in the last decade. A feature of GBM that makes it particularly difficult to treat is its heterogeneity, in part created by glioma stem cells (GSCs) within the solid tumor. GSCs have high plasticity and the ability to self-renew and differentiate into various heterogenic cancer cell populations. GSCs are kept in a ‘stem’- like state with unlimited self-replication without differentiation and maturation, which helps maintain tumor heterogeneity and growth. This state also prevents them from being targeted effectively by traditional therapeutics. Histone modifications keep late-glial genes unreachable by transcription factors, promoting transcription of replication and early-glial genes, maintaining stem-ness. A major player in this process is the imitation switch (ISWI) family of ATP-dependent chromatin remodelers, which have been found to have widespread aberrant expression in cancers, including gliomas. The ISWI complex can change the spacing of histones on the chromatin, and is primarily involved in the repression of gene expression. It contains two catalytic subunits, SMARCA1 and SMARCA5, which can have disparate expression patterns and modifications. SMARCA5 in particular is a drug-able target and has been shown to be more highly expressed in GBM than SMARCA1, and miRNA silencing of SMARCA5 has been shown to limit GSC stem-ness. If SMARCA5 is successfully inhibited and doing so enables transcription factor machinery to access the late-glial genes blocked by ISWI, resulting chromatin modification and gene expression would end the GSC cycle of self-replication and inhibit associated malignancies. We hypothesize that SMARCA5 is vital to maintaining a stem-like state in GSCs and to promoting tumor growth, and is therefore a promising therapeutic target. To test this, we will manipulate SMARCA5 expression through genetic knockdowns and pharmacological inhibition. Aim 1: Test the hypothesis that SMARCA5 is essential to maintaining GSC stem-ness, looking in vitro at measure of stem-like state and heterogeneity. Aim 2: To interrogate the effects of SMARCA5 on chromatin and on changes to gene expression in GSCs using sequencing like RNAseq, ATACseq, and CUT&TAG. We will examine differential expression of differentiation- related genes and other changes created by SMARCA5 depletion. Aim 3: To test the hypothesis that SMARCA5 inhibition in vivo extends animal survival and is an effective treatment strategy in mice models. Showing that SMARCA5 depletion is also effective at targeting GSCs in vivo will further confirm it as a potential therapeutic target for GBM.