Zinc Finger MYND-Type Containing 8 (ZMYND8) is epigenetically regulated in mutant Isocitrate Dehydrogenase 1 (IDH1) glioma to promote radioresistance [ChIP-seq]

Mutant isocitrate dehydrogenase 1 (mIDH1) alters the epigenetic regulation of chromatin, leading to a hypermethylation phenotype in adult glioma. This work focuses on identifying gene targets epigenetically dysregulated by mIDH1 to confer therapeutic resistance to ionizing radiation (IR). We evaluated changes in the transcriptome and epigenome in a radioresistant mIDH1 patient-derived glioma cell culture (GCC) following treatment with an mIDH1 specific inhibitor AGI-5198. We identified Zinc Finger MYND-Type Containing 8 (ZMYND8) as potential target of mIDH1 reprogramming. We suppressed ZMYND8 expression by shRNA knockdown and genetic knockout (KO) in mIDH1 glioma cells then assessed cellular viability to IR. We assessed the sensitivity of mIDH1 GCCS to pharmacological inhibition of ZMYND8-interacting partners: HDAC, BRD4, and PARP. Inhibition of mIDH1 lead to an upregulation of gene networks involved in replication stress. We found that the expression of ZMYND8, a regulator of DNA damage response was decreased in three patient-derived mIDH1 GCCs after treatment with AGI-5198. Knockdown of ZMYND8 expression sensitized mIDH1 GCCs to radiotherapy marked by decreased cellular viability. Following IR, mIDH1 glioma cells with ZMYND8 knockout (KO) exhibit significant phosphorylation of ATM and sustained ?H2AX activation. ZMYND8 KO mIDH1 GCCs were further responsive to IR when treated with either BRD4 or HDAC inhibitors. PARP inhibition further enhanced the efficacy of radiotherapy in ZMYND8 KO mIDH1 glioma cells. These findings indicate the impact of ZMYND8 in the maintenance of genomic integrity and repair of IR-induced DNA damage in mIDH1 glioma. Overall design: In this study, we sought to determine radioresistance mechanisms in IDH-mutant gliomas that contribute to glioma cell survival in response to radiotherapy. We utilized a radioresistant patient-derived glioma cell culture SF10602, which retained the endogenous mutations in IDH1-R132H, ATRX and TP53 after adaptation to in vitro culture. In order to identify pathwaysaltered by mIDH1 inhibition in SF10602, we performed ChIP-seq by administering 5µM AGI-5198 every 2 days for 10 days.