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Reduced chromatin binding of MYC is a key effect of HDAC inhibition in MYC amplified meduloblastoma [expression]

ABSTRACT: MYC is a driver oncogene in many cancers. Inhibition of MYC promises high therapeutic potential, but specific MYC inhibitors remain unavailable for clinical use. Previous studies suggest that MYC amplified Medulloblastoma cells are vulnerable to HDAC inhibition. Using co-immunoprecipitation, mass spectrometry and ChIP-sequencing we show that HDAC2 is a cofactor of MYC in MYC amplified primary medulloblastoma and cell lines. The MYC-HDAC2 complex is bound to genes defining the MYC-dependent transcriptional profile. Class I HDAC inhibition leads to stabilization and reduced DNA binding of MYC protein inducing a down-regulation of MYC activated genes (MAGs) and up-regulation of MYC repressed genes (MRGs). MAGs and MRGs are characterized by opposing biological functions and distinct E-box distribution. We conclude that MYC and HDAC2 (class I) are localized in a complex in MYC amplified medulloblastoma and drive a MYC-specific transcriptional program, which is reversed by the class I HDAC inhibitor entinostat. Thus, the development of HDAC inhibitors for treatment of MYC amplified medulloblastoma should include HDAC2 in its profile in order to directly target MYC´s trans-activating and trans-repressing function.

ORGANISM(S): Homo sapiens

PROVIDER: GSE143384 | GEO | 2020/09/01

REPOSITORIES: GEO

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Project description:MYC-driven Group 3 medulloblastoma (MB) (subtype II) is a highly aggressive childhood brain tumor. Sensitivity of MYC-driven MBs to class I histone deacetylase inhibitors (HDACi) has been previously demonstrated in vitro and in vivo. We here characterize the transcriptional effects of class I HDAC inhibition in MYC-driven MB and explore beneficial drug combinations. MYC-amplified Group 3 MB cells (HD-MB03) were treated with class I HDACi entinostat. Changes in the gene expression profile compared to untreated control were quantified on a microarray. Gene set enrichment analysis, cytoscape enrichment mapping and ingenuity pathway analysis led to the identification of pathways affected by entinostat treatment. Five drugs interfering with these pathways (olaparib, idasanutlin, ribociclib, selinexor, vinblastine) were tested as single agents in metabolic activity assays in three MYC-amplified and two non-MYC-amplified MB cell lines. Synergy with entinostat was evaluated by dose response curve shift, combination index and zero interaction potency synergy model and validated in cell count and flow cytometry experiments in two MYC-amplified and one non-MYC-amplified MB cell line. The effect of the most promising drug combination (entinostat and olaparib) on DNA damage was evaluated by γH2A.X quantification in immunoblotting, fluorescence microscopy and flow cytometry. Entinostat treatment changed the expression of genes involved in 22 pathways, including downregulation of DNA damage response. The PARP1 inhibitors olaparib and pamiparib showed synergy with entinostat. The combination of entinostat and olaparib led to increased cell death, decreased viability and increased formation of double strand breaks selectively in MYC-amplified MB cells. MYC-amplified MB cells treated with entinostat and olaparib were particularly vulnerable to additional induction of DNA damage by doxorubicin. Non-MYC-amplified MB cells and normal human fibroblasts were not susceptible to this triple treatment. Our study identifies the combination of entinostat with olaparib and doxorubicin as a new potential therapeutic approach for MYC-driven Group 3 MB.

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Reduced chromatin binding of MYC is a key effect of HDAC inhibition in MYC amplified meduloblastoma [expression]

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