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HDACi and PLK1i synergize in MYC-amplified MB

ABSTRACT: We and others have demonstrated that MYC-amplified medulloblastoma (MB) cells are susceptible towards treatment with class I histone deacetylase inhibitors (HDACi). However, single drug treatment with HDACi has shown limited clinical efficacy. We hypothesized that addition of a second compound acting synergistically with HDACi may enhance efficacy. Gene expression changes in HDACi entinostat-treated cells identified, the cell cycle protein PLK1 as a potential second target. Indeed, MYC-amplified tumor cells are highly sensitive towards treatment with ATP-competitive PLK1 inhibitors as monotherapy. Moreover, entinostat and PLK1i in combination act synergistically in MYC-driven MB, exerting cytotoxic effects at clinically relevant concentrations. The downstream effect of both drugs as monotherapy and in combination is exerted via MYC-related pathways, pointing out the potential of MYC amplification as a clinically feasible predictive biomarker for patient selection. While entinostat significantly extended survival of mice implanted with orthotopic MYC-amplified MB PDX, there was no evidence of the improvement of survival when treating the animals with combination. However, further screening of blood-brain barrier penetrating PLK1is is necessary to determine the true potential of the combination. We use microarry to interrogate the expression differences in vehicle, entinostat, volasertib or combination treated cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE220748 | GEO | 2023/05/15

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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HDACi and PLK1i synergize in MYC-amplified MB

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