Combined Targeting of Mutant p53 and Jumonji Family Histone Demethylase Augments Therapeutic Efficacy of Radiation in H3K27M DIPG.

Anatoly Nikolaev,John B. Fiveash,Eddy S. Yang

doi:10.3390/ijms21020490

Abstract

Diffuse intrinsic pontine glioma (DIPG) is an aggressive pediatric brainstem tumor with a 5-year survival of <1%. Up to 80% of the DIPG tumors contain a specific K27M mutation in one of the two genes encoding histone H3 (H3K27M). Furthermore, p53 mutations found in >70–80% of H3K27M DIPG, and mutant p53 status is associated with a decreased response to radiation treatment and worse overall prognosis. Recent evidence indicates that H3K27M mutation disrupts tri-methylation at H3K27 leading to aberrant gene expression. Jumonji family histone demethylases collaborates with H3K27 mutation in DIPG by erasing H3K27 trimethylation and thus contributing to derepression of genes involved in tumorigenesis. Since the first line of treatment for pediatric DIPG is fractionated radiation, we investigated the effects of Jumonji demethylase inhibition with GSK-J4, and mutant p53 targeting/oxidative stress induction with APR-246, on radio-sensitization of human H3K27M DIPG cells. Both APR-246 and GSK-J4 displayed growth inhibitory effects as single agents in H3K27M DIPG cells. Furthermore, both of these agents elicited mild radiosensitizing effects in human DIPG cells (sensitizer enhancement ratios (SERs) of 1.12 and 1.35, respectively; p < 0.05). Strikingly, a combination of APR-246 and GSK-J4 displayed a significant enhancement of radiosensitization, with SER of 1.50 (p < 0.05) at sub-micro-molar concentrations of the drugs (0.5 μM). The molecular mechanism of the observed radiosensitization appears to involve DNA damage repair deficiency triggered by APR-246/GSK-J4, leading to the induction of apoptotic cell death. Thus, a therapeutic approach of combined targeting of mutant p53, oxidative stress induction, and Jumonji demethylase inhibition with radiation in DIPG warrants further investigation.

Highlights

Diffuse intrinsic pontine glioma (DIPG) is an aggressive pediatric brainstem tumor, which constitutes about 75% of all brainstem malignancies found in children [1,2]
Given the important role of p53 tumor suppressor activities and H3K27 methylation in DNA damage response [21,22], we investigated the efficacy of mutant p53 targeting, oxidative stress induction, and Jumonji family histone demethylase JMJD3 inhibition combined with therapeutic radiation in human DIPG cells
Since mutations in TP53 gene are present in the majority of DIPG cases, and given the increased tumor aggressiveness and worse overall prognosis associated with TP53 mutations DIPG, we investigated the efficacy of mutant p53 targeting with APR-246, a molecular agent shown to form covalent bonds with mutant p53 protein and to induce oxidative stress by glutathione depletion and thioredoxin reductase inactivation in a variety of cancer types [14,18]

Summary

Introduction

Diffuse intrinsic pontine glioma (DIPG) is an aggressive pediatric brainstem tumor, which constitutes about 75% of all brainstem malignancies found in children [1,2]. Up to 80% of DIPG tumors contain a specific K27M mutation in one of two genes encoding histone H3 (H3K27M). A specific inhibitor of Jumonji family histone demethylase GSK-J4 was recently reported to restore H3K27 tri-methylation patterns in human DIPG cells and improve survival of H3K27M mutant orthotopic xenograft brainstem tumor models [16,17]. Given the important role of p53 tumor suppressor activities and H3K27 methylation in DNA damage response [21,22], we investigated the efficacy of mutant p53 targeting, oxidative stress induction, and Jumonji family histone demethylase JMJD3 inhibition combined with therapeutic radiation in human DIPG cells. Our hypothesis was that dual targeting of the proposed epigenetic mechanisms of disease pathogenesis mediated by H3K27M and TP53 mutations would sensitize DIPG cells to therapeutic radiation

Results

Materials and Methods

Conclusions