Epigenetic targets of histone bromodomain and demethylase in DIPG therapy

ayman’s Summary Diffuse intrinsic pontine gliomas (DIPGs) carry a very poor prognosis despite the use of intensive multi-modality treatment. No significant advances in the survival of patients with DIPG have been made over the last few decades, and new therapeutic approaches are desperately needed. Recent genetic analysis found a novel gene mutation in DIPG that changes a DNA binding protein, histone H3.3, and our recently published work was the first to demonstrate that pharmacologic inhibition of the histone modifying enzyme increases histone methylation in the mutant DIPG cells, while showing strong anti-tumor activity. In addition, recent study of over expressing the histone mutation shows that histone H3 acetylation levels and its binding protein (bromodomain protein) are increased in the nucleosomes. As such, the molecular as well as tumor biological consequences of, and therapeutic options for treating DIPGs are subjects of intense interest. Major goal of this project is to investigate whether targeting multiple histone modifiers is a potential intervention strategy for the treatment of DIPG. This project will determine whether combination of two histone modifiers provides synergistic benefits, and will inform how best to maximize the clinical potential of epigenetic combination therapy for effective treatment of children with DIPG. Scientific Summary Diffuse intrinsic pontine gliomas (DIPGs) continue to carry a very poor prognosis despite the use of multi-modality treatment. No significant advances in the survival of DIPG patients have been made over the last few decades. Recent genetic screenings in DIPG samples identified oncogenic H3F3A gene mutations, resulting in replacement of lysine 27 by methionine (K27M) in the encoded histone H3.3 protein. This discovery of histone mutations affecting chromatin regulation has dramatically improved our understanding of disease pathogenesis, and these findings have stimulated the development of novel therapeutic approaches targeting epigenetic regulators for disease treatment. We have recently shown that inhibition of the histone H3K27 demethylase JMJD3 acts to restore H3K27 methylation in DIPG cells, while demonstrating potent anti-tumor activity in vitro and in vivo. In addition, recent study from Drosophila melanogaster constitutively expressing K27M indicates that H3K27 acetylation levels and bromodomain-containing proteins are increased in K27M–containing nucleosomes. As such, the molecular as well as tumor biological consequences of, and therapeutic options for treating DIPGs are subjects of intense interest. Major goal of this project is to investigate whether targeting histone modifiers by GSKJ4 and JQ1 is a potential intervention strategy for the treatment of DIPG. We will determine whether two histone modifiers provide synergistic benefits, and may also synergize with other targeted modifiers. This “combination” approach will not only potentially increase therapeutic efficacy but also reduce the likelihood of drug resistance. Our results from combination therapy of GSKJ4 and JQ1 will provide a potential molecular mechanistic basis between H3K27 methylation and acetylation for any observed enhancement anti-tumor activity, and will inform how best to maximize the clinical potential of epigenetic histone modifiers for effective treatment of DIPG.