DIPG-01. Targeting p300: A master regulator of childhood diffuse intrinsic pontine glioma (DIPG)

Abstract

Abstract Diffuse intrinsic pontine gliomas (DIPG) are heterogeneous, highly aggressive, accounting for ~10% of all childhood central nervous system tumors that are poorly understood. The heterogeneity of the cell populations could contribute to major variability in tumor growth and chemoresistance followed by inadequate treatment responses. Approximately 80% of DIPG patients harbor mutations on lysine-27 of histone-3 (H3K27M), which forms heterotypic nucleosomes with normal, acetylated-H3K27 (H3K27ac), and colocalizes with bromodomain proteins to sites of active transcription. p300 (or EP300) bromodomain has recently been exploited as a potential therapeutic target in other cancer, with a small molecule inhibitor showing antiproliferative activity. Bromodomain inhibitors (BrDi) have been suggested as a potential therapeutic target for DIPG too which showed antiproliferative activity in vitro. We therefore hypothesize that p300 bromodomain inhibition is a potential therapeutic strategy that must be urgently explored in DIPG. p300 is a multi-domain enhancer protein, expressed in 80% of gliomas, responsible for H3K27ac mark and localizes to sites of H3K27ac enrichment, where it serves as an essential binding partner of histones to various transcription factors. p300 interacts with BMI-1, a polycomb repressive complex 1 (PRC1) group of transcription factor, through an intermediate protein NANOG, which promotes cell proliferation in head-neck squamous cell carcinoma. However, immunohistochemical study demonstrated that there is no NANOG expression found in DIPG patient samples. Therefore, we propose that p300 and BMI-1 interact with each other directly or through an intermediate molecule, essential for tumor growth and thus can be considered as a possible therapeutic target for DIPG. The overall outcome of this research will reveal the unexplored mechanisms of DIPG cell proliferation to overcome chemoresistance in sick children and develop drug/combination against this deadly malignancy, which can be used for future clinical trials.