Dual Targeting of the Epigenome Via Facilitates Chromatin Transcription Complex (FACT) and Histone Deacetylase is a Potent Treatment Strategy for DIPG

Abstract

Diffuse intrinsic pontine glioma (DIPG) is an aggressive and incurable childhood brain tumor for which new treatments are needed. A high throughput drug screen of 3600 pharmaceutical compounds found that anti-malarials, including quinacrine had potent activity against DIPG neurospheres. CBL0137 is a novel anti-cancer compound developed from quinacrine, which targets Facilitates Chromatin Transcription (FACT), a chromatin remodelling complex involved in transcription, replication, and DNA repair. We have found that CBL0137 displays profound cytotoxic activity against a panel of patient derived DIPG cultures, inhibiting cell proliferation and clonogenic potential, restoring tumor suppressor TP53 and Rb activity and inducing cell death through induction of apoptosis. Moreover, in an orthotopic model of DIPG, treatment with CBL0137 significantly extended animal survival. Histone mutations leading to the loss of histone trimethylation result in epigenetic dysregulation driving DIPG tumorigenesis. Treatment with CBL0137 targets this epigenetic defect, restoring both histone H3.3 acetylation and trimethylation and leading to tumor cell death. Combined epigenetic treatment with the histone deacetylase (HDAC) inhibitor panobinostat led to inhibition of the Rb/E2F1 pathway, and increased the enzymatic activity of enhancer of zeste homolog 2 (EZH2), leading to the restoration of H3K27 trimethylation. This combination therapy had synergistic activity against DIPG neurospheres with induction of apoptosis. Consistent with the in vitro results, the combination of CBL0137 and panobinostat significantly prolonged the survival of mice bearing DIPG orthografts suggesting a potential treatment strategy for DIPG.