Abstract 1746: The BET inhibitor JQ-1 enhances radio-sensitivity in pediatric cancer cell lines by sustained p-gH2AX expression and enhanced differentiation

Abstract

Abstract Purpose: Pediatric high grade gliomas (HGG), high risk medulloblastomas (MB) and neuroblastomas (NB) are malignant neurological tumors with poor prognosis despite major advancements in current therapeutic interventions. The standard of care therapy for such high risk tumors includes surgical resection, when possible, and radio-therapy with or without chemo-therapy. Therapeutic failure may be due to radio- and/or chemo-resistance and the maintenance of an aggressive stem-like sub-population of cells within the bulk tumors. Epigenetic deregulation is implicated in pediatric neurological cancer malignancies where the bromo- and extra-terminal domain (BET) protein activity may play a role in histone H3K27 acetylation leading to tumorigenesis and radio-resistance. Methods and Results: We used the BET inhibitor JQ-1 to determine the radio-sensitizing effect on a panel of human pediatric neurological cancer cell lines including: NB (IMR-32 and SKNSH), MB (D556 and D283) and HGG (GBM01 and DIPG07). Cells were seeded 24 hours (h) before treatment with 1 µM dose of JQ-1 for an additional 24 h before irradiation (IR) with 6Gy (JL Shepherd Mark 1 137Cs Irradiator). IncuCyte (Essen Biosciences, Ann Arbor, MI) live cell imaging recorded cellular proliferation (confluency) over 6 days post IR, revealing that while single treatment with JQ-1 or 6Gy irradiation alone significantly reduced cell proliferation in all the tested cell lines, the combination of JQ-1 pre-treatment followed by 6Gy IR differentially impaired proliferation capacity in all cell lines except DIPG07 by further reducing cell proliferation. To determine the mechanism of radio-sensitization induced by JQ-1, Western blot and Immunofluorescence analysis revealed increased p-γH2AX foci at 24 h post IR in JQ-1 pre-treated cells. Furthermore, the stem cell maintenance and tumorigenic proteins OCT-4, MYCN, HSP90, L1-CAM, RAB5C and FABP5 were differentially expressed after JQ-1 treatment. Next we assessed the effect of JQ-1 on cellular migration and stem-cell maintenance using the ‘wound-healing' scratch and tumor-sphere self-renewal assays, respectively. Cell migration was significantly (P < 0.05) inhibited with JQ-1 in both human NB (IMR-32 and SKNSH) and MB (D556 and D283) cell lines. Tumor-sphere formation efficiency was significantly (P < 0.05) reduced in IMR-32, SKNSH, D556, D283 and DIPG cells after treatment with JQ-1. Morphological cellular differentiation, evidenced by long neurite extensions, was induced after JQ-1 treatment in the D556, IMR-32 and SKNSH cells. Conclusions: Our data show potent anti-stem cell activity as well as decreased proliferation, migration and enhanced radiosensitivity following JQ-1 treatment. These effects may be due to delayed DNA repair mechanisms, differential expression of stem cell maintenance and tumorigenic proteins and induced differentiation of the malignant cancer stem cells. Citation Format: Tamara Mary Abou-Antoun, Jad Abdallah, Amanda R. Khater, Sarra El-Soussi, Aysegul Balyimez, Shinjini Ganguly, Anthony Sandler, Omar Mian. The BET inhibitor JQ-1 enhances radio-sensitivity in pediatric cancer cell lines by sustained p-gH2AX expression and enhanced differentiation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1746.