Abstract 3314: Glioblastoma treatment using epigenetic modification induced by microsecond pulsed electric field (µsPEF) exposure

Abstract

Abstract Epigenetic modifications derived from changes in sub-cellular localization and activity of the post-translational histone modifying enzymes, histone deacetylases (HDACs) are one of the strategies to treat various types of cancer. Aberrant HDAC activity is an indicator of glioblastoma multiforme (GBM), generally leading to hypoacetylation of histones and a transcriptionally repressed chromatin state. Most noticeably, HDAC4 expression increases 61,000% in brain tumors!1 Upregulation of HDAC4 in human glioma cells (U87-MG) stimulates proliferation and invasiveness, making HDAC4 a therapeutic target. The effectiveness of pharmacological HDAC inhibitors is hampered by non-specific targeting and low selectivity, especially in solid tumors like GBM, and by side-effects with systemic delivery, e.g. cardiac toxicity.2 Existing electroporation-based approaches to GBM aim to induce cell death either directly3 or in combination with adjuvants such as excess extracellular calcium4 or chemotherapy drugs5.A cytostatic approach is introduced in which the initial electroporation from non-thermal, localized µsPEF exposure elicits downstream epigenetic responses that decrease cell proliferation, circumventing obstacles experienced by pharmacological agents. Accumulation of HDAC4 in the nucleus of U87-MG cells following exposure to µsPEF is hypothesized to lead in a dose-dependent manner to cell death via apoptosis and decreased proliferation.A BTX GeminiX2 electroporator delivered square-wave µsPEF of 100 µs and 1.45 kV/cm, while the number of pulses (0, 1, 10, 20 pulses, delivered at 1 Hz) were varied to determine thresholds for HDAC4 translocation and proliferation reduction of U87-MG cells. For immunofluorescence assay to track HDAC4 location at 3 h after exposure, cells were cultured and exposed on glass-bottom dishes. For MTT and ATP kinase assays, cells were exposed in electroporation cuvettes and transferred to 96-well plates to measure proliferation at 6, 24 and 72 h after exposure. The ratio of HDAC4 in the nucleus compared to the cytoplasm (N/C ratio) more than doubles after 20 pulses, compared to sham control with no µsPEF exposure. Cell concentration relative to control drops over 90% given 20 pulses. Our data reflect the inhibition of cell proliferation and HDAC4 accumulation in nuclei. Although electroporation-based therapies for GBM have been studied pre-clinically, this study delves further into fundamental mechanisms and optimization of the energy delivered by µsPEF exposure that induces cell death with respect to epigenetic modification. 1. Lee P. et al. Anticancer Res, 35:615, 2015.2. Slingerland M. et al. Anticancer Drugs, 25:140, 2014.3. Rossmeisl J.H. et al. J Neurosurg, 123:1008, 2015.4. Wasson E.M. et al. Ann Biomed Eng, 45:2535, 2017.5. Sharabi S. et al. Sci Rep, 10:2178, 2020. Citation Format: Zahra Safaei, Gary L Thompson. Glioblastoma treatment using epigenetic modification induced by microsecond pulsed electric field (µsPEF) exposure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3314.