Immunomodulatory Activity Of Epigenetic Drugs: Laying The Ground For New Combined Immunotherapeutic Strategies For Glioblastoma

Rationale: Glioblastoma multiforme (GBM) is the most common and deadliest primary brain tumour in adults, with a very dismal prognosis and limited effective therapies. Immunotherapy may play a role in treating GBM, though the initial clinical results are still poor, and novel combined treatment(s) could possibly improve its efficacy. Manipulating the epigenome has been considered a therapeutic opportunity in GBM, since epigenetic modifications regulate glioma proliferation, metastasis, invasion, and prognosis. In addition, epigenetic alterations may negatively regulate the cross-talk between GBM and immune cells in GBM microenvironment (TME), thus limiting the efficacy of immunotherapy. We previously demonstrated the immunomodulatory potential of epigenetic drugs in cancer cells, and translated this notion in the clinic to improve efficacy of immunotherapy of melanoma patients (Di Giacomo AM, CCR 2019). Accordingly, this study aimed to evaluate the immunomodulatory potential of epigenetic drugs in GBM, and to provide the scientific rationale for new combinatorial therapeutic approaches in GBM patients. Methods: Patient-derived GBM (pGBM) cell lines (n=10) were established from surgically-removed GBM lesions and treated with the DNA hypomethylating agent guadecitabine (1 µM); commercially available human GBM (cGBM) cell lines (n=3) were treated with guadecitabine (1 µM) and/or with the EZH2-inhibitor GSK126 (10 µM). Expression of HLA class I and ICAM-1 by GBM cells was investigated by flow-cytometry; cancer testis antigens (CTA, i.e., NY-ESO, MAGE-A1 and MAGE-A3) and the epithelial-mesenchymal transition (EMT)-regulating cadherins (i.e., CDH1 and CDH2) expression was analyzed by quantitative Real-Time PCR. Results: A positive modulation of immune profile was observed in all investigated guadecitabine-treated GBM cells. Specifically, in untreated vs guadecitabine-treated cells, MFI mean values ± SD of HLA class I were 402±326 vs 442±303 in pGBM cells, and 277±127 vs 381±138 in cGBM cells; MFI mean values ± SD of ICAM-1 were 53±72 vs 92±116 in pGBM cells, and 5±6 vs 26±17 in cGBM cells. Though a slight increment was induced by GSK126 for HLA class I (312±169) and ICAM-1 (9±11) expression in cGBM, an additive effect was detected with GSK126+guadecitabine (405±261 for HLA class I and 35±22 for ICAM-1) in cGBM cells. Guadecitabine induced NY-ESO-1, MAGE-A1, and MAGE-A3 expression in 9/10, 6/10, and 5/8 pGBM cells, respectively and in all cGBM cells. Levels of CTA expression were increased in cGBM by GSK126+guadecitabine vs guadecitabine with mean Fold Change (FC) of 1.5, 1.6 and 1.6 for NY-ESO-1, MAGE-A1 and MAGE-A3 expression. Finally, CDH1 expression was induced in 1/3 and in 2/3 cGBM cells by guadecitabine and guadecitabine+GSK126, respectively; CDH2-positive expression was upregulated by guadecitabine (mean FC=2.45) but not by guadecitabine+GSK126. Conclusions: Immunomodulatory properties of epigenetic drugs in GBM should be exploited to improve the efficacy of GBM immunotherapy. Citation Format: Maria Fortunata Lofiego, Francesca Piazzini, Carolina Fazio, Ornella Cutaia, Carla Chiarucci, Sara Cannito, Elisabetta Gambale, Monica Valente, Anna Maria Di Giacomo, Sandra Coral, Clelia Miracco, Giuseppe Oliveri, Michele Maio, Alessia Covre. Immunomodulatory activity of epigenetic drugs: Laying the ground for new combined immunotherapeutic strategies for glioblastoma [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 4488.