EZH2 inhibition upregulates GD2 to enhance anti-GD2 immunotherapy in Ewing sarcoma

Introduction: Ewing sarcoma (ES) is a rare and aggressive malignancy of the bones and soft tissue for which substantial improvements in treatment options are desperately needed. ES cells heterogeneously express GD2, a surface marker for which there are targeted immunotherapies that are effective in other pediatric malignancies. The use of EZH2 inhibitors has been reported to increase expression of GD2 on the surface of sarcoma tumor cells. This study investigated the in vitro efficacy of an EZH2 inhibitor at increasing GD2 expression on ES cells with the aim of sensitizing them to anti-GD2 antibody treatment. Methods: Both commercial and patient derived ES cell lines were treated with low dose tazemetostat for an extended period, up to 28 days, followed by a withdrawal from treatment for 7 days. GD2 expression, cell cycle, and markers of apoptosis were evaluated at regular timepoints using a novel mass cytometry panel (CyTOF). OMIQ was used for data analysis and visualization. Efficacy of naxitamab was examined using immune cell killing assays on an Incucyte S3. Results: Tazemetostat treatment was found to increase GD2 expression on ES cells without significant impact on cell cycle or apoptosis. Elevation of GD2 expression was reversed upon withdrawal of drug. The addition of naxitamab displayed increased NK cell-mediated cell death in ES cells in response to increased GD2 expression. When pretreated with tazemetostat, GD2-low cell lines exhibit higher levels of apoptosis after treatment with naxitamab compared to untreated cells. Conclusions: This data supports the use of the EZH2 inhibitor tazemetostat for ES tumors that express low or heterogeneous levels of GD2 to enhance the effectiveness of GD2-targeting immunotherapeutic approaches. This study demonstrates the capability of CyTOF to look at multiple markers simultaneously to achieve a comprehensive characterization of various samples.