GD2 Induction by Combination Chromatin-Directed Inhibitors Enhances Targeting of Ewing Sarcoma and Osteosarcoma by CAR T Cells

Adoptive cellular therapies depend on the adequate expression of target antigens on tumors. The disialoganglioside GD2, a target of chimeric antigen receptor (CAR) T cells (GD2.CAR T cells) and monoclonal antibodies, is variably expressed in Ewing sarcoma and osteosarcoma. We investigated the ability of chromatin-directed small molecules to enhance tumor GD2 and sensitize tumors to GD2.CAR T cells. Although the EZH2 inhibitor tazemetostat increased GD2 levels in culture and in xenografted mice, tazemetostat treatment was unable to maintain sufficient tumor GD2 levels necessary to enable tumor control in a metastatic xenograft model. We performed a screen of chromatin-directed small molecules to identify additional compounds capable of regulating tumor GD2 and identified multiple compounds, including the HDAC inhibitor entinostat and the DOT1L inhibitor pinometostat. Both compounds greatly enhanced tumor GD2 expression by tazemetostat in culture but did not limit CAR T-cell activity. In multiple xenograft models, the combination of tazemetostat and entinostat resulted in enhanced tumor GD2 expression and led to long-term tumor control by GD2.CAR T cells. These data offer preclinical support for the incorporation of chromatin-directed inhibitors into ongoing CAR T-cell trials for Ewing sarcoma and osteosarcoma.