Abstract
Diffuse intrinsic pontine glioma (DIPG) is one of the most lethal pediatric brain tumors. DIPG is insensitive to chemotherapy and surgically inaccessible, creating an urgent need for novel therapeutic approaches. We have been evaluating peptide vaccine immunotherapies that target glioma-associated antigens (GAAs). Enhancing the expression of these immunogenic GAAs and MHC I on tumor cells may promote immune-mediated tumor recognition and killing following peptide vaccine immunotherapy. DNA methyltransferase (DNMT) inhibitors have been shown to augment the expression of MHC, tumor antigens, and other immunosensitizing molecules. Guadecitabine (SGI-110), a next-generation DNMT inhibitor, has been developed to prolong tumor cell exposure to its active metabolite, decitabine. In this study, we investigated whether SGI-110 can immunosensitize glioma cells to peptide vaccine immunotherapy by enhancing their surface expression of MHC I and a GAA, EphA2. We developed a novel C57BL/6-syngeneic DIPG model by culturing cells from a Sleeping Beauty de novo DIPG induced in a neonatal mouse using a K27M-mutated histone 3.3 plasmid and other oncogenic plasmids (SB-DIPG-11). Flow cytometry analysis showed that SB-DIPG-11 cells express both MHC I (H-2Kb/H-2Db) and EphA2 on their surface. In vitro, treatment of SB-DIPG-11 or C57BL/6-syngeneic GL261 cells with SGI-110 resulted in a dose-dependent increase of MHC I and EphA2 surface expression. In vivo, subcutaneous administration of SGI-110 in combination with an EphA2-targeted peptide vaccine significantly prolonged the survival of mice bearing orthotopic DIPG-like tumors compared with the control treatment. Analysis of dissociated tumor tissue by flow cytometry showed elevated levels of MHC I and EphA2 in mice receiving SGI-110 or SGI-110 and peptide vaccine. Based on these data, we have begun evaluating SGI-110 with peptide vaccine in a distinct highly immunogenic syngeneic glioma model and whether subcutaneous or intracerebroventricular administration of the drug is more effective. Overall, SGI-110 may sensitize children with DIPG to peptide vaccine immunotherapy.