TMIC-79. MYELOID-DIRECTED TREATMENT USING THE TLR7/8 AGONIST RESIQUIMOD IMPROVES THE SURVIVAL OF MICE WITH MEDULLOBLASTOMA AND ENHANCES EFFICACY OF RADIOTHERAPY Free

We show the therapeutic potential of myeloid-directed immunomodulatory treatment for medulloblastoma. Patients with medulloblastoma, the most common malignant pediatric brain tumor, need new treatments, as standard therapy produces disabling neurotoxicities and fails 20% of patients. About 30% of medulloblastomas show hyperactivation of the SHH (Sonic Hedgehog) signaling pathway, and these tumors have large myeloid populations in the tumor microenvironment (TME). We analyzed whether activating toll-like receptors on these myeloid cells would slow tumor growth. Our prior single-cell RNA sequencing studies in both patient samples and mouse models showed that 10% of the cells in SHH medulloblastoma are myeloid cells and that these cells uniquely express TLR7 and TLR8. We treated mice genetically engineered to develop SHH medulloblastomas with the TLR7/8 agonist resiquimod, administered systemically either as free drug or in polyoxazoline nanoparticles (POx-resiquimod), and compared POx-resiquimod+radiotherapy to radiotherapy alone. We found that POx-resiquimod extended the survival time of mice with medulloblastoma, while free drug failed to show benefit. PK studies showed that POx-resiquimod increased tumor drug exposure, consistent with increased efficacy. Mechanistically, POx-resiquimod increases tumor myeloid populations and decreased the fraction of myeloid cells that expressed IGF1. POx-resiquimod plus radiation therapy, moreover, was superior to either POx-resiquimod alone, or radiotherapy alone. Together our data show that the TLR7/8 agonist resiquimod, delivered in nanoparticle formulation, produces a significant anti-tumor effect in SHH medulloblastoma, and increased the efficacy of radiotherapy. As radiotherapy is the mainstay of current medulloblastoma treatment, we propose that TLR7/8-agonist therapy such as resiquimod may be added to current regimens to reduce the radiation dose needed for efficacy, and to increase the fraction of successfully treated patients.