DDEL-17. INTRA-TUMORAL CONVECTION ENHANCED DELIVERY OF DEXAMETHASONE REDUCES INFLAMMATORY SIGNATURES AND EXTENDS SURVIVAL IN GBM MODEL

Abstract Dexamethasone is the most widely utilized drug for glioblastoma (GBM). However, systemic delivery of dexamethasone in GBM patients is associated with significant side effects and increasing doses with worse survival. Convection-enhanced delivery (CED) can deliver high doses of immunotherapy directly into the tumor microenvironment (TME) while avoiding systemic toxicity. Here, we report that high doses of dexamethasone can be delivered locally by CED without side effects and increase survival in a GBM model along with reduced inflammatory myeloid signatures. We investigated CED of dexamethasone treatment on survival(n=40), adverse side effects, and the immunological TME through peripheral analyses, liquid chromatography–mass spectrometry, and histology in a preclinical syngeneic mouse model. Additionally, we assessed the transcriptional responses of human GBM slices and stem-cell-derived human microglia after steroid treatment through bulk and single-cell RNA sequencing. We found that 7-day treatment with CED of dexamethasone produced a significant survival advantage in glioma-bearing mice compared to non-treated control(p=0.03). Systemic dexamethasone achieved low levels of drug in the TME and caused dysregulated blood glucose, blood counts, and peripheral organ weights, while high CED doses avoided these side effects(p< 0.05 each). Steroid treatment of acute GBM slices and lipopolysaccharide-activated microglia in-vitro both reversed inflammatory myeloid signatures associated with poor survival and recurrence on RNA sequencing analyses. We demonstrate the preclinical efficacy of delivering high local doses of dexamethasone in a GBM model through CED and observed prolonged survival along with reduced adverse inflammatory myeloid signatures. No side effects were demonstrated after chronic CED treatment of dexamethasone while systemic delivery achieved poor tumor penetration and caused known hematologic and metabolic side effects supporting the potential to optimize the clinical use of this therapy. CED of dexamethasone provides us a new treatment paradigm to locally control inflammatory signatures in the glioma TME in a controlled fashion.