Abstract 3948: Enhancing immune checkpoint delivery to diffuse midline glioma (DMG) using focused ultrasound

Brain tumors, such as diffuse midline glioma (DMG), remain the leading cause of cancer-related death in pediatric oncology due to their universal fatality and limited treatment options. Treatment of DMG is hindered by the blood-brain barrier (BBB) presenting a roadblock in the clinical translation of therapies, particularly for larger therapeutic agents such as antibodies (e.g., immune checkpoint inhibitors). Focused ultrasound (FUS) and cavitating microbubbles provide a solution to this by transiently disrupting the BBB in a controlled and safe manner, allowing significantly enhanced drug delivery to a brain tumor whilst avoiding healthy tissue. In this study, we investigated the use of immune checkpoint inhibitors in in vitro and in vivo (orthotopic murine) DMG models. An in vitro transwell model in combination with FUS was used to determine if immune checkpoint inhibitors can pass through an endothelial layer (BENd3) following FUS blood-brain barrier opening (BBBO) at therapeutic concentrations, using fluorescence imaging and flow cytometry. We further tested our immune checkpoint inhibitors in an in vivo orthotopic murine DMG model (mDMG-3.3). Uptake enhancement following FUS was determined using fluorescence imaging. The results demonstrated a significant increase in the delivery of antibodies across the BBB following FUS in vitro. We also showed that FUS BBBO had no significant effect on endothelial cell viability. FUS-induced BBBO was performed in tumor-bearing mice using systemically administered SonoVue microbubbles (2 mL/kg), and FUS (peak-negative pressure = 320 kPa, cycle number = 500, pulse repetition frequency (Hz) = 5, number of pulses = 600). T1-weighted MRI was used immediately after FUS-induced BBB opening to confirm that the BBB had opened. Real-time passive cavitation detection was also used to record the harmonic signals of the cavitating microbubbles to control BBB opening, and for post-experiment analysis of microbubble behavior. Immediately following BBBO, mice were dosed with fluorescently labelled antibody (10 mg/kg) i.v., and then FUS BBBO was shown to cause a significant enhancement in uptake of the labelled antibody into the sonicated region. These results suggest that FUS-BBBO is a suitable technology to safely enhance the uptake of immune checkpoint inhibitors into DMG tumors. Future work will include evaluation of the survival benefits of immune checkpoint inhibitors in our mouse DMG models. Citation Format: Amelia Claxton, Paul Cressey, David Thurston, Esther Hulleman, Antonios Pouliopoulos, Darren Hargrave, Maya Thanou. Enhancing immune checkpoint delivery to diffuse midline glioma (DMG) using focused ultrasound [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3948.