EXTH-49. STING-induced blood-brain barrier opening in combination with radiation therapy potentiates anti-glioma immune and therapeutic activity monitored with [18F]-FLT PET

Radiation therapy (RT) is the standard of care for glioblastoma but is not curative. Triggering the cGAS/STING pathway with potent agonists such as 8803 exerts marked monotherapeutic activity across high-grade glioma preclinical models through the induction of anti-tumor immune responses. To determine if the combination of 8803 with radiation therapy (RT) warrants consideration in the upfront treatment setting and to clarify the underlying mechanisms of therapeutic activity, C57BL/6 mice harboring intracerebral CT-2A or QPP8v high-grade gliomas were treated with RT (2 Gy), 8803, or both. 8803 with RT resulted in 80% long-term and undefined median survival (MS) relative to monotherapy (control MS: 25; 8803 MS: 36; RT MS: 38 days) in the high-grade CT-2A glioma model (combination vs. control p<0.0001), but not in the radiation-resistant QPP8v model. CRISPR gene editing was used to knock out (KO) STING in CT-2A glioma cells to model the epigenetic silencing of STING expression in human glioblastoma. Nonetheless, the combinatorial therapeutic effect is maintained in the STING KO CT-2A glioma model, indicating that the immune system mediates the survival benefit. STING activation can be visualized longitudinally with [18F]-FLT uptake in the CT-2A-bearing mice, with peak uptake at 48-96 hours concordant with sequential multiplex immunofluorescence p-IRF-3 expression. Sc-RNA sequencing of the CT-2A glioma during the therapeutic window identified a nitric oxide synthase gene signature in the Inflam-TAM(2) population, contributing to combinatorial efficacy. A single intracranial injection of 8803, but not RT monotherapy, in non-tumor bearing C57BL/6J mice, induces diffuse bi-hemispheric blood-brain barrier (BBB) opening, shown by fluorescent imaging up to 24 hours, which is abolished in STING KO background mice. As such, 8803 combined with RT triggers distinctive anti-glioma immune reactivity, facilitates brain immune infiltration through opening of the BBB, and warrants consideration for clinical trials in the up-front setting for glioblastoma that can be monitored with PET imaging.

Duke Scholars

Author David Michael Ashley Neurosurgery