BSBM-11 COMBINING IMMUNOTHERAPY AND WHOLE-BRAIN RADIATION THERAPY IN A NOVEL SYNGENEIC LUNG CANCER BRAIN METASTASIS PRECLINICAL MODEL: DOES TIMING OF ADMINISTRATION MATTER?

Approximately 50% of all brain metastasis cases originate from primary lung tumors. Whole-brain radiation therapy (WBRT) is a common treatment for patients with multiple brain metastases, but patients rarely survive longer than one year after diagnosis. Recent studies demonstrate improved outcomes with combinatorial radiotherapy and immunotherapy, but the optimal timing of immunotherapy administration is unclear. Eliciting a robust immune response post-immunotherapy is vital for therapeutic efficacy. Our work shows that the BBB is disrupted and proinflammatory cytokines are increased in the brain 12 hours post-WBRT in immunocompetent but not immunocompromised mice. Additionally, efflux transporter activity is decreased at this time point. This study utilizes a novel Lewis Lung Carcinoma cell line, LLC-Br, which was developed in our laboratory to preferentially metastasize to the brain. Mice were treated with immune checkpoint inhibitors (ICIs) before or after WBRT then we evaluated tumor progression, survival, and blood-tumor barrier (BTB) permeability. We hypothesized administration of ICI following WBRT would increase survival, decrease tumor burden, and increase BTB permeability in our preclinical syngeneic lung cancer brain metastasis model.