Abstract PO-052: Radiation regimen and timing of PD1 blockade critically influence response to combination therapy in head and neck squamous cell carcinoma

Abstract

Abstract Head and neck squamous cell carcinoma (HNSCC) constitute the sixth most common cancer worldwide, with a 5-year survival of less than 50% for advanced HNSCC patients. Radiation therapy (RT) is widely used in the treatment of HNSCC patients. Preclinical studies have shown that RT can trigger immune mediated response that potentiates tumor regression. However, the use of RT in combination with immune checkpoint inhibitor, specifically programmed death protein-1 blockade (αPD-1), has not been extensively examined in HNSCC. In vitro studies in our laboratory revealed that radiation increased PD-L1 expression in HNSCC tumor cells in a dose-dependent manner. Based on this observation, we hypothesized that the efficacy of RT and αPD-1 therapy would be critically influenced by the timing of αPD-1 of administration. To test this hypothesis, we conducted a preclinical study using a novel orthotopic immunocompetent mouse model of HNSCC (RPMOC1). Tumor bearing mice were randomized into the following arms: RT (single dose 10 Gy), fractionated RT (fRT- 2Gy x 5), RT prior to αPD-1(200 μg), RT post αPD-1, fRT prior to αPD-1 and fRT post αPD-1. Non-invasive magnetic resonance imaging (MRI) was used to monitor tumor response to therapy. All treatment regimens were well tolerated and did not result in weight loss during the experiment. The most potent tumor growth inhibition was observed in the RT (10 Gy) and αPD-1 combination therapy group. RT given either before or after αPD-1 therapy resulted in a significant decrease in tumor volumes (p<0.05) compared to other groups. Combination therapy with fractionated radiation did not show improved response compared to monotherapy. Overall, our observations indicate that tumor response to combined radiation and immunotherapy is critically influenced by the radiation regimen and timing of PD1 blockade in HNSCC. Citation Format: Aparajita Verma, Michael Habitzruther, Kristopher Attwood, Mukund Seshadri. Radiation regimen and timing of PD1 blockade critically influence response to combination therapy in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-052.