Abstract 2388: Non-invasive imaging of hypoxia as a biomarker of immunotherapeutic efficacy in head and neck cancer
Authors: DeJohn Celia , Verma Aparajita , Vincent-Chong Vui King , Seshadri Mukund 
Published: April 2023

Abstract
Tumor hypoxia has long been recognized as a negative prognosticator in patients with head and neck squamous cell carcinomas (HNSCC). Recent studies have also demonstrated that hypoxia promotes an immunosuppressive tumor microenvironment. However, the potential of non-invasive imaging of tumor hypoxia as a biomarker of immunotherapeutic efficacy has not been previously studied in HNSCC. To address this gap in knowledge, in the present study, we employed photoacoustic imaging (PAI) with co-registered ultrasound (US) for spatiotemporal profiling of tumor hypoxia in orthotopic models of HNSCC. Orthotopic RP-MOC1 and SCCVII tumors were established in female albino C57Bl/6 and C3H/HeJ mice, respectively. Longitudinal measurements of PAI-based biomarkers of tumor vascularity (hemoglobin concentration; HbT) and hypoxia (oxygen saturation; sO2) were obtained during initial tumor growth and following treatment with anti-programmed death-1 antibody treatment (αPD1; 200 µg, 3 doses administered once every 3 days). PAI-based measures of HbT and sO2 were validated using immunohistochemical markers of proliferation (Ki67), vascularity (CD31), hypoxia (CAIX), CD8+ T cell levels and treatment outcomes (US-based tumor volumes). Prior to treatment, SCCVII tumors exhibited rapid growth kinetics on US that was associated with decreased HbT and sO2 levels on PAI . Consistent with these findings, immunohistochemical analysis of SCCVII tumors revealed higher numbers of Ki67+ cells, higher levels of CAIX and low CD8+ T cell levels. In comparison, RP-MOC1 tumors showed a slower tumor growth rate on US and higher levels of HbT and sO2 on PAI prior to treatment. Ex-vivo analysis of RP-MOC1 tumors showed lower CAIX staining and higher CD8+ T cells validating PAI observations. Treatment with αPD1 yielded distinct therapeutic response profiles between the two tumor models. While SCCVII tumors were consistently resistant to αPD1, RP-MOC1 tumors exhibited a differential response to immunotherapy with 47% of tumors showing regression (responders) and 53% of tumors displaying continued increase in growth (non-responders). Notably, αPD1 responsive tumors showed an early (24h post 1st dose) increase in HbT and sO2, likely reflective of increased vessel perfusion and alleviation of hypoxia mediated by CD8+ T cell accumulation and IFNγ production, as previously reported in colon cancer models. Collectively, our observations highlight the impact of hypoxia on the tumor immune microenvironment and demonstrate, for the first time, the potential of PAI with co-registered US as an early non-invasive biomarker of immunotherapeutic efficacy in head and neck cancer.
Citation Format: Celia DeJohn, Aparajita Verma, Vui King Vincent-Chong, Mukund Seshadri. Non-invasive imaging of hypoxia as a biomarker of immunotherapeutic efficacy in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2388.