ET-9 Development of photosensitive antibodies for near-infrared light immunotherapy targeting EGFR and IL13Rα2 of malignant gliomas and investigation of their photodynamic cytotoxic activity in vitro

Introduction: Near-Infrared Photoimmunotherapy (NIR-PIT) is a recently developed hybrid cancer therapy based on photodynamic cytotoxicity and anti-tumor immunopotentiation, utilizing a photosensitive antibody drug (PSAD). A global Phase III trial of NIR-PIT with an anti-EGFR-PSAD in patients with recurrent head and neck squamous cell carcinoma (HNSCC) is already underway, and NIR-PIT is expected to have therapeutic applications also in malignant gliomas. Methods: In this study, monoclonal antibodies to EGFR and IL13Rα2 were conjugated to the photosensitive dye IRDye700DX (IR700) to produce PSADs (EGFR-Ab/IR700 and IL13Rα2-Ab/IR700) and in vitro PDT assays using these PSADs were performed on four human glioma cell lines (U87MG, U251, U138, A172).Five groups were studied: EGFR-Ab/IR700 monotherapy: 5 μg/ml or 10 μg/ml, IL13Rα2-Ab/IR700 monotherapy: 5 μg/ml or 10 μg/ml, and EGFR-Ab/IR700: 5 μg/ml + IL13Rα2-Ab/IR700: 5 μg/ml combination therapy. The cytotoxic activity of each group was compared after irradiation with 690 nm light at 16 J/cm2. Results: Significantly higher cytotoxic activity was observed in all four glioma cell lines when EGFR-Ab/IR700 and IL13Rα2-Ab/IR700 were used in combination at 5 μg/ml each, than when each PSAD was treated with a doubled dose (10 μg/ml).Conclusion: Malignant gliomas show extensive cellular heterogeneity with diverse expression of cell surface antigens. The present results suggest that a therapeutic strategy using several different photosensitive antibodies simultaneously may lead to the release of tumor antigens from a greater number of tumor cells, resulting in a more efficient host immune response for therapeutic purposes.