A Dual Function Antibody Conjugate Enabled Photoimmunotherapy Complements Fluorescence and Photoacoustic Imaging of Head and Neck Cancer Spheroids

Several molecular-targeted imaging and therapeutic agents are in clinical trials for image-guided surgery and photoimmunotherapy (PIT) of head and neck cancers. In this context, we have previously reported the development, characterization, and specificity of a dual function antibody conjugate (DFAC) for multi-modal imaging and photoimmunotherapy (PIT) of EGFR over-expressing cancer cells. The DFAC reported previously and used in the present study, comprises of an EGFR targeted antibody – Cetuximab conjugated to Benzoporphyrin derivative (BPD) for fluorescence imaging and PIT, and a Si-centered naphthalocyanine dye for photoacoustic imaging. We report here the evaluation and performance of DFAC in detecting microscopic cancer spheroids by fluorescence and photoacoustic imaging along with their treatment by PIT. We demonstrate that while fluorescence imaging can detect spheroids with volumes greater than 0.049 mm 3 , photoacoustic imaging-based detection was possible even for the smallest spheroids (0.01 mm 3 ), developed in the study. When subjected to PIT, the spheroids showed a dose-dependent response with smaller spheroids (0.01 and 0.018 mm 3 ) showing a complete response with no recurrence when treated with 100 J/cm 2 . Together our results demonstrate the complementary imaging and treatment capacity of DFAC. This potentially enables fluorescence imaging to assess tumor presence on a macroscopic scale followed by photoacoustic imaging for delineating tumor margins guiding surgical resection and elimination of any residual microscopic disease by PIT, in a single intra-operative setting.