(A588) Optimal timing of Panitumab-IRDye800CW administration for surgical fluorescence imaging for Head and Neck cancer

Introduction: Surgical fluorescence imaging with EGFR targeting antibodies, including panitumumab-IRDye800CW (Pan-800), has been previously demonstrated to identify cancer in real time. In this study, we evaluate the optimal timing of administration of Pan-800 prior to surgery.

Methods: We evaluated 14 patients who received a 50mg dose of Pan-800 administered 2-7 days preoperatively prior to head and neck cancer surgery (NCT #05945875, #04511078). Quantitative and qualitative assessment of fluorescent intensity was performed on plasma and tumor tissues to correlate the concentration of pan-800 relative to the timing between infusion and surgery . In addition, paraffin blocks of primary tumor site tissue were pathologically divided into malignant and normal sections to evaluate mean fluorescence intensity (MFI) as a surrogate for drug concentration.

Results: Pan-800 concentrations in fresh samples negatively correlated with the time from infusion to surgery in both plasma (rs=-0.83, p=0.0005) and tissue (rs=-0.62, p=0.045). The percentage of intact Pan-800 based on SDS-PAGE also negatively correlated with time in both plasma (rs=-0.73, p=0.0039) and tissues (rs=-0.83, p=0.0023). The median MFI of malignant blocks was significantly higher on day 2-3 compared to day 4-7 (MFI 899 vs 232, p< 0.001). However, the signal-to-background ratio (SBR), calculated by dividing the MFI of the malignant blocks by the MFI of normal blocks, did not change over time (rs=-0.42, p=0.13).

Conclusions: The intensity of the Pan-800 signal degrades in both plasma and tissues after 3 days. The optimal timing for surgical imaging using antibody-based fluorophores is likely between 1-3 days.