Abstract 1870: Fluorescence-guided soft tissue sarcoma surgery using a cetuximab-imaging probe conjugate

BACKGROUND: Soft tissue sarcomas (STS) are a heterogeneous group of solid malignancies whose treatment includes margin-negative resection. Large tumor size and anatomic constraints make margin assessment challenging. Fluorescence-guided surgical resection can help delineate intraoperative margins; preclinical studies demonstrate improved oncologic outcomes in other malignancies using cancer-specific imaging probes. Recent literature describes cathepsin activated probes selective for STS, but no studies using disease-specific chemotherapeutic agents conjugated to imaging probes. This novel strategy has potential to decrease unnecessary healthy tissue resection and improve oncologic outcomes by reducing margin-positive resections. Epidermal growth factor receptor (EGFR) is overexpressed in multiple subtypes of STS and is a potential target for fluorescence-guided surgery. Recent studies show fluorescently labeled cetuximab, an FDA-approved, anti-EGFR antibody, to be safe and useful for margin assessment in other malignancies. Our aim was to evaluate its potential for STS, examining tumor-targeting specificity of two drug-probe conjugates, and comparing them to the described cathepsin-activated probes. We hypothesize the drug-probe conjugates would successfully target STS, with superior tumor specificity. We also aimed to determine the smallest tumor detectable by our conjugate. METHODS: Athymic nude mice with subcutaneous HT1080 fibrosarcoma tumors were injected with one of five probes: IRDye800CW fluorescent probe conjugated to either cetuximab (anti-EGFR) or DC101 (anti-VEGFR2), IRDye800CW conjugated to an isotype control (IgG), or a cathepsin-activated probe (IntegriSense 750 and Prosense 750). Fluorescence imaging was performed daily with open- and closed-field systems. Tumor-to-background ratios (TBR), signal washout times and normalized signal averages were evaluated. On day 9, smallest resectable game evaluation was performed to assess sensitivity for detecting residual post-resection tumor RESULTS: At day 9 post-injection, the TBR of the cetuximab-IRDye800CW group (11.1) was significantly greater than Integrisense750 (6.88, p=0.005), the IgG-IRDye800CW control (4.44, p=0.00005), Prosense750 (2.35, p=0.00009), and DC101-IRDye800CW (1.87, p=0.00003). During in vivo imaging, cetuximab-IRDye800CW outperformed all other agents by several folds of contrast enhancement. The smallest resectable game evaluation demonstrated 1mm3 fragment detection using the c