Development of a drug–device combination for fluorescence-guided surgery in neuroendocrine tumors

Significance: The use of cancer-targeted contrast agents in fluorescence-guided surgery (FGS) has the potential to improve intraoperative visualization of tumors and surgical margins. However, evaluation of their translational potential is challenging. Aim: We examined the utility of a somatostatin receptor subtype-2 (SSTR2)-targeted fluorescent agent in combination with a benchtop near-infrared fluorescence (NIRF) imaging system to visualize mouse xenografts under conditions that simulate the clinical FGS workflow for open surgical procedures. Approach: The dual-labeled somatostatin analog, Ga67-MMC(IR800)-TOC, was injected into mice (n = 24) implanted with SSTR2-expressing tumors and imaged with the customized OnLume NIRF imaging system (Madison, Wisconsin). In vivo and ex vivo imaging were performed under ambient light. The optimal dose (0.2, 0.5, and 2 nmol) and imaging time point (3, 24, 48, and 72 h) were determined using contrast-to-noise ratio (CNR) as the image quality parameter. Video captures of tumor resections were obtained to provide an FGS readout that is representative of clinical utility. Finally, a log-transformed linear regression model was fitted to assess congruence between fluorescence readouts and the underlying drug distribution. Results: The drug–device combination provided high in vivo and ex vivo contrast (CNRs > 3, except lung at 3 h) at all time points with the optimal dose of 2 nmol. The optimal imaging time point was 24-h post-injection, where CNRs > 6.5 were achieved in tissues of interest (i.e., pancreas, small intestine, stomach, and lung). Intraoperative FGS showed excellent utility for examination of the tumor cavity pre- and post-resection. The relationship between fluorescence readouts and gamma counts was linear and strongly correlated (n = 334, R2 = 0.71; r = 0.84; P