uPAR targeted near infrared guided imaging for resection of primary tumor and metastases in an orthotopic pancreas xenograft model.

Objectives The objective of our study was to investigate the benefit of fluorescence guided surgery using a newly developed probe ICG-Glu-Glu-AE105 targeted against uPAR compared to white light surgery in pancreatic cancer.

Methods An orthotopic human xenograft tumor model was established by inoculation of BXPC3.luc into the head of the pancreas in nude mice. The primary tumor was detected and resected under fluorescence guidance with a clinically approved near-infrared (NIR) camera 12-15h post systemic injection of ICG-Glu-Glu-AE105 (10 nmol) After primary resection the animal model was allowed to grow and develop metastases. When metastases developed a second surgery was performed with injection of ICG-Glu-Glu-AE105 pre-operatively. First intended complete resection of all visible tumor deposits under white light (WL) was performed. Then the NIR camera was activated and additional metastases were identified with fluorescent imaging (FLI). When all fluorescent foci were removed bioluminescence imaging (BLI) was performed to detect and resect additional tumor foci. All resected tumor deposits were analyzed by immunohistochemistry for uPAR expression.

Results All mice developed a localized primary tumor which clearly could be identified by fluorescence with a mean tumor to background ratio (TBR) of 3.35. The primary tumor was removed under fluorescence guidance, however despite clear margins on microscopy, metastases were still seen in all animals. We speculate whether this is due to microscopic spread of tumor cell in the peritoneal fluid which was not visible with fluorescence. During a second cytoreductive surgery (n=8) the metastatic deposits could be detected with WL (67.4%), FLI (81.4%) and BLI (100%) respectively. The metastases removed with fluorescent guidance could be identified clearly with a mean TBR of 2.86, and deposits below 1mm3 were detected. All tumor foci detected by FLI had high expression of uPAR when analyzed by IHC.

Conclusions This study demonstrates the utility of NIR-guided surgery with the novel probe ICG-AE105 directed against uPAR for both primary and recurrent disease in pancreatic cancer. All primary tumors could be detected with NIR imaging and upon recurrence an additional 13.9% metastases were found with fluorescence guided surgery. However 18.6% of the metastases were not detected by NIR imaging which may be due to inadequate tissue penetration of NIR photons, a lower limit of tumor volume for detection or sensitivity of the NIR camera system. We concluded that ICG-AE105 has the potential for clinical translation allowing real-time NIR-imaging in the surgical management of the primary tumor and metastases in pancreatic cancer and other types of uPAR expressing cancers.