Fluorescence colon tumor imaging by i.v. administered indocyanine green in a rat model of colon carcinogenesis

Tumor imaging using indocyanine green (ICG) has been reported in a variety of tumor types. Currently, there are reported several possible mechanisms of the tumor imaging by IV ICG injection. We previously reported that the tumor tissue preference of the ICG in a mouse xenograft tumor model using human colon cancer cell line is responsible for the tumor cellular uptake of ICG. We also reported that the tissue preference of the ICG in a mouse model of colitisassociated colon cancer can be attributable to the tumor interstitial uptake of ICG. The aim of the present study is to investigate the tumor imaging capability and the imaging mechanism of IV administered ICG in a rat colon carcinogenesis model. Fluorescence imaging experiments were carried out one day after the IV injection of ICG. The ICG fluorescence was observed in the colon tumor tissues, with sufficient tumor to normal tissue ratio. Fluorescence endoscopy detected these ICG+ colon tumors in vivo. High magnification imaging of excised colon tissues revealed that ICG fluorescence in the tumor tissues was localized in the stromal cells at the vascular interstitial tissue at the luminal surface. Collectively, these results suggest that fluorescence imaging following the IV administration of ICG can detect the colon tumor tissues in the current model. The tumor tissue preference of ICG is likely to be responsible for the perivascular stromal cellular uptake of ICG. Our previous and present data will be helpful in exploring the appropriate clinical applications of the tumor imaging by IV ICG administration.