In vivo real-time imaging of tumor microcirculatory alterations in colorectal liver metastatic xenografts by chemotherapy using multiphoton microscopy

e21053 Background: Tumor endothelium is a distinct target for anticancer treatments of metastatic colorectal cancer. Various chemotherapeutics themselves have anti-angiogenic effects on tumor microenvironment by targeting proliferative endothelial cells during tumor angiogenesis. In this study, we imaged the dynamics of tumor microcirculation of colorectal liver metastasis in living mice in vivo real-time using two-photon laser scanning microscopy (TPLSM), and evaluated the microcirculatory alterations in tumor microenvironment by chemotherapy. Methods: Red fluorescent protein expressing human colorectal cancer cell line (HT29) was inoculated to the spleen of green fluorescent protein expressing nude mice. 5-fluorouracil or irinotecan was administered three times a week for more than three weeks for metronomic scheduling. Intravital TPLSM was performed at multiple time points for time-series imaging of liver metastatic xenografts in the same mice. The alterations in tumor microcirculation during chemotherapy was evaluated by measuring blood flows at tumor vessels of colorectal liver metastasis and hepatic sinusoids of adjacent normal liver. Results: At the first TPLSM imaging, the blood flow, as determined from the movement of platelets, was heterogeneous and non-directional in the tumor vessels of liver metastatic xenografts. The blood flow was relatively slower in tumor vessels than normal hepatic sinusoids. At the second TPLSM imaging after chemotherapy, platelet aggregation was observed in tumor vessels of the same mice. Aggregated platelets were frequently adhered to the tumor endothelium, suggesting tumor vessel damage or intratumoral coagulation abnormality by chemotherapy. There was no difference in chemotherapeutics with regard to these findings. Conclusions: Intravital TPLSM imaging of tumor microcirculation at metastatic tumor xenografts is a useful tool to evaluate anti-angiogenic drugs in preclinical models.