Tumor Cells with Organ-specific Metastatic Ability Show Distinctive Trafficking in Vivo: Analyses by Positron Emission Tomography and Bioimaging

To elucidate the behavior of various metastatic tumor cells with different characteristics in the blood flow, we have developed a system to investigate real-time trafficking using positron emission tomography. In this study, positron-labeled cells, i.e. , lung-metastatic B16BL6 melanoma and two sublines of liver-metastatic RAW117 large cell lymphoma, were injected i.v., and the trafficking of these cells was noninvasively determined. All sublines tested accumulated in the lungs immediately after injection, presumably because the lungs were the first organ passed through after i.v. injection. The elimination of RAW117 cells from the lungs, however, was fast compared with that of B16BL6 cells. The latter showed a release rate from the lungs of less than 1%/min, whereas that of RAW117 cells was greater than 2%/min. Reflecting the elimination from lungs, RAW117 cells accumulated in the liver in a time-dependent manner. Biodistribution of metastatic cells was also analyzed by whole-body autoradiography after injection of 5-[125I]iodo-2′-deoxyuridine-labeled cells, using a bioimaging analyzer system. The method is invasive; however, it enables a precise determination of the biodistribution of metastatic cells. Bioimaging analyzer system analysis also showed the organ-specific accumulation of these metastatic cells. Furthermore, colonized distribution of B16BL6 cells in the lungs and that of RAW117 cells in the liver were observed. The present data suggest that the trafficking of metastatic tumor cells greatly influences the organ specificity of cancer metastasis.