Color-coded Imaging Distinguishes Cancer Cells, Stromal Cells, and Recombinant Cancer-stromal Cells in the Tumor Microenvironment During Metastasis

Background/Aim: Our laboratory pioneered color-coded imaging of the tumor microenvironment (TME). We observed recruitment of cancer and stromal cells to the TME and recombination between cancer and stromal cells. The aim of the present study was to observe the dynamics of the TME by color-coded imaging during metastasis and in the formation of a pre-metastatic niche. Materials and Methods: Red-fluorescent protein (RFP-expressing) mouse colon-cancer 26 cells were initially injected subcutaneously in green fluorescent protein (GFP) nude mice. The resulting subcutaneous tumors were harvested and cultured. The cultured subcutaneous tumors contained RFP colon cancer cells, GFP stromal cells and recombinant cancer-stromal cells expressing yellow fluorescence. After 14 days culture, the cells were injected into the spleen. Results: After splenic injection, colon-cancer 26 metastases were observed in the liver, ascites, and bone marrow. Using the Olympus FV1000 confocal microscope, the cells cultured from tumors and metastasis in each site were visualized. RFP colon-cancer cells, GFP stromal cells derived from host GFP nude mice, and recombinant yellow-fluorescent cells were observed in each organ. In addition, in the liver, areas with only GFP stromal cells were observed and assumed to be a pre-metastatic niche. Conclusion: Color-coded imaging demonstrated the dynamics of colon cancer and stromal cells at different metastatic sites including the formation of recombinant cancer-stromal cells.