The cyan fluorescent protein nude mouse as a host for multicolor-coded imaging models of primary and metastatic tumor microenvironments.

The tumor microenvironment (TME) has an important influence on tumor progression. For example, we have discovered that passenger stromal cells are necessary for metastasis. In this report, we describe six different cyan fluorescent protein (CFP) multicolor TME nude mouse models. The six different implantation models were used to image the TME using multiple colors of fluorescent proteins: I) Red fluorescent protein (RFP)- or green fluorescent protein (GFP)-expressing HCT-116 human colon cancer cells were implanted subcutaneously in the CFP-expressing nude mice. CFP stromal elements from the subcutaneous TME were visualized interacting with the RFP- or GFP-expressing tumors. II) RFP-expressing HCT-116 cells were transplanted into the spleen of CFP nude mice, and experimental metastases were then formed in the liver. CFP stromal elements from the liver TME were visualized interacting with the RFP-expressing tumor. III) RFP-expressing HCT-116 cancer cells were transplanted in the tail vein of CFP-expressing nude mice, forming experimental metastases in the lung. CFP stromal elements from the lung were visualized interacting with the RFP-expressing tumor. IV) In order to visualize two different tumors in the TME, GFP-expressing and RFP-expressing HCT-116 cancer cells were co-implanted subcutaneously in CFP-expressing nude mice. A 3-color TME was formed subcutaneously in the CFP mouse, and CFP stromal elements were visualized interacting with the RFP- and GFP-expressing tumors. V) In order to have two different colors of stromal elements, GFP-expressing HCT-116 cells were initially injected subcutaneously in RFP-expressing nude mice. After 14 days, the tumor, which consisted of GFP cancer cells and RFP stromal cells derived from the RFP nude mouse, was harvested and transplanted into the CFP nude mouse. CFP stromal cells invaded the growing transplanted tumor containing GFP cancer cells and RFP stroma. VI) Mouse mammary tumor (MMT) cells expressing GFP in the nucleus and RFP in the cytoplasm were implanted in the spleen of a CFP nude mouse. Cancer cells were imaged in the liver 3 days after cell injection. The dual-color dividing MMT cells and CFP hepatocytes, as well as CFP non-parenchymal cells of the liver were imaged interacting with the 2-color cancer cells. CFP-expressing host cancer-associated fibroblasts (CAFs) were predominantly observed in the TME models developed in the CFP nude mouse. Thus, the CFP nude mouse adds another color to the pallet of the TME, allowing multiple types of color-coded cancer and stromal cells to be imaged simultaneously. The multi-colored models described in this report provide new opportunities to study the cellular interactions in the live primary and metastatic TME.