External whole-body image of EGFP gene expression.

Whole-body optical imaging is an external and noninvasive procedure that enables the continuous visual monitoring of malignant growth and spread within intact animals. The human colon adenocarcinoma cell-line HCT-15 was transfected with a pIRES 2-EGFP vector, and stable enhanced green fluorescence protein (EGFP) expression was established (Fig.1). Approximately 10(6) HCT-15 EGFP stable transfectant cells were subcutaneously injected into the left flank of six-week-old male Balb/c-nu/nu mice. On post-injection day 78, the size of the subcutaneous tumor was 13.1 mm x 15.4 mm in diameter, as observed using an ORCA-C 7780-20 three-chip cooled color charge-coupled-device camera (Hamamatsu Photonics Systems, Hamamatsu City, Japan). An external fluorescent image of the tumor was acquired through the skin (Fig.2B). The tumor could be seen more clearly once the skin was removed (Fig.2D). Furthermore, in the peritoneal metastasis (Fig.3B) and liver metastasis models (Fig.3D), metastasis could also be seen through the skin. This new technology is a useful method for investigating tumor growth in vivo. In the future, this method could be applied to the detection of peritoneal, liver and lung metastasis in living animals.