We have imaged, in real time, fluorescent
tumors growing and metastasizing in live mice. The whole-body optical imaging system is external and noninvasive. It affords unprecedented continuous visual monitoring of malignant growth and spread within intact animals. We have established new human and rodent
tumors that stably express very high levels of the
Aequorea victoria green fluorescent protein (GFP) and transplanted these to appropriate animals. B16F0-GFP mouse
melanoma cells were injected into the tail vein or portal vein of 6-week-old C57BL/6 and nude mice. Whole-body optical images showed metastatic lesions in the brain, liver, and bone of B16F0-GFP that were used for real time, quantitative measurement of
tumor growth in each of these organs. The AC3488-GFP human
colon cancer was surgically implanted orthotopically into nude mice. Whole-body optical images showed, in real time, growth of the primary colon
tumor and its metastatic lesions in the liver and skeleton. Imaging was with either a trans-illuminated epifluorescence microscope or a fluorescence light box and thermoelectrically cooled color charge-coupled device camera. The depth to which
metastasis and
micrometastasis could be imaged depended on their size. A 60-microm diameter
tumor was detectable at a depth of 0.5 mm whereas a 1, 800-microm
tumor could be visualized at 2.2-mm depth. The simple, noninvasive, and highly selective imaging of growing
tumors, made possible by strong GFP fluorescence, enables the detailed imaging of
tumor growth and
metastasis formation. This should facilitate studies of modulators of
cancer growth including inhibition by potential chemotherapeutic agents.