New radiopharmaceuticals and new applications in medicine

Establishment of red fluorescent protein-tagged HeLa tumor metastasis models: determination of DsRed2 insertion effects and comparison of metastatic patterns after subcutaneous, intraperitoneal, or intravenous injection

Metastasis is the leading cause of death in patients with cervical cancer. In this report, we establish novel fluorescent HeLa tumor metastasis models to determine whether HeLa transfected with the enhanced red fluorescent protein (DsRed2) gene in vitro and xenotransplanted through subcutaneous, intraperitoneal, or intravenous route into SCID mice would permit the detection of tumor micro-metastasis in vivo. Our results showed that DsRed2 insertions did not interfere the tumorigenic properties of HeLa cells. We also demonstrated that DsRed2-transduced HeLa cells maintained stable high-level DsRed2 expressions during their growth in vivo. DsRed2 fluorescence clearly demarcated the primary seeding place and readily allowed for the visualization of distant micro-metastasis and local invasion at the single-cell level. Lung metastasis, the major cause of cervical carcinoma related death, was found in all three models. However, intravenous injections of the HeLa-DsRed2 cells established tumor foci in the lung, while subcutaneous and intraperitoneal injections only established lung metastasis at single-cell levels. The DsRed2 tagged HeLa cancer model allowed detection and investigation of physiologically relevant patterns of cancer invasion and metastasis in vivo.

Establishment of fluorescent lung carcinoma metastasis model and its real-time microscopic detection in SCID mice

Lung cancer is the most prevalent malignant tumor in the world. Metastasis of the disease causes death in lung cancer patients. Recent study has shown that multiple cascades of gene defects occur in lung cancer. In this report, we established a novel H1299/EGFP tumor model to determine whether H1299 transfected with the enhanced green fluorescent protein (EGFP) gene in vitro and xenotransplanted into SCID mouse lung would permit the detection of lung cancer micrometastasis in vivo. We demonstrated that EGFP-transduced H1299 cells maintained stable high-level EGFP expressions during their growth in vivo. EGFP fluorescence clearly demarcated the primary seeding place and readily allowed for the visualization of distant micrometastasis and local invasion at the single-cell level. Small metastatic and locally invasive foci, including those immediately adjacent to the tumor's leading invasive edge, were almost undetectable by routine hematoxylin and eosin staining and immunohistochemistry. The GFP tagged lung cancer model is superior for the detection and study of physiologically relevant patterns of lung cancer invasion and metastasis in vivo.

Whole-body optical imaging of green fluorescent protein-expressing tumors and metastases

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.

In vivo imaging of tumors with protease-activated near-infrared fluorescent probes

We have developed a method to image tumor-associated lysosomal protease activity in a xenograft mouse model in vivo using autoquenched near-infrared fluorescence (NIRF) probes. NIRF probes were bound to a long circulating graft copolymer consisting of poly-L-lysine and methoxypolyethylene glycol succinate. Following intravenous injection, the NIRF probe carrier accumulated in solid tumors due to its long circulation time and leakage through tumor neovasculature. Intratumoral NIRF signal was generated by lysosomal proteases in tumor cells that cleave the macromolecule, thereby releasing previously quenched fluorochrome. In vivo imaging showed a 12-fold increase in NIRF signal, allowing the detection of tumors with submillimeter-sized diameters. This strategy can be used to detect such early stage tumors in vivo and to probe for specific enzyme activity.