Subcellular Imaging of Cancer Cells in Live Mice

Dual-color fluorescent cells, with one color in the nucleus and the other in the cytoplasm, enable real-time nuclear-cytoplasmic dynamics to be visualized in living cells in vivo as well as in vitro. To obtain the dual-color cells, red fluorescent protein (RFP) is expressed in the cytoplasm of cancer cells, and green fluorescent protein (GFP) linked to histone H2B is expressed in the nucleus. Nuclear GFP expression allows visualization of nuclear dynamics, whereas simultaneous cytoplasmic RFP expression allows visualization of nuclear-cytoplasmic ratios as well as simultaneous cell and nuclear shape changes. This methodology has allowed us to show that the cells and nuclei of cancer cells in the capillaries elongate to fit the width of these vessels. The average length of the major axis of the cancer cells in the capillaries increased to approximately four times their normal length. The nuclei increased their length 1.6 times. Cancer cells in capillaries over 8 �m in diameter were shown to migrate at up to 48.3 �m/h. With the use of dual-color fluorescent cells and the Olympus OV100, a highly sensitive whole-mouse imaging system with both macrooptics and microoptics, it is possible to achieve subcellular real-time imaging of cancer cell trafficking in live mice. Extravasation can also be imaged in real time. Dual-color imaging showed that cytoplasmic processes of cancer cells exited the vessels first, with nuclei following along the cytoplasmic projections. Dual-color in vivo cellular imaging was also used to visualize trafficking, nuclear-cytoplasmic dynamics, and the viability of cancer cells after their injection into the portal vein of mice.