In vivo optical imaging of cancer metastasis using multiphoton microscopy: a short review.

Intravital (in vivo) microscopy using fluorescently-tagged proteins is a valuable tool for imaging the expression of a specific protein, its subcellular location and the dynamics of specific cell populations in living animals. Recently, multiphoton microscopy including two-photon laser scanning microscopy (TPLSM) has been used in the field of tumor biology due to its ability to image target organs at higher magnification and at deeper depths from the tissue surface for longer time periods. We developed a method of in vivo real-time imaging for tumor metastasis using TPLSM with an organ stabilizing system, which allow us to observe not only a single tumor cell and its microenvironment for a long time, but also to observe the same organ of the same mouse at multiple time points in preclinical models. Here, we presented in vivo real-time images of 1) tumor cell arrest, 2) tumor cell-platelet interaction, 3) tumor cell-leukocyte interaction, and 4) metastatic colonization at the secondary organs as representative steps of metastatic process of experimental liver metastasis models using TPLSM.