Frontiers in intravital multiphoton microscopy of cancer

Background: Cancer is a highly complex disease, which involves the cooperation of tumor cells with multiple types of host cells and the extracellular matrix. Cancer studies that rely solely on static measurements of individual cell types are insufficient to dissect this complexity. In the last two decades, intravital microscopy has established itself as a powerful technique that can significantly improve our understanding of cancer by revealing the dynamic interactions governing cancer initiation, progression, and treatment effects in living animals. This review focuses on intravital multiphoton microscopy (IV-MPM) applications in mouse models of cancer. Recent findings: IV-MPM studies have already enabled a deeper understanding of the complex events occurring in cancer at the molecular, cellular, and tissue levels. Multiple cell types present in different tissues influence cancer cell behavior via activation of distinct signaling pathways. As a result, the boundaries in the field of IV-MPM are continuously being pushed to provide an integrated comprehension of cancer. We propose that optics, informatics, and cancer (cell) biology are coevolving as a new field. We have identified four emerging themes in this new field. First, new microscopy systems and image processing algorithms are enabling the simultaneous identification of multiple interactions between the tumor cells and the components of the tumor microenvironment. Second, techniques from molecular biology are being exploited to visualize subcellular structures and protein activities within individual cells of interest and relate those to phenotypic decisions, opening the door for “in vivo cell biology”. Third, combining IV-MPM with additional imaging modalities or omics studies holds promise for linking the cell phenotype to its genotype, metabolic state, or tissue location. Finally, the clinical use of IV-MPM for analyzing efficacy of anticancer treatments is steadily growing, suggesting a future role of IV-MPM for personalized medicine. Conclusion: IV-MPM has revolutionized visualization of tumor-microenvironment interactions in real time. Moving forward, incorporation of novel optics, automated image processing, and omics technologies in the study of cancer biology, will not only advance our understanding of the underlying complexities but will also leverage the unique aspects of IV-MPM for clinical use.