Expansion of the lymphatic vasculature in cancer and inflammation: new opportunities for in vivo imaging and drug delivery.

Over the last 15 years, discovery of key growth factors and specific molecular markers for lymphatic vessels has enabled a new era of molecular research on the lymphatic vascular system. As a result, it has been found that lymphangiogenesis, the expansion of existing lymphatic vessels, plays an important role in tumor progression and in the control of chronic inflammation. At the same time, technical advancements have been made to improve the visualization of the lymphatic system. We have recently developed liposomal and polymer-based formulations of near-infrared lymphatic-specific imaging tracers for the non-invasive quantitative in vivo imaging of lymphatic vessel function. Using these tracers, a near-infrared stereomicroscope system allows imaging of initial and collecting lymphatic vessels with high spatial and temporal resolution in mice. In addition, we have developed a new method, using antibodies to a lymphatic specific marker and positron emission tomography, to sensitively detect lymphatic expansion in lymph nodes as the earliest sign of cancer metastasis. These imaging methods have great potential to provide non-invasive measures to assess the functionality of the lymphatic system and to assess the efficiency of lymphatic drug delivery.