Use of a PEG-conjugated bright near-infrared dye for functional imaging of rerouting of tumor lymphatic drainage after sentinel lymph node metastasis.

Tumor lymphangiogenesis promotes metastatic cancer spread to lymph nodes and beyond. However, the potential remodeling and functionality of tumor-draining lymphatic vessels has remained unclear. Thus, we aimed to develop non-invasive imaging methods for repeated quantitative imaging of lymphatic drainage and of contractile collecting lymphatic vessel function in mice, with colloidal near-infrared (NIR) tracers and a custom fluorescence stereomicroscope specially adapted for NIR sensitive imaging. Using these tools, we quantitatively determined pulse rates and valvular function of collecting lymphatic vessels with high resolution. Unexpectedly, we found that tumor-draining lymphatic vessels in a melanoma footpad model initially were dilated but remained functional, despite lower pulse rates. In two independent tumor models, impaired lymphatic function was detected once metastases were present in draining lymph nodes. Importantly, we found that lymphatic dysfunction, induced by metastatic tumor spread to sentinel lymph nodes, can lead to a rerouting of lymphatic flow away from the metastatic lymph node, via collateral lymphatic vessels, to alternate lymph nodes. These findings might have important clinical implications for the procedure of sentinel lymph node mapping that represents the standard of care for determining prognosis and treatment of melanoma and breast cancer patients.