02358nas a2200241   4500008004100000245016500041210006900206260001400275300001400289490000700303520155700310100001501867700001901882700002001901700002101921700002201942700002501964700002001989700001702009700002302026700001802049856004902067       2005                        eng d00aVascular endothelial cell growth factor receptor 3-mediated activation of lymphatic endothelium is crucial for tumor cell entry and spread via lymphatic vessels0 aVascular endothelial cell growth factor receptor 3mediated activ  c2005/Jun/  a4739 - 460 v653 aLymphangiogenic growth factors vascular endothelial growth factor (VEGF)-C and VEGF-D have been shown to promote lymphatic metastasis by inducing tumor-associated lymphangiogenesis. In this study, we have investigated how tumor cells gain access into lymphatic vessels and at what stage tumor cells initiate metastasis. We show that VEGF-C produced by tumor cells induced extensive lymphatic sprouting towards the tumor cells as well as dilation of the draining lymphatic vessels, suggesting an active role of lymphatic endothelial cells in lymphatic metastasis. A significant increase in lymphatic vessel growth occurred between 2 and 3 weeks after tumor xenotransplantation, and lymph node metastasis occurred at the same stage. These processes were blocked dose-dependently by inhibition of VEGF receptor 3 (VEGFR-3) signaling by systemic delivery of a soluble VEGFR-3-immunoglobulin (Ig) fusion protein via adenoviral or adeno-associated viral vectors. However, VEGFR-3-Ig did not suppress lymph node metastasis when the treatment was started at a later stage after the tumor cells had already spread out, suggesting that tumor cell entry into lymphatic vessels is a key step during tumor dissemination via the lymphatics. Whereas lymphangiogenesis and lymph node metastasis were significantly inhibited by VEGFR-3-Ig, some tumor cells were still detected in the lymph nodes in some of the treated mice. This indicates that complete blockade of lymphatic metastasis may require the targeting of both tumor lymphangiogenesis and tumor cell invasion.1 aHe, Yulong1 aRajantie, Iiro1 aPajusola, Katri1 aJeltsch, Michael1 aHolopainen, Tanja1 aYla-Herttuala, Seppo1 aHarding, Thomas1 aJooss, Karin1 aTakahashi, Takashi1 aAlitalo, Kari  uhttp://view.ncbi.nlm.nih.gov/pubmed/15930292