Antitumor activity of endogenous mFlt4 displayed on a T4 phage nanoparticle surface.

AIM: Flt4 plays a key role in promoting tumor metastasis by stimulating solid tumor lymphangiogenesis. In this study, mouse Flt4 (mFlt4) was displayed on T4 phage in order to explore the feasibility of breaking immune tolerance to "self-antigens" and to evaluate the phage's antitumor activity. METHODS: A T4 phage nanometer particle expressing mFlt4 on the surface was constructed for evaluation as a recombinant vaccine. The presence of the mFlt4 gene in the T4-mFlt4 recombinant vaccine was verified by PCR and Western blot analysis. The immunotherapeutic potential of T4-mFlt4 was tested in mice injected with Lewis lung carcinoma (LLC) cells. Anti-Flt4 antibody producing B cells were detected by ELISPOT. The effects of T4-mFlt4 on lymphatic metastasis and lymphangiogenesis were investigated in a mouse antimetastasis assay and by Flt4 and CD105 immunohistochemistry. RESULTS: The T4-mFlt4 recombinant vaccine demonstrated antitumor activity and elicited autoantibodies against mFlt4. Mice carrying LLC-derived tumors exhibited prolonged survival when given the vaccine compared with control-treated animals. The vaccine also inhibited lymphangiogenesis and tumor metastasis in the mouse models. However, T4-mFlt4 was not observed to inhibit tumor growth. CONCLUSION: The T4-mFlt4 recombinant vaccine induced protective antitumor immunity and antimetastasis against LLC. Induction of an autoimmune response directed against tumor progression merits further study as a new strategy for immunotherapy in cancer.

Vascular endothelial cell growth factor receptor 3-mediated activation of lymphatic endothelium is crucial for tumor cell entry and spread via lymphatic vessels.

Lymphangiogenic 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.