One known complication of patients under chronic immunosuppression after transplantation is the recurrence of tumors or de novo malignancies. FTY720 is an immunosuppressant that reduces the number of lymphocytes in peripheral blood via agonistic action on sphingosine-1 phosphate receptor 1 (S1P1). Importantly, FTY720 was recently shown to prevent tumor growth and metastasis. Here, we examined effects of FTY720 on lymph- and hem-angiogenesis.

Methods: To evaluate the anti-proliferative and anti-angiogenic properties of FTY720 we employed an MTT proliferation/viability assay and a spheroid model using human umbilical vein endothelial cells (HUVECs) and lymph endothelial cells (LECs). To substantiate our in vitro findings, the effect of FTY720 on tumor growth was illustrated in a Lewis Lung Carcinoma (LLC1) model for hem-angiogenesis and in a B16 melanoma model for lymphogenic metastasis. Both cell types were injected subcutaneously into the back of syngeneic C57BL/6 mice. Animals were treated with FTY720 or saline as control, tumor size was measured periodically. 8 (local tumor) or 15 (lung and lymph node metastases) days after injection, tumors were harvested and analyzed histologically.

Results: FTY720 showed a strong in vitro growth-suppressive as well as anti-hem-angiogenic and anti-lymph-angiogenic effect. The vascular sprouting of VEGF-A stimulated HUVEC spheroids and VEGF-C stimulated LEC spheroids, respectively, was significantly inhibited at nanomolar concentrations. Interestingly, in a coculture model using HUVECs and smooth muscle cells (SMCs), micromolar concentrations of FTY720 were needed to accomplish the same effect, indicating the stabilizing properties of SMCs towards the endothelial cells. Consequently, FTY720 significantly inhibited subcutaneous tumor growth in both models. Additionally, the microvessel density of the tumors was reduced significantly in the FTY720-treated mice as compared to saline treated control mice. In the B16 lymphogenic tumor metastasis model, the number of lung and lymph node metastases was reduced dose-dependently in FTY720-treated animals. In preliminary results CXCR4 seemed to be involved in metastatic spread.

Conclusion: FTY720 demonstrates a strong anti-angiogenic activity in vitro translating into a substantial anti-tumor and anti-lymph-metastatic effect in vivo. Therefore, following organ transplantation, a treatment regimen using FTY720 in combination with other anti-tumorigenic immunosuppressants may proof to be beneficial in preventing tumor development and progression in high-risk patients.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA