Antiproliferative effects of 1α,25-dihydroxyvitamin D3 and vitamin D analogs on tumor-derived endothelial cells

Although there is abundant evidence that lalpha,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] inhibits the growth of several cancer cell types, inhibition of angiogenesis may also play a role in mediating the antitumor effects of 1,25-(OH)(2)D-3. We examined the ability of 1,25-(OH)(2)D-3 to inhibit the growth of tumor-derived endothelial cells (TDECs) and normal endothelial cells and to modulate angiogenic signaling. 1,25-(OH)(2)D-3 inhibited the growth of TDECs from two tumor models at nanomolar concentrations, but was less potent against normal aortic or yolk sac endothelial cells. The vitamin D analogs Ro-25-6760, EB1089, and ILX23-7553 were also potent inhibitors of TDEC proliferation. Furthermore, the combination of 1,25-(OH)(2)D-3 and dexamethasone had greater activity than either agent alone. 1,25-(OH)(2)D-3 increased vitamin D receptor and p27(kip1) protein levels in TDECs, whereas phospho-ERK1/2 and phospho-Akt levels were reduced. These changes were not observed in normal aortic endothelial cells. In squamous cell carcinoma and radiation-induced fibrosarcoma-1 cells, 1,25(OH)(2)D-3 treatment caused a reduction in the angiogenic signaling molecule, angiopoietin-2. In conclusion, 1,25-(OH)(2)D-3 and its analogs directly inhibit TDEC proliferation at concentrations comparable to those required to inhibit tumor cells. Further, 1,25-(OH)(2)D-3 modulates cell cycle and survival signaling in TDECs and affects angiogenic signaling in cancer cells. Thus, our work supports the hypothesis that angiogenesis inhibition plays a role in the antitumor effects of 1,25-(OH)(2)D-3.