Luteolin Suppresses Three Angiogenesis Modes and Cell Interaction in Uveal Melanoma in Vitro

Uveal melanoma is a high-vascularized tumor that lacks effective systemic therapies. Most anti-angiogenesis drug therapies only target endothelial cell-dependent angiogenesis but not vasculogenic mimicry (VM), which supplies blood to tumors independent of endothelial cells. Thus, we aimed to explore the inhibitory effects of luteolin on proliferation, migration, invasiveness, angiogenesis, and VM activity of uveal melanoma. We further explored the signaling pathway underlying the mechanism of action of luteolin.Monocultures of uveal melanoma C918 cells, human umbilical vein endothelial cells (HUVECs), and co-cultures of these two cell lines were established. Angiogenesis of HUVECs, VM formation of C918 cells, and the mosaic vessels formed by both cell types were observed under an inverted microscope. Cell counting kit-8, 5-ethynyl-2'-deoxyuridine (EdU), wound scratch, Transwell cell migration, and invasion assays were performed. VEGF levels were detected by ELISA. Western blotting was used to detect the expression of PI3K, p-PI3K P85, Akt, and p-Akt Ser473 proteins.Luteolin inhibited all three modes of angiogenesis observed in uveal melanoma in vitro. Luteolin effectively inhibited the proliferation, migration, and invasion of C918 cells and proliferation and migration of HUVECs. Furthermore, luteolin could inhibit the interaction between the endothelial cells and C918 cells. VEGF secretion in C918 cells and HUVECs treated with luteolin was inhibited. Luteolin decreased the levels of phosphorylated Akt kinase.We demonstrated the anti-angiogenic effects of luteolin, including against the VM type, in addition to suppressing tumor cell proliferation and migration in vitro. Furthermore, luteolin likely exerts its inhibitory effects via the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. Luteolin might be an effective therapeutic candidate for treating highly vascularized uveal melanoma tumors.