The Amaryllidaceae alkaloid narciclasine inhibits angiogenic key features in human endothelial cells

Plants of the Amaryllidaceae family have been used in traditional medicine for the treatment of cancer for a long time. Narciclasine, an isocarbostyril alkaloid from Narcissus and Haemanthus species, was reported to block tumor cell growth in vitro and in vivo. Potential effects of narciclasine on endothelial cells in the context of tumor angiogenesis have been neglected so far. Thus, we aimed to elucidate the action of narciclasine on in vitro key features of angiogenesis, i.e. on the proliferation, migration, tube formation, and angiogenic sprouting of human primary endothelial cells (ECs).

Treatment of ECs with narciclasine up to a concentration of 300 nM (24 or 48h) did not affect the metabolic activity, while cell proliferation was concentration-dependently reduced (IC₅₀: 61 nM). The compound lowered the number of endothelial cells in the S- and G2/M-phase of the cell cycle (PI staining/flow cytometry). Interestingly, narciclasine did neither inhibit the activation of Erk and Akt (Western blot analysis), nor interfere with endothelial nitric oxide production (arginine/citrulline conversion). Moreover, narciclasine (300 nM) reduced the undirected migration of ECs (scratch assay) by 54% and the chemotactic migration (Boyden chamber) by 77%. Microscopical analysis of the cytoskeleton revealed that narciclasine increased the formation of F-actin stress fibers. Most importantly, the alkaloid diminished both the formation of endothelial tube-like structures on Matrigel and the VEGF-induced sprouting of EC spheroids (100 and 300 nM).

Taken together, we could demonstrate that the isocarbostyril alkaloid narciclasine effectively decreases key features of angiogenesis in endothelial cells. Thus, narciclasine might represent an interesting anti-angiogenic lead compound that warrants further preclinical investigations.

Keywords: Narciclasine, proliferation, migration, angiogenesis, human primary endothelial cells.