Ellagic acid exerts anti-angiogenesis effects by blocking VEGFR-2 signaling pathway in breast cancer

Abstract

Angiogenesis is one of the essential hallmarks of cancer, typically breast

cancer. Signaling from VEGFR-2 is necessary for the execution of

VEGF-induced proliferation, migration, and tube formation of cultured

endothelial cells in vitro and the onset of angiogenesis on tumors in vivo.

Ellagic acid is a naturally existing small molecular polyphenol widely found

in fruits and vegetables. It was reported that ellagic aicd interfered with some

angiogenesis-dependent pathologies. Yet the mechanisms involved were not

fully understood.

Thus we analyzed its anti-angiogenesis effects and mechanisms on human

breast cancer utilizing in vitro and in vivo methodologies. Besides, the in

silico analysis was carried out to further analyze the structure-based

interaction between ellagic aicd and VEGFR-2. The influences of ellagic aicd

on VEGF-induced endothelial cells were studied by proliferation, tube

formation and migration in vitro experiments. Kinase activity assay and

western blotting were utilized to explore the effects of ellagic aicd on

VEGFR-2 induced signaling pathway. Organ-based chick aortic ring model, in

vivo Chorioallantoic membrane model and in vivo breast cancer xenografts

were built to determine the anti-angiogenesis effects of ellagic aicd. Besides,

software LigandFit algorithm in Discovery Studio 2.1 (Accelrys Inc., San

Diego, CA) was applied to further understand the structure-based interaction

between ellagic aicd and VEGFR-2.

We found that ellagic aicd impeded a series of VEGF-induced angiogenesis

processes including proliferation, migration and tube formation of endothelial

cells. Besides, it directly inhibited VEGFR-2 tyrosine kinase activity and its

downstream signaling pathways including MAPK and PI3K/Akt on

endothelial cells. Ellagic aicd also obviously inhibited sprouts formation from

chicken aorta and neo-vessel formation in chick chorioallantoic membrane.

The growth and the P-VEGFR2 expression in breast tumors treated with

ellagic aicd were also significantly suppressed. In the molecular docking

simulation experiment, the structure-based interaction of VEGFR-2 with

ellagic acid was found to be stable conformation by hydrogen bonds within

residues Lys866 and Glu883 as well as by π–π interactions within residue

Phe1045 at ATP binding pocket of VEGFR-2 catalytic domain. Taken together,

ellagic aicd could exert anti-angiogenesis effects via VEGFR-2 signaling

pathway in breast cancer.