The role of angiogenesis in
tumor growth and
metastasis is well established. Identification of a small molecule that blocks
tumor angiogenesis and is safe and affordable has been a challenge in
drug development. In this study, we showed that
acetyl-11-keto-beta-boswellic acid (AKBA), an active component from an Ayurvedic medicinal plant (Boswellia serrata), could strongly inhibit
tumor angiogenesis. AKBA suppressed
tumor growth in the human prostate
tumor xenograft mice treated daily (10 mg/kg AKBA) after solid
tumors reached approximately 100 mm(3) (n = 5). The inhibitory effect of AKBA on
tumor growth was well correlated with suppression of angiogenesis. When examined for the molecular mechanism, we found that AKBA significantly inhibited blood vessel formation in the
Matrigel plug assay in mice and effectively suppressed
vascular endothelial growth factor (
VEGF)-induced microvessel sprouting in rat aortic ring assay ex vivo. Furthermore, AKBA inhibited
VEGF-induced cell proliferation, chemotactic motility, and the formation of capillary-like structures from primary cultured human umbilical vascular endothelial cells in a dose-dependent manner. Western blot analysis and in vitro
kinase assay revealed that AKBA suppressed
VEGF-induced phosphorylation of
VEGF receptor 2 (VEGFR2)
kinase (KDR/Flk-1) with IC(50) of 1.68 micromol/L. Specifically, AKBA suppressed the downstream
protein kinases of VEGFR2, including
Src family kinase,
focal adhesion kinase, extracellular signal-related
kinase, AKT,
mammalian target of rapamycin, and
ribosomal protein S6 kinase. Our findings suggest that AKBA potently inhibits human prostate
tumor growth through inhibition of angiogenesis induced by VEGFR2 signaling pathways.