Specific inhibition of hypoxia-inducible factor (HIF)-1α activation and of vascular endothelial growth factor (VEGF) production by flavonoids

Screening using a reporter under the control of the hypoxia-response element (HRE) identified several flavonoids and homoisollavonoids that inhibit the activation of HRE under hypoxic conditions. Among various compounds, isorhamnetin, luteolin, quercetin, and methyl ophiopogonanone B (MOB) were effective at 3 to 9 mug/ml in inhibiting the reporter activity. The expression of vascular endothelial growth factor (VEGF) mRNA during hypoxia was also inhibited by MOB in HepG2 cells, but the effective doses were 10 to 20 mug/ml. MOB caused destabilization of hypoxia-inducible factor (HIF)-2alpha, as revealed by Western blotting, that was dependent on proteasome activity and the tumor suppressor, p53. The tubular formation and migration of human umbilical vein endothelial cells was also inhibited by MOB. MOB is expected to act as an inhibitor of angiogenesis.