Luteolin inhibits vascular endothelial growth factor-induced angiogenesis; inhibition of endothelial cell survival and proliferation by targeting phosphatidylinositol 3'-kinase activity.
In an attempt to identify phytochemicals contributing to the well-documented preventive effect of plant-based diets on cancer incidence and mortality, we have previously shown that certain flavonoids inhibit in vitro angiogenesis. Here, we show that the flavonoid luteolin inhibited tumor growth and angiogenesis in a murine xenograft model. Furthermore, luteolin inhibited vascular endothelial growth factor (VEGF)-induced in vivo angiogenesis in the rabbit corneal assay. In agreement, luteolin inhibited both VEGF-induced survival and proliferation of human umbilical vein endothelial cells (HUVECs) with an IC(50) of about 5 mumol/L. Luteolin inhibited VEGF-induced phosphatidylinositol 3'-kinase (PI3K) activity in HUVECs, and this inhibition was critical for both the antisurvival and antimitotic affects of the compound. Indeed, luteolin abolished VEGF-induced activation of Akt, a downstream target of PI3K conveying both survival and mitotic downstream signals. Because overexpression of a constitutively active form of Akt rescued HUVECs only from the antisurvival effects of luteolin, the result indicated that luteolin targeted mainly the survival signals of the PI3K/Akt pathway. With regard to its antimitotic activity, luteolin inhibited VEGF-induced phosphorylation of p70 S6 kinase (S6K), a downstream effector of PI3K responsible for G(1) progression. Indeed, VEGF-induced proliferation of HUVECs was sensitive to rapamycin, an inhibitor of p70 S6K activation. Surprisingly, luteolin did not affect VEGF-induced phosphorylation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinases, a pathway that is considered important for the mitotic effects of VEGF. Thus, blockade of PI3K by luteolin was responsible for the inhibitory effects of the compound on VEGF-induced survival and proliferation of HUVECs. The antisurvival effects of luteolin were mediated via blockage of PI3K/Akt-dependent pathways, whereas inhibition of the PI3K/p70 S6K pathway mediated the antimitotic effects of the compound.
Bagli
Eleni
E
Laboratory of Biological Chemistry and Department of Ophthalmology, Medical School, University of Ioannina, Ioannina, Greece.
Stefaniotou
Maria
M
Morbidelli
Lucia
L
Ziche
Marina
M
Psillas
Konstantinos
K
Murphy
Carol
C
Fotsis
Theodore
T
D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects*; D005260:Female; D006801:Humans; D047311:Luteolin / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009374:Neoplasms, Experimental / Q000098:blood supply / Q000188:drug therapy; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011817:Rabbits; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D020533:Angiogenesis Inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D042461:Vascular Endothelial Growth Factor A; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D047311:Luteolin