Silibinin strongly inhibits growth and survival of human endothelial cells via cell cycle arrest and downregulation of survivin, Akt and NF-κB: implications for angioprevention and antiangiogenic therapy

Abstract

Recently, we observed that suppression of tumor xenograft growth by silibinin was associated with reduction in tumor vasculature and an increased apoptosis. Here, we provide evidence for molecular events associated with antiangiogenic efficacy of pharmacologically achievable doses of silibinin in endothelial cell culture system. Our data show that silibinin almost completely (Po0.001) inhibits growth of human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (HMVEC-dermal origin) together with induction of cell death in a dose-and time-dependent manner. Growth inhibition was associated with a strong induction of G1 arrest accompanied by an increase in Kip1/p27, Cip1/p21 and p53. Apoptosis induction (up to 14-to 17-fold in both cell lines, Po0.001) was an underlying mechanism in silibinin-induced death of endothelial cells. In the studies elucidating the molecular events involved in apoptosis, silibinin caused loss of mitochondrial membrane potential and an increase in cytochrome c release from mitochondria. An increase in Bax and a decrease in Mcl-1 proteins were also observed. Silibinin-induced apoptosis involved both caspase-dependent and -independent mechanisms. Silibinin also decreased survivin level and inhibited Akt and NF-jB signaling. Two different PI-3K inhibitors, wortmannin and LY294002, showed Akt-independent activation of NF-jB. Further, silibinin showed a concentration-dependent strong inhibition of capillary tube formation on matrigel, retraction and disintegration of preformed capillary network, inhibition of matrigel invasion and migration, and a decrease in matrix metalloproteinase-2 secretion by HUVEC. Together, these findings identify pleiotropic mechanisms for antiangiogenic efficacy of silibinin, and suggest its usefulness in angioprevention and antiangiogenic therapy.

Silibinin inhibits translation initiation: implications for anticancer therapy

“…Some reports have documented that silibinin inhibits Akt phosphorylation (23,38). However, in our study, silibinin was found to induce the activation of the prosurvival kinase Akt in MCF-7 breast cancer cells (Fig.…”

“…Treatment of cells with silibinin has also been shown to inhibit expression of Mcl-1 and survivin (23,24), two eIF4E-responsive genes (25,26). Identification of other mRNAs, the translation of which may be affected by silibinin, will require more intensive microarray analysis of transcripts in polysomes of silibinin-treated cells.…”

Downregulation of type I collagen expression in silibinin-treated human skin fibroblasts by blocking the activation of Smad2/3-dependent signaling pathways: Potential therapeutic use in the chemoprevention of keloids

“…It has been reported that silibinin possesses antioxidant, antiapoptotic, anti-inflammatory and anti-fibrotic properties (1)(2)(3). However, the effects of silibinin on type I collagen expression in human skin fibroblasts (HSFs) and the related signaling pathways remain unclear.…”

“…Non-cytotoxic effect of silibinin on human skin fibroblasts. Cells were plated at a density of 4x10 3 /cm 2 in 96-well plates. Cells were cultured with or without silibinin for 2 days.…”

Hypoxia modulates the effect of dihydroartemisinin on endothelial cells

“…The G 2 cell cycle arrest could be caused by DNA damage [60], which activates the so called "G 2 checkpoint", preventing cells from proceeding into mitosis, with a consequent accumulation of cells in the G2 phase. It is interesting to note that the anti-angiogenic drugs proposed for anti-cancer therapy alter endothelial cell cycle either inducing a G 0 or a G 2 arrest [61][62][63], thus confirming the potential for artemisinins as anti-angiogenic drugs.…”