Molecular targets for apigenin-induced cell cycle arrest and apoptosis in prostate cancer cell xenograft

Abstract

Apigenin (4V ,5,7-trihydroxyflavone) is a promising chemopreventive agent abundantly present in fruits and vegetables that has been shown to promote cell cycle arrest and apoptosis in various malignant cell lines. To determine whether pharmacologic intervention with apigenin has a direct growth inhibitory effect on human prostate tumors implanted in athymic nude mice, we examined cell cycle regulatory molecules as precise molecular targets of apigenin action. Apigenin feeding by gavage to these mice at doses of 20 and 50 Mg/mouse/d in 0.2 mL of a vehicle containing 0.5% methyl cellulose and 0.025% Tween 20 resulted in significant decreases in tumor volume and mass of androgen-sensitive 22Rv1 and androgen-insensitive PC-3-implanted cells. Oral intake of apigenin resulted in dose-dependent (a) increase in the protein expression of WAF1/p21, KIP1/p27, INK4a/p16, and INK4c/p18; (b) down-modulation of the protein expression of cyclins D1, D2, and E; and cyclin-dependent kinases (cdk), cdk2, cdk4, and cdk6; (c) decrease in retinoblastoma phosphorylation at serine 780; (d) increase in the binding of cyclin D1 toward WAF1/p21 and KIP1/p27; and (e) decrease in the binding of cyclin E toward cdk2 in both types of tumors. In addition, apigenin feeding resulted in stabilization of p53 by phosphorylation at serine 15 in 22Rv1 tumors, which seems to exhibit p53-dependent growth inhibitory responses. Apigenin intake by these mice also resulted in induction of apoptosis, which positively correlated with serum and tumor apigenin levels. Taken together, this is the first systematic in vivo study showing the involvement of cell cycle regulatory proteins as potential molecular targets of apigenin. [Mol Cancer Ther 2006;5(4):843 -52]

Apigenin-induced prostate cancer cell death is initiated by reactive oxygen species and p53 activation

“…The second and third groups of animals received 20 and 50 μg/mouse/day doses of apigenin in vehicle, respectively, for 10 weeks. These doses are comparable to the daily consumption of flavonoid in humans as reported in previously published studies [33,34]. Apigenin feeding was started 2 weeks before cell inoculation and was continued for 10 weeks.…”

“…This induction of apoptosis is accompanied by increases in ROS production, p53 phosphorylation, and p21/WAF-1 induction; alterations in MDM2/p14 ARF ; a decrease in NF-κB/p65 transcriptional activity leading to loss of mitochondrial membrane potential; and caspase activation. Although our study and prior studies have shown that apigenin-induced p53-dependent apoptosis occurs in prostate cancer and other malignancies, the pathways whereby p53 leads to execution of the apoptosis program are not well characterized.There is accumulating evidence that apigenin can suppress the growth of malignant prostate cells as well as tumor xenografts in vivo by causing cell cycle arrest and apoptosis [31][32][33][34]36]. In this study we have demonstrated that the p53-associated pathway is required for apigenin-mediated apoptosis, as evidenced by the p53 antisense oligonucleotide experiment.…”

“…We also observed that apigenin induces apoptosis in solid tumors through upregulation of . More recently, we have demonstrated that apigenininduced suppression of tumor proliferation correlates with downregulation of cyclin D1 expression and cdk4-mediated Rb phosphorylation, induction of p21/WAF-1, and p53 stabilization [34]. However, the mechanisms by which apigenin influences p53-mediated apoptosis are not clearly understood.…”

ProstaCaid™ inhibits tumor growth in a xenograft model of human prostate cancer

“…Therefore, one of the possible molecular targets in cancer cells is the activation of CDK inhibitors. Indeed, our observation that PC treatment significantly increased expression of CDK inhibitor CDKN1A-p21, is in agreement with recent studies demonstrating that some natural compounds (apigenin, silibinin, white cocoa tea extract) inhibited growth of PC-3 tumor xenografts and increased protein levels of p21 in these tumors (27)(28)(29).…”

Preclinical Colorectal Cancer Chemopreventive Efficacy and p53-Modulating Activity of 3′,4′,5′-Trimethoxyflavonol, a Quercetin Analogue

“…The study of CP-31398 (17) referred to in the introduction provides convincing support for the notion that increasing expression and activation of wild-type p53 reduces intestinal adenoma development in the Apc Min mouse, probably through the suppression of adenoma cell proliferation and induction of apoptosis. The p53-modulating ability of flavonoids in cells in vitro has been described before (10,11,(43)(44)(45)(46), although flavonoid-mediated upregulation of p53 in intact animals has to our knowledge been shown previously only for the flavone apigenin (4′,5,7-trihydroxyflavone) in mice bearing the 22Rv1 prostate tumor xenograft (45). TMFol at 10 μmol/L doubled p53 protein expression in HCT116 cells in vitro, and fisetin has been reported to have a similar effect (44).…”