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

Abstract

Apigenin, a plant flavone, potentially activates wild-type p53 and induces apoptosis in cancer cells. We conducted detailed studies to understand its mechanism of action. Exposure of human prostate cancer 22Rv1 cells, harboring wild-type p53, to growth-suppressive concentrations (10-80 μM) of apigenin resulted in the stabilization of p53 by phosphorylation on critical serine sites, p14 ARFmediated downregulation of MDM2 protein, inhibition of NF-κB/p65 transcriptional activity, and induction of p21/WAF-1 in a dose-and time-dependent manner. Apigenin at these doses resulted in ROS generation, which was accompanied by rapid glutathione depletion, disruption of mitochondrial membrane potential, cytosolic release of cytochrome c, and apoptosis. Interestingly, we observed accumulation of a p53 fraction to the mitochondria, which was rapid and occurred between 1 and 3 h after apigenin treatment. All these effects were significantly blocked by pretreatment of cells with the antioxidant N-acetylcysteine, p53 inhibitor pifithrin-α, and enzyme catalase. Apigenin-mediated p53 activation and apoptosis were further attenuated by p53 antisense oligonucleotide treatment. Exposure of cells to apigenin led to a decrease in the levels of Bcl-XL and Bcl-2 and increase in Bax, triggering caspase activation. Treatment with the caspase inhibitors Z-VAD-FMK and DEVD-CHO partially rescued these cells from apigenin-induced apoptosis. In vivo, apigenin administration demonstrated p53-mediated induction of apoptosis in 22Rv1 tumors. These results indicate that apigenin-induced apoptosis in 22Rv1 cells is initiated by a ROS-dependent disruption of the mitochondrial membrane potential through transcriptional-dependent and -independent p53 pathways. KeywordsReactive oxygen species; Apoptosis; p53; Prostate cancer; Apigenin; Free radicals Cancer prevention is profoundly dependent on the p53 tumor suppressor protein, as it functions in regulating cellular growth and protecting cells from malignant transformation [1,2]. Several studies have demonstrated the anticancer activities of p53, and in fact, p53 is the most *Corresponding author. Department of Urology, Case Western Reserve University, Cleveland, OH 44106, USA. Fax: +1 216 368 0213. E-mail address: sanjay.gupta@case.edu (S. Gupta). This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright NIH Public Access NIH-PA Author ManuscriptNIH-PA A...

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