Xanthohumol, a prenylflavonoid derived from hops induces apoptosis and inhibits NF-kappaB activation in prostate epithelial cells

Abstract

There is increasing evidence that certain natural compounds found in plants may be useful as cancer chemopreventive or chemotherapeutic agents. Limited in vitro studies indicate that several prenylated flavonoids present in the hop plant (Humulus lupulus) possess anticarcinogenic properties. The purpose of this study was to investigate the anti-tumorigenic effects of xanthohumol (XN), the major prenylflavonoid in hops, on prostate cancer and benign prostate hyperplasia. BPH-1 and PC3 cell lines were used in our study to represent both non-tumorigenic hyperplasia and malignant prostate cancer. In both BPH-1 and PC3 cells, XN and its oxidation product, XAL, decreased cell viability in a dose dependent manner (2.5–20 μM) as determined by MTT assay and caused an increase in the formation of early and late apoptotic cells as determined by Annexin V staining and multicaspase assays. XN and its oxygenated derivative also induced cell cycle changes in both cells lines, seen in an elevated sub G1 peak at 48 h treatment. Western blot analysis was performed to confirm the activation of proapoptotic proteins, Bax and p53. XN and its derivative caused decreased activation of NFκB. This work suggests that XN and its oxidation product, XAL, may be potentially useful as a chemopreventive agent during prostate hyperplasia and prostate carcinogenesis, acting via induction of apoptosis and down-regulation of NFκB activation in BPH-1 cells.

Introduction

Xanthohumol (XN) is the principal flavonoid found in the hop plant, Humulus lupulus L. (Cannabaceae). Hops are traditionally used to add bitterness and flavor to beer; however, more recently alternative uses for hop compounds and their effects on biological processes have become an area of interest. In particular, XN has been shown to bear anti-cancer properties [1], [2], [3], [4]. XN is characterized as a ‘broad spectrum’ chemopreventive agent because it is able to inhibit initiation, promotion, and progression stages of carcinogenesis. Previous studies indicate that XN acts as an anti-initiating agent by modulating enzyme activity of pro-carcinogen activating enzymes and carcinogen detoxifying enzymes [5]. Also, XN exhibits strong antioxidant and free radical scavenging properties [3], [6]. The ability of XN to induce apoptosis in cancer cells and limit tumor cell invasiveness suggests suppression of cancer development post-initation as well [7], [8], [9].

Prostate cancer remains a considerable health problem for men around the world, accounting for an anticipated 30,000 deaths in 2005 in the United States alone. In fact, prostate cancer is the most frequently diagnosed non-cutaneous cancer and is the second leading cause of cancer death in American men. With little progress being made in reduction of these rates, identification and utilization of novel compounds for cancer prevention has become an important issue in public health related research [10]. There is an increasing body of evidence that certain phytochemicals have the potential to act as chemopreventive or chemotherapeutic agents and perhaps ultimately reduce prostate cancer morbidity and mortality rates [11]. Based on data from limited in vitro studies, we set out to test the anticarcinogenic properties of XN in prostate cancer cells and to define possible mechanisms.

Control of cell cycle and apoptosis are key mechanisms linked to the suppression of cell proliferation in several chemopreventive agents. In addition, inhibition of NFκB activation has been another key chemoprevention target. Constitutive activation of NFκB is common in various human malignancies, including prostate and leads to up-regulation of genes encoding adhesion molecules, inflammatory cytokines, growth factors, and anti-apoptotic genes [12], [13]. The goal of this study was to examine the effects of XN and its oxidation product, XAL, on cell proliferation/viability, cell cycle, expression of caspases, apoptosis and NFκB activation in hyperplasia and prostate cancer cells BPH-1 and PC3 cells. This data will provide evidence for the possible use of XN as an effective chemopreventive and chemotherapeutic agent for prostate hyperplasia and/or cancer.