Jeremy J. Johnson

S100A4 accelerates tumorigenesis and invasion of human prostate cancer through the transcriptional regulation of matrix metalloproteinase 9

We previously showed that the calcium-binding protein S100A4 is overexpressed during the progression of prostate cancer (CaP) in humans and in the TRAMP (transgenic adenocarcinoma of the mouse prostate) mouse model. We tested a hypothesis that the S100A4 gene plays a role in the invasiveness of human CaP and may be associated with its metastatic spread. We observed that siRNA-mediated suppression of the S100A4 gene significantly reduced the proliferative and invasive capability of the highly invasive CaP cells PC-3. We evaluated the mechanism through which the S100A4 gene controls invasiveness of cells by using a macroarray containing 96 well characterized metastatic genes. We found that matrix metalloproteinase 9 (MMP-9) and its tissue inhibitor (TIMP-1) were highly responsive to S100A4 gene suppression. Furthermore, S100A4 suppression significantly reduced the expression and proteolytic activity of MMP-9. By employing an MMP-9-promoter reporter, we observed a significant reduction in the transcriptional activation of the MMP-9 gene in S100A4-siRNA-transfected cells. Cells overexpressing the S100A4 gene (when transfected with pcDNA3.1-S100A4 plasmid) also significantly expressed MMP-9 and TIMP-1 genes with increased proteolytic activity of MMP-9 concomitant to increased transcriptional activation of the MMP-9 gene. S100A4-siRNA-transfected cells exhibited a reduced rate of tumor growth under in vivo conditions. Our data demonstrate that the S100A4 gene controls the invasive potential of human CaP cells through regulation of MMP-9 and that this association may contribute to metastasis of CaP cells. We suggest that S100A4 could be used as a biomarker for CaP progression and a novel therapeutic or chemopreventive target for human CaP treatment.

A plant flavonoid fisetin induces apoptosis in colon cancer cells by inhibition of COX2 and Wnt/EGFR/NF-κB-signaling pathways

Overexpression of cyclooxygenase 2 (COX2) and uncontrolled wingless and Int (Wnt)-signaling pathway have long been suggested to play crucial roles in colorectal cancer. Studies show that selective COX2 inhibitors possess great potential as chemopreventive agents for colon cancer. Recent studies suggest that targeting COX2 and epidermal growth factor receptor (EGFR) may provide better therapeutic strategy than inhibiting either single target and that this may alleviate the problem of COX2 inhibitor-associated side effects. Therefore, there have been intensive efforts to develop novel dietary substances that target COX2 and EGFR activation. Fisetin is a naturally occurring flavonoid commonly found in various vegetables and fruits. We found that the treatment of COX2-overexpressing HT29 human colon cancer cells with fisetin (30-120 microM) resulted in induction of apoptosis, downregulation of COX2 protein expression without affecting COX1 and inhibited the secretion of prostaglandin E2. Treatment of cells with fisetin also inhibited Wnt-signaling activity through downregulation of beta-catenin and T cell factor 4 and decreased the expression of target genes such as cyclin D1 and matrix metalloproteinase 7. Fisetin treatment of cells also inhibited the activation of EGFR and nuclear factor-kappa B (NF-kappaB). Finally, the formation of colonies in soft agar was suppressed by fisetin treatment. Taken together, we provide evidence that the plant flavonoid fisetin can induce apoptosis and suppress the growth of colon cancer cells by inhibition of COX2- and Wnt/EGFR/NF-kappaB-signaling pathways. We suggest that fisetin could be a useful agent for prevention and treatment of colon cancer.

Green tea polyphenols for prostate cancer chemoprevention: a translational perspective.

Every year nearly 200,000 men in the United States are diagnosed with prostate cancer (PCa), and another 29,000 men succumb to the disease. Within certain regions of the world population based studies have identified a possible role for green tea in the prevention of certain cancers, especially PCa. One constituent in particular, epigallocatechin-3-gallate also known as EGCG has been shown in cell culture models to decrease cell viability and promote apoptosis in multiple cancer cell lines including PCa with no effect on non-cancerous cell lines. In addition, animal models have consistently shown that standardized green tea polyphenols when administered in drinking water delay the development and progression of PCa. Altogether, three clinical trials have been performed in PCa patients and suggest that green tea may have a distinct role as a chemopreventive agent. This review will present the available data for standardized green tea polyphenols in regard to PCa chemoprevention that will include epidemiological, mechanism based studies, safety, pharmacokinetics, and applicable clinical trials. The data that has been collected so far suggests that green tea may be a promising agent for PCa chemoprevention and further clinical trials of participants at risk of PCa or early stage PCa are warranted.

Carnosol: A promising anti-cancer and anti-inflammatory agent

The Mediterranean diet and more specifically certain meats, fruits, vegetables, and olive oil found in certain parts of the Mediterranean region have been associated with a decreased cardiovascular and diabetes risk. More recently, several population based studies have observed with these lifestyle choices have reported an overall reduced risk for several cancers. One study in particular observed an inverse relationship between consumption of Mediterranean herbs such as rosemary, sage, parsley, and oregano with lung cancer. In light of these findings there is a need to explore and identify the anti-cancer properties of these medicinal herbs and to identify the phytochemicals therein. One agent in particular, carnosol, has been evaluated for anti-cancer property in prostate, breast, skin, leukemia, and colon cancer with promising results. These studies have provided evidence that carnosol targets multiple deregulated pathways associated with inflammation and cancer that include nuclear factor kappa B (NFκB), apoptotic related proteins, phosphatidylinositol-3-kinase (PI3 K)/Akt, androgen and estrogen receptors, as well as molecular targets. In addition, carnosol appears to be well tolerated in that it has a selective toxicity towards cancer cells versus non-tumorigenic cells and is well tolerated when administered to animals. This mini-review reports on the pre-clinical studies that have been performed to date with carnosol describing mechanistic, efficacy, and safety/tolerability studies as a cancer chemoprevention and anti-cancer agent.

Fisetin induces autophagic cell death through suppression of mTOR signaling pathway in prostate cancer cells

The mammalian target of rapamycin (mTOR) kinase is an important component of PTEN/PI3K/Akt signaling pathway, which is frequently deregulated in prostate cancer (CaP). Recent studies suggest that targeting PTEN/PI3K/Akt and mTOR signaling pathway could be an effective strategy for the treatment of hormone refractory CaP. Here, we show that the treatment of androgen-independent and PTEN-negative human CaP PC3 cells with fisetin, a dietary flavonoid, resulted in inhibition of mTOR kinase signaling pathway. Treatment of cells with fisetin inhibited mTOR activity and downregulated Raptor, Rictor, PRAS40 and GbetaL that resulted in loss of mTOR complexes (mTORC)1/2 formation. Fisetin also activated the mTOR repressor TSC2 through inhibition of Akt and activation of AMPK. Fisetin-mediated inhibition of mTOR resulted in hypophosphorylation of 4EBP1 and suppression of Cap-dependent translation. We also found that fisetin treatment leads to induction of autophagic-programmed cell death rather than cytoprotective autophagy as shown by small interfering RNA Beclin1-knockdown and autophagy inhibitor. Taken together, we provide evidence that fisetin functions as a dual inhibitor of mTORC1/2 signaling leading to inhibition of Cap-dependent translation and induction of autophagic cell death in PC3 cells. These results suggest that fisetin could be a useful chemotherapeutic agent in treatment of hormone refractory CaP.

α-Mangostin, a xanthone from mangosteen fruit, promotes cell cycle arrest in prostate cancer and decreases xenograft tumor growth

There is a need to characterize promising dietary agents for chemoprevention and therapy of prostate cancer (PCa). We examined the anticancer effect of α-mangostin, derived from the mangosteen fruit, in human PCa cells and its role in targeting cell cycle-related proteins involved in prostate carcinogenesis. Using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, we found that α-mangostin significantly decreases PCa cell viability in a dose-dependent manner. Further analysis using flow cytometry identified cell cycle arrest along with apoptosis. To establish a more precise mechanism of action, we performed a cell free biochemical kinase assay against multiple cyclins/cyclin-dependent kinases (CDKs) involved in cell cycle progression; the most significant inhibition in the cell free-based assays was CDK4, a critical component of the G1 phase. Through molecular modeling, we evaluated α-mangostin against the adenosine triphosphate-binding pocket of CDK4 and propose three possible orientations that may result in CDK4 inhibition. We then performed an in vivo animal study to evaluate the ability of α-mangostin to suppress tumor growth. Athymic nude mice were implanted with 22Rv1 cells and treated with vehicle or α-mangostin (100 mg/kg) by oral gavage. At the conclusion of the study, mice in the control cohort had a tumor volume of 1190 mm(3), while the treatment group had a tumor volume of 410 mm(3) (P < 0.01). The ability of α-mangostin to inhibit PCa in vitro and in vivo suggests α-mangostin may be a novel agent for the management of PCa.

Lupeol inhibits proliferation of human prostate cancer cells by targeting β-catenin signaling

Lupeol, a dietary triterpene, was shown to decrease serum prostate-specific antigen levels and inhibit the tumorigenicity of prostate cancer (CaP) cells in vivo. Here, we show that Lupeol inhibits the proliferative potential of CaP cells and delineated its mechanism of action. Employing a focused microarray of human CaP-associated genes, we found that Lupeol significantly modulates the expression level of genes such as ERBB2, tissue inhibitor of metalloproteinases-3, cyclin D1 and matrix metalloproteinase (MMP)-2 that are known to be associated with proliferation and survival. A common feature of these genes is that all of them are known to either regulate or act as downstream target of beta-catenin signaling that is highly aberrant in CaP patients. Lupeol treatment significantly (1) reduced levels of beta-catenin in the cytoplasmic and nuclear fractions, (2) modulated expression levels of glycogen synthase kinase 3 beta (GSK3beta)-axin complex (regulator of beta-catenin stability), (3) decreased the expression level and enzymatic activity of MMP-2 (downstream target of beta-catenin), (4) reduced the transcriptional activation of T Cell Factor (TCF) responsive element (marker for beta-catenin signaling) in pTK-TCF-Luc-transfected cells and (5) decreased the transcriptional activation of MMP-2 gene in pGL2-MMP-2-Luc-transfected cells. Effects of Lupeol treatment on beta-catenin degradation were significantly reduced in CaP cells where axin is knocked down through small interfering RNA transfection and GSK3beta activity is blocked. Collectively, these data suggest the multitarget efficacy of Lupeol on beta-catenin-signaling network thus resulting in the inhibition CaP cell proliferation. We suggest that Lupeol could be developed as an agent for chemoprevention as well as chemotherapy of human CaP.

Disruption of androgen and estrogen receptor activity in prostate cancer by a novel dietary diterpene carnosol: implications for chemoprevention

Emerging data are suggesting that estrogens, in addition to androgens, may also be contributing to the development of prostate cancer (PCa). In view of this notion, agents that target estrogens, in addition to androgens, may be a novel approach for PCa chemoprevention and treatment. Thus, the identification and development of nontoxic dietary agents capable of disrupting androgen receptor (AR) in addition to estrogen receptor (ER) could be extremely useful in the management of PCa. Through molecular modeling, we found that carnosol, a dietary diterpene, fits within the ligand-binding domain of both AR and ER-α. Using a time-resolved fluorescence resonance energy transfer assay, we found that carnosol interacts with both AR and ER-α and additional experiments confirmed that it functions as a receptor antagonist with no agonist effects. LNCaP, 22Rv1, and MCF7 cells treated with carnosol (20-40 μmol/L) showed decreased protein expression of AR and ER-α. Oral administration of carnosol at 30 mg/kg 5 days weekly for 28 days to 22Rv1 PCa xenografted mice suppressed tumor growth by 36% (P = 0.028) and was associated with a decrease in serum prostate-specific antigen by 26% (P = 0.0042). These properties make carnosol unique to any known antiandrogen or antiestrogen investigated thus far for the simultaneous disruption of AR and ER-α. We suggest that carnosol may be developed or chemically modified through more rigorous structure-activity relationship studies for a new class of investigational agents—a dual AR/ER modulator. Cancer Prev Res; 3(9); 1112–23. ©2010 AACR.

Rosemary (Rosmarinus officinalis) Extract Modulates CHOP/GADD153 to Promote Androgen Receptor Degradation and Decreases Xenograft Tumor Growth

The Mediterranean diet has long been attributed to preventing or delaying the onset of cardiovascular disease, diabetes and various solid organ cancers. In this particular study, a rosemary extract standardized to carnosic acid was evaluated for its potential in disrupting the endoplasmic reticulum machinery to decrease the viability of prostate cancer cells and promote degradation of the androgen receptor. Two human prostate cancer cell lines, 22Rv1 and LNCaP, and prostate epithelial cells procured from two different patients undergoing radical prostatectomy were treated with standardized rosemary extract and evaluated by flow cytometry, MTT, BrdU, Western blot and fluorescent microscopy. A significant modulation of endoplasmic reticulum stress proteins was observed in cancer cells while normal prostate epithelial cells did not undergo endoplasmic reticulum stress. This biphasic response suggests that standardized rosemary extract may preferentially target cancer cells as opposed to “normal” cells. Furthermore, we observed standardized rosemary extract to decrease androgen receptor expression that appears to be regulated by the expression of CHOP/GADD153. Using a xenograft tumor model we observed standardized rosemary extract when given orally to significantly suppress tumor growth by 46% compared to mice not receiving standardized rosemary extract. In the last several years regulatory governing bodies (e.g. European Union) have approved standardized rosemary extracts as food preservatives. These results are especially significant as it is becoming more likely that individuals will be receiving standardized rosemary extracts that are a part of a natural preservative system in various food preparations. Taken a step further, it is possible that the potential benefits that are often associated with a “Mediterranean Diet” in the future may begin to extend beyond the Mediterranean diet as more of the population is consuming standardized rosemary extracts.

Polyphenols from the Mediterranean herb rosemary (Rosmarinus officinalis) for prostate cancer

The Mediterranean diet is rich in fruits and vegetables and has been associated with a variety of health benefits including cancer prevention. One aspect of the diet that has not received enough attention is Mediterranean herbs. Specifically, rosemary and its polyphenolic diterpenes (carnosic acid and carnosol) are known to possess anti-oxidant activity that may be beneficial for cancer control. Herein, we describe the in vitro and in vivo studies carried out towards understanding the molecular mechanisms of carnosic acid and carnosol leading to inhibition of prostate cancer. The reported findings suggest that these polyphenols target multiple signaling pathways involved in cell cycle modulation and apoptosis. Further work is required to understand its potential for health promotion and potential drug discovery for prostate cancer chemoprevention.