Anna A. Powolny

Multitargeted prevention and therapy of cancer by diallyl trisulfide and related Allium vegetable-derived organosulfur compounds

Allium vegetables, such as garlic, have been used for medicinal purposes throughout the recorded history. The known health benefits of Allium vegetables constituents include cardiovascular effects, improvement of the immune function, lowering of blood glucose level, radioprotection, protection against microbial infections, and anti-cancer effects. Initial evidence for the anti-cancer effect of Allium vegetables was provided by population-based case-control studies. Subsequent laboratory studies showed that the Allium vegetable constituents, such as diallyl disulfide, S-allylcysteine, and ajoene can not only offer protection against chemically induced cancer in animal models by altering carcinogen metabolism, but also suppress growth of cancer cells in culture and in vivo by causing cell cycle arrest and apoptosis induction. Suppression of angiogenesis and experimental metastasis by Allium constituents has also been reported. Defining the mechanism by which sulfur compounds derived from Allium vegetables inhibit cancer cell growth has been the topic of intense research in the last two decades. Some Allium vegetable constituents have also entered clinical trials to assess their safety and anti-cancer efficacy. This article summarizes preclinical and limited clinical data to warrant further clinical evaluation of Allium vegetable constituents for prevention and therapy of human cancers.

Sulforaphane inhibits prostate carcinogenesis and pulmonary metastasis in TRAMP mice in association with increased cytotoxicity of natural killer cells.

The present study shows that oral gavage of 6 mumol d,l-sulforaphane (SFN), a synthetic analogue of cruciferous vegetable-derived L isomer, thrice per week beginning at 6 weeks of age, significantly inhibits prostate carcinogenesis and pulmonary metastasis in TRAMP mice without causing any side effects. The incidence of the prostatic intraepithelial neoplasia and well-differentiated (WD) carcinoma were approximately 23% to 28% lower (P < 0.05 compared with control by Mann-Whitney test) in the dorsolateral prostate (DLP) of SFN-treated mice compared with controls, which was not due to the suppression of T-antigen expression. The area occupied by the WD carcinoma was also approximately 44% lower in the DLP of SFN-treated mice relative to that of control mice (P = 0.0011 by Mann Whitney test). Strikingly, the SFN-treated mice exhibited approximately 50% and 63% decrease, respectively, in pulmonary metastasis incidence and multiplicity compared with control mice (P < 0.05 by t test). The DLP from SFN-treated mice showed decreased cellular proliferation and increased apoptosis when compared with that from control mice. Additionally, SFN administration enhanced cytotoxicity of cocultures of natural killer (NK) cells and dendritic cells (DC) against TRAMP-C1 target cells, which correlated with infiltration of T cells in the neoplastic lesions and increased levels of interleukin-12 production by the DC. In conclusion, the results of the present study indicate that SFN administration inhibits prostate cancer progression and pulmonary metastasis in TRAMP mice by reducing cell proliferation and augmenting NK cell lytic activity.

Atg5 Regulates Phenethyl Isothiocyanate–Induced Autophagic and Apoptotic Cell Death in Human Prostate Cancer Cells

Phenethyl isothiocyanate (PEITC) is a promising cancer chemopreventive agent but the mechanism of its anticancer effect is not fully understood. We now show, for the first time, that PEITC treatment triggers Atg5-dependent autophagic and apoptotic cell death in human prostate cancer cells. Exposure of PC-3 (androgen independent, p53 null) and LNCaP (androgen responsive, wild-type p53) human prostate cancer cells to PEITC resulted in several specific features characteristic of autophagy, including appearance of membranous vacuoles, formation of acidic vesicular organelles, and cleavage and recruitment of microtubule-associated protein 1 light chain 3 (LC3) to autophagosomes. A normal human prostate epithelial cell line (PrEC) was markedly more resistant toward PEITC-mediated cleavage and recruitment of LC3 compared with prostate cancer cells. Although PEITC treatment suppressed activating phosphorylations of Akt and mammalian target of rapamycin (mTOR), which are implicated in regulation of autophagy by different stimuli, processing and recruitment of LC3 was only partially/marginally reversed by ectopic expression of constitutively active Akt or overexpression of mTOR-positive regulator Rheb. The PEITC-mediated apoptotic DNA fragmentation was significantly attenuated in the presence of a pharmacologic inhibitor of autophagy (3-methyl adenine). Transient transfection of LNCaP and PC-3 cells with Atg5-specific small interfering RNA conferred significant protection against PEITC-mediated autophagy as well as apoptotic DNA fragmentation. A xenograft model using PC-3 cells and Caenorhabditis elegans expressing a lgg-1:GFP fusion protein provided evidence for occurrence of PEITC-induced autophagy in vivo. In conclusion, the present study indicates that Atg5 plays an important role in regulation of PEITC-induced autophagic and apoptotic cell death.

Phenethyl isothiocyanate inhibits oxidative phosphorylation to trigger reactive oxygen species-mediated death of human prostate cancer cells

Phenethyl isothiocyanate (PEITC), a constituent of edible cruciferous vegetables such as watercress, not only affords significant protection against chemically induced cancer in experimental rodents but also inhibits growth of human cancer cells by causing apoptotic and autophagic cell death. However, the underlying mechanism of PEITC-induced cell death is not fully understood. Using LNCaP and PC-3 human prostate cancer cells as a model, we demonstrate that the PEITC-induced cell death is initiated by production of reactive oxygen species (ROS) resulting from inhibition of oxidative phosphorylation (OXPHOS). Exposure of LNCaP and PC-3 cells to pharmacologic concentrations of PEITC resulted in ROS production, which correlated with inhibition of complex III activity, suppression of OXPHOS, and ATP depletion. These effects were not observed in a representative normal human prostate epithelial cell line (PrEC). The ROS production by PEITC treatment was not influenced by cyclosporin A. The Rho-0 variants of LNCaP and PC-3 cells were more resistant to PEITC-mediated ROS generation, apoptotic DNA fragmentation, and collapse of mitochondrial membrane potential compared with respective wild-type cells. The PEITC treatment resulted in activation of Bax in wild-type LNCaP and PC-3 cells, but not in their respective Rho-0 variants. Furthermore, RNA interference of Bax and Bak conferred significant protection against PEITC-induced apoptosis. The Rho-0 variants of LNCaP and PC-3 cells also resisted PEITC-mediated autophagy. In conclusion, the present study provides novel insight into the molecular circuitry of PEITC-induced cell death involving ROS production due to inhibition of complex III and OXPHOS.

Mitochondria-mediated apoptosis by diallyl trisulfide in human prostate cancer cells is associated with generation of reactive oxygen species and regulated by Bax/Bak

Garlic constituent diallyl trisulfide (DATS) inhibits growth of cancer cells in vitro and in vivo by causing apoptosis, but the sequence of events leading to cell death is not fully understood. We now show that DATS treatment triggers mitochondria-mediated apoptosis program in human prostate cancer cells (LNCaP, LNCaP-C81, LNCaP-C4-2) irrespective of their androgen responsiveness. Interestingly, a normal prostate epithelial cell line (PrEC) is significantly more resistant to apoptosis induction by DATS compared with prostate cancer cells. The DATS-induced apoptosis in LNCaP cells correlated with the collapse of mitochondrial membrane potential, modest increase in protein level of Bak, and down-regulation of Bcl-2 and Bcl-xL protein levels. The DATS-induced apoptosis was significantly attenuated by knockdown of Bax and Bak proteins, but not by ectopic expression of either Bcl-2 or Bcl-xL. The DATS treatment caused generation of reactive oxygen species (ROS) in LNCaP cells, but not in PrEC, which was attenuated by pretreatment with antioxidant N-acetylcysteine. The N-acetylcysteine pretreatment conferred significant protection against DATS-mediated disruption of the mitochondrial membrane potential and apoptosis. In conclusion, the present study reveals that the mitochondria-mediated cell death by DATS is associated with ROS generation and regulated by Bax/Bak but independent of Bcl-2 or Bcl-xL. [Mol Cancer Ther 2007;6(5):1599–609]

Role of Reactive Oxygen Intermediates in Cellular Responses to Dietary Cancer Chemopreventive Agents

Epidemiological studies continue to support the premise that diets rich in fruits and vegetables may offer protection against cancer of various anatomic sites. This correlation is quite persuasive for vegetables including ALLIUM (e. g., garlic) and cruciferous (e. g., broccoli and watercress) vegetables. The bioactive food components responsible for the cancer chemopreventive effects of various edible plants have been identified. For instance, the anticancer effects of ALLIUM and cruciferous vegetables are attributed to organosulfur compounds (e. g., diallyl trisulfide) and isothiocyanates (e. g., sulforaphane and phenethyl isothiocyanate), respectively. Bioactive food components with anticancer activity are generally considered to be antioxidants due to their ability to modulate expression/activity of antioxidative and phase 2 drug-metabolizing enzymes and scavenging free radicals. At the same time, more recent studies have provided convincing evidence to indicate that certain dietary cancer chemopreventive agents cause generation of reactive oxygen species (ROS) to trigger signal transduction culminating in cell cycle arrest and/or programmed cell death (apoptosis). Interestingly, the ROS generation by some dietary anticancer agents is tumor cell specific and does not occur in normal cells. This review summarizes experimental evidence supporting the involvement of ROS in cellular responses to cancer chemopreventive agents derived from common edible plants.

Molecular targets of cancer chemoprevention by garlic-derived organosulfides

AbstractThe medicinal benefits of Allium vegetables, especially garlic, have been noted throughout recorded history. The known health benefits of Allium vegetables and their constituents include cardiovascular protective effects, stimulation of immune function, reduction of blood glucose level, radioprotection, improvement of memory loss, protection against microbial, viral and fungal infections, as well as anticancer effects. Population-based case control studies have suggested an inverse correlation between dietary intake of Allium vegetables and the risk of different types of cancers. The anticarcinogenic effect of Allium vegetables including garlic is attributed to organosulfur compounds (OSC), which are highly effective in affording protection against cancer in animal models induced by a variety of chemical carcinogens. More recent studies have shown that certain naturally occurring OSC analogues can suppress proliferation of cancer cells in culture and in vivo. The OSC-induced changes in the proliferation of cancer cells are frequently associated with perturbations in cell cycle progression and induction of G2/M phase arrest. The OSC have also been demonstrated to induce apoptosis via the intrinsic pathway by altering the ratio of the Bcl-2 family of proteins both in cell culture and in in vivo models. Anti-angiogenic activity for garlic-derived OSC has also been documented. This article summarizes current knowledge on molecular targets of cancer chemoprevention by OSC.

Plumbagin-induced Apoptosis in Human Prostate Cancer Cells is Associated with Modulation of Cellular Redox Status and Generation of Reactive Oxygen Species

PurposeTo investigate the mechanism of human prostate cancer cell growth inhibition by plumbagin, a constituent of the widely used medicinal herb Plumbago zeylanica L.Materials and MethodsCell viability was determined by trypan blue dye exclusion assay. Apoptosis induction was assessed by analysis of cytoplasmic histone-associated DNA fragmentation. Cell cycle distribution and generation of reactive oxygen species (ROS) were determined by flow cytometry. The effect of plumbagin treatment on cellular redox status was determined by analysis of intracellular glutathione (GSH) levels and expression of genes involved in ROS metabolism.ResultsPlumbagin treatment decreased viability of human prostate cancer cells (PC-3, LNCaP, and C4-2) irrespective of their androgen responsiveness or p53 status. Plumbagin-mediated decrease in cell viability correlated with apoptosis induction, which was accompanied by ROS generation and depletion of intracellular GSH levels. Pretreatment of cells with the antioxidant N-acetylcysteine inhibited plumbagin-mediated ROS generation and apoptosis. Plumbagin treatment also resulted in altered expression of genes responsible for ROS metabolism, including superoxide dismutase 2 (Mn-SOD).ConclusionThe present study points towards an important role of ROS in plumbagin-induced apoptosis in human prostate cancer cells.

Chemopreventative Potential of the Cruciferous Vegetable Constituent Phenethyl Isothiocyanate in a Mouse Model of Prostate Cancer

BACKGROUND This study was undertaken to determine the chemopreventative efficacy of phenethyl isothiocyanate (PEITC), a bioactive constituent of many edible cruciferous vegetables, in a mouse model of prostate cancer, and to identify potential biomarker(s) associated with PEITC response. METHODS The chemopreventative activity of dietary PEITC was investigated in Transgenic Adenocarcinoma of Mouse Prostate mice that were fed a control diet or one containing 3 μmol PEITC/g (n = 21 mice per group) for 19 weeks. Dorsolateral prostate tissue sections were stained with hematoxylin and eosin for histopathologic evaluations and subjected to immunohistochemistry for analysis of cell proliferation (Ki-67 expression), autophagy (p62 and LC3 protein expression), and E-cadherin expression. Autophagosomes were visualized by transmission electron microscopy. Apoptotic bodies were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. Plasma proteomics was performed by two-dimensional gel electrophoresis followed by mass spectrometry to identify potential biomarkers of PEITC activity. All statistical tests were two-sided. RESULTS Administration of PEITC (3 μmol/g diet) decreased incidence (PEITC diet vs control diet, mean = 21.65 vs 57.58%, difference = -35.93%, 95% confidence interval = -45.48% to -13.10%, P = .04) as well as burden (affected area) (PEITC diet vs control diet, mean = 18.53% vs 45.01%, difference = -26.48%, 95% confidence interval = -49.78% to -3.19%, P = .02) of poorly differentiated tumors in the dorsolateral prostate of transgenic mice compared with control mice, with no toxic effects. PEITC-mediated inhibition of prostate carcinogenesis was associated with induction of autophagy and overexpression of E-cadherin in the dorsolateral prostate. However, PEITC treatment was not associated with a decrease in cellular proliferation, apoptosis induction, or inhibition of neoangiogenesis. Plasma proteomics revealed distinct changes in the expression of several proteins (eg, suppression of clusterin protein) in the PEITC-treated mice compared with control mice. CONCLUSIONS In this transgenic model, dietary PEITC suppressed prostate cancer progression by induction of autophagic cell death. Potential biomarkers to assess the response to PEITC treatment in plasma were identified.

Garlic Constituent Diallyl Trisulfide Prevents Development of Poorly Differentiated Prostate Cancer and Pulmonary Metastasis Multiplicity in TRAMP Mice

Identification of agents that are nontoxic but can delay onset and/or progression of prostate cancer, which is the second leading cause of cancer-related deaths among men in the United States, is highly desirable. We now show that p.o. gavage of garlic constituent diallyl trisulfide (DATS; 1 and 2 mg/day, thrice/week for 13 weeks beginning at age 8 weeks) significantly inhibits progression to poorly differentiated prostate carcinoma and pulmonary metastasis multiplicity in transgenic adenocarcinoma of mouse prostate (TRAMP) mice without any side effects. There was a trend of a decrease in average wet weights of the urogenital tract and prostate gland in 1 and 2 mg DATS-treated mice compared with controls ( approximately 25-46% decrease in DATS-treated mice compared with controls). The incidence and the area of the dorsolateral prostate occupied by the poorly differentiated carcinoma were significantly lower in both 1 and 2 mg DATS-treated mice compared with control mice. In addition, DATS administration resulted in a statistically significant decrease in pulmonary metastasis multiplicity compared with controls (P = 0.002). The dorsolateral prostate from DATS-treated TRAMP mice exhibited decreased cellular proliferation in association with induction of cyclinB1 and securin protein levels, and suppression of the expression of neuroendocrine marker synaptophysin. However, DATS administration did not have any appreciable effect on apoptosis induction, angiogenesis, or natural killer and dendritic cell function. In conclusion, the results of the present study show, for the first time, that DATS administration prevents progression to invasive carcinoma and lung metastasis in TRAMP mice.