Polyozellus multiplex, a Korean wild mushroom, as a potent chemopreventive agent against stomach cancer

Polyozellus multiplex, a Korean wild mushroom, was extracted using methanol, and the extract was further fractionated with water and ethylacetate. Assay of each fraction with MTT revealed significant tumoristatic effects of the water fraction of Polyozellus multiplex against human gastric and other cancer cells but not normal human lymphocytes. Modifying effects of the water fraction on glandular stomach mucosa were investigated in male Wistar rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The dietary 0.5% or 1% water fraction of Polyozellus multiplex significantly increased glutathione S-transferase (GST) and superoxide dismutase (SOD) activities, and showed a tendency for increase in glutathione (GSH) levels, compared to the MNNG alone group. It also caused a significant reduction in proliferating cell nuclear antigen (PCNA)-labeling index of the glandular stomach epithelium, along with increase in p53 tumor suppressor gene expression. These results suggest that Polyozellus multiplex is a candidate for chemoprevention against gastric cancer.     

Use of letrozole as a chemopreventive agent in aromatase overexpressing transgenic mice

Our recent studies have shown that overexpression of aromatase results in increased tissue estrogenic activity and induction of hyperplastic and dysplastic lesions in mammary glands, and gynecomastia and testicular cancer in male aromatase transgenic mice. Our studies also have shown that aromatase overexpression-induced changes in mammary glands can be abrogated with very low concentrations of letrozole, an aromatase inhibitor without any effect on normal physiology. In the present study, we have examined the effect of prior low dose letrozole treatment on pregnancy and lactation. We have also investigated the effect of low dose letrozole treatment on subsequent mammary growth and biochemical changes in these animals. There was no change in the litter size, birth weight and no visible birth defects in letrozole-treated animals. Although, there was an insignificant increase in mammary growth in aged animals after 6 weeks of letrozole treatment, the levels of expression of estrogen receptor, progesterone receptor and genes involved in cell cycle and cell proliferation remained low compared to control untreated animals. These observations indicate that aromatase inhibitors such as letrozole can be used as chemopreventive agents without effecting normal physiology in aromatase transgenic mice.     

Topical polyethylene glycol as a novel chemopreventive agent for oral cancer via targeting of epidermal growth factor response

Head and neck squamous cell carcinoma (HNSCC) is a major cause of morbidity and mortality underscoring the need for safe and effective chemopreventive strategies. Targeting epidermal growth factor receptor (EGFR) is attractive in that it is an early critical event in HNSCC pathogenesis. However, current agents lack efficacy or have unacceptable toxicity. Several groups have demonstrated that the over-the-counter medication, polyethylene glycol (PEG) has remarkable chemopreventive efficacy against colon carcinogenesis. Importantly, we reported that this effect is mediated through EGFR internalization/degradation. In the current study, we investigated the chemopreventive efficacy of this agent against HNSCC, using both the well validated animal model 4-NQO (4-nitroquinoline 1-oxide) rat model and cell culture with the human HNSCC cell line SCC-25. We demonstrated that daily topical application of 10% PEG-8000 in the oral cavity (tongue and cavity wall) post 4NQO initiation resulted in a significant reduction in tumor burden (both, tumor size and tumors/tumor bearing rat) without any evidence of toxicity. Immunohistochemical studies depicted decreased proliferation (number of Ki67-positive cells) and reduced expression of EGFR and its downstream effectors cyclin D1 in the tongue mucosa of 4NQO-rats treated with PEG. We showed that EGFR was also markedly downregulated in SCC-25 cells by PEG-8000 with a concomitant induction of G1-S phase cell-cycle arrest, which was potentially mediated through upregulated p21(cip1/waf1). In conclusion, we demonstrate, for the first time, that PEG has promising efficacy and safety as a chemopreventive efficacy against oral carcinogenesis.     

A cancer chemopreventive agent silibinin, targets mitogenic and survival signaling in prostate cancer

There are many epigenetic variables that affect the biological responses of autocrine, paracrine and endocrine regulatory molecules, which determine the growth and development of different cancers including prostate cancer (PCA). One of the focuses of the current cancer chemoprevention studies is the search for non-toxic chemopreventive agents that inhibit mitogenic and cell survival signaling in cancer cells. In general, advanced stage cancer cells harbor many constitutively active mitogenic signaling and anti-apoptotic mechanisms, which make them less dependent on external growth factors as well as resistant to chemotherapeutic agents. In this regard, silibinin (a naturally occurring flavanone) has shown the pleiotropic anticancer effects in different cancer cells. Our extensive studies with PCA have shown that inhibition of mitogenic and cell survival signaling, such as epidermal growth factor receptor, insulin-like growth factor receptor type I and nuclear factor kappa B signaling are the most likely molecular targets of silibinin's efficacy in PCA. We have observed that silibinin inhibits prostate tumor growth in animal models without any apparent signs of toxicity. At the same time, silibinin is also physiologically available in different organs of the body including plasma and prostate, which is generally required for the pharmacological dosing and translational mechanistic studies of the compound. There are substantial amount of data to support the inhibitory effect of silibinin on mitogenic and cell survival signaling in PCA, which are reviewed in the present communication.     

ent-Rosane and abietane diterpenoids as cancer chemopreventive agents

Two ent-rosane- (cuzcol, 1 and 6-dehydroxycuzcol, 2) and a abietatriene- (salvadoriol, 3) type diterpenoids have been isolated from Maytenus cuzcoina and Crossopetalum uragoga, respectively, along with five known diterpene compounds (4-8). Their stereostructures have been elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR techniques, and computational data. The absolute configuration of cuzcol was determined by application of Riguera ester procedure. This is the first instance of isolation of ent-rosane diterpenoids from species of the Celastraceae. The isolated diterpenes were found to be potent anti-tumour-promoter agents, and carnosol (7) also showed a remarkable chemopreventive effect in an in vivo two-stage carcinogenesis model.     

Natural sulforaphane as a functional chemopreventive agent: including a review of isolation,purification and analysis methods

Epidemiological data show that a diet rich in fruits and vegetables can reduce the risk from a number of cancers and chronic diseases. Sulforaphane (SF), a phytochemical constituent of cruciferous vegetables, has been widely researched in recent decades as a potential chemopreventive compound. Nonexistent in intact vegetables, natural SF, is formed from glucoraphanin hydrolyzed by myrosinase. This review summarizes and compares different analysis, isolation and purification methods engaged in SF research. Major important chemopreventive properties of SF investigated in existing research are reviewed and discussed, including antioxidant, anticarcinogenic and anti-inflammatory functions. Considering the potential applications of SF in the future, metabolism, stability and formulation developments of SF are also discussed. Research opportunities are identified based on the review of existing studies to facilitate future explorations on SF, a promising natural compound in chemopreventive therapy.     

Natural sulforaphane as a functional chemopreventive agent: including a review of isolation, purification and analysis methods

Epidemiological data show that a diet rich in fruits and vegetables can reduce the risk from a number of cancers and chronic diseases. Sulforaphane (SF), a phytochemical constituent of cruciferous vegetables, has been widely researched in recent decades as a potential chemopreventive compound. Nonexistent in intact vegetables, natural SF, is formed from glucoraphanin hydrolyzed by myrosinase. This review summarizes and compares different analysis, isolation and purification methods engaged in SF research. Major important chemopreventive properties of SF investigated in existing research are reviewed and discussed, including antioxidant, anticarcinogenic and anti-inflammatory functions. Considering the potential applications of SF in the future, metabolism, stability and formulation developments of SF are also discussed. Research opportunities are identified based on the review of existing studies to facilitate future explorations on SF, a promising natural compound in chemopreventive therapy.     

Retinoids as chemopreventive agents

Retinoids are promising agents for cancer chemoprevention. The myriad effects of retinoids on biological processes including development, differentiation, homeostasis, carcinogenesis and apoptosis are mediated through their molecular targets, the retinoid and rexinoid receptors. Tissue specific expression patterns, ligand specificities, receptor numbers, their distinct functions and functional redundancy make retinoid signaling highly complex. The cross-talks of these receptors with cell surface receptors signaling pathways, as well as their interactions with multiple co-activators and co-repressors further add to the complexity of the pleiotropic effects of retinoids. Elucidation of retinoid signaling pathways and indepth understanding of the mechanisms that underlie the anti-proliferative and apoptotic action of retinoids has paved the way for designing synthetic retinoids for effective chemoprevention and therapy of cancer. Development of receptor selective synthetic retinoids is a major focus of molecular retinoid development. Other new avenues encompass identification of novel retinoid regulated genes, orphan-receptor ligands/functions, novel retinoid mechanisms involving receptor-independent apoptosis inducing activity and synergistic combinations with other agents for cancer prevention and therapy. This review focuses on recent advances in the understanding of molecular mechanisms underlying the action of retinoids and retinoid molecular targeting studies designed primarily to develop retinoids with reduced toxicity, while maintaining or enhancing activity in context of chemoprevention. The clinical efficacy of retinoid based chemoprevention trials is discussed.     

Pre-clinical evaluation of cinobufotalin as a potential anti-lung cancer agent

Lung cancer is a major cause of cancer-related mortality in the United States and around the world. Due to the pre-existing or acquired chemo-resistance, the current standard chemotherapy regimens only show moderate activity against lung cancer. In the current study, we explored the potential anti-lung cancer activity of cinobufotalin in vivo and in vitro, and studied the underlying mechanisms. We demonstrated that cinobufotalin displayed considerable cytotoxicity against lung cancer cells (A549, H460 and HTB-58 lines) without inducing significant cell apoptosis. Our data suggest that mitochondrial protein cyclophilin D (Cyp-D)-dependent mitochondrial permeability transition pore (mPTP) opening mediates cinobufotalin-induced non-apoptotic death of lung cancer cells. The Cyp-D inhibitor cyclosporine A (CsA), the mPTP blocker sanglifehrin A (SfA), and Cyp-D shRNA-silencing significantly inhibited cinobufotalin-induced mitochondrial membrane potential (MMP) reduction and A549 cell death (but not apoptosis). Using a mice xenograft model, we found that cinobufotalin inhibited A549 lung cancer cell growth in vivo. Thus, cinobufotalin mainly induces Cyp-D-dependent non-apoptotic death in cultured lung cancer cells. The results of this study suggest that cinobufotalin might be further investigated as a novel anti-lung cancer agent.     

Pseudomonas protegens CS1 from the lemon phyllosphere as a candidate for citrus canker biocontrol agent

• Citrus canker is a worldwide‐distributed disease caused by Xanthomonas citri subsp. citri. One of the most used strategies to control the disease is centred on copper‐based compounds that cause environmental problems. Therefore, it is of interest to develop new strategies to manage the disease. Previously, we reported the ability of the siderophore pyochelin, produced by the opportunistic human pathogen Pseudomonas aeruginosa, to inhibit in vitro several bacterial species, including X. citri subsp. citri. The action mechanism, addressed with the model bacterium Escherichia coli, was connected to the generation of reactive oxygen species (ROS). This work aimed to find a non‐pathogenic strain from the lemon phyllosphere that would produce pyochelin and therefore serve in canker biocontrol.
• An isolate that retained its capacity to colonise the lemon phyllosphere and inhibit X. citri subsp. citri was selected and characterised as Pseudomonas protegens CS1. From a liquid culture of this strain, the active compound was purified and identified as the pyochelin enantiomer, enantio‐pyochelin.
• Using the producing strain and the pure compound, both in vitro and in vivo, we determined that the action mechanism of X. citri subsp. citri inhibition also involved the generation of ROS. Finally, the potential application of P. protegens CS1 was evaluated by spraying the bacterium in a model that mimics the natural X. citri subsp. citri infection.
• The ability of P. protegens CS1 to reduce canker formation makes this strain an interesting candidate as a biocontrol agent.

     

N-acetil-l-cysteine and 2-amino-2-thiiazoline N-acetyl-l-cysteinate as a possible cancer chemopreventive agents in murine models

The aim of this study was to investigate N-acetyl-cysteine (NAC) and its 2-amino-2-thiazoline salt (NACAT) as potential chemopreventive agents on experimentally induced lung tumours by urethane (U) in mice. Female BALB/c mice were used. U was given by intraperitoneal injections during 2 weeks (single dose - 10 mg/mouse, total - 50 mg/mouse). Mice were treated daily per os with NAC 1/10 LD50, NACAT 1/10 or 1/100 LD50 starting 2 weeks prior U administration, then during U treatment and thereafter for 2 months. The duration of experiment was 4 months. The results showed that NAC (1000 mg/kg) reduced the lung tumour incidence to 30% that of controls, P < or = 0.05. Most effective of NACAT was 100 mg/kg dose; it reduced an average of lung adenomas per mouse by 26%, P < or = 0.05, but lower dose (10 mg/kg) was less effective. In order to achieve similar chemopreventive effect (approximately 30%) on mice, it is necessary to use 0.38 mM/kg of NACAT or 6.13 mM/kg of NAC. It means that 16 times less of NACAT is required, if calculated by molar concentration. In general, NAC and NACAT have a moderate chemopreventive effect on lung tumorigenesis induced by urethane in mice.     

Evaluation of sphinganine and sphingosine as human breast cancer chemotherapeutic and chemopreventive agents

No comparative study of the effects of sphingolipid metabolites on proliferation and differentiation in normal human breast epithelial cells versus stem cells and tumorigenic cells has been reported. The purpose of this study was to evaluate the chemotherapeutic and chemopreventive potential of sphingoid bases (sphingosine and sphinganine) using a novel cell culture system of normal human breast epithelial cells (HBEC) developed from breast tissues of healthy women obtained during reduction mammoplasty (Type I HBEC with stem cell characteristics and Type II HBEC with basal epithelial cell phenotypes) and transformed tumorigenic Type I HBEC. The results show that sphinganine inhibited the growth and induced apoptosis of transformed tumorigenic Type I HBEC more potently than sphingosine (IC(50) for sphinganine 4 microM; sphingosine 6.4 microM). Both sphinganine and sphingosine at high concentrations (8-10 lM) arrested the cell cycle at G(2)/M. Sphinganine inhibited the growth and caused death of Type I HBEC more strongly than sphingosine. In comparison, Type II HBEC (normal differentiated cells) were less sensitive to the growth-inhibitory effects of sphingoid bases than Type I HBEC (stem cells) or transformed tumorigenic Type I HBEC, suggesting that sphingoid bases may serve as chemotherapeutic agents. At concentrations (0.05, 0.1, and 0.5 microM) that are below the growth-inhibitory range, sphingoid bases induced differentiation of Type I HBEC to Type II HBEC, as detected morphologically and via expression of a tumor suppressor protein, maspin, which is a marker of Type II HBEC. Thus, sphingoid bases may function as chemotherapeutic as well as chemopreventive agents by preferentially inhibiting cancer cells and eliminating stem cells from which most breast cancer cells arise.     

L-Canavanine as a radiosensitization agent for human pancreatic cancer cells

This study evaluated the in vitro effect of L-canavanine on cell cycle progression in the two human pancreatic cancer cells lines PANC-1 and MIA PaCa-2. After 72 h of exposure to L-canavanine, the percentage of cells in the radiosensitive G₂/M phase of the cell cycle increased 6-fold in PANC-1 cells and 4-fold in MIA PaCa-2 cells, when compared to untreated cells. The capacity of L-canavanine to redistribute cells into the G₂/M phase of the cell cycle was both concentration- and time-dependent. Since many drugs that cause cells to accumulate in the G₂/M phase of the cell cycle are effective radiosensitization agents, the potential of L-canavanine to synergistically enhance the effects of ionizing radiation also was evaluated. The interaction between these treatment modalities was quantified using the median-effect equation and combination index analysis. L-Canavanine was found to be synergistic with radiation when either PANC-1 or MIA PaCa-2 cells were exposed to L-canavanine for 72 h prior to irradiation. These results suggest that L-canavanine in combination with radiation may have clinical potential in the treatment of pancreatic cancer.     

The cancer chemopreventive agent resveratrol is incorporated into model membranes and inhibits protein kinase C alpha activity

Resveratrol is a phytoalexin found in grapes and other foods that cancer chemopreventive and other biological activities have been attributed recently. We report that resveratrol is able to incorporate itself into model membranes in a location that is inaccessible to the fluorescence quencher, acrylamide. Differential scanning calorimetry revealed that resveratrol considerably affected the gel to liquid-crystalline phase transition of multilamellar vesicles made of phosphatidylcholine/phosphatidylserine and increased the temperature at which the fluid lamellar to H(II) inverted hexagonal transition took place in multilamellar vesicles made of 1,2-dielaidoyl-sn-phosphatidylethanolamine. Such a transition totally disappeared at 2.5 mM of resveratrol (resveratrol/lipid molar ratio of 2:1). This effect on 1, 2-dielaidoyl-sn-phosphatidylethanolamine polymorphism was confirmed through (31)P-NMR, which showed that an isotropic peak appeared at high temperature instead of the H(II)-characteristic peak of 42 mM of resveratrol (resveratrol/lipid molar ratio of 1.5:1). Finally, resveratrol inhibited PKCalpha when activated by phosphatidylcholine/phosphatidylserine vesicles with an IC(50) of 30 microM, whereas when the enzyme was activated by Triton X-100 micelles the IC(50) was 300 microM. These results indicate that the inhibition of PKCalpha by resveratrol can be mediated, at least partially, by membrane effects exerted near the lipid-water interface.     

Carnosic acid: A potent chemopreventive agent against oral carcinogenesis

The present study was aimed to investigate the chemopreventive potential of carnosic acid in 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. The chemopreventive potential was assessed by analyzing the tumor incidence, tumor volume and burden as well as by measuring the status of lipid peroxidation, non-enzymatic and enzymatic antioxidants and phase I and phase II detoxification enzymes. Oral squamous cell carcinoma was developed in the buccal pouch of golden Syrian hamsters by painting with 0.5% DMBA in liquid paraffin three times a week for 14 weeks. In the present study, 100% tumor formation was observed in hamsters treated with DMBA alone. Also, the status of lipid peroxidation, antioxidants and phase I and phase II detoxification enzymes were significantly altered during DMBA-induced oral carcinogenesis. Oral administration of carnosic acid at a dose of 10 mg/kg body weight/day to DMBA-treated animals completely prevented the tumor formation in the hamsters’ buccal pouches. Also, carnosic acid exerted potent anti-lipid peroxidative function and stimulated the detoxification cascade during DMBA-induced hamster buccal pouch carcinogenesis. The results of the present study suggest that the chemopreventive potential of carnosic acid is probably due to its anti-lipid peroxidative potential and modulating effect on carcinogen detoxification enzymes during DMBA-induced oral carcinogenesis.     

Overview of mechanisms of cancer chemopreventive agents

Epidemiological data provide evidence that it is possible to prevent cancer and other chronic diseases, some of which share common pathogenetic mechanisms, such as DNA damage, oxidative stress, and chronic inflammation. An obvious approach is avoidance of exposure to recognized risk factors. As complementary strategies, it is possible to render the organism more resistant to mutagens/carcinogens and/or to inhibit progression of the disease by administering chemopreventive agents. In a primary prevention setting, addressed to apparently healthy individuals, it is possible to inhibit mutation and cancer initiation by triggering protective mechanisms either in the extracellular environment or inside cells, e.g., by modifying transmembrane transport, modulating metabolism, blocking reactive species, inhibiting cell replication, maintaining DNA structure, modulating DNA metabolism and repair, and controlling gene expression. Tumor promotion can be counteracted by inhibiting genotoxic effects, favoring antioxidant and anti-inflammatory activity, inhibiting proteases and cell proliferation, inducing cell differentiation, modulating apoptosis and signal transduction pathways, and protecting intercellular communications. In a secondary prevention setting, when a premalignant lesion has been detected, it is possible to inhibit tumor progression via the same mechanisms, and in addition by affecting the hormonal status and the immune system in various ways, and by inhibiting tumor angiogenesis. Although tertiary prevention, addressed to cancer patients after therapy, is outside the classical definition of chemoprevention, it exploits similar mechanisms. It is also possible to affect cell-adhesion molecules, to activate antimetastasis genes, and to inhibit proteases involved in basement membrane degradation.     

Apoptosis induction by the natural product cancer chemopreventive agent deguelin is mediated through the inhibition of mitochondrial bioenergetics

Deguelin exhibits chemopreventive properties in animal carcinogenesis models. The mechanism underpinning the chemopreventive effects of deguelin has not been fully elucidated. However, it has been suggested that this agent reduces ornithine decarboxylase activity, and perhaps the activity of other signaling intermediates associated with tumorigenesis, by inhibiting mitochondrial bioenergetics. We sought to determine if deguelin could trigger apoptosis by inhibiting mitochondrial bioenergetics. Therefore, we compared and contrasted the effects of deguelin on cells from two human cutaneous squamous cell carcinoma cell lines (parental cells) and their respiration-deficient clones lacking mitochondrial DNA (rho0). While deguelin promoted marked apoptosis in the parental cells in a dose- and time-dependent manner, it failed to do so in the rho0 clones. Furthermore, short-term exposure to deguelin diminished oxygen consumption by the parental cells and promoted mitochondrial permeability transition as evidenced by the dissipation of mitochondrial inner transmembrane potential, reactive oxygen species production, cardiolipin peroxidation, caspase activation, and mitochondrial swelling. Mitochondrial permeability transition was not observed in the rho0 clones exposed to deguelin. These results demonstrate that deguelin induces apoptosis in skin cancer cells by inhibiting mitochondrial bioenergetics and provide a novel mechanism for the putative anticancer activity of this agent.     

Modulation of apoptosis by cancer chemopreventive agents

A review of almost 2000 studies showed that the large majority of 39 putative cancer chemopreventive agents induced "spontaneous" apoptosis. Inhibition of the programmed cell death triggered by a variety of stimuli was consistently reported only with ascorbic acid, alpha-tocopherol, and N-acetylcysteine (NAC). We performed experimental studies in rodents exposed to cigarette smoke, either mainstream (MCS) or environmental (ECS), and UV-A/B-containing light. The nonsteroidal anti-inflammatory drug sulindac did not affect the apoptotic process in the skin of light-exposed mice and in the lungs of ECS-exposed mice. Likewise, 5,6-benzoflavone, indole-3-carbinol, 1,2-dithiole-3-thione and oltipraz failed to modulate apoptosis in the respiratory tract of ECS-exposed rats. Phenethyl isothiocyanate further enhanced the frequency of apoptosis in pulmonary alveolar macrophages and bronchial epithelial cells, and upregulated several genes in the lung of ECS-exposed rats. Both individually and in combination with oltipraz, NAC inhibited apoptosis in the respiratory tract of rats exposed either to MCS or ECS. Moreover, NAC attenuated the ECS-related overexpression of proapoptotic genes and normalized the levels of proapoptotic proteins in rat lung. The transplacental administration of NAC to mice considerably attenuated gene overexpression in the liver of fetuses exposed to ECS throughout pregnancy. Inhibition of apoptosis by chemopreventive agents reflects their ability to counteract certain upstream signals, such as genotoxic damage, redox imbalances, and other forms of cellular stress that trigger apoptosis. On the other hand, enhancement of apoptosis is a double-edged sword, since it represents a protective mechanism in carcinogenesis but may contribute to the pathogenesis of other degenerative diseases. We suggest that stimulation of apoptosis by so many chemopreventive agents, as reported in the literature, may often reflect the occurrence of toxic effects at high doses.