Special Issue "Natural Compounds for Cancer Treatment and Prevention"

Abstract: The objectives of this study were to isolate various isoflavone fractions andextracts from soybean cake by preparative column chromatography and compare themwith isoflavone standards with regards to inhibition of HepG2 cancer cell proliferation.Four fractions, including malonylglucoside, glucoside, acetylglucoside and aglycone, andtwo isoflavone extracts, ISO-1 and ISO-2, were collected for evaluation. MTT test resultsshowed that most treatments were slightly protective against HepG2 cell growth at a lowdose of isoflavone (5 and 10 μg/mL). However, at elevated concentration of isoflavone(20-50 μg/mL), both aglycone and acetylglucoside fractions as well as a mixture ofisoflavone standards were the most effective in inhibition, demonstrating a possiblesynergistic phenomenon. Genistein showed a better retardation effect than daidzein. Forcell cycle analysis, both aglycone and acetylglucoside fractions and a mixture ofisoflavone standards exhibited a high G2/M ratio, correlating well with the result of MTTtest. The presence of some other functional components in soybean cake like saponinsand phenolic compounds may also play a vital role in inhibiting HepG2 cell growth.

Abstract: Ginkgolide B, the major active component of Ginkgo biloba extracts, can bothstimulate and inhibit apoptotic signaling. Here, we demonstrate that ginkgolide B caninduce the production of reactive oxygen species in MCF-7 breast cancer cells, leading toan increase in the intracellular concentrations of cytoplasmic free Ca²⁺ and nitric oxide(NO), loss of mitochondrial membrane potential (MMP), activation of caspase-9 and -3,and increase the mRNA expression levels of p53 and p21, which are known to be involvedin apoptotic signaling. In addition, prevention of ROS generation by pretreatment withN-acetyl cysteine (NAC) could effectively block intracellular Ca²⁺ concentrationsincreases and apoptosis in ginkgolide B-treated MCF-7 cells. Moreover, pretreatment withnitric oxide (NO) scavengers could inhibit ginkgolide B-induced MMP change andsequent apoptotic processes. Overall, our results signify that both ROS and NO playedimportant roles in ginkgolide B-induced apoptosis of MCF-7 cells. Based on these studyresults, we propose a model for ginkgolide B-induced cell apoptosis signaling cascades inMCF-7 cells.

Abstract: DNA topoisomerases (topos) and DNA polymerases (pols) are involved in manyaspects of DNA metabolism such as replication reactions. We found that long chainunsaturated fatty acids such as polyunsaturated fatty acids (PUFA) (i.e., eicosapentaenoicacid (EPA) and docosahexaenoic acid (DHA)) inhibited the activities of eukaryotic pols andtopos in vitro, and the inhibitory effect of conjugated fatty acids converted from EPA andDHA (cEPA and cDHA) on pols and topos was stronger than that of normal EPA and DHA.cEPA and cDHA did not affect the activities of plant and prokaryotic pols or other DNAmetabolic enzymes tested. cEPA was a stronger inhibitor than cDHA with IC50 values formammalian pols and human topos of 11.0 - 31.8 and 0.5 - 2.5 μM, respectively. cEPAinhibited the proliferation of two human leukemia cell lines, NALM-6, which is a p53-wildtype, and HL-60, which is a p53-null mutant, and the inhibitory effect was stronger than thatof normal EPA. In both cell lines, cEPA arrested in the G1 phase, and increased cyclin Eprotein levels, indicating that it blocks the primary step of in vivo DNA replication byinhibiting the activity of replicative pols rather than topos. DNA replication-relatedproteins, such as RPA70, ATR and phosphorylated-Chk1/2, were increased by cEPAtreatment in the cell lines, suggesting that cEPA led to DNA replication fork stressinhibiting the activities of pols and topos, and the ATR-dependent DNA damage response pathway could respond to the inhibitor of DNA replication. The compound induced cellapoptosis through both p53-dependent and p53-independent pathways in cell lines NALM-6and HL-60, respectively. These results suggested the therapeutic potential of conjugatedPUFA, such as cEPA, as a leading anti-cancer compound that inhibited pols and toposactivities.

Abstract: TRAIL is a promising candidate for cancer therapeutics that preferentially induces apoptosis in cancer cells. The combined treatment flavonoids with TRAIL might be promising as a chemoprevention and/or new therapy against malignant tumors. We examined the cytotoxic effect of dietary flavonoids in combination with TRAIL on HeLa cells. It was found that treatment with noncytotoxic concentration of some flavonoids significantly sensititizes to TRAIL induced death in HeLa cells. Our study demonstrated that flavone, apigenin and genistein markedly augmented TRAIL mediated cytotoxicity against HeLa, whereas kaempferol and quercetin produced no effect.

Abstract: Polyphenols, occurring in fruit and vegetables, wine, tea, extra virgin olive oil, chocolate and other cocoa products, have been demonstrated to have clear antioxidant properties in vitro, and many of their biological actions have been attributed to their intrinsic reducing capabilities. However, it has become clear that, in complex biological systems, polyphenols exhibit several additional properties which are yet poorly understood. Apoptosis is a genetically controlled and evolutionarily conserved form of cell death of critical importance for the normal embryonic development and for the maintenance of tissue homeostasis in the adult organism. The malfunction of the death machinery may play a primary role in various pathological processes, since too little or too much apoptosis can lead to proliferative or degenerative diseases, respectively. Cancer cells are characterized by a deregulated proliferation, and/or an inability to undergo programmed cell death. A large body of evidence indicates that polyphenols can exert chemopreventive effects towards different organ specific cancers, affecting the overall process of carcinogenesis by several mechanisms: inhibition of DNA synthesis, modulation of ROS production, regulation of cell cycle arrest, modulation of survival/proliferation pathways. In addition, polyphenols can directly influence different points of the apoptotic process, and/or the expression of Int. J. Mol. Sci. 2008, 9 214 regulatory proteins. Although the bulk of data has been obtained in in vitro systems, a number of clinical studies suggesting a preventive and therapeutic effectiveness of polyphenols in vivo is available. However, a deeper knowledge of the underlying mechanisms responsible for the modulation of apoptosis by polyphenols, and their real effectiveness, is necessary in order to propose them as potential chemopreventive and chemotherapeutic candidates for cancer treatment.

Abstract: DNA damage is a pre-requisite for the initiation of cancer and agents that reduce this damage are useful in cancer prevention. In this study, we evaluated the ability of whole berries and berry phytochemical, ellagic acid to reduce endogenous oxidative DNA damage. Ellagic acid was selected based on >95% inhibition of 8-oxodeoxyguosine (8-oxodG) and other unidentified oxidative DNA adducts induced by 4-hydroxy-17ß-estradiol and CuCl2 in vitro. Inhibition of the latter occurred at lower concentrations (10 μM) than that for 8-oxodG (100 μM). In the in vivo study, female CD-1 mice (n=6) were fed either a control diet or diet supplemented with ellagic acid (400 ppm) and dehydrated berries (5% w/w) with varying ellagic acid contents – blueberry (low), strawberry (medium) and red raspberry (high), for 3 weeks. Blueberry and strawberry diets showed moderate reductions in endogenous DNA adducts (25%). However, both red raspberry and ellagic acid diets showed a significant reduction of 59% (p <0.001) and 48% (p < 0.01), respectively. Both diets also resulted in a 3-8 fold over-expression of genes involved in DNA repair such as xeroderma pigmentosum group A complementing protein (XPA), DNA excision repair protein (ERCC5) and DNA ligase III (DNL3). These results suggest that red raspberry and ellagic acid reduce endogenous oxidative DNA damage by mechanisms which may involve increase in DNA repair.

Abstract: Mangosteen, Garcinia mangostana Linn, is a tree found in South East Asia, and its pericarps have been used as traditional medicine. Phytochemical studies have shown that they contain a variety of secondary metabolites, such as oxygenated and prenylated xanthones. Recent studies revealed that these xanthones exhibited a variety of biological activities containing anti-inflammatory, anti-bacterial, and anti-cancer effects. We previously investigated the anti-proliferative effects of four prenylated xanthones from the pericarps; α-mangostin, β-mangostin, γ-mangostin, and methoxy-β-mangostin in various human cancer cells. These xanthones are different in the number of hydroxyl and methoxy groups. Except for methoxy-β-mangostin, the other three xanthones strongly inhibited cell growth at low concentrations from 5 to 20 μM in human colon cancer DLD-1 cells. Our recent study focused on the mechanism of α-mangostin-induced growth inhibition in DLD-1 cells. It was shown that the anti-proliferative effects of the xanthones were associated with cell-cycle arrest by affecting the expression of cyclins, cdc2, and p27; G1 arrest by α- mangostin and β-mangostin, and S arrest by γ-mangostin. α-Mangostin found to induce apoptosis through the activation of intrinsic pathway following the down-regulation of signaling cascades involving MAP kinases and the serine/threonine kinase Akt. Synergistic effects by the combined treatment of α-mangostin and anti-cancer drug 5-FU was to be noted. α-Mangostin was found to have a cancer preventive effect in rat carcinogenesis bioassay and the extract from pericarps, which contains mainly α-mangostin and γ- mangostin, exhibited an enhancement of NK cell activity in a mouse model. These findings could provide a relevant basis for the development of xanthones as an agent for cancer prevention and the combination therapy with anti-cancer drugs.

Abstract: Pericosines are unique C₇ cyclohexenoid metabolites of Periconia byssoides OUPS-N133 fungus that was originally isolated from the sea hare, Aplysia kurodai. Pericosines show significant in vitro cytotoxicity against P388 lymphocytic leukemia cells. Pericosine A, in particular, shows the most potent activity and significant in vivo antitumor activity against P388 cells. Thus, pericosines are promising candidates for seed compounds of anticancer drugs. However, before the total syntheses of pericosines were accomplished, their stereo structures could not be determined by spectral analyses because they have multifunctionalized cyclohexenoid structures with torsional strain. In this review, synthetic efforts for pericosines in this decade are surveyed.

Abstract: Conventional cancer therapies, the second leading cause of death worldwide, result in serious side effects and, at best, merely extend the patient's lifespan by a few years. Searching for effective prevention is of high priority in both basic and clinical sciences. In recent decades natural products have been considered to be an important source of cancer chemopreventive agents. Red wine polyphenols, which consisted of various powerful antioxidants such as flavonoids and stilbenes, have been implicated in cancer prevention and that promote human health without recognizable side effects. Since resveratrol, a major component of red wine polyphenols, has been studied and reviewed extensively for its chemopreventive activity to interfere with the multi-stage carcinogenesis, this review focuses on recent progress in studies on cancer chemopreventive activities of red wine polyphenol extracts and fractions as well as other red wine polyphenols, like procyanidin B5 analogues and myricetin.

Abstract: Probiotics are live bacteria that could exert health beneficial effects upon consumption. In additional to their conventional use as gut modulators, probiotics are investigated for their role to prevent cancer. In-vivo and molecular studies have demonstrated encouraging outcomes, mainly attributed to its antimicrobial effects against carcinogen-producing microorganisms, antimutagenic properties, and alteration of the tumor differentiation processes. Prebiotics are indigestible food components that could promote the growth of beneficial bacteria including probiotics. Present studies have suggested that prebiotics also possess protective effect against colon carcinogenesis, mainly attributed to the production of short chain fatty acids upon its fermentation by gut microflora, and alteration of gene-expressions in tumor cells. Synbiotic (combination of probiotic and prebiotic) has been found to exert a synergistic effect in improving colon carcinogenesis compared to when both were used individually. This paper highlights the colon cancer preventive effects by probiotics, prebiotics and synbiotics. In addition, the controversial outcomes on the insignificant effect of these food adjuncts will be discussed.

Abstract: A novel carbamate prodrug 2 containing a pentagastrin moiety was synthesized. 2 was designed as a detoxified analogue of the highly cytotoxic natural antibiotic duocarmycin SA (1) for the use in a targeted prodrug monotherapy of cancers expressing cholecystokinin (CCK-B)/gastrin receptors. The synthesis of prodrug 2 was performed using a palladium-catalyzed carbonylation of bromide 6, followed by a radical cyclisation to give the pharmacophoric unit 10, coupling of 10 to the DNA-binding subunit 15 and transformation of the resulting seco-drug 3b into the carbamate 2 via addition of a pentagastrin moiety.

Abstract: For possible future use in Photodynamic Therapy (PDT) and/or Photothermal Therapy (PTT) of cancer and screening of cancer cells a new type of ionic liquid photosensitizer –Cholinium-Purpurin-18 (Chol-Pu-18) – was synthesized and small gold (Au) nanoparticles, stabilized by this photosensitizer were prepared without adding any particular reducing agents and CTAB. UV-Vis spectroscopy and Transmission Electron Microscopy (TEM) were used for characterization of the nanoparticles and FAB-MS and NMR of the ionic liquid choline hydroxide, purpurin carboxylate and their ionic liquid type of photosensitizer were obtained.

Abstract: Tea is one of the most popular beverages consumed worldwide. Epidemiologic studies show an inverse relationship between consumption of tea, especially green tea, and development of cancers. Numerous in vivo and in vitro studies indicate strong chemopreventive effects for green tea and its constituents against cancers of various organs. (–)-Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, appears to be the most biologically active constituent in tea with respect to inhibiting cell proliferation and inducing apoptosis in cancer cells. Recent studies indicate that the receptor tyrosine kinases (RTKs) are one of the critical targets of EGCG to inhibit cancer cell growth. EGCG inhibits the activation of EGFR (erbB1), HER2 (neu/erbB2) and also HER3 (neu/erbB3), which belong to subclass I of the RTK superfamily, in various types of human cancer cells. The activation of IGF-1 and VEGF receptors, the other members of RTK family, is also inhibited by EGCG. In addition, EGCG alters membrane lipid organization and thus inhibits the dimerization and activation of EGFR. Therefore, EGCG inhibits the Ras/MAPK and PI3K/Akt signaling pathways, which are RTK-related cell signaling pathways, as well as the activation of AP-1 and NF-κB, thereby modulating the expression of target genes which are associated with induction of apoptosis and cell cycle arrest in cancer cells. These findings are significant because abnormalities in the expression and function of RTKs and their downstream effectors play a critical role in the development of several types of human malignancies. In this paper we review evidence indicating that EGCG exerts anticancer effects, at least in part, through inhibition of activation of the specific RTKs and conclude that targeting RTKs and related signaling pathway by tea catechins might be a promising strategy for the prevention of human cancers.

Abstract: Betulinic acid is a natural product with a range of biological effects, for example potent antitumor activity. This anticancer property is linked to its ability to induce apoptotic cell death in cancer cells by triggering the mitochondrial pathway of apoptosis. In contrast to the cytotoxicity of betulinic acid against a variety of cancer types, normal cells and tissue are relatively resistant to betulinic acid, pointing to a therapeutic window. Compounds that exert a direct action on mitochondria present promising experimental cancer therapeutics, since they may trigger cell death under circumstances in which standard chemotherapeutics fail. Thus, mitochondrion-targeted agents such as betulinic acid hold great promise as a novel therapeutic strategy in the treatment of human cancers.

Abstract: In this study, we first measured some cytokine concentrations in the serum of patients treated with Juzentaihoto (JTT). Of the cytokines measured interleukin (IL) -18 was the most prominently up-regulated cytokine in the serum of patients under long term JTT administration. We next evaluated the effects of JTT in mice, focusing especially on natural killer T (NKT) cell induction. Mice fed JTT were compared to control group ones. After sacrifice, the liver was fixed, embedded and stained. Transmission electron microscope (TEM) observations were performed. Although the mice receiving the herbal medicine had same appearance, their livers were infiltrated with massive mononuclear cells, some of which were aggregated to form clusters. Immunohistochemical staining revealed that there was abundant cytokine expression of IL-12 and IL-18 in the liver of JTT treated mice. To clarify what the key molecules that induce immunological restoration with JTT might be, we next examined in vitro lymphocyte cultures. Mononuclear cells isolated and prepared from healthy volunteers were cultured with and without JTT. Within 24 hours, JTT induced the IL-12 and IL-18 production and later (72 hours) induction of interferon (IFN)-gamma. Oral administration of JTT may induce the expression of IL-12 in the early stage, and IL-18 in the chronic stage, followed by NKT induction. Their activation, following immunological restoration could contribute to anti-tumor effects.

Abstract: Many plant-derived, dietary polyphenols have been studied for their chemopreventive and chemotherapeutic properties against human cancers, including green tea polyphenols, genistein (found in soy), apigenin (celery, parsley), luteolin (broccoli), quercetin (onions), kaempferol (broccoli, grapefruits), curcumin (turmeric), etc. The more we understand their involved molecular mechanisms and cellular targets, the better we could utilize these “natural gifts” for the prevention and treatment of human cancer. Furthermore, better understanding of their structure-activity relationships will guide synthesis of analog compounds with improved bio-availability, stability, potency and specificity. This review focuses on green tea polyphenols and seeks to summarize several reported biological effects of tea polyphenols in human cancer systems, highlight the molecular targets and pathways identified, and discuss the role of tea polyphenols in the prevention and treatment of human cancer. The review also briefly describes several other dietary polyphenols and their biological effects on cancer prevention and chemotherapy.

Abstract: We have designed imidazolium and piperazinium salts of pyropheophorbide-a in order to develop effective photosensitizers which have good solubility in polar and non polar media and to reveal the possible influences of the piperazine and imidazole moieties on the biological activities of pyropheophorbide-a. The phototoxicity of those pyropheophorbide-a salts against A549 cells was studied in vitro and compared with that of pyropheophorbide-a. The result showed that complexing piperazine and imidazole into pyropheophorbide-a decreases its dark toxicity without greatly decreasing phototoxicity and, enhances its phototoxicity without greatly increasing dark toxicity, respectively. This work not only describes novel amphiphilic salt complexes of pyropheophobide-a which retain the biological activities of the parent compound pyropheophorbide-a and could be effective candidate for PDT, but also reveals the possibility of developing effective photosensitizers by complexing imidazole and piperazine into other hydrophobic photosensitizers.