Inhibition of growth and induction of differentiation of metastatic melanoma cells in vitro by genistein: chemosensitivity is regulated by cellular p53

Medicinal Plants Towards Modeling Skin Cancer

Skin cancer remains a major cause of mortality worldwide. It can be divided into melanoma and non-melanoma cancer, which comprise mainly squamous cell carcinoma and basal cell carcinoma. Although conventional therapies have ameliorated the management of skin cancer, the search for chemopreventive compounds is still the most effective and safer strategy to treat cancer. Nowadays, chemoprevention is recognized as a novel approach to prevent or inhibit carcinogenesis steps with the use of natural products. Crude extracts of plants and isolated phytocompounds are considered chemopreventive agents since they harbor anti-inflammatory, antioxidant and anti-oncogenic properties against many types of diseases and cancers. In this review, we will discuss the therapeutic effect and preventive potential of selected medicinal plants used as crude extracts or as phytocompounds against melanoma and non-melanoma cutaneous cancers.

Unraveling the molecular mechanisms and the potential chemopreventive/therapeutic properties of natural compounds in melanoma

Melanoma is the most fatal form of skin cancer. Current therapeutic approaches include surgical resection, chemotherapy, targeted therapy and immunotherapy. However, these treatment strategies are associated with development of drug resistance and severe side effects. In recent years, natural compounds have also been extensively studied for their anti-melanoma effects, including tumor growth inhibition, apoptosis induction, angiogenesis and metastasis suppression and cancer stem cell elimination. Moreover, a considerable number of studies reported the synergistic activity of phytochemicals and standard anti-melanoma agents, as well as the enhanced effectiveness of their synthetic derivatives and novel formulations. However, clinical data confirming these promising effects in patients are still scanty. This review emphasizes the anti-tumor mechanisms and potential application of the most studied natural products for melanoma prevention and treatment.

Phytochemicals in Skin Cancer Prevention and Treatment: An Updated Review

Skin is the largest human organ, our protection against various environmental assaults and noxious agents. Accumulation of these stress events may lead to the formation of skin cancers, including both melanoma and non-melanoma skin cancers. Although modern targeted therapies have ameliorated the management of cutaneous malignancies, a safer, more affordable, and more effective strategy for chemoprevention and treatment is clearly needed for the improvement of skin cancer care. Phytochemicals are biologically active compounds derived from plants and herbal products. These agents appear to be beneficial in the battle against cancer as they exert anti-carcinogenic effects and are widely available, highly tolerated, and cost-effective. Evidence has indicated that the anti-carcinogenic properties of phytochemicals are due to their anti-oxidative, anti-inflammatory, anti-proliferative, and anti-angiogenic effects. In this review, we discuss the preventive potential, therapeutic effects, bioavailability, and structure–activity relationship of these selected phytochemicals for the management of skin cancers. The knowledge compiled here will provide clues for future investigations on novel oncostatic phytochemicals and additional anti-skin cancer mechanisms.

Phytochemical-induced reactive oxygen species and endoplasmic reticulum stress-mediated apoptosis and differentiation in malignant melanoma cells

BACKGROUND

Phytochemicals are derived from plants, vegetables and daily products and exert chemopreventive effects. Malignant melanoma is highly metastatic, and melanoma patients can develop chemotherapeutic resistance against conventional melanoma therapies.

METHODS

In the present study, we investigated the anti-cancer effect of the phytochemicals kaempferol (Kaem), genistein (Gen), and 3'3-diindolylmethane (DIM) on melanoma cell viability. We also evaluated the altered expression of cell cycle-related genes. We verified the production of intracellular reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress at both the protein and cellular level using a western blot, TUNEL assay, and Dihydrodichlorofluorescein diacetate (DCF-DA) assay.

RESULTS

Treatment of A375SM melanoma cells with phytochemicals resulted in inhibition of cell growth. Treatment with phytochemicals increased the gene expression of p21 and decreased the gene expression of cyclin E and/or cyclin B. The three phytochemicals activated the ROS-p38-p53 apoptotic pathway by increasing the level of phosphorylated p38 MAPK and p53, and they activated the ER stress-mediated apoptotic pathway by increasing the level of phosphorylated eIF2α and C/EBP homologous protein (CHOP). Both the ROS-p38-p53 and ER stress-mediated pathway induced the mitochondrial apoptotic pathway by attenuating Bcl-2 expression and upregulating BAX. Detection of morphological changes demonstrated that Kaem and Gen can induce differentiation in A375SM cell line.

CONCLUSION

These results indicate that phytochemicals are potentially useful in treatments for melanoma due to their ability to inhibit melanoma cell growth and division via the ROS and ER stress pathway.

Estrogen Receptor β in Melanoma: From Molecular Insights to Potential Clinical Utility

Cutaneous melanoma is an aggressive tumor; its incidence has been reported to increase fast in the past decades. Melanoma is a heterogeneous tumor, with most patients harboring mutations in the BRAF or NRAS oncogenes, leading to the overactivation of the MAPK/ERK and PI3K/Akt pathways. The current therapeutic approaches are based on therapies targeting mutated BRAF and the downstream pathway, and on monoclonal antibodies against the immune checkpoint blockade. However, treatment resistance and side effects are common events of these therapeutic strategies. Increasing evidence supports that melanoma is a hormone-related cancer. Melanoma incidence is higher in males than in females, and females have a significant survival advantage over men. Estrogens exert their effects through estrogen receptors (ERα and ERβ) that affect cancer growth in an opposite way: ERα is associated with a proliferative action and ERβ with an anticancer effect. ERβ is the predominant ER in melanoma, and its expression decreases in melanoma progression, supporting its role as a tumor suppressor. Thus, ERβ is now considered as an effective molecular target for melanoma treatment. 17β-estradiol was reported to inhibit melanoma cells proliferation; however, clinical trials did not provide the expected survival benefits. In vitro studies demonstrate that ERβ ligands inhibit the proliferation of melanoma cells harboring the NRAS (but not the BRAF) mutation, suggesting that ERβ activation might impair melanoma development through the inhibition of the PI3K/Akt pathway. These data suggest that ERβ agonists might be considered as an effective treatment strategy, in combination with MAPK inhibitors, for NRAS mutant melanomas. In an era of personalized medicine, pretreatment evaluation of the expression of ER isoforms together with the concurrent oncogenic mutations should be considered before selecting the most appropriate therapeutic intervention. Natural compounds that specifically bind to ERβ have been identified. These phytoestrogens decrease the proliferation of melanoma cells. Importantly, these effects are unrelated to the oncogenic mutations of melanomas, suggesting that, in addition to their ERβ activating function, these compounds might impair melanoma development through additional mechanisms. A better identification of the role of ERβ in melanoma development will help increase the therapeutic options for this aggressive pathology.

Phytochemicals for the Management of Melanoma

Melanoma claims approximately 80% of skin cancer-related deaths. Its life-threatening nature is primarily due to a propensity to metastasize. The prognosis for melanoma patients with distal metastasis is bleak, with median survival of six months even with the latest available treatments. The most commonly mutated oncogenes in melanoma are BRAF and NRAS accounting approximately 60% and 20% of cases, respectively. In malignant melanoma, accumulating evidence suggests that multiple signaling pathways are constitutively activated and play an important role in cell proliferation, cell survival, epithelial to mesenchymal transition, metastasis and resistance to therapeutic regimens. Phytochemicals are gaining considerable attention because of their low toxicity, low cost, and public acceptance as dietary supplements. Cell culture and animals studies have elucidated several cellular and molecular mechanisms by which phytochemicals act in the prevention and treatment of metastatic melanoma. Several promising phytochemicals, such as, fisetin, epigallocatechin-3-gallate, resveratrol, curcumin, proanthocyanidins, silymarin, apigenin, capsaicin, genistein, indole-3-carbinol, and luteolin are gaining considerable attention and found in a variety of fresh fruits, vegetables, roots, and herbs. In this review, we will discuss the preventive potential, therapeutic effects, bioavailability and structure activity relationship of these selected phytochemicals for the management of melanoma.

Risks and benefits of dietary isoflavones for cancer

A high intake of fruits and vegetables is associated with a lower risk of cancer. In this context, considerable attention is paid to Asian populations who consume high amounts of soy and soy-derived isoflavones, and have a lower risk for several cancer types such as breast and prostate cancers than populations in Western countries. Hence, interest focuses on soyfoods, soy products, and soy ingredients such as isoflavones with regard to their possible beneficial effects that were observed in numerous experiments and studies. The outcomes of the studies are not always conclusive, are often contradictory depending on the experimental conditions, and are, therefore, difficult to interpret. Isoflavone research revealed not only beneficial but also adverse effects, for instance, on the reproductive system. This is also the case with tumor-promoting effects on, for example, breast tissue. Isoflavone extracts and supplements are often used for the treatment of menopausal symptoms and for the prevention of age-associated conditions such as cardiovascular diseases and osteoporosis in postmenopausal women. In relation to this, questions about the effectiveness and safety of isoflavones have to be clarified. Moreover, there are concerns about the maternal consumption of isoflavones due to the development of leukemia in infants. In contrast, men may benefit from the intake of isoflavones with regard to reducing the risk of prostate cancer. Therefore, this review examines the risks but also the benefits of isoflavones with regard to various kinds of cancer, which can be derived from animal and human studies as well as from in vitro experiments.

Botanicals for the prevention and treatment of cutaneous melanoma

Cutaneous melanoma, a cancer of melanocytes, when detected at later stages is arguably one of the most lethal cancers and the cause of more years of lost life than any other cancer among young adults. There is no standard therapy for advanced-stage melanoma and the median survival time for patients with metastatic melanoma is <1 yr. An urgent need for novel strategies against melanoma has directed research towards the development of new chemotherapeutic and biologic agents that can target the tumor by several different mechanisms. Recently, several dietary agents are being investigated for their role in the prevention and treatment of various forms of cancer and may represent the future modality of the treatment. Here, we have reviewed emerging data on botanicals that are showing promise for their potential inhibitory effect against cutaneous melanoma.

Potential health-modulating effects of isoflavones and metabolites via activation of PPAR and AhR

Isoflavones have multiple actions on cell functions. The most prominent one is the activation of estrogen receptors. Other functions are often overlooked, but are equally important and explain the beneficial health effects of isoflavones. Isoflavones are potent dual PPARα/γ agonists and exert anti-inflammatory activity, which may contribute to the prevention of metabolic syndrome, atherosclerosis and various other inflammatory diseases. Some isoflavones are potent aryl hydrocarbon receptor (AhR) agonists and induce cell cycle arrest, chemoprevention and modulate xenobiotic metabolism. This review discusses effects mediated by the activation of AhR and PPARs and casts a light on the concerted action of isoflavones.

Effects of phyto-oestrogens on tissues

Recent investigations on the effects of phyto-oestrogens on various tissues have revealed that these diverse molecules may improve human health, particularly by protecting against certain chronic diseases. After a brief examination of the food sources, structures, and general cellular actions of the major phyto-oestrogens, current research findings on cardiovascular disease, skeletal tissues, and reproductive cancers are reviewed. Phyto-oestrogen concentrations in blood may be maintained at high levels in those consuming soyabean (Glycine max)-based food daily at several meals and exert their effects on target cells through either genomic effects via the classical oestrogen receptors or non-genomic effects mediated by membrane-bound oestrogen receptors or other cellular proteins. The expression of oestrogen receptor (OR) subtypes alpha (a) and beta (beta) varies across tissues, and cells that preferentially express OR-beta, which may include bone cells, are more likely to respond to phyto-oestrogens. Conversely, reproductive tissues contain relatively more OR-a and may, thus, be differently affected by phyto-oestrogens. Soyabean phyto-oestrogens appear to prevent the progression of atherosclerosis through multiple interactions, including lowering of plasma lipids and lipoproteins, increased vasodilatation and, possibly, decreased activation of blood platelets and vascular smooth muscle cells. However, a favourable impact on cardiovascular disease morbidity and mortality by a soyabean-enriched western-type diet remains to be shown, and unresolved questions remain regarding dose and form of the phyto-oestrogens in relation to risks and benefits. The isoflavones of soyabean have been shown consistently to have bone-retentive effects in animal studies by several investigators using rodent models, although intakes must be above a relatively high threshold level for a lengthy period of time, and little or no extra benefit is observed with intakes above this threshold level. The reports of modest or no effects on prevention of bone loss in human and non-human primate studies respectively, may be due to the limited doses tested so far. The relationship between soyabean-food intake and cancer risk has been more extensively investigated than for any other disease, but with less certainty about the benefits of long-term consumption of phyto-oestrogen-containing foods on prevention of cancer. The observations that breast and prostate cancer rates are lower in Asian countries, where soyabean foods are consumed at high levels, and the high isoflavone content of soyabeans have led to examination of the potential protective effects of phyto-oestrogens. Establishing diet-cancer relationships has proved difficult, in part because of the conflicting data from various studies of effects of soyabean-diets on cancer. Epidemiological evidence, though not impressive, does suggest that soyabean intake reduces breast cancer risk. The isoflavone genistein has a potent effect on breast cancer cells in vitro, and early exposure of animals to genistein has been effective in reducing later development of mammary cancer. Thus, continuous consumption of soyabean foods in early life and adulthood may help explain the low breast cancer mortality rates in Asian countries. Although the evidence for a protective effect against prostate cancer may be slightly more supportive, more research is needed before any firm conclusions can be made about the phyto-oestrogen-cancer linkages.

N-Myc down regulation induced differentiation, early cell cycle exit, and apoptosis in human malignant neuroblastoma cells having wild type or mutant p53

Neuroblastomas, which mostly occur in children, are aggressive metastatic tumors of the sympathetic nervous system. The failure of the previous therapeutic regimens to target multiple components of N-Myc pathway resulted in poor prognosis. The present study investigated the efficacy of the combination of N-(4-hydroxyphenyl) retinamide (4-HPR, 0.5 microM) and genistein (GST, 25 microM) to control the growth of human neuroblastoma cells (SH-SY5Y and SK-N-BE2) harboring divergent molecular attributes. Combination of 4-HPR and GST down regulated N-Myc, Notch-1, and Id2 to induce neuronal differentiation. Transition to neuronal phenotype was accompanied by increase in expression of e-cadherin. Induction of neuronal differentiation was associated with decreased expression of hTERT, PCNA, survivin, and fibronectin. This is the first report that combination of 4-HPR and GST mediated reactivation of multiple tumor suppressors (p53, p21, Rb, and PTEN) for early cell cycle exit (due to G1/S phase arrest) in neuroblastoma cells. Reactivation of tumor suppressor(s) repressed N-Myc driven growth factor mediated angiogenic and invasive pathways (VEGF, b-FGF, MMP-2, and MMP-9) in neuroblastoma. Repression of angiogenic factors led to the blockade of components of mitogenic pathways [phospho-Akt (Thr 308), p65 NF-kappaB, and p42/44 Erk 1/2]. Taken together, the combination of 4-HPR and GST effectively blocked survival, mitogenic, and angiogenic pathways and activated proteases for apoptosis in neuroblastoma cells. These results suggested that combination of 4-HPR and GST could be effective for controlling the growth of heterogeneous human neuroblastoma cell populations.

Synthesis and cytotoxic evaluation of novel 7-O-modified genistein derivatives

Two series of genistein (=5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) derivatives with heterocycles were prepared, in which genistein and heterocyclic moieties were separated by C(2) and C(3) spacers. Among the 24 compounds we prepared, 22, i.e., 3a-3k and 4a-4k, were reported for the first time, while the preparation of 2a and 2b was reported in our recent paper. The cytotoxic activities of these compounds were evaluated against human chronic myeloid leukemia cells (K562) and a human nasopharyngeal epidermoid tumor cell line (KB). Compounds 4a, 4d, 4e, 4h, and 4i showed remarkable anticancer activities in vitro that are comparable with 5-fluorouracil, an canonical anticancer drug. Structure-effect relationships were also discussed based on the experimental data obtained.

Effect of genistein on mouse blastocyst development in vitro

AIM

To examine the cytotoxic effects of genistein, an isoflavone compound, on early postimplantation embryonic development in vitro.

METHODS

Mouse blastocysts were incubated in medium with or without genistein (25 or 50 micromol/L) or daidzein (50 micromol/L) for 24 h. Cell proliferation and growth was investigated by dual differential staining, apoptosis was analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, and apoptotic or necrotic cells were visualized by Annexin-V and propidium iodide (PI) staining. Implantation and postimplantation development of embryos were measured by in vitro development analysis.

RESULTS

TUNEL staining and Annexin-V/PI staining showed that genistein dose-dependently increased apoptosis in mouse blastocysts, while daidzein, another soy isoflavone, had no such effect. The pretreatment of the blastocysts with genistein caused fewer cells than the control group and this effect was primary in the inner cell mass. The genistein-pretreated blastocysts showed normal levels of implantation on culture dishes in vitro, but significantly fewer genistein-pretreated embryos reached the later stages of embryonic development versus the controls, with many of the former embryos dying at relatively early stages of development. In addition, genistein treatment decreased the development of morulas into blastocysts, and dietary genistein was found to induce cell apoptosis and decrease cell proliferation in an animal assay model of embryogenesis.

CONCLUSIONS

Our results collectively indicate that genistein treatment of mouse blastocysts induces apoptosis, decreases cell numbers, retards early postimplantation blastocyst development, and increases early-stage blastocyst death in vitro, while dietary genistein appears to negatively affect mouse embryonic development in vivo by inducing cell apoptosis and inhibiting cell proliferation. These novel findings provide important new insights into the effect of genistein on mouse blastocysts.

Melanoma chemoprevention

BACKGROUND

Despite efforts to promote sun protection behaviors, melanoma incidence continues to increase. The prognosis of advanced melanoma remains extremely poor in spite of treatment advances, emphasizing the importance of exploring additional preventive measures.

OBJECTIVE

We sought to summarize the results of published research on candidate chemoprevention agents for melanoma.

METHODS

We conducted a narrative review of the literature.

RESULTS

Investigation into a possible role in melanoma chemoprevention continues for multiple agents, including sunscreen, lipid-lowering medications, nonsteroidal anti-inflammatory drugs, dietary nutrients, immunomodulators, and other drugs, including retinoids, difluoromethylornithine, and T4 endonuclease V.

LIMITATIONS

Systematic review of the literature was not performed.

CONCLUSION

Because no agent yet emerges as a clear choice for effective melanoma chemoprevention, sun avoidance and sun protection remain the mainstay of melanoma prevention for persons at high risk.

Phenoxodiol: isoflavone analog with antineoplastic activity

Phenoxodiol, a synthetic analog of the plant isoflavone genistein, represents a new generation of oncology drugs acting as multiple signal transduction regulators. Phenoxodiol exerts its effect mainly by the induction of apoptosis through multiple mechanisms resulting in degradation of antiapoptotic proteins, with increased levels being linked to chemoresistance in tumor cells. Preclinical studies with this agent showed promising anticancer activity leading to a potential role in the treatment of a wide range of solid and hematologic cancers. Early clinical studies, especially in chemotherapy-resistant ovarian cancer, showed minimal toxicity with minor antitumor activity. Hormone-refractory prostate cancer is another promising area in which phenoxodiol is being actively tested. Studies are ongoing to define the optimal use of this novel anticancer agent.

Longer aging time increases the anticancer and antimetastatic properties of doenjang

OBJECTIVE

Fermented soy foods, such as doenjang, are important components of the Korean diet. Doenjang has been shown to have greater antimutagenic and anticancer activities than other fermented soybean foods such as chungkukjang (Korean-style natto) and miso and non-fermented soybeans. This study investigated the effects of fermentation time of doenjang on its inhibitory activity against solid tumor formation and lung metastasis.

METHODS

Effects of methanol extracts from doenjang prepared with long-term fermentation on tumor formation, natural killer cell activity in spleen, and glutathione S-transferase activity in liver were investigated in sarcoma-180 cell-transplanted mice. Inhibitory effects of these samples on lung metastasis of colon 26-M3.1 cells were also evaluated in Balb/c mice. To determine the effect of aging on functionality, doenjang fermented for 3, 6, and 24 mo were evaluated.

RESULTS

Doenjang fermented for 24 mo exhibited a two- to three-fold increase in antitumor effects on sarcoma-180-injected mice and antimetastatic effects in colon 26-M 3.1 cells in mice compared with the 3- or 6-mo fermented doenjang. The 24-mo fermentation was the most effective in preventing cancer by decreasing tumor formation and increasing natural killer cell activity in spleens and glutathione S-transferase activity in livers of mice.

CONCLUSIONS

Prolonging the fermentation period when making doenjang increases its antitumor and antimetastatic effects in vivo.

Phase I trial of phenoxodiol delivered by continuous intravenous infusion in patients with solid cancer

BACKGROUND

Phenoxodiol is a multi-pathway initiator of apoptosis with broad anti-tumor activity and high specificity for tumor cells. Its biochemical effects are particularly suited to reversal of chemo-resistance, and the drug is being developed as a chemo-sensitizer of standard chemotherapeutics in solid cancers. This phase I, single-center trial was conducted to test a continuous intravenous dosing regimen of phenoxodiol in patients with late-stage, solid tumors to determine toxicity, pharmacokinetics, and preliminary efficacy.

METHODS

Phenoxodiol given by intravenous infusion continuously for 7 days on 14-day cycles was dose-escalated on an inter-patient basis at dosages of 0.65,1.3, 3.3, 20.0, and 27.0 mg/kg/day (three to four patients per stratum). Treatment cycles continued until disease progression. Toxicity was based on standard criteria; efficacy was based on changes in tumor burden (WHO); pharmacokinetic analysis was conducted on plasma samples at specified time points during treatment cycles.

RESULTS

Nineteen heavily-pre-treated patients with solid tumors received a median of three cycles of treatment (range 1-13); two patients received >or= 12 cycles. No dose-limiting toxicities were encountered, with emesis and fatigue (one patient) and rash (one patient) the only significant toxicities. Stabilized disease was the best efficacy outcome, with one patient showing stable disease at 24 weeks. Pharmacokinetics suggested a linear relationship between dosage and mean steady-state plasma concentrations of phenoxodiol.

CONCLUSION

A 7-day continuous infusion of phenoxodiol given every 2 weeks is well tolerated up to a dose of 27.0 mg/kg/day.

Novel Approach for Evaluation of Estrogenic and Anti-Estrogenic Activities of Genistein and Daidzein using B16 Melanoma Cells and Dendricity Assay

The effects of soy isoflavones, genistein and daidzein, which exhibit estrogenic, anti-estrogenic and/or tyrosine kinase inhibitory activity, on the dendritic morphology of B16 mouse melanoma cells were quantitatively evaluated and compared with those of 17 beta-estradiol (Est) and tyrphostin, a tyrosine kinase inhibitor. Dendricity was significantly stimulated in the order of Est >> genistein > daidzein = tyrphostin, but not by glycosides of genistein and daidzein. In competition experiments, Est counteracted the stimulatory activity of genistein and daidzein, but enhanced the activity of tyrphostin additively, suggesting that genistein and daidzein agonized Est. In addition, when the concentration ratios of genistein/Est and daidzein/Est were higher than 5000 and 50,000, respectively, genistein and daidzein agonized Est. In contrast, when the ratio of daidzein/Est was lower than 500, daidzein antagonized Est. Furthermore, genistein and daidzein competed with each other in stimulatory activity. These observations suggest that: 1) dendricity is stimulated by agonists (genistein and daidzein) of Est and tyrosine kinase inhibitors (genistein and tyrphostin), 2) the concentration ratio of isoflavone aglycone/Est is very important as one regulatory factor for estrogenic and/or anti-estrogenic activity, and 3) daidzein antagonizes not only Est but also genistein. It is concluded that a quantitative and simple dendricity assay using B16 mouse melanoma cells is available to evaluate estrogenic and anti-estrogenic activity in vitro.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

Antimutagenic effects of doenjang (Korean fermented soypaste) and its active compounds

Doenjang (Korean fermented soypaste) is one of the important fermented foods of Korea. Doenjang has been traditionally manufactured from meju, which is fermented rectangular shape molded from crushed cooked soybeans. The main microorganisms involved for meju fermentation are Bacillus subtilis and molds such as Rizopus sp., Mucor sp., and Aspergillus sp. We have already reported that doenjang is safe from mycotoxin, especially, aflatoxin contamination due to the manufacturing process of the doenjang. We have demonstrated that the doenjang extracts showed strong antimutagenic activities against various carcinogens/mutagens including aflatoxin B(1). The traditionally fermented soypaste, doenjang showed higher antimutagenic activity than the raw soybeans, cooked soybeans, meju and other fermented soybeans in the Ames test. The active compounds that were identified are genistein, linoleic acid, beta-sitosterol glucoside, soyasaponin, etc. The active compounds exhibited strong antimutagenic activities in the Ames test, SOS chromotest and Drosophila wing spot test. More genistein was formed during the doenjang fermentation from genistin in the soybeans. Genistein and linoleic acid were the most effective active compounds found in doenjang.

Bottlenecks for metabolic engineering of isoflavone glycoconjugates in Arabidopsis

In view of their perceived chemopreventive activities against hormone-dependent cancers, cardiovascular disease, and postmenopausal ailments, there is considerable interest in engineering plants to contain isoflavone phytoestrogens. However, attempts to date have only resulted in low levels of isoflavone accumulation in non-legumes. Introducing soybean isoflavone synthase (IFS) into Arabidopsis thaliana leads to accumulation of low levels of genistein glycosides. Leaves of wild-type A. thaliana contain high levels of similar conjugates of the flavonols quercetin and kaempferol, which could be increased by threefold on introduction of an alfalfa chalcone isomerase transgene. Levels of genistein were not increased by expressing both IFS and alfalfa chalcone isomerase, but levels of flavonol conjugates were reduced to a greater extent than could be accounted for by flux into isoflavone. Introduction of IFS into the tt6/tt3 double mutant blocked in flavonol, and anthocyanin synthesis resulted in high levels of genistein. The bottleneck for constitutive isoflavone production in Arabidopsis is, therefore, competition for flavanone between IFS and endogenous flavonol synthesis, and the flavonol pathway is reciprocally but disproportionately affected by IFS.

Effects of genistein and daidzein on the cell growth, cell cycle, and differentiation of human and murine melanoma cells(1)

Genistein and daidzein are two major isoflavonoids in dietary soybean that have inhibition effect on the cell growth of different tumor cell lines. We previously reported the anti-tumor activities of genistein and daidzein in human co1on tumor (HCT) cells and their different ability to enhance the activation of murine lymphocytes. In the present study, the effect of genistein and daidzein on the cell growth, cell cycle progression, and differentiation of murine K1735M2 and human WM451 cel1s was investigated. It was found that genistein could inhibit the cell growth of two metastatic melanoma cell lines, murine Kl735M2 and human WM45l in a dose-dependent manner. Flow cytometry showed that genistein could cause arrest of both Kl735M2 and WM45l at G(2)/M phase, while daidzein increased the cell numbers at S phase, decreased the cell numbers at G(1) phase. Detection of melanin and morphological observation showed that genistein can induce Kl735M2 and WM45l to produce dendrite-like structure and produce more melanin by 80%. In contrast, daidzein only retarded the growth of K1735M2 and did not induce differentiation in either K1735M2 or WM451. These results suggest that genistein and daidzein in soybean can inhibit certain malignant phenotype of melanoma via different mechanisms and be potential medical candidates for melanoma cancer therapy.

Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectiveness and development of side effects

Several studies suggest that dietary supplementation with antioxidants can influence the response to chemotherapy as well as the development of adverse side effects that results from treatment with antineoplastic agents. Administration of antineoplastic agents results in oxidative stress, i.e., the production of free radicals and other reactive oxygen species (ROS). Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and mutagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented by antioxidants, and agents that interfere with these side effects may also interfere with the anticancer effects of chemotherapy.

Effects of structurally related flavonoids on cell cycle progression of human melanoma cells: regulation of cyclin-dependent kinases CDK2 and CDK1

We have investigated the effects of a series of flavonoids on cell proliferation and cell cycle distribution in human melanoma cells OCM-1. Among the compounds that potently inhibited OCM-1 cell proliferation, we show that the presence of a hydroxyl group at the 3'-position of the ring B in quercetin and luteolin, correlated to a G1 cell cycle arrest while its absence in kaempferol and apigenin correlated to a G2 block. Genistein with a hydroxyl at 5-position of the ring A arrested cells in G2 while daidzein which lacks it, induced an accumulation of cells in G1. We demonstrate that flavonoids, which induced a cell cycle block in G1, inhibited the activity of CDK2 by 40-60%. By contrast, those which caused an accumulation of cells in G2/M were without effect. On the other hand, while quercetin, daidzein and luteolin did not alter the activity of CDK1, kaempferol, apigenin and genistein inhibited this kinase by 50-70%. We demonstrate that the up-regulation of the CDK inhibitors p27(KIP1) and p21(CIP1) is likely responsible for the inhibition of CDK2 while inhibition of CDK1 was rather due to the phosphorylation of the kinase on Tyr15 residue.

The therapeutic potential of flavonoids

Four most widely investigated flavonoids, flavopiridol, catechins, genistein and quercetin are reviewed in this article. Flavopiridol is a novel semisynthetic flavone analogue of rohitukine, a leading anticancer compound from an Indian tree. Flavopiridol inhibits most cyclin-dependent kinases and displays unique anticancer properties. It is the first cyclin-dependent kinase inhibitor to be tested in Phase II clinical trials. Catechin and its gallate are major ingredients in green tea and their anti-oxidant and cancer preventive effects have been widely investigated. A Phase I study of green tea extract GTE-TP91 has been conducted in adult patients with solid tumours. Similarly, genistein is a major ingredient in soybean and has been shown to prevent cancer and have antitumour, anti-oxidant and anti-inflammatory effects. Two antibody-genistein conjugates, B43-genistein and EGF-genistein, are currently in clinical development for the treatment of acute lymphoblastic leukaemia and breast cancer, respectively. Finally, most recent updates of quercetin are briefly described.

Flavonoids inhibit cell growth and induce apoptosis in B16 melanoma 4A5 cells

We investigated the growth inhibitory activity of several flavonoids, including apigenin, luteolin, kaempherol, quercetin, butein, isoliquiritigenin, naringenin, genistein, and daizein against B16 mouse melanoma 4A5 cells. Isoliquiritigenin and butein, belonging to the chalcone group, markedly suppressed the growth of B16 melanoma cells and induced cell death. The other flavonoids tested showed little growth inhibitory activity and scarcely caused cell death. In cells treated with isoliquiritigenin or butein, condensation of nuclei and fragmentation of nuclear DNA, which are typical phenomena of apoptosis, were observed by Hoechst 33258 staining and by agarose gel electrophoresis of DNA. Flowcytometric analysis showed that isoliquiritigenin and butein increased the proportion of hypodiploid cells in the population of B16 melanoma cells. These results demonstrate that isoliquiritigenin and butein inhibit cell proliferation and induce apoptosis in B16 melanoma cells. Extracellular glucose decreased the proportion of hypodiploid cells that appeared as a result of isoliquiritigenin treatment. p53 was not detected in cells treated with either of these chalcones, however, protein of the Bcl-2 family were detected. The level of expression of Bax in cells treated with either of these chalcones was markedly elevated and the level of Bcl-XL decreased slightly. Isoliquiritigenin did not affect Bcl-2 expression, but butein down-regulated Bcl-2 expression. From these results, it seems that the pathway by which the chalcones induce apoptosis may be independent of p53 and dependent on proteins of the Bcl-2 family. It was supposed that isoliquiritigenin induces apoptosis in B16 cells by a mechanism involving inhibition of glucose transmembrane transport and promotion of Bax expression. On the other hand, it was suggested that butein induces apoptosis via down-regulation of Bcl-2 expression and promotion of Bax expression. This mechanism differs from the isoliquiritigenin induction pathway.

Distinct Chk2 activation pathways are triggered by genistein and DNA-damaging agents in human melanoma cells

Genistein, a natural isoflavone found in soybeans, exerts a number of biological actions suggesting that it may have a role in cancer prevention. We have previously shown that it potently inhibits OCM-1 melanoma cell proliferation by inducing a G(2) cell cycle arrest. Here we show that genistein exerts this effect by impairing the Cdc25C-dependent Tyr-15 dephosphorylation of Cdk1, as the overexpression of this phosphatase allows the cells to escape G(2) arrest and enter an abnormal chromatin condensation stage. Caffeine totally overrides the genistein-induced G(2) arrest, whereas the block caused by etoposide is not bypassed and that caused by adriamycin is only partially abolished. We also report that genistein activates the checkpoint kinase Chk2 as efficiently as the two genotoxic agents and that caffeine may counteract the activation of Chk2 by genistein but not by etoposide. In contrast, caffeine abolishes the accumulation of p53 caused by all the compounds. Wortmannin does not suppress the Chk2 activation in any situation, suggesting that the ataxia telangiectasia-mutated kinase is not involved in this regulation. Finally, unlike etoposide and adriamycin, genistein induces only a weak response in terms of DNA damage in OCM-1 cells. Taken together, these results suggest that the G(2) checkpoints activated by genistein and the two genotoxic agents involve different pathways.

Inhibition of UV irradiation-induced oxidative stress and apoptotic biochemical changes in human epidermal carcinoma A431 cells by genistein

Ultraviolet (UV) light is a strong apoptotic trigger that can induce a caspase-dependent biochemical change in cells. We previously showed that UV irradiation can elicit caspase-3 activation and the subsequent cleavage and activation of p21-activated kinase 2 (PAK2) in human epidermal carcinoma A431 cells. We report that genistein, an isoflavone compound with known inhibitory activities to protein tyrosine kinases (PTKs) and topoisomerase-II (topo-II), can prevent UV irradiation-induced apoptotic biochemical changes (DNA fragmentation, caspase-3 activation, and cleavage/activation of PAK2) in A431 cells. Surprisingly, two typical PTK inhibitors (tyrphostin A47 and herbimycin A) and three known topo-II inhibitors (etoposide, daunorubicin, and novomycin) had no effect on UV irradiation-induced apoptotic biochemical changes, suggesting that the inhibitory effect of genistein is not dependent on its property as a PTK/topo-II inhibitor. In contrast, azide, a reactive oxygen species (ROS) scavenger, could effectively block the UV irradiation-induced apoptotic cell responses. Flow cytometric analysis using the cell-permeable dye 2',7'-dichlorofluorescin diacetate as an indicator of the generation of ROS showed that UV irradiation caused increase of the intracellular oxidative stress and that this increase could be abolished by azide, suggesting that oxidative stress plays an important role in mediating the apoptotic effect of UV irradiation. Importantly, the UV irradiation-induced oxidative stress in cells could be significantly attenuated by genistein, suggesting that impairment of ROS formation during UV irradiation is responsible for the antiapoptotic effect of genistein. Collectively, our results demonstrate the involvement of oxidative stress in the UV irradiation-induced caspase activation and the subsequent apoptotic biochemical changes and show that genistein is a potent inhibitor for this process.

p53-independent induction of p21 (WAF1/CIP1), reduction of cyclin B1 and G2/M arrest by the isoflavone genistein in human prostate carcinoma cells

Genistein, a natural isoflavonoid phytoestrogen, is a strong inhibitor of protein tyrosine kinase and DNA topoisomerase II activities. Genistein has been shown to have anticancer proliferation, differentiation and chemopreventive effects. In the present study, we have addressed the mechanism of action by which genistein suppressed the proliferation of p53-null human prostate carcinoma cells. Genistein significantly inhibited the cell growth, which effect was reversible, and induced dendrite-like structure. The inhibitory effects of genistein on cell growth proliferation were associated with a G2/M arrest in cell cycle progression concomitant with a marked inhibition of cyclin B1 and an induction of Cdk inhibitor p21 (WAF1/CIP1) in a p53-independent manner. Following genistein treatment of cells, an increased binding of p21 with Cdk2 and Cdc2 paralleled a significant decrease in Cdc2 and Cdk2 kinase activity with no change in Cdk2 and Cdc2 expression. Genistein also induced the activation of a p21 promoter reporter construct, utilizing a sequence distinct from the p53-binding site. Analysis of deletion constructs of the p21 promoter indicated that the response to genistein could be localized to the 300 base pairs proximal to the transcription start site. These data suggest that genistein may exert a strong anticarcinogenic effect, and that this effect possibly involves an induction of p21, which inhibits the threshold kinase activities of Cdks and associated cyclins, leading to a G2/M arrest in the cell cycle progression.

Legumes and soybeans: overview of their nutritional profiles and health effects

Legumes play an important role in the traditional diets of many regions throughout the world. In contrast in Western countries beans tend to play only a minor dietary role despite the fact that they are low in fat and are excellent sources of protein, dietary fiber, and a variety of micronutrients and phytochemicals. Soybeans are unique among the legumes because they are a concentrated source of isoflavones. Isoflavones have weak estrogenic properties and the isoflavone genistein influences signal transduction. Soyfoods and isoflavones have received considerable attention for their potential role in preventing and treating cancer and osteoporosis. The low breast cancer mortality rates in Asian countries and the putative antiestrogenic effects of isoflavones have fueled speculation that soyfood intake reduces breast cancer risk. The available epidemiologic data are limited and only weakly supportive of this hypothesis, however, particularly for postmenopausal breast cancer. The data suggesting that soy or isoflavones may reduce the risk of prostate cancer are more encouraging. The weak estrogenic effects of isoflavones and the similarity in chemical structure between soybean isoflavones and the synthetic isoflavone ipriflavone, which was shown to increase bone mineral density in postmenopausal women, suggest that soy or isoflavones may reduce the risk of osteoporosis. Rodent studies tend to support this hypothesis, as do the limited preliminary data from humans. Given the nutrient profile and phytochemical contribution of beans, nutritionists should make a concerted effort to encourage the public to consume more beans in general and more soyfoods in particular.

Differentiation of human malignant melanoma cells that escape apoptosis after treatment with 9-nitrocamptothecin in vitro

After in-vitro exposure to 0.05 micromol/L 9-nitrocamptothecin (9NC) for periods of time longer than 5 days, 65% to 80% of the human malignant melanoma SB1B cells die by apoptosis, whereas the remaining cells are arrested at the G2-phase of the cell cycle. Upon discontinuation of exposure to 9NC the G2-arrested cells resume cell cycling or remain arrested depending on the duration of 9NC exposure. In contrast to cycling malignant cells, the cells irreversibly arrested at G2 exhibit features of normal-like cells, the melanocytes, as assessed by the appearance of dendrite-like structures; loss of proliferative activity; synthesis of the characteristic pigment, melanin; and, particularly, loss of tumorigenic ability after xenografting in immunodeficient mice. Further, the expression of the cyclin-dependent kinase inhibitor p16 is upregulated in the 9NC-treated, G2-arrested, but downregulated in density G1-arrested cells, whereas the reverse is observed in the expression of another cyclin-dependent kinase inhibitor, p21. These results suggest that malignant melanoma SB1B cells that escape 9NC-induced death by apoptosis undergo differentiation toward nonmalignant, normal-like cells.

Phytoestrogens and breast cancer

Phytoestrogens are paradoxical. Because of their structural similarity to the physiological oestrogens, they have been assumed to increase the risk of breast cancer. However, nations where the largest amounts of phytoestrogens are consumed in the diet have the lowest incidence of and rate of death from breast cancer. Although these epidemiological observations do not prove that phytoestrogens have anti-cancer properties, many preclinical experiments support this concept. Some indicate that early life exposure to phytoestrogens may be critical for breast cancer prevention. Clinical studies to define the effect of phytoestrogens on breast cancer recurrence are underway. The recent discovery of a second class of oestrogen receptors, with a differential distribution among the tissues, may enable an explanation of the phytoestrogen paradox. These receptors have opened a way of utilizing phytoestrogens in the treatment of oestrogen-sensitive chronic diseases such as atherosclerosis and osteoporosis.

Soyfoods, isoflavones and risk of colonic cancer: a review of the in vitro and in vivo data

Soy foods and soybean components have received considerable attention of late for their potential role in reducing cancer risk. Although the relationship between soy intake and the risk of breast and prostate cancer has been the focus of most interest, the relationship between soy intake and other cancers, including colorectal cancer, has also been studied. Several anti-carcinogens have been identified in soybeans, but most enthusiasm for the potential anti-cancer effects of soy undoubtedly stems from work involving soybean isoflavones. Isoflavones have a limited distribution in nature, and, for practical purposes, soyfoods are the only nutritionally relevant dietary source of these phytochemicals. Isoflavones are weak oestrogens but possess other potentially important biological attributes independent of their ability to bind to the oestrogen receptor. The isoflavone genistein inhibits the growth of most types of hormone-dependent and hormone-independent cancer cells in vitro, including colonic cancer cells. Several mechanisms for the in vitro anti-cancer effects of genistein have been proposed, including effects on signal transduction. A number of epidemiological studies, primarily of Asian origin, have examined the relationship between soy intake and the risk of colorectal cancer. Although these studies provide little support for a protective effect of soy, concerns have been raised about the completeness of the soy intake data, since soy was not the focus of these studies and most of this research was conducted prior to the recent interest in the anti-cancer effects of soy. The effect of soy/isoflavone intake has also been studied in rodents, but again these data are conflicting and provide only modest support for a protective effect. Although the relationship between soy intake and colonic cancer risk is certainly worthy of further investigation, there is, at the moment, very limited support for soy exerting a protective effect against this type of cancer.

Genistein induces p21(Cip1/WAF1) expression and blocks the G1 to S phase transition in mouse fibroblast and melanoma cells

Genistein, the principal isoflavonoid in soybeans, is reported to inhibit cell cycle progression, but the molecular basis for this event is unknown. Here we show that genistein inhibits DNA synthesis and suppresses cyclin E-associated cyclin-dependent kinase-2 (CDK2) activity when quiescent BALB/c 3T3 fibroblasts are stimulated with serum. In these cells, a CDK2 inhibitor, p21(Cip1/WAF1), is markedly increased by genistein, but another CDK2 inhibitor, p27(Kip1), is not increased. In exponentially growing BALB/c 3T3 cells, genistein inhibits proliferation of the cells in a dose-dependent manner. Flow cytometric analysis and measurement of DNA synthesis indicate that genistein blocks the G1 to S phase transition of these cells, which is concomitant with G2-M arrest. In mouse B16-F1 melanoma cells, genistein also blocks the transition of G1 to S phase without arresting at G2-M at low doses. In both cell lines, genistein suppresses cyclin E/CDK2 activity and induces p21(Cip1/WAF1) expression. These results suggest that genistein affects the restriction point control of the cell cycle by inducing p21(Cip1/WAF1) expression in mouse fibroblast and melanoma cells.

Suppression of tumorigenic and metastatic potentials of human melanoma cell lines by mutated (143 Val-Ala) p53

Metastatic melanoma, compared with other cancers, appears to be unusual because of its low frequency of p53 mutations and prevalence of wild-type p53 protein in advanced malignancy. Here, we examined the effects of wild-type and mutated p53 (143 Val-Ala) on tumorigenic and metastatic potential of two human melanoma cell lines. The cell line UISO-MEL-4 contains wild-type p53 and is tumorigenic, whereas UISO-MEL-6 lacks p53 and produces lung and liver metastasis upon s.c. injection into athymic mice. Our study showed that UISO-MEL-4 stably transfected with wild-type p53 cDNA driven by cytomegalovirus promoter-enhancer sequences expressed high levels of p53 and p21 and formed s.c. tumours in vivo. Mutated p53 (143 Val-Ala) expression, on the other hand, inhibited tumour growth in 50% of cases and produced significantly slower growing non-metastatic tumours. Reduced tumour growth involved necrotic as well as apoptotic cell death. Inhibition of tumour growth was abrogated by the addition of Matrigel (15 mg ml(-1)). With UISO-MEL-6 cells, stably transfected with mutant p53, tumour growth was delayed and metastasis was inhibited. In soft agar colony formation assay, both wild-type and mutant p53 transfectants reduced anchorage-independent colony formation in vitro. These data suggest that mutated (143 Val-Ala) p53, which retains DNA binding and some of the transactivation functions of the wild-type p53 protein, suppresses tumorigenic and metastatic potentials of human melanoma cell lines in vivo.

The chemopreventive properties of soy isoflavonoids in animal models of breast cancer

Genistein (5,7,4'-trihydroxyisoflavone), one of two major isoflavonoids in soy, has anti-proliferative effects on mitogen-stimulated cell growth of human breast cancer cells in culture and is a candidate for use in the prevention of breast cancer. Soy protein preparations containing isoflavonoid conjugates have chemopreventive activity in carcinogen-induced rat models of breast cancer. Recent experiments in these models with purified genistein have revealed that the timing of the exposure of rats to this isoflavonoid is critical. Rats treated neonatally or prepuberally with genistein have a longer latency before the appearance of 7,12-dimethylbenz[a]anthracene-induced mammary tumors and a marked reduction in tumor number. The mechanism of genistein's preventive action is in part dependent on its estrogenic activity, which causes a more rapid differentiation of the cells of the mammary gland, and analogous to the effects of an early pregnancy. Rats administered genistein after 35 days of age have smaller alterations in breast cancer risk, with a maximum reduction in mammary tumor number of 27%. In ovariectomized nude mice, dietary genistein increases cell proliferation of human breast cancer MCF-7 cell xenografts compared with a control diet. This estrogen-like effect of genistein is not observed in non-ovariectomized rats. Future studies on the anticancer potential of soy isoflavonoids should examine their interaction with other phytochemical components of soybeans and exploit newly developed animal models of breast cancer in which specific genes have been activated or inactivated.