Chemopreventive effects of a flavonoid antioxidant silymarin on N-butyl-N-(4-hydroxybutyl)nitrosamine-induced urinary bladder carcinogenesis in male ICR mice

Mechanistic Insights into the Pharmacological Significance of Silymarin

Medicinal plants are considered the reservoir of diverse therapeutic agents and have been traditionally employed worldwide to heal various ailments for several decades. Silymarin is a plant-derived mixture of polyphenolic flavonoids originating from the fruits and akenes of Silybum marianum and contains three flavonolignans, silibinins (silybins), silychristin and silydianin, along with taxifolin. Silybins are the major constituents in silymarin with almost 70–80% abundance and are accountable for most of the observed therapeutic activity. Silymarin has also been acknowledged from the ancient period and is utilized in European and Asian systems of traditional medicine for treating various liver disorders. The contemporary literature reveals that silymarin is employed significantly as a neuroprotective, hepatoprotective, cardioprotective, antioxidant, anti-cancer, anti-diabetic, anti-viral, anti-hypertensive, immunomodulator, anti-inflammatory, photoprotective and detoxification agent by targeting various cellular and molecular pathways, including MAPK, mTOR, β-catenin and Akt, different receptors and growth factors, as well as inhibiting numerous enzymes and the gene expression of several apoptotic proteins and inflammatory cytokines. Therefore, the current review aims to recapitulate and update the existing knowledge regarding the pharmacological potential of silymarin as evidenced by vast cellular, animal, and clinical studies, with a particular emphasis on its mechanisms of action.

Role of Silymarin in Cancer Treatment: Facts, Hypotheses, and Questions

The flavonoid silymarin extracted from the seeds of Sylibum marianum is a mixture of 6 flavolignan isomers. The 3 more important isomers are silybin (or silibinin), silydianin, and silychristin. Silybin is functionally the most active of these compounds. This group of flavonoids has been extensively studied and they have been used as hepato-protective substances for the mushroom Amanita phalloides intoxication and mainly chronic liver diseases such as alcoholic cirrhosis and nonalcoholic fatty liver. Hepatitis C progression is not, or slightly, modified by silymarin. Recently, it has also been proposed for SARS COVID-19 infection therapy. The biochemical and molecular mechanisms of action of these substances in cancer are subjects of ongoing research. Paradoxically, many of its identified actions such as antioxidant, promoter of ribosomal synthesis, and mitochondrial membrane stabilization, may seem protumoral at first sight, however, silymarin compounds have clear anticancer effects. Some of them are: decreasing migration through multiple targeting, decreasing hypoxia inducible factor-1α expression, inducing apoptosis in some malignant cells, and inhibiting promitotic signaling among others. Interestingly, the antitumoral activity of silymarin compounds is limited to malignant cells while the nonmalignant cells seem not to be affected. Furthermore, there is a long history of silymarin use in human diseases without toxicity after prolonged administration. The ample distribution and easy accessibility to milk thistle-the source of silymarin compounds, its over the counter availability, the fact that it is a weed, some controversial issues regarding bioavailability, and being a nutraceutical rather than a drug, has somehow led medical professionals to view its anticancer effects with skepticism. This is a fundamental reason why it never achieved bedside status in cancer treatment. However, in spite of all the antitumoral effects, silymarin actually has dual effects and in some cases such as pancreatic cancer it can promote stemness. This review deals with recent investigations to elucidate the molecular actions of this flavonoid in cancer, and to consider the possibility of repurposing it. Particular attention is dedicated to silymarin's dual role in cancer and to some controversies of its real effectiveness.

Cytoprotective Activities of Milk Thistle Seed Oil Used in Traditional Tunisian Medicine on 7-Ketocholesterol and 24S-Hydroxycholesterol-Induced Toxicity on 158N Murine Oligodendrocytes

The Asteraceae family is economically very important, because many of these plants are grown mainly for their food value, such as lettuce (Lactuca), chicory (Cichorium), and sunflower (Heliantus aminus). One of the typical properties of this family, which includes milk thistle (Sylibum marianum), is the richness of the oil in various compounds (flavonoids, alkaloids, tocopherols, and unsaturated fatty acids). Currently, and for the coming decades, age-related diseases, including neurodegenerative diseases, are a major public health problem. Preventing their appearance or opposing their evolution is a major objective. In this context, the cytoprotective activities of milk thistle seed oil produced in Tunisia were studied on the 158N model using 7-ketocholesterol (7KC) and 24S-hydroxycholesterol (24S) as cytotoxic agents. 7KC and 24S were used because they can be increased in the brain and body fluids of patients with major age-related neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases. In order to evaluate the cytoprotective properties of milk thistle seed oil, complementary techniques of microscopy, flow cytometry, and biochemistry were used. The chemical composition of milk thistle seed oil has also been determined by various chromatography techniques. Milk thistle seed oils from different area of Tunisia are rich in tocopherols and are strongly antioxidant according to various biochemical tests (KRL (Kit Radicaux Libres), FRAP (Ferric Reducing Antioxidant Power), and DPPH (2,2-diphenyl-1-picrylhydrazyl)). The main fatty acids are linoleic acid (C18:2 n-6) and oleic acid (C18:1 n-9). The main polyphenols identified are homovanillic acid, p-coumaric acid, quercetin, and apigenin, with a predominance of vanillic acid. On 158N cells, milk thistle seed oil attenuates the cytotoxicity of 7KC and 24S including: loss of cell adhesion, increased plasma membrane permeability, mitochondrial dysfunction, overproduction of reactive oxygen species, induction of apoptosis, and autophagy. The attenuation of the cytotoxicity of 7KC and 24S observed with the milk thistle seed oil is in the order of that observed with α-tocopherol used as a positive control. In the presence of nigella seed oil, considered potentially cytotoxic, no cytoprotective effects were observed. Given the chemical characteristics, antioxidant properties, and cytoprotective activities of milk thistle seed oil, our results highlight the potential benefit of this oil for human health.

Chemopreventive Efficacy of Silymarin in Skin and Prostate Cancer

Prevention and therapeutic intervention by phytochemicals are newer dimensions in the arena of cancer management. In this regard, the cancer chemopreventive role of silymarin (Silybum marianum) has been extensively studied and has shown anticancer efficacy against various cancer sites, especially skin and prostate. In skin cancer, silymarin treatment inhibits ultraviolet B radiation or chemically initiated or promoted carcinogenesis. These effects of silymarin against skin carcinogenesis have been attributed to its strong antioxidant and anti-inflammatory action as well as its inhibitory effect on mitogenic signaling. Similarly, silymarin treatment inhibits 3, 2-dimethyl-4-aminobiphenyl—induced prostate carcinogenesis and retards the growth of advanced prostate tumor xenograft in athymic nude mice. In prostate cancer, silymarin treatment down-regulates androgen receptor—, epidermal growth factor receptor—, and nuclear factor-κB— mediated signaling and induces cell cycle arrest. Extensive preclinical findings have supported the anticancer potential of silymarin, and now its efficacy is being evaluated in cancer patients.

Effects of aqueous extract from Silybum marianum on adenosine deaminase activity in cancerous and noncancerous human gastric and colon tissues

Objective:

Investigation of possible effects of Silybum marianum extract (SME) on adenosine deaminase (ADA) activity in cancerous and noncancerous human gastric and colon tissues to obtain information about possible mechanism of anticancer action of S. marianum.

Materials and Methods:

Cancerous and noncancerous human gastric and colon tissues removed from patients by surgical operations were used in the studies. The extract was prepared in distilled water. Before and after treatment with the extract, ADA activities in the samples were measured.

Results:

ADA activity was found to be lowered significantly in cancerous gastric tissues but not in noncancerous gastric tissues after treatment with the SME. In the colon tissues, ADA activities were however found to increase after the treatment of SME.

Conclusion:

Our results suggest that the aqueous extract from S. marianum inhibits ADA activity in cancerous gastric tissues significantly. It is suggested that in addition to other proposed mechanisms, accumulated adenosine due to the inhibition of ADA might also play a part in the anticancer properties of the S. marianum.

Modulation of cutaneous wound healing by silymarin in rats

OBJECTIVE

To investigate the effect of topical application of silymarin on full-thickness cutaneous wounds in rats.

METHOD

A full-thickness cutaneous defect (2×2cm) was induced on the back of 85 male and female Wister rats. The animals were randomly divided into four groups (n=20 in each group), treated with 1ml basal cream (placebo group), low-dose (6mg/ml/rat) and high-dose (12mg/ml/rat) silymarin, and untreated (control). Five rats remained uninjured to serve as comparisons for biomechanical analysis. Wounds were evaluated 10, 20 and 30 days after injury, through histopathologic, biochemical and biomechanical analyses.

RESULTS

There was a significant (p < 0.05) increase observed in the amount of glycosaminoglycans and collagen present on days 10, 20 and 30 for both low-dose and high-dose silymarin groups. Low-dose silymarin reduced the number of lymphocytes and enhanced the number of fibrocytes at the earlier stages of wound healing; however, high-dose silymarin reduced both lymphocytes and macrophages, and increased number of fibrocytes at the later stages of wound healing. Silymarin significantly improved alignment of the healing tissue, enhanced maturity of the collagen fibres and fibroblasts (p < 0,05), and increased the ultimate tensile strength and stress of the healing tissue.

CONCLUSION

The results suggest that topical application of silymarin improved the morphological, biochemical and biomechanical properties of experimentally-induced wound defects in rats.

DECLARATION OF INTEREST

There were no external sources of funding for this study. The authors have no conflicts of interest to declare.

New Therapeutic Potentials of Milk Thistle (Silybum marianum)

Silymarin is a bioflavonoid complex extract derived from dry seeds of Milk thistle [( Silybum marianum(L.) Gaernt. (Fam. Asteraceae/Compositaceae)] whose hepatoprotective effect has clinically been proved. Low toxicity, favorable pharmacokinetics, powerful antioxidant, detoxifying, preventive, protective and regenerative effects and side effects similar to placebo make silymarin extremely attractive and safe for therapeutic use. The medicinal properties of silymarin and its main component silibinin have been studied in the treatment of Alzheimer's disease, Parkinson's disease, sepsis, burns, osteoporosis, diabetes, cholestasis and hypercholesterolemia. Owing to its apoptotic effect, without cytotoxic effects, silymarin possesses potential applications in the treatment of various cancers. Silymarin is being examined as a neuro-, nephro- and cardio-protective in the damage of different etiologies due to its strong antioxidant potentials. Furthermore, it has fetoprotective (against the influence of alcohol) and prolactin effects and is safe to be used during pregnancy and lactation. Finally, the cosmetics industry is examining the antioxidant and UV-protective effects of silymarin. Further clinical studies and scientific evidence that silymarin and silibinin are effective in the therapy of various pathologies are indispensable in order to confirm their different flavonolignan pharmacological effects.

p53-stabilizing agent CP-31398 prevents growth and invasion of urothelial cancer of the bladder in transgenic UPII-SV40T mice

The high prevalence of bladder cancer and its recurrence make it an important target for chemoprevention. About half of invasive urothelial tumors have mutations in p53. We determined the chemopreventive efficacy of a p53-stabilizing agent, CP-31398, in a transgenic UPII-SV40T mouse model of bladder transitional cell carcinoma (TCC) that strongly resembles human TCC. After genotyping, six-week-old UPII-SV40T mice (n = 30/group) were fed control (AIN-76A) or experimental diets containing 150 or 300 ppm of CP-31398 for 34 weeks. Progression of bladder cancer growth was monitored by magnetic resonance imaging. At 40 weeks of age, all mice were killed; urinary bladders were collected to determine weights, tumor incidence, and histopathology. There was a significant increase in bladder weights of transgenic versus wild-type mice (male: 140.2 mg vs 27.3 mg, P < .0001; female: 34.2 mg vs 14.8 mg, P < .0001). A significant decrease in the bladder tumor weights (by 68.6-80.2%, P < .0001 in males and by 36.9-55.3%, P < .0001 in females) was observed in CP-31398-treated mice. Invasive papillary TCC incidence was 100% in transgenic mice fed control diet. Both male and female mice exposed to CP-31398 showed inhibition of invasive TCC. CP-31398 (300 ppm) completely blocked invasion in female mice. Molecular analysis of the bladder tumors showed an increase in apoptosis markers (p53, p21, Bax, and Annexin V) with a decrease in vascular endothelial growth factor in transgenic mice fed CP-31398. These results suggest that p53-modulating agents can serve as potential chemopreventive agents for bladder TCC.

A Comparison of the Diastereoisomers, Silybin A and Silybin B, on the Induction of Apoptosis in K562 cells

Two diastereoisomers of silybin, silybin A and silybin B, were separated from silymarin by HPLC in our previous study. The present study assessed the effects of the diastereoisomers on cell apoptosis, and compared these with their mixture, silybin, in human chronic myeloid leukemia K562 cells. Both isomers showed stronger effects on cell growth inhibition and apoptosis induction than silybin. Compared with silybin B, silybin A showed higher effects on the production of intracellular reactive oxygen species and Ca2+. These results suggest that silybin A and silybin B have similar potency on apoptosis induction with different oxidative effects. Antagonistic effects may exist between silybin A and silybin B, partially through ROS production and Ca2+ increase.

Pathobiology and chemoprevention of bladder cancer

Our understanding of the pathogenesis of bladder cancer has improved considerably over the past decade. Translating these novel pathobiological discoveries into therapies, prevention, or strategies to manage patients who are suspected to have or who have been diagnosed with bladder cancer is the ultimate goal. In particular, the chemoprevention of bladder cancer development is important, since urothelial cancer frequently recurs, even if the primary cancer is completely removed. The numerous alterations of both oncogenes and tumor suppressor genes that have been implicated in bladder carcinogenesis represent novel targets for therapy and prevention. In addition, knowledge about these genetic alterations will help provide a better understanding of the biological significance of preneoplastic lesions of bladder cancer. Animal models for investigating bladder cancer development and prevention can also be developed based on these alterations. This paper summarizes the results of recent preclinical and clinical chemoprevention studies and discusses screening for bladder cancer.

Paeonia lactiflora Pall inhibits bladder cancer growth involving phosphorylation of Chk2 in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts of Paeonia lactiflora Pall (RPA), a traditional Chinese medicines has been shown to treat cancers.

AIM OF THE STUDY

The purpose of this study is to evaluate the anticancer effect of RPA in urinary bladder carcinoma in vitro and in vivo.

MATERIALS AND METHODS

The cell viability was analyzed with DAPI. Flow cytometry and Western blot were used to study the apoptosis and cell cycle related mechanism. A rat model of bladder cancer was induced by N-butyl-N-(4-hydroxybutyl) nitrosamine (OH-BBN). Tumors were analyzed with immunohistochemical analysis.

RESULTS

Our data suggested that RPA inhibits growth of bladder cancer via induction of apoptosis and cell cycle arrest. Treatment of TSGH-8301 cells with RPA resulted in G2-M phase arrest that was associated with a marked decline in protein levels of cdc2, cyclin B1, cell division cycle 25B (Cdc25B) and Cdc25C. We also reported that RPA-mediated growth inhibition of TSGH-8301 cells was correlated with activation of checkpoint kinase 2 (Chk2). Herein, we further evaluated urinary bladder cancer using a model of bladder cancer induced by OH-BBN. Analysis of tumors from RPA-treated rats showed significant decrease in the expression of Bcl2, cyclin D1, and PCNA, and increase in the expression of p-Chk2 (Thr-68), Bax, and Cip1/p21.

CONCLUSION

Our data provide the experimental evidence that RPA could modulate apoptosis in models of bladder cancer.

Consumption of silibinin, a flavonolignan from milk thistle, and mammary cancer development in the C3(1) SV40 T,t antigen transgenic multiple mammary adenocarcinoma (TAg) mouse

Silibinin is a flavonolignan extracted from milk thistle with cancer chemopreventive activity in preclinical models of prostate and colorectal cancer. A milk thistle extract, of which silibin is a major component, has recently been shown to exacerbate mammary carcinogenesis in two rodent models. We tested the hypothesis that consumption of silibinin or silipide, a silibinin formulation with pharmaceutical properties superior to the unformulated agent, affect breast cancer development in the C3(1) SV40 T,t antigen transgenic multiple mammary adenocarcinoma mouse model. Mice received silibinin or silipide (0.2% silibinin equivalents) with their diet from weaning, and tumour development was monitored by weekly palpation and the number and weight of neoplasms at the end of the experiment. Intervention neither promoted, nor interfered with, tumour development. The result suggests that promotion of carcinogenesis is not a feature of silibinin consistent across rodent models of mammary carcinogenesis.

Effect of cranberry juice concentrate on chemically-induced urinary bladder cancers

The chemopreventive efficacy of cranberry juice concentrate in an experimental model of urinary bladder cancer was evaluated using female Fischer-344 rats. The animals received N-butyl-N-(4-hydroxybutyl)-nitrosamine (OH-BBN) for a period of eight weeks. Cranberry juice concentrate was administered at doses of 1.0 or 0.5 ml/rat/day beginning one week after the final OH-BBN treatment and continuing until the end of the study. The urinary bladders of all the rats were weighed and examined grossly for lesions, and all masses were submitted for pathological evaluation. A dose-dependent preventive effect of cranberry treatment was observed, with a reduced number of urinary bladder cancers (38%) in the 1.0 ml/rat/day group versus the control group. The cranberry extract neither affected body weight gain nor caused other signs of toxicity. For the metabolic studies, serum and urine were collected at 4 and 12 h after the administration of the cranberry juice concentrate and were analyzed by LC-MS/MS. Quercetin and its methylated derivative were detected in the urine samples. However, no quercetin was detected in the serum samples, indicating its poor bioavailability. These data suggest that components of cranberries may be effective in preventing urinary bladder carcinogenesis.

Multitargeted therapy of cancer by silymarin

Silymarin, a flavonolignan from milk thistle (Silybum marianum) plant, is used for the protection against various liver conditions in both clinical settings and experimental models. In this review, we summarize the recent investigations and mechanistic studies regarding possible molecular targets of silymarin for cancer prevention. Number of studies has established the cancer chemopreventive role of silymarin in both in vivo and in vitro models. Silymarin modulates imbalance between cell survival and apoptosis through interference with the expressions of cell cycle regulators and proteins involved in apoptosis. In addition, silymarin also showed anti-inflammatory as well as anti-metastatic activity. Further, the protective effects of silymarin and its major active constituent, silibinin, studied in various tissues, suggest a clinical application in cancer patients as an adjunct to established therapies, to prevent or reduce chemotherapy as well as radiotherapy-induced toxicity. This review focuses on the chemistry and analogues of silymarin, multiple possible molecular mechanisms, in vitro as well as in vivo anti-cancer activities, and studies on human clinical trials.

Oral silibinin inhibits in vivo human bladder tumor xenograft growth involving down-regulation of survivin

PURPOSE

Chemoprevention is an upcoming approach to control bladder cancer, which is one of the commonly diagnosed malignancies showing recurrence rate of 70% or even higher. Recently, we observed the in vitro efficacy of silibinin, a flavanolignan, in human bladder transitional cell papilloma RT4 cells. Here, we investigated the antitumor efficacy and associated mechanisms of silibinin in RT4 tumor xenograft.

EXPERIMENTAL DESIGN

RT4 tumor xenograft was implanted s.c. in athymic nude mice, and then animals were oral gavaged with silibinin at 100 and 200 mg/kg doses, 5 days/week for 12 weeks. Tumor growth, body weight, and diet consumption were recorded, and tumors were analyzed for proliferation, apoptosis, and angiogenesis biomarkers and molecular alterations by immunohistochemistry, immunoblot analysis, and ELISA. p53 small interfering RNA was used in cell culture to examine the role of p53 in survivin expression.

RESULTS

Silibinin feeding inhibited tumor xenograft growth without any gross signs of toxicity. Silibinin decreased tumor volume by 51% to 58% (P <or= 0.01) and tumor weight by 44% to 49% (P < 0.05). Silibinin moderately (P < 0.001) decreased cell proliferation and microvessel density and strongly (P < 0.001) increased apoptosis in tumors. Silibinin robustly decreased survivin protein expression and its nuclear localization, as well as tumor-secreted level in mouse plasma, but increased p53 and cleaved caspase-3 levels in tumors. Silibinin-caused decrease in survivin was independent of p53.

CONCLUSION

These findings identified in vivo antitumor efficacy of silibinin against human bladder tumor cells involving down-regulation of survivin and an increase in p53 expression together with enhanced apoptosis.

Evaluation of the cancer chemopreventive efficacy of silibinin in genetic mouse models of prostate and intestinal carcinogenesis: relationship with silibinin levels

Silibinin, a flavonolignan from milk thistle seeds, possesses cancer chemopreventive properties in rodent models of carcinogenesis. We tested the hypotheses that silibinin or silipide, silibinin formulated with phospholipids, delays tumour development in TRAMP or Apc(Min) mice, genetic models of prostate or intestinal malignancies, respectively. Mice received silibinin or silipide with their diet (0.2% silibinin equivalents) from weaning. Intervention with silipide reduced the size of well differentiated TRAMP adenocarcinomas by 31%. Silipide and silibinin decreased the incidence of poorly differentiated carcinomas by 61% compared to mice on control diet. Silipide decreased plasma levels of insulin-like growth factor (IGF)-1 by 36%. Levels of circulating IGF binding protein (IGFBP)-3 in mice on silipide or silibinin were 3.9- or 5.9-fold, respectively, elevated over those in control TRAMP mice. In Apc(Min) mice silibinin, but not silipide, had only a marginal adenoma number-reducing effect. The results cautiously support the advancement of silipide to the stage of clinical investigation in prostate cancer.

Silibinin synergizes with mitoxantrone to inhibit cell growth and induce apoptosis in human prostate cancer cells

The purpose of these experiments was to assess the synergistic activity of silibinin with chemotherapy agents in clinical use against prostate cancer. Silybin-phytosome, a commercially available formulation containing silibinin, has recently been studied in a phase I clinical trial. The silibinin doses used in the present study are clinically achievable based on the preliminary phase I data. DU145, PC-3 and LNCaP prostate cancer cells were seeded in 96-well plates in triplicate. Twenty-four hours later, silibinin (10, 20 and 40 microM) and either mitoxantrone or docetaxel were added to the designated wells. Seventy-two hours post-treatment, cell viability was determined with a tetrazolium-based assay. The combination index (CI) for determination of a synergistic effect was calculated, with values of <0.9 indicating synergy and values >1.1 antagonism. Apoptosis was also assessed using a luminescent assay after 72 hr of treatment with media alone, silibinin, mitoxantrone, or silibinin plus mitoxantrone. Silibinin showed a synergistic effect with mitoxantrone, as measured by reduction in cell viability. The CI values ranged from 0.413 to 2.650 for the combination of silibinin and mitoxantrone; in contrast, treatment with docetaxel and silibinin showed little or no synergy, with CI values of 0.898-4.469. In concordance with these findings, the addition of silibinin increased the level of apoptosis compared to mitoxantrone alone, particularly in the PC-3 cells. The combination of silibinin and mitoxantrone exhibits a pattern of synergy in reducing cell viability with increased apoptosis. These data are important in the planning of future clinical applications of silibinin.

Effect of the silybin-phosphatidylcholine complex (IdB 1016) on the development of mammary tumors in HER-2/neu transgenic mice

Silybin, a main component of the milk thistle of Silybum marianum, has been reported to possess anticancer activity. We investigated the effects of IdB 1016, a complex of silybin with phosphatidylcholine, on the development of mammary tumors appearing spontaneously in HER-2/neu transgenic mice. The mechanisms involved in the antitumor effect of IdB 1016 were evaluated by studying the apoptosis, senescent-like growth arrest, intratumoral leukocyte infiltrate, and the expression of HER-2/neu and p53 in tumoral mammary glands from transgenic mice and in human breast SKBR3 tumor cells. The administration of IdB 1016 delayed the development of spontaneous mammary tumors, reduced the number and size of mammary tumor masses, and diminished lung metastasization in HER-2/neu transgenic mice. In tumoral mammary glands from IdB 1016-treated mice, a down-regulation of HER-2/neu gene expression was associated with an increased senescent-like growth arrest of tumor cells, and an increased infiltrate of neutrophils, CD4, and CD8 T cells. Both senescent-like growth arrest and apoptosis were significantly increased and were associated with a reduced p185(HER-2/neu) protein and an increased p53 mRNA in SKBR3 in vitro treated with IdB 1016 in comparison with control cells. The results show the antitumor effect of IdB 1016 in the development of spontaneous mammary tumors in HER-2/neu transgenic mice. The effect of IdB 1016 might be related to the down-regulation of HER-2/neu expression and the induction of senescent-like growth arrest and apoptosis through a p53-mediated pathway in tumor cells.

Silymarin and epithelial cancer chemoprevention: how close we are to bedside?

Failure and high systemic toxicity of conventional cancer therapies have accelerated the focus on the search for newer agents, which could prevent and/or slow-down cancer growth and have more human acceptability by being less or non-toxic. Silymarin is one such agent, which has been extensively used since ages for the treatment of liver conditions, and thus has possibly the greatest patient acceptability. In recent years, increasing body of evidence has underscored the cancer preventive efficacy of silymarin in both in vitro and in vivo animal models of various epithelial cancers. Apart from chemopreventive effects, other noteworthy aspects of silymarin and its active constituent silibinin in cancer treatment include their capability to potentiate the efficacy of known chemotherapeutic drugs, as an inhibitor of multidrug resistance-associated proteins and as an adjunct to the cancer therapeutic drugs due to their organ-protective efficacy specifically liver, and immunostimulatory effects. Widespread use of silymarin for liver health in humans and commercial availability of its formulations with increased bioavailability, further underscore the necessity of carrying out controlled clinical trials with these agents in cancer patients. In this review, we will briefly discuss the outcomes of clinical trials being conducted by us and others in cancer patients to provide insight into the clinical relevance of the observed chemopreventive effects of these agents in various epithelial cancer models.

A phase I and pharmacokinetic study of silybin-phytosome in prostate cancer patients

Silibinin is a polyphenolic flavonoid isolated from milk thistle with anti-neoplastic activity in several in vitro and in vivo models of cancer, including prostate cancer. Silybin-phytosome is a commercially available formulation containing silibinin. This trial was designed to assess the toxicity of high-dose silybin-phytosome and recommend a phase II dose. Silybin-phytosome was administered orally to prostate cancer patients, giving 2.5-20 g daily, in three divided doses. Each course was 4 weeks in duration. Thirteen patients received a total of 91 courses of silybin-phytosome. Baseline patient characteristics included: median age of 70 years, median baseline prostate specific antigen (PSA) of 4.3 ng/ml, and a median ECOG performance status of 0. The most prominent adverse event was hyperbilirubinemia, with grade 1-2 bilirubin elevations in 9 of the 13 patients. The only grade 3 toxicity observed was elevation of alanine aminotransferase (ALT) in one patient; no grade 4 toxicity was noted. No objective PSA responses were observed. We conclude that 13 g of oral silybin-phytosome daily, in 3 divided doses, appears to be well tolerated in patients with advanced prostate cancer and is the recommended phase II dose. Asymptomatic liver toxicity is the most commonly seen adverse event.

Suppression of N-nitrosodiethylamine induced hepatocarcinogenesis by silymarin in rats

Antioxidants are one of the key players in tumorigenesis, several natural and synthetic antioxidants were shown to have anticancer effects. In the present investigation the efficacy of silymarin on the antioxidant status of N-nitrosodiethylamine (NDEA) induced hepatocarcinogenesis in Wistar albino male rats were assessed. The animals were divided into five groups. The animals in the groups 1 and 3 were normal control and silymarin control, respectively. Groups 2, 4 and 5 were administered with 0.01% NDEA in drinking water for 15 weeks to induce hepatocellular carcinoma (HCC). Starting 1 week prior to NDEA administration group 4 animals were treated with silymarin in diet for 16 weeks, 10 weeks after NDEA administration group 5 animals were treated with silymarin and continued till the end of the experiment period (16 weeks). After the experimental period the body weight, relative liver weight, number of nodules, size of nodules, the levels of lipid peroxidation, glutathione (GSH), and the activities of antioxidant enzymes were assessed in both haemolysate and liver tissue. In group 2 hepatocellular carcinoma induced animals there was an increase in the number of nodules, relative liver weight. The levels of lipid peroxides were elevated with subsequent decrease in the body weight, (glutathione) GSH, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD). In contrast, silymarin + NDEA treated groups 4 and 5 animals showed a significant decrease in the number of nodules with concomitant decrease in the lipid peroxidation status. The levels of GSH and the activities of antioxidant enzymes in both haemolysate and liver were improved when compared with hepatocellular carcinoma induced group 2 animals. The electron microscopy studies were also carried out which supports the chemopreventive action of the silymarin against NDEA administration during liver cancer progression. These findings suggest that silymarin suppresses NDEA induced hepatocarcinogenesis by modulating the antioxidant defense status of the animals.

Pilot study of oral silibinin, a putative chemopreventive agent, in colorectal cancer patients: silibinin levels in plasma, colorectum, and liver and their pharmacodynamic consequences

Silibinin, a flavonolignan from milk thistle, has intestinal cancer chemopreventive efficacy in rodents. It is a strong antioxidant and modulates the insulin-like growth factor (IGF) system by increasing circulating levels of IGF-binding protein 3 (IGFBP-3) and decreasing levels of IGF-I. Here, the hypothesis was tested that administration of oral silibinin generates agent levels in human blood and colorectal and hepatic tissues consistent with pharmacologic activity. Patients with confirmed colorectal adenocarcinoma received silibinin formulated with phosphatidylcholine (silipide) at dosages of 360, 720, or 1,440 mg silibinin daily for 7 days. Blood and biopsy samples of normal and malignant colorectum or liver were obtained before dosing, and blood and colorectal or hepatic tissues were collected at resection surgery after the final silipide dose. Levels of silibinin were quantified by high-pressure liquid chromatography-UV, and plasma metabolites were identified by liquid chromatography-mass spectrometry. Blood levels of IGFBP-3, IGF-I, and the oxidative DNA damage pyrimidopurinone adduct of deoxyguanosine (M1dG) were determined. Repeated administration of silipide was safe and achieved levels of silibinin of 0.3 to 4 micromol/L in the plasma, 0.3 to 2.5 nmol/g tissue in the liver, and 20 to 141 nmol/g tissue in colorectal tissue. Silibinin monoglucuronide, silibinin diglucuronide, silibinin monosulfate, and silibinin glucuronide sulfate were identified in the plasma. Intervention with silipide did not affect circulating levels of IGFBP-3, IGF-I, or M1dG. The high silibinin levels achieved in the human colorectal mucosa after consumption of safe silibinin doses support its further exploration as a potential human colorectal cancer chemopreventive agent.

Suppressive effect of 1,4-phenylene diisothiocyanate on N-butyl-N-(4-hydroxybutyl)nitrosamine-induced urinary bladder carcinogenesis in male ICR mice

The modifying effects of dietary administration of 1,4-phenylene diisothiocyanate (DITC) on N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced urinary bladder carcinogenesis during the initiation and post-initiation phases were examined in male ICR mice. Five-week-old animals were divided into 5 groups. Groups 1-3 were given BBN (500 ppm) in drinking water for 6 weeks starting at age 6 week. Mice in Group 2 were given the diet containing 100 ppm DITC for 8 weeks during the initiation phase, starting 1 week before BBN exposure. Animals in Group 3 were fed the experimental diet for 24 weeks during the post-initiation phase starting 1 week after the cessation of BBN exposure. Mice in Group 4 were given only the diet containing the test compound, and those in Group 5 were given the basal diet alone throughout the experiment (32 weeks). The frequency of bladder lesions, neoplasms, dysplasia and hyperplasia, was analyzed histopathologically. The cell-proliferation activity estimated by the 5-bromodeoxyuridine labeling index (BrdU-LI), and cell cycle progression by counting cyclin D1-positive cell ratios were compared among the groups using immunohistochemistry. Administration of DITC in the initiation phase reduced significantly the incidence of urinary bladder carcinoma and dysplasia. The frequencies of any lesions of urinary bladder were not reduced by DITC in post-initiation phase. Dietary exposure of this agent in initiation phase reduced significantly both BrdU-LI and cyclin D1-positive cell ratios in any bladder lesions. Administration of DITC in post-initiation phase also significantly reduced BrdU-LI in bladder neoplasms and hyperplasia and cyclin D1-positive cell ratios in urinary bladder carcinoma as well as dysplasia. These results suggest that dietary DITC could be a preventive agent against BBN-induced bladder carcinogenesis in mice when fed during the initiation phase.

Dietary Supplementation with Silymarin Inhibits 3,2'-Dimethyl-4-Aminobiphenyl-Induced Prostate Carcinogenesis in Male F344 Rats

PURPOSE

Silymarin has been shown to be a potent anticarcinogenic agent. Here, we investigated the modifying effects of dietary feeding with a naturally occurring polyphenolic antioxidant flavonoid silymarin on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced prostatic carcinogenesis in male F344 rats.

EXPERIMENTAL DESIGN

Male F344 rats were given s.c. injections of DMAB (25 mg/kg body weight) every other week for 20 weeks. They also received the experimental diet containing 100 or 500 ppm silymarin for 40 weeks, starting 1 week after the last dosing of DMAB. All of the rats were sacrificed 60 weeks after the start of the experiment. Histopathology and immunohistochemistry for proliferative cell nuclear antigen, cyclin D1, and apoptotic indices were done in the prostatic lesions, including invasive adenocarcinomas, intraepithelial neoplasms, and nonlesional glands.

RESULTS

Dietary feeding with 500 ppm silymarin significantly inhibited the incidence of prostatic adenocarcinoma when compared with the DMAB-alone group (17.6% versus 50.0%, P < 0.05). The proliferative cell nuclear antigen- and cyclin D1-positive indices in adenocarcinomas, prostatic intraepithelial neoplasm, and nonlesional glands in rats treated with DMAB and silymarin were slightly lower than that of the DMAB-alone group. Also, dietary administration of silymarin increased apoptotic index in prostatic adenocarcinoma by measuring immunohistochemically positive nuclei for ssDNA.

CONCLUSIONS

Our results indicate that silymarin exerts chemopreventive ability against chemically induced prostatic carcinogenesis through apoptosis induction and modification of cell proliferation.

Silybin and silymarin--new effects and applications

This article aims to review critically literature published mainly within this millennium on the new and emerging applications of silymarin, the polyphenolic fraction from the seeds of Silybum marianum and its main component silybin. Silymarin and silybin used so far mostly as hepatoprotectants were shown to have other interesting activities as e.g., anticancer and canceroprotective. These activities were demonstrated in a large variety of illnesses of different organs as e.g., prostate, lungs, CNS, kidneys, pancreas and others. Besides the cytoprotective activity of silybin mediated by its antioxidative and radical-scavenging properties also new activities based on the specific receptor interaction were discovered--e.g., inhibition and modulation of drug transporters, P-glycoproteins, estrogenic receptors, nuclear receptors and some others. New derivatives of silybin open new ways to its therapeutic applications. Pharmacology dealing with optically pure silybin diastereomers may suggest new mechanisms of its action.

Cancer prevention by natural compounds

Increasing attention is being paid to the possibility of applying cancer chemopreventive agents for individuals at high risk of neoplastic development. For this purpose by natural compounds have practical advantages with regard to availability, suitability for oral application, regulatory approval and mechanisms of action. Candidate substances such as phytochemicals present in foods and their derivatives have been identified by a combination of epidemiological and experimental studies. Plant constituents include vitamin derivatives, phenolic and flavonoid agents, organic sulfur compounds, isothiocyanates, curcumins, fatty acids and d-limonene. Examples of compounds from animals are unsaturated fatty acids and lactoferrin. Recent studies have indicated that mechanisms underlying chemopreventive potential may be combinations of anti-oxidant, anti-inflammatory, immune-enhancing, and anti-hormone effects, with modification of drug-metabolizing enzymes, influence on the cell cycle and cell differentiation, induction of apoptosis and suppression of proliferation and angiogenesis playing roles in the initiation and secondary modification stages of neoplastic development. Accordingly, natural agents are advantageous for application to humans because of their combined mild mechanism. Here we review naturally occurring compounds useful for cancer chemprevention based on in vivo studies with reference to their structures, sources and mechanisms of action.

Anti-tumour effects of nobiletin, a citrus flavonoid, on gastric cancer include: antiproliferative effects, induction of apoptosis and cell cycle deregulation

AIM

To demonstrate the antitumour effects of nobiletin (5,6,7,8,3',4'-hexamethoxyflavone), a citrus flavonoid extracted from Citrus depressa Hayata, on human gastric cancer cell lines TMK-1, MKN-45, MKN-74 and KATO-III.

MATERIALS AND METHODS

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, the TdT-mediated dUTP biotin nick-end labelling (TUNEL) method and cell-cycle analysis revealed that nobiletin acted on these cells in several ways, namely by direct cytotoxicity, induction of apoptosis and modulation of cell cycle. The efficacy of combined treatment of nobiletin with a conventional anticancer drug, CDDP, was also examined. Treatment with nobiletin 24 h prior to CDDP administration showed a synergistic effect compared to the control.

CONCLUSIONS

Although the effective dose and administration route of nobiletin require further investigation, our study represents a potential successful linking of this compound with the treatment of gastric cancer.

Silymarin, a naturally occurring polyphenolic antioxidant flavonoid, inhibits azoxymethane-induced colon carcinogenesis in male F344 rats

The modifying effect of dietary administration of the polyphenolic antioxidant flavonoid silymarin, isolated from milk thistle [Silybum marianum (L.) Gaertneri], on AOM-induced colon carcinogenesis was investigated in male F344 rats. In the short-term study, the effects of silymarin on the development of AOM-induced colonic ACF, being putative precursor lesions for colonic adenocarcinoma, were assayed to predict the modifying effects of dietary silymarin on colon tumorigenesis. Also, the activity of detoxifying enzymes (GST and QR) in liver and colonic mucosa was determined in rats gavaged with silymarin. Subsequently, the possible inhibitory effects of dietary feeding of silymarin on AOM-induced colon carcinogenesis were evaluated using a long-term animal experiment. In the short-term study, dietary administration of silymarin (100, 500 and 1,000 ppm in diet), either during or after carcinogen exposure, for 4 weeks caused significant reduction in the frequency of colonic ACF in a dose-dependent manner. Silymarin given by gavage elevated the activity of detoxifying enzymes in both organs. In the long-term experiment, dietary feeding of silymarin (100 and 500 ppm) during the initiation or postinitiation phase of AOM-induced colon carcinogenesis reduced the incidence and multiplicity of colonic adenocarcinoma. The inhibition by feeding with 500 ppm silymarin was significant (p < 0.05 by initiation feeding and p < 0.01 by postinitiation feeding). Also, silymarin administration in the diet lowered the PCNA labeling index and increased the number of apoptotic cells in adenocarcinoma. beta-Glucuronidase activity, PGE(2) level and polyamine content were decreased in colonic mucosa. These results clearly indicate a chemopreventive ability of dietary silymarin against chemically induced colon tumorigenesis and will provide a scientific basis for progression to clinical trials of the chemoprevention of human colon cancer.