Safety of purified isoflavones in men with clinically localized prostate cancer

Anti-cancer potential of synergistic phytochemical combinations is influenced by the genetic profile of prostate cancer cell lines

Introduction

Despite strong epidemiological evidence that dietary factors modulate cancer risk, cancer control through dietary intervention has been a largely intractable goal for over sixty years. The effect of tumour genotype on synergy is largely unexplored.

Methods

The effect of seven dietary phytochemicals, quercetin (0-100 μM), curcumin (0-80 μM), genistein, indole-3-carbinol (I3C), equol, resveratrol and epigallocatechin gallate (EGCG) (each 0-200 μM), alone and in all paired combinations om cell viability of the androgen-responsive, pTEN-null (LNCaP), androgen-independent, pTEN-null (PC-3) or androgen-independent, pTEN-positive (DU145) prostate cancer (PCa) cell lines was determined using a high throughput alamarBlue^® assay. Synergy, additivity and antagonism were modelled using Bliss additivism and highest single agent equations. Patterns of maximum synergy were identified by polygonogram analysis. Network pharmacology approaches were used to identify interactions with known PCa protein targets.

Results

Synergy was observed with all combinations. In LNCaP and PC-3 cells, I3C mediated maximum synergy with five phytochemicals, while genistein was maximally synergistic with EGCG. In contrast, DU145 cells showed resveratrol-mediated maximum synergy with equol, EGCG and genistein, with I3C mediating maximum synergy with only quercetin and curcumin. Knockdown of pTEN expression in DU145 cells abrogated the synergistic effect of resveratrol without affecting the synergy profile of I3C and quercetin.

Discussion

Our study identifies patterns of synergy that are dependent on tumour cell genotype and are independent of androgen signaling but are dependent on pTEN. Despite evident cell-type specificity in both maximally-synergistic combinations and the pathways that phytochemicals modulate, these combinations interact with similar prostate cancer protein targets. Here, we identify an approach that, when coupled with advanced data analysis methods, may suggest optimal dietary phytochemical combinations for individual consumption based on tumour molecular profile.Graphical abstract.

A phase II randomized clinical trial using aglycone isoflavones to treat patients with localized prostate cancer in the pre-surgical period prior to radical prostatectomy

Prostate cancer (PCa) is the most common cancer in American men. Additionally, African American Men (AAM) are 60% more likely to be diagnosed with PCa and 2.4 times more likely to die from this disease compared to Caucasian men (CM). To date, there are few strategies effective for chemoprevention for men with localized PCa. There is thus a need to continue to evaluate agents and strategies for chemoprevention of prostate cancer. Epidemiological, laboratory and early phase clinical trials have shown that the isoflavones modulates several biomarkers implicated in prostate carcinogenesis. The goal of this phase II randomized clinical trial was to explore the comparative effectiveness and safety of 40 mgs of aglycone isoflavones in AAM and CM with localized PCa in the pre-surgical period prior to radical prostatectomy. Thirty six participants (25 CM, 6AAM) were randomized to the isoflavone arm and 34 (25 CM, 7AAM) to the placebo arm, with 62 completing the intervention. Results indicated that isoflavones at a dose of 20 mgs BID for 3-6 weeks was well tolerated but did not reduce tissue markers of proliferation. A significant reduction in serum PSA was observed with isoflavone supplementation in CM compared to the placebo arm, but not observed in AAM. We observed no changes in serum steroid hormones with isoflavone supplementation. In AAM, a reduction in serum IGF-1 concentrations and IGF1: IGFBP-3 ratios were observed with isoflavone supplementation. Well-powered studies for longer duration of intervention may inform future trials with isoflavones, for chemoprevention of PCa.

American Ginseng (Panax quinquefolium L.) as a Source of Bioactive Phytochemicals with Pro-Health Properties

Panax quinquefolium L. (American Ginseng, AG) is an herb characteristic for regions of North America and Asia. Due to its beneficial properties it has been extensively investigated for decades. Nowadays, it is one of the most commonly applied medical herbs worldwide. Active compounds of AG are ginsenosides, saponins of the glycosides group that are abundant in roots, leaves, stem, and fruits of the plant. Ginsenosides are suggested to be primarily responsible for health-beneficial effects of AG. AG acts on the nervous system; it was reported to improve the cognitive function in a mouse model of Alzheimer's disease, display anxiolytic activity, and neuroprotective effects against neuronal damage resulting from ischemic stroke in animals, demonstrate anxiolytic activity, and induce neuroprotective effects against neuronal damage in ischemic stroke in animals. Administration of AG leads to inhibition of hypertrophy in heart failure by regulation of reactive oxygen species (ROS) in mice as well as depletion of cardiac contractile function in rats. It also has an anti-diabetic and anti-obesity potential as it increases insulin sensitivity and inhibits formation of adipose tissue. AG displays anti-cancer effect by induction of apoptosis of cancer cells and reducing local inflammation. It exerts antimicrobial effects against several pathogenic strains of bacteria. Therefore, AG presents a high potential to induce beneficial health effects in humans and should be further explored to formulate precise nutritional recommendations, as well as to assess its value in prevention and therapy of some disorders, including cancer.

Recent progress on nutraceutical research in prostate cancer

Recently, nutraceuticals have received increasing attention as the agents for cancer prevention and supplement with conventional therapy. Prostate cancer (PCa) is the most frequently diagnosed cancer and second leading cause of cancer-related death in men in the US. Growing evidences from epidemiological studies, in vitro experimental studies, animal studies, and clinical trials have shown that nutraceuticals could be very useful for the prevention and treatment of PCa. Several nutraceuticals including isoflavone, indole-3-carbinol, 3,3'-diindolylmethane, lycopene, (-)-epigallocatechin-3-gallate, and curcumin are known to downregulate the signal transductions in AR, Akt, NF-κB, and other signal transduction pathways which are vital for the development of PCa and the progression of PCa from androgen-sensitive to castrate-resistant PCa. Therefore, nutraceutical treatment in combination with conventional therapeutics could achieve better treatment outcome in prostate cancer therapy. Interestingly, some nutraceuticals could regulate the function of cancer stem cell (CSC)-related miRNAs and associated molecules, leading to the inhibition of prostatic CSCs which are responsible for drug resistance, tumor progression, and recurrence of PCa. Hence, nutraceuticals may serve as powerful agents for the prevention of PCa progression and they could also be useful in combination with chemotherapeutics or radiotherapy. Such strategy could become a promising newer approach for the treatment of metastatic PCa with better treatment outcome by improving overall survival.

Soy and soy isoflavones in prostate cancer: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

To evaluate the evidence from randomized controlled trials (RCTs) on the efficacy and safety of soy/isoflavones in men with prostate cancer (PCa) or with a clinically identified risk of PCa.

PATIENTS AND METHODS

MEDLINE, EMBASE, the Allied and Complementary Medicine (AMED), the Cumulative Index to Nursing and Allied Health Literature (CINAHL) and the Cochrane Library databases were searched. We identified RCTs investigating soy/soy isoflavones as dietary supplements or dietary components for the secondary prevention or treatment of PCa in men with PCa or with a clinically identified risk of developing PCa. Studies of multi-component formulations were excluded. Six authors were contacted for further information for the meta-analyses. Methodological quality was assessed using the Cochrane Collaboration's risk-of- bias tool. The PRISMA statement for reporting systematic reviews was followed.

RESULTS

Of the eight RCTs that met the inclusion criteria, six restricted recruitment to men diagnosed with PCa, while two included men with clinically identified risk of PCa. A large degree of heterogeneity was found with respect to dosages and preparations of soy/isoflavones administered. Most studies had small sample sizes and were of short duration. The risk of bias was assessed as low in all assessed studies except for one, for which the risk of bias was unclear. Meta-analyses of the two studies including men with identified risk of PCa found a significant reduction in PCa diagnosis after administration of soy/soy isoflavones (risk ratio = 0.49, 95% CI 0.26, 0.95). Meta-analyses indicated no significant differences between groups for prostate-specific antigen (PSA) levels or sex steroid endpoints (sex hormone-binding globulin [SHBG], testosterone, free testosterone, oestradiol and dihydrotestosterone).

CONCLUSIONS

The results of a meta-analysis of two studies suggest there may be support for epidemiological findings of a potential role for soy/soy isoflavones in PCa risk reduction; however, a clear understanding of the impact of soy/isoflavones on PSA, total testosterone, free testosterone and SHBG levels in men with, or at identified risk of, PCa could not be derived from these data, given the limitations of sample size and study duration in individual trials. A good safety profile is shown by this meta-analysis for soy/soy isoflavones supplementation.

Proceedings of the Indo-U.S. bilateral workshop on accelerating botanicals/biologics agent development research for cancer chemoprevention, treatment, and survival

With the evolving evidence of the promise of botanicals/biologics for cancer chemoprevention and treatment, an Indo-U.S. collaborative Workshop focusing on “Accelerating Botanicals Agent Development Research for Cancer Chemoprevention and Treatment” was conducted at the Moffitt Cancer Center, 29–31 May 2012. Funded by the Indo-U.S. Science and Technology Forum, a joint initiative of Governments of India and the United States of America and the Moffitt Cancer Center, the overall goals of this workshop were to enhance the knowledge (agents, molecular targets, biomarkers, approaches, target populations, regulatory standards, priorities, resources) of a multinational, multidisciplinary team of researcher's to systematically accelerate the design, to conduct a successful clinical trials to evaluate botanicals/biologics for cancer chemoprevention and treatment, and to achieve efficient translation of these discoveries into the standards for clinical practice that will ultimately impact cancer morbidity and mortality. Expert panelists were drawn from a diverse group of stakeholders, representing the leadership from the National Cancer Institute's Office of Cancer Complementary and Alternative Medicine (OCCAM), NCI Experimental Therapeutics (NExT), Food and Drug Administration, national scientific leadership from India, and a distinguished group of population, basic and clinical scientists from the two countries, including leaders in bioinformatics, social sciences, and biostatisticians. At the end of the workshop, we established four Indo-U.S. working research collaborative teams focused on identifying and prioritizing agents targeting four cancers that are of priority to both countries. Presented are some of the key proceedings and future goals discussed in the proceedings of this workshop.

Advances in prostate cancer chemoprevention: a translational perspective

Chemopreventive interventions are steadily emerging as an important aspect of cancer management and control. Herein, we have discussed the major epidemiological and clinical studies advocating the role of androgen inhibitors, flavonoids and antioxidants in preventing prostate cancer (PCa). Androgen inhibitors have lately been discussed not only in treatment of PCa, but also as preventive agents especially after trials with Finasteride and Dutasteride. Flavonoids such as silibinin, green tea polyphenols, genistein, curcumin have shown great promise, but avenues to improve their bioavailability are requisite. Agents with antioxidant potentials like lycopene, selenium, and vitamin E have also been explored. Antioxidant trials have yielded mixed results or benefitted only a subgroup of population, although further studies are needed to establish them as preventive agent. Although a majority of the trials resulted in positive outcomes supporting their role as preventive agents; one should be cautious of neutral or negative results as well. For clinical applicability of these agents, we need to identify the ideal target population, time of intervention, appropriate dosage, and extent of intervention required. Incoherency of data with these agents urges for a stringent study design and thorough interpretation to accurately judge the necessity and feasibility of the preventive measures.

Chemoprevention of prostate cancer by isoflavonoids

In Europe, prostate cancer (PC) is the most common malignancy in males. There are three known risk factors strongly coherent to the development of PC: heredity, ethnical origin, and age. Migration studies have shown that environmental factors may influence the development of PC. In this context, specific nutritional components may exert an influence on the tumorigenesis of PC. Primary prevention of PC is still an important issue due to its high prevalence, treatment-associated morbidities, and long-term complications. Phytoestrogenes as flavonoids seem to play an essential role in the chemoprevention of PC which is possibly due to their hormonal function and antioxidative capability. Flavonoids and their subgroups are naturally existent in traditional asian and vegetarian nutrients as coverings of plants, fruits, and vegetables. Two of the most frequently investigated flavonoids are genistein and quercetin. These nutritional components may have therapeutic potential and may impact the development of PC. Even though these flavonoids show promising results in the chemoprevention of PC, the literature is almost experimental, epidemiological, and retrospective with a missing long-term follow-up. Therefore, randomized clinical trials are urgently needed to evaluate in depth its oncologic effects in PC.

Prostate cancer chemoprevention in men of African descent: current state of the art and opportunities for future research

Prostate cancer is the most frequently diagnosed malignancy in men. However, African American/Black men are 60 % more likely to be diagnosed with and 2.4 times more likely to die from prostate cancer, compared to Non-Hispanic White men. Despite the increased burden of this malignancy, no evidence-based recommendation regarding prostate cancer screening exists for the high-risk population. Moreover, in addition to screening and detection, African American men may constitute a prime population for chemoprevention. Early detection and chemoprevention may thus represent an integral part of prostate cancer control in this population. Importantly, recent research has elucidated biological differences in the prostate tumors of African American compared to European American men. The latter may enable a more favorable response in African American men to specific chemopreventive agents that target relevant signal transduction pathways. Based on this evolving evidence, the aims of this review are threefold. First, we aim to summarize the biological differences that were reported in the prostate tumors of African American and European American men. Second, we will review the single- and multi-target chemopreventive agents placing specific emphasis on the pathways implicated in prostate carcinogenesis. And lastly, we will discuss the most promising nutraceutical chemopreventive compounds. Our review underscores the promise of chemoprevention in prostate cancer control, as well as provides justification for further investment in this filed to ultimately reduce prostate cancer morbidity and mortality in this high-risk population of African American men.

Molecular Targeted Therapies Using Botanicals for Prostate Cancer Chemoprevention

In spite of the large number of botanicals demonstrating promise as potential cancer chemopreventive agents, most have failed to prove effectiveness in clinical trials. Critical requirements for moving botanical agents to recommendation for clinical use include adopting a systematic, molecular-target based approach and utilizing the same ethical and rigorous methods that are used to evaluate other pharmacological agents. Preliminary data on a mechanistic rationale for chemoprevention activity as observed from epidemiological, in vitro and preclinical studies, phase I data of safety in suitable cohorts, duration of intervention based on time to progression of pre-neoplastic disease to cancer and using a valid panel of biomarkers representing the hypothesized carcinogenesis pathway for measuring efficacy must inform the design of clinical trials. Botanicals have been shown to influence multiple biochemical and molecular cascades that inhibit mutagenesis, proliferation, induce apoptosis, suppress the formation and growth of human cancers, thus modulating several hallmarks of carcinogenesis. These agents appear promising in their potential to make a dramatic impact in cancer prevention and treatment, with a significantly superior safety profile than most agents evaluated to date. The goal of this paper is to provide models of translational research based on the current evidence of promising botanicals with a specific focus on targeted therapies for PCa chemoprevention.

Prostate Cancer Chemoprevention Targeting High Risk Populations: Model for Trial Design and Outcome Measures

Inspite of the large number of promising nutrient-derived agents demonstrating promise as potential chemopreventive agents, most have failed to prove effectiveness in clinical trials. Critical requirements for moving nutrient-derived agents to recommendation for clinical use include adopting a systematic, molecular-mechanism based approach and utilizing the same ethical and rigorous methods such as are used to evaluate other pharmacological agents. Preliminary data on a mechanistic rationale for chemoprevention activity as observed from epidemiological, in vitro and preclinical studies, phase I data of safety in high-risk cohorts are required to inform design of phase II clinical trials. Additionally, a valid panel of biomarkers representing the hypothesized carcinogenesis pathway for measuring efficacy must be utilized to evaluate effectiveness in these trials. The goal of this paper is to provide a model, using a systematic approach for evaluating the safety, effectiveness and mechanism of action of a well characterized nutrient-derived agent-isoflavones - in a phase II clinical trial for prostate cancer (CaP) chemoprevention, targeting a population of African American (AA) and Caucasian men. Based on our previous observations, we hypothesize that the effects of isoflavones on prostate carcinogenesis are mainly mediated through the down regulation of androgen receptor (AR) and AR activity in AA men is higher due to its shorter length of Glutamine repeats in its N-terminus. We thus believe that isoflavones will exert a stronger protective effect for CaP in AA men and cause a higher activation of FOXO factors and their target genes. The aim of the study is to evaluate the comparative effectiveness of the study agent and placebo, in addition to a comparison of the effectiveness and safety in African American men compared to Caucasian men treated with this agent.

Soy isoflavones sensitize cancer cells to radiotherapy

Soy isoflavones are dietary compounds isolated from soybeans, which are safe for human use and have mild anti-cancer properties. Soy isoflavones inhibit the activity of transcription factors and genes essential for tumor cell proliferation, invasion, and neovascularization, and it appears that soy isoflavones may enhance the effectiveness of conventional therapies against cancer. Soy isoflavones could be an effective complementary treatment given that they inhibit the survival signaling pathways of various cancer cells through altered activation of APE1/Ref-1, NF-κB, and HIF-1α, which are genes essential for tumor cell survival, tumor growth, and angiogenesis, thus making such cells more sensitive to radiotherapy. Studies in which soy isoflavones were given in conjunction with radiotherapy to prostate cancer patients suggest that soy isoflavones might also mitigate the adverse effects of radiation on normal tissues, probably by acting as antioxidants. These observations open new avenues for exploiting soy isoflavones as supplements to conventional therapies.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.

Role of phytoestrogens in cancer therapy

Cancer is a leading cause of death worldwide, and the numbers of new cancer cases are expected to continue to rise. The main goals of cancer therapy include removing the primary tumor, preventing the spread of distant metastases, and improving survival and quality of life for the patients. To attain these goals of cancer therapy, the combination of different chemotherapeutics, as opposed to the conventional single-agent treatment, is an emerging area of research. Given the potential risks of drug toxicity in such treatment, the focus is to have a second compound that increases the anticancer potential of the primary agent but which reduces toxicity. There is an ever growing interest in treatment with natural compounds, such as plant phytoestrogens, as an adjuvant cancer therapy along with conventional cancer therapy. The question remains whether or not adding these compounds to the cancer therapy regimen as a second agent would be beneficial, and if they are safe to be used among cancer patients. The current literature suggests that phytoestrogen treatment is capable of inducing G2/M cell cycle arrest in a number of cancer cell lines, as well as upregulating cell cycle inhibitory molecules. Phytoestrogen therapy has been shown to inhibit inflammation, angiogenesis and metastases in various IN VIVO tumor models, and pronounced benefits have been observed when combined with radiation therapy. The lack of side effects from phase I and II clinical trials of phytoestrogens in cancer therapy points towards their safety, but to further understand their added benefit clinical studies with large sample sizes are required. We have reviewed the recent research studies in these areas in an attempt to find evidence for their role in cancer therapy as well as safety.

Effects of a high dose, aglycone-rich soy extract on prostate-specific antigen and serum isoflavone concentrations in men with localized prostate cancer

The efficacy and safety of consuming high-dose isoflavone supplements for prostate cancer is not clear. A double-blind, placebo controlled, randomized trial was conducted in 53 men with prostate cancer enrolled in an active surveillance program. The treatment group consumed a supplement containing 450 mg genistein, 300 mg daidzein, and other isoflavones daily for 6 mo. Prostate-specific antigen (PSA) was measured in both groups at baseline, 3 mo, and 6 mo, and serum concentrations of genistein, daidzein, and equol were assessed at baseline and 6 mo in the treatment group. Following the completion of the 6-mo double-blind study, men were enrolled in a 6-mo open label trial with the same isoflavone-rich supplement, and PSA was measured at 3 and 6 mo. PSA concentrations did not change in either group after 6 mo or after 12 mo when the open-label study was included. The 6 mo serum concentrations of genistein and daidzein (39.85 and 45.59 μmol/l, respectively) were significantly greater than baseline values and substantially higher than levels previously reported in other studies. Equol levels did not change. Although high amounts of aglycone isoflavones may result in significantly elevated serum concentrations of genistein and daidzein, these dietary supplements alone did not lower PSA levels in men with low-volume prostate cancer.

Results of a randomized phase I dose-finding trial of several doses of isoflavones in men with localized prostate cancer: administration prior to radical prostatectomy

The purpose of this phase I dose-finding randomized controlled trial was to evaluate the safe and effective dose of isoflavones to be used in future clinical trials for prostate cancer prevention. Forty-five eligible men were supplemented with 40, 60, and 80 mg of purified isoflavones or no supplement from biopsy to prostatectomy. Compliance with the study agent, toxicity, and changes in plasma isoflavones, serum steroid hormones, prostate-specific antigen (PSA), and tissue Ki-67 were analyzed from baseline to completion of the study. Forty-four subjects completed the study with a duration of intervention of 30 (+/- 3) days. We observed significant increases in plasma isoflavones with treatment for all doses compared with controls without producing any toxicity. Significant increases in serum total estradiol were observed in the 40 and 60 mg isoflavone-treated arms. However, a significant increase in serum free testosterone was observed in the 60 mg isoflavone-treated arm. Changes in serum sex hormone-binding globulin, PSA, and percentage of tissue Ki-67 were not statistically significant with treatment for this sample size and duration of intervention. Our results identify a safe dose of purified isoflavones for future clinical trials and establish the need for further definitive, well-powered trials to examine the role of isoflavones in prostate carcinogenesis.

Isoflavone supplements stimulated the production of serum equol and decreased the serum dihydrotestosterone levels in healthy male volunteers

The aim of this study was to evaluate the effect of supplementing healthy men with soy isoflavones on the serum levels of sex hormones implicated in prostate cancer development. A total of 28 Japanese healthy volunteers (18 equol producers and 10 equol non-producers) between 30 and 59 years of age were given soy isoflavones (60 mg daily) supplements for 3 months, and the changes in their sex hormone levels were investigated at the baseline and after administration. The serum and urine concentrations of daidzein, genistein, and the levels of equol in the fasting blood samples and 24-h stored urine samples were also measured. All 28 volunteers completed the 3-month supplementation with isoflavone. No changes in the serum levels of estradiol and total testosterone were detected after 3-month supplementation. The serum levels of sex hormone-binding globulin significantly increased, and the serum levels of free testosterone and dihydrotestosterone (DHT) decreased significantly after 3-month supplementation. Among the 10 equol non-producers, equol became detectable in the serum of two healthy volunteers after 3-month supplementation. This study revealed that short-term administration of soy isoflavones stimulated the production of serum equol and decreased the serum DHT level in Japanese healthy volunteers. These results suggest the possibility of converting equol non-producers to producers by prolonged and consistent soy isoflavones consumption.