Effects of dietary energy repletion and IGF-1 infusion on the inhibition of mammary carcinogenesis by dietary energy restriction

Dietary Factors and Prostate Cancer Development, Progression, and Reduction

Due to the constantly increasing number of cases, prostate cancer has become one of the most important health problems of modern societies. This review presents the current knowledge regarding the role of nutrients and foodstuff consumption in the etiology and development of prostate malignancies, including the potential mechanisms of action. The results of several in vivo and in vitro laboratory experiments as well as those reported by the clinical and epidemiological research studies carried out around the world were analyzed. The outcomes of these studies clearly show the influence of both nutrients and food products on the etiology and prevention of prostate cancer. Consumption of certain nutrients (saturated and trans fatty acids) and food products (e.g., processed meat products) leads to the disruption of prostate hormonal regulation, induction of oxidative stress and inflammation, and alteration of growth factor signaling and lipid metabolism, which all contribute to prostate carcinogenesis. On the other hand, a high consumption of vegetables, fruits, fish, and whole grain products exerts protective and/or therapeutic effects. Special bioactive functions are assigned to compounds such as flavonoids, stilbenes, and lycopene. Since the influence of nutrients and dietary pattern is a modifiable risk factor in the development and prevention of prostate cancer, awareness of the beneficial and harmful effects of individual food ingredients is of great importance in the global strategy against prostate cancer.

Dynamics of breast tumor incidence, tumor volume and serum metabolic hormones in calorie restricted rats

Reports of the effects of calorie restriction on tumors after the tumor has developed are uncommon and limited to a few tumor types. We investigated the effects of calorie restriction on tumor growth in breast cancer after tumor growth had progressed. We used the N-nitroso-N-methylurea (NMU) induced breast cancer model in rats. In addition to a healthy control group (C), rats with 10 - 12 mm tumors were divided into three groups: cancer control group (CC), alternate day feeding group (ADF) and calorie restriction group (CR-50%). At the end of the experimental period the volume of tumors was decreased in the CR-50% group compared to the CC group. Serum adiponectin concentrations for the C and ADF groups were higher than for the CC group. All tumors of the CR-50% group were benign. The highest incidence of malignant and invasive tumors occurred in the CC group. A 50% calorie restriction appears to be an effective dietary intervention for advanced tumors.

Effect of Intermittent versus Chronic Calorie Restriction on Tumor Incidence: A Systematic Review and Meta-Analysis of Animal Studies

Both chronic calorie restriction (CCR) and intermittent calorie restriction (ICR) have shown anticancer effects. However, the direct evidence comparing ICR to CCR with respect to cancer prevention is controversial and inconclusive. PubMed and Web of Science were searched on November 25, 2015. The relative risk (RR) [95% confidence interval (CI)] was calculated for tumor incidence, and the standardised mean difference (95% CI) was computed for levels of serum insulin-like growth factor-1 (IGF-1), leptin, and adiponectin using a random-effects meta-analysis. Sixteen studies were identified, including 11 using genetically engineered mouse models (908 animals with 38-76 weeks of follow-up) and 5 using chemically induced rat models (379 animals with 7-18 weeks of follow-up). Compared to CCR, ICR decreased tumor incidence in genetically engineered models (RR = 0.57; 95% CI: 0.37, 0.88) but increased the risk in chemically induced models (RR = 1.53, 95% CI: 1.13, 2.06). It appears that ICR decreases IGF-1 and leptin and increases adiponectin in genetically engineered models. Thus, the evidence suggests that ICR exerts greater anticancer effect in genetically engineered mouse models but weaker cancer prevention benefit in chemically induced rat models as compared to CCR. Further studies are warranted to confirm our findings and elucidate the mechanisms responsible for these effects.

Gender Differences in Response to Prolonged Every-Other-Day Feeding on the Proliferation and Apoptosis of Hepatocytes in Mice

Intermittent fasting decreases glucose and insulin levels and increases insulin sensitivity and lifespan. Decreased food intake influences the liver. Previous studies have shown gender differences in response to various types of caloric restriction, including every-other-day (EOD) feeding, in humans and rodents. Our goal was to show the influence of prolonged EOD feeding on the morphology, proliferation and apoptosis of livers from male and female mice. After nine months of an EOD diet, the livers from male and female mice were collected. We examined their morphology on histological slides using the Hematoxilin and Eosine (H_E) method and Hoechst staining of cell nuclei to evaluate the nuclear area of hepatocytes. We also evaluated the expression of mRNA for proto-oncogens, pro-survival proteins and apoptotic markers using Real Time Polimerase Chain Reaction (PCR). We noted increased lipid content in the livers of EOD fed female mice. EOD feeding lead to a decrease of proliferation and apoptosis in the livers of female and male mice, which suggest that tissue maintenance occurred during EOD feeding. Our experiment revealed sex-specific expression of mRNA for proto-oncogenes and pro-survival and pro-apoptotic genes in mice as well as sex-specific responses to the EOD treatment.

Hepatocellular carcinoma and lifestyles

The majority of hepatocellular carcinoma occurs over pre-existing chronic liver diseases that share cirrhosis as an endpoint. In the last decade, a strong association between lifestyle and hepatocellular carcinoma has become evident. Abundance of energy-rich food and sedentary lifestyles have caused metabolic conditions such as obesity and diabetes mellitus to become global epidemics. Obesity and diabetes mellitus are both tightly linked to non-alcoholic fatty liver disease and also increase hepatocellular carcinoma risk independent of cirrhosis. Emerging data suggest that physical activity not only counteracts obesity, diabetes mellitus and non-alcoholic fatty liver disease, but also reduces cancer risk. Physical activity exerts significant anticancer effects in the absence of metabolic disorders. Here, we present a systematic review on lifestyles and hepatocellular carcinoma.

Roles of caloric restriction, ketogenic diet and intermittent fasting during initiation, progression and metastasis of cancer in animal models: a systematic review and meta-analysis

BACKGROUND

The role of dietary restriction regimens such as caloric restriction, ketogenic diet and intermittent fasting in development of cancers has been detected via abundant preclinical experiments. However, the conclusions are controversial. We aim to review the relevant animal studies systematically and provide assistance for further clinical studies.

METHODS

Literatures on associations between dietary restriction and cancer published in PubMed in recent twenty years were comprehensively searched. Animal model, tumor type, feeding regimen, study length, sample size, major outcome, conclusion, quality assessment score and the interferential step of cancer were extracted from each eligible study. We analyzed the tumor incidence rates from 21 studies about caloric restriction.

RESULTS

Fifty-nine studies were involved in our system review. The involved studies explored roles of dietary restriction during initiation, progression and metastasis of cancer. About 90.9% of the relevant studies showed that caloric restriction plays an anti-cancer role, with the pooled OR (95%CI) of 0.20 (0.12, 0.34) relative to controls. Ketogenic diet was also positively associated with cancer, which was indicated by eight of the nine studies. However, 37.5% of the related studies obtained a negative conclusion that intermittent fasting was not significantly preventive against cancer.

CONCLUSIONS

Caloric restriction and ketogenic diet are effective against cancer in animal experiments while the role of intermittent fasting is doubtful and still needs exploration. More clinical experiments are needed and more suitable patterns for humans should be investigated.

Weight control, endocrine hormones and cancer prevention

The prevalence of obesity is increasing which becomes worrisome due to its association with several diseases and certain types of cancers. While weight control through dietary caloric restriction and/or physical activity protects against cancer in animal models, the underlying mechanisms are not fully defined. Weight loss due to negative energy balance is associated with alterations of multiple growth factors and endocrine hormones. The altered hormones and hormone-related functions appear to be responsible for anti-cancer mechanisms. In this review, we summarize the recent studies related to weight loss and the altered endocrine hormones, focusing on the reduced levels of the mitogenic insulin-like growth factor 1 (IGF-1) and adipokine leptin as well as the raised levels of adiponectin and glucocorticoids. The potential molecular targets of these hormone-dependent signalling pathways are also discussed. Considering the increasing trends of obesity throughout the world, a better understanding of the underlying mechanisms between body weight, endocrine hormones and cancer risk may lead to novel approaches to cancer prevention and treatment.

The ketogenic diet and hyperbaric oxygen therapy prolong survival in mice with systemic metastatic cancer

Introduction

Abnormal cancer metabolism creates a glycolytic-dependency which can be exploited by lowering glucose availability to the tumor. The ketogenic diet (KD) is a low carbohydrate, high fat diet which decreases blood glucose and elevates blood ketones and has been shown to slow cancer progression in animals and humans. Abnormal tumor vasculature creates hypoxic pockets which promote cancer progression and further increase the glycolytic-dependency of cancers. Hyperbaric oxygen therapy (HBO₂T) saturates tumors with oxygen, reversing the cancer promoting effects of tumor hypoxia. Since these non-toxic therapies exploit overlapping metabolic deficiencies of cancer, we tested their combined effects on cancer progression in a natural model of metastatic disease.

Methods

We used the firefly luciferase-tagged VM-M3 mouse model of metastatic cancer to compare tumor progression and survival in mice fed standard or KD ad libitum with or without HBO₂T (2.5 ATM absolute, 90 min, 3x/week). Tumor growth was monitored by in vivo bioluminescent imaging.

Results

KD alone significantly decreased blood glucose, slowed tumor growth, and increased mean survival time by 56.7% in mice with systemic metastatic cancer. While HBO₂T alone did not influence cancer progression, combining the KD with HBO₂T elicited a significant decrease in blood glucose, tumor growth rate, and 77.9% increase in mean survival time compared to controls.

Conclusions

KD and HBO₂T produce significant anti-cancer effects when combined in a natural model of systemic metastatic cancer. Our evidence suggests that these therapies should be further investigated as potential non-toxic treatments or adjuvant therapies to standard care for patients with systemic metastatic disease.

Defining the role of histone deacetylases in the inhibition of mammary carcinogenesis by dietary energy restriction (DER): effects of suberoylanilide hydroxamic acid (SAHA) and DER in a rat model

Dietary energy restriction (DER) inhibits experimentally induced mammary cancer, an effect accompanied by elevated levels of silent information regulator 2 (SIRT1), a class III histone deacetylase (HDAC). However, the effect of DER on targets of other classes of HDACs has not been reported, a highly relevant issue given evidence that HDAC induction favors the development of cancer and tumor growth. Experiments were carried out to determine whether suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor with broad activity, would affect the anti-cancer activity of DER. Female Sprague Dawley rats (n = 30/group) were injected with 1-methyl-1-nitrosourea (50 mg/kg) at 21 days of age and 7 days thereafter were randomized to groups fed: (i) control diet (AIN-93G), (ii) 0.1% SAHA (w/w), (iii) 40% DER, or (iv) 0.1% SAHA + 40% DER. An additional group was fed 0.1% SAHA + 40%DER for 5 weeks and released to control diet for 3 weeks. DER significantly reduced mammary cancer incidence, multiplicity, and cancer burden and prolonged cancer latency (P < 0.01). Cancer inhibition was maintained in SAHA + DER, despite evidence that histone (H2A(Lys9), H2B(Lys5), and H4(Lys5/8/12/16), but not H3(Lys9); P < 0.001) and non-histone protein deacetylation (p53(Lys373) and p53(Lys382); P < 0.001) induced by DER was reversed by SAHA. This indicates that the inhibition of DER of cancer is not dependent on HDAC induction. After releasing rats from DER + SAHA, cancer multiplicity remained lower than control (P < 0.05), consistent with apoptosis-mediated cell deletion. These findings support further investigation of the hypothesis that HDAC induction by DER blunts its anti-carcinogenic impact.

Obesity and cancer risk: evidence, mechanisms, and recommendations

Obesity, a growing health problem worldwide, has been associated with the metabolic syndrome, diabetes, cardiovascular disease, hypertension, and other chronic diseases. Recently, the obesity–cancer link has received much attention. Epidemiological studies have shown that obesity is also associated with increased risk of several cancer types, including colon, breast, endometrium, liver, kidney, esophagus, gastric, pancreatic, gallbladder, and leukemia, and can also lead to poorer treatment and increased cancer-related mortality. Biological mechanisms underlying the relationship between obesity and cancer are not well understood. They include modulation of energy balance and calorie restriction, growth factors, multiple signaling pathways, and inflammatory processes. Key among the signaling pathways linking obesity and cancer is the PI3K/Akt/mTOR cascade, which is a target of many of the obesity-associated factors and regulates cell proliferation and survival. Understanding the molecular and cellular mechanisms of the obesity–cancer connection is important in developing potential therapeutics. The link between obesity and cancer underscores the recommendation to maintain a healthy body weight throughout life as one of the most important ways to protect against cancer.

Dose-dependent effects of calorie restriction on gene expression, metabolism, and tumor progression are partially mediated by insulin-like growth factor-1

The prevalence of obesity, an established risk and progression factor for breast and many other cancer types, remains very high in the United States and throughout the world. Calorie restriction (CR), a reduced-calorie dietary regimen typically involving a 20-40% reduction in calorie consumption, prevents or reverses obesity, and inhibits mammary and other types of cancer in multiple tumor model systems. Unfortunately, the mechanisms underlying the tumor inhibitory effects of CR are poorly understood, and a better understanding of these mechanisms may lead to new intervention targets and strategies for preventing or controlling cancer. We have previously shown that the anticancer effects of CR are associated with decreased systemic levels of insulin-like growth factor-1 (IGF-1), the primary source of which is liver. We have also reported that CR strongly suppresses tumor development and growth in multiple mammary cancer models. To identify CR-responsive genes and pathways, and to further characterize the role of IGF-1 as a mediator of the anticancer effects of CR, we assessed hepatic and mammary gland gene expression, hormone levels and growth of orthotopically transplanted mammary tumors in control and CR mice with and without exogenous IGF-1. C57BL/6 mice were fed either control AIN-76A diet ad libitum (AL), subjected to 20%, 30%, or 40% CR plus placebo timed-release pellets, or subjected to 30% or 40% CR plus timed-release pellets delivering murine IGF-1 (mIGF-1, 20 μg/day). Compared with AL-fed controls, body weights were decreased 14.3% in the 20% CR group, 18.5% in the 30% CR group, and 38% in the 40% CR group; IGF-1 infusion had no effect on body weight. Hepatic transcriptome analyses indicated that compared with 20% CR, 30% CR significantly modulated more than twice the number of genes and 40% CR more than seven times the number of genes. Many of the genes specific to the 40% CR regimen were hepatic stress-related and/or DNA damage-related genes. Exogenous IGF-1 rescued the hepatic expression of several metabolic genes and pathways affected by CR. Exogenous IGF-1 also rescued the expression of several metabolism- and cancer-related genes affected by CR in the mammary gland. Furthermore, exogenous IGF-1 partially reversed the mammary tumor inhibitory effects of 30% CR. We conclude that several genes and pathways, particularly those associated with macronutrient and steroid hormone metabolism, are associated with the anticancer effects of CR, and that reduced IGF-1 levels can account, at least in part, for many of the effects of CR on gene expression and mammary tumor burden.

Effects of energy restriction and wheel running on mammary carcinogenesis and host systemic factors in a rat model

Limiting energy availability via diet or physical activity has health benefits; however, it is not known whether these interventions have similar effects on the development of cancer. Two questions were addressed as follows: (i) Does limiting energy availability by increasing physical activity have the same effect on mammary carcinogenesis as limiting caloric intake? and (ii) Are host systemic factors, implicated as risk biomarkers for breast cancer, similarly affected by these interventions? Female Sprague Dawley rats were injected with 50-mg 1-methyl-1-nitrosourea per kg body weight at 21 days of age and randomized to one of five groups (30 rats per group) as follows: (i) sham running wheel control; (ii) restricted fed to 85% of the sham control; (iii and iv) voluntary running in a motorized activity wheel (37 m/min) to a maximum of 3,500 m/d or 1,750 m/d; and (v) sedentary ad libitum fed control with no access to a running wheel. The three energetics interventions inhibited the carcinogenic response, reducing cancer incidence (P = 0.01), cancer multiplicity (P < 0.001), and cancer burden (P < 0.001) whereas prolonging cancer latency (P = 0.004) although differences among energetics interventions were not significant. Of the plasma biomarkers associated with the development of cancer, the energetics interventions reduced bioavailable insulin-like growth factor-1 (IGF-1), insulin, interleukin-6, serum amyloid protein, TNF-α, and leptin and increased IGF-binding protein 3 (IGFBP-3) and adiponectin. Plasma-fasting glucose, C-reactive protein, estradiol, and progesterone were unaffected. The plasma biomarkers of greatest value in predicting the carcinogenic response were adiponectin > IGF-1/IGFBP-3 > IGFBP-3 > leptin > IGF-1.

POTENTIAL MECHANISMS OF CANCER PREVENTION BY WEIGHT CONTROL

Weight control via dietary caloric restriction and/or physical activity has been demonstrated in animal models for cancer prevention. However, the underlying mechanisms are not fully understood. Body weight loss due to negative energy balance significantly reduces some metabolic growth factors and endocrinal hormones such as IGF-1, leptin, and adiponectin, but enhances glucocorticoids, that may be associated with anti-cancer mechanisms. In this review, we summarized the recent studies related to weight control and growth factors. The potential molecular targets focused on those growth factors- and hormones-dependent cellular signaling pathways are further discussed. It appears that multiple factors and multiple signaling cascades, especially for Ras-MAPK-proliferation and PI3K-Akt-anti-apoptosis, could be involved in response to weight change by dietary calorie restriction and/or exercise training. Considering prevalence of obesity or overweight that becomes apparent over the world, understanding the underlying mechanisms among weight control, endocrine change and cancer risk is critically important. Future studies using "-omics" technologies will be warrant for a broader and deeper mechanistic information regarding cancer prevention by weight control.

Dietary energy balance modulation of epithelial carcinogenesis: a role for IGF-1 receptor signaling and crosstalk

Obesity affects more than one third of the U.S. population and is associated with increased risk and/or disease severity for several chronic diseases, including cancer. In contrast, calorie restriction (CR) consistently inhibits cancer across species and cancer types. Differential effects on globally active circulatory proteins, particularly insulin-like growth factor-1 (IGF-1), provide a plausible mechanistic explanation for the energy balance-cancer link. Diet-induced changes in circulating IGF-1 modulate IGF-1R/EGFR activation and downstream signaling to Akt and mTOR. These dietary energy balance effects on signaling ultimately modulate the levels and/or activity of cell cycle regulatory proteins, regulating proliferation, and modulating susceptibility to tumor development. Selective targeting of mTORC1 potently inhibits tumorigenesis in several model systems producing CR mimetic effects. Targeting this and other pathways modulated by dietary energy balance may lead to the development of strategies for cancer chemoprevention and for reversing the effects of obesity on cancer development and progression.

Metformin as an energy restriction mimetic agent for breast cancer prevention

Background:

This study examined whether metformin administration inhibited chemically induced mammary carcinogenesis in rats. In cancer prevention, metformin may act (1) indirectly through reducing systemic risk factors; or (2) directly through AMPK-mediated signaling. To begin to delineate clinically relevant mechanisms for breast cancer prevention, metformin was also studied along with dietary energy restriction.

Materials and Methods:

Mammary cancer was induced in female Sprague--Dawley rats (50 mg/kg MNU, i.p.). Metformin was fed alone (AIN93G + 0.05 to 1.0% w/w metformin) or combined with 40% dietary energy restriction. Plasma analytes (e.g., insulin, glucose, IGF-1) and protein expression (e.g., AMPK, mTOR, Akt) in mammary carcinomas and liver were evaluated. Additional studies included (1) aldehyde dehydrogenase flow cytometry, to gauge potential for cancer-initiated cells in mammary carcinomas to respond to metformin; (2) cell culture, to understand dose response (0.02--20 mM) of different cancer cell line molecular subtypes to metformin; and (3) analysis of a rat mammary epithelial cell microarray database, to examine expression of genes related to metformin pharmacokinetics (e.g., organic cation transporters) and pharmacodynamics (e.g., complex I of electron transport).

Results:

While a dosing regimen of 1.0%/0.25% metformin-reduced palpable mammary carcinoma incidence, multiplicity, and tumor burden and prolonged latency, lower doses of metformin failed to inhibit carcinogenesis despite effects on plasma insulin. Human breast cancer cell growth inhibition in response to metformin was only observed at high concentrations. Poor in vivo and in vitro response to metformin may be the result of pharmacokinetic (OCT-1 expression was low in rat mammary cells; OCT-3 was downregulated in mammary carcinoma) and pharmacodynamic (complex I transcripts were higher in mammary epithelial cells from carcinomas versus uninvolved gland) effects. In combination with dietary energy restriction, metformin offered protection against new tumor occurrence following release from combined treatment. Flow cytometry indicated the presence of cancer-initiated cells in mammary carcinomas.

Conclusions:

As a single agent, metformin possessed limited cancer inhibitory activity. However, metformin may be an effective component of multiagent interventions that target cancer-initiated cells. There is a clear need to identify the conditions under which metformin is likely to benefit prevention and control of breast cancer.

Cancer as a metabolic disease

Emerging evidence indicates that impaired cellular energy metabolism is the defining characteristic of nearly all cancers regardless of cellular or tissue origin. In contrast to normal cells, which derive most of their usable energy from oxidative phosphorylation, most cancer cells become heavily dependent on substrate level phosphorylation to meet energy demands. Evidence is reviewed supporting a general hypothesis that genomic instability and essentially all hallmarks of cancer, including aerobic glycolysis (Warburg effect), can be linked to impaired mitochondrial function and energy metabolism. A view of cancer as primarily a metabolic disease will impact approaches to cancer management and prevention.

Calories and carcinogenesis: lessons learned from 30 years of calorie restriction research

Calorie restriction (CR) is arguably the most potent, broadly acting dietary regimen for suppressing the carcinogenesis process, and many of the key studies in this field have been published in Carcinogenesis. Translation of the knowledge gained from CR research in animal models to cancer prevention strategies in humans is urgently needed given the worldwide obesity epidemic and the established link between obesity and increased risk of many cancers. This review synthesizes the evidence on key biological mechanisms underlying many of the beneficial effects of CR, with particular emphasis on the impact of CR on growth factor signaling pathways and inflammatory processes and on the emerging development of pharmacological mimetics of CR. These approaches will facilitate the translation of CR research into effective strategies for cancer prevention in humans.

Candidate mechanisms accounting for effects of physical activity on breast carcinogenesis

Evidence is strong that a reduction in risk for breast cancer is associated with moderate to vigorous physical activity (PA); however, there is limited understanding of the role of type, intensity, duration, and frequency of PA and their mechanisms in accounting for this health benefit. The objective of this review is to stimulate investigations of candidate mechanisms that may account for the effects of the intensity and duration of aerobic PA on breast cancer risk and tumor burden. Three hypotheses are considered: 1) the mTOR network hypothesis: PA inhibits carcinogenesis by suppressing the activation of the mTOR signaling network in mammary carcinomas; 2) the hormesis hypothesis: the carcinogenic response to PA is nonlinear and accounted for by a physiological cellular stress response; and 3) the metabolic reprogramming hypothesis: PA limits the amount of glucose and glutamine available to mammary carcinomas thereby inducing apoptosis because tumor-associated metabolic programming is reversed. To link these hypotheses to systemic effects of PA, it is recommended that consideration be given to determining: 1) what contracting muscle releases into circulation or removes from circulation that would directly modulate the carcinogenic process in epithelial cells; 2) whether the effects of muscle contraction on epithelial cell carcinogenesis are exerted in an endocrine, paracrine, autocrine, or intracrine manner; and 3) if the effects of muscle contraction on malignant cells differ from effects on normal or premalignant cells that do not manifest the hallmarks of malignancy.

Serum insulin-like growth factor-I and mammary tumor development in ad libitum-fed, chronic calorie-restricted, and intermittent calorie-restricted MMTV-TGF-alpha mice

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum insulin-like growth factor (IGF)-I levels and mammary tumor (MT) development was investigated. Ten-week-old MMTV-TGF-alpha female mice were assigned to ad libitum-fed (AL; AIN-93M diet), ICR [3-week 50% caloric restriction using AIN-93M-mod diet, 2x protein, fat, vitamins, and minerals followed by 3 weeks of daily 100% AL consumption of AIN-93M ( approximately 75% of AL for each 6-week cycle)], and CCR (calorie and nutrient intake matched for each 6-week ICR cycle) groups. Half of the mice from each group were sacrificed at 79 (end of restriction) or 82 (end of refeeding) weeks of age. Serum was obtained at euthanasia and in cycles 1, 3, 5, 8, and 11. MT incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice. ICR-Restricted mice had significantly lower terminal serum IGF-I and IGF-I/IGF binding protein-3 (IGFBP-3) ratio than CCR, ICR-Refed, and AL mice. There were no differences in terminal IGFBP-3. Final body, internal, and mammary fat pad weights correlated positively with IGF-I and negatively with IGFBP-3. Few changes were found for protein expression of IGF-IRalpha and IGFBP-3 in mammary tissue and MTs. During the study, IGF-I levels of ICR-Restricted mice were reduced, whereas refeeding allowed partial recovery. For all groups, elevated IGF-I levels preceded MT detection, although not all values were significant versus mice without MTs. However, the specific role of IGF-I in the protective effect of calorie restriction remains to be determined. These results confirm that ICR prevents MT development to a greater extent than CCR.

Energy restriction for breast cancer prevention

Weight gain in adult life is an important risk factor for breast cancer. Observational studies indicate that pre- or postmeno-pausal weight loss is associated with a reduction in risk of postmenopausal breast cancer. Here we summarise lifestyle changes including continuous or intermittent energy restriction and/or exercise which may be beneficial for preventing breast cancer and also potential pharmacological approaches to prevention using energy restriction mimetic agents (ERMAs).

Effect of nonmotorized wheel running on mammary carcinogenesis: circulating biomarkers, cellular processes, and molecular mechanisms in rats

The objective of this experiment was to identify circulating growth factors, hormones, and cellular and molecular mechanisms that account for the effects of physical activity on mammary carcinogenesis. A total of 120 female Sprague-Dawley rats were injected with 1-methyl-1-nitrosourea (50 mg/kg) and 7 days thereafter were randomized to either a physically active or a sedentary control group. Individually housed rats were given free access to a nonmotorized, computer-controlled activity wheel and running behavior was reinforced by food reward. Rats self-determined their daily intensity and duration of running. Sedentary control rats received the same amount of food as the physically active rats to which they were paired. Physical activity reduced mammary cancer incidence (P = 0.015) and cancer multiplicity (P = 0.01). Physical activity induced changes in plasma insulin, insulin-like growth factor-I, and corticosterone, suggesting that mechanisms regulating glucose homeostasis were affected. Western blot analyses of mammary carcinomas revealed that proteins involved in cell proliferation were reduced (P < 0.001) and those involved in apoptosis via the mitochondrial pathway were elevated (P < 0.001) by physical activity. The hypothesis that these effects were mediated by activation of AMP-activated protein kinase, and down-regulation of protein kinase B, which collectively down-regulate the activity of the mammalian target of rapamycin, was evaluated. Evidence in support of this hypothesis was found in the Western blot analyses of mammary carcinomas, mammary gland, liver, and skeletal muscle. Collectively, these findings provide a rationale for additional studies of energy-sensing pathways in the elucidation of mechanisms that account for the inhibition of carcinogenesis by physical activity.

Akt-dependent proapoptotic effects of dietary restriction on late-stage management of a phosphatase and tensin homologue/tuberous sclerosis complex 2-deficient mouse astrocytoma

PURPOSE

Malignant astrocytomas exhibit constitutive Akt phosphorylation due to reduced phosphatase and tensin homologue (PTEN) tumor suppressor expression or to increased growth factor receptor tyrosine kinase activation. Many astrocytomas are also tuberous sclerosis complex 2 (TSC2) protein deficient and exhibit constitutive mammalian target of rapamycin (mTOR) activity. Astrocytomas harboring PTEN/Akt/TSC2 pathway mutations are dependent on glycolysis to satisfy their bioenergetic requirements. Therapies that disrupt energy homeostasis can potentially manage astrocytoma growth and progression. Although dietary restriction (DR) reduces glycolysis and manages early-stage astrocytoma growth, no prior studies have identified the mechanisms involved or determined if DR can also manage late-stage tumor growth.

EXPERIMENTAL DESIGN

The effects of a late-onset intermittent DR feeding paradigm were examined in adult C57BL/6J mice bearing the syngeneic CT-2A malignant astrocytoma grown orthotopically or subcutaneously.

RESULTS

In contrast to contralateral normal brain, CT-2A was PTEN/TSC2 protein deficient; exhibited constitutive Akt, mTOR, and BAD phosphorylation; and overexpressed insulin-like growth factor-I (IGF-I), IGF-I receptor, hypoxia-inducible transcription factor-1alpha (HIF-1alpha), type 1 glucose transporter protein (GLUT1), and pyruvate kinase. DR initiated 10 to 14 days after tumor implantation (late onset) reduced CT-2A growth, delayed malignant progression, and significantly extended survival. DR suppressed phosphorylation of Akt and BAD while reducing expression of IGF-I, HIF-1alpha, and GLUT1. DR also enhanced procaspase-9/procaspase-3 cleavage but had no effect mTOR phosphorylation.

CONCLUSIONS

Our findings indicate that IGF-I/Akt signaling is associated with the antiapoptotic and glycolytic phenotype of the CT-2A astrocytoma and that DR targets this pathway. Moreover, PTEN/TSC2 deficiency may impair adaptation to the DR-induced disruption of energy homeostasis, thus enhancing apoptosis. Our findings highlight the efficacy of late-onset DR in managing astrocytoma growth and suggest that DR may be an effective broad-spectrum inhibitor of Akt signaling in PTEN/TSC2-deficient astrocytomas.

Obesity accelerates mouse mammary tumor growth in the absence of ovarian hormones

Obesity increases incidence and mortality of breast cancer in postmenopausal women. Mechanisms underlying this association are poorly understood. Suitable animal models are needed to elucidate potential mechanisms for this association. To determine the effects of obesity on mammary tumor growth, nonovariectomized and ovariectomized C57BL/6 mice of various body weights (lean, overweight, and obese) were implanted subcutaneously with mammary tumor cells from syngeneic Wnt-1 transgenic mice. In mice, the lean phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status. Ovariectomy delayed Wnt-1 tumor growth consistent with the known hormone responsiveness of these tumors. However, obesity accelerated tumor growth in ovariectomized but not in nonovariectomized animals. Diet-induced obesity in a syngeneic mouse model of breast cancer enhanced tumor growth, specifically in the absence of ovarian hormones. These results support epidemiological evidence that obesity is associated with increased breast cancer incidence and mortality in postmenopausal but not premenopausal women. In contrast, maintaining a lean body weight phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status.

Interrelationships between dietary restriction, the IGF-I axis, and expression of vascular endothelial growth factor by prostate adenocarcinoma in rats

Human studies suggest that excessive energy intake and obesity may influence prostate cancer progression. Rodent experiments demonstrate that diet restriction attenuates tumor growth in parallel with reduced vascular density. The present study examines changes in the insulin-like growth factor I (IGF-I) axis caused by dietary restriction and their association with the expression of vascular endothelial growth factor (VEGF) in prostate cancer. Weanling male Copenhagen rats were randomized into control or 40% dietary restricted groups (n = 5). After 8 wk, rats were implanted with rat AT6.3 prostate adenocarcinoma cells. Two weeks later, the animals were sacrificed and serum, normal prostate, liver, and prostate tumor samples were collected for analyses. Dietary restriction reduced serum concentrations of IGF-I by 35% (P < 0.05) and increased IGF-binding protein-3 (IGFBP3) by sevenfold (P < 0.0001). Lower circulating IGF-I concentrations were correlated with reduced IGF-I mRNA expression in the liver, the primary source of circulating IGF-I. Dietary restriction also lowered mRNA expression of IGF-I (45%, P = 0.0242) and its receptor IGFIR (40%, P = 0.0083) in prostate tumors. Similarly, reduced VEGF mRNA (30%, P = 0.0176) and secreted VEGF protein (33%, P = 0.0003) were observed in prostate cancer of restricted rats. An in vitro study employing AT6.3 prostate cancer cells demonstrated dose- and time-dependent stimulation of VEGF expression by IGF-I. These results suggest that dietary restriction reduces endocrine and prostate tumor autocrine/paracrine IGF-I expression, which contributes to reduced VEGF expression and signaling, to inhibit tumor angiogenesis associated with prostate tumorigenesis.

Dietary energy restriction modulates the activity of AMP-activated protein kinase, Akt, and mammalian target of rapamycin in mammary carcinomas, mammary gland, and liver

Dietary energy restriction (DER) inhibits mammary carcinogenesis, yet mechanisms accounting for its protective activity have not been fully elucidated. In this study, we tested the hypothesis that DER exerts effects on intracellular energy sensing pathways, resulting in alterations of phosphorylated proteins that play a key role in the regulation of cancer. Experiments were conducted using the 1-methyl-1-nitrosourea-induced mammary cancer model in which rats were 0%, 20%, or 40% energy restricted during the postinitiation stage of carcinogenesis. Parallel experiments were done in non-carcinogen-treated rats in which effects of DER at 0%, 5%, 10%, 20%, or 40% in liver were investigated. In a DER dose-dependent manner, levels of Thr(172) phosphorylated AMP-activated protein kinase (AMPK) increased in mammary carcinomas with a concomitant increase in phosphorylated acetyl-CoA-carboxylase, a direct target of AMPK, the phosphorylation of which is regarded as an indicator of AMPK activity. Levels of phosphorylated mammalian target of rapamycin (mTOR) decreased with increasing DER, and down-regulation of mTOR activity was verified by a decrease in the phosphorylation state of two mTOR targets, 70-kDa ribosomal protein S6 kinase (p70S6K) and eukaryote initiation factor 4E binding protein 1 (4E-BP1). Coincident with changes in mTOR phosphorylation, levels of activated protein kinase B (Akt) were also reduced. Similar patterns were observed in mammary glands and livers of non-carcinogen-treated rats. This work identifies components of intracellular energy sensing pathways, specifically mTOR, its principal upstream regulators, AMPK and Akt, and its downstream targets, p70S6K and 4E-BP1, as candidate molecules on which to center mechanistic studies of DER.

Dietary energy balance modulates signaling through the Akt/mammalian target of rapamycin pathways in multiple epithelial tissues

The prevalence of obesity, an established risk factor for several types of cancer, has increased steadily over the past several decades in the United States. New targets and strategies for offsetting the effect of obesity on cancer risk are urgently needed. In the present study, we examined the effect of dietary energy balance manipulation on steady-state signaling in multiple epithelial tissues, with a focus on the Akt and mammalian target of rapamycin (mTOR) pathways. For these experiments, male FVB/N and C57BL/6 and female ICR mice were maintained on a control (10 kcal% fat) diet, a diet-induced obesity (DIO; 60 kcal% fat) regimen, or a 30% calorie restriction (CR) regimen for 15 to 17 weeks. Relative to the control group, the DIO regimen increased, whereas CR decreased, circulating insulin-like growth factor-I (IGF-I) as has previously been reported. Western blot analyses showed that the DIO regimen enhanced, whereas CR inhibited, activation of Akt and mTOR, regardless of epithelial tissue or genetic background. In contrast, activation of AMP-activated protein kinase was modulated by dietary energy balance manipulation in the liver but not in the epidermis or dorsolateral prostate. Western blot analyses of epidermal extracts taken from ICR mice also revealed reduced activation of both the IGF-I receptor and epidermal growth factor receptor in CR mice, compared with control mice or mice maintained on the DIO regimen. Taken together, these novel findings suggest that dietary energy balance modulates signaling through cell-surface receptors (i.e., IGF-I receptor and epidermal growth factor receptor), affecting activation of multiple downstream pathways including Akt and mTOR, thus providing important dietary and pharmacologic targets for disrupting the obesity-cancer link.

Effects of dietary energy restriction on gene regulation in mammary epithelial cells

The objective of this study was to determine whether dietary energy restriction (DER) affects the pattern of gene expression in three interrelated energy metabolism pathways: glycolysis, gluconeogenesis, and the citric acid cycle. Mammary carcinogenesis was initiated by the i.p. injection of female Sprague-Dawley rats with 50 mg of 1-methyl-1-nitrosourea per kilogram of body weight. Five days following 1-methyl-1-nitrosourea administration, animals were fed ad libitum or 80% or 60% of the ad libitum intake. Epithelial cells were harvested from histologically confirmed adenocarcinomas (adenocarcinoma epithelial cell; ACEC) and uninvolved mammary gland (mammary gland epithelial cells; MGEC) via laser capture microdissection, whereas isolated RNA was arrayed on Affymetrix R230 2.0 genome chips. Principal components analysis revealed complete separation of the patterns of gene expression between ACEC versus MGEC. Further examination of the data set revealed an up-regulated pattern of expression in the ACEC of genes involved in glycolysis, whereas gluconeogenesis was suppressed. In general, genes involved in the citric acid cycle were not differentially expressed; however, pyruvate dehydrogenase expression was down-regulated and lactate dehydrogenase expression was increased in ACEC versus MGEC. Collectively, the observed patterns of expression were consistent with the Warburg effect. DER exerted no effect on the Warburg pattern of gene expression or on other aspects of these energy metabolism pathways. These findings imply that efforts to target the Warburg effect for cancer prevention are mechanistically distinct from those modulated by DER and provide a rationale for the combination of approaches that target basic defects in energy metabolism and energy-sensing pathways for the prevention of breast cancer.

Type 5 adenylyl cyclase disruption increases longevity and protects against stress

Mammalian models of longevity are related primarily to caloric restriction and alterations in metabolism. We examined mice in which type 5 adenylyl cyclase (AC5) is knocked out (AC5 KO) and which are resistant to cardiac stress and have increased median lifespan of approximately 30%. AC5 KO mice are protected from reduced bone density and susceptibility to fractures of aging. Old AC5 KO mice are also protected from aging-induced cardiomyopathy, e.g., hypertrophy, apoptosis, fibrosis, and reduced cardiac function. Using a proteomic-based approach, we demonstrate a significant activation of the Raf/MEK/ERK signaling pathway and upregulation of cell protective molecules, including superoxide dismutase. Fibroblasts isolated from AC5 KO mice exhibited ERK-dependent resistance to oxidative stress. These results suggest that AC is a fundamentally important mechanism regulating lifespan and stress resistance.

Transient caloric restriction and cancer risk (The Netherlands)

Over the past century, many animal experiments have shown that caloric restriction can reduce the risk of cancer, a finding that proved to be highly reproducible. Many papers have been published on its potential for human health, but until know little evidence is available on its actual effects in humans. In Utrecht, The Netherlands, we have been investigating the effects of the 1944–1945 Dutch famine on breast cancer risk factors and breast cancer risk, and paradoxically the relatively short-term famine seemed to be related to increased breast cancer risk in later life. One of the differences between the famine situation and the large body of evidence from animal experiments is the duration of caloric restriction. Almost all animal experiments investigated sustained caloric restriction and information on the effects of short-term transient caloric restriction is very scarce. A search in the literature identified some animal experiments on short-term transient caloric restriction and these seemed to be at least supportive to the famine findings. Because caloric restriction in humans for preventive health measures would be mostly short-term, it is important to extend animal research on short-term caloric restriction.

2-Deoxyglucose as an energy restriction mimetic agent: effects on mammary carcinogenesis and on mammary tumor cell growth in vitro

Dietary energy restriction (DER) is a potent inhibitor of carcinogenesis, but chronic DER in human populations is difficult to sustain. Consequently, interest exists in identifying energy restriction mimetic agents (ERMAs), agents that provide the health benefits of DER without reducing caloric intake. The selection of a candidate ERMAs for this study was based on evidence that DER inhibits carcinogenesis by limiting glucose availability. The study objective was to determine if 2-deoxyglucose (2-DG), a glucose analogue that blocks its metabolism, would inhibit mammary carcinogenesis. Pilot studies were done to establish a dietary concentration of 2-DG that would not affect growth. For the carcinogenesis study, ninety 21-day-old female Sprague-Dawley rats were injected i.p. with 50 mg of 1-methyl-1-nitrosourea per kilogram of body weight. Following injection, animals were ad libitum fed AIN-93G diet containing 0.00%, 0.02%, or 0.03% (w/w) 2-DG for 5 weeks. 2-DG decreased the incidence and multiplicity of mammary carcinomas and prolonged cancer latency (P < 0.05). The 0.02% dose of 2-DG had no effect on circulating levels of glucose, insulin, insulin-like growth factor-I, IGF binding protein-3, leptin, or body weight gain. Using MCF-7 human breast cancer cells to investigate the signaling pathways perturbed by disruption of glucose metabolism, 2-DG reduced cell growth and intracellular ATP in a dose- and time-dependent manner (P < 0.01). Treatment with 2-DG increased levels of phosphorylated AMP-activated protein kinase and Sirt-1 and reduced phosphorylated Akt (P < 0.05). These studies support the hypothesis that DER inhibits carcinogenesis, in part, by limiting glucose availability and that energy metabolism is a target for the development of ERMA for chemoprevention.