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

A hypothetical method for controlling highly glycolytic cancers and metastases

Most proliferating cancer cells and cancer-associated tumor stroma have an upregulated glucose energy demand in relation to normal cells. Cancer cells are further less metabolically flexible than normal cells. They can therefore not survive metabolic stress as well as normal cells can. Metabolic deprivation thus provides a potential therapeutic window. Unfortunately, current glucose blockers have toxicity problems. An alternative way to reduce a cancer patient's blood glucose (BG), for a short-term period to very low levels, without the concomitant toxicity, is hypothesized in this paper. In vitro tests have shown that short-term BG deprivation to 2 mmol/L for 180 min is an effective cancer treatment. This level of hypoglycaemia can be maintained in vivo with a combination of very low-dose insulin and the suppression of the glucose counter-regulation system. Such suppression can be safely achieved by the infusion of somatostatin and a combination of both α and β-blockers. The proposed short-term in vivo method, was shown to be non-toxic and safe for non-cancer patients. The next step is to test the effect of the proposed method on cancer patients. It is also suggested to incorporate well-known, long-term BG deprivation treatments to achieve maximum effect.

Onco-metabolism: defining the prognostic significance of obesity and diabetes in women with brain metastases from breast cancer

PURPOSE

Metabolic dysregulation has been implicated as a molecular driver of breast cancer in preclinical studies, especially with respect to metastases. We hypothesized that abnormalities in patient metabolism, such as obesity and diabetes, may drive outcomes in breast cancer patients with brain metastases.

METHODS

We retrospectively identified 84 consecutive patients with brain metastases from breast cancer treated with intracranial radiation therapy. Radiation was delivered as whole-brain radiation to a median dose of 3000 cGy or stereotactic radiosurgery to a median dose of 2100 cGy. Kaplan Meier curves were generated for overall survival (OS) data and Mantel-Cox regression was performed to detect differences in groups.

RESULTS

At analysis, 81 survival events had occurred and the median OS for the entire cohort was 21.7 months. Despite similar modified graded prognostic assessments, resection rates, and receptor status, BMI ≥ 25 kg/m² (n = 45) was associated with decreased median OS (13.7 vs. 30.6 months; p < 0.001) and median intracranial progression-free survival (PFS) (7.4 vs. 10.9 months; p = 0.04) compared to patients with BMI < 25 kg/m² (n = 39). Similar trends were observed among all three types of breast cancer. Patients with diabetes (n = 17) had decreased median OS (11.8 vs. 26.2 months; p < 0.001) and median intracranial PFS (4.5 vs. 10.3 months; p = 0.001) compared to non-diabetics (n = 67). On multivariate analysis, both BMI ≥ 25 kg/m² [HR 2.35 (1.39-3.98); p = 0.002] and diabetes [HR 2.77 (1.454-5.274); p = 0.002] were associated with increased mortality.

CONCLUSIONS

Elevated BMI or diabetes may negatively impact both overall survival and local control in patients with brain metastases from breast cancer, highlighting the importance of the translational development of therapeutic metabolic interventions. Given its prognostic significance, BMI should be used as a stratification in future clinical trial design in this patient population.

Employing proteomics to understand the effects of nutritional intervention in cancer treatment

Lifestyle optimizations are implementable changes that can have an impact on health and disease. Nutrition is a lifestyle optimization that has been shown to be of great importance in cancer initiation, progression, and metastasis. Dozens of clinical trials are currently in progress that focus on the nutritional modifications that cancer patients can make prior to and during medical care that increase the efficacy of treatment. In this review, we discuss various nutritional inventions for cancer patients and the analytical approaches to characterize the downstream molecular effects. We first begin by briefly explaining the many different forms of nutritional intervention currently being used in cancer treatment as well as their motivating biology. The forms of nutrient modulation described in this review include calorie restriction, the different practices of fasting, and carbohydrate restriction. The review then shifts to explain how proteomics is used to determine biomarkers of cancer and how it can be utilized in the future to determine the metabolic phenotype of a tumor, and inform physicians if nutritional intervention should be recommended for a cancer patient. Nutrigenomics aims to understand the relationship of nutrients and gene expression and can be used to understand the downstream molecular effects of nutrition restriction, partially through proteomic analysis. Proteomics is just beginning to be used as cancer diagnostic and predictive tools. However, these approaches have not been used to their full potential to understand nutritional intervention in cancer. Graphical abstract ᅟ.

Short-Term, Intermittent Fasting Induces Long-Lasting Gut Health and TOR-Independent Lifespan Extension

Intermittent fasting (IF) can improve function and health during aging in laboratory model organisms, but the mechanisms at work await elucidation. We subjected fruit flies (Drosophila melanogaster) to varying degrees of IF and found that just one month of a 2-day fed:5-day fasted IF regime at the beginning of adulthood was sufficient to extend lifespan. This long-lasting, beneficial effect of early IF was not due to reduced fecundity. Starvation resistance and resistance to oxidative and xenobiotic stress were increased after IF. Early-life IF also led to higher lipid content in 60-day-old flies, a potential explanation for increased longevity. Guts of flies 40 days post-IF showed a significant reduction in age-related pathologies and improved gut barrier function. Improved gut health was also associated with reduced relative bacterial abundance. Early IF thus induced profound long-term changes. Pharmacological and genetic epistasis analysis showed that IF acted independently of the TOR pathway because rapamycin and IF acted additively to extend lifespan, and global expression of a constitutively active S6K did not attenuate the IF-induced lifespan extension. We conclude that short-term IF during early life can induce long-lasting beneficial effects, with robust increase in lifespan in a TOR-independent manner, probably at least in part by preserving gut health.

Altered exocrine function can drive adipose wasting in early pancreatic cancer

Malignancy is accompanied by changes in the metabolism of both cells and the organism1,2. Pancreatic ductal adenocarcinoma (PDAC) is associated with wasting of peripheral tissues, a metabolic syndrome that lowers quality of life and has been proposed to decrease survival of patients with cancer3,4. Tissue wasting is a multifactorial disease and targeting specific circulating factors to reverse this syndrome has been mostly ineffective in the clinic5,6. Here we show that loss of both adipose and muscle tissue occurs early in the development of pancreatic cancer. Using mouse models of PDAC, we show that tumour growth in the pancreas but not in other sites leads to adipose tissue wasting, suggesting that tumour growth within the pancreatic environment contributes to this wasting phenotype. We find that decreased exocrine pancreatic function is a driver of adipose tissue loss and that replacement of pancreatic enzymes attenuates PDAC-associated wasting of peripheral tissues. Paradoxically, reversal of adipose tissue loss impairs survival in mice with PDAC. When analysing patients with PDAC, we find that depletion of adipose and skeletal muscle tissues at the time of diagnosis is common, but is not associated with worse survival. Taken together, these results provide an explanation for wasting of adipose tissue in early PDAC and suggest that early loss of peripheral tissue associated with pancreatic cancer may not impair survival.

Effects of mesenchymal stem cells on solid tumor metastasis in experimental cancer models: a systematic review and meta-analysis

Background

It has been reported mesenchymal stem cells (MSCs) are recruited to and become integral parts of the tumor microenvironment. MSCs might have an active role in solid tumor progression, especially cancer metastasis. However, the contribution of MSCs in the process of cancer metastasis is still controversial. In this review, we performed a meta-analysis on the effects of MSCs administration on cancer metastasis based on published preclinical studies.

Methods

The PRISMA guidelines were used. A total of 42 publications met the inclusion criteria. Outcome data on the incidence and the number of cancer metastasis as well as study characteristics were extracted. Quality of the studies was assessed according to SYRCLE Risk of Bias tool. Random-effects meta-analysis was used to pool estimates.

Results

Of the 42 studies included, 32 reported that MSCs administration promoted outcome events (numbers or incidences of cancer metastasis), and 39 reported data suitable for meta-analysis. The median effect size (RR) was 2.04 for the incidence of cancer metastasis (95% CI 1.57–2.65, I² = 21%), and the median effect size (SMD) was 1.23 for the number of cancer metastasis (95% CI 0.43–2.03, I² = 89%). Heterogeneity was observed, with the greater impact based on study length and different ways of metastasis measurement and MSCs administration.

Conclusion

Our results suggested MSCs administration increased the number and the incidence of cancer metastasis in experimental cancer models. High heterogeneity and poor reported risk of bias limit the quality of these findings. Further preclinical studies with better design and adequate reporting are still needed.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1484-9) contains supplementary material, which is available to authorized users.

Translating Mechanism-Based Strategies to Break the Obesity-Cancer Link: A Narrative Review

Prevalence of obesity, an established risk factor for many cancers, has increased dramatically over the past 50 years in the United States and across the globe. Relative to normoweight cancer patients, obese cancer patients often have poorer prognoses, resistance to chemotherapies, and are more likely to develop distant metastases. Recent progress on elucidating the mechanisms underlying the obesity-cancer connection suggests that obesity exerts pleomorphic effects on pathways related to tumor development and progression and, thus, there are multiple opportunities for primary prevention and treatment of obesity-related cancers. Obesity-associated alterations, including systemic metabolism, adipose inflammation, growth factor signaling, and angiogenesis, are emerging as primary drivers of obesity-associated cancer development and progression. These obesity-associated host factors interact with the intrinsic molecular characteristics of cancer cells, facilitating several of the hallmarks of cancer. Each is considered in the context of potential preventive and therapeutic strategies to reduce the burden of obesity-related cancers. In addition, this review focuses on emerging mechanisms behind the obesity-cancer link, as well as relevant dietary interventions, including calorie restriction, intermittent fasting, low-fat diet, and ketogenic diet, that are being implemented in preclinical and clinical trials, with the ultimate goal of reducing incidence and progression of obesity-related cancers.

Starvation, Stress Resistance, and Cancer

Cancer cells are characterized by dysregulation in signal transduction and metabolic pathways leading to increased glucose uptake, altered mitochondrial function, and the evasion of antigrowth signals. Fasting and fasting-mimicking diets (FMDs) provide a particularly promising intervention to promote differential effects in normal and malignant cells. These effects are caused in part by the reduction in IGF-1, insulin, and glucose and the increase in IGFBP1 and ketone bodies, which generate conditions that force cancer cells to rely more on metabolites and factors that are limited in the blood, thus resulting in cell death. Here we discuss the cellular and animal experiments demonstrating the differential effects of fasting on normal and cancer cells and the mechanisms responsible for these effects.

A Ketogenic Formula Prevents Tumor Progression and Cancer Cachexia by Attenuating Systemic Inflammation in Colon 26 Tumor-Bearing Mice

Low-carbohydrate, high-fat diets (ketogenic diets) might prevent tumor progression and could be used as supportive therapy; however, few studies have addressed the effect of such diets on colorectal cancer. An infant formula with a ketogenic composition (ketogenic formula; KF) is used to treat patients with refractory epilepsy. We investigated the effect of KF on cancer and cancer cachexia in colon tumor-bearing mice. Mice were randomized into normal (NR), tumor-bearing (TB), and ketogenic formula (KF) groups. Colon 26 cells were inoculated subcutaneously into TB and KF mice. The NR and TB groups received a standard diet, and the KF mice received KF ad libitum. KF mice preserved their body, muscle, and carcass weights. Tumor weight and plasma IL-6 levels were significantly lower in KF mice than in TB mice. In the KF group, energy intake was significantly higher than that in the other two groups. Blood ketone body concentrations in KF mice were significantly elevated, and there was a significant negative correlation between blood ketone body concentration and tumor weight. Therefore, KF may suppress the progression of cancer and the accompanying systemic inflammation without adverse effects on weight gain, or muscle mass, which might help to prevent cancer cachexia.

Intermittent calorie restriction enhances epithelial-mesenchymal transition through the alteration of energy metabolism in a mouse tumor model

The effect of intermittent calorie restriction (ICR) on cancer is controversial. In this study, we examined the effects of ICR and food content in syngeneic BALB/c mice injected with CT26 mouse colon cancer cells. Mice were subjected to 24-h fasting once a week for 4 weeks, and then provided with a control, high-calorie, or trans fatty acid-rich diet. While ICR resulted in increases in tumor weights, metastasis and in the number of cancer stem cells (CSCs) in the tumors or blood of mice fed the control and high-fat diets, it had no effect on body weight after 4 weeks. In particular, we detected increases in the numbers of CSCs in the tumor or blood on the day after starvation, when food overconsumption was detected. Conversely, continuous calorie restriction had no effect on tumor weight, metastasis, or the number of CSCs in tumors or blood. In the post-starvation period, energy metabolism in the tumor was altered from oxidative phosphorylation to glycolysis/lactate fermentation, with the acquisition of the epithelial-mesenchymal transition (EMT) phenotype. Hyperglycemia at the post-starvation period induced the expression of insulin-like growth factor-1, hypoxia-induced factor-1α and Nanog, as well as the phosphorylation of Stat3. Taken together, these findings suggest that ICR induces an increase in the number of CSCs and enhances EMT by promoting the Warburg/Crabtree effect following post-fasting food overconsumption.

Combination of metronomic cyclophosphamide and dietary intervention inhibits neuroblastoma growth in a CD1-nu mouse model

BACKGROUND

MYCN-amplification in high-grade Neuroblastoma (NB) tumors correlates with increased vascularization and therapy resistance. This study combines an anti-angiogenic approach with targeting NB metabolism for treatment.

METHODS AND RESULTS

Metronomic cyclophosphamide (MCP) monotherapy significantly inhibited NB growth and prolonged host survival. Growth inhibition was more pronounced in MYCN-amplified xenografts. Immunohistochemical evaluation of this subtype showed significant decrease in blood vessel density and intratumoral hemorrhage accompanied by blood vessel maturation and perivascular fibrosis. Up-regulation of VEGFA was not sufficient to compensate for the effects of the MCP regimen. Reduced Bcl-2 expression and increased caspase-3 cleavage were evident. In contrast non MYCN-amplified tumors developed resistance, which was accompanied by Bcl-2-up-regulation. Combining MCP with a ketogenic diet and/or calorie-restriction significantly enhanced the anti-tumor effect. Calorie-restricted ketogenic diet in combination with MCP resulted in tumor regression in all cases.

CONCLUSIONS

Our data show efficacy of combining an anti-angiogenic cyclophosphamide dosing regimen with dietary intervention in a preclinical NB model. These findings might open a new front in NB treatment.

The influence of ketogenic therapy on the 5 R's of radiobiology

PURPOSE

Radiotherapy (RT) is a mainstay in the treatment of solid tumors and works by inducing free radical stress in tumor cells, leading to loss of reproductive integrity. The optimal treatment strategy has to consider damage to both tumor and normal cells and is determined by five factors known as the 5 R's of radiobiology: Reoxygenation, DNA repair, radiosensitivity, redistribution in the cell cycle and repopulation. The aim of this review is (i) to present evidence that these 5 R's are strongly influenced by cellular and whole-body metabolism that in turn can be modified through ketogenic therapy in form of ketogenic diets and short-term fasting and (ii) to stimulate new research into this field including some research questions deserving further study.

CONCLUSIONS

Preclinical and some preliminary clinical data support the hypothesis that ketogenic therapy could be utilized as a complementary treatment in order to improve the outcome after RT, both in terms of higher tumor control and in terms of lower normal tissue complication probability. The first effect relates to the metabolic shift from glycolysis toward mitochondrial metabolism that selectively increases ROS production and impairs ATP production in tumor cells. The second effect is based on the differential stress resistance phenomenon, which is achieved when glucose and growth factors are reduced and ketone bodies are elevated, reprogramming normal but not tumor cells from proliferation toward maintenance and stress resistance. Underlying both effects are metabolic differences between normal and tumor cells that ketogenic therapy seeks to exploit. Specifically, the recently discovered role of the ketone body β-hydroxybutyrate as an endogenous class-I histone deacetylase inhibitor suggests a dual role as a radioprotector of normal cells and a radiosensitzer of tumor cells that opens up exciting possibilities to employ ketogenic therapy as a cost-effective adjunct to radiotherapy against cancer.

Potential Role of Metabolic Intervention in the Management of Advanced Differentiated Thyroid Cancer

Well-differentiated thyroid carcinoma (DTC) is the most common endocrine malignancy that has an excellent prognosis with a 5-year survival rate of about 98%. However, approximately 50% of the patients with DTC who present with distant metastases (advanced DTC) die from the disease within 5 years of initial diagnosis even after getting the appropriate therapy. Apart from recent advancements in chemotherapy agents, the potential role of metabolic interventions, including the use of metformin, ketogenic diet, and high-dose vitamin C in the management of advanced cancers have been investigated as a less toxic co-adjuvant therapies. The role of vitamin C has been of interest again after a preclinical mice study showed that high-dose vitamin C is selectively lethal to KRAS and BRAF mutant colorectal cancer cells by targeting the glutathione pathway. This raises the possibility of utilizing high-doses of vitamin C in the treatment of aDTC where KRAS and BRAF mutations are common. Similarly, alteration of cellular metabolism by low-carbohydrate ketogenic diets can be an important therapeutic strategy to selectively kill cancer cells that mainly survive on glycolysis. Among the potential adjuvant therapies proposed in this paper, metformin is the only agent that has shown benefit in human model of aDTC, the others have shown benefit but in preclinical/animal studies only and need to be further evaluated in large clinical trials. In conclusion, in addition to concurrent chemotherapy options, these metabolic interventions may have a great potential as co-adjuvant therapy in the management of aDTC.

Metabolic Effects of Intermittent Fasting

The objective of this review is to provide an overview of intermittent fasting regimens, summarize the evidence on the health benefits of intermittent fasting, and discuss physiological mechanisms by which intermittent fasting might lead to improved health outcomes. A MEDLINE search was performed using PubMed and the terms "intermittent fasting," "fasting," "time-restricted feeding," and "food timing." Modified fasting regimens appear to promote weight loss and may improve metabolic health. Several lines of evidence also support the hypothesis that eating patterns that reduce or eliminate nighttime eating and prolong nightly fasting intervals may result in sustained improvements in human health. Intermittent fasting regimens are hypothesized to influence metabolic regulation via effects on (a) circadian biology, (b) the gut microbiome, and (c) modifiable lifestyle behaviors, such as sleep. If proven to be efficacious, these eating regimens offer promising nonpharmacological approaches to improving health at the population level, with multiple public health benefits.

Fasting inhibits hepatic stellate cells activation and potentiates anti-cancer activity of Sorafenib in hepatocellular cancer cells

Hepatocellular carcinoma (HCC) has a poor outcome. Most HCCs develop in the context of liver fibrosis and cirrhosis caused by chronic inflammation. Short-term fasting approaches enhance the activity of chemotherapy in preclinical cancer models, other than HCC. Multi-tyrosine kinase inhibitor Sorafenib is the mainstay of treatment in HCC. However, its benefit is frequently short-lived. Whether fasting can alleviate liver fibrosis and whether combining fasting with Sorafenib is beneficial remains unknown. A 24 hr fasting (2% serum, 0.1% glucose)-induced changes on human hepatic stellate cells (HSC) LX-2 proliferation/viability/cell cycle were assessed by MTT and flow cytometry. Expression of lypolysaccharide (LPS)-induced activation markers (vimentin, αSMA) was evaluated by qPCR and immunoblotting. Liver fibrosis and inflammation were evaluated in a mouse model of steatohepatitis exposed to cycles of fasting, by histological and biochemical analyses. A 24 hr fasting-induced changes were also analyzed on the proliferation/viability/glucose uptake of human HCC cells exposed to Sorafenib. An expression panel of genes involved in survival, inflammation, and metabolism was examined by qPCR in HCC cells exposed to fasting and/or Sorafenib. Fasting decreased the proliferation and the activation of HSC. Repeated cycles of short term starvation were safe in mice but did not improve fibrosis. Fasting synergized with Sorafenib in hampering HCC cell growth and glucose uptake. Finally, fasting normalized the expression levels of genes which are commonly altered by Sorafenib in HCC cells. Fasting or fasting-mimicking diet diets should be evaluated in preclinical studies as a mean to potentiate the activity of Sorafenib in clinical use.

Glucose Restriction Combined with Autophagy Inhibition and Chemotherapy in HCT 116 Spheroids Decreases Cell Clonogenicity and Viability Regulated by Tumor Suppressor Genes

Drug resistance is a prevalent phenomenon that decreases the efficacy of cancer treatments and contributes to cancer progression and metastasis. Weakening drug-resistant cancer cells prior to chemotherapy is a potential strategy to combat chemoresistance. One approach to damage resistant cancer cells is modulation of nutritional intake. The combination of nutrient restriction with targeted compound treatment results in pronounced molecular changes. This study provides valuable information about augmenting existing chemotherapeutic regimes with simultaneous glucose restriction and autophagy inhibition in colorectal cancer cells. In this study, we explore the chemical pathways that drive the cellular response to nutrient restriction, autophagy inhibition, and the chemotherapy irinotecan using global quantitative proteomics and imaging mass spectrometry. We determined that significant pathways were altered including autophagy and metabolism via glycolysis, gluconeogenesis, and sucrose degradation. We also found that period circadian clock 2 (PER2), a tumor suppressor protein, was significantly up-regulated only when glucose was restricted with autophagy inhibition and chemotherapy. The upstream regulators of these differentially regulated pathways were determined to have implications in cancer, showing an increase in tumor suppressor proteins and a decrease in nuclear protein 1 (NUPR1) an important protein in chemoresistance. We also evaluated the phenotypic response of these cells and discovered autophagy inhibition and chemotherapy treatment increased apoptosis and decreased cell clonogenicity and viability. When glucose restriction was combined with autophagy inhibition and chemotherapy, all of the phenotypic results were intensified. In sum, our results indicate that glucose metabolism is of great importance in the ability of cancer cells to survive chemotherapy. By weakening cancer cells with glucose restriction and autophagy inhibition prior to chemotherapy, cancer cells become more sensitive to therapy.

Beneficial effects of ketogenic diets for cancer patients: a realist review with focus on evidence and confirmation

Ketogenic diets (KDs) have gained popularity among patients and researchers alike due to their putative anti-tumor mechanisms. However, the question remains which conclusions can be drawn from the available human data thus far concerning the safety and efficacy of KDs for cancer patients. A realist review utilizing a matrix analytical approach was conducted according to the RAMESES publication standards. All available human studies were systematically analyzed and supplemented with results from animal studies. Evidence and confirmation were treated as separate concepts. In total, 29 animal and 24 human studies were included in the analysis. The majority of animal studies (72%) yielded evidence for an anti-tumor effect of KDs. Evidential support for such effects in humans was weak and limited to individual cases, but a probabilistic argument shows that the available data strengthen the belief in the anti-tumor effect hypothesis at least for some individuals. Evidence for pro-tumor effects was lacking completely. Feasibility of KDs for cancer patients has been shown in various contexts. The probability of achieving an anti-tumor effect seems greater than that of causing serious side effects when offering KDs to cancer patients. Future controlled trials would provide stronger evidence for or against the anti-tumor effect hypothesis.

When less may be more: calorie restriction and response to cancer therapy

Calorie restriction (CR) extends lifespan and has been shown to reduce age-related diseases including cancer, diabetes, and cardiovascular and neurodegenerative diseases in experimental models. Recent translational studies have tested the potential of CR or CR mimetics as adjuvant therapies to enhance the efficacy of chemotherapy, radiation therapy, and novel immunotherapies. Chronic CR is challenging to employ in cancer patients, and therefore intermittent fasting, CR mimetic drugs, or alternative diets (such as a ketogenic diet), may be more suitable. Intermittent fasting has been shown to enhance treatment with both chemotherapy and radiation therapy. CR and fasting elicit different responses in normal and cancer cells, and reduce certain side effects of cytotoxic therapy. Findings from preclinical studies of CR mimetic drugs and other dietary interventions, such as the ketogenic diet, are promising for improving the efficacy of anticancer therapies and reducing the side effects of cytotoxic treatments. Current and future clinical studies will inform on which cancers, and at which stage of the cancer process, CR, fasting, or CR mimetic regimens will prove most effective.

A Nutritional Perspective of Ketogenic Diet in Cancer: A Narrative Review

The predominant use of glucose anaerobically by cancer cells (Warburg effect) may be the most important characteristic the majority of these cells have in common and, therefore, a potential metabolic pathway to be targeted during cancer treatment. Because this effect relates to fuel oxidation, dietary manipulation has been hypothesized as an important strategy during cancer treatment. As such, the concept of a ketogenic diet (KD) in cancer emerged as a metabolic therapy (ie, targeting cancer cell metabolism) rather than a dietary approach. The therapeutic mechanisms of action of this high-fat, moderate-to-low protein, and very-low-carbohydrate diet may potentially influence cancer treatment and prognosis. Considering the lack of a dietetics-focused narrative review on this topic, we compiled the evidence related to the use of this diet in humans with diverse cancer types and stages, also focusing on the nutrition and health perspective. The use of KD in cancer shows potentially promising, but inconsistent, results. The limited number of studies and differences in study design and characteristics contribute to overall poor quality evidence, limiting the ability to draw evidence-based conclusions. However, the potential positive influences a KD may have on cancer treatment justify the need for well-designed clinical trials to better elucidate the mechanisms by which this dietary approach affects nutritional status, cancer prognosis, and overall health. The role of registered dietitian nutritionists is demonstrated to be crucial in planning and implementing KD protocols in oncology research settings, while also ensuring patients' adherence and optimal nutritional status.

Press-pulse: a novel therapeutic strategy for the metabolic management of cancer

BACKGROUND

A shift from respiration to fermentation is a common metabolic hallmark of cancer cells. As a result, glucose and glutamine become the prime fuels for driving the dysregulated growth of tumors. The simultaneous occurrence of "Press-Pulse" disturbances was considered the mechanism responsible for reduction of organic populations during prior evolutionary epochs. Press disturbances produce chronic stress, while pulse disturbances produce acute stress on populations. It was only when both disturbances coincide that population reduction occurred.

METHODS

This general concept can be applied to the management of cancer by creating chronic metabolic stresses on tumor cell energy metabolism (press disturbance) that are coupled to a series of acute metabolic stressors that restrict glucose and glutamine availability while also stimulating cancer-specific oxidative stress (pulse disturbances). The elevation of non-fermentable ketone bodies protect normal cells from energy stress while further enhancing energy stress in tumor cells that lack the metabolic flexibility to use ketones as an efficient energy source. Mitochondrial abnormalities and genetic mutations make tumor cells vulnerable metabolic stress.

RESULTS

The press-pulse therapeutic strategy for cancer management is illustrated with calorie restricted ketogenic diets (KD-R) used together with drugs and procedures that create both chronic and intermittent acute stress on tumor cell energy metabolism, while protecting and enhancing the energy metabolism of normal cells.

CONCLUSIONS

Optimization of dosing, timing, and scheduling of the press-pulse therapeutic strategy will facilitate the eradication of tumor cells with minimal patient toxicity. This therapeutic strategy can be used as a framework for the design of clinical trials for the non-toxic management of most cancers.

Caloric restriction - A promising anti-cancer approach: From molecular mechanisms to clinical trials

Cancer is the second leading cause of death worldwide and the morbidity is growing in developed countries. According to WHO, >14 million people per year are diagnosed with cancer and about 8 million die. Anti-cancer strategy includes chemo-, immune- and radiotherapy or their combination. Unfortunately, these widely used strategies often have insufficient efficacy and significant toxic effects on healthy cells. Consequently, the improvement of treatment approaches is an important goal. One of promising schemes to enhance the effect of therapy is the restriction of calorie intake or some nutrients. The combination of caloric restriction or its chemical mimetics along with anti-cancer drugs may suppress growth of tumor cells and enhance death of cancer cells. That will allow the dose of therapeutic drugs to be decreased and their toxic effects to be reduced. Here the possibility of using this combinatory therapy as well as the molecular mechanisms underlying this approach will be discussed.

Tumor Metabolism, the Ketogenic Diet and β-Hydroxybutyrate: Novel Approaches to Adjuvant Brain Tumor Therapy

Malignant brain tumors are devastating despite aggressive treatments such as surgical resection, chemotherapy and radiation therapy. The average life expectancy of patients with newly diagnosed glioblastoma is approximately ~18 months. It is clear that increased survival of brain tumor patients requires the design of new therapeutic modalities, especially those that enhance currently available treatments and/or limit tumor growth. One novel therapeutic arena is the metabolic dysregulation that results in an increased need for glucose in tumor cells. This phenomenon suggests that a reduction in tumor growth could be achieved by decreasing glucose availability, which can be accomplished through pharmacological means or through the use of a high-fat, low-carbohydrate ketogenic diet (KD). The KD, as the name implies, also provides increased blood ketones to support the energy needs of normal tissues. Preclinical work from a number of laboratories has shown that the KD does indeed reduce tumor growth in vivo. In addition, the KD has been shown to reduce angiogenesis, inflammation, peri-tumoral edema, migration and invasion. Furthermore, this diet can enhance the activity of radiation and chemotherapy in a mouse model of glioma, thus increasing survival. Additional studies in vitro have indicated that increasing ketones such as β-hydroxybutyrate (βHB) in the absence of glucose reduction can also inhibit cell growth and potentiate the effects of chemotherapy and radiation. Thus, while we are only beginning to understand the pluripotent mechanisms through which the KD affects tumor growth and response to conventional therapies, the emerging data provide strong support for the use of a KD in the treatment of malignant gliomas. This has led to a limited number of clinical trials investigating the use of a KD in patients with primary and recurrent glioma.

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.

A Systematic Literature Review and Meta-Regression Analysis on Early-Life Energy Restriction and Cancer Risk in Humans

Background

In animal models, long-term moderate energy restriction (ER) is reported to decelerate carcinogenesis, whereas the effect of severe ER is inconsistent. The impact of early-life ER on cancer risk has never been reviewed systematically and quantitatively based on observational studies in humans.

Objective

We conducted a systematic review of observational studies and a meta-(regression) analysis on cohort studies to clarify the association between early-life ER and organ site-specific cancer risk.

Methods

PubMed and EMBASE (1982 –August 2015) were searched for observational studies. Summary relative risks (RRs) were estimated using a random effects model when available ≥3 studies.

Results

Twenty-four studies were included. Eleven publications, emanating from seven prospective cohort studies and some reporting on multiple cancer endpoints, met the inclusion criteria for quantitative analysis. Women exposed to early-life ER (ranging from 220–1660 kcal/day) had a higher breast cancer risk than those not exposed (RR_{RE all ages} = 1.28, 95% CI: 1.05–1.56; RR_{RE for 10–20 years of age} = 1.21, 95% CI: 1.09–1.34). Men exposed to early-life ER (ranging from 220–800kcal/day) had a higher prostate cancer risk than those not exposed (RR_RE = 1.16, 95% CI: 1.03–1.30). Summary relative risks were not computed for colorectal cancer, because of heterogeneity, and for stomach-, pancreas-, ovarian-, and respiratory cancer because there were <3 available studies. Longer duration of exposure to ER, after adjustment for severity, was positively associated with overall cancer risk in women (p = 0.02). Ecological studies suggest that less severe ER is generally associated with a reduced risk of cancer.

Conclusions

Early-life transient severe ER seems to be associated with increased cancer risk in the breast (particularly ER exposure at adolescent age) and prostate. The duration, rather than severity of exposure to ER, seems to positively influence relative risk estimates. This result should be interpreted with caution due to the limited number of studies and difficulty in disentangling duration, severity, and geographical setting of exposure.

Anti-Tumor Effects of Ketogenic Diets in Mice: A Meta-Analysis

Background

Currently ketogenic diets (KDs) are hyped as an anti-tumor intervention aimed at exploiting the metabolic abnormalities of cancer cells. However, while data in humans is sparse, translation of murine tumor models to the clinic is further hampered by small sample sizes, heterogeneous settings and mixed results concerning tumor growth retardation. The aim was therefore to synthesize the evidence for a growth inhibiting effect of KDs when used as a monotherapy in mice.

Methods

We conducted a Bayesian random effects meta-analysis on all studies assessing the survival (defined as the time to reach a pre-defined endpoint such as tumor volume) of mice on an unrestricted KD compared to a high carbohydrate standard diet (SD). For 12 studies meeting the inclusion criteria either a mean survival time ratio (MR) or hazard ratio (HR) between the KD and SD groups could be obtained. The posterior estimates for the MR and HR averaged over four priors on the between-study heterogeneity τ² were MR = 0.85 (95% highest posterior density interval (HPDI) = [0.73, 0.97]) and HR = 0.55 (95% HPDI = [0.26, 0.87]), indicating a significant overall benefit of the KD in terms of prolonged mean survival times and reduced hazard rate. All studies that used a brain tumor model also chose a late starting point for the KD (at least one day after tumor initiation) which accounted for 26% of the heterogeneity. In this subgroup the KD was less effective (MR = 0.89, 95% HPDI = [0.76, 1.04]).

Conclusions

There was an overall tumor growth delaying effect of unrestricted KDs in mice. Future experiments should aim at differentiating the effects of KD timing versus tumor location, since external evidence is currently consistent with an influence of both of these factors.

Attacking the supply wagons to starve cancer cells to death

The constitutive anabolism of cancer cells not only supports proliferation but also addicts tumor cells to a steady influx of exogenous nutrients. Limiting access to metabolic substrates could be an effective and selective means to block cancer growth. In this review, we define the pathways by which cancer cells acquire the raw materials for anabolism, highlight the actionable proteins in each pathway, and discuss the status of therapeutic interventions that disrupt nutrient acquisition. Critical open questions to be answered before apical metabolic inhibitors can be successfully and safely deployed in the clinic are also outlined. In summary, recent studies provide strong support that substrate limitation is a powerful therapeutic strategy to effectively, and safely, starve cancer cells to death.

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.

Long-term High Fat Ketogenic Diet Promotes Renal Tumor Growth in a Rat Model of Tuberous Sclerosis

Nutritional imbalance underlies many disease processes but can be very beneficial in certain cases; for instance, the antiepileptic action of a high fat and low carbohydrate ketogenic diet. Besides this therapeutic feature it is not clear how this abundant fat supply may affect homeostasis, leading to side effects. A ketogenic diet is used as anti-seizure therapy i.a. in tuberous sclerosis patients, but its impact on concomitant tumor growth is not known. To examine this we have evaluated the growth of renal lesions in Eker rats (Tsc2+/−) subjected to a ketogenic diet for 4, 6 and 8 months. In spite of existing opinions about the anticancer actions of a ketogenic diet, we have shown that this anti-seizure therapy, especially in its long term usage, leads to excessive tumor growth. Prolonged feeding of a ketogenic diet promotes the growth of renal tumors by recruiting ERK1/2 and mTOR which are associated with the accumulation of oleic acid and the overproduction of growth hormone. Simultaneously, we observed that Nrf2, p53 and 8-oxoguanine glycosylase α dependent antitumor mechanisms were launched by the ketogenic diet. However, the pro-cancerous mechanisms finally took the ascendency by boosting tumor growth.

Dietary and pharmacological modification of the insulin/IGF-1 system: exploiting the full repertoire against cancer

As more and more links between cancer and metabolism are discovered, new approaches to treat cancer using these mechanisms are considered. Dietary restriction of either calories or macronutrients has shown great potential in animal studies to both reduce the incidence and growth of cancer, and to act synergistically with other treatment strategies. These studies have also shown that dietary restriction simultaneously targets many of the molecular pathways that are targeted individually by anticancer drugs. The insulin/insulin-like growth factor-1 (IGF-1) system has thereby emerged as a key regulator of cancer growth pathways. Although lowering of insulin levels with diet or drugs such as metformin and diazoxide seems generally beneficial, some practitioners also utilize strategic elevations of insulin levels in combination with chemotherapeutic drugs. This indicates a broad spectrum of possibilities for modulating the insulin/IGF-1 system in cancer treatment. With a specific focus on dietary restriction, insulin administration and the insulin-lowering drug diazoxide, such modifications of the insulin/IGF-1 system are the topic of this review. Although preclinical data are promising, we point out that insulin regulation and the metabolic response to a certain diet often differ between mice and humans. Thus, the need for collecting more human data has to be emphasized.

Ramadan Fasting and Patients with Cancer: State-of-the-Art and Future Prospects

Ramadan fasting represents one of the five pillars of the Islam creed. Even though some subjects (among which patients) are exempted from observing this religious duty, they may be eager to share this particular moment of the year with their family and peers. However, there are no guidelines or standardized protocols that can help physicians to properly address the issue of patients with cancer fasting in Ramadan and correctly advising them. Moreover, in a more interconnected and globalized society, in which more and more Muslim patients live in the Western countries, this topic is of high interest also for the general practitioner. For this purpose, we carried out a systematic review on the subject. Our main findings are that (1) very few studies have been carried out, addressing this issue, (2) evidence concerning quality of life and compliance to treatment is contrasting and scarce, and (3) generally speaking, few patients ask their physicians whether they can safely fast or not. For these reasons, further research should be performed, given the relevance and importance of this topic.

Intermittent Moderate Energy Restriction Improves Weight Loss Efficiency in Diet-Induced Obese Mice

Background

Intermittent severe energy restriction is popular for weight management. To investigate whether intermittent moderate energy restriction may improve this approach by enhancing weight loss efficiency, we conducted a study in mice, where energy intake can be controlled.

Methods

Male C57/Bl6 mice that had been rendered obese by an ad libitum diet high in fat and sugar for 22 weeks were then fed one of two energy-restricted normal chow diets for a 12-week weight loss phase. The continuous diet (CD) provided 82% of the energy intake of age-matched ad libitum chow-fed controls. The intermittent diet (ID) provided cycles of 82% of control intake for 5–6 consecutive days, and ad libitum intake for 1–3 days. Weight loss efficiency during this phase was calculated as (total weight change) ÷ [(total energy intake of mice on CD or ID)–(total average energy intake of controls)]. Subsets of mice then underwent a 3-week weight regain phase involving ad libitum re-feeding.

Results

Mice on the ID showed transient hyperphagia relative to controls during each 1–3-day ad libitum feeding period, and overall ate significantly more than CD mice (91.1±1.0 versus 82.2±0.5% of control intake respectively, n = 10, P<0.05). There were no significant differences between CD and ID groups at the end of the weight loss or weight regain phases with respect to body weight, fat mass, circulating glucose or insulin concentrations, or the insulin resistance index. Weight loss efficiency was significantly greater with ID than with CD (0.042±0.007 versus 0.018±0.001 g/kJ, n = 10, P<0.01). Mice on the CD exhibited significantly greater hypothalamic mRNA expression of proopiomelanocortin (POMC) relative to ID and control mice, with no differences in neuropeptide Y or agouti-related peptide mRNA expression between energy-restricted groups.

Conclusion

Intermittent moderate energy restriction may offer an advantage over continuous moderate energy restriction, because it induces significantly greater weight loss relative to energy deficit in mice.

A Supplemented High-Fat Low-Carbohydrate Diet for the Treatment of Glioblastoma

PURPOSE

Dysregulated energetics coupled with uncontrolled proliferation has become a hallmark of cancer, leading to increased interest in metabolic therapies. Glioblastoma (GB) is highly malignant, very metabolically active, and typically resistant to current therapies. Dietary treatment options based on glucose deprivation have been explored using a restrictive ketogenic diet (KD), with positive anticancer reports. However, negative side effects and a lack of palatability make the KD difficult to implement in an adult population. Hence, we developed a less stringent, supplemented high-fat low-carbohydrate (sHFLC) diet that mimics the metabolic and antitumor effects of the KD, maintains a stable nutritional profile, and presents an alternative clinical option for diverse patient populations.

EXPERIMENTAL DESIGN

The dietary paradigm was tested in vitro and in vivo, utilizing multiple patient-derived gliomasphere lines. Cellular proliferation, clonogenic frequency, and tumor stem cell population effects were determined in vitro using the neurosphere assay (NSA). Antitumor efficacy was tested in vivo in preclinical xenograft models and mechanistic regulation via the mTOR pathway was explored.

RESULTS

Reducing glucose in vitro to physiologic levels, coupled with ketone supplementation, inhibits proliferation of GB cells and reduces tumor stem cell expansion. In vivo, while maintaining animal health, the sHFLC diet significantly reduces the growth of tumor cells in a subcutaneous model of tumor progression and increases survival in an orthotopic xenograft model. Dietary-mediated anticancer effects correlate with the reduction of mTOR effector expression.

CONCLUSIONS

We demonstrate that the sHFLC diet is a viable treatment alternative to the KD, and should be considered for clinical testing. Clin Cancer Res; 22(10); 2482-95. ©2015 AACR.

Non-Toxic Metabolic Management of Metastatic Cancer in VM Mice: Novel Combination of Ketogenic Diet, Ketone Supplementation, and Hyperbaric Oxygen Therapy

The Warburg effect and tumor hypoxia underlie a unique cancer metabolic phenotype characterized by glucose dependency and aerobic fermentation. We previously showed that two non-toxic metabolic therapies - the ketogenic diet with concurrent hyperbaric oxygen (KD+HBOT) and dietary ketone supplementation - could increase survival time in the VM-M3 mouse model of metastatic cancer. We hypothesized that combining these therapies could provide an even greater therapeutic benefit in this model. Mice receiving the combination therapy demonstrated a marked reduction in tumor growth rate and metastatic spread, and lived twice as long as control animals. To further understand the effects of these metabolic therapies, we characterized the effects of high glucose (control), low glucose (LG), ketone supplementation (βHB), hyperbaric oxygen (HBOT), or combination therapy (LG+βHB+HBOT) on VM-M3 cells. Individually and combined, these metabolic therapies significantly decreased VM-M3 cell proliferation and viability. HBOT, alone or in combination with LG and βHB, increased ROS production in VM-M3 cells. This study strongly supports further investigation into this metabolic therapy as a potential non-toxic treatment for late-stage metastatic cancers.

Inhibition of Neuroblastoma Tumor Growth by Ketogenic Diet and/or Calorie Restriction in a CD1-Nu Mouse Model

INTRODUCTION

Neuroblastoma is a malignant pediatric cancer derived from neural crest cells. It is characterized by a generalized reduction of mitochondrial oxidative phosphorylation. The goal of the present study was to investigate the effects of calorie restriction and ketogenic diet on neuroblastoma tumor growth and monitor potential adaptive mechanisms of the cancer's oxidative phosphorylation system.

METHODS

Xenografts were established in CD-1 nude mice by subcutaneous injection of two neuroblastoma cell lines having distinct genetic characteristics and therapeutic sensitivity [SH-SY5Y and SK-N-BE(2)]. Mice were randomized to four treatment groups receiving standard diet, calorie-restricted standard diet, long chain fatty acid based ketogenic diet or calorie-restricted ketogenic diet. Tumor growth, survival, metabolic parameters and weight of the mice were monitored. Cancer tissue was evaluated for diet-induced changes of proliferation indices and multiple oxidative phosphorylation system parameters (respiratory chain enzyme activities, western blot analysis, immunohistochemistry and mitochondrial DNA content).

RESULTS

Ketogenic diet and/or calorie restriction significantly reduced tumor growth and prolonged survival in the xenograft model. Neuroblastoma growth reduction correlated with decreased blood glucose concentrations and was characterized by a significant decrease in Ki-67 and phospho-histone H3 levels in the diet groups with low tumor growth. As in human tumor tissue, neuroblastoma xenografts showed distinctly low mitochondrial complex II activity in combination with a generalized low level of mitochondrial oxidative phosphorylation, validating the tumor model. Neuroblastoma showed no ability to adapt its mitochondrial oxidative phosphorylation activity to the change in nutrient supply induced by dietary intervention.

CONCLUSIONS

Our data suggest that targeting the metabolic characteristics of neuroblastoma could open a new front in supporting standard therapy regimens. Therefore, we propose that a ketogenic diet and/or calorie restriction should be further evaluated as a possible adjuvant therapy for patients undergoing treatment for neuroblastoma.

Mitochondria: The ketogenic diet--A metabolism-based therapy

Mitochondria are the energy-producing organelles of the cell, generating ATP via oxidative phosphorylation mainly by using pyruvate derived from glycolytic processing of glucose. Ketone bodies generated by fatty acid oxidation can serve as alternative metabolites for aerobic energy production. The ketogenic diet, which is high in fat and low in carbohydrates, mimics the metabolic state of starvation, forcing the body to utilize fat as its primary source of energy. The ketogenic diet is used therapeutically for pharmacoresistant epilepsy and for "rare diseases" of glucose metabolism (glucose transporter type 1 and pyruvate dehydrogenase deficiency). As metabolic reprogramming from oxidative phosphorylation toward increased glycolysis is a hallmark of cancer cells; there is increasing evidence that the ketogenic diet may also be beneficial as an adjuvant cancer therapy by potentiating the antitumor effect of chemotherapy and radiation treatment. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.