Increased cancer-related mortality for patients with type 2 diabetes who use sulfonylureas or insulin

Obesity related hyperinsulinaemia and hyperglycaemia and cancer development

Excess body weight in combination with physical inactivity is a major determinant for the development of insulin resistance with associated hyperglycaemia and hyperinsulinaemia and further leads to tumour development. Several prospective epidemiological studies have shown a direct association between excess weight and common malignancies, such as colon, breast (post-menopausal), endometrial, gallbladder, pancreatic, kidney and oesophageal cancers, but also less frequent malignancies, such as leukaemia, multiple myeloma and non-Hodgkin lymphoma. Insulin resistance and hyperinsulinaemia are certainly key biological mechanisms underlying the relationship between adiposity and tumour development. The anti-diabetic drug, metformin, in addition to reduction of insulin resistance has also shown anti-tumour properties, and is increasingly being considered as a drug to prevent and treat obesity-related cancers. Several biological pathways have been involved in the association between excess body weight, insulin resistance and cancer, such as chronic low-grade inflammation, glucose toxicity, AGE product metabolism and the adenosine monophosphate kinase pathway.

LKB1 and AMP-activated protein kinase control of mTOR signalling and growth

The AMP-activated serine/threonine protein kinase (AMPK) is a sensor of cellular energy status found in all eukaryotes that is activated under conditions of low intracellular ATP following stresses such as nutrient deprivation or hypoxia. In the past 5 years, work from a large number of laboratories has revealed that one of the major downstream signalling pathways regulated by AMPK is the mammalian target-of-rapamycin [mammalian target of rapamycin (mTOR) pathway]. Interestingly, like AMPK, the mTOR serine/threonine kinase plays key roles not only in growth control and cell proliferation but also in metabolism. Recent work has revealed that across eukaryotes mTOR orthologues are found in two biochemically distinct complexes and only one of those complexes (mTORC1 in mammals) is acutely sensitive to rapamycin and regulated by nutrients and AMPK. Many details of the molecular mechanism by which AMPK inhibits mTORC1 signalling have also been decoded in the past 5 years. AMPK directly phosphorylates at least two proteins to induce rapid suppression of mTORC1 activity, the TSC2 tumour suppressor and the critical mTORC1 binding subunit raptor. Here we explore the molecular connections between AMPK and mTOR signalling pathways and examine the physiological processes in which AMPK regulation of mTOR is critical for growth or metabolic control. The functional conservation of AMPK and TOR in all eukaryotes, and the sequence conservation around the AMPK phosphorylation sites in raptor across all eukaryotes examined suggest that this represents a fundamental cell growth module connecting nutrient status to the cell growth machinery. These findings have broad implications for the control of cell growth by nutrients in a number of cellular and organismal contexts.

Energy homeostasis and cancer prevention: the AMP-activated protein kinase

Caloric restriction has long been recognized as an extremely effective cancer preventive. Current population demographics suggest that caloric excess and obesity will lead to increased cancer incidence, underscoring the need to elucidate the molecular mechanisms that couple dysregulated energy homeostasis to aberrant cell growth. The AMP-activated protein kinase (AMPK) is a critical monitor of cellular energy status, largely studied for its importance in metabolic regulation. AMPK also controls processes relevant to tumor development, including cell cycle progression, protein synthesis, cell growth, and survival. Several tumor suppressors impinge on AMPK signaling, and activation of the kinase inhibits tumor growth. However, AMPK can also promote cancer in some settings, necessitating a more complete understanding of the complexities of this signaling network. Because dysregulated energy balance is a nexus for multiple chronic diseases of aging, drugs that target these pathways may find broad utility in aging populations.

The effects of adiponectin and metformin on prostate and colon neoplasia involve activation of AMP-activated protein kinase

Population studies provide evidence that obesity and insulin resistance are associated not only with elevated serum insulin levels and reduced serum adiponectin levels but also with increased risk of aggressive prostate and colon cancer. We show here that adiponectin activates AMP-activated protein kinase (AMPK) in colon (HT-29) and prostate (PC-3) cancer cells. These results are consistent with prior observations in myocytes, but we show that in epithelial cancer cells AMPK activation is associated with reduction in mammalian target of rapamycin activation as estimated by Ser(2448) phosphorylation, with reduction in p70S6 kinase activation as estimated by Thr(389) phosphorylation, with ribosomal protein S6 activation as estimated by Ser(235/236) phosphorylation, with reduction in protein translation as estimated by [(35)S]methionine incorporation, and with growth inhibition. Adiponectin-induced growth inhibition is significantly attenuated when AMPK level is reduced using small interfering RNA, indicating that AMPK is involved in mediating the antiproliferative action of this adipokine. Thus, adiponectin has the characteristics of a AMPK-dependent growth inhibitor that is deficient in obesity, and this may contribute to the adverse effects of obesity on neoplastic disease. Furthermore, metformin was observed to activate AMPK and to have growth inhibitory actions on prostate and colon cancer cells, suggesting that this compound may be of particular value in attenuating the adverse effects of obesity on neoplasia.

AMPK and the biochemistry of exercise: implications for human health and disease

AMPK (AMP-activated protein kinase) is a phylogenetically conserved fuel-sensing enzyme that is present in all mammalian cells. During exercise, it is activated in skeletal muscle in humans, and at least in rodents, also in adipose tissue, liver and perhaps other organs by events that increase the AMP/ATP ratio. When activated, AMPK stimulates energy-generating processes such as glucose uptake and fatty acid oxidation and decreases energy-consuming processes such as protein and lipid synthesis. Exercise is perhaps the most powerful physiological activator of AMPK and a unique model for studying its many physiological roles. In addition, it improves the metabolic status of rodents with a metabolic syndrome phenotype, as does treatment with AMPK-activating agents; it is therefore tempting to attribute the therapeutic benefits of regular physical activity to activation of AMPK. Here we review the acute and chronic effects of exercise on AMPK activity in skeletal muscle and other tissues. We also discuss the potential role of AMPK activation in mediating the prevention and treatment by exercise of specific disorders associated with the metabolic syndrome, including Type 2 diabetes and Alzheimer's disease.

Is it time to test metformin in breast cancer clinical trials?

Several studies have identified an increased risk of cancer in type 2 diabetic patients and this is in accordance with the hypothesis that increased insulin levels might promote cancer. Thus, there is a great interest in exploring the possibility that antidiabetic therapies lowering insulin levels could decrease cancer incidence or cancer-related mortality. Recent observational studies have shown that metformin, an oral safe and well-tolerated insulin-sensitizer antidiabetic drug, has been associated with reduced cancer risk. Recently, several preclinical studies have evaluated the effect of metformin in vivo on nude mice and showed a significant reduction of both breast epithelial cell proliferation and protein synthesis. Further investigations in the clinical setting are well-supported by the promising results obtained thus far. At the European Institute of Oncology, the Division of Cancer Prevention and Genetics is planning to conduct a clinical trial to evaluate the activity of metformin on tumor cell proliferation in breast cancer patients undergoing surgery. It will be a presurgical randomized, double blind, placebo-controlled phase II biomarker trial: 100 histologically confirmed breast cancer patients will be randomly assigned to metformin (850 mg twice/daily) or placebo for 28+7 days till surgery to assess drug activity on tumor proliferation, as measured by Ki-67. The confirmation of the efficacy of metformin on cancer cell proliferation may lead the way to larger chemoprevention clinical trials.

Insulin-lowering effects of metformin in women with early breast cancer

BACKGROUND

Obesity has been associated with poor breast cancer outcomes. Insulin may mediate this effect, interacting with insulin receptors on breast cancer cells. Metformin, a biguanide derivative used in the treatment of diabetes, reduces insulin levels in subjects with type 2 diabetes and other insulin-resistant states. If metformin lowers insulin levels in women with breast cancer, it may also improve breast cancer outcomes.

PATIENTS AND METHODS

We administered metformin (1500 mg per day) to 32 women with early breast cancer whose baseline insulin levels were at least 45 pmol/L to determine its effect on insulin levels.

RESULTS

Twenty-two (69%) women completed the 6-month intervention. Four women (12.5%) dropped out because of gastrointestinal side effects; the others withdrew for reasons not related to toxicity. Completers were similar to noncompleters for all baseline characteristics apart from global health, overall physical condition, overall quality of life, physical function, and social function (HRQOL), which was decreased in noncompleters. Metformin significantly lowered fasting insulin levels by 15.8 pmol/L (22.4%; P=.024) and improved insulin sensitivity by 25.6% (P=.018), total cholesterol by 5.3%, and low-density lipoprotein (LDL) cholesterol by 9.1%. Metformin reduced weight by 1.9 kg (2.5%; P=.01), and it had no significant effects on HRQOL or specific gastrointestinal symptoms (appetite, nausea/vomiting, diarrhea, constipation).

CONCLUSION

Metformin significantly lowers insulin levels, and it improves insulin resistance in nondiabetic women with breast cancer. A phase III randomized trial to evaluate its effects on breast cancer outcomes is recommended.

Balancing the decision of cell proliferation and cell fate

The control of cellular proliferation is key in the proper development of a complex organism, the maintenance of tissue homeostasis and the ability to respond to various hormonal and other inducers. Key in the control of proliferation is the retinoblastoma (Rb) protein which regulates the activity of a family of transcription factors known as E2Fs. The E2F proteins are now recognized to regulate the expression of a large number of genes associated with cell proliferation including genes encoding DNA replication as well as mitotic activities. What has also become clear over the past several years is the intimate relationship between the control of cell proliferation and the control of cell fate, particularly the activation of apoptotic pathways. Central in this connection is the Rb/E2F pathway that not only provides the primary signals for proliferation but at the same time, connects with the p53-dependent apoptotic pathway. This review addresses this inter-connection and the molecular mechanisms that control the decision between proliferation and cell death.

Fatty acid synthase: association with insulin resistance, type 2 diabetes, and cancer

BACKGROUND

An emerging paradigm supports the notion that deregulation of fatty acid synthase (FASN)-catalyzed de novo FA biogenesis could play a central role in the pathogenesis of metabolic diseases sharing the hallmark of insulin-resistance.

CONTENT

We reviewed pharmacological and genetic alterations of FASN activity that have been shown to significantly influence energy expenditure rates, fat mass, insulin sensitivity, and cancer risk. This new paradigm proposes that insulin-resistant conditions such as obesity, type 2 diabetes, and cancer arise from a common FASN-driven "lipogenic state". An important question then is whether the development or the progression of insulin-related metabolic disorders can be prevented or reversed by the modulation of FASN status. If we accept the paradigm of FASN dysfunction as a previously unrecognized link between insulin resistance, type 2 diabetes, and cancer, the use of insulin sensitizers in parallel with forthcoming FASN inhibitors should be a valuable therapeutic approach that, in association with lifestyle interventions, would concurrently improve energy-flux status, ameliorate insulin sensitivity, and alleviate the risk of lipogenic carcinomas.

CONCLUSIONS

Although the picture is currently incomplete and researchers in the field have plenty of work ahead, the latest clinical and experimental evidence that we discuss illuminates a functional and drug-modifiable link that connects FASN-driven endogenous FA biosynthesis, insulin action, and glucose homeostasis in the natural history of insulin-resistant pathologies.

Relationships between cancer and aging: a multilevel approach

The incidence of cancer increases with age in humans and in laboratory animals alike. There are different patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer in two ways: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine systems. Increased susceptibility to the effects of tumor promoters is found both in aged animals and aged humans, as predicted by the multistage model of carcinogenesis. Aging is associated with a number of events at the molecular, cellular and physiological levels that influence carcinogenesis and subsequent cancer growth. An improved understanding of age-associated variables impacting on the tumor microenvironment, as well as the cancer cells themselves, will result in improved treatment modalities in geriatric oncology.

Energy metabolism, cancer risk, and cancer prevention

Research concerning "cancer energetics" has become a popular area of investigation. This topic comprises two distinct fields: energetics at (1) the cellular level and (2) the whole organism level. Both of these have relevance to Cancer Risk and Cancer Prevention.

Gender risk of nonfatal stroke in type 2 diabetic patients differs depending on the type of treatment

BACKGROUND

The gender differences in stroke risk among diabetic patients with different treatments have not been studied previously. We aim to determine if there is a gender difference in nonfatal stroke risk in diabetic patients receiving different types of glucose-lowering treatments.

METHODS

In December 2005, data of type 2 diabetic patients were extracted from a nationwide population-based diabetes registry covering 11 Ukrainian regions. Male/female odds ratios (OR) for nonfatal stroke were calculated in three treatment groups: diet only 7,273/15,901, oral glucose-lowering drugs 15,109/33,913, and insulin 5,529/12,462 male/female. Male/female ORs of stroke were estimated using a logistic regression model.

RESULTS

The age-adjusted ORs of stroke were higher among diabetic men compared with diabetic women with oral glucose-lowering drug treatment (OR 1.37, 95% CI 1.22-1.54) and diet treatment only (OR 1.53, 95% CI 1.35-1.73). No differences were found among patients who used insulin (OR 0.97, 95% CI 0.84-1.11). Further adjustment for duration of type 2 diabetes, body mass index (BMI), systolic blood pressure, total cholesterol, and smoking affected the results only slightly.

CONCLUSIONS

The gender risks of nonfatal stroke in patients with type 2 diabetes appear to differ considerably depending on treatment types.

Therapeutic metformin/AMPK activation promotes the angiogenic phenotype in the ERalpha negative MDA-MB-435 breast cancer model

Metformin, a first line treatment for type 2 diabetes, has been implicated as a potential anti-neoplastic agent for breast cancers as well as other cancers. Metformin is known to work in part through the activation of AMP-dependent kinase (AMPK). AMPK is a key regulator of cellular energy homeostasis, especially under stress conditions where biosynthetic pathways are blocked by the phosphorylation of downstream AMPK substrates. Stimulation of AMPK by metformin resulted in a significant repression of cell proliferation and active MAPK1/2 in both estrogen receptor alpha (ERalpha) negative (MDA-MB-231, MDA-MB-435) and positive (MCF-7, T47D) human breast cancer cell lines. However, when ERalpha negative MDA-MB-435 cells were treated with metformin, they demonstrated increased expression of vascular endothelial growth factor (VEGF) in an AMPK dependent manner; while the ERalpha positive MCF-7 cells did not. Systemic therapy with metformin was tested for efficacy in an orthotopic model of ERalpha negative breast cancer performed in athymic nude mice. Surprisingly, metformin therapy significantly improved tumorigenic progression as compared to untreated controls. The metformin-treated group showed increased VEGF expression, intratumoral microvascular density and reduced necrosis. Metformin treatment was sufficient, however, to reduce systemic IGF-1 and the proliferation rate of tumor cells in vascularized regions. The data presented here suggests that, although metformin significantly represses breast cancer cell growth in vitro, the efficacy with respect to its therapeutic application for ERalpha negative breast cancer lesions in vivo may result in promotion of the angiogenic phenotype and increased tumorigenic progression.

Cell cycle arrest in Metformin treated breast cancer cells involves activation of AMPK, downregulation of cyclin D1, and requires p27Kip1 or p21Cip1

BACKGROUND

The antihyperglycemic drug metformin may have beneficial effects on the prevention and treatment of cancer. Metformin is known to activate AMP-activated protein kinase (AMPK). It has also been shown to inhibit cyclin D1 expression and proliferation of some cultured cancer cells. However, the mechanisms of action by which metformin mediates cell cycle arrest are not completely understood.

RESULTS

In this study, metformin was found to inhibit proliferation of most cultured breast cancer cell lines. This was independent of estrogen receptor, HER2, or p53 status. Inhibition of cell proliferation was associated with arrest within G0/G1 phase of the cell cycle. As in previous studies, metformin treatment led to activation of (AMPK) and downregulation of cyclin D1. However, these events were not sufficient for cell cycle arrest because they were also observed in the MDA-MB-231 cell line, which is not sensitive to growth arrest by metformin. In sensitive breast cancer lines, the reduction in cyclin D1 led to release of sequestered CDK inhibitors, p27Kip1 and p21Cip1, and association of these inhibitors with cyclin E/CDK2 complexes. The metformin-resistant cell line MDA-MB-231 expresses significantly lower levels of p27Kip1 and p21Cip1 than the metformin-sensitive cell line, MCF7. When p27Kip1 or p21Cip1 were overexpressed in MDA-MB-231, the cells became sensitive to cell cycle arrest in response to metformin.

CONCLUSION

Cell cycle arrest in response to metformin requires CDK inhibitors in addition to AMPK activation and cyclin D1 downregulation. This is of interest because many cancers are associated with loss or downregulation of CDK inhibitors and the results may be relevant to the development of anti-tumor reagents that target the AMPK pathway.

Insulin and insulin-like growth factor signalling in neoplasia

Insulin and insulin-like growth factors (IGFs) are well known as key regulators of energy metabolism and growth. There is now considerable evidence that these hormones and the signal transduction networks they regulate have important roles in neoplasia. Epidermiological, clinical and laboratory research methods are being used to investigate novel cancer prevention and treatment strategies related to insulin and IGF signalling. Pharmacological strategies under study include the use of novel receptor-specific antibodies, receptor kinase inhibitors and AMP-activated protein kinase activators such as metformin. There is evidence that insulin and IGF signalling may also be relevant to dietary and lifestyle factors that influence cancer risk and cancer prognosis. Recent results are encouraging and have justified the expansion of many translational research programmes.

The prince and the pauper. A tale of anticancer targeted agents

Cancer rates are set to increase at an alarming rate, from 10 million new cases globally in 2000 to 15 million in 2020. Regarding the pharmacological treatment of cancer, we currently are in the interphase of two treatment eras. The so-called pregenomic therapy which names the traditional cancer drugs, mainly cytotoxic drug types, and post-genomic era-type drugs referring to rationally-based designed. Although there are successful examples of this newer drug discovery approach, most target-specific agents only provide small gains in symptom control and/or survival, whereas others have consistently failed in the clinical testing. There is however, a characteristic shared by these agents: -their high cost-. This is expected as drug discovery and development is generally carried out within the commercial rather than the academic realm. Given the extraordinarily high therapeutic drug discovery-associated costs and risks, it is highly unlikely that any single public-sector research group will see a novel chemical "probe" become a "drug". An alternative drug development strategy is the exploitation of established drugs that have already been approved for treatment of non-cancerous diseases and whose cancer target has already been discovered. This strategy is also denominated drug repositioning, drug repurposing, or indication switch. Although traditionally development of these drugs was unlikely to be pursued by Big Pharma due to their limited commercial value, biopharmaceutical companies attempting to increase productivity at present are pursuing drug repositioning. More and more companies are scanning the existing pharmacopoeia for repositioning candidates, and the number of repositioning success stories is increasing. Here we provide noteworthy examples of known drugs whose potential anticancer activities have been highlighted, to encourage further research on these known drugs as a means to foster their translation into clinical trials utilizing the more limited public-sector resources. If these drug types eventually result in being effective, it follows that they could be much more affordable for patients with cancer; therefore, their contribution in terms of reducing cancer mortality at the global level would be greater.

Association between hepatocellular carcinoma and type 2 diabetes mellitus in Italy: Potential role of insulin

AIM: To investigate the relationships between Type 2 diabetes mellitus (DM2) and the risk of hepatocellular carcinoma (HCC).

METHODS: We studied the association between DM2 and HCC in a large case-control study that enrolled 465 consecutive Caucasian patients with HCC (78.3% males, mean age 68.5 ± 8.9 years) compared with an age and sex matched control group of 490 subjects.

RESULTS: Prevalence of DM2 was significantly higher in HCC patients (31.2% vs 12.7%; OR = 3.12, 95% CI: 2.22-4.43) and in HCC cases with alcohol abuse. DM2 has been diagnosed before the appearance of HCC in 84.1% of diabetic HCC subjects with mean duration of 141.5 mo, higher in cases treated with insulin than in those with oral antidiabetic agents (171.5 vs 118.7 mo). Compared to controls, males DM2 with HCC were more frequently treated with insulin (38.1% vs 17.6%, P = 0.009) and with sulfonylurea with or without metformin than with diet with or without metformin (84% vs 68.3%, P = 0.049).

CONCLUSION: DM2 in our patients is associated with a 3-fold increase risk of HCC. In most of our cases DM2 pre-existed to HCC. Patients with DM2 and chronic liver disease, particularly insulin treated males, should be considered for HCC close surveillance programs.

Metformin therapy and clinical uses

Metformin is now established as a first-line antidiabetic therapy for the management of type 2 diabetes. Its early use in treatment algorithms is supported by lack of weight gain, low risk of hypoglycaemia and its mode of action to counter insulin resistance. The drug's anti-atherosclerotic and cardioprotective effects have recently been confirmed in prospective and retrospective studies, and appear to reflect a collection of glucose-independent effects on the vascular endothelium, suppressant effects on glycation, oxidative stress and formation of adhesion molecules, stimulation of fibrinolysis and favourable effects on the lipid profile. Although avoidance of troublesome gastrointestinal tolerability issues requires careful dose titration, the risk of serious adverse events is considered low provided that contra-indications (especially with respect to renal function) are observed. As many of its actions go beyond glucose lowering, emerging evidence indicates potential benefits in other insulin-resistant states and possibly tumour suppression.

Nutrition, metabolic factors and cancer risk

Excess body weight (adiposity) and physical inactivity are increasingly being recognized as major nutritional risk factors for cancer, and especially for many of those cancer types that have increased incidence rates in affluent, industrialized parts of the world. In this review, an overview is presented of some key biological mechanisms that may provide important metabolic links between nutrition, physical activity and cancer, including insulin resistance and reduced glucose tolerance, increased activation of the growth hormone/IGF-I axis, alterations in sex-steroid synthesis and/or bioavailability, and low-grade chronic inflammation through the effects of adipokines and cytokines.

Insulin, insulin-like growth factors and neoplasia

Over the past decade, dozens of epidemiological studies and laboratory experiments have provided evidence for relationships between insulin-like growth factor (IGF) physiology and neoplasia. Population studies provide evidence for a modestly increased risk of a subsequent cancer diagnosis in subjects with IGF-I levels at the high end of the broad normal range, as compared to those at the low end of the normal range. At the cellular level, IGF-I receptor signalling has been shown to play an important role in facilitating the transforming action of a variety of oncogenes. Reducing receptor function with anti-receptor antibodies or specific tyrosine kinase inhibitors reduces the proliferation of many cancers in vitro and in vivo. At present, clinical relevance of the relationship between circulating IGF-I level and cancer risk is limited, but in terms of experimental therapeutics, many clinical trials have been initiated to investigate the possibility that the paradigm of hormonal treatment of cancer may be extended from targeting gonadal steroids to targeting the growth hormone-IGF-I axis.

Effects of chronic hyperinsulinemia in insulin-resistant patients

Selective insulin resistance influences pathogenesis and treatment of type 2 diabetes and metabolic syndrome. Downregulation of the antiatherogenic pathway and maintained activity of the proatherogenic and cancerogenic pathways lead to atherosclerosis and cancer. Exogenous insulin added to "compensatory" hyperinsulinemia might worsen the primary end points, resulting in potential increase in cardiovascular and cancer events in spite of improvement of surrogate metabolic end points. Conversely, metformin can improve primary and surrogate end points.

Cardiorespiratory fitness as a predictor of cancer mortality among men with pre-diabetes and diabetes

OBJECTIVE

The purpose of this article was to examine the risk of cancer mortality across levels of fitness and to examine the fitness-mortality relation for site-specific cancers in men with pre-diabetes and diabetes.

RESEARCH DESIGN AND METHODS

We examined the fitness-mortality relation for all-cause and site-specific cancer mortality among 18,858 men with pre-diabetes and 2,805 men with diabetes (aged 46.3 +/- 9.7 years [mean +/- SD]) from the Aerobics Center Longitudinal Study. We identified 719 cancer deaths during 354,558 person-years of risk. The duration of follow-up was 16.4 +/- 7.8 years (range <1-30.0 years).

RESULTS

In men with pre-diabetes, moderate (hazard ratio 0.71 [95% CI 0.57-0.88]) and high fitness (0.76 [0.60-0.96]) were associated with lower risks of cancer mortality compared with the low-fit group in a model adjusted for age, examination year, smoking, alcohol use, fasting glucose concentration, previous cancer, and BMI. Similarly, for individuals with diabetes, moderate (0.53 [0.35-0.82]) and high fitness (0.44 [0.26-0.73]) were associated with lower risks of cancer mortality compared with the low-fit group. Among all men, being fit was associated with a lower risk of mortality from gastrointestinal (0.55 [0.39-0.77]), colorectal (0.53 [0.30-0.96]), liver (0.22 [0.07-0.71]), and lung cancer (0.43 [0.30-0.60]).

CONCLUSIONS

In men with pre-diabetes and diabetes, higher levels of cardiorespiratory fitness were associated with lower risk of cancer mortality, particularly as a result of cancers of the gastrointestinal tract, compared with those who had low levels of fitness.

[Lights and shades in the application of new guidelines for the management of type 2 diabetes mellitus. Practical advice about combined therapy and insulin therapy]

Type 2 diabetes is a disease with an increasing prevalence due to the ageing and sedentary lifestyle of the general population. Its associated with the risk of developing a series of chronic complications in mid/long-term. The current guidelines recommend certain therapy targets that have proven difficult to achieve due to poor compliance or because doctors do not always adhere to expert guidelines. The inability to achieve an adequate glycemic control in the course of diabetes may result in part from the typical conservative stepwise treatment approach that includes monotherapy initiated alter failure of diet and exercise, followed by a combination of oral antiglycemic agents, and ultimately insulin therapy. With respect to insulin therapy, the availability of different analogues as well as the new routes of administration (e.g., inhaled insulin) may allow the early introduction of this therapy, which may be more readily accepted by the patient.

The role of insulin receptors and IGF-I receptors in cancer and other diseases

There is evidence, both in vitro and in vivo, that receptor tyrosine kinases play a key role in the formation and progression of human cancer. In particular, the insulin-like growth factor receptor (IGF-IR), a tyrosine kinase receptor for IGF-I and IGF-II, has been well documented in cell culture, animal studies, and humans to play a role in malignant transformation, progression, protection from apoptosis, and metastasis. In addition, the hormone insulin (which is very closely related to the IGFs) and its tyrosine kinase receptor (the IR, which is very closely related to the IGR-IR) have been documented both in vitro and in vivo to play a key role in cancer biology. Indeed, several epidemiological studies have shown that insulin resistance status, characterized by hyperinsulinaemia, is associated with an increased risk for a number of malignancies, including carcinomas of the breast, prostate, colon and kidney. Recent data have elucidated some molecular mechanisms by which IR is involved in cancer. IR is over-expressed in several human malignancies. Interestingly, one of the two IR isoform (IR-A) is especially over-expressed in cancer. IR-A is the IR foetal isoform and has the peculiar characteristic to bind not only insulin but also IGF-II. In addition, the IR contributes to formation of hybrid receptors with the IGF-IR (HR). By binding to hybrid receptors, insulin may stimulate specific IGF-IR signalling pathways. Over-expression of IR-A is, therefore, a major mechanism of IGF system over-activation in cancer. In this respect, IR-A isoform and hybrid receptors should be regarded as potential molecular targets, in addition to IGF-IR, for novel anti-cancer therapy. These findings may have important implications for both the prevention and treatment of common human malignancies. They underline the concept that hyperinsulinaemia, associated with insulin resistance and obesity, should be treated by changes in life style and/or pharmacological approaches to avoid an increased risk for cancer. Moreover, native insulin and insulin analogue administration should be carefully evaluated in terms of the possible increase in cancer risk.

Type 2 diabetes mellitus as risk factor for colorectal cancer

Colorectal cancer occurs more frequently in patients with type 2 diabetes mellitus. The hyperinsulinemia-hypothesis suggests that elevated levels of insulin and free IGF-1 promote proliferation of colon cells and lead to a survival benefit of transformed cells, ultimately resulting in colorectal cancer. In patients with type 2 diabetes mellitus, epidemiological studies show an increased risk for colorectal cancer and an even higher risk if patients are treated with sulphonylureas or insulin. Moreover, tumour progression at hyperinsulinemia is more rapid and tumour-associated mortality is increased. Colorectal cancer can be avoided by screening. Recommendations for colorectal cancer screening should employ the recent epidemiologic evidence. All patients with type 2 diabetes mellitus should be recommended to undergo colonoscopy before starting insulin therapy, and screening intervals should not exceed 5 years. For this concept, a review of the evidence is presented, and a screening algorithm for colorectal cancer in patients with type 2 diabetes mellitus is proposed.

Hyper-insulinaemia and cancer, meta-analyses of epidemiological studies

BACKGROUND

A substantial body of evidence links sex hormones, diet, excess body weight and physical activity to the risk of developing cancer at several sites common in affluent countries. The hypothesis that high circulating levels of insulin could be the underlying factor increasing cancer risk has been proposed. Epidemiological studies on markers of hyper-insulinaemia and cancer are reviewed and summarized.

METHODS

Studies of cancers of the colon and rectum, pancreas, breast, and endometrium examining the association with blood levels of C-peptide, insulin, glucose, glycated haemoglobin (HbA1c) were searched in PubMed. Multivariate, adjusted relative risks (RR) and their 95% confidence intervals were abstracted and summarized by meta-analyses.

RESULTS

Most of the studies identified were cohorts that relied on measurements obtained at baseline or assessed in blood stored at low temperature several years before the onset of cancer. The meta-analyses showed excess risks of colorectal and pancreatic cancers associated with higher levels of circulating C-peptide/insulin and with markers of glycaemia. Significant heterogeneity was found among four epidemiological studies of endometrial cancer and C-peptide giving a summary RR compatible with no association. Overall breast cancer risk was significantly higher in the upper categories of C-peptide/insulin, however, the excess derived entirely from retrospective studies.

CONCLUSION

Current evidence suggests that subjects who develop colorectal and pancreatic cancers have increased pre-diagnostic blood levels of insulin and glucose.

Prognostic value of serum liver enzymes levels in type 2 diabetic patients

BACKGROUND

Elevated liver enzymes are associated with cardiovascular disease, while their relationship with cancer-related mortality has not been assessed so far in diabetic patients.

METHODS

An observational cohort study was performed on a consecutive series of 1952 type 2 diabetic patients. The association of liver enzymes with all-cause and cause-specific mortality was assessed. Information on all-cause mortality was obtained by the City of Florence Registry Office.

RESULTS

The average duration of follow-up was 6.4 +/- 2.7 years. Over that period, 362 deaths were recorded (26.9%), with a yearly mortality rate of 4.2%. Age- and sex-adjusted HR of all-cause mortality for gamma glutamyl-transpeptidase (gamma-GT) gamma-GT > 40 U/l was 1.610 [1.245-2.082]. An increased cardiovascular mortality rate was observed in patients with elevation of gamma-GT, and gamma-GT and/or alanine aminotransferase (ALT), when compared with the rest of the sample (15.3 vs 10.8%, p < 0.05; and 15.2 vs 10.7%, p < 0.05, respectively). Similar results were observed when considering cancer-related mortality. The association of higher gamma-GT levels with all-cause, cardiovascular, and cancer-related mortality was confirmed at a multivariate analysis after adjustment for potential confounders.

CONCLUSIONS

The present study shows that, in type 2 diabetic patients, higher gamma-GT, but not ALT, is associated with increased mortality for cardiovascular disease and malignancies.

Insulin, insulin-like growth factors, insulin resistance, and neoplasia

An accumulating body of epidemiologic and laboratory evidence suggests that insulin and insulin-like growth factors influence both the risk and the prognosis of cancer. In this brief review, I highlight topics covered in my lecture on research directions in this field, including the view that metformin deserves investigation as a potential adjunct in the treatment or prevention of cancer in persons with hyperinsulinemia.

Are sulphonylureas all the same? A cohort study on cardiovascular and cancer-related mortality

BACKGROUND

Aim of the present study is the comparison of all-cause, cardiovascular and non-cardiovascular mortality, and cardiac morbidity, between patients treated with glibenclamide and gliclazide.

METHODS

A retrospective observational cohort study was performed on a consecutive series of 568 outpatients (282 women, 286 men) with type 2 diabetes treated with either glibenclamide (n = 378) or gliclazide (n = 190). Information on all-cause mortality and on causes of death up to 31 December 2004 was obtained by the City of Florence Registry Office. Non-fatal cases requiring hospitalization were identified through the regional hospital discharge system using International Classification of Diseases.

RESULTS

Mean follow-up was 5.0 +/- 1.6 and 4.4 +/- 2.0 years for death and cardiac events, respectively; during follow-up, 33 and 11 deaths were observed in the glibenclamide and gliclazide groups, with a yearly mortality rate of 4.3 and 2.2%, respectively (p < 0.05). At Cox regression, after adjustment for potential confounders, including comorbidity, glibenclamide treatment was associated with a significant increase in all-cause mortality [OR 2.1(1.2;2.7), p < 0.05], while the difference in cardiovascular mortality was not statistically significant after adjustment for age and sex. Mortality for malignancies was significantly higher in patients treated with glibenclamide after adjustment for age, sex, BMI, and insulin and metformin treatment, [OR 3.6(1.1;11.9); p < 0.05]. A higher incidence of cardiac events was associated with glibenclamide treatment only in patients with previously known ischaemic heart disease.

CONCLUSIONS

Treatment with glibenclamide could be associated with higher mortality for cardiovascular diseases and malignancies, in comparison with gliclazide.

Systemic treatment with the antidiabetic drug metformin selectively impairs p53-deficient tumor cell growth

The effect of the antidiabetic drug metformin on tumor growth was investigated using the paired isogenic colon cancer cell lines HCT116 p53(+/+) and HCT116 p53(-/-). Treatment with metformin selectively suppressed the tumor growth of HCT116 p53(-/-) xenografts. Following treatment with metformin, we detected increased apoptosis in p53(-/-) tumor sections and an enhanced susceptibility of p53(-/-) cells to undergo apoptosis in vitro when subject to nutrient deprivation. Metformin is proposed to function in diabetes treatment as an indirect activator of AMP-activated protein kinase (AMPK). Treatment with AICAR, another AMPK activator, also showed a selective ability to inhibit p53(-/-) tumor growth in vivo. In the presence of either of the two drugs, HCT116 p53(+/+) cells, but not HCT116 p53(-/-) cells, activated autophagy. A similar p53-dependent induction of autophagy was observed when nontransformed mouse embryo fibroblasts were treated. Treatment with either metformin or AICAR also led to enhanced fatty acid beta-oxidation in p53(+/+) MEFs, but not in p53(-/-) MEFs. However, the magnitude of induction was significantly lower in metformin-treated cells, as metformin treatment also suppressed mitochondrial electron transport. Metformin-treated cells compensated for this suppression of oxidative phosphorylation by increasing their rate of glycolysis in a p53-dependent manner. Together, these data suggest that metformin treatment forces a metabolic conversion that p53(-/-) cells are unable to execute. Thus, metformin is selectively toxic to p53-deficient cells and provides a potential mechanism for the reduced incidence of tumors observed in patients being treated with metformin.

Obesity, diabetes, and risk of prostate cancer: results from the prostate cancer prevention trial

Studies on the relationship between obesity and prostate cancer incidence are inconsistent. In part, this inconsistency may be due to a differential effect of obesity on low-grade and high-grade cancer or confounding of the association of obesity with prostate cancer risk by diabetes. We investigated the associations of obesity and diabetes with low-grade and high-grade prostate cancer risk. Data were from 10,258 participants (1,936 prostate cancers) in the Prostate Cancer Prevention Trial who all had cancer presence or absence determined by prostate biopsy. Multiple logistic regression was used to model the risk of total prostate cancer, and polytomous logistic regression was used to model the risk of low-grade and high-grade prostate cancer. Compared with men with body mass index < 25, obese men (body mass index > or =30) had an 18% [odds ratio (OR), 0.82; 95% confidence interval (95% CI), 0.69-0.98] decreased risk of low-grade prostate cancer (Gleason <7) and a 29% (OR, 1.29; 95% CI, 1.01-1.67) increased risk of high-grade prostate cancer (Gleason > or =7) or, alternatively, a 78% (OR, 1.78; 95% CI, 1.10-2.87) increased risk defining high-grade cancer as Gleason sum 8 to 10. Diabetes was associated with a 47% (OR, 0.53; 95% CI, 0.34-0.83) reduced risk of low-grade prostate cancer and a 28% (OR, 0.72; 95% CI, 0.55-0.94) reduced risk of high-grade prostate cancer. Associations of obesity or diabetes with cancer risk were not substantially changed by mutually statistical controlling for each other. Obesity increases the risk of high-grade but decreases the risk of low-grade prostate cancer, and this relationship is independent of the lower risk for prostate cancer among men with diabetes.

AMP-activated protein kinase as a drug target

The AMP-activated protein kinase (AMPK) system is a regulator of energy balance at both the cellular and whole-body levels that, once activated by low energy status, effects a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. It now appears to be the major target for two existing classes of drug used to treat type 2 diabetes, i.e., the biguanides and thiazolidinediones. However, in both cases these activate AMPK indirectly, and an interesting question concerns whether a drug that directly activated AMPK would retain the therapeutic benefits of the existing drugs while eliminating unwanted side effects. AMPK activators also now have potential as anticancer drugs.

Insulin-like growth factor-related signaling and cancer development

In this review, selected examples of recent research developments concerning insulin-like growth factors (IGFs) and insulin in the context of cancer risk assessment and prevention will be discussed. We reviewed background information related to IGF physiology at the cellular and whole-organism levels, together with prior work concerning IGF-I levels and risk of a variety of cancers, including breast, prostate, colon, and lung in 2004 (Pollak et al. 2004). A comprehensive update to that general review (Pollak et al. 2004) is scheduled for Nature Reviews Cancer in early 2007.

Biology of aging and cancer

BACKGROUND

The incidence of cancer increases with age in both humans and laboratory animals. A clear understanding of the causes of the age-related increase in cancer incidence is needed to develop a strategy for primary cancer prevention.

METHODS

We summarized the data available in the literature and our own experience in hormonal metabolic shifts in organisms and disturbances at tissue and cellular levels observed in natural aging and in different types of carcinogenesis in vivo.

RESULTS

There are incongruent patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer by at least two mechanisms: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine system. Increased susceptibility to the effects of tumor promoters is found in both aged animals and aged humans, as predicted by the multistage model of carcinogenesis.

CONCLUSIONS

Aging is associated with a number of events at the molecular, cellular and physiologic levels that influence carcinogenesis and subsequent cancer growth. A clearer understanding of these events will help in predicting and treating cancer more effectively.

Metformin Is an AMP Kinase–Dependent Growth Inhibitor for Breast Cancer Cells

Recent population studies provide clues that the use of metformin may be associated with reduced incidence and improved prognosis of certain cancers. This drug is widely used in the treatment of type 2 diabetes, where it is often referred to as an "insulin sensitizer" because it not only lowers blood glucose but also reduces the hyperinsulinemia associated with insulin resistance. As insulin and insulin-like growth factors stimulate proliferation of many normal and transformed cell types, agents that facilitate signaling through these receptors would be expected to enhance proliferation. We show here that metformin acts as a growth inhibitor rather than an insulin sensitizer for epithelial cells. Breast cancer cells can be protected against metformin-induced growth inhibition by small interfering RNA against AMP kinase. This shows that AMP kinase pathway activation by metformin, recently shown to be necessary for metformin inhibition of gluconeogenesis in hepatocytes, is also involved in metformin-induced growth inhibition of epithelial cells. The growth inhibition was associated with decreased mammalian target of rapamycin and S6 kinase activation and a general decrease in mRNA translation. These results provide evidence for a mechanism that may contribute to the antineoplastic effects of metformin suggested by recent population studies and justify further work to explore potential roles for activators of AMP kinase in cancer prevention and treatment.

Glucose metabolism and cancer

The first identified biochemical hallmark of tumor cells was a shift in glucose metabolism from oxidative phosphorylation to aerobic glycolysis. We now know that much of this metabolic conversion is controlled by specific transcriptional programs. Recent studies suggest that activation of the hypoxia-inducible factor (HIF) is a common consequence of a wide variety of mutations underlying human cancer. HIF stimulates expression of glycolytic enzymes and decreases reliance on mitochondrial oxidative phosphorylation in tumor cells, which occurs even under aerobic conditions. In addition, recent efforts have also connected the master metabolic regulator AMP-activated protein kinase (AMPK) to several human tumor suppressors. Several promising therapeutic strategies based on modulation of AMPK, HIF and other metabolic targets have been proposed to exploit the addiction of tumor cells to increased glucose uptake and glycolysis.

The LKB1 tumor suppressor kinase in human disease

Inactivating germline mutations in the LKB1 gene underlie Peutz-Jeghers syndrome characterized by hamartomatous polyps and an elevated risk for cancer. Recent studies suggest the involvement of LKB1 also in more common human disorders including diabetes and in a significant fraction of lung adenocarcinomas. These observations have increased the interest towards signaling pathways of this tumor suppressor kinase. The recent breakthroughs in understanding the molecular functions of the LKB1 indicate its contribution as a regulator of cell polarity, energy metabolism and cell proliferation. Here we review how the substrates and cellular functions of LKB1 may be linked to Peutz-Jeghers syndrome and other diseases, and discuss how some of the molecular changes associated with altered LKB1 signaling might be used in therapeutic approaches.

AMPK and cell proliferation--AMPK as a therapeutic target for atherosclerosis and cancer

AMPK is a serine/threonine protein kinase, which serves as an energy sensor in all eukaryotic cell types. Published studies indicate that AMPK activation strongly suppresses cell proliferation in non-malignant cells as well as in tumour cells. These actions of AMPK appear to be mediated through multiple mechanisms including regulation of the cell cycle and inhibition of protein synthesis, de novo fatty acid synthesis, specifically the generation of mevalonate as well as other products downstream of mevalonate in the cholesterol synthesis pathway. Cell cycle regulation by AMPK is mediated by up-regulation of the p53-p21 axis as well as regulation of TSC2-mTOR (mammalian target of rapamycin) pathway. The AMPK signalling network contains a number of tumour suppressor genes including LKB1, p53, TSC1 and TSC2, and overcomes growth factor signalling from a variety of stimuli (via growth factors and by abnormal regulation of cellular proto-oncogenes including PI3K, Akt and ERK). These observations suggest that AMPK activation is a logical therapeutic target for diseases rooted in cellular proliferation, including atherosclerosis and cancer. In this review, we discuss about exciting recent advances indicating that AMPK functions as a suppressor of cell proliferation by controlling a variety of cellular events in normal cells as well as in tumour cells.

A cross-sectional study of health-related quality of life deficits in individuals with comorbid diabetes and cancer

BACKGROUND

Numerous studies have identified a reduced health related quality of life (HRQL) in patients that have either diabetes or cancer. We assessed the HRQL burden in patients with these comorbid conditions, postulating that they would have even greater HRQL deficits.

METHODS

Data from the Public Use File of the Canadian Community Health Survey (PUF CCHS) Cycle 1.1 (September 2000-November 2001) were used for this analysis. The total sample size of the CCHS PUF is 130,880 individuals. We used the Health Utilities Index Mark 3 (HUI3) to assess HRQL in patients with: 1) comorbid diabetes and cancer, 2) diabetes alone, 3) cancer alone, and 4) no diabetes or cancer. Analysis of covariance was used to compare the mean overall HUI3 score, controlling for age, sex, marital status, body mass index (BMI), physical activity level, smoking status, education level, depression status, and other chronic conditions.

RESULTS

We identified 113,587 individuals (87%) with complete data for the analysis. The comorbid diabetes and cancer group were older and a larger proportion reported being obese, inactive, having less than a secondary education and more chronic conditions when compared to the other three cohorts (p < 0.0001). However, the diabetes and cancer cohort was less likely to be depressed (p < 0.0001). Overall HUI3 scores were significantly lower for the diabetes and cancer group (unadjusted mean (SD): 0.67 (0.30)), compared to diabetes (0.78 (0.27)), cancer (0.78 (0.25)), and the reference group (0.89 (0.18)) (p < 0.0001). After adjusting for covariates, the comorbid diabetes and cancer group continued to have significantly lower overall HUI3 scores than the reference group (unstandardized mean difference: -0.11, 95% CI: -0.13 to -.0.09) (p < 0.0001).

CONCLUSION

Individuals with diabetes and cancer had a clinically important and significantly lower HRQL than those with either condition alone. A better understanding of the relationship between diabetes and cancer, and their associated comorbidities, complications, and HRQL deficits may have important implications for prevention and management strategies.