The effect of leptin administration on mammary tumor growth in diabetic mice

Obesity is associated with hyperleptinemia and this has led to the suggestion that leptin maybe a factor in cancer progression. To study the effect of leptin on cancer progression we used a mouse model of diabetes that was shown to enhance tumor progression and thereby determine if leptin affects cancer progression despite improvements in metabolic status. Mammary tumors were allowed to develop in male and female mice following orthotopic injection of cells expressing oncogenes. After 2 weeks leptin was administered to the mice using Alzet pumps. In these mice leptin failed to stimulate tumor progression; indeed, in those studies where glucose tolerance improved tumor growth was actually inhibited. Thus, the possibility exists that the effect of leptin on tumor progression maybe opposed by improvements in metabolism.

Effect of online diabetes training for hospitalists on inpatient glycaemia

AIM

An online diabetes course for medical residents led to lower patient blood glucose, but also increased hypoglycaemia despite improved trainee confidence and knowledge. Based on these findings, we determined whether an optimized educational intervention delivered to hospitalists (corresponding to an Acute Physician or Specialist in Acute Hospital Medicine in the UK) improved inpatient glycaemia without concomitant hypoglycaemia.

METHODS

All 22 hospitalists at an academic medical centre were asked to participate in an online curriculum on the management of inpatient dysglycaemia in autumn 2009 and a refresher course in spring 2010.

RESULTS

All hospitalists completed the initial intervention. Median event blood glucose decreased from 9.3 mmol/l (168 mg/dl) pre-intervention to 7.8 mmol/l (141 mg/dl) post-intervention and 8.5 mmol/l (153 mg/dl) post-refresher (P < 0.001 for both). Hospitalizations categorized as hyperglycaemia decreased from 83.3 to 55.6% (P = 0.014), with a trend towards euglycaemia (10-28.9%, P = 0.08) and no change in hypoglycaemia. Hyperglycaemic patient-days decreased from 72.0 to 57.3% (P = 0.004), with greater target glycaemia (27.3-39.4%, P = 0.016) and no change in hypoglycaemia.

CONCLUSIONS

An optimized online educational intervention delivered to hospitalists yielded significant improvements in inpatient glycaemia without increased hypoglycaemia.

Does a single nucleotide polymorphism in the FGFR explain the connection between diabetes and cancer?

A polymorphism in the fibroblast growth factor receptor 4 gene has been associated with cancer progression and treatment resistance and is now reported to increase insulin secretion, providing a possible genetic link between hyperinsulinemia and cancer (Ezzat et al., 2013).

Personalized management of hyperglycemia in type 2 diabetes: reflections from a Diabetes Care Editors' Expert Forum

In June 2012, 13 thought leaders convened in a Diabetes Care Editors' Expert Forum to discuss the concept of personalized medicine in the wake of a recently published American Diabetes Association/European Association for the Study of Diabetes position statement calling for a patient-centered approach to hyperglycemia management in type 2 diabetes. This article, an outgrowth of that forum, offers a clinical translation of the underlying issues that need to be considered for effectively personalizing diabetes care. The medical management of type 2 diabetes has become increasingly complex, and its complications remain a great burden to individual patients and the larger society. The burgeoning armamentarium of pharmacological agents for hyperglycemia management should aid clinicians in providing early treatment to delay or prevent these complications. However, trial evidence is limited for the optimal use of these agents, especially in dual or triple combinations. In the distant future, genotyping and testing for metabolomic markers may help us to better phenotype patients and predict their responses to antihyperglycemic drugs. For now, a personalized ("n of 1") approach in which drugs are tested in a trial-and-error manner in each patient may be the most practical strategy for achieving therapeutic targets. Patient-centered care and standardized algorithmic management are conflicting approaches, but they can be made more compatible by recognizing instances in which personalized A1C targets are warranted and clinical circumstances that may call for comanagement by primary care and specialty clinicians.

Hyperinsulinemia promotes metastasis to the lung in a mouse model of Her2-mediated breast cancer

The Her2 oncogene is expressed in ∼25% of human breast cancers and is associated with metastatic progression and poor outcome. Epidemiological studies report that breast cancer incidence and mortality rates are higher in women with type 2 diabetes. Here, we use a mouse model of Her2-mediated breast cancer on a background of hyperinsulinemia to determine how elevated circulating insulin levels affect Her2-mediated primary tumor growth and lung metastasis. Hyperinsulinemic (MKR(+/+)) mice were crossed with doxycycline-inducible Neu-NT (MTB/TAN) mice to produce the MTB/TAN/MKR(+/+) mouse model. Both MTB/TAN and MTB/TAN/MKR(+/+) mice were administered doxycycline in drinking water to induce Neu-NT mammary tumor formation. In tumor tissues removed at 2, 4, and 6 weeks of Neu-NT overexpression, we observed increased tumor mass and higher phosphorylation of the insulin receptor/IGF1 receptor, suggesting that activation of these receptors in conditions of hyperinsulinemia could contribute to the increased growth of mammary tumors. After 12 weeks on doxycycline, although no further increase in tumor weight was observed in MTB/TAN/MKR(+/+) compared with MTB/TAN mice, the number of lung metastases was significantly higher in MTB/TAN/MKR(+/+) mice compared with controls (MTB/TAN/MKR(+/+) 16.41±4.18 vs MTB/TAN 5.36±2.72). In tumors at the 6-week time point, we observed an increase in vimentin, a cytoskeletal protein and marker of mesenchymal cells, associated with epithelial-to-mesenchymal transition and cancer-associated fibroblasts. We conclude that hyperinsulinemia in MTB/TAN/MKR(+/+) mice resulted in larger primary tumors, with more mesenchymal cells and therefore more aggressive tumors with more numerous pulmonary metastases.

Post-transcriptional activation of PPAR alpha by KLF6 in hepatic steatosis

BACKGROUND & AIMS

Dysregulated glucose homeostasis and lipid accumulation characterize non-alcoholic fatty liver disease (NAFLD), but underlying mechanisms are obscure. We report here that Krüppel-like factor 6 (KLF6), a ubiquitous transcription factor that promotes adipocyte differentiation, also provokes the metabolic abnormalities of NAFLD by post-transcriptionally activating PPARα-signaling.

METHODS

Mice with either hepatocyte-specific depletion of KLF6 ('ΔHepKlf6') or global KLF6 heterozygosity (Klf6+/-) were fed a high fat diet (HFD) or chow for 8 or 16 weeks. Glucose and insulin tolerance tests were performed to assess insulin sensitivity. Overexpression and knockdown of KLF6 in cultured cells enabled the elucidation of underlying mechanisms. In liver samples from a cohort of 28 NAFLD patients, the expression of KLF6-related target genes was quantified.

RESULTS

Mice with global- or hepatocyte-depletion of KLF6 have reduced body fat content and improved glucose and insulin tolerance, and are protected from HFD-induced steatosis. In hepatocytes, KLF6 deficiency reduces PPARα-regulated genes (Trb3, Pepck) with diminished PPARα protein but no change in Pparα mRNA, which is explained by the discovery that KLF6 represses miRNA 10b, which leads to induction of PPARα. In NAFLD patients with advanced disease and inflammation, the expression of miRNA 10b is significantly downregulated, while PEPCK mRNA is upregulated; KLF6 mRNA expression also correlates with TRB3 as well as PEPCK gene expression.

CONCLUSIONS

KLF6 increases PPARα activity, whereas KLF6 loss leads to PPARα repression and attenuation of lipid and glucose abnormalities associated with a high fat diet. The findings establish KLF6 as a novel regulator of hepatic glucose and lipid metabolism in fatty liver.

Investigating new therapeutic strategies targeting hyperinsulinemia's mitogenic effects in a female mouse breast cancer model

Epidemiological and experimental studies have identified hyperinsulinemia as an important risk factor for breast cancer induction and for the poor prognosis in breast cancer patients with obesity and type 2 diabetes. Recently it was demonstrated that both the insulin receptor (IR) and the IGF-IR mediate hyperinsulinemia's mitogenic effect in several breast cancer models. Although IGF-IR has been intensively investigated, and anti-IGF-IR therapies are now in advanced clinical trials, the role of the IR in mediating hyperinsulinemia's mitogenic effect remains to be clarified. Here we aimed to explore the potential of IR inhibition compared to dual IR/IGF-IR blockade on breast tumor growth. To initiate breast tumors, we inoculated the mammary carcinoma Mvt-1 cell line into the inguinal mammary fat pad of the hyperinsulinemic MKR female mice, and to study the role of IR, we treated the mice bearing tumors with the recently reported high-affinity IR antagonist-S961, in addition to the well-documented IGF-IR inhibitor picropodophyllin (PPP). Although reducing IR activation, with resultant severe hyperglycemia and hyperinsulinemia, S961-treated mice had significantly larger tumors compared to the vehicle-treated group. This effect maybe secondary to the severe hyperinsulinemia mediated via the IGF-1 receptor. In contrast, PPP by partially inhibiting both IR and IGF-IR activity reduced tumor growth rate with only mild metabolic consequences. We conclude that targeting (even partially) both IR and IGF-IRs impairs hyperinsulinemia's effects in breast tumor development while simultaneously sparing the metabolic abnormalities observed when targeting IR alone with virtual complete inhibition.

Mammary tumor growth and pulmonary metastasis are enhanced in a hyperlipidemic mouse model

Dyslipidemia has been associated with an increased risk for developing cancer. However, the implicated mechanisms are largely unknown. To explore the role of dyslipidemia in breast cancer growth and metastasis, we used the apolipoprotein E (ApoE) knockout mice (ApoE(-/-)), which exhibit marked dyslipidemia, with elevated circulating cholesterol and triglyceride levels in the setting of normal glucose homeostasis and insulin sensitivity. Non-metastatic Met-1 and metastatic Mvt-1 mammary cancer cells derived from MMTV-PyVmT/FVB-N transgenic mice and c-Myc/vegf tumor explants respectively, were injected into the mammary fat pad of ApoE(-/-) and wild-type (WT) females consuming a high-fat/high-cholesterol diet and tumor growth was evaluated. ApoE(-/-) mice exhibited increased tumor growth and displayed a greater number of spontaneous metastases to the lungs. Furthermore, intravenous injection of Mvt-1 cells resulted in a greater number of pulmonary metastases in the lungs of ApoE(-/-) mice compared with WT controls. To unravel the molecular mechanism involved in enhanced tumor growth in ApoE(-/-) mice, we studied the response of Mvt-1 cells to cholesterol in vitro. We found that cholesterol increased Akt(S473) phosphorylation in Mvt-1 cells as well as cellular proliferation, whereas cholesterol depletion in the cell membrane abrogated Akt(S473) phosphorylation induced by exogenously added cholesterol. Furthermore, in vivo administration of BKM120, a small-molecule inhibitor of phosphatidylinositol 3-kinase (PI3K), alleviated dyslipidemia-induced tumor growth and metastasis in Mvt-1 model with a concomitant decrease in PI3K/Akt signaling. Collectively, we suggest that the hypercholesterolemic milieu in the ApoE(-/-) mice is a favorable setting for mammary tumor growth and metastasis.

The epidemiology and molecular mechanisms linking obesity, diabetes, and cancer

The worldwide epidemic of obesity is associated with increasing rates of the metabolic syndrome and type 2 diabetes. Epidemiological studies have reported that these conditions are linked to increased rates of cancer incidence and mortality. Obesity, particularly abdominal obesity, is associated with insulin resistance and the development of dyslipidemia, hyperglycemia, and ultimately type 2 diabetes. Although many metabolic abnormalities occur with obesity and type 2 diabetes, insulin resistance and hyperinsulinemia appear to be central to these conditions and may contribute to dyslipidemia and altered levels of circulating estrogens and androgens. In this review, we will discuss the epidemiological and molecular links between obesity, type 2 diabetes, and cancer, and how hyperinsulinemia and dyslipidemia may contribute to cancer development. We will discuss how these metabolic abnormalities may interact with estrogen signaling in breast cancer growth. Finally, we will discuss the effects of type 2 diabetes medications on cancer risk.

Obesity, type 2 diabetes, and cancer: the insulin and IGF connection

Epidemiological studies suggest a positive association between obesity and type 2 diabetes mellitus (T2D) with the risk of cancer and cancer-related mortality. Insulin resistance, hyperinsulinemia, increased levels of IGF, elevated levels of steroid and peptide hormones, and inflammatory markers appear to play a role in the connection between these different diseases. Medications, such as metformin and exogenous insulin, used to treat T2D may affect the risk of cancer and cancer-related mortality. Newer therapies targeting the insulin and IGF1 systems are being developed for use in cancer therapy.

Diabetes, glucose control, glucose lowering medications, and cancer risk: a 10-year population-based historical cohort

Background

Both diabetes and glucose-lowering medications have been associated with an increased risk of cancer incidence. This study will compare cancer incidence rates in individuals with and without diabetes; and will investigate, in individuals with diabetes, an association between glucose control and cancer incidence; and between the use of specific glucose-lowering medications, as well as no drug exposure, and cancer incidence.

Methods/design

This is a population based historical cohort study of all individuals aged 21 years or older (about 2,300,000) who were insured by Clalit Health Services, the largest health maintenance organization in Israel during a ten-year study period. Four study groups will be established according to the status of diabetes and cancer at study entry, Jan 1, 2002: cancer free, diabetes free; cancer free, diabetes prevalent; cancer prevalent, diabetes free; and cancer prevalent, diabetes prevalent. Individuals without diabetes at study entry will be followed for diabetes incidence, and all four groups will be followed for specific cancer incidence, including second primary neoplasms. Glucose control will be assessed by HbA1c and by fasting plasma glucose levels. Time dependent regression models for cancer incidence will account for glucose-lowering medications as they are added and changed over the follow-up period. A large number of demographic and clinical variables will be considered, including: age, gender, BMI, smoking status, concomitant medications, glucose control (assessed by HbA1c and by fasting plasma glucose) and cancer screening tests.

Discussion

Strengths of this study include the large population; high quality comprehensive data; comparison to individuals without diabetes, and to those with diabetes but not treated with glucose-lowering medications; and the extensive range of variables available for analysis. The great increases in diabetes prevalence and in treatment options render this study particularly relevant and timely. The Israeli national healthcare system, characterized by high standard and uniform healthcare, offers an advantageous environment for its conduct.

Determining mammosphere-forming potential: application of the limiting dilution analysis

Originally adapted from the neurosphere assay, the nonadherent mammosphere assay has been utilized to assess early progenitor/stem cell frequency in a given population of mammary epithelial cells. This method has also been used to measure the frequency of tumorsphere initiating cells in both primary mammary tumors as well as in tumor cell lines. Although, the mammosphere assay has been used extensively in the mammary gland field, a standard method of quantifying and analyzing sphere growth in this assay has remained undefined. Here, we discuss the use and benefit of using a limiting dilution analysis to quantify sphere-forming frequency in primary mammary epithelial cells grown in nonadherent conditions.

Fibronectin glycation increases IGF-I induced proliferation of human aortic smooth muscle cells

The advanced glycation end products, namely AGEs, contribute to long-termed complications of diabetes mellitus, including macroangiopathy, where smooth muscle cells (SMC) proliferation stimulated by platelet-derived growth factor (PDGF) isoforms and insulin-like growth factor-I (IGF-I) plays an important role. The objective of the present study was to investigate the effect of an AGE-modified extracellular matrix protein on IGF-I induced SMC proliferation and on the IGF-I-IGF binding protein 4 (IGFBP-4) axis under basal conditions and after stimulation with PDGF-BB. IGF-I resulted in significantly higher thymidine incorporation in SMC seeded on AGE-modified fibronectin (AGE-FN) in comparison to cells seeded on fibronectin (FN). This augmented proliferation could not be accounted for by increased expression of IGF-IR, by decreased secretion of IGFBP-4, a binding protein that inhibits IGF-I mitogenic effects or by increased IGF-IR autophosphorylation. PDGF-BB did not modulate IGF-IR and IGFBP-4 mRNA expression in any of the substrata, however, this growth factor elicited opposite effects on the IGFBP-4 content in the conditioned media, increasing it in cells plated on FN and diminishing it in cells plated on AGE-FN. These findings suggest that one mechanism by which AGE-modified proteins is involved in the pathogenesis of diabetes-associated atherosclerosis might be by increasing SMC susceptibility to IGF-I mitogenic effects.

The worldwide diabetes epidemic

PURPOSE OF REVIEW

An overview of the global epidemic of diabetes and its impact on the understanding of the disease.

RECENT FINDINGS

Once thought of as a disease of the West, the prevalence of diabetes mellitus is increasing at alarming rates in many other areas of the world. In recent years, significant attention has been placed on the growing Asian diabetes epidemic. As a result, the medical community has come to understand that previously defined risk factors, particularly BMI, may not be applicable to the global community. The heterogeneity of the disease has been demonstrated both through anthropometric and genetic studies. Despite this heterogeneity, some treatments, particularly lifestyle interventions, have been found to have an ethnic nonspecific positive impact on the disease.

SUMMARY

Diabetes promises to become an even larger public health issue with significant social and economic burden with clinical practice and public health policy implications. Further population studies and identification of ethnic specific risk factors will guide research to develop a better understanding of the disease.

Insulin-like growth factor 1 attenuates antiestrogen- and antiprogestin-induced apoptosis in ER+ breast cancer cells by MEK1 regulation of the BH3-only pro-apoptotic protein Bim

Introduction

In this pre-clinical in vitro study conducted in estrogen receptor positive (ER+) breast cancer cells, we have characterized the effects of insulin-like growth factor I (IGF-1) on the cytostatic and cytotoxic action of antiestrogen treatment when used as a single agent or in combination with the antiprogestin mifepristone (MIF). Our goal was to identify new molecular targets to improve the efficacy of hormonal therapy in breast cancer patients that have a poor response to hormonal therapy, in part, due to high circulating levels of unbound insulinIGF-1.

Methods

IGF-1-mediated effects on cytostasis and apoptotic cell death were determined with cell counts conducted in the presence and absence of trypan blue; enzyme-linked immunosorbent assays to determine the intracellular levels of cleaved cytokeratin 18, a marker of epithelial cancer cell apoptosis; and immunoblot analysis to determine the levels of cleaved poly-ADP ribose polymerase (PARP) and lamin A that result from caspase-dependent apoptosis. Cytotoxicity was further characterized by determination of the levels of reactive oxygen species (ROS) and the percent of mitochondrial membrane depolarization in cell populations treated with the different hormones in the presence and absence of IGF-1. Small molecule inhibitors of the dual-specificity protein kinase MEK1, MEK1 siRNA, Bim siRNA, and vectors overexpressing MEK1 wild type and mutant, dominant negative cDNA were used to identify key IGF-1 downstream prosurvival effectors.

Results

IGF-1, at physiologically relevant levels, blocked the cytotoxic action(s) of the antiestrogens 4-hydroxytamoxifen (4-OHT) and tamoxifen (TAM) when used as single agents or in combination with the antiprogestin MIF. The antiapoptotic action of IGF-1 was mediated primarily through the action of MEK1. MEK1 expression reduced the levels of ROS and mitochondrial membrane depolarization induced by the hormonal treatments via a mechanism that involved the phosphorylation and proteasomal turnover of the proapoptotic BH3-only Bcl-2 family member Bim. Importantly, small-molecule inhibitors of MEK1 circumvented the prosurvival action of IGF-1 by restoring Bim to levels that more effectively mediated apoptosis in ER⁺ breast cancer cells.

Conclusion

his study provides strong support for the use of MEK1 inhibitors in combination with hormonal therapy to effectively affect cytostasis and activate a Bim-dependent apoptotic pathway in ER⁺ breast cancer cells. We discuss that MEK1 blockade may be a particularly effective treatment for women with high circulating levels of IGF-1, which have been correlated to a poor prognosis.

Diabetes, cancer, and metformin: connections of metabolism and cell proliferation

Diabetes is associated with an increased risk of developing and dying from cancer. This increased risk may be due to hyperglycemia, hyperinsulinemia, and insulin resistance or other factors. Metformin has recently gained much attention as it appears to reduce cancer incidence and improve prognosis of patients with diabetes. In vitro data and animal studies support these findings from human epidemiological studies. Metformin has multiple potential mechanisms by which it inhibits cancer development and growth. For example, metaformin inhibits hepatic gluconeogenesis, thus decreasing circulating glucose levels, and it increases insulin sensitivity, thus reducing circulating insulin levels. Intracellularly, metformin activates AMPK, which decreases protein synthesis and cell proliferation. Metaformin also reduces aromatase activity in the stromal cells of the mammary gland. Finally, metformin may diminish the recurrence and aggressiveness of tumors by reducing the stem cell population and inhibiting epithelial to mesenchymal transition. Here, we discuss the metabolic abnormalities that occur in tumor development and some of the mechanisms through which metformin may alter these pathways and reduce tumor growth.

Hyperinsulinemia enhances c-Myc-mediated mammary tumor development and advances metastatic progression to the lung in a mouse model of type 2 diabetes

INTRODUCTION

Hyperinsulinemia, which is common in early type 2 diabetes (T2D) as a result of the chronically insulin-resistant state, has now been identified as a specific factor which can worsen breast cancer prognosis. In breast cancer, a high rate of mortality persists due to the emergence of pulmonary metastases.

METHODS

Using a hyperinsulinemic mouse model (MKR+/+) and the metastatic, c-Myc-transformed mammary carcinoma cell line Mvt1, we investigated how high systemic insulin levels would affect the progression of orthotopically inoculated primary mammary tumors to lung metastases.

RESULTS

We found that orthotopically injected Mvt1 cells gave rise to larger mammary tumors and to a significantly higher mean number of pulmonary macrometastases in hyperinsulinemic mice over a period of six weeks (hyperinsulinemic, 19.4 ± 2.7 vs. control, 4.0 ± 1.3). When Mvt1-mediated mammary tumors were allowed to develop and metastasize for approximately two weeks and were then surgically removed, hyperinsulinemic mice demonstrated a significantly higher number of lung metastases after a four-week period (hyperinsulinemic, 25.1 ± 4.6 vs. control, 7.4 ± 0.42). Similarly, when Mvt1 cells were injected intravenously, hyperinsulinemic mice demonstrated a significantly higher metastatic burden in the lung than controls after a three-week period (hyperinsulinemic, 6.0 ± 1.63 vs. control, 1.5 ± 0.68). Analysis of Mvt1 cells both in vitro and in vivo revealed a significant up-regulation of the transcription factor c-Myc under hyperinsulinemic conditions, suggesting that hyperinsulinemia may promote c-Myc signaling in breast cancer. Furthermore, insulin-lowering therapy using the beta-adrenergic receptor agonist CL-316243 reduced metastatic burden in hyperinsulinemic mice to control levels.

CONCLUSIONS

Hyperinsulinemia in a mouse model promotes breast cancer metastasis to the lung. Therapies to reduce insulin levels in hyperinsulinemic patients suffering from breast cancer could lessen the likelihood of metastatic progression.

Targeted loss of GHR signaling in mouse skeletal muscle protects against high-fat diet-induced metabolic deterioration

Growth hormone (GH) exerts diverse tissue-specific metabolic effects that are not revealed by global alteration of GH action. To study the direct metabolic effects of GH in the muscle, we specifically inactivated the growth hormone receptor (ghr) gene in postnatal mouse skeletal muscle using the Cre/loxP system (mGHRKO model). The metabolic state of the mGHRKO mice was characterized under lean and obese states. High-fat diet feeding in the mGHRKO mice was associated with reduced adiposity, improved insulin sensitivity, lower systemic inflammation, decreased muscle and hepatic triglyceride content, and greater energy expenditure compared with control mice. The obese mGHRKO mice also had an increased respiratory exchange ratio, suggesting increased carbohydrate utilization. GH-regulated suppressor of cytokine signaling-2 (socs2) expression was decreased in obese mGHRKO mice. Interestingly, muscles of both lean and obese mGHRKO mice demonstrated a higher interleukin-15 and lower myostatin expression relative to controls, indicating a possible mechanism whereby GHR signaling in muscle could affect liver and adipose tissue function. Thus, our study implicates skeletal muscle GHR signaling in mediating insulin resistance in obesity and, more importantly, reveals a novel role of muscle GHR signaling in facilitating cross-talk between muscle and other metabolic tissues.