Yvonne Fierz

Insulin-Mediated Acceleration of Breast Cancer Development and Progression in a Nonobese Model of Type 2 Diabetes

Epidemiologic studies suggest that type 2 diabetes (T2D) increases breast cancer risk and mortality, but there is limited experimental evidence supporting this association. Moreover, there has not been any definition of a pathophysiological pathway that diabetes may use to promote tumorigenesis. In the present study, we used the MKR mouse model of T2D to investigate molecular mechanisms that link T2D to breast cancer development and progression. MKR mice harbor a transgene encoding a dominant-negative, kinase-dead human insulin-like growth factor-I receptor (IGF-IR) that is expressed exclusively in skeletal muscle, where it acts to inactivate endogenous insulin receptor (IR) and IGF-IR. Although lean female MKR mice are insulin resistant and glucose intolerant, displaying accelerated mammary gland development and enhanced phosphorylation of IR/IGF-IR and Akt in mammary tissue, in the context of three different mouse models of breast cancer, these metabolic abnormalities were found to accelerate the development of hyperplastic precancerous lesions. Normal or malignant mammary tissue isolated from these mice exhibited increased phosphorylation of IR/IGF-IR and Akt, whereas extracellular signal-regulated kinase 1/2 phosphorylation was largely unaffected. Tumor-promoting effects of T2D in the models were reversed by pharmacological blockade of IR/IGF-IR signaling by the small-molecule tyrosine kinase inhibitor BMS-536924. Our findings offer compelling experimental evidence that T2D accelerates mammary gland development and carcinogenesis,and that the IR and/or the IGF-IR are major mediators of these effects.

Insulin-Sensitizing Therapy Attenuates Type 2 Diabetes–Mediated Mammary Tumor Progression

OBJECTIVE Type 2 diabetes increases breast cancer risk and mortality, and hyperinsulinemia has been identified as a major factor linking these two diseases. Thus, we hypothesized that pharmacological reduction of elevated insulin levels would attenuate type 2 diabetes–mediated mammary tumor progression. RESEARCH DESIGN AND METHODS We studied mammary tumor development in MKR+/+ mice, a nonobese, hyperinsulinemic mouse model of type 2 diabetes. MKR+/+ mice were either crossed with mice expressing the polyoma virus middle T oncogene specifically in the mammary gland or inoculated orthotopically with the mouse mammary tumor cell lines Met-1 and MCNeuA. MKR+/+ or control mice harboring tumors were treated with CL-316243, a specific β3-adrenergic receptor agonist, which sensitizes insulin action but has no direct effect on the mouse mammary epithelium or Met-1 and MCNeuA cells. RESULTS CL-316243 treatment significantly reduced the elevated insulin levels in MKR+/+ mice and, as a consequence, attenuated mammary tumor progression in the three tumor models tested. This effect was accompanied by reductions in phosphorylation of insulin and IGF-I receptors in transformed mammary tissue. CONCLUSIONS Insulin-sensitizing treatment is sufficient to abrogate type 2 diabetes–mediated mammary tumor progression. Therefore, early administration of insulin-sensitizing therapy may reduce breast cancer risk and mortality in patients with type 2 diabetes.

Type 2 Diabetes and Cancer: What Is the Connection?

Epidemiological studies have demonstrated an association between type 2 diabetes and cancer. Type 2 diabetes is characterized by insulin resistance and hyperinsulinemia. Hyperinsulinemia may lead to cancer through insulins effect on its cognate receptor and the insulin-like growth factor system. The effects of insulin and insulin-like growth factor I on cancer development and progression have been demonstrated in animal and human studies. Type 2 diabetes has been positively associated with cancers of the breast, colon, and pancreas. An inverse relationship has been observed between type 2 diabetes and prostate cancer, and this may be due to lower testosterone levels in men with type 2 diabetes. Medications used to treat type 2 diabetes may affect cancer cells directly or indirectly by affecting serum insulin levels. Hyperinsulinemia may be an important risk factor for cancer as well as a target for cancer therapy.

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

IntroductionHyperinsulinemia, 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.MethodsUsing 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.ResultsWe 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.ConclusionsHyperinsulinemia 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.

The pathway from diabetes and obesity to cancer, on the route to targeted therapy.

OBJECTIVE To review the epidemiologic studies that describe the relationships among diabetes, obesity, and cancer; animal studies that have helped to decipher the mechanisms of cancer development; and some of the therapeutic targets undergoing investigation. METHODS An electronic search was performed of Medline, Scopus, Google Scholar, and ClinicalTrials.gov to identify English-language articles and studies published from 1995 through 2010 relating to obesity, insulin, insulinlike growth factors, diabetes mellitus, and cancer. RESULTS Epidemiologic studies have reported that diabetes and obesity are linked to an increased risk of certain cancers in association with higher levels of insulin, C-peptide, and insulinlike growth factor 1. Animal models have demonstrated that increased insulin, insulinlike growth factor 1, and insulinlike growth factor 2 signaling can enhance tumor growth, while inhibiting this signaling can reduce tumorigenesis. Therapies that target insulin and insulinlike growth factor 1 signaling pathways have been developed and are currently in clinical trials to treat cancer. CONCLUSIONS Insulin, insulinlike growth factor 1, and insulinlike growth factor 2 signaling through the insulin receptor and the insulinlike growth factor 1 receptor can induce tumorigenesis, accounting to some extent for the link between diabetes, obesity, and cancer. Knowledge of these pathways has enhanced our understanding of tumor development and allowed for the discovery of novel cancer treatments.

Inhibiting PI3K reduces mammary tumor growth and induces hyperglycemia in a mouse model of insulin resistance and hyperinsulinemia

Women with type 2 diabetes mellitus (T2DM) are at a greater risk of developing and dying from breast cancer than women without T2DM. Insulin resistance and hyperinsulinemia underlie the pathogenesis of T2DM. In the MKR mouse model of insulin resistance, we have previously shown increased activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathway in association with accelerated mammary tumor growth. In this study, we demonstrate that inhibiting PI3K with the oral pan-class I PI3K inhibitor, NVP-BKM120 reduced the growth of Met-1 and MCNeuA mammary tumor orthografts in the MKR mouse. NVP-BKM120 treatment decreased phosphorylation of Akt and S6 ribosomal protein (S6rp); no change in Erk1/2 phosphorylation was seen. Hyperglycemia, hypertriglyceridemia and greater hyperinsulinemia developed in the MKR mice treated with NVP-BKM120. We previously reported reduced tumor growth using intraperitoneal rapamycin in the MKR mouse, with the development of hyperglycemia and hypertriglyceridemia. Therefore, we examined whether the oral PI3K/mTOR inhibitor NVP-BEZ235 augmented the tumor suppressing effects of PI3K inhibition. We also investigated the effect of targeted PI3K/mTOR inhibition on PI3K/Akt/mTOR and Erk1/2 signaling, and the potential effects on glycemia. NVP-BEZ235 suppressed the growth of Met-1 and MCNeuA tumor orthografts, and decreased Akt and S6rp phosphorylation, despite increased Erk1/2 phosphorylation in Met-1 orthografts of MKR mice. Less marked hyperglycemia and hyperinsulinemia developed with NVP-BEZ235 than NVP-BKM120. Overall, the results of this study demonstrated that inhibiting PI3K/Akt/mTOR signaling with the oral agents NVP-BKM120 and NVP-BEZ235 decreased mammary tumor growth in the hyperinsulinemic MKR mouse. Inhibiting PI3K alone led to more severe metabolic derangement than inhibiting both PI3K and mTOR. Therefore, PI3K may be an important target for the treatment of breast cancer in women with insulin resistance. Monitoring for hyperglycemia and dyslipidemia should be considered when using these agents in humans, given the metabolic changes detected in this study.

Mammalian target of rapamycin inhibition abrogates insulin-mediated mammary tumor progression in type 2 diabetes

Type 2 diabetes increases breast cancer risk and mortality, and hyperinsulinemia is a major mediator of this effect. The mammalian target of rapamycin (mTOR) is activated by insulin and is a key regulator of mammary tumor progression. Pharmacological mTOR inhibition suppresses tumor growth in numerous mammary tumor models in the non-diabetic setting. However, the role of the mTOR pathway in type 2 diabetes-induced tumor growth remains elusive. Herein, we investigated whether the mTOR pathway is implicated in insulin-induced mammary tumor progression in a transgenic mouse model of type 2 diabetes (MKR mice) and evaluated the impact of mTOR inhibition on the diabetic state. Mammary tumor progression was studied in the double transgenic MMTV-Polyoma Virus middle T antigen (PyVmT)/MKR mice and by orthotopic inoculation of PyVmT- and Neu/ErbB2-driven mammary tumor cells (Met-1 and MCNeuA cells respectively). mTOR inhibition by rapamycin markedly suppressed tumor growth in both wild-type and MKR mice. In diabetic animals, however, the promoting action of insulin on tumor growth was completely blunted by rapamycin, despite a worsening of the carbohydrate and lipid metabolism. Taken together, pharmacological mTOR blockade is sufficient to abrogate mammary tumor progression in the setting of hyperinsulinemia, and thus mTOR inhibitors may be an attractive therapeutic modality for breast cancer patients with type 2 diabetes. Careful monitoring of the metabolic state, however, is important as dose adaptations of glucose- and/or lipid-lowering therapy might be necessary.

The GH/IGF-1 Axis in Growth and Development: New Insights Derived from Animal Models

L ongitudinal growth in humans follows a unique pattern that is characterized by rapid fetal growth, deceleration immediately after birth, a prolonged childhood growth phase, an additional deceleration prepubertally, and a dramatic adolescent growth spurt leading ultimately to stagnancy in adulthood [1]. Linear bone growth, which accompanies longitudinal body growth, occurs during development and the childhood years until epiphyseal fusion occurs after puberty [2]. Growth is dynamic in nature and is influenced by nutritional, neuronal, and hormonal factors [3]. Growth hormone (GH), a hormone secreted from the anterior pituitary gland, is a major regulator of somatic growth. The mammalian GH gene (also known as GH-normal or GH-N) belongs to a family of genes that includes the genes for GH, prolactin (PRL), and the placental lactogens [4]. The human GH-N heterogeneous nuclear RNA transcript undergoes alternative splicing, which leads to the creation of 2 mature mRNA transcripts, which then encode 2 polypeptides with molecular weights of 22 kDa and 20 kDa. In the circulation, the majority of human GH protein is the 22 kDa isoform; whereas, a small amount is the 20 kDa isoform [4]. GH is secreted from the anterior pituitary gland in a pulsatile fashion [5]. GH secretion exhibits sexual dimorphism in humans and rats. In humans, women exhibit more irregularity in GH secretion than men [6]. Two hypothalamic factors regulate and maintain the pulsatile secretion of GH from pituitary somatotrophs [7,8]. Growth hormone releasing hormone (GHRH) stimulates GH release; whereas, somatostatin release-inhibiting factor (SRIF, or somatostatin) inhibits GH release [7,8]. In the circulation, GH binds to the growth hormone binding protein (GHBP), a truncated form of the growth hormone receptor (GHR). GHBP contains the extracellular portion of the GHR [9–12]. In humans, the GHBP has been suggested to be formed by

Physical and functional interaction between polyoma virus middle T antigen and insulin and IGF-I receptors is required for oncogene activation and tumour initiation

Polyoma virus middle T antigen (PyVmT) is a powerful viral oncogene; however, the mechanisms of PyVmT activation are poorly understood. The insulin-like growth factor I receptor (IGF-IR) and the insulin receptor (IR) are known to be implicated in the development of many cancers. Furthermore, PyVmT-overexpressing mouse mammary carcinoma Met-1 cells are highly responsive to IGF-I and insulin. Herein, we demonstrate that PyVmT physically interacts with IGF-IR and IR in Met-1 cells. Insulin and IGF-I increase association of the IR and IGF-IR with PyVmT, enhance tyrosine phosphorylation of PyVmT and augment the recruitment of Src and PLCγ1 to PyVmT. This is accompanied by robust and sustained phosphorylation of Akt and ERK1/2, which are implicated in both PyVmT and IGF-IR/IR signalling. Both ligands significantly increase proliferation, survival, migration and invasion of Met-1 cells. Furthermore, orthotopic inoculation of Met-1 cells with shRNAmir-mediated knockdown of IR or IGF-IR fails to initiate tumour growth in recipient mice. In conclusion, our data indicate that the physical and functional interaction between PyVmT and cellular receptor tyrosine kinases, including IR and IGF-IR, is critical for PyVmT activation and tumour initiation. These results also provide a novel mechanism for oncogene activation in the host cell.

Animal Models of Hyperinsulinemia, Insulin Resistance, and Cancer

Numerous lines of evidence indicate that insulin and its receptor regulate cell proliferation, survival and transformation, and thus, tumorigenesis [52]. Indeed, the fact that insulin has a potent tumor-promoting activity has been known for a long time. In wild-type animals, administration of exogenous insulin markedly enhances development of experimental breast and colon tumors [34, 68, 117]. In contrast, insulinopenia in animals with chemically-induced type 1 diabetes (T1D) results in a significantly reduced tumor growth, which is restored after insulin administration [29, 67, 112, 113]. Moreover, intraportal implantation of pancreatic islets in rats with T1D creates an insulin-enriched microenvironment, which promotes hepatocarcinogenesis [43]. The aforementioned studies thus link insulin and cancer mechanistically, and indicate that insulin plays the role of both a tumor initiator and promoter.