The proliferating role of insulin and insulin-like growth factors in cancer

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.

Mitogenic insulin receptor-A is overexpressed in human hepatocellular carcinoma due to EGFR-mediated dysregulation of RNA splicing factors

Insulin receptor (IR) exists as two isoforms resulting from the alternative splicing of IR pre-mRNA. IR-B promotes the metabolic effects of insulin, whereas IR-A rather signals proliferative effects. IR-B is predominantly expressed in the adult liver. Here, we show that the alternative splicing of IR pre-mRNA is dysregulated in a panel of 85 human hepatocellular carcinoma (HCC) while being normal in adjacent nontumor liver tissue. An IR-B to IR-A switch is frequently observed in HCC tumors regardless of tumor etiology. Using pharmacologic and siRNA approaches, we show that the autocrine or paracrine activation of the EGF receptor (EGFR)/mitogen-activated protein/extracellular signal-regulated kinase pathway increases the IR-A:IR-B ratio in HCC cell lines, but not in normal hepatocytes, by upregulating the expression of the splicing factors CUGBP1, hnRNPH, hnRNPA1, hnRNPA2B1, and SF2/ASF. In HCC tumors, there is a significant correlation between the expression of IR-A and that of splicing factors. Dysregulation of IR pre-mRNA splicing was confirmed in a chemically induced model of HCC in rat but not in regenerating livers after partial hepatectomy. This study identifies a mechanism responsible for the generation of mitogenic IR-A and provides a novel interplay between IR and EGFR pathways in HCC. Increased expression of IR-A during neoplastic transformation of hepatocytes could mediate some of the adverse effects of hyperinsulinemia on HCC.

Targeting the insulin-like growth factor-1 receptor in human cancer

The insulin-like growth factor (IGF) signaling system plays a crucial role in human cancer and the IGF-1 receptor (IGF-1R) is an attractive drug target against which a variety of novel anti-tumor agents are being developed. Deregulation of the IGF signaling pathway frequently occurs in human cancer and involves the establishment of autocrine loops comprising IGF-1 or IGF-2 and/or IGF-1R over-expression. Epidemiologic studies have documented a link between elevated IGF levels and the development of solid tumors, such as breast, colon, and prostate cancer. Anti-cancer strategies targeting the IGF signaling system involve two main approaches, namely neutralizing antibodies and small molecule inhibitors of the IGF-1R kinase activity. There are numerous reports describing anti-tumor activity of these agents in pre-clinical models of major human cancers. In addition, multiple clinical trials have started to evaluate the safety and efficacy of selected IGF-1R inhibitors, in combination with standard chemotherapeutic regimens or other targeted agents in cancer patients. In this mini review, I will discuss the role of the IGF signaling system in human cancer and the main strategies which have been so far evaluated to target the IGF-1R.

Meta-analysis of the association between insulin-like growth factor binding protein 3 genetic polymorphisms and colorectal cancer susceptibility

Insulin-like growth factor binding protein 3 (IGFBP-3) plays an important role in the development and progress of cancers. The association between IGFBP-3 polymorphisms and colorectal cancer remains controversial and ambiguous. The aim of this study is to explore the association between IGFBP3 A-202C and Gly32Ala polymorphisms and colorectal cancer susceptibility using meta-analyisi. Case-control studies on the association between IGFBP3 A-202C and Gly32Ala polymorphisms and colorectal cancer, which had sufficient data for estimating an odds ratio (OR) with 95% confidence interval (CI), were included in the meta-analysis. Abstracts, case reports, editorials, and review articles were excluded. Heterozygous and homozygous mutants were compared with the wild types to estimate combined OR values and 95%CIs with Review Manager 5.0. Six eligible studies were included, with 3157 patients and 6027 controls for A-202C and 1711 patients and 2995 controls for Gly32Ala. No significant association was found in all genetic models (for A-202C, AC vs. AA, OR = 0.99(0.88–1.11), CC vs. AA, OR = 1.06(0.92–1.22), dominant model, OR = 0.98(0.88–1.09), recessive model, OR = 0.94(0.84–1.05); and for Gly32Ala polymorphism, GC vs. GG, OR = 1.10(0.92–1.31), CC vs. GG, OR = 0.93(0.76–1.14), dominant model, OR = 1.05(0.89–1.24), recessive model, OR = 0.90(0.77–1.05)). The results suggest that the IGFBP3 A-202C and Gly32Ala polymorphisms are not associated with colorectal cancer susceptibility.

MicroRNA-497 is a potential prognostic marker in human cervical cancer and functions as a tumor suppressor by targeting the insulin-like growth factor 1 receptor

BACKGROUND

Increasing evidence has shown that microRNAs function as oncogenes or tumor suppressors in human malignancies, but the roles of microRNA (miR)-497 in human cervical cancer still remain unclear. Our aim was to analyze the clinicopathologic and prognostic significance of miR-497 in human cervical cancer and to investigate the effects of miR-497 on the malignant phenotype of cervical cancer cells.

METHODS

First, we detected miR-497 expression in the HPV-16-immortalized cervical epithelial cell lines and 4 other cervical cancer cell lines (HeLa, Caski, SiHa, and HeLa-S3). Then the expression of miR-497 was analyzed in cervical cancer tissues and paired nontumor tissues, and its correlation with clinicopathologic features and survival was analyzed. Finally, the roles of miR-497 in regulation of tumor proliferation, apoptosis, migration, invasion, and target gene expression were further investigated.

RESULTS

MiR-497 was downregulated in cervical cancer cells or tissues compared with HPV-16-immortalized cervical epithelial cell lines or the paired nontumor tissues. Also, the decrease in miR-497 correlated closely with the criteria of the International Federation of Gynaecology and Obstetrics stage and lymph node metastases in patients with cervical cancer. Multivariate Cox analysis showed that low miR-497 expression appeared to be an unfavorable prognostic factor. Transient forced expression of miR-497 decreased the growth and colony-formation capacity of HeLa and SiHa cells by inducing Caspase-3-dependent apoptosis. Forced expression of miR-497 suppressed the migration and invasiveness of cervical cancer cells. By computational miRNA target prediction and functional analysis, miR-497 was demonstrated to bind to the 3' untranslated regions of IGF-1R mRNA, and upregulation of miR-497 downregulated IGF-1R protein expression. Further investigation showed that small interfering RNA-mediated IGF-1R knockdown could mimic the effect of enforced miR-497 expression on the malignant phenotypes of cervical cancer cells.

CONCLUSION

MiR-497 may be a potential prognostic marker and functions as a tumor suppressor in human cervical cancer by post-transcriptionally targeting IGF-1R.

Stimulatory effect of insulin on theca-interstitial cell proliferation and cell cycle regulatory proteins through MTORC1 dependent pathway

The present study examined the effect of insulin-mediated activation of the mammalian target of rapamycin complex 1 (MTORC1) signaling network on the proliferation of primary culture of theca-interstitial (T-I) cells. Our results show that insulin treatment increased proliferation of the T-I cells through the MTORC1-dependent signaling pathway by increasing cell cycle regulatory proteins. Inhibition of ERK1/2 signaling caused partial reduction of insulin-induced phosphorylation of RPS6KB1 and RPS6 whereas inhibition of PI3-kinase signaling completely blocked the insulin response. Pharmacological inhibition of MTORC1 with rapamycin abrogated the insulin-induced phosphorylation of EIF4EBP1, RPS6KB1 and its downstream effector, RPS6. These results were further confirmed by demonstrating that knockdown of Mtor using siRNA reduced the insulin-stimulated MTORC1 signaling. Furthermore, insulin-stimulated T-I cell proliferation and the expression of cell cycle regulatory proteins CDK4, CCND3 and PCNA were also blocked by rapamycin. Taken together, the present studies show that insulin stimulates cell proliferation and cell cycle regulatory proteins in T-I cells via activation of the MTORC1 signaling pathway.

Epitope-specific mechanisms of IGF1R inhibition by ganitumab

Background

Therapeutic antibodies targeting the IGF1R have shown diverse efficacy and safety signals in oncology clinical trials. The success of these agents as future human therapeutics depends on understanding the specific mechanisms by which these antibodies target IGF1R signaling.

Methodology/Principal Findings

A panel of well-characterized assays was used to investigate the mechanisms by which ganitumab, a fully human anti-IGF1R antibody undergoing clinical testing, inhibits IGF1R activity. Epitope mapping using IGF1R subdomains localized the ganitumab binding site to the L2 domain. Binding of ganitumab inhibited the high-affinity interaction of IGF-1 and IGF-2 required to activate IGF1R in cells engineered for IGF1R hypersensitivity and in human cancer cell lines, resulting in complete blockade of ligand-induced cellular proliferation. Inhibition of IGF1R activity by ganitumab did not depend on endosomal sequestration, since efficient ligand blockade was obtained without evidence of receptor internalization and degradation. Clinically relevant concentrations of ganitumab also inhibited the activation of hybrid receptors by IGF-1 and IGF-2. Ganitumab was not an agonist of homodimeric IGF1R or hybrid receptors in MCF-7 and COLO 205 cells, but low-level IGF1R activation was detected in cells engineered for IGF1R hypersensitivity. This activation seems biologically irrelevant since ganitumab completely inhibited ligand-driven proliferation. The in vivo efficacy profile of ganitumab was equivalent or better than CR and FnIII-1 domain-specific antibodies, alone or in combination with irinotecan. CR domain-specific antibodies only blocked IGF-1 binding to IGF1R but were more potent than ganitumab at inducing homodimer and hybrid receptor downregulation in vitro, however this difference was less obvious in vivo. No inhibition of hybrid receptors was observed with the FnIII-1 domain antibodies, which were relatively strong homodimer and hybrid agonists.

Conclusions/Significance

The safety and efficacy profile of ganitumab and other anti-IGF1R antibodies may be explained by the distinct molecular mechanisms by which they inhibit receptor signaling.

Obesity as a major risk factor for cancer

The number of cancer cases caused by being obese is estimated to be 20% with the increased risk of malignancies being influenced by diet, weight change, and body fat distribution together with physical activity. Reports from the International Agency for Research into Cancer and the World Cancer Research Fund (WCRF) have shown that the strongest evidence exists for an association of obesity with the following cancer types: endometrial, esophageal adenocarcinoma, colorectal, postmenopausal breast, prostate, and renal, whereas the less common malignancies are leukemia, non-Hodgkin's lymphoma, multiple myeloma, malignant melanoma, and thyroid tumours. To be able to develop novel methods in prevention and treatment, we first must understand the underlying processes which link cancer to obesity. Four main systems have been identified as potential producers of cancer in obesity: insulin, insulin-like growth factor-I, sex steroids, and adipokines. Various novel candidate mechanisms have been proposed: chronic inflammation, oxidative stress, crosstalk between tumour cells and surrounding adipocytes, migrating adipose stromal cells, obesity-induced hypoxia, shared genetic susceptibility, and the functional defeat of immune function. Herein, we review the major pathogenic links between obesity and susceptibility to cancer.

Insulin receptor isoforms A and B as well as insulin receptor substrates-1 and -2 are differentially expressed in prostate cancer

Aims/Hypothesis

In different cancers types, insulin receptor isoform composition or insulin receptor substrate (IRS) isoforms are different to healthy tissue. This may be a molecular link to increased cancer risk in diabetes and obesity. Since this is yet unclear for prostate cancer, we investigated IR isoform composition and IRS balance in prostate cancer compared to benign and tumor adjacent benign prostate tissue and brought this into relation to cell proliferation.

Methods

We studied 23 benign prostate samples from radical cystectomy or benign prostatic hyperplasia surgery, 30 samples from benign tissue directly adjacent to prostate cancer foci and 35 cancer samples from different patients. RNA expression levels for insulin receptor isoforms A and B, IRS-1, IRS-2, and IGF-1 receptor were assessed by quantitative real-time RT-PCR. In addition, RNA- and protein expression of the cell cycle regulator p27^Kip1 was quantified by real-time RT-PCR and immunohistochemistry.

Results

Insulin receptor isoform A to B ratio was significantly higher in cancer as well as in tumor adjacent benign prostate tissue compared to purely benign prostates (p<0.05). IRS-1 to IRS-2 ratios were lower in malignant than in benign prostatic tissue (p<0.05). These altered ratios both in cancer and adjacent tissue were significantly associated with reduced p27^Kip1 content (p<0.02). Interestingly, IGF-1 receptor levels were significantly lower in patients with type 2 diabetes (p = 0.0019).

Conclusions/Interpretation

We found significant differences in the insulin signaling cascade between benign prostate tissue and prostate cancer. Histological benign tissue adjacent to cancer showed expression patterns similar to the malignancies. Our findings suggest a role of the insulin signaling pathway in prostate cancer and surrounding tissue and can hence be relevant for both novel diagnostic and therapeutic approaches in this malignancy.

The cellular and molecular mechanisms by which insulin influences breast cancer risk and progression

Epidemiological studies have related hyperinsulinemia and type 2 diabetes to an increased breast cancer risk, an aggressive and metastatic phenotype, and a poor prognosis. Furthermore, diabetic retinopathy arises from pathological angiogenesis, which is also essential for breast cancer growth and metastasis. Insulin stimulates the proliferation of some human breast cancer cell lines in vitro by mechanisms that use both the phosphatidylinositol-3 kinase and the mitogen-activated protein kinase/Akt signaling pathways; it is also a cell survival (anti-apoptotic) agent and enhances tumor cell migration and invasive capacity. Hyperinsulinemia affects breast cancer cells via the endocrine system, but experimental studies suggest the importance of paracrine mechanisms operating by the effects of insulin on the secretion of adipokines from tumor-associated adipose tissue. In such a system, one adipokine, leptin, has stimulatory paracrine effects on breast cancer cell proliferation and survival, while a second, adiponectin, is inhibitory. Leptin, vascular endothelial growth factor, another insulin-regulated adipokine, and insulin itself also stimulate angiogenesis. Insulin has complex interactions with estrogens: it induces adipose stromal cell aromatase and tumor cell sex steroid hormone receptor expression and suppresses sex hormone-binding globulin, which may enhance estrogen synthesis and bioactivity with consequent promotion of estrogen-dependent breast cancer. All these actions influence the later steps in breast cancer development but genetic studies are also revealing connections between gene abnormalities related to type 2 diabetes and the initiation stage of breast carcinogenesis. Understanding the various mechanisms by which insulin participates in breast cancer cell biology provides opportunities for novel approaches to treatment.

PI3K and Akt as molecular targets for cancer therapy: current clinical outcomes

The PI3K-Akt pathway is a vital regulator of cell proliferation and survival. Alterations in the PIK3CA gene that lead to enhanced PI3K kinase activity have been reported in many human cancer types, including cancers of the colon, breast, brain, liver, stomach and lung. Deregulation of PI3K causes aberrant Akt activity. Therefore targeting this pathway could have implications for cancer treatment. The first generation PI3K-Akt inhibitors were proven to be highly effective with a low IC(50), but later, they were shown to have toxic side effects and poor pharmacological properties and selectivity. Thus, these inhibitors were only effective in preclinical models. However, derivatives of these first generation inhibitors are much more selective and are quite effective in targeting the PI3K-Akt pathway, either alone or in combination. These second-generation inhibitors are essentially a specific chemical moiety that helps to form a strong hydrogen bond interaction with the PI3K/Akt molecule. The goal of this review is to delineate the current efforts that have been undertaken to inhibit the various components of the PI3K and Akt pathway in different types of cancer both in vitro and in vivo. Our focus here is on these novel therapies and their inhibitory effects that depend upon their chemical nature, as well as their development towards clinical trials.

The ghrelin axis--does it have an appetite for cancer progression?

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHSR), is a peptide hormone with diverse physiological roles. Ghrelin regulates GH release, appetite and feeding, gut motility, and energy balance and also has roles in the cardiovascular, immune, and reproductive systems. Ghrelin and the GHSR are expressed in a wide range of normal and tumor tissues, and a fluorescein-labeled, truncated form of ghrelin is showing promise as a biomarker for prostate cancer. Plasma ghrelin levels are generally inversely related to body mass index and are unlikely to be useful as a biomarker for cancer, but may be useful as a marker for cancer cachexia. Some single nucleotide polymorphisms in the ghrelin and GHSR genes have shown associations with cancer risk; however, larger studies are required. Ghrelin regulates processes associated with cancer, including cell proliferation, apoptosis, cell migration, cell invasion, inflammation, and angiogenesis; however, the role of ghrelin in cancer is currently unclear. Ghrelin has predominantly antiinflammatory effects and may play a role in protecting against cancer-related inflammation. Ghrelin and its analogs show promise as treatments for cancer-related cachexia. Further studies using in vivo models are required to determine whether ghrelin has a role in cancer progression.

Parental imprinting regulates insulin-like growth factor signaling: a Rosetta Stone for understanding the biology of pluripotent stem cells, aging and cancerogenesis

In recent years, solid evidence has accumulated that insulin-like growth factor-1 (IGF-1) and 2 (IGF-2) regulate many biological processes in normal and malignant cells. Recently, more light has been shed on the epigenetic mechanisms regulating expression of genes involved in IGF signaling (IFS) and it has become evident that these mechanisms are crucial for initiation of embryogenesis, maintaining the quiescence of pluripotent stem cells deposited in adult tissues (for example, very-small embryonic-like stem cells), the aging process, and the malignant transformation of cells. The expression of several genes involved in IFS is regulated at the epigenetic level by imprinting/methylation within differentially methylated regions (DMRs), which regulate their expression from paternal or maternal chromosomes. The most important role in the regulation of IFS gene expression is played by the Igf-2-H19 locus, which encodes the autocrine/paracrine mitogen IGF-2 and the H19 gene, which gives rise to a non-coding RNA precursor of several microRNAs that negatively affect cell proliferation. Among these, miR-675 has recently been demonstrated to downregulate expression of the IGF-1 receptor. The proper imprinting of DMRs at the Igf-2-H19 locus, with methylation of the paternal chromosome and a lack of methylation on the maternal chromosome, regulates expression of these genes so that Igf-2 is transcribed only from the paternal chromosome and H19 (including miR-675) only from the maternal chromosome. In this review, we will discuss the relevance of (i) proper somatic imprinting, (ii) erasure of imprinting and (iii) loss of imprinting within the DMRs at the Igf-2-H19 locus to the expression of genes involved in IFS, and the consequences of these alternative patterns of imprinting for stem cell biology.

Establishment of phosphatidylinositol 3-kinase inhibitor-resistant cancer cell lines and therapeutic strategies for overcoming the resistance

Acquired resistance is a major obstacle for conventional cancer chemotherapy, and also for some of the targeted therapies approved to date. Long-term treatment using protein tyrosine kinase inhibitors (TKIs), such as gefitinib and imatinib, gives rise to resistant cancer cells carrying a drug-resistant gatekeeper mutation in the kinase domain of the respective target genes, EGFR and BCR-ABL. As for the phosphatidylinositol 3-kinase inhibitors (PI3Kis), little is known about their acquired resistance, although some are undergoing clinical trials. To address this issue, we exposed 11 human cancer cell lines to ZSTK474, a PI3Ki we developed previously, for a period of more than 1 year in vitro. Consequently, we established ZSTK474-resistant cells from four of the 11 cancer cell lines tested. The acquired resistance was not only to ZSTK474 but also to other PI3Kis. None of the PI3Ki-resistant cells, however, contained any mutation in the kinase domain of the PIK3CA gene. Instead, we found that insulin-like growth factor 1 receptor (IGF1R) was overexpressed in all four resistant cells. Interestingly, targeted knockdown of IGF1R expression using specific siRNAs or inhibition of IGF1R using IGF1R-TKIs reversed the acquired PI3Ki resistance. These results suggest that long-term treatment with PI3Kis may cause acquired resistance, and targeting IGF1R is a promising strategy to overcome the resistance.

The sirtuin SIRT6 blocks IGF-Akt signaling and development of cardiac hypertrophy by targeting c-Jun

Abnormal activation of insulin-like growth factor (IGF)-Akt signaling is implicated in the development of various diseases, including heart failure. However, the molecular mechanisms that regulate activation of this signaling pathway are not completely understood. Here we show that sirtuin 6 (SIRT6), a nuclear histone deacetylase, functions at the level of chromatin to directly attenuate IGF-Akt signaling. SIRT6-deficient mice developed cardiac hypertrophy and heart failure, whereas SIRT6 transgenic mice were protected from hypertrophic stimuli, indicating that SIRT6 acts as a negative regulator of cardiac hypertrophy. SIRT6-deficient mouse hearts showed hyperactivation of IGF signaling-related genes and their downstream targets. Mechanistically, SIRT6 binds to and suppresses the promoter of IGF signaling-related genes by interacting with c-Jun and deacetylating histone 3 at Lys9 (H3K9). We also found reduced SIRT6 expression in human failing hearts. These findings disclose a new link between SIRT6 and IGF-Akt signaling and implicate SIRT6 in the development of cardiac hypertrophy and failure.

Is body size associated with ovarian cancer in southern Chinese women?

PURPOSE

To investigate the association between risk of ovarian cancer and body size among southern Chinese women.

METHODS

A hospital-based case-control study was undertaken in Guangzhou, Guangdong Province, from 2006 to 2008. Participants were 500 incident ovarian cancer patients and 500 controls, with a mean age of 59 years. Information on adult height and weight was obtained via face-to-face interview using a structured questionnaire. Logistic regression analyses were performed to assess the association between anthropometric factors and the ovarian cancer risk.

RESULTS

Compared with women having body weight ≤50 kg and body mass index (BMI) <18.5 kg/m(2), the adjusted odds ratios (ORs) of ovarian cancer were 1.84 (95 % confidence interval (CI) 1.34-2.54) and 1.77 (95 % CI 1.04-3.02) in those women who had body weight >55 kg and BMI ≥23 kg/m(2), respectively. Significant dose-response relationships were also observed for both weight and BMI (p < 0.01). Body height was not significantly associated with ovarian cancer risk.

CONCLUSION

Body weight and BMI were associated with increased risk of ovarian cancer in southern Chinese women.

Akt1 and insulin-like growth factor 2 (Igf2) regulate placentation and fetal/postnatal development

Phenotypic characterization of Akt1 and Igf2 null mice has revealed roles for each in the regulation of placentation, and fetal and postnatal growth. Insulin-like growth factor 2 (IGF2) is encoded by the Igf2 gene and influences cellular function, at least in part, through activation of an intracellular serine/threonine kinase called AKT1. Akt1 and Igf2 null mice were originally characterized on inbred and mixed genetic backgrounds, prohibiting direct comparisons of their phenotypes. The impact of loss of AKT1 or IGF2 on placental, fetal, and postnatal function were examined following transfer of Akt1 and Igf2 null mutations to an outbred CD1 genetic background. Disruption of IGF2 did not affect AKT expression or activation. Both Akt1-/- and Igf2-/- mice exhibited decreased placental weight, fetal weight and viability. Deregulation of placental growth was similar in Akt1 and Igf2 nulls; however, disruption of Igf2 had a more severe impact on prenatal survival and postnatal growth. Placental structure, including organization of junctional and labyrinth zones and development of the interstitial, invasive, trophoblast lineage, were similar in mutant and wild-type mice. Akt1 and Igf2 null mutations affected postnatal growth. The relative impact of each gene differed during pre-weaning versus post-weaning growth phases. AKT1 had a more significant role during pre-weaning growth, whereas IGF2 was a bigger contributor to post-weaning growth. Akt1 and Igf2 null mutations impact placental, fetal and postnatal growth. Placental phenotypes are similar; however, fetal and postnatal growth patterns are unique to each mutation.

Inhibition of IGF-IR increases chemosensitivity in human colorectal cancer cells through MRP-2 promoter suppression

The emergence of multidrug resistance (MDR) in cancer cells has made many of the currently available chemotherapeutic agents ineffective. However, the mechanism involved in mediating this effect is not yet fully understood. Here, we found the overexpression of type I insulin-like growth factor receptor (IGF-IR) in established colorectal MDR cells. Specific siRNA of IGF-IR decreases cell proliferation, exert synergistic effect with anticancer drugs. The downstream signaling of IGF-IR, PI3K/AKT pathway, was altered upon IGF-IR silencing. The expression of multidrug-resistance-associated protein 2 (MRP-2) was suppressed due to the nuclear translocation of nuclear factor-like 2 (Nrf2). Then the intracellular drug concentration was increased and the drug-resistant phenotype was reversed. Our findings improve current understanding of the biology of IGF-IR and MDR and have significant therapeutic implications on colorectal MDR cancer.

Glucagon-like peptide-1 (GLP-1) receptor agonism or DPP-4 inhibition does not accelerate neoplasia in carcinogen treated mice

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) are secreted in parallel from the intestinal endocrine cells after nutrient intake. GLP-1 is an incretin hormone and analogues are available for the treatment of type 2 diabetes mellitus (T2DM). GLP-2 is an intestinal growth hormone and is shown to promote growth of colonic adenomas in carcinogen treated mice. Both peptides are degraded by dipeptidyl peptidase-4 (DPP-4) into inactive metabolites. DPP-4 inhibitors are therefore also in use for treatment of T2DM. It is possible that DPP-4 inhibition by enhancing the exposure of endogenous GLP-2 to the intestinal epithelia also might mediate growth and promote neoplasia. We investigated the intestinal growth effect of the GLP-1 receptor agonists (GLP-1 RAs) (liraglutide and exenatide) and DPP-4 inhibition (sitagliptin) in healthy mice. We also investigated the potential tumour promoting effect of liraglutide and sitaglitin in the colon of carcinogen treated mice. We used GLP-2 as a positive control.

METHODS

For the growth study we treated healthy CD1 mice with liraglutide (300 μg×2), exenatide (12.5 μg×2) or vehicle subcutaneously and sitagliptin (8mg×2) or water by oral gavage for 10 or 30 days. We measured intestinal weight, cross sectional area, villus height and crypt depth. For the tumour study we treated carcinogen treated mice (1,2 dimethylhydrazine 21 mg/kg/week for 12 weeks) with liraglutide (300 μg×2), Gly2-GLP-2 (25 μg×2) or vehicle subcutaneously and sitagliptin (8 mg×2) or water by oral gavage for 45 days. We counted aberrant crypt foci (ACF), mucin depleted foci (MDF) and adenomas in the colon. Using COS-7 cells transfected with a GLP-2 receptor, we tested if liraglutide or exenatide could activate the receptor.

RESULTS

In the 10 days experiment the relative small intestinal weight was increased with 56% in the liraglutide group (p<0.001) and 26% in the exenatide group (p<01) compared with vehicle treated mice. After 30 days of treatment, liraglutide did also increase the colonic weight (p<0.01). By morphometry the growth pattern mimicked that of GLP-2. Sitagliptin treatment had only a minor effect. In the carcinogen treated mice we found no increase of ACF in any of the groups, the numbers of MDF and adenomas after liraglutide and sitagliptin treatments were similar to their respective control groups. Neither liraglutide nor exenatide stimulated cAMP release from GLP-2 receptor transfected cells.

CONCLUSION

Both GLP-1 analogues were potent growth stimulators of the healthy mouse intestine. No agonism was found for GLP-1 RAs at the GLP-2 receptor. Despite of the growth effect, liraglutide did not promote dysplasia in the colon. Sitagliptin did not show any tumour promoting effects, and non considerable growth effects.

SRC Homology 2 Domain Binding Sites in Insulin, IGF-1 and FGF receptor mediated signaling networks reveal an extensive potential interactome

Specific peptide ligand recognition by modular interaction domains is essential for the fidelity of information flow through the signal transduction networks that control cell behavior in response to extrinsic and intrinsic stimuli. Src homology 2 (SH2) domains recognize distinct phosphotyrosine peptide motifs, but the specific sites that are phosphorylated and the complement of available SH2 domains varies considerably in individual cell types. Such differences are the basis for a wide range of available protein interaction microstates from which signaling can evolve in highly divergent ways. This underlying complexity suggests the need to broadly map the signaling potential of systems as a prerequisite for understanding signaling in specific cell types as well as various pathologies that involve signal transduction such as cancer, developmental defects and metabolic disorders. This report describes interactions between SH2 domains and potential binding partners that comprise initial signaling downstream of activated fibroblast growth factor (FGF), insulin (Ins), and insulin-like growth factor-1 (IGF-1) receptors. A panel of 50 SH2 domains screened against a set of 192 phosphotyrosine peptides defines an extensive potential interactome while demonstrating the selectivity of individual SH2 domains. The interactions described confirm virtually all previously reported associations while describing a large set of potential novel interactions that imply additional complexity in the signaling networks initiated from activated receptors. This study of pTyr ligand binding by SH2 domains provides valuable insight into the selectivity that underpins complex signaling networks that are assembled using modular protein interaction domains.

In vitro and in vivo antitumoral action of metformin on hepatocellular carcinoma

AIMS

  Metformin is a biguanide that has been widely used to treat type 2 diabetes. Several studies have shown that metformin is also effective in treating cancer, including hepatocellular carcinoma (HCC). The objective of this study was to evaluate the antitumor effects of metformin in HCC, and to investigate the potential molecular target(s) of metformin-mediated antitumor activity.

METHODS

  The antiproliferative effects of metformin were assessed in human HCC cell lines and normal human liver cells at various concentrations. Orthotopic xenograft tumors were established in athymic nude mice, and tumor growth was monitored after metformin treatment. Western blot analysis and cell cycle regulation were performed to determine the involvement of various mediators of apoptosis.

RESULTS

  Metformin specifically inhibited the growth of HCC cells without affecting the growth of normal liver cells both in vitro and in vivo. Metformin caused cell cycle arrest in HCC cells, which resulted in caspase-3 activation. Livin levels decreased in a dose-dependent manner upon metformin treatment. Metformin activated 5'-adenosine monophosphate-activated protein kinase, inhibited the mammalian target of rapamycin pathway and downregulated Livin protein expression.

CONCLUSION

  Our findings indicate that metformin is effective at initiating apoptosis and inhibiting key survival signaling pathways in HCC cells. These data provide a foundation for further studies to evaluate metformin in the clinic either as a single agent or in combination with other first-line agents as a treatment option for HCC.

IGF-1 deficiency in combination with a low basic hBD-2 and hBD-3 gene expression might counteract malignant transformation in pleomorphic adenomas in vitro

This study investigated the IGF-1-influence on oncological relevant genes in pleomorphic adenomas. Therefore A64-tumor cells were stimulated by recombinant IGF-1. After RNA-extraction, transcript levels of hBD-1, hBD-2, hBD-3, DEFA1/3, DEFA4, S100A4, Psoriasin, DOC-1, EGF, EGFR, and IGFR were analyzed by qRT-PCR at t = 0, 4, 8, 24, 48, and 72 hr. The gene-products were visualized by immunostaining. A64-tumor-cells were deficient for hBD-1 and IGF-1. IGF-1 downregulates hBD-2 and hBD-3 without influencing hBD-1-expression. IGF-1 only slightly affects DEFA1/3-, DEFA4-, S100A4-, Psoriasin-, DOC-1-, EGF-, EGFR-, and IGFR-gene-expression. IGF-1-deficiency combined with low basic hBD-2-gene-expression and hBD-3-gene-expression might counteract, whereas hBD-1-deficiency promotes malignant transformation in pleomorphic adenomas.

Acquired resistance to tamoxifen is associated with loss of the type I insulin-like growth factor receptor: implications for breast cancer treatment

The role of the insulin-like growth factor (IGF) system in breast cancer is well defined, and inhibitors of this pathway are currently in clinical trials. The majority of anti-IGF1R clinical trials are in estrogen receptor-positive patients who have progressed on prior endocrine therapy; early reports show no benefit for addition of IGF1R inhibitors to endocrine therapy in this setting. In this study, we examined the effectiveness of IGF1R inhibitors in vitro by generating tamoxifen-resistant (TamR) cells. We found that TamR cells had diminished levels of IGF1R with unchanged levels of insulin receptor (IR), and failed to respond to IGF-I-induced Akt activation, proliferation, and anchorage-independent growth while retaining responsiveness to both insulin and IGF-II. The IGF1R antibody dalotuzumab inhibited IGF-I-mediated Akt phosphorylation, proliferation, and anchorage-independent growth in parental cells, but had no effect on TamR cells. An IGF1R tyrosine kinase inhibitor, AEW541, with equal potency for the IGF1R and IR, inhibited IGF-I-, IGF-II-, and insulin-stimulated Akt phosphorylation, proliferation, and anchorage-independent growth in parental cells. Interestingly, AEW541 also inhibited insulin- and IGF-II-stimulated effects in TamR cells. Tamoxifen-treated xenografts also had reduced levels of IGF1R, and dalotuzumab did not enhance the effect of tamoxifen. We conclude that cells selected for tamoxifen resistance in vitro have downregulated IGF1R making antibodies directed against this receptor ineffective. Inhibition of IR may be necessary to manage tamoxifen-resistant breast cancer.

The insulin receptor/insulin-like growth factor receptor family as a therapeutic target in oncology

Over the past decade, encouraging preclinical and early clinical data concerning the relevance of the insulin receptor/insulin-like growth factor (IGF) receptor family to neoplasia led to ambitious clinical trial programs of more than a dozen drug candidates that target these receptors. These candidates include antireceptor antibodies, antiligand antibodies, receptor-specific tyrosine kinase inhibitors, and agents such as picropodophyllin and metformin that have novel mechanisms of action. Several recently reported phase III clinical trials of anti-IGF-I receptor antibodies have been disappointing and are sufficient to disprove the hypothesis that the antibodies tested have large favorable impacts on unselected patients with cancer. However, many of these trials were designed prior to recent insights concerning pathophysiology and predictive biomarkers. Future studies are required, but it will be important to optimize their design rather than simply repeat the approaches taken to date.

IGF-I and IGFBP-3 before and after inpatient alcohol detoxification in alcohol-dependent subjects

Background

It is unclear whether alcohol detoxification has an effect on factors that are involved in growth, metabolic functions and cell proliferation. Alcohol abuse is associated with low IGF-I levels that tend to rise after alcohol withdrawal. There is a paucity of studies on the course of IGFBP-3 (the main binding protein for IGF-I) after alcohol detoxification.

Material/Methods

We prospectively assessed IGF-I and IGFBP-3 changes at the time of admission and after 4 to 6 weeks of detoxification in an inpatient alcohol detoxification facility in 118 alcohol-dependent subjects given a regular hospital diet. No participants dropped out of the study.

Results

Changes in IGF-I after alcohol detoxification showed a marked dimorphism in altered hepatic biochemistry upon admission, with a rise in those with normal liver enzymes upon admission (p=0.016, Kruskall-Wallis) and a drop in those with elevated liver enzymes upon admission (p=0.05); the latter was noted in subjects that had consumed alcohol close to the time of admission. Overall, however, IGF-I and IGFBP-3 were within normal limits for most subjects both upon admission and after alcohol detoxification; no significant differences were detected among the examined parameters in men vs. women, and there were no significant correlations of IGF-I, IGFBP-3 or the IGF-I/IGFBP-3 molar ratio with BMI or age.

Conclusions

Regardless of hepatic enzymes’ elevation, alcohol detoxification had overall slight effects on IGF-I and IGFBP-3.

The safety profile of exogenous insulin in people with type 2 diabetes: justification for concern

There is no doubt about the value of exogenous insulin for people with type 1 diabetes. The purpose of this commentary is to discuss emerging evidence that this may not be the case for the majority of people with type 2 diabetes.

Diet-induced hyperinsulinemia accelerates growth of androgen-independent PC-3 cells in vitro

We investigated the effect of insulin and diet-induced hyperinsulinemia on the growth of the PC-3 cells in vitro and discerned the growth promoting effect of insulin in the androgen-independent cells. Sprague-Dawley rats were kept on a high-fat diet for 4 wk for the induction of insulin resistance and hyperinsulinemia. Insulin alone or serum of the rats kept on either normal-pellet diet or high-fat diet was used to stimulate the serum-starved PC-3 cells growth in culture. S961, a high-affinity insulin-receptor antagonist, was used to confirm the insulin-mediated effects. Significant impairment in the glucose disposal rate and increase in the serum glucose and insulin levels was observed in the high-fat-diet-fed rats. The media supplemented with the serum of the high-fat-diet-fed rats accelerated the growth of the PC-3 cells in comparison to that of normal-pellet-diet-fed rats. Insulin treatment led to accelerated growth of the serum-starved PC-3 cells in a dose-dependent manner and inhibited by the S961 pretreatment. Insulin and serum of the diet-induced hyperinsulinemic rats promote the growth of androgen-independent prostate cancer PC-3 cells. Further, our results provide support for the concept that diet-associated elevation in insulin level may augment the growth of prostate cancer cells.

Programmed cell removal: a new obstacle in the road to developing cancer

The development of cancer involves mechanisms by which aberrant cells overcome normal regulatory pathways that limit their numbers and their migration. The evasion of programmed cell death is one of several key early events that need to be overcome in the progression from normal cellular homeostasis to malignant transformation. Recently, we provided evidence in mouse and human cancers that successful cancer clones must also overcome programmed cell removal. In this Opinion article, we explore the role of programmed cell removal in both normal and neoplastic cells, and we place this pathway in the context of the initiation of programmed cell death.

Obesity and breast cancer: a clinical biochemistry perspective

OBJECTIVES

To evaluate the laboratory diagnosis aspects of obesity-related health problems with special reference to postmenopausal breast cancer.

DESIGN AND METHODS

We conducted a systemic search of the literature primarily from the PubMed to obtain the relevant data.

RESULTS

Obesity is associated with the dysregulations of a number of body components such as blood constituents, extracellular matrix, and hormones/growth factors axes, which could be utilized for early diagnosis.

CONCLUSIONS

Obesity-related disorders including breast cancer have emerged as major health problems in almost all the nations. There is a need to elucidate different biochemical markers that are being used in the clinics or have the potential for such use. A precise understanding of the complex pathologies related with obesity is useful in prevention, early diagnosis and overall clinical management.

Signalling pathways of insulin-like growth factors (IGFs) and IGF binding protein-3

Although the insulin-like growth factor (IGF) system is essential for normal growth and development, its dysregulation has been implicated in a range of pathological states. The peptide growth factors IGF-I and IGF-II exert their effects by binding to cell-surface heterotetrameric tyrosine kinase receptors and activating multiple intracellular signalling cascades, leading to changes in the expression of proteins essential for cell proliferation, survival and differentiation. The IGF system comprises multiple ligands, receptors and high-affinity IGF binding proteins (IGFBPs), with added complexity arising from crosstalk between its receptors and other key growth-regulatory pathways such as those activated by steroid hormones, integrins and other receptor tyrosine kinases. The IGFBPs are also increasingly recognised for their intrinsic growth-regulatory activity, and the ability of IGFBP-3 to modulate signalling pathways of nuclear hormone and growth factor receptors, as well as novel receptors, is believed to play a role both in normal physiology and in disease.

Understanding the mechanism of insulin and insulin-like growth factor (IGF) receptor activation by IGF-II

Background

Insulin-like growth factor-II (IGF-II) promotes cell proliferation and survival and plays an important role in normal fetal development and placental function. IGF-II binds both the insulin-like growth factor receptor (IGF-1R) and insulin receptor isoform A (IR-A) with high affinity. Interestingly both IGF-II and the IR-A are often upregulated in cancer and IGF-II acts via both receptors to promote cancer proliferation. There is relatively little known about the mechanism of ligand induced activation of the insulin (IR) and IGF-1R. The recently solved IR structure reveals a folded over dimer with two potential ligand binding pockets arising from residues on each receptor half. Site-directed mutagenesis has mapped receptor residues important for ligand binding to two separate sites within the ligand binding pocket and we have recently shown that the IGFs have two separate binding surfaces which interact with the receptor sites 1 and 2.

Methodology/Principal Findings

In this study we describe a series of partial IGF-1R and IR agonists generated by mutating Glu12 of IGF-II. By comparing receptor binding affinities, abilities to induce negative cooperativity and potencies in receptor activation, we provide evidence that residue Glu12 bridges the two receptor halves leading to receptor activation.

Conclusions/Significance

This study provides novel insight into the mechanism of receptor binding and activation by IGF-II, which may be important for the future development of inhibitors of its action for the treatment of cancer.

Insulin-like growth factor binding protein-3 inhibits migration of endometrial cancer cells

Cell migration and invasion leading to metastasis is a major cause of death from endometrial cancer (EC). We have shown that the rate of EC cell migration is inversely related to the level of insulin-like growth factor protein-3 (IGFBP-3). Down-regulation of IGFBP-3 by siRNA in EC cells accelerated migration without affecting proliferation and cells displayed a more migratory phenotype, with co-localization of migration-associated markers at the leading edge of cell membranes. Opposite effects were seen with either the addition of recombinant IGFBP-3 or overexpression of IGFBP-3. Cells with mutated PTEN had the highest IGFBP-3 expression and the slowest migration rates. This study demonstrates that endogenous IGFBP-3 modulates adhesion-migration dynamics in EC cells, implying that it may be important in regulating metastasis in this disease.

The link between the metabolic syndrome and cancer

Since the incidence of the metabolic syndrome is on the rise in the western world, its coherence to cancer is becoming more apparent. In this review we discuss the different potential factors involved in the increase of cancer in the metabolic syndrome including obesity, dyslipidemia and Type 2 Diabetes Mellitus (T2DM) as well as inflammation and hypoxia. We especially focus on the insulin and IGF systems with their intracellular signaling cascades mediated by different receptor subtypes, and suggest that they may play major roles in this process. Understanding the mechanisms involved will be helpful in developing potential therapeutics.

Perceived protein needs and measured protein intake in collegiate male athletes: an observational study

BACKGROUND

Protein needs for athletes are likely higher than those for the general population. However, athletes may perceive their protein needs to be excessively high. The purpose of this research was to compare collegiate athletes' perceived protein needs and measured protein intake to the recommended protein intake (RDI) for healthy adults (i.e. 0.8 g/kg/d) and to the maximum beneficial level for strength-trained athletes (i.e. 2.0 g/kg/day).

METHODS

Perceived protein needs were quantified in 42 strength-trained collegiate male athletes by using a survey that asked the athletes to provide their perception about protein needs in specific quantitative terms (i.e. g/kg/d). Perceived protein needs were also determined by having the athletes select a daylong menu that they perceived to have adequate protein content from a collection of 5 isoenergetic menus, which differed in terms of protein content. Actual protein intake was quantified using 3-day food records and nutrient analysis. Single sample t-tests were used to compare protein intake and perceived protein needs to 0.8 g/kg/day and 2.0 g/kg/day.

RESULTS

When asked to provide, in quantitative terms, protein needs for athletes, 67% of the athletes indicated "do not know." Of the remaining 33% of athletes, all gave values greater than 2.0 g/kg/d (mean 21.5 ± 11.2 g/kg/d, p = 0.14 vs. 2.0 g/kg/d). Based on the menu selection method for determining perceived protein needs, the athletes indicated that their protein needs were 2.4 ± 0.2 g/kg/d, which was greater than the RDI for protein (p < 0.0001) and tended to be greater than the maximally beneficial protein intake of 2.0 g/kg/d (p = 0.13). Measured protein intake was 2.0 ± 0.1 g/kg/d, which was greater than the RDI (p < 0.0001) but not different from the maximally beneficial protein intake of 2.0 g/kg/d (p = 0.84).

CONCLUSIONS

Male collegiate athletes recognize that their protein needs are higher than that of the general population and consume significantly more protein than recommended in the RDI. However, it also appears that athletes are not aware of objective recommendations for protein intake and may perceive their needs to be excessively high. This study highlights the need for nutrition education in collegiate athletes, in particular nutrition education on macronutrient distribution and protein needs.

Is growth hormone resistance/IGF-1 reduction good for you?

GH, IGF-1, and insulin are emerging as important and independent mediators of tumor development and aging. Two recent studies report that humans with GH-receptor deficiency are protected from developing cancer through alterations in GH, IGF-1, and insulin signaling, decreasing the susceptibility of cells to DNA damage and abnormal proliferation.

The size of adrenal incidentalomas correlates with insulin resistance. Is there a cause-effect relationship?

CONTEXT

Adrenal incidentalomas (AI) have often been associated with a high prevalence of insulin resistance (IR) and cardiovascular risk factors, although direct measurement of insulin sensitivity (IS) has never been carried out.

OBJECTIVE

We aimed to investigate whether the morphological and hormonal features of AI correlate with the presence and severity of IR, using the hyperinsulinaemic euglycaemic clamp (HEC).

DESIGN AND MEASUREMENTS

Forty patients with AI (22 women) with a mean age of 58.5±11.1 years underwent hormonal and morphological evaluation. Nineteen patients with AI without known history of diabetes mellitus (DM) or impaired glucose tolerance (IGT) and 17 matched controls underwent oral glucose tolerance test (OGTT) and hyperinsulinaemic euglycaemic clamp (HEC).

RESULTS

Diabetes mellitus was observed in 13 patients (33%), while three (8%) had IGT. Thirty-one of the AI were nonfunctioning (82.5%), whereas two (5%) secreted cortisol (Cushing's syndrome) and seven (12.5%) showed subclinical secretion of cortisol. The 19 patients with nonfunctioning AI were more insulin resistant than controls (glucose up-take: 4.58±1.80 vs 5.85±2.48 mg/kg/min respectively; P=0.01); IS was inversely related to the mass size (r=-0.57; P=0.04), free urinary cortisol (r=-0.68; P=0.01), serum cortisol after 1-mg dexamethasone suppression (-0.65; P=0.02) and percentage of trunk fat mass (-0.77; P=0.02) and directly related to serum adreno cortico tropic hormone (ACTH) (r=0.62; P=0.03). After performing multivariate regression, the mass size was found to be the most powerful predictor of IR.

CONCLUSION

Our study showed a high prevalence of insulin resistance in patients with nonfunctioning AI and suggests its possible involvement in AI growth.

Cellular metabolic stress: considering how cells respond to nutrient excess

Nutrient stress is generally considered from the standpoint of how cells detect and respond to an insufficient supply of nutrients to meet their bioenergetic needs. However, cells also experience stress as a result of nutrient excess, during which reactive oxygen species (ROS) production exceeds that required for normal physiological responses. This may occur as a result of oncogene activation or chronic exposure to growth factors combined with high levels of nutrients. As a result, multiple mechanisms have evolved to allow cells to detect and adapt to elevated levels of intracellular metabolites, including promotion of signaling and proliferation by ROS, amino acid-dependent mTOR activation, and regulation of signaling and transcription through metabolite-sensitive protein modifications. We discuss how each of these responses can contribute to the development and/or progression of cancer under conditions of cellular nutrient excess and their potential roles in linking chronic organismal over-nutrition (obesity) with cancer.