Type I insulin-like growth factor receptor function in breast cancer

Bitter melon extract suppresses metastatic breast cancer cells (MCF-7 cells) growth possibly by hindering glucose uptake

Breast cancer is one of the most commonly diagnosed cancers among women, however the complete cure for metastatic breast cancer is lacking due to poor prognosis. There has been an increasing trend of dietary modifications including consumption of natural food for the prevention of cancer. One of the popular natural foods is bitter melon. Bitter melon grows in tropical and subtropical areas. Some of the beneficial effects of bitter melon towards disease including cancer have been reported at the whole body/organismal level. However, specific cellular mechanisms by which bitter melon exerts beneficial effects in breast cancer are lacking. In this study, we used a human metastatic breast cancer cell line, MCF-7 cell, to study if bitter melon alters glucose clearance from the culture medium. We co-cultured MCF-7 cells with bitter melon extract in the presence and absence of supplemented insulin and subsequently measured MCF-7 cells viability. In this study, we report a noble finding that bitter melon extract exerts cytotoxic effects on MCF-7 cells possibly via inhibition of glucose uptake. Our findings show that insulin rescues MCF-7 cells from the effects of bitter melon extract.

Silencing HS6ST3 inhibits growth and progression of breast cancer cells through suppressing IGF1R and inducing XAF1

Heparan sulfate 6-O-sulfation is biologically edited by 6-O-sulfotransferases (HS6STs) within heparan sulfate chains. Three isoforms of HS6ST have been identified. These enzymes are found to be differentially expressed in a variety of tissues. Recently, several studies have shown that dysregulation of 6-O-sulfotransferases could be involved in tumorigenesis of several cancers. This study aimed to analyze the expression and function of HS6ST3 in breast cancer. HS6ST3 was found up-regulated in T47D, MCF7 and MDA-MB231 breast cancer cell lines. HS6ST3 was then silenced in T47D and MCF7 using siRNA. Silencing HS6ST3 diminished tumor cell growth, migration and invasion, but enhanced cell adhesion and apoptosis in breast cancer. Gene microarray analysis revealed that silencing HS6ST3 significantly changed the expression of IGF1R and XAF1 in breast cancer cells. Further functional studies showed that the cellular processes were mediated by IGF1R and XAF1 after silencing HS6ST3 in breast cancer cells. Together these results indicate that HS6ST3 might be involved in the tumorigenesis of breast cancer and it could be a promising target in breast cancer therapy.

Effects of Obesity and Obesity-Related Molecules on Canine Mammary Gland Tumors

Obesity can affect the clinical course of a number of diseases, including breast cancer in women and mammary gland tumors in female dogs, via the secretion of various cytokines and hormones. The objective of this study was to examine the expression patterns of obesity-related molecules such as aromatase, leptin, and insulin-like growth factor 1 receptor (IGF-1 R) in canine mammary carcinomas (CMCs) on the basis of the body condition score (BCS). Comparative analyses of the expression of these molecules, together with prognostic factors for CMCs, including hormone receptors (HRs; estrogen and progesterone receptors), lymphatic invasion, central necrosis of the tumor, and histologic grade, were performed on 56 CMCs. The mean age of CMC onset was lower in the overweight or obese group (8.7 ± 1.9 years) than in the lean or ideal body weight group (10.4 ± 2.7 years). The proportion of poorly differentiated (grade III) tumors was significantly higher in the overweight or obese female dogs. Aromatase expression was significantly higher in the overweight or obese group and was correlated with the expression of HRs (P = .025). These findings suggest that overweight or obese status might affect the development and behavior of CMCs by tumor-adipocyte interactions and increased HR-related tumor growth.

IGF-1 regulates Cyr61 induced breast cancer cell proliferation and invasion

Background

Studies from our laboratory and others have shown that cysteine-rich 61 (Cyr61) may be involved in tumor proliferation and invasion. In earlier studies, we demonstrated increased insulin-like growth factor-I (IGF-1) is associated with breast tumor formation and poor clinical outcomes. In our current study we have investigated IGF-1 regulation of Cyr61 and whether targeting IGF-1 could inhibit Cyr61 induced tumor growth and proliferation.

Methods

Several ATCC derived normal and breast cancer cell lines were used in this study: MDA-MB231, BT474, MCF-7, and SKBR3. We also tested cells stably transfected in our laboratory with active Akt1 (pAkt; SKBR3/AA and MCF-7/AA) and dominant negative Akt1 (SKBR3/DN and MCF-7/DN). In addition, we used MCF-7 cells transfected with full length Cyr61 (CYA). Monolayer cultures treated with IGF-1 were analyzed for Cyr61 expression by RT-PCR and immunohistochemical staining. Migration assays and MTT based proliferation assays were used to determine invasive characteristics in response to IGF-1/Cyr61 activation.

Results

Cells with activated Akt have increased levels of Cyr61. Conversely, cells with inactive Akt have decreased levels of Cyr61. IGF-1 treatment increased Cyr61 expression significantly and cells with high level of Cyr61 demonstrate increased invasiveness and proliferation. Cyr61 overexpression and activation led to decrease in E-cadherin and decrease in FOXO1. Inhibition of the PI3K and MAPK pathways resulted in significant decrease in invasiveness and proliferation, most notably in the PI3K pathway inhibited cells.

Conclusion

The findings of this study show that IGF-1 upregulates Cyr61 primarily through activation of the Akt-PI3K pathway. IGF-1 induced MAPK plays a partial role. Increase in Cyr61 leads to increase in breast cancer cell growth and invasion. Hence, targeting Cyr61 and associated pathways may offer an opportunity to inhibit IGF-1 mediated Cyr61 induced breast cancer growth and invasion.

Modulation of insulin/IGFs pathways by sirtuin-7 inhibition in drug-induced chemoreistance

Background

Insulin and insulin-like growth factors (IGFs) are key regulators of metabolism and growth. Recent evidences suggest a key role of these pathways in non-classical tissues and the metabolic pathways by which these hormones exert their effects in neoplasia is unclear.

Aims

To study insulin/IGFs pathways in drug sensitive and resistant cancer cells representing breast cancer (MCF-7), osteosarcoma (SaOS-2), and ovarian cancer (A2780) and to examine the effect of Sirtuin-7 (Sirt7) inhibition on insulin/IGFs pathways in MCF-7 cell line.

Methods

Drug resistant cells were generated by continuous incubation of parental cell lines with stepwise increases in Doxorubicin or Cisplatin over a period of 3 to 6 months. MCF-7 cells were transfected with cloned hairpin siRNA template for Sirt7 using the Amaxa GmbH transfection system. mRNA expression of Sirt7, INSR, IRS-1, IRS-2, IRS-4, IGF-1, IGF-2, MDR-1, MRP-1, BCRP was measured by qPCR and Sirt7 by standard Western blotting. FITC-insulin uptake was imaged with Leica Confocal Microscope.

Results

Insulin receptor (INSR), insulin receptor substrate-1 (IRS-1) were inhibited in drug-induced resistance, whereas IRS-2 was significantly induced in all the chemoresistant cells tested when compared to their parental counterparts. IGF-1 and IGF-2 were also upregulated in all the drug resistant cells tested. Sirt7 was significantly reduced in all chemoresistant cells tested. Knockdown of Sirt7 expression in human breast MCF-7 cell line by siRNA induced premature senescence-like phenotype and multi-drug resistance, suggesting that this gene may play an active role in regulating cancer cell response to stress. Suppression of Sirt7 selectively inhibited INSR and IRS-1, whereas it had minimal effect on that of IRS-2. Sirt7 suppression in MCF-7 also inhibited insulin uptake. Additionally, Sirt7 inhibition upregulated IGF-1, IGF-2 and IGFR expression.

Conclusion

Our data demonstrate that stress-induced Sirt7 inhibition significantly increases stress resistance and modulates insulin/IGF-1 signaling pathways. More importantly, this study links Sir2 family proteins to insulin/IGF signaling in drug-induced stress resistance in neoplasia.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1135426681234493

Loss of Akt1 or Akt2 delays mammary tumor onset and suppresses tumor growth rate in MTB-IGFIR transgenic mice

Background

Akt is a serine/threonine kinase that mediates signaling downstream of tyrosine kinase receptors like the type I insulin-like growth factor receptor (IGF-IR). In fact, we have previously shown that mammary tumors induced by elevated expression of the IGF-IR are associated with hyperactivation of Akt. However, there are three mammalian isoforms of Akt (Akt1, Akt2 and Akt3) and these isoforms regulate distinct physiologic properties within cells. In this manuscript, the impact of disrupting Akt1 or Akt2 in mammary tumors induced by IGF-IR overexpression were examined to determine whether specific Akt isoforms regulate different aspects of mammary tumorigenesis.

Methods

Akt1 and Akt2 levels were stably ablated in mammary tumors of MTB-IGFIR transgenic mice by crossing MTB-IGFIR transgenic mice with either Akt1^−/− or Akt2^−/− mice. Tumor onset, growth rate, and metastasis were determined.

Results

Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis. Despite the absence of Akt1 or Akt2, mammary tumors that developed in the MTB-IGFIR mice maintained detectable levels of phosphorylated Akt. Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors.

Conclusions

Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated. Despite the complete loss of Akt1 or Akt2, the level of total phosphorylated Akt remained largely unaffected in the mammary tumors suggesting that loss of one Akt isoform is compensated by enhanced activation of the remaining Akt isoforms. These findings indicate that therapeutic strategies targeting the activation of individual Akt isoforms will prove less effective than simultaneously inhibiting the activity of all three Akt isoforms for the treatment of breast cancer.

Resveratrol regulates the cell viability promoted by 17β-estradiol or bisphenol A via down-regulation of the cross-talk between estrogen receptor α and insulin growth factor-1 receptor in BG-1 ovarian cancer cells

Endocrine disrupting chemicals (EDCs) and estrogens appear to promote development of estrogen-dependent cancers, including breast and ovarian carcinomas. In this study, we evaluated the cell viability effect of BPA on BG-1 human ovarian cancer cells, along with the growth inhibitory effect of resveratrol (trans-3,4,5-trihydroxystilbene; RES), a naturally occurring phytoestrogen. In addition, we investigated the underlying mechanism(s) of BPA and RES in regulating the interaction between estrogen receptor alpha (ERα) and insulin-like growth factor-1 receptor (IGF-1R) signals, a non- genomic pathway induced by 17β-estradiol (E2). BPA induced a significant increase in BG-1 cell growth and up-regulated mRNA levels of ERα and IGF-1R. In parallel with its mRNA level, the protein expression of ERα was induced, and phosphorylated insulin receptor substrate-1 (p-IRS-1), phosphorylated Akt1/2/3, and cyclin D1 were increased by BPA or E2. However, RES effectively reversed the BG-1 cell proliferation induced by E2 or BPA by inversely down-regulating the expressions of ERα, IGF-1R, p-IRS-1, and p-Akt1/2/3, and cyclin D1 at both transcriptional and translational levels. Taken together, these results suggest that RES is a novel candidate for prevention of tumor progression caused by EDCs, including BPA via effective inhibition of the cross-talk of ERα and IGF-1R signaling pathways.

Caveolin-1 and polymerase I and transcript release factor: new players in insulin-like growth factor-I receptor signaling

Caveolae are plasma membrane regions enriched in Caveolin proteins which regulate vesicular transport, endocytosis, and cell signaling. IGF-I receptor (IGF-IR) localizes in caveolae and tyrosine phosphorylates Caveolin-1 (Cav-1), the most represented caveolar protein. Cav-1 participates to IGF-IR internalization and signaling directly interacting with IGF-IR and its substrates. Recently, polymerase I and transcript release factor (PTRF) or Cavin-1, has been identified in the caveolar backbone. PTRF does not play a Cav-1 ancillary role and emerging data support a direct role of PTRF in IGF-IR signaling. PTRF and Cav-1 can bind IGF-IR and regulate IGF-IR internalization and plasma membrane replacement, mechanisms frequently deregulated in cancer cells. Although the exact roles of Cav-1 and IGF-IR in human cancer continue to be a matter of some debate, there is a strong evidence for an association between Cav-1 and IGF-IR in cancer development. With the discovery of IGF-IR interaction with PTRF in caveolae, new insight emerged to understand the growing functions of these domains in IGF-I action.

erbB3 recruitment of insulin receptor substrate 1 modulates insulin-like growth factor receptor signalling in oestrogen receptor-positive breast cancer cell lines

Introduction

Recently we reported that insulin receptor substrate 1 (IRS-1), classically an adaptor protein for the insulin-like growth factor type I receptor (IGF-IR), associates with the epidermal growth factor receptor in oestrogen receptor (ER)-positive (ER+) tamoxifen-resistant breast cancer cells. In this study, we examined whether IRS-1 also associates with another erbB receptor family member, erbB3, and what impact this might have on IGF-IR signalling in three ER+ breast cancer cell lines.

Methods

Immunoprecipitation and Western blot analysis were utilised to examine the potential association between erbB3 and IRS-1 in MCF-7, T47D and BT-474 cells in the absence and presence of the erbB3/4 ligand heregulin β1 (HRGβ1). Subsequently, the impact of a selective IGF-IR/IR inhibitor 4-anilino-5-bromo-2-[4-(2-hydroxy-3-(N, N-dimethylamino)propoxy)anilino]pyrimidine on this association and HRGβ1 signalling was assessed in these cell lines. Immunohistochemical analysis of a small cohort of ER+ breast cancer patient samples was also performed to determine the potential clinical relevance of this novel interaction.

Results

Immunoprecipitation and Western blot analysis revealed an interaction between erbB3 and IRS-1 in MCF-7, T47D and BT-474 cells, with HRGβ1 significantly enhancing this recruitment and promoting IRS-1 phosphorylation at Y612. IRS-1 participates in erbB3 signalling in MCF-7 and T47D cells as IRS-1 knockdown impaired HRGβ1 signalling. Importantly, recruitment of IRS-1 by erbB3 reduced IRS-1 association with IGF-IR in MCF-7 and T47D cells, whilst blockade of IGF-IR-enhanced erbB3-IRS-1 interaction and sensitised both cell lines to HRGβ1, allowing HRGβ1 to override IGF-IR blockade. Consequently, suppression of IRS-1 signalling enhanced the effects of IGF-IR inhibition in these cells. This novel interaction may have clinical relevance, as immunohistochemical analysis of a small ER+ breast tumour series revealed significant positive correlations between phosphorylated IRS-1 Y612 expression and total erbB3, phosphorylated Akt and Ki-67 expression.

Conclusions

IRS-1 can be recruited to IGF-IR and erbB3 in ER+ breast cancer cells, and this provides an adaptive resistance mechanism when these receptors are targeted individually. Consequently, cotargeting IGF-IR and either erbB3 or IRS-1 should prove to be a more effective strategy for the treatment of ER+ breast cancer.

Chemokines: key players in cancer progression and metastasis

Instructed cell migration is a fundamental component of various biological systems and is critical to the pathogenesis of many diseases including cancer. Role of chemokines in providing navigational cues to migrating cancer cells bearing specific receptors is well established. However, functional mechanisms of chemokine are not well implicit, which is crucial for designing new therapeutics to control tumor growth and metastasis. Multiple functions and mode of actions have been advocated for chemokines and their receptors in the progression of primary and secondary tumors. In this review, we have discussed current advances in understanding the role of the chemokines and their corresponding receptor in tumor progression and metastasis.

Breast cancer cell survival signal is affected by bergapten combined with an ultraviolet irradiation

In this study we have reported that bergapten (B) and bergapten plus UV (PUVA) are able to significantly affect MCF-7, ZR-75 and SKBR-3 breast cancer cell proliferations. B induced a lowering of PI3K/AKT survival signal in MCF-7 cells even in presence of IGF-I stimulation. Furthermore, B and in a higher extent, PUVA up-regulated the p53 mRNA and the protein content. An increased co-association between p21 WAF and proliferating cell nuclear antigen (PCNA) has been observed in PUVA-treated MCF-7 cells, thus inhibiting DNA replication. These results highlight how B, and its photoactivated compound, exert antiproliferative effects and induce apoptotic responses in breast cancer cells.

Identification of Insulin-Like Growth Factor-I Receptor (IGF-IR) Gene Promoter-Binding Proteins in Estrogen Receptor (ER)-Positive and ER-Depleted Breast Cancer Cells

The insulin-like growth factor I receptor (IGF-IR) has been implicated in the etiology of breast cancer. Overexpression of the IGF-IR gene is a typical feature of most primary breast cancers, whereas low IGF-IR levels are seen at advanced stages. Hence, evaluation of IGF-IR levels might be important for assessing prognosis. In the present study, we employed a proteomic approach based on DNA affinity chromatography followed either by mass spectroscopy (MS) or Western blot analysis to identify transcription factors that may associate with the IGF-IR promoter in estrogen receptor (ER)-positive and ER-depleted breast cancer cells. A biotinylated IGF-IR promoter fragment was bound to streptavidin magnetic beads and incubated with nuclear extracts of breast cancer cells. IGF-IR promoter-binding proteins were eluted with high salt and analyzed by MS and Western blots. Among the proteins that were found to bind to the IGF-IR promoter we identified zinc finger transcription factors Sp1 and KLF6, ER-α, p53, c-jun, and poly (ADP-ribosylation) polymerase. Furthermore, chromatin immune-precipitation (ChIP) analysis confirmed the direct in vivo binding of some of these transcription factors to IGF-IR promoter DNA. The functional relevance of binding data was assessed by cotransfection experiments with specific expression vectors along with an IGF-IR promoter reporter. In summary, we identified nuclear proteins that are potentially responsible for the differential expression of the IGF-IR gene in ER-positive and ER-depleted breast cancer cells.

Serum insulin-like growth factor-I and mammary tumor development in ad libitum-fed, chronic calorie-restricted, and intermittent calorie-restricted MMTV-TGF-alpha mice

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum insulin-like growth factor (IGF)-I levels and mammary tumor (MT) development was investigated. Ten-week-old MMTV-TGF-alpha female mice were assigned to ad libitum-fed (AL; AIN-93M diet), ICR [3-week 50% caloric restriction using AIN-93M-mod diet, 2x protein, fat, vitamins, and minerals followed by 3 weeks of daily 100% AL consumption of AIN-93M ( approximately 75% of AL for each 6-week cycle)], and CCR (calorie and nutrient intake matched for each 6-week ICR cycle) groups. Half of the mice from each group were sacrificed at 79 (end of restriction) or 82 (end of refeeding) weeks of age. Serum was obtained at euthanasia and in cycles 1, 3, 5, 8, and 11. MT incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice. ICR-Restricted mice had significantly lower terminal serum IGF-I and IGF-I/IGF binding protein-3 (IGFBP-3) ratio than CCR, ICR-Refed, and AL mice. There were no differences in terminal IGFBP-3. Final body, internal, and mammary fat pad weights correlated positively with IGF-I and negatively with IGFBP-3. Few changes were found for protein expression of IGF-IRalpha and IGFBP-3 in mammary tissue and MTs. During the study, IGF-I levels of ICR-Restricted mice were reduced, whereas refeeding allowed partial recovery. For all groups, elevated IGF-I levels preceded MT detection, although not all values were significant versus mice without MTs. However, the specific role of IGF-I in the protective effect of calorie restriction remains to be determined. These results confirm that ICR prevents MT development to a greater extent than CCR.

The insulin-like growth factor-I receptor as an oncogene

The insulin-like growth factor-I receptor (IGF-IR) mediates the biological actions of both IGF-I and IGF-II. The IGF-IR is expressed in most transformed cells, where it displays potent antiapoptotic, cell-survival, and transforming activities. IGF-IR expression is a fundamental prerequisite for the acquisition of a malignant phenotype, as suggested by the finding that IGF-IR-null cells (derived from IGF-IR knock-out embryos) are unable to undergo transformation when exposed to cellular or viral oncogenes. This review article will focus on the underlying molecular mechanisms that are responsible for the normal, physiological control of IGF-IR gene expression, as well as the cellular pathways that underlie its aberrant expression in cancer. Examples from the clinics will be presented, including a description of how the IGF system is involved in breast, prostate, pediatric, and gynecological cancers. Finally, current attempts to target the IGF-IR as a therapeutic approach will be described.

The impact of transgenic IGF-IR overexpression on mammary development and tumorigenesis

Insulin-like growth factor-I and -II (IGF-I and IGF-II) and/or the type I insulin-like growth factor receptor (IGF-IR) have been implicated in a number of human tumors including breast cancer. However, despite being implicated in breast cancer for approximately 25 years and given that transgenic technology has been available for about the same period of time, it is surprising that transgenic mice overexpressing the IGF-IR in the mammary gland have only recently been characterized. This review will describe the effects of IGF-IR overexpression on mammary ductal morphogenesis and mammary tumorigenesis in the two available transgenic models.

Characterization of a novel primary mammary tumor cell line reveals that cyclin D1 is regulated by the type I insulin-like growth factor receptor

The importance of type I insulin-like growth factor receptor (IGF-IR) overexpression in mammary tumorigenesis was recently shown in two separate transgenic models. One of these models, the MTB-IGFIR transgenics, was generated in our lab to overexpress IGF-IR in mammary epithelial cells in a doxycycline (Dox)-inducible manner. To complement this transgenic model, primary cells that retained Dox-inducible expression of IGF-IR were isolated from a transgenic mammary tumor. This cell line, RM11A, expressed high levels of IGF-IR, phosphorylated Akt, and phosphorylated extracellular signal-regulated kinase 1/2 in the presence of Dox. IGF-IR overexpression provided the primary tumor cells with a survival advantage in serum-free media and seemed to induce ligand-independent activation of the IGF-IR because RM11A cells cultured in the presence of Dox were largely nonresponsive to exogenous IGFs. IGF-IR overexpression also augmented the growth of RM11A cells in vivo because injection of these cells into mammary glands of wild-type mice produced palpable tumors in 15.8 +/- 3.4 days when the mice were administered Dox, compared with 57.8 +/- 6.3 days in the absence of Dox. DNA microarray analysis revealed a number of genes regulated by IGF-IR, one of which was cyclin D1. Suppression of IGF-IR expression in vitro or in vivo was associated with a decrease in cyclin D1 protein, suggesting that at least some of the proliferative actions of IGF-IR are mediated through cyclin D1. Therefore, this article characterizes the first primary murine mammary tumor cell line with inducible IGF-IR expression. These cells provide a powerful in vitro/in vivo model to examine the function of IGF-IR in mammary tumorigenesis.

Proliferative effects of insulin analogues on mammary epithelial cells

Structural modification of insulin results in the generation of insulin analogues that show altered binding affinities to the insulin receptor and/or IGF-I receptor. As a consequence these insulin analogues may have increased mitogenic potency. Nine benign or malignant human mammary epithelial cells, which show different insulin receptor and IGF-I receptor expression patterns, were studied regarding mitogenicity of insulin and insulin analogues. Only insulin glargine showed a significantly higher proliferative effect on MCF-7 breast cancer cells compared to regular insulin among a panel of short- or long-acting insulin analogues, that are in clinical use.

Genomic and nongenomic effects of estrogen signaling in human endometrial cells: involvement of the growth factor receptor signaling downstream AKT pathway

For the endometrium, estradiol and tamoxifen induce proliferation, and consequently, tamoxifen treatment of breast cancer results in a 2-fold to 7-fold increased risk for endometrial cancer. Here, the role of activation of growth factor receptor signaling in mediating the effects of estrogen and tamoxifen is determined. Microarray analysis of ECC-1 cells treated with estradiol or tamoxifen indicate that rapid responses to treatment (1 hour) are very distinct from long-term responses (>24 hours). Furthermore, estradiol and tamoxifen are observed to induce AKT activation. Comparing long-term estrogen- and tamoxifen-regulated genes with genes regulated by insulin-like growth factor 1 and amphiregulin reveals that the late effects of estrogen and tamoxifen signaling may partly be mediated via activation of growth factor receptor signaling pathways. It is hypothesized that both early and late effects of estrogen and tamoxifen signaling in the endometrium are partly mediated via the activation of growth factor receptor signaling, putatively at the level of AKT activation.

Insulin receptor substrate 1 knockdown in human MCF7 ER+ breast cancer cells by nuclease-resistant IRS1 siRNA conjugated to a disulfide-bridged D-peptide analogue of insulin-like growth factor 1

IRS-1 overexpression has been associated with breast cancer development, hormone independence and antiestrogen resistance. IRS-1 is a major downstream signaling protein for insulin and IGF1 receptors, conveying signals to PI-3K/Akt and ERK1/2 pathways. In estrogen-sensitive breast cancer cell lines, the widely used antiestrogen tamoxifen treatment reduces IRS-1 expression and function, thereby inhibiting IRS-1/PI-3K signaling. IRS-1 may serve as an alternative target to overexpressed IGF1R in breast cancer. While siRNA technology has become commonplace in many laboratories for in vitro gene knockdown studies, and in vivo stability issues are largely solved, its use in vivo is limited by an inability to efficiently and specifically deliver it to the intended site of action. We previously reported reduced survival of human MCF7 estrogen receptor positive breast cancer cells treated with a normal IRS1 siRNA delivered by a cationic lipid, plus an additive effect in combination with tamoxifen. We now report enhanced cellular uptake, relative to the unconjugated serum-stabilized IRS1 siRNA, of a serum-stabilized IRS1 siRNA conjugated with our previously characterized peptide mimetic of IGF1, D-(Cys-Ser-Lys-Cys), without the use of cationic lipids or electroporation, in MCF7 cells that overexpress IGF1R. Excess native IGF1 blocked uptake. An IRS1 siRNA cholesterol conjugate, targeted universally to cell membranes, was taken up by MCF7 cells as much as the peptide mimetic conjugate. IRS1 mRNA knockdown and IRS-1 protein knockdown were comparable for the IGF1 peptide and cholesterol conjugates. The unconjugated serum-stabilized IRS1 siRNA control showed negligible effects. Viability assays showed additive effects of siRNA treatment in combination with tamoxifen. In summary, we have taken the first step in converting an siRNA into a pharmacologically active agent for breast cancer.

IGF-1 activates hEAG K(+) channels through an Akt-dependent signaling pathway in breast cancer cells: role in cell proliferation

Previous work from our laboratory has shown that human ether à go-go (hEAG) K(+) channels are crucial for breast cancer cell proliferation and cell cycle progression. In this study, we investigated the regulation of hEAG channels by an insulin-like growth factor-1 (IGF-1), which is known to stimulate cell proliferation. Acute applications of IGF-1 increased K(+) current-density and hyperpolarized MCF-7 cells. The effects of IGF-1 were inhibited by hEAG inhibitors. Moreover, IGF-1 increased mRNA expression of hEAG in a time-dependent manner in parallel with an enhancement of cell proliferation. The MCF-7 cell proliferation induced by IGF-1 is inhibited pharmacologically by Astemizole or Quinidine or more specifically using siRNA against hEAG channel. Either mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3-kinase (PI3K) are known to mediate IGF-1 cell proliferative signals through the activation of extracellular signal-regulated kinase 1/2 (Erk 1/2) and Akt, respectively. In MCF-7 cells, IGF-1 rapidly stimulated Akt phosphorylation, whereas IGF-1 had little stimulating effect on Erk 1/2 which seems to be constitutively activated. The application of wortmannin was found to block the effects of IGF-1 on K(+) current. Moreover, the inhibition of Akt phosphorylation by the application of wortmannin or by a specific reduction of Akt kinase activity reduced the hEAG mRNA levels. Taken together, our results show, for the first time, that IGF-1 increases both the activity and the expression of hEAG channels through an Akt-dependent pathway. Since a hEAG channel is necessary for cell proliferation, its regulation by IGF-1 may thus play an important role in IGF-1 signaling to promote a mitogenic effect in breast cancer cells.

Glioma risk in relation to serum levels of insulin-like growth factors

Several studies have suggested that insulin-like growth factors (IGF) are related to cancer risk. We investigated the associations between serum levels of IGF-I and IGF-binding protein-3 and glioma risk. A nested case-control study was conducted within a cancer prevention study, including 29,133 men (ages 50-69 years). In total, 22 glioma cases and 400 randomly selected controls were included. Serum samples were collected a minimum of 5 years before cancer diagnosis. Serum concentrations were measured using ELISA and divided into tertiles based on measurements among controls. Odds ratios and 95% confidence intervals were calculated using the lowest tertile as the reference category. No statistical association was detected between glioma and IGF-binding protein-3. IGF-I was inversely associated with glioma when comparing the lowest tertile with the other tertiles combined (odds ratio, 0.3; 95% confidence interval, 0.1-0.7). The results encourage future research on IGFs in relation to brain tumors in larger studies.

Estrogen Receptor α and the Activating Protein-1 Complex Cooperate during Insulin-like Growth Factor-I-induced Transcriptional Activation of the pS2/TFF1 Gene

Insulin like growth factor I (IGF-I) displays estrogenic activity in breast cancer cells. This activity is strictly dependent on the presence of estrogen receptor alpha (ERalpha). However the precise molecular mechanisms involved in this process are still unclear. IGF-I treatment induces phosphorylation of the AF1 domain of ERalpha and activation of estrogen regulated genes. These genes are characterized by important differences in promoter architecture and response element composition. We show that promoter structure is crucial for IGF-I-induced transcription activation. We demonstrate that on a complex promoter such as the pS2/TFF1 promoter, which contains binding sites for ERalpha and for the activating protein-1 (AP1) complex, transcriptional activation by IGF-I requires both ERalpha and the AP1 complex. IGF-I is unable to stimulate transcription of an estrogen-regulated gene under the control of a minimal promoter containing only a binding site for ERalpha. We propose a molecular mechanism with stepwise assembly of the AP1 complex and ERalpha during transcription activation of pS2/TFF1 by IGF-I. IGF-I stimulation induces rapid phosphorylation and an increase in protein levels of the AP1 complex. Binding of the phosphorylated AP1 complex to the pS2/TFF1 promoter allows recruitment of the chromatin remodeling factor Brg1 followed by binding of ERalpha via its interaction with c-Jun.

Lymph node status as a guide to selection of available prognostic markers in breast cancer: the clinical practice of the future?

Prognosticators evaluating survival in breast cancer vary in significance in respect to lymph node status. Studies have shown e.g. that HER2/neu immunohistochemistry or HER2/neu gene amplification analysis do perform well as prognosticators in lymph node positive (LN +) patients but are less valuable in lymph node negative (LN -) patients. We collected data from different studies and tried to evaluate the relative significance of different prognosticators in LN+/LN- patient groups. In LN+ patients HER2/neu and E-cadherin immunohistochemistry were the statistically most significant prognosticators followed by proliferation associated features (mitotic counts by SMI (standardised mitotic index) or MAI (mitotic activity index), or S-phase fraction). Bcl-2 immunohistochemistry was also significant but p53 and cystatin A had no significance as prognosticators. In LN- patients proliferation associated prognosticators (SMI, MAI, Ki-67 index, PCNA immunohistochemistry, S-phase fraction) are especially valuable and also Cathepsin D, cystatin A, and p53 are significant, but HER2/neu or bcl-2, or E-cadherin less significant or without significance. We find that in studies evaluating single prognosticators one should distinguish between prognosticators suitable for LN+ and LN- patients. This will allow the choice of best prognosticators in evaluating the prospects of the patient. The distinction between LN+ and LN- patients in this respect may also be of special value in therapeutic decisions.

Transgenic overexpression of IGF-IR disrupts mammary ductal morphogenesis and induces tumor formation

Overexpression and hyperactivation of the type I insulin-like growth factor receptor (IGF-IR) has been observed in human breast tumor biopsies. In addition, in vitro studies indicate that overexpression of IGF-IR is sufficient to transform cells such as mouse embryo fibroblasts and this receptor promotes proliferation and survival in breast cancer cell lines. To fully understand the function of the IGF-IR in tumor initiation and progression, transgenic mice containing human IGF-IR under a doxycycline-inducible MMTV promoter system were generated. Administration of 2 mg/ml doxycycline in the animals' water supply beginning at 21 days of age resulted in elevated levels of IGF-IR in mammary epithelial cells as detected by Western blotting and immunohistochemistry. Whole mount analysis of 55-day-old mouse mammary glands revealed that IGF-IR overexpression significantly impaired ductal elongation. Moreover, histological analyses revealed multiple hyperplasic lesions in the mammary glands of these 55-day-old mice. The formation of palpable mammary tumors was evident at approximately 2 months of age and was associated with increased levels of IGF-IR signaling molecules including phosphorylated Akt, Erk1/Erk2 and STAT3. Therefore, these transgenic mice provide evidence that IGF-IR overexpression is sufficient to induce mammary epithelial hyperplasia and tumor formation in vivo and provide a model to further understand the function of IGF-IR in mammary epithelial transformation.

Modulation of p53 and c-myc in DMBA-Induced Mammary Tumors by Oral Glutamine

Previous studies established that oral glutamine (GLN) reduced tumor development in implantable and 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer models. This finding was associated with a decrease in tumor glutathione (GSH) levels, while maintaining normal gut, blood, and breast GSH. Alterations in GSH levels contribute to the control of apoptotic and cell cycle-regulating signaling. The aim of this study was to examine the role of dietary GLN on activation of p53 and c-myc, which play critical roles in cancer development and sensitivity to radiation and chemotherapy. Mammary gland carcinomas were induced in rats by DMBA. The rats were gavaged daily with GLN or water (controls), starting 1 wk prior DMBA-application and throughout the duration of the experiment (11 wk after DMBA). Tumor DNA was examined for mutations in p53 exons 5 and 6. Protein and mRNA levels of p53, p21(WAF1/CIP1), PTEN, IGF-IR, mdm2, and c-myc in tumors of GLN-supplemented rats were compared with those of the control rats (received water). The sequencing of p53 showed that it was wild type. Increased phosphorylation of p53, as well as higher mRNA and protein levels of p21(WAF1/CIP1), PTEN, and mdm2, and lower levels of IGF-IR were detected in tumors of GLN-supplemented rats vs. controls. Both phosphorylated c-myc and c-myc mRNA levels were reduced by GLN. The up-regulation of tumor p53 signaling and down-regulation of c-myc, in addition to previously established inhibition of Akt signaling in DMBA-breast cancer model, suggest that dietary GLN could be a useful approach for increasing the effectiveness of cancer treatment.

Transcriptional regulation of the insulin-like growth factor-I receptor gene in breast cancer

The insulin-like growth factor-I receptor (IGF-IR) has an important role in normal mammary gland growth and morphogenesis. In addition, the IGF-IR has been implicated in the initiation and progression of breast cancer. Previous studies have indicated that acquisition of the malignant phenotype in breast cancer is initially IGF-IR dependent. Most breast cancer-derived cell lines and primary tumors express high levels of IGF-IR mRNA and protein, whereas metastatic stages are usually associated with a decrease in IGF-IR levels. Transcription of the IGF-IR gene is controlled by complex interactions involving DNA-binding and non DNA-binding transcription factors. This review highlights selected examples of tumor suppressors, including BRCA1, p53, and WT1, whose mechanism of action involves regulation of IGF-IR gene expression.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

IGF-II induces CREB phosphorylation and cell survival in human lung cancer cells

We have previously shown that lung tumors arising in MMTV-IGF-II transgenic mice displayed elevated levels of phosphorylated cAMP response element binding protein (CREB). To investigate the role that insulin-like growth factor II (IGF-II) and CREB play in human lung tumorigenesis, A549 and NCI-H358 cells were examined. In these cell lines, IGF-II administration enhances human tumor cell survival and CREB phosphorylation. Further, the effects of IGF-II on cell survival and CREB phosphorylation appeared to be mediated, at least in part, by activation of the Erk pathways, as inhibition of these signaling pathways reduced tumor cell survival and CREB phosphorylation. Specifically, Erk5 appeared as the predominant mediator of CREB phosporylation. To further verify the importance of CREB in human lung tumorigenesis, A549 and NCI-H358 cells were stably transfected with a vector containing a dominant negative CREB construct (KCREB). KCREB transfection significantly inhibited the soft agar growth of both human tumor cell lines. In contrast, overexpression of wild-type CREB in the normal human bronchial epithelial cell line, HBE135, enhanced soft agar growth. Therefore, our results indicate that CREB and its associated proteins play a significant role in lung adenocarcinoma and IGF-II induces CREB phosphorylation, at least in part, via the Erk5 signaling pathway.

Hexachlorobenzene is a tumor co-carcinogen and induces alterations in insulin-growth factors signaling pathway in the rat mammary gland

Hexachlorobenzene (HCB) is a widespread environmental pollutant. Controversy still exists about the breast carcinogenic properties of organochlorines in humans. The ligands, receptors, and related signaling proteins of the insulin growth factor family are involved in the regulation of breast-cancer cell growth. The aims of this study were to determine: (1) whether HCB is co-carcinogenic in a medium term assay of N-nitroso N-methylurea (NMU)-induced mammary tumors in rats; (2) the effect of HCB on insulin receptor (IR), insulin-like growth factor-I receptor (IGF-IR) and insulin receptor substrate-1 (IRS-1) levels and on IRS-1 phosphorylation; (3) microsomal and cytosolic Protein Tyrosine Kinase (PTK) activities in mammary glands and NMU-induced tumors. Sprague Dawley rats were injected with 50 mg/kg body weight of NMU at 50, 80, and 110 days old. HCB (100 mg/kg body weight) was administered three times a week from 65 to 110 days of age. Rats were separated in four groups: control, NMU, HCB, and NMU-HCB. HCB alone did not induce tumor development. Parameters of tumor development were increased in NMU-HCB compared to NMU rats. A higher cellular undifferentiation was observed in NMU-HCB tumors. IR, IGF-IR, and IRS-1 levels were higher in HCB than in controls. Conversely IGF-IR levels decreased in NMU-HCB vs. NMU group. The IRS-1 phosphorylation increased in HCB rats; however, it decreased in NMU-HCB vs. NMU. HCB decreased microsomal PTK activity in tumors. This study showed for the first time that HCB is a co-carcinogenic agent in NMU-induced mammary tumors in rats. Our results suggest that the IR and/or IGF-IR signaling pathway may be involved in the mechanism of action of HCB.

Expression of some tumor associated factors in human carcinogenesis and development of gastric carcinoma

AIM: To study the effect of IGF-1/IGF-1R and gastrin/CCK-BR on carcinogenesis and development of human gastric carcinoma and to explore its mechanism and provide a credible theoretical foundation for early diagnosis and molecular therapy of gastric carcinoma.

METHODS: mRNA expression levels of IGF-1/IGF-1R and gastrin/CCK-BR were assessed by RT-PCR method in gastric cancer tissues, adjacent mucosa, and tumor-free tissues from 56 patients with gastric carcinoma and normal gastric mucosae from 56 healthy controls. Tissue specimens were obtained by biopsy and confirmed by histological evaluation.

RESULTS: The mRNA levels of IGF-1/IGF-1R were increased in gastric cancer tissues compared with normal tissues from healthy controls and successively increased in tumor-free tissues, adjacent mucosa, and gastric cancer tissues. The mRNA levels of gastrin/CCK-BR were increased in gastric cancer tissues compared with normal tissues from healthy controls. There was a significant difference between gastric cancer tissues and adjacent mucosa and tumor-free tissues, but the mRNA levels of gastrin were not significantly increased in adjacent mucosa and gastric cancer tissues compared with tumor-free tissues. The mRNA levels of CCK-BR were increased in gastric cancer tissues and adjacent mucosa compared with tumor-free tissues, but not significantly increased in adjacent mucosa and gastric cancer tissues compared with gastric cancer tissues.

CONCLUSION: Overexpression of IGF-1/IGF-1R and gastrin/CCK-BR promotes the disorderly proliferation of gastric mucosa epithelia and it is of great significance in the carcinogenesis and development of gastric carcinoma.

Gene expression profiles in cells transformed by overexpression of the IGF-I receptor

To identify genes associated with insulin-like growth factor-I receptor (IGF-IR)-mediated cellular transformation, we isolated genes that are differentially expressed in R- cells (derived from the IGF-IR knockout mouse) and R+ cells (R- cells that overexpress the IGF-IR). From these, 45 genes of known function were expressed at higher levels in R+ cells and 22 were expressed at higher levels in R- cells. Differential expression was confirmed by Northern blot analysis of R+ and R- cells. Genes expressed more abundantly in R+ cells are associated with (1) tumour growth and metastasis including, betaigH3, mts1, igfbp5 protease, and mystique; (2) cell division, including cyclin A1 and cdk1; (3) signal transduction, including pkcdeltabp and lmw-ptp; and (4) metabolism including ATPase H+ transporter and ferritin. In MCF-7 cells IGF-I induced expression of two genes, lasp-1 and mystique, which could contribute to metastasis. Lasp-1 expression required activity of the PI3-kinase signalling pathway. Mystique was highly expressed in metastatic but not in androgen-dependent prostate cancer cell lines and Mystique overexpression in MCF-7 cells promoted cell migration and invasion. We conclude that genes identified in this screen may mediate IGF-IR function in cancer progression.

Factors associated with circulating levels of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in 740 women at risk for breast cancer

Prospective studies have shown an association between elevated plasma levels of insulin-like growth factor-I (IGF-I) and/or decreased levels of its major circulating carrier protein insulin-like growth factor binding protein-3 (IGFBP-3) and increased risk of major cancers. Identifying the factors which affect these biomarkers is of particular interest as subjects at increased risk could benefit from lifestyle changes, and/or chemoprevention intervention. We evaluated the association between constitutional, hormonal and clinical factors and IGF-I and IGFBP-3 in 740 women, including 376 unaffected women and 364 women with intraepithelial neoplasia (IEN) or early invasive breast cancer enrolled in breast cancer chemoprevention trials, conducted at a single institution. Age, body mass index (BMI), height, waist to hip girth ratio (WHR), parity, menopausal status, age at menarche, number of affected first degree relatives, number of biopsies and breast cancer status were considered in the analysis. Women with early breast cancer had 21% higher IGF-I levels (p = 0.033) and 19% higher IGF-I/IGFBP-3 molar ratio (p = 0.047) than unaffected women. In unaffected women, age was negatively associated with IGF-I (p = 0.002) and IGF-I/IGFBP-3 (p = 0.001), while age at menarche was negatively associated with IGFBP-3 levels (p = 0.043). In women with IEN or early breast cancer, IGF-I levels were negatively associated with age (p < 0.001), and positively associated with prior biopsies for benign disease (p = 0.013), while age, parity and menopausal status were significant predictors of IGF-I/IGFBP-3 molar ratio. We conclude that circulating IGF-I levels are higher in women with prior breast cancer compared to unaffected women, and that IGF-I and/or IGFBP-3 levels are influenced by age and by reproductive and hormonal factors. These findings support their putative role as breast cancer risk biomarker.

Estrogen and insulin/IGF-1 cooperatively stimulate cell cycle progression in MCF-7 breast cancer cells through differential regulation of c-Myc and cyclin D1

Estrogen and insulin/insulin-like growth factor-I (IGF-I) are major mitogens for breast epithelial cells and when co-administered, synergistically induce G(1)-S phase cell cycle progression. We investigated this cooperativity by evaluating if the key cell cycle regulators, c-Myc and cyclin D1, represent points of convergence in the action of these mitogens in MCF-7 breast cancer cells. These studies demonstrated that estrogen significantly increased both c-Myc and cyclin D1 protein, while insulin predominantly increased cyclin D1 levels. This cumulative increase in c-Myc and cyclin D1 contributes to the cooperativity of these mitogens, since ectopic expression of c-Myc or cyclin D1 cooperates with either the estrogen or insulin signaling pathways to increase cell cycle progression. Inhibition of the MAPK or PI3-kinase pathways significantly reduced c-Myc and cyclin D1 protein levels and cell cycle progression. Ectopic expression of cyclin D1 partially overcame this inhibition, while ectopic expression of c-Myc partially overcame MAPK but not PI3-kinase inhibition. Therefore, estrogen and insulin/IGF-1 differentially regulate c-Myc and cyclin D1 to cooperatively stimulate breast cancer cell proliferation.

A recombinant humanized anti-insulin-like growth factor receptor type I antibody (h7C10) enhances the antitumor activity of vinorelbine and anti-epidermal growth factor receptor therapy against human cancer xenografts

Interaction of insulin-like growth factor receptor I (IGF-IR) with its ligands has been reported to induce cell proliferation, transformation and blockade of cell apoptotic functions. IGF-IR is overexpressed on numerous tumor cell types and its blockade could be of importance for anti-cancer therapy. We have generated a humanized anti-IGF-IR antibody h7C10 that blocks in vitro IGF-I and IGF-II-induced cell proliferation of MCF-7 breast cancer cells. Analysis of the IGF-I transduction cascade demonstrated that the humanized anti-IGF-IR antibody and its murine parental form block IGF-I-induced tyrosine phosphorylation, both its beta-chain and IRS-1 tyrosine phosphorylation. This presumably leads to cell cycle arrest and, consequently, growth inhibition. Treatment of nude mice bearing either human breast cancer cells (MCF-7) or non small lung cancer cells (A549) with h7C10, or its murine parental form 7C10, inhibited significantly tumor growth. An almost complete inhibition of A549 tumor growth was observed when mice were treated with the anti-IGF-IR antibody combined with either a chemotherapeutic agent, Vinorelbine or an anti-epidermal growth factor receptor (EGFR) antibody, 225. Combined therapy prolonged significantly the life span of mice in an orthotopic in vivo model of A549; the combination of the anti-IGF-IR antibody with an anti-EGFR antibody was superior to the Vinorelbine combination. The present results indicate that the humanized anti-IGF-IR antibody h7C10 has a great potential for cancer therapy when combined with either a chemotherapeutic agent or an antibody that targets other growth factor receptors, such as the epidermal growth factor receptor.

IGF-I receptor, cell-cell adhesion, tumour development and progression

The insulin-like growth factor I receptor (IGF-IR) has been implicated in the development and progression of many common cancers and other neoplastic diseases. The tumorigenic potential of IGF-IR relies on its antiapoptotic and transforming activities. The molecular mechanisms by which IGF-IR controls the proliferation and survival of tumour cells have been extensively studied and many pathways have been delineated. However, the role of IGF-IR in the regulation of non-mitogenic cell functions is less well understood. Here we focus on IGF-IR-dependent cell-cell adhesion. Limited studies suggested that IGF-IR can regulate cell aggregation and intercellular adhesion mediated by cadherins and cadherin-associated proteins. We review the mechanisms of this process and discuss the impact of IGF-IR-dependent cell-cell adhesion on the phenotype of tumour cells.

Gene expression profiling of epithelial ovarian tumours correlated with malignant potential

Background

Epithelial ovarian tumours exhibit a range of malignant potential, presenting distinct clinical phenotypes. Improved knowledge of gene expression changes and functional pathways associated with these clinical phenotypes may lead to new treatment targets, markers for early detection and a better understanding of disease progression.

Results

Gene expression profiling (Affymetrix, U95Av2) was carried out on 18 ovarian tumours including benign adenomas, borderline adenocarcinomas of low malignant potential and malignant adenocarcinomas. Clustering the expression profiles of samples from patients not treated with chemotherapy prior to surgery effectively classified 92% of samples into their proper histopathological group. Some cancer samples from patients treated with chemotherapy prior to surgery clustered with the benign adenomas. Chemotherapy patients whose tumours exhibited benign-like expression patterns remained disease free for the duration of this study as indicated by continued normal serum CA-125 levels. Statistical analysis identified 163 differentially expressed genes: 61 genes under-expressed in cancer and 102 genes over-expressed in cancer. Profiling the functional categories of co-ordinately expressed genes within this list revealed significant correlation between increased malignant potential and loss of both IGF binding proteins and cell adhesion molecules. Interestingly, in several instances co-ordinately expressed genes sharing biological function also shared chromosomal location.

Conclusion

Our findings indicate that gene expression profiling can reliably distinguish between benign and malignant ovarian tumours. Expression profiles of samples from patients pre-treated with chemotherapy may be useful in predicting disease free survival and the likelihood of recurrence. Loss of expression of IGF binding proteins as well as specific cell adhesion molecules may be a significant mechanism of disease progression in ovarian cancer. Expression levels in borderline tumours were intermediate between benign adenomas and malignant adenocarcinomas for a significant portion of the differentially expressed genes, suggesting that borderline tumours are a transitional state between benign and malignant tumours. Finally, genes displaying coordinated changes in gene expression were often genetically linked, suggesting that changes in expression for these genes are the consequence of regional duplications, deletions or epigenetic events.

Somatostatin inhibits IGF-1 mediated induction of VEGF in human retinal pigment epithelial cells

Neovascularization stimulated by IGF-1 mediated induction of vascular endothelial growth factor (VEGF) is one of the leading causes of blindness in humans. It plays a central role in the pathogenesis of proliferative diabetic retinopathy (DR), neovascular glaucoma, exudative age-related macular degeneration (AMD) and retinopathy of prematurity. Neovascularization is a multi-step process that involves complex interactions of a variety of mitogenic factors such as VEGF and IGF-I which are produced locally in the human eye by a variety of cells including retinal pigment epithelial (RPE) cells, retinal capillary pericytes, endothelial cells, Mueller cells and ganglion cells. We hypothesized that somatostatin would inhibit the IGF-1 signal transduction pathway in RPE cells, resulting in decreased VEGF production. We have observed expression of somatostatin receptor protein in retinal pigment epithelial (RPE) cells of the human eye using immunohistochemistry and have confirmed expression of somatostatin receptors in cultured human RPE cells using reverse transcriptase-PCR. IGF-1 induced a dose dependent increase in IGF-1R phosphorylation and in VEGF mRNA levels in cultured human RPE cells. Somatostatin and octreotide, a somatostatin analogue, inhibited IGF-1 receptor (IGF-1R) phosphorylation and decreased VEGF production. Both IGF-1R phosphorylation and accumulation of VEGF mRNA were inhibited by physiological levels of somatostatin and octreotide (1 nM). These results demonstrate somatostatin and octreotide mediated attenuation of both IGF-1R signal transduction and VEGF mRNA accumulation via somatostatin receptor type 2 (sst2). Furthermore, these data suggest a rationale for the use of octreotide as a prophylactic and therapeutic option in disease states that cause ocular neovascularization.

Receptor Imaging in Oncology by Means of Nuclear Medicine: Current Status

To date, our understanding of the role of receptors and their cognate ligands in cancer is being successfully translated into the design and development of an arsenal of new, less toxic, and more specific anticancer drugs. Because most of these novel drugs are cytostatic, objective response as measured by morphologic imaging modalities (eg, computed tomography or magnetic resonance imaging) cannot be used as a surrogate marker for drug development or for clinical decision making. Positron emission tomography (PET) can be used to image and quantify the in vivo distribution of positron-emitting radioisotopes such as oxygen-15, carbon-11, and fluorine-18 that can be substituted or added into biologically relevant and specific receptor radioligands. Similarly, single-photon emission computed tomography (SPECT) can be used to image and quantify the in vivo distribution of receptor targeting compounds labeled with indium-111, technetium-99m, and iodine-123. By virtue of their whole-body imaging capacity and the absence of errors of sampling and tissue manipulation as well as preparation, both techniques have the potential to address locoregional receptor status noninvasively and repetitively. This article reviews available data on the in vivo evaluation of receptor systems by means of PET or SPECT for identifying and monitoring patients with sufficient receptor overexpression for tailored therapeutic interventions, and also for depicting tumor tissue and determining the currently largely unknown heterogeneity in receptor expression among different tumor lesions within and between patients.

Inhibition of in vivo breast cancer growth by antisense oligodeoxynucleotides to type I insulin-like growth factor receptor mRNA involves inactivation of ErbBs, PI-3K/Akt and p42/p44 MAPK signaling pathways but not modulation of progesterone receptor activity

The present study addresses the effect of targeting type I insulin-like growth factor receptor (IGF-IR) with antisense strategies in in vivo growth of breast cancer cells. Our research was carried out on C4HD tumors from an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice. We employed two different experimental strategies. With the first one we demonstrated that direct intratumor injection of phosphorothioate antisense oligodeoxynucleotides (AS[S]ODNs) to IGF-IR mRNA resulted in a significant inhibition of C4HD tumor growth. In the second experimental strategy, we assessed the effect of intravenous (i.v.) injection of AS [S]ODN on C4HD tumor growth. This systemic treatment also resulted in significant reduction in tumor growth. The antitumor effect of IGF-IR AS[S]ODNs in both experimental protocols was due to a specific antisense mechanism, since growth inhibition was dose-dependent and no abrogation of tumor proliferation was observed in mice treated with phosphorothioate sense ODNs (S[S]ODNs). In addition, IGF-IR expression was inhibited in tumors from mice receiving AS[S]ODNs, as compared to tumors from control groups. We then investigated signal transduction pathways modulated in vivo by AS[S]ODNs treatment. Tumors from AS[S]ODN-treated mice of both intratumoral and intravenous protocols showed a significant decrease in the degree of insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation. Activation of two of the main IGF-IR signaling pathways, phosphatidylinositol 3-kinase (PI-3K)/Akt and p42/p44 mitogen-activated protein kinases (MAPK) was abolished in tumors growing in AS[S]ODN-treated animals. Moreover, ErbB-2 tyrosine phosphorylation was blocked by in vivo administration of AS[S]ODNs. On the other hand, we found no regulation of either progesterone receptor expression or activity by in vivo AS[S]ODNs administration. Our results for the first time demonstrated that breast cancer growth can be inhibited by direct in vivo administration of IGF-IR AS[S]ODNs.

The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture

OBJECTIVES

To evaluate the effects of MK-0677, an orally active growth hormone (GH) secretagogue, on functional recovery from hip fracture in previously mobile older individuals.

DESIGN

Placebo-controlled, randomized, double-blind trial.

SETTING

Thirteen medical centers in England, Sweden, Denmark, Belgium, Switzerland, Canada, and the United States. Patients were recruited between 3 and 14 days postoperatively, or no more than 18 days postfracture, at acute care hospitals and rehabilitation centers.

PARTICIPANTS

One hundred sixty-one hip-fracture patients were enrolled. Entry criteria included consenting hip-fracture patients who were aged 65 and older and who were ambulatory before their fracture, medically stable postoperatively, and mentally competent. Patients were excluded if they had multiple fractures or severe trauma, diabetes mellitus, cancer, uncontrolled hypertension, congestive heart failure, or total hip replacement in the involved extremity.

INTERVENTION

Random assignment to 6 months of daily treatment with MK-0677 or placebo. Patients were followed for an additional 6 months after completion of therapy.

MEASUREMENTS

Change from Week 6 to Week 26 in a panel of functional performance measures. Additional outcome measures included change in the Sickness Impact Profile for Nursing Homes (SIP-NH), the ability to live independently, and insulin-like growth factor I (IGF-I) levels.

RESULTS

MK-0677 treatment increased serum IGF-I levels by 84% (95% confidence interval (CI)=63-107), compared with an increase of 17% (95% CI=8-28) on placebo. There were no significant differences between MK-0677 and placebo in improvement in functional performance measures or in the overall SIP-NH score. Although MK-0677 patients showed greater improvement relative to placebo in three of four lower extremity functional performance measures, in the physical domain of the SIP, and in the ability to live independently, these differences were not statistically significant.

CONCLUSION

Although MK-0677 treatment increased serum IGF-I, it is uncertain whether clinically significant effects on physical function were achieved. Measuring function in clinical trials in hip-fracture patients is difficult because of the lack of validated outcome measures, high variability, and the lack of a baseline assessment. Present functional performance measures may not be sufficiently responsive for use as the primary endpoint of small intervention studies; alternatively, stimulation of GH may not result in significant functional improvement.

Insulin-like growth factor-I regulates glucose-induced mitochondrial depolarization and apoptosis in human neuroblastoma

Neuroblastoma, a pediatric peripheral nervous system tumor, frequently contains alterations in apoptotic pathways, producing chemoresistant disease. Insulin-like growth factor (IGF) system components are highly expressed in neuroblastoma, further protecting these cells from apoptosis. This study investigates IGF-I regulation of apoptosis at the mitochondrial level. Elevated extracellular glucose causes rapid mitochondrial enlargement coupled with an increase in the mitochondrial membrane potential (Delta Psi(M)) followed by mitochondrial membrane depolarization (MMD), uncoupling protein 3 (UCP3) downregulation, caspase-3 activation and decreased Bcl-2. MMD inhibition by Bongkrekic acid prevents high-glucose-induced loss of UCP3 and apoptosis. Glucose exposure induces caspase-9 cleavage within 30 min, and caspase-9 inhibition prevents glucose-mediated apoptosis. IGF-I prevents caspase activation and mitochondrial events leading to apoptosis. These results suggest that elevated glucose produces early initiator caspase activation, followed by Delta Psi(M) changes, in neuroblastoma cells; in turn, IGF-I prevents apoptosis by preventing downstream caspase activation, maintaining Delta Psi(M) and regulating Bcl proteins.

Anti-insulin-like growth factor strategies in breast cancer

The insulin-like growth factors (IGF-I and -II) are potent mitogens and survival factors for both normal and malignant breast cells. These effects are mediated primarily through the IGF-I receptor (IGF-IR), which is significantly overexpressed and highly activated in breast tumors. The IGF-binding proteins are competitive inhibitors of IGF/IGF-IR interaction, limiting cellular proliferation and survival. Higher serum IGF-I levels or an increased ratio of IGF-I to IGF binding protein-3 is associated with an increased risk of developing breast cancer. Hence, interest in the IGF system as a potential target for the development of novel antineoplastic therapies has ensued. Several strategies to interrupt IGF-IR signaling are currently being evaluated for the treatment of breast cancer, including suppression of IGF production, reduction of functional IGF-IR levels, neutralization of IGF action, and inhibition of IGF-IR activation.

Long-term exposure to beta-hexachlorocyclohexane (beta-HCH) promotes transformation and invasiveness of MCF-7 human breast cancer cells

Due to its lipophilicity and persistence, an organochlorine compound, beta-hexachlorocyclohexane (beta-HCH), is known to frequently accumulate in human adipose and breast tissues. An epidemiological study has indicated that exposure to beta-HCH could be one of the significant environmental risk factors for the development of human breast cancers. Additionally, beta-HCH has recently been identified as an environmental estrogen capable of activating estrogen receptor (ER) through a ligand-independent pathway. In the present investigation, we examined the impact of long-term in vitro exposure to beta-HCH on cell transformation and the metastatic potentials of MCF-7 cells. We found that continuous exposure of MCF-7 cells to beta-HCH at 100 nM and 1 microM or to 17beta-estradiol (E(2)) at 1 nM for up to 13 months (33 passages) not only enhanced their transformation tendencies but also promoted their invasiveness. Western blot analysis revealed that beta-HCH induced transformation-related biochemical changes in MCF-7 cells, such as a decline in the levels of ERalpha and p44/42 MAP kinase and a significant increase in expression of c-ErbB2 and MMP-9 levels. In contrast, long-term E(2) treatment resulted in the downregulation of ERalpha and p44/42 MAP kinase and upregulation of MMP-9 only, but no changes in c-ErbB2. Together, these results indicate that these biochemical changes induced by beta-HCH are consistent with the events taking place in these cells to promote the phenotypical expression of transformed cells. Our results provide the in vitro mechanistic basis supporting the hypothesis that beta-HCH is one of the epigenetic risk factors assisting the progression of breast cancer cells to an advanced state of malignancy.

Growth factors and chemotherapeutic modulation of breast cancer cells

A variety of molecules including growth factors are involved in the metastasis of breast cancer cells to bone. We have investigated the effects of osteoblast derived growth factors, such as insulin-like growth factor-1 (IGF-1) and transforming growth factor beta-1 (TGF-beta1), on doxorubicin (adriamycin)-induced apoptosis and growth arrest of estrogen receptor positive (ER+) (MCF-7) and negative (ER-) (MDA-MB-435) breast cancer cell lines. Human breast normal epithelial (MCF-10A), breast cancer (MCF-7) and metastatic breast cancer (MDA-MB-435) cell lines were exposed to different doses of doxorubicin (0.1, 1 or 10 microM) at various exposure times (12, 24 or 48 h). The doxorubicin cytotoxicity was found to be higher in cancer cell lines (MDA-MB-435 and MCF-7) compared with normal breast epithelial cells (MCF-10A cells). Doxorubicin appeared to exert a blockade of MCF-7 and MDA-MB-435 cells at the G2/M phase, and induced apoptosis in MDA-MB-435 (29 +/- 4.2% vs 3.4 +/- 1.9% control) as assessed by flow cytometry, DNA fragmentation and terminal deoxynucleotidyl-transferase mediated deoxyuridine 5-triphosphate and biotin nick-end labelling (TUNEL) assays. Estradiol (E2) stimulated the growth of MCF-7 cells and increased the distribution of the cells at the G2/M and S phases. Exogenous IGF-1 partially neutralized the doxorubicin cytotoxicity in both cancer cell lines (MCF-7 and MDA-MB-435). Similarly, TGF-beta1 partially neutralized the doxorubicin cytotoxicity in MDA-MB-435 cells by reducing the number of cells at the <G1 phase (from 29% to 6.4%) and enhanced the doxorubicin blockade of MCF-7 (E2-) at the G0/G1 phase. Results showed that the osteoblast-derived growth factors could affect the chemotherapy response of breast cancer cells, thereby allowing for the possibility of chemotherapeutic modulation.

Overexpression of insulin-like growth factor II (IGFII) in ZR-75-1 human breast cancer cells: higher threshold levels of receptor (IGFIR) are required for a proliferative response than for effects on specific gene expression

Previous transfection experiments using a zinc-inducible expression vector have shown that overexpression of insulin-like growth factor II (IGFII) in MCF7 human breast cancer cells can reduce dependence on oestrogen for cell growth in vitro (DALY RJ, HARRIS WH, WANG DY, DARBRE PD. (1991) Cell Growth Differentiation 2, 457-464.). Parallel transfections now performed into another oestrogen-dependent human breast cancer cell line (ZR-75-1) yielded three clones of transfected ZR-75-1 cells that produced levels of zinc-inducible IGFII mRNA and secreted mature IGFII protein similar to those found in the transfected MCF7 cells. However, unlike in MCF7 cells, no resulting effects were found on cell growth in the ZR-75-1 clones, even though the ZR-75-1 clones possessed receptors capable of binding 125I-IGFI and showed a growth response to exogenously added IGFII. Medium conditioned by the ZR-75-1 clones could stimulate growth of untransfected MCF7 cells, indicating that the secreted IGFII protein was bioactive. Furthermore, zinc-induced IGFII was capable of increasing both pS2 mRNA levels and CAT activity from a transiently transfected AP1-CAT gene in the ZR-75-1 clones. Constitutive co-overexpression of the protein processing enzyme PC2 resulted in reduced levels of large forms of zinc-inducible IGFII, but zinc treatment still produced no effect on cell growth rate. Finally, however, constitutive co-overexpression of the type I IGF receptor (IGFIR) did result in zinc-inducible increased basal cell growth and reduced dependence on oestrogen for cell growth. These results demonstrate that while overexpression of IGFII per se was sufficient to deregulate MCF7 cell growth, the ZR-75-1 cells are limited in their proliferative response by their intrinsic receptor levels. However, although the proliferative response was limited, molecular responses (expression of pS2 and AP1-CAT) were not limited, indicating that different cellular responses can have different threshold receptor level requirements.

The GH-IGF-I axis and breast cancer

The growth hormone-insulin-like growth factor-I (GH-IGF-I) axis plays a fundamental role in the development of the breast. The maintenance of breast tissue architecture is aided by its effect on proliferation, differentiation and apoptosis. There has been increasing recognition of its role as a major determinant of breast cancer and, more recently, its involvement in the development of resistance to both tamoxifen and an important novel therapy for advanced disease, trastuzumab (Herceptin). Here, we discuss the influence of the GH-IGF-I axis in normal mammary development and homeostasis, its putative role in breast tumorigenesis and its interactions with estrogen signalling.

IGF-2 is a mediator of prolactin-induced morphogenesis in the breast

The mechanisms by which prolactin controls proliferation of mammary epithelial cells (MECs) and morphogenesis of the breast epithelium are poorly understood. We show that cyclin D1(-/-) MECs fail to proliferate in response to prolactin and identify IGF-2 as a downstream target of prolactin signaling that lies upstream of cyclin D1 transcription. Ectopic IGF-2 expression restores alveologenesis in prolactin receptor(-/-) epithelium. Alveologenesis is retarded in IGF-2-deficient MECs. IGF-2 and prolactin receptor mRNAs colocalize in the mammary epithelium. Prolactin induces IGF-2 mRNA and IGF-2 induces cyclin D1 protein in primary MECs. Thus, IGF-2 is a mediator of prolactin-induced alveologenesis; prolactin, IGF-2, and cyclin D1, all of which are overexpressed in breast cancers, are components of a developmental pathway in the mammary gland.

N-Myc and Bcl-2 coexpression induces MMP-2 secretion and activation in human neuroblastoma cells

Neuroblastoma is a peripheral nervous system tumor that accounts for 8-10% of all solid childhood tumors. N-Myc is the most reliable prognostic indicator for neuroblastoma. Bcl-2 is detected in 40-60% of primary neuroblastoma tumors and demonstrates anti-apoptotic action by conferring resistance to chemotherapy and radiation treatment. In neuroblastoma cell lines, the coexpression of N-Myc and Bcl-2 leads to increased tumorigenic properties. Matrix metalloproteinases (MMPs) are endopeptidases that degrade a wide range of basement membrane components, a process important for tumor invasion. This study investigates the effect of N-Myc and Bcl-2 on MMP expression and activation. MMP-2 expression and secretion are increased in SHEP neuroblastoma cells expressing Bcl-2 alone (SHEP/Bcl-2 cells) or both N-Myc and Bcl-2 (SHEP/N-Myc/Bcl-2 cells). MMP-2 activity is increased in the SHEP/N-Myc/Bcl-2 cells yet remains unchanged in SHEP/Bcl-2 cells. TIMP-2 expression is high in SHEP/Bcl-2 cells, which likely inhibits MMP-2 activity, and absent in SHEP/N-Myc/Bcl-2 cells, allowing MMP-2 activity. Invasion is increased in SHEP/N-Myc/Bcl-2 cells and prevented by the use of a pharmacologic MMP-2 inhibitor. These data imply that N-Myc and Bcl-2 cooperate to increase the expression, secretion, and activation of MMP-2, which likely leads to a more tumorigenic phenotype due to increased MMP-2 mediated invasion.

Treatment of murine breast cancer cells with antisense RNA to the type I insulin-like growth factor receptor decreases the level of plasminogen activator transcripts, inhibits cell growth in vitro, and reduces tumorigenesis in vivo

AIMS

To establish that cells from the murine mammary carcinoma cell line, EMT6, express type I insulin-like growth factor receptor (IGF-IR), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). To investigate the role of IGF-IR in growth, transformation, and tumorigenesis in addition to its relation to tPA and uPA in EMT6 cells. To assess the suitability of the EMT6/syngeneic mouse model for studying the role of IGF-IR in tumorigenesis.

METHODS

The presence of transcripts for IGF-IR, tPA, and uPA was determined by northern blot analysis using poly (A(+)) RNA derived from EMT6 cells transfected with an antisense IGF-IR construct or a construct lacking the antisense IGF-IR insert. Flow cytometry was used to measure IGF-IR protein. Assays were performed to determine cell proliferation, transformation, and the tumorigenicity of antisense IGF-IR transfected EMT6 cells and control transfected EMT6 cells.

RESULTS

There was strong expression of IGF-IR, tPA, and uPA in EMT6 cells. EMT6 cells from clones carrying antisense IGF-IR displayed a significant decrease in cell proliferation and lost the ability to form colonies in soft agar. A decrease in tumour size occurred when cells carrying the antisense IGF-IR were injected into syngeneic mice. Reduced expression of tPA and uPA was seen in EMT6 cells carrying the antisense IGF-IR construct.

CONCLUSIONS

The IGF-IR plays a role in the progression, transformation, and tumorigenesis of EMT6 murine mammary carcinoma cells. The suppression of IGF-IR mRNA in EMT6 cells decreases tPA and uPA expression. EMT6 cells and the syngeneic mouse provide a suitable model for studying the role of IGF-IR in breast tumour progression.

Synergistic proliferative action of insulin-like growth factor I and 17 beta-estradiol in MCF-7S breast tumor cells

We have analyzed the mechanism by which the combination of insulin-like growth factor I (IGF-I) and 17 beta-estradiol (E2) induces cell cycle progression in MCF-7S cells. This cell line differs from many other breast cancer-derived cell lines in that E2 (1 nM) does not induce cell cycle progression, whereas the combination of submitogenic concentrations of IGF-I (2 ng/ml) and E2 does. We find that addition of IGF-I to MCF-7S cells leads to a dose-dependent activation of the IGF type I receptor and of the MAP kinase and PI3-kinase signaling pathways. No synergy of IGF-I and E2 was detected in the activation of these signaling cascades. In terms of cell cycle-related molecules, we find that IGF-I dose-dependently raises cyclin D1 levels in serum-starved cells. Subsequent activation of cyclin E/CDK2, hyperphosphorylation of pRb, and DNA synthesis are only induced by mitogenic concentrations of IGF-I (> or =20 ng/ml). Treatment of the cells with E2 also results in the induction of cyclin D1, but in the absence of IGF-I the cells remain arrested in G1 phase. We conclude that in MCF-7S cells, the synergistic action of E2 and IGF-I derives from the ability of both hormones to induce cyclin D1 expression. The action of IGF-I is required in these cells to induce activity of the cyclin D1/CDK4 complex, which triggers progression through the cell cycle.