Insulin-like growth factor 1 receptors in human breast tumour: localisation and quantification by histo-autoradiographic analysis

Epithelial-to-mesenchymal transition in breast cancer: a role for insulin-like growth factor I and insulin-like growth factor-binding protein 3?

Evidence indicates that for most human cancers the problem is not that gene mutations occur but is more dependent upon how the body deals with damaged cells. It has been estimated that only about 1% of human cancers can be accounted for by unmistakable hereditary cancer syndromes, only up to 5% can be accounted for due to high-penetrance, single-gene mutations, and in total only 5%-15% of all cancers may have a major genetic component. The predominant contribution to the causation of most sporadic cancers is considered to be environmental factors contributing between 58% and 82% toward different cancers. A nutritionally poor lifestyle is associated with increased risk of many cancers, including those of the breast. As nutrition, energy balance, macronutrient composition of the diet, and physical activity levels are major determinants of insulin-like growth factor (IGF-I) bioactivity, it has been proposed that, at least in part, these increases in cancer risk and progression may be mediated by alterations in the IGF axis, related to nutritional lifestyle. Localized breast cancer is a manageable disease, and death from breast cancer predominantly occurs due to the development of metastatic disease as treatment becomes more complicated with poorer outcomes. In recent years, epithelial-to-mesenchymal transition has emerged as an important contributor to breast cancer progression and malignant transformation resulting in tumor cells with increased potential for migration and invasion. Furthermore, accumulating evidence suggests a strong link between components of the IGF pathway, epithelial-to-mesenchymal transition, and breast cancer mortality. Here, we highlight some recent studies highlighting the relationship between IGFs, IGF-binding protein 3, and epithelial-to-mesenchymal transition.

Insulin-like growth factor-1 receptor (IGF-1R) expression does not predict for resistance to trastuzumab-based treatment in patients with Her-2/neu overexpressing metastatic breast cancer

PURPOSE

Her-2/neu and the insulin-like growth factor-1 receptor (IGF-1R) share common postreceptor-signaling pathways, and pre-clinical models have implicated IGF-1R-signaling in resistance to treatment with the anti-Her-2/neu antibody trastuzumab. The present analysis was performed to evaluate the clinical relevance of IGF-1R expression within the context of trastuzumab-based therapy.

PATIENTS AND METHODS

We performed immunohistochemical (IHC) analysis for IGF-1R expression in tumor specimens from 72 patients receiving trastuzumab-based treatment for Her-2/neu-overexpressing metastatic breast cancer at a single institution. IGF-1R status was evaluated using different cut-offs for positivity regarding staining intensity and staining pattern. IGF-1R positivity was then correlated with clinical patient and biological tumor characteristics and the clinical course of disease of patients under trastuzumab-based therapy.

RESULTS

No pattern or intensity of staining for IGF-1R correlated with any of the clinical or biological characteristics. Likewise, response, clinical benefit, progression-free and overall survival were independent of IGF-1R expression in both, univariate and multivariate analyses (all P>0.05).

CONCLUSIONS

We conclude that IGF-1R expression is not a major predictor of the clinical efficacy of trastuzumab-based treatment in patients with Her-2/neu- overexpressing metastatic breast cancer.

The insulin-like growth factor system in advanced breast cancer

Despite improvements in therapy, the prognosis for advanced breast cancer is poor and a search for new treatment targets and key regulators of tumour growth is warranted. Extensive data are available on the importance of the insulin-like growth factor (IGF) system in growth regulation of breast cancer cell lines in vitro, indicating that the IGF-I receptor (IGF-IR), IGF-I (and IGF-II) function as survival factors, while IGF binding protein (IGFBP)-3 may act as a growth inhibitor. There is a tight link between the growth regulatory pathways of IGFs and oestrogens in oestrogen-receptor(OR)-positive breast cancer cells. In vivo studies indicate a role of IGF-I and IGF-IR in breast cancer development. However, the importance of the IGF system in metastatic and highly aggressive breast tumours in vivo is not clear, and therapeutic strategies designed to interrupt IGF signalling have not yet proved to be an effective treatment modality in patients with metastatic breast cancer.

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.

BRCA1 suppresses insulin-like growth factor-I receptor promoter activity: potential interaction between BRCA1 and Sp1

The insulin-like growth factor I receptor (IGF-I-R) has an important role in breast cancer etiology. The receptor is overexpressed by most breast cancers, where it functions as a potent antiapoptotic agent. BRCA1 is a tumor suppressor gene that is mutated in a large fraction of familial breast and ovarian cancers. Cotransfection of Saos-2, MCF7, and CHO cells with IGF-I-R promoter constructs driving luciferase reporter genes, and with a BRCA1 expression vector, suppressed promoter activity in a dose-dependent manner. Functional interactions between BRCA1 and Sp1 in the regulation of the IGF-I-R gene were studied in Schneider cells, a Drosophila cell line which lacks endogenous Sp1. In these cells BRCA1 suppressed 45% of the Sp1-induced trans-activation of the IGF-I-R promoter. These results suggest that BRCA1 is capable of suppressing the IGF-I-R promoter in a number of cell lines, thus resulting in low levels of receptor mRNA and protein. Mutant versions of BRCA1 lacking trans-activational activity can potentially derepress the IGF-I-R promoter. Activation of the overexpressed receptor by locally produced or circulating IGFs may be a crucial step in breast and ovarian cancer progression.

The localization of the insulin-like growth factor receptor 1 (IGFR-1) in benign and malignant breast tissue

Insulin-like growth factors (IGFs) play an important role in normal cellular growth and development and have been implicated in the regulation of tumour growth. Two receptors are recognized, IGFR-1 and IGFR-2, of which one, IGFR-1, is a transmembrane heterodimer structurally similar to the insulin receptor. Studies using ligand-binding assays have suggested that the proportion of human breast carcinomas expressing IGFR-1 varies between 39 and 93 per cent and all suggest a lower level of IGFR-1 expression in benign mammary epithelia. As there is this variation between studies and since no study appears to have examined the immunohistochemical localization of IGFR-1 within breast tissue, a series of 79 infiltrating ductal carcinomas, 11 infiltrating lobular carcinomas, three cases of pure ductal carcinoma in situ (DCIS), seven fibroadenomas, and eight normal breast specimens have been studied utilizing the monoclonal antibody alpha IR3. IGFR-1 localized to the epithelial component of 90 per cent of the carcinomas, with only cytoplasmic (21 per cent), only membrane (5 per cent), or a mixture of both cytoplasmic and membrane (64 per cent) staining patterns. In some tumours, distinct basolateral distribution of the receptor was observed. Invasive lobular carcinoma showed significantly less labelling than ductal (P = 0.0009). There was a significant correlation between the level of IGFR-1 immunostaining with both oestrogen receptor (P < 0.001) and progesterone receptor (P = 0.0018) positivity within the malignant group. All normal mammary epithelium showed strong labelling, which was often at an intensity matching that of the most strongly labelled carcinoma and occasionally visualized as basolateral staining of the luminal cells. Weak to moderate staining of endothelial cells was also observed. It is concluded that IGFR-1 immunoreactivity is found in the majority of breast carcinomas, where it correlates most closely with oestrogen receptor status. The high intensity labelling of normal cells seen in this study contrasts with the low levels inferred from ligand-binding-based techniques and emphasizes the importance of the morphological approach in the investigation of novel molecules.

Growth factor-induced transcription via the serum response element is inhibited by cyclic adenosine 3',5'-monophosphate in MCF-7 breast cancer cells

The effect of increased intracellular cAMP on MCF-7 breast cancer cell growth was examined by treating cells with either forskolin, an activator of adenylate cyclase, or 8-[4-chlorophenylthio]-cAMP (8-CPT-cAMP), a cAMP analog. Compared to cells maintained in control medium, treatment with either 1 or 10 microM forskolin decreased cell growth by 17% and 68%, respectively, whereas treatment with 250 microM 8-CPT-cAMP decreased cell growth by 29%. To determine whether this effect of cAMP on cell growth was mediated by inhibition of the activity of extracellular signal-regulated kinases 1 and 2 (ERK1 and -2), two mitogen-activated protein kinases, the effect of cAMP on growth factor-induced ERK activity in MCF-7 cells was examined. Treatment with either insulin-like growth factor I (IGF-I) or epidermal growth factor (EGF) for 10 min stimulated a 4- to 8-fold increase in ERK1 and -2 activity. This effect of IGF-I and EGF was not inhibited by increased intracellular cAMP generated by pretreatment of the cells with 10 microM forskolin. Similarly, 10 microM forskolin had no effect on IGF-I- or EGF-induced ERK activity in cells treated with growth factor for 30 min. To determine whether cAMP inhibits other growth factor-mediated effects, its effect on the activity of the serum response element (SRE), a DNA promoter element whose activity is regulated by a variety of growth-promoting events, was examined. For these assays, MCF-7 cells were transiently transfected with pTK81-SRE-Luc, a luciferase fusion gene that contains the SRE cloned 5' to a minimal thymidine kinase promoter and the luciferase gene. Treatment with either IGF-I or EGF increased pTK81-SRE-Luc activity in a dose-dependent fashion. Pretreatment of cells with 10 microM forskolin decreased IGF-I- and EGF-stimulated luciferase activity by approximately 75%. An intermediate effect was observed using 1 microM forskolin. When intracellular cAMP levels were increased using 8-CPT-cAMP, similar results were obtained. SRE activity is dependent upon the activation by phosphorylation of a ternary complex factor; included among the ternary complex factors is Elk-1. When MCF-7 cells were cotransfected with a vector that expresses a Gal4/Elk-1 fusion protein and UAS-TK-Luc, a plasmid that contains two Gal4 DNA recognition sites cloned 5' to a thymidine kinase promoter and the luciferase gene, treatment with forskolin partially inhibited the activation of Elk-1 by IGF-I and EGF. These data demonstrate that in MCF-7 breast cancer cells, cAMP has no effect on IGF-I- or EGF-induced ERK activity, but it inhibits growth factor-induced transcription. Taken together with the effects of cAMP on IGF-I- and EGF-induced Elk-1 activation, these data suggest that the effect of cAMP on SRE activity occurs distal to ERK activation, possibly via inhibition of an ERK-independent pathway. Finally, these data indicate that the effect of increased intracellular cAMP on breast cancer growth may be mediated through inhibition of specific growth factor-induced effects, including gene transcription.

Dairy products and breast cancer: the IGF-I, estrogen, and bGH hypothesis

Research on the role of dietary factors in breast cancer causation has focused predominantly on fat intake. While some studies have examined associations between breast cancer rates and consumption of whole milk, there has been less attention given to dairy products in general. Dairy products contain both hormones and growth factors, in addition to fat and various chemical contaminants, that have been implicated in the proliferation of human breast cancer cells. This literature review evaluates the epidemiological and mechanistic evidence linking dairy consumption with breast cancer risk.

Type I insulin-like growth factor receptor gene expression in normal human breast tissue treated with oestrogen and progesterone

The epithelial proliferation of normal human breast tissue xenografts implanted into athymic nude mice is significantly increased from basal levels by oestradiol (E2), but not progesterone (Pg) treatment at serum concentrations similar to those observed in the luteal phase of the human menstrual cycle. Type I IGF receptor (IGFR-I) mRNA and protein have been shown to be up-regulated by E2 in MCF-7 breast cancer cells in vitro in which IGF-I and E2 act synergistically to stimulate proliferation. We have investigated the expression of the IGFR-I mRNA in normal human breast xenografts treated with or without E2 or Pg alone and in combination. Northern analysis of 20 micrograms of RNA extracted from the breast xenograft samples showed no hybridization with 32P-labelled IGFR-I probe, although an 11-kb species of IGFR-I mRNA could be seen when 20 micrograms of RNA extracted from either MCF-7 breast cancer cells or human breast carcinomas was examined in this way. In order to analyse the expression of IGFR-I mRNA in breast xenografts, a quantitative reverse transcription-polymerase chain reaction (RT-PCR) was employed in which RNA loading, reverse transcription and PCR efficiencies were internally controlled. The data indicate that the IGFR-I mRNA is up-regulated by two to threefold compared with untreated levels by 7 and 14 days E2 treatment. In contrast, 7 or 14 days Pg treatment down-regulates the receptor mRNA to approximately half that of untreated levels, whereas combination E2 and Pg treatment produced a twofold increase in IGFR-I mRNA levels compared with untreated tissue. The results are consistent with the suggestion that E2 may act to stimulate proliferation indirectly via a paracrine mechanism involving IGFs in normal as well as malignant human breast epithelial cells.

Insulin-like growth factors in breast cancer

Insulin-like growth factor (IGF)-I is one of the most potent mitogens to many breast cancer cell lines in vitro. Effective growth inhibition in vitro may be achieved by antibodies to the type I IGF receptor (IGF-IR) or by using antisense strategies. Most human breast cancers express IGF-IR in vivo. Thus, different therapeutic strategies aimed at inhibiting ligand stimulation of the IGF-IR may be an attractive treatment option against breast cancer. Several drugs commonly used in breast cancer influence the IGF system both in vitro and in vivo. While antioestrogens such as tamoxifen and droloxifene reduce the expression of IGF-IR in vitro and suppress plasma levels of IGF-I but elevate IGF-binding protein-1 in vivo, megestrol acetate may reduce the delivery of IGFs to the tissues by inhibition of IGFBP-3 protease activity.

Mechanisms of action of endocrine treatment in breast cancer

Endocrine treatment plays an important role in the therapy of breast cancer. While the basic mechanisms are understood, additional mechanisms may be of importance to their action and they may also contribute to the mechanism(s) of acquired resistance. Currently, several novel drugs are entering into clinical trials. Observations of the absence or presence of cross resistance to novel 'pure' steroidal antiestrogens and the non-steroidal tamoxifen may add important information to our understanding of the mechanisms of action of both classes of drugs. Similarly, exploration of different aromatase inhibitors in sequence or concert, as well as the combining of different endocrine treatment options may be warranted. Additionally, alterations in different biochemical parameters such as growth factors should not only be carefully explored in relation to treatment options but should also be followed during the course of treatment to asess alterations over time and in relation to the development of drug resistance.

Insulin-like growth factor-I is an autocrine regulator for the brain metastatic variant of a human non-small cell lung cell line

Insulin-like growth factor (IGF-I) is associated with autocrine and paracrine stimulation for cell growth and development of brain tumor cells. The function of IGF-I in the brain metastatic variant of human lung cancer cells is investigated. The cells used here were derived in vivo with intracarotid injection of human non-small cell lung carcinoma NCI-H226. The tumor was developed as a cultured cell line, H226Br. Unlike the parental cells, H226Br was tumorigenic in nu/nu nude mice. Reverse transcriptase-polymerase chain reaction showed that IGF-I transcript of H226Br is increased compared to that of parental cells. The amount of IGF-I secreted in cultured medium of H226Br is higher than that of cultured parental cells. The IGF-I receptor-specific antibody, alpha IR3, inhibits H226Br growth in serum-free culture. The results established that IGF-I is an autocrine growth regulator for human non-small cell lung cancer cells that progressed to brain.

Type I insulin-like growth factor receptors in human colorectal cancer

Type I insulin-like growth factor (IGF) receptors have been recently characterised in human colorectal cancers. The aim of this study was to determine whether type I IGF receptor concentration may be related to prognostic variables in colorectal cancers. Saturation experiments with [125I]IGF-I were performed on membrane preparations of 46 frozen specimens (20 tumours, 26 controls) and analysed according to the Scatchard method. In all the studied cases, we found a single class of high affinity binding sites in both normal and malignant colorectal tissues (median 0.17 and 0.15 nmol/l, respectively). Using paired analysis, we found no significant difference in terms of type I IGF receptor concentration between malignant and normal colorectal tissues. There was also no relationship between type I IGF receptors and any of the tumour characteristics studied. This study does not support a critical role of the type I IGF receptors in the clinical management of colorectal cancers.

The insulin-like growth factor system as a target in breast cancer

Evidence from several experimental systems has shown that the insulin-like growth factors (IGFs) can stimulate breast cancer proliferation. Since IGF action is mediated by interaction with specific cell surface receptors, interruption of these signalling pathways could result in inhibition of cellular growth. In all extracellular fluids, the IGFs are associated with high affinity binding proteins, the IGFBPs can bind the IGFs and prevent receptor activation, and thus might have a role in a targeted approach to breast cancer therapy. Here we present our studies using IGFBP-1 to inhibit growth of the breast cancer cell line MCF-7.

Effect of two-4-hydroxyandrostenedione doses on serum insulin-like growth factor I levels in advanced breast cancer

A number of endocrine treatments for advanced breast cancer seem to affect serum insulin-like growth factor I (IGF-I). The aim of our study was to investigate IGF-I levels in 33 postmenopausal patients with metastatic disease receiving the selective aromatase inhibitor 4-hydroxyandrostenedione: 250 mg (16 patients) or 500 mg (17 patients) i.m. fortnightly. Blood samples were collected before, and at one month and 3 months after the beginning of treatment for radioimmunoassay determinations. The median patient age was 56 and 60 years in the 250 and 500 mg groups respectively. Most patients had a disease free interval > or = 2 years and were oestrogen receptor positive. Objective responses were obtained in 3 patients (complete response, 1) in the 250 mg group, and in 7 patients (complete response, 3) in the 500 mg group. No significant IGF-I variations were seen in the 250 mg group, whereas a significant increase after 3 months (181.57 +/- 84.78 ng/ml versus 272.47 +/- 213.22 ng/ml, p = 0.0032) was observed in the 500 mg group. No IGF-I variations were seen between responsive and unresponsive patients in either treatment group. Our results in the 500 mg group are close to those obtained with aminoglutethimide and seem to agree with the hypothesis of an oestrogen-induced suppression of IGF-I circulating levels.

Plasma insulin-like growth factor-1 (IGF-1) concentrations in human breast cancer

Insulin-like growth factor-1 (IGF-1) is capable of stimulating breast cancer cell growth in vitro and the presence of IGF-1 receptors has been demonstrated in primary breast cancers. We determined plasma IGF-1 in a primary breast cancer population and in a control population. Radioimmunoassays were performed either directly on plasma, IGF-1 (NE), or after an acid-ethanol extraction of the plasma, IGF-1 (E). We demonstrated an inverse correlation between age and IGF-1: for this reason, only results obtained in females of the same age range (> 35 years) were compared. Median concentrations of IGF-1 were significantly higher in primary breast cancers [IGF-1 (E) = 152 ng/ml, IGF-1 (NE) = 26 ng/ml, n = 44] than in controls [IGF-1 (E) = 115 ng/ml, IGF-1 (NE) = 20 ng/ml, n = 92]. To our knowledge such a growth factor increase has never been described in breast cancer. We conclude that IGF-1 could be an important factor involved in the development of breast cancer and that treatment reducing IGF-1 levels could be beneficial for patients.