The anti-proliferative effect of suramin towards tamoxifen-sensitive and resistant human breast cancer cell lines in relation to expression of receptors for epidermal growth factor and insulin-like growth factor-I: growth stimulation in the presence of tamoxifen

Deregulation of IGF-binding proteins -2 and -5 contributes to the development of endocrine resistant breast cancer in vitro

Tamoxifen (TAM) remains the adjuvant therapy of choice for pre-menopausal women with ERα-positive breast cancer. Resistance and recurrence remain, however, a major challenge with many women relapsing and subsequently dying. The insulin-like growth factor (IGF) axis is involved in breast cancer pathogenesis and progression to endocrine resistant disease, but there is very little data on the expression and potential role of IGF-binding proteins (IGFBP) during acquisition of the resistant phenotype. The aim of this study was to determine the expression and functional role of IGFBP-2 and -5 in the development of TAM resistance (TamR) in vitro and to test retrospectively whether they were predictive of resistance in a tissue microarray of 77 women with primary breast cancers who relapsed on/after endocrine therapy and 193 who did not with long term follow up. Reciprocal expression of IGFBP-2 and IGFBP-5 was observed at both mRNA and protein level in TamR cells. IGFBP-2 expression was increased by 10-fold while IGFBP-5 was decreased by 100-fold, compared to TAM-sensitive control cells. shRNA-mediated silencing of IGFBP-2 in TamR cells restored TAM sensitivity suggesting a causal role for this gene in TamR. While silencing of IGFBP-5 in control cells had no effect on TAM sensitivity, it significantly increased the migratory capacity of these cells. Quantitative image analysis of immunohistochemical data failed, however, to demonstrate an effect of IGFBP2 expression in endocrine-relapsed patients. Likewise, IGFBP-2 and IGFBP-5 expression failed to show any significant associations with survival either in patients relapsing or those not relapsing on/after endocrine therapy. By contrast, in silico mining of a separate published dataset showed that in patients who received endocrine treatment, loss of expression of IGBP-5 was significantly associated with worse survival. Overall these data suggest that co-ordinated and reciprocal alteration in IGFBP-2 and −5 expression may play a role in the acquisition of endocrine resistance.

Protein Kinase A-induced tamoxifen resistance is mediated by anchoring protein AKAP13

Background

Estrogen Receptor alpha (ERα)-positive breast cancer patients receive endocrine therapy, often in the form of tamoxifen. However, resistance to tamoxifen is frequently observed. A signalling cascade that leads to tamoxifen resistance is dictated by activation of the Protein Kinase A (PKA) pathway, which leads to phosphorylation of ERα on Serine 305 and receptor activation, following tamoxifen binding. Thus far, it remains elusive what protein complexes enable the PKA-ERα interaction resulting in ERα Serine 305 phosphorylation.

Methods

We performed immunohistochemistry to detect ERαSerine 305 phosphorylation in a cohort of breast cancer patients who received tamoxifen treatment in the metastatic setting. From the same tumor specimens, Agilent 44 K gene expression analyses were performed and integrated with clinicopathological data and survival information. In vitro analyses were performed using MCF7 breast cancer cells, which included immunoprecipitations and Fluorescence Resonance Energy Transfer (FRET) analyses to illustrate ERα complex formation. siRNA mediated knockdown experiments were performed to assess effects on ERαSerine 305 phosphorylation status, ERα/PKA interactions and downstream responsive gene activity.

Results

Stratifying breast tumors on ERα Serine 305 phosphorylation status resulted in the identification of a gene network centered upon AKAP13. AKAP13 mRNA expression levels correlate with poor outcome in patients who received tamoxifen treatment in the metastatic setting. In addition, AKAP13 mRNA levels correlate with ERαSerine 305 phosphorylation in breast tumor samples, suggesting a functional connection between these two events. In a luminal breast cancer cell line, AKAP13 was found to interact with ERα as well as with a regulatory subunit of PKA. Knocking down of AKAP13 prevented PKA-mediated Serine 305 phosphorylation of ERα and abrogated PKA-driven tamoxifen resistance, illustrating that AKAP13 is an essential protein in this process.

Conclusions

We show that the PKA-anchoring protein AKAP13 is essential for the phosphorylation of ERαS305, which leads to tamoxifen resistance both in cell lines and tamoxifen-treated breast cancer patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1591-4) contains supplementary material, which is available to authorized users.

IGFBP-2 and -5: important regulators of normal and neoplastic mammary gland physiology

The insulin-like growth factor (IGF) axis plays an important role in mammary gland physiology. In addition, dysregulation of this molecular axis may have a causal role in the aetiology and development of breast cancer (BC). This report discusses the IGF axis in normal and neoplastic mammary gland with special reference to IGF binding proteins (IGFBPs) -2 and -5. We describe how these high affinity binders of IGF-1 and IGF-2 may regulate local actions of growth factors in an autocrine and/or paracrine manner and how they also have IGF-independent effects in mammary gland. We discuss clinical studies which investigate both the prognostic value of IGFBP-2 and -5 expression in BC and possible involvement of these genes in the development of resistance to adjuvant endocrine therapies.

Insulin-like growth factor - oestradiol crosstalk and mammary gland tumourigenesis

Development and differentiation of the mammary gland are dependent on the appropriate temporal expression of both systemically acting hormones and locally produced growth factors. A large body of evidence suggests that molecular crosstalk between these hormonal and growth factor axes is crucial for appropriate cell and tissue function. Two of the most important trophic factors involved in this process are the oestrogen (E) and insulin-like growth factor (IGF) molecular axes. The reciprocal crosstalk that exists between these pathways occurs at transcriptional/post-transcriptional and translational/post-translational levels regulate the expression and activity of genes involved in this process. In a clinical context an important consequence of such crosstalk in the mammary gland is the role which it may play in the aetiology, maintenance and development of breast tumours. Although oestradiol (E2) acting through oestrogen receptors α and β (ERα/β) is important for normal mammary gland function it can also provide a mitogenic drive to ER+ breast tumours. Therefore over several years anti-oestrogen therapeutic regimens in the form of selective oestrogen receptor modulators (SERMs - e.g. tamoxifen), aromatase inhibitors (AI e.g. anastrozole) or selective oestrogen receptor down regulators (SERDs - e.g. fulvestrant) have been used in an adjuvant setting to control tumour growth. Although initial response is usually encouraging, large cohorts of patients eventually develop resistance to these treatments leading to tumour recurrence and poor prognosis. There are potentially many routes by which breast cancer (BC) cells could escape anti-oestrogen based therapeutic strategies and one of the most studied is the possible growth factor mediated activation of ER(s). Because of this, growth factor modulation of ER activity has been an intensively studied route of molecular crosstalk in the mammary gland. The insulin-like growth factors (IGF-1 and -2) are amongst the most potent mitogens for mammary epithelial cells and there is accumulating evidence that they interact with the E2 axis to regulate mitogenesis, apoptosis, adhesion, migration and differentiation of mammary epithelial cells. Such interactions are bi-directional and E2 has been shown to regulate the expression and activity of IGF axis genes with the general effect of sensitising breast epithelial cells to the actions of IGFs and insulin. In this short review we discuss the evidence for the involvement of crosstalk between the insulin-like growth factor (IGF) and oestrogen axes in the mammary gland and comment on the relevance of such studies in the aetiology and treatment of BC.

Monocytes/macrophages support mammary tumor invasivity by co-secreting lineage-specific EGFR ligands and a STAT3 activator

Background

Tumor-associated macrophages (TAM) promote malignant progression, yet the repertoire of oncogenic factors secreted by TAM has not been clearly defined. We sought to analyze which EGFR- and STAT3-activating factors are secreted by monocytes/macrophages exposed to tumor cell-secreted factors.

Methods

Following exposure of primary human monocytes and macrophages to supernatants of a variety of tumor cell lines, we have analyzed transcript and secreted protein levels of EGFR family ligands and of STAT3 activators. To validate our findings, we have analyzed TAM infiltration levels, systemic and local protein levels as well as clinical data of primary breast cancer patients.

Results

Primary human monocytes and macrophages respond to tumor cell-derived factors by secreting EGFR- and STAT3-activating ligands, thus inducing two important oncogenic pathways in carcinoma cells. Tumor cell-secreted factors trigger two stereotype secretory profiles in peripheral blood monocytes and differentiated macrophages: monocytes secrete epiregulin (EREG) and oncostatin-M (OSM), while macrophages secrete heparin-binding EGF-like growth factor (HB-EGF) and OSM. HB-EGF and OSM cooperatively induce tumor cell chemotaxis. HB-EGF and OSM are co-expressed by TAM in breast carcinoma patients, and plasma levels of both ligands correlate strongly. Elevated HB-EGF levels accompany TAM infiltration, tumor growth and dissemination in patients with invasive disease.

Conclusions

Our work identifies systemic markers for TAM involvement in cancer progression, with the potential to be developed into molecular targets in cancer therapy.

Reversal of antiprogestin resistance and progesterone receptor isoform ratio in acquired resistant mammary carcinomas

To explore mechanisms related to hormone resistance, three resistant variants of the MPA mouse breast cancer tumor model with low levels of progesterone receptor (PR) isoform A (PR-A)/high PR-B expression were developed by prolonged selective pressure with antiprogestins. The resistant phenotype of one tumor line was reversed spontaneously after several consecutive passages in syngeneic BALB/c mice or by 17-beta-estradiol or tamoxifen treatment, and this reversion was significantly associated with an increase in PR-A expression. The responsive parental tumors disclosed low activation of ERK and high activation of AKT; resistant tumors on the other hand, showed the opposite, and this was associated with a higher metastatic potential, that did not revert. This study shows for the first time in vivo a relationship between PR isoform expression and antiprogestin responsiveness, demonstrating that, whereas acquired resistance may be reversed, changes in kinase activation and metastatic potential are unidirectional associated with tumor progression.

Surviving cell death through epidermal growth factor (EGF) signal transduction pathways: Implications for cancer therapy

There is a balance between cell death and survival in living organisms. The ability of cells to sense their environment and decide to survive or die is dependent largely upon growth factors. Epidermal growth factor (EGF) is a key growth factor regulating cell survival. Through its binding to cell surface receptors, EGF activates an extensive network of signal transduction pathways that include activation of the PI3K/AKT, RAS/ERK and JAK/STAT pathways. These pathways predominantly lead to activation or inhibition of transcription factors that regulate expression of both pro- and anti-apoptotic proteins effectively blocking the apoptotic pathway. In cancer, EGF signaling pathways are often dysfunctional and targeted therapies that block EGF signaling have been successful in treating cancers. In this review, we will discuss the EGF survival signaling network, how it cross-talks with the apoptotic signaling pathways and the therapeutic drugs targeting the EGF survival pathway used to treat cancers.

Cancer biology and hormesis: human tumor cell lines commonly display hormetic (biphasic) dose responses

This article assesses the nature of the dose-response relationship of human tumor cell lines with a wide range of agents including antineoplastics, toxic substances (i.e., environmental pollutants), nonneoplastic drugs, endogenous agonists, and phyto-compounds. Hormetic-like biphasic dose responses were commonly reported and demonstrated in 136 tumor cell lines from over 30 tissue types for over 120 different agents. Quantitative features of these hormetic dose responses were similar, regardless of tumor cell line or agent tested. That is, the magnitude of the responses was generally modest, with maximum stimulatory responses typically not greater than twice the control, while the width of the stimulatory concentration range was usually less than 100-fold. Particular attention was directed to possible molecular mechanisms of the biphasic nature of the dose response, as well as clinical implications in which a low concentration of chemotherapeutic agent may stimulate tumor cell proliferation. Finally, these findings further support the conclusion that hormetic dose responses are broadly generalizable, being independent of biological model, endpoint measured, and stressor agent, and represent a basic feature of biological responsiveness to chemical and physical stressors.

A Fully Human Recombinant IgG-like Bispecific Antibody to Both the Epidermal Growth Factor Receptor and the Insulin-like Growth Factor Receptor for Enhanced Antitumor Activity

Both the epidermal growth factor receptor (EGFR) and the insulin-like growth factor receptor (IGFR) have been implicated in the tumorigenesis of a variety of cancers. Here we propose that simultaneous targeting of both receptors with a bispecific antibody would lead to enhanced antitumor activity. To this end, we produced a recombinant human IgG-like bispecific antibody, a Di-diabody, using the variable regions from two antagonistic antibodies: IMC-11F8 to EGFR and IMC-A12 to IGFR. The Di-diabody binds to both EGFR and IGFR and effectively blocked both EGF- and IGF-stimulated receptor activation and tumor cell proliferation. The Di-diabody also inherited the biological properties from both of its parent antibodies; it triggers rapid and significant IGFR internalization and degradation and mediates effective antibody-dependent cellular cytotoxicity in a variety of tumor cells. Finally, the Di-diabody strongly inhibited the growth of two different human tumor xenografts in vivo. Our results underscore the benefits of simultaneous targeting of two tumor targets with bispecific antibodies.

Anti-angiogenic therapies in cancer clinical trials

Strategies involving vasculature have widely been acknowledged to have therapeutic potential in the management of cancer and other diseases. Based on a large body of evidence from preclinical studies and early clinical trials there is considerable optimism that anti-angiogenesis and vascular targeting will be a major clinical therapy. This review considers some 30 anti-angiogenic and vascular targeting agents that are currently in cancer clinical trials and highlights specific problems relating to the assessment of the activity of these agents in patients, trial design, potential toxicities and resistance mechanisms.

Simultaneous blockade of both the epidermal growth factor receptor and the insulin-like growth factor receptor signaling pathways in cancer cells with a fully human recombinant bispecific antibody

Both the epidermal growth factor receptor (EGFR) and the insulin-like growth factor receptor (IGFR) have been implicated in the tumorigenesis of a variety of human cancers. Effective tumor inhibition has been achieved both experimentally and clinically with a number of strategies that antagonize either receptor activity. Here we constructed and produced two fully human recombinant bispecific antibodies (BsAb) that target both EGFR and IGFR, using two neutralizing human antibodies originally isolated from a phage display library. The BsAb not only retained the antigen binding capacity of each of the parent antibodies, but also were capable of binding to both targets simultaneously as demonstrated by a cross-linking enzyme-linked immunosorbent assay. Furthermore, the BsAb effectively blocked both ligands, EGF and IGF, from binding to their respective receptors, and inhibited tumor cell proliferation as potently as a combination of both the parent antibodies. More importantly, the BsAb were able to completely block activation of several major signal transduction molecules, including Akt and p44/p42 MAP kinases, by both EGF and IGF, whereas each individual parent antibody was only effective in inhibiting those signal molecules activated by the relevant single growth factor. The BsAb molecules retained good antigen binding activity after incubation with mouse serum at 37 degrees C for up to 6 days. Taken together, our results underscore the benefits of simultaneous targeting multiple growth factor receptor pathways for more efficacious cancer treatment. This report describes the first time use of a recombinant BsAb for targeting two tumor-associated molecules on either a single or adjacent tumor cells for enhanced antitumor activity.

Toward checkmate: biology and breast cancer therapy for the new millennium

A better understanding of the biology of breast cancer should lead to the rational development of new treatments and the ability to customize therapy for individual patients. Though promising in theory, translating advances in biological knowledge to the clinic has been difficult. Recently several areas of research have produced treatments which have entered clinical trials: three will be reviewed here. The growth of breast cancer is regulated by growth factors and their receptors; amplification or overexpression is associated with poor prognosis. As such inhibition of growth factors and/or growth factor receptors may provide an ideal therapeutic target. Herceptin binds to c-erbB-2, a member of the epidermal growth factor receptor family. Significant responses were seen in patients with c-erbB-2 overexpressing breast cancer with Herceptin administered as a single agent or in combination with chemotherapy. Herceptin was approved by the Food and Drug Administration in late 1998. Breast cancer invasion and metastasis requires degradation of the surrounding basement membrane by matrix metalloproteinases and other proteolytic enzymes. Synthetic inhibitors of these enzymes are now in clinical trials. Breast cancers must stimulate angiogenesis, the growth of new blood vessels, in order to grow beyond a few millimeters in diameter. This nascent vascular network provides another opportunity for therapy. Preclinical models support the critical role of angiogenesis and the therapeutic benefit of angiogenesis inhibition; clinical trials are underway.

Changes in the secretion of insulin-like growth factor binding proteins -2 and -4 associated with the development of tamoxifen resistance and estrogen independence in human breast cancer cell lines

We investigated the secretion of insulin-like growth factor binding proteins (IGFBPs) by estrogen-dependent ZR-75-1 and MCF-7 human breast cancer cells, and tamoxifen-resistant (ZR-75-9a1 and LY2) and estrogen-independent (ZR-PR-LT) variants which express altered levels of IGF-I receptor. IGFBP species (35 kDa and 44 kDa) were detectable in conditioned serum-free medium (SFM) by immunoblotting and positively identified as IGFBP-2 and -3, respectively. Secretion of IGFBP-2 into SFM by the tamoxifen-resistant and estrogen-independent cell lines was markedly reduced and secretion into SFM of the 24-kDa species, assigned the identity of IGFBP-4, was also reduced in the tamoxifen-resistant lines. There was no clear correlation between patterns of IGFBP secretion and IGF-I receptor expression.