Epidermal growth factor receptor expression in breast cancer: association with response to endocrine therapy

Clinical Outcomes Following Letrozole Treatment according to Estrogen Receptor Expression in Postmenopausal Women: LETTER Study (KBCSG-006)

Purpose

In this trial, we investigated the efficacy and safety of adjuvant letrozole for hormone receptor (HR)-positive breast cancer. Here, we report the clinical outcome in postmenopausal women with HR-positive breast cancer treated with adjuvant letrozole according to estrogen receptor (ER) expression levels.

Methods

In this multi-institutional, open-label, observational study, postmenopausal patients with HR-positive breast cancer received adjuvant letrozole (2.5 mg/daily) for 5 years unless they experienced disease progression or unacceptable toxicity or withdrew their consent. The patients were stratified into the following 3 groups according to ER expression levels using a modified Allred score (AS): low, intermediate, and high (AS 3–4, 5–6, and 7–8, respectively). ER expression was centrally reviewed. The primary objective was the 5-year disease-free survival (DFS) rate.

Results

Between April 25, 2010, and February 5, 2014, 440 patients were enrolled. With a median follow-up of 62.0 months, the 5-year DFS rate in all patients was 94.2% (95% confidence interval [CI], 91.8–96.6). The 5-year DFS and recurrence-free survival (RFS) rates did not differ according to ER expression; the 5-year DFS rates were 94.3% and 94.1%in the low-to-intermediate and high expression groups, respectively (p = 0.6), and the corresponding 5-year RFS rates were 95.7% and 95.4%, respectively (p = 0.7). Furthermore, 25 patients discontinued letrozole because of drug toxicity.

Conclusion

Treatment with adjuvant letrozole showed very favorable treatment outcomes and good tolerability among Korean postmenopausal women with ER-positive breast cancer, independent of ER expression.

Trial Registration

ClinicalTrials.gov Identifier: NCT01069211

Comparative Analysis of the Development of Acquired Radioresistance in Canine and Human Mammary Cancer Cell Lines

Research using in vitro canine mammary cancer cell lines and naturally-occurring canine mammary tumors are not only fundamental models used to advance the understanding of cancer in veterinary patients, but are also regarded as excellent translational models of human breast cancer. Human breast cancer is commonly treated with radiotherapy; however, tumor response depends on both innate radiosensitivity and on tumor repopulation by cells that develop radioresistance. Comparative canine and human studies investigating the mechanisms of radioresistance may lead to novel cancer treatments that benefit both species. In this study, we developed a canine mammary cancer (REM-134) radioresistant (RR) cell line and investigated the cellular mechanisms related to the development of acquired radioresistance. We performed a comparative analysis of this resistant model with our previously developed human breast cancer radioresistant cell lines (MCF-7 RR, ZR-751 RR, and MDA-MB-231 RR), characterizing inherent differences through genetic, molecular, and cell biology approaches. RR cells demonstrated enhanced invasion/migration capabilities, with phenotypic evidence suggestive of epithelial-to-mesenchymal transition. Similarities were identified between the REM-134 RR, MCF-7 RR, and ZR-751 RR cell lines in relation to the pattern of expression of both epithelial and mesenchymal genes, in addition to WNT, PI3K, and MAPK pathway activation. Following the development of radioresistance, transcriptomic data indicated that parental MCF-7 and ZR-751 cell lines changed from a luminal A classification to basal/HER2-overexpressing (MCF-7 RR) and normal-like/HER2-overexpressing (ZR-751 RR). These radioresistant subtypes were similar to the REM-134 and REM-134 RR cell lines, which were classified as HER2-overexpressing. To our knowledge, our study is the first to generate a canine mammary cancer RR cell line model and provide a comparative genetic and phenotypic analysis of the mechanisms of acquired radioresistance between canine and human cancer cell lines. We demonstrate that the cellular processes that occur with the development of acquired radioresistance are similar between the human and canine cell lines; our results therefore suggest that the canine model is appropriate to study both human and canine radioresistant mammary cancers, and that treatment strategies used in human medicine may also be applicable to veterinary patients.

Loss of ZIP facilitates JAK2-STAT3 activation in tamoxifen-resistant breast cancer

Tamoxifen is beneficial in treating estrogen receptor–positive breast cancer, but resistance to this treatment eventually ensues. A method to identify mechanisms of tamoxifen resistance identified the histone deacetylase ZIP, leading to the finding that increased expression of the tyrosine kinase JAK2 is one important factor. As a result of this discovery, it may be possible to use an inhibitor of JAK2 to block the aberrant activation of STAT3 caused by ZIP deficiency to help overcome or prevent tamoxifen resistance.

Tamoxifen, a widely used modulator of the estrogen receptor (ER), targets ER-positive breast cancer preferentially. We used a powerful validation-based insertion mutagenesis method to find that expression of a dominant-negative, truncated form of the histone deacetylase ZIP led to resistance to tamoxifen. Consistently, increased expression of full-length ZIP gives the opposite phenotype, inhibiting the expression of genes whose products mediate resistance. An important example is JAK2. By binding to two specific sequences in the promoter, ZIP suppresses JAK2 expression. Increased expression and activation of JAK2 when ZIP is inhibited lead to increased STAT3 phosphorylation and increased resistance to tamoxifen, both in cell culture experiments and in a mouse xenograft model. Furthermore, data from human tumors are consistent with the conclusion that decreased expression of ZIP leads to resistance to tamoxifen in ER-positive breast cancer.

EGF receptor stimulation shifts breast cancer cell glucose metabolism toward glycolytic flux through PI3 kinase signaling

Breast cancers that express epidermal growth factor (EGF) receptors (EGFRs) are associated with poor prognosis. Our group recently showed in breast cancer patients that EGFR expression is strongly correlated with high tumor uptake of the glucose analogue, ¹⁸F-fluorodeoxyglucose (FDG). Here, we explored the cellular mechanism and signaling pathways that can explain the relation between EGFR and breast cancer cell glucose metabolism. FDG uptake, lactate production and hexokinase (HK) activity were measured, and proliferation assays and western blots were performed. EGF stimulated an increase of FDG uptake in EGFR-positive T47D and MDA-MB-468 cells, but not in MCF-7 cells. In T47D cells, the effect was dose-dependent and was accompanied by increased lactate production, indicating a shift toward glycolytic flux. This metabolic response occurred through enhanced HK activity and upregulated glucose transporter 1 (GLUT1) expression. EGFR stimulation also increased T47D cell proliferation. Blocking EGFR activation with BIBX1382 or gefitinib completely abolished both FDG uptake and proliferation effects. EGFR stimulation induced MAP kinase (MAPK) and PI3 kinase (PI3K) activation. Increased cell proliferation by EGFR stimulation was completely abolished by MAPK inhibition with PD98059 or by PI3K inhibition with LY294002. Increased FDG uptake was also completely abrogated by PI3K inhibition but was uninfluenced by MAPK inhibition. These findings suggest that the association between breast tumor EGFR expression and high FDG uptake might be contributed by stimulation of the PI3K pathway downstream of EGFR activation. This was in contrast to EGFR-mediated cell proliferation that required MAPK as well as PI3K signaling.

Development and characterisation of acquired radioresistant breast cancer cell lines

BACKGROUND

Radiotherapy plays an important role in the multimodal treatment of breast cancer. The response of a breast tumour to radiation depends not only on its innate radiosensitivity but also on tumour repopulation by cells that have developed radioresistance. Development of effective cancer treatments will require further molecular dissection of the processes that contribute to resistance.

METHODS

Radioresistant cell lines were established by exposing MDA-MB-231, MCF-7 and ZR-751 parental cells to increasing weekly doses of radiation. The development of radioresistance was evaluated through proliferation and colony formation assays. Phenotypic characterisation included migration and invasion assays and immunohistochemistry. Transcriptomic data were also generated for preliminary hypothesis generation involving pathway-focused analyses.

RESULTS

Proliferation and colony formation assays confirmed radioresistance. Radioresistant cells exhibited enhanced migration and invasion, with evidence of epithelial-to-mesenchymal-transition. Significantly, acquisition of radioresistance in MCF-7 and ZR-751 cell lines resulted in a loss of expression of both ERα and PgR and an increase in EGFR expression; based on transcriptomic data they changed subtype classification from their parental luminal A to HER2-overexpressing (MCF-7 RR) and normal-like (ZR-751 RR) subtypes, indicating the extent of phenotypic changes and cellular plasticity involved in this process. Radioresistant cell lines derived from ER+ cells also showed a shift from ER to EGFR signalling pathways with increased MAPK and PI3K activity.

CONCLUSIONS

This is the first study to date that extensively describes the development and characterisation of three novel radioresistant breast cancer cell lines through both genetic and phenotypic analysis. More changes were identified between parental cells and their radioresistant derivatives in the ER+ (MCF-7 and ZR-751) compared with the ER- cell line (MDA-MB-231) model; however, multiple and likely interrelated mechanisms were identified that may contribute to the development of acquired resistance to radiotherapy.

Cytokine-mediated therapeutic resistance in breast cancer

Therapeutic resistance leading to tumor relapse is a major challenge in breast cancer (BCa) treatment. Numerous factors involved in multiple mechanisms promote the development of tumor chemo/radio-resistance. Cytokines/chemokines are important inflammatory factors and highly related to tumorigenesis, metastasis and tumors responses to treatment. A large number of studies have demonstrated that the network of cytokines activates multiple cell signaling pathways to promote tumor cell survival, proliferation, invasion, and migration. Particularly in BCa, cytokines-enhanced the epithelial-mesenchymal transition (EMT) process plays a pivotal role in the progression of metastatic phenotypes and resistance to the traditional chemo/radio-therapy. Virtually, therapeutic resistance is not entirely determined by tumor cell intrinsic characteristics but also dependent upon synchronized effects by numerous of local microenvironmental factors. Emerging evidence highlighted that exosomes secreted from various types of cells promote intercellular communication by transferring bioactive molecules including miRNAs and cytokines, suggesting that exosomes are essential for sustentation of tumor progression and therapeutic resistance within the tumor microenvironment. In this review, we discuss the mechanisms by which cytokines promote therapeutic resistance of BCa and suggest a potential approach for improving BCa therapeutics by inhibition of exosome function.

Clinical Utility of Determination of HER-2/neu and EGFR Fragments in Serum of Patients with Metastatic Breast Cancer

Introduction

The growth factor receptors EGFR and HER-2/neu are targets for new treatment strategies and are of potential use as prognostic and predictive factors. However, the optimal method of determination in order to obtain clinically relevant information remains a source of controversy.

Methods

HER-2/neu and EGFR expression was examined by immunohistochemistry in primary tumors of patients with breast cancer. In addition, serum was tested for the extracellular domains of HER-2/neu (HER-2/neu ECD) and EGFR (sEGFR) before initiation of therapy for metastatic disease (n=76). The course of disease from the time of metastasis with regard to these parameters was evaluated by univariate and multivariate analyses.

Results

HER-2/neu ECD levels at the time of metastatic disease were correlated with HER-2/neu expression determined by immunohistochemistry from primary tumors (p=0.001). No correlation was observed between expression of EGFR in primary tumors and sEGFR serum levels. HER-2/neu ECD and sEGFR levels at the onset of metastatic disease did not show a significant impact on overall survival.

Conclusions

Determination of HER-2/neu ECD levels in the serum measured by ELISA at the onset of metastatic disease could offer an alternative to immunohistochemistry of the primary tumor since serum levels are correlated with protein expression in primary tumors. In contrast, no such correlation was observed for EGFR.

HIF2α contributes to antiestrogen resistance via positive bilateral crosstalk with EGFR in breast cancer cells

The majority of breast cancers express estrogen receptor α (ERα), and most patients with ERα-positive breast cancer benefit from antiestrogen therapy. The ERα-modulator tamoxifen and ERα-downregulator fulvestrant are commonly employed antiestrogens. Antiestrogen resistance remains a clinical challenge, with few effective treatments available for patients with antiestrogen-resistant breast cancer. Hypoxia, which is intrinsic to most tumors, promotes aggressive disease, with the hypoxia-inducible transcription factors HIF1 and HIF2 regulating cellular responses to hypoxia. Here, we show that the ERα-expressing breast cancer cells MCF-7, CAMA-1, and T47D are less sensitive to antiestrogens when hypoxic. Furthermore, protein and mRNA levels of HIF2α/HIF2A were increased in a panel of antiestrogen-resistant cells, and antiestrogen-exposure further increased HIF2α expression. Ectopic expression of HIF2α in MCF-7 cells significantly decreased sensitivity to antiestrogens, further implicating HIF2α in antiestrogen resistance. EGFR is known to contribute to antiestrogen resistance: we further show that HIF2α drives hypoxic induction of EGFR and that EGFR induces HIF2α expression. Downregulation or inhibition of EGFR led to decreased HIF2α levels. This positive and bilateral HIF2-EGFR regulatory crosstalk promotes antiestrogen resistance and, where intrinsic hypoxic resistance exists, therapy itself may exacerbate the problem. Finally, inhibition of HIFs by FM19G11 restores antiestrogen sensitivity in resistant cells. Targeting HIF2 may be useful for counteracting antiestrogen resistance in the clinic.

Hormonal Modulation of Breast Cancer Gene Expression: Implications for Intrinsic Subtyping in Premenopausal Women

Clinics are increasingly adopting gene-expression profiling to diagnose breast cancer subtype, providing an intrinsic, molecular portrait of the tumor. For example, the PAM50-based Prosigna test quantifies expression of 50 key genes to classify breast cancer subtype, and this method of classification has been demonstrated to be superior over traditional immunohistochemical methods that detect proteins, to predict risk of disease recurrence. However, these tests were largely developed and validated using breast cancer samples from postmenopausal women. Thus, the accuracy of such tests has not been explored in the context of the hormonal fluctuations in estrogen and progesterone that occur during the menstrual cycle in premenopausal women. Concordance between traditional methods of subtyping and the new tests in premenopausal women is likely to depend on the stage of the menstrual cycle at which the tissue sample is taken and the relative effect of hormones on expression of genes versus proteins. The lack of knowledge around the effect of fluctuating estrogen and progesterone on gene expression in breast cancer patients raises serious concerns for intrinsic subtyping in premenopausal women, which comprise about 25% of breast cancer diagnoses. Further research on the impact of the menstrual cycle on intrinsic breast cancer profiling is required if premenopausal women are to benefit from the new technology of intrinsic subtyping.

ZIP restores estrogen receptor expression and response to Tamoxifen in estrogen receptor negative tumors

As a component of NURD histone deacetylase complex, ZIP serves as a tumor suppressor gene in the development of breast tumors. However, whether it takes part in chemotherapy resistance remains poorly defined. In the present study, we reported that ZIP enhanced the response to SERM chemotherapy in ER-negative cells. Overexpression of ZIP suppressed EGFR expression level and restored ERalpha protein level in cells resistant to Tamoxifen. In vivo data confirmed those in vitro findings.

Review of hormone-based treatments in postmenopausal patients with advanced breast cancer focusing on aromatase inhibitors and fulvestrant

Background

Endocrine therapy constitutes a central modality in the treatment of oestrogen receptor (ER)-positive advanced breast cancer.

Purpose

To evaluate the evidence for endocrine treatment in postmenopausal patients with advanced breast cancer focusing on the aromatase inhibitors, letrozole, anastrozole, exemestane and fulvestrant.

Methods

A review was carried out using PubMed. Randomised phase II and III trials reporting on ≥100 patients were included.

Results

35 trials met the inclusion criteria. If not used in the adjuvant setting, a non-steroid aromatase inhibitor was the optimal first-line option. In general, the efficacy of the different aromatase inhibitors and fulvestrant was similar in tamoxifen-refractory patients. A randomised phase II trial of palbociclib plus letrozole versus letrozole alone showed significantly increased progression-free survival (PFS) when compared with endocrine therapy alone in the first-line setting (20.2 vs 10.2 months). Furthermore, the addition of everolimus to exemestane in the Breast Cancer Trials of OraL EveROlimus-2 (BOLERO-2) study resulted in an extension of median PFS by 4.5 months after recurrence/progression on a non-steroid aromatase inhibitor. However, overall survival was not significantly increased.

Conclusion

Conventional treatment with an aromatase inhibitor or fulvestrant may be an adequate treatment option for most patients with hormone receptor-positive advanced breast cancer. Mammalian target of rapamycin (mTOR) inhibition and cyclin-dependent kinase 4/6 (CDK4/6) inhibition might represent substantial advances for selected patients in some specific settings. However, there is an urgent need for prospective biomarker-driven trials to identify patients for whom these treatments are cost-effective.

The Association between EGFR and cMET Expression and Phosphorylation and Its Prognostic Implication in Patients with Breast Cancer

EGFR and cMET cross-talk is involved in breast cancer (BC) progression and resistance to different targeted therapies, however little is known about the co-expression patterns of EGFR and cMET or its prognostic significance in BC. Protein levels of EGFR, cMET and their phosphorylated proteins were measured in 825 BC samples using reverse phase protein array (RPPA). Given unimodal distribution of proteins, the median was selected as a cut-off after sensitivity analyses. Kaplan-Meier survival curves were used to estimate relapse-free (RFS) and overall survival (OS). Cox-proportional hazards models were utilized to determine associations between EGFR and cMET with outcomes. Mean age was 58 years with 457 (55%) hormone receptor (HR) positive, 211 (26%) triple-negative (TN) and 148 (18%) HER2 positive tumors (HER2+). HER2+ was associated with higher EGFR expression and phosphorylation, compared to HR and TN (p<0.05). High EGFR expression was associated with higher phosphorylated-cMET (p-cMET) but not cMET (ANOVA p-cMET p < 0.001; cMET p = 0.34). The same association was found with high phosphorylated-EGFR (p-EGFR) group at Tyr992 and Tyr1068 (both p < 0.001). High expressions in either of two p-EGFRs were linked with higher cMET as well (all p<0.001). For the TN subtype, high expression in EGFR and p-EGFR at Tyr992 but not at Tyr1068 was associated with higher p-cMET (p<0.00, p = 0.012, p = 0.4 respectively). Only high expression in p-EGFR at Tyr992 was linked with higher expression of cMET (p = 0.02). In contrast, among HER2 subtype, high expression in p-EGFR at Tyr1068 but not at Tyr992 was associated with higher cMET and p-cMET (cMET p = 0.023;p-cMET p<0.001). Four subgroups of patients defined by dichotomized EGFR/p-EGFR and cMET/p-cMET level demonstrated no significant differences in survival. In multivariate analyses, neither cMET nor EGFR expression/activation was found to be an independent prognostic factor in survival outcome.

Phosphatidic Acid Increases Epidermal Growth Factor Receptor Expression by Stabilizing mRNA Decay and by Inhibiting Lysosomal and Proteasomal Degradation of the Internalized Receptor

Overexpression of epidermal growth factor receptor (EGFR) is one of the frequent mechanisms implicated in cancer progression, and so is the overexpression of the enzyme phospholipase D (PLD) and its reaction product, phosphatidic acid (PA). However, an understanding of how these signaling molecules interact at the level of gene expression is lacking. Catalytically active PLD enhanced expression of EGFR in human breast cancer cells. Overexpression of the PLD2 isoform increased EGFR mRNA and protein expression. It also negated an EGFR downregulation mediated by small interfering RNA targeting EGFR (siEGFR). Several mechanisms contributed to the alteration in EGFR expression. First was the stabilization of EGFR transcripts as PLD2 delayed mRNA decay, which prolonged their half-lives. Second, RNase enzymatic activity was inhibited by PA. Third, protein stabilization also occurred, as indicated by PLD resistance to cycloheximide-induced EGFR protein degradation. Fourth, PA inhibited lysosomal and proteasomal degradation of internalized EGFR. PLD2 and EGFR colocalized at the cell membrane, and JAK3 phosphorylation at Tyr980/Tyr981 followed receptor endocytosis. Further, the presence of PLD2 increased stabilization of intracellular EGFR in large recycling vesicles at ∼15 min of EGF stimulation. Thus, PLD2-mediated production of PA contributed to the control of EGFR exposure to ligand through a multipronged transcriptional and posttranscriptional program during the out-of-control accumulation of EGFR signaling in cancer cells.

ARF1 regulates adhesion of MDA-MB-231 invasive breast cancer cells through formation of focal adhesions

Adhesion complex formation and disassembly is crucial for maintaining efficient cell movement. During migration, several proteins act in concert to promote remodeling of the actin cytoskeleton and we have previously shown that in highly invasive breast cancer cells, this process is regulated by small GTP-binding proteins of the ADP-ribosylation factor (ARF) family. These are overexpressed and highly activated in these cells. Here, we report that one mechanism by which ARF1 regulates migration is by controlling assembly of focal adhesions. In cells depleted of ARF1, paxillin is no longer colocalized with actin at focal adhesion sites. In addition, we demonstrate that this occurs through the ability of ARF1 to regulate the recruitment of key proteins such as paxillin, talin and FAK to ß1-integrin. Furthermore, we show that the interactions between paxillin and talin together and with FAK are significantly impaired in ARF1 knocked down cells. Our findings also indicate that ARF1 is essential for EGF-mediated phosphorylation of FAK and Src. Finally, we report that ARF1 can be found in complex with key focal adhesion proteins such as ß1-integrin, paxillin, talin and FAK. Together our findings uncover a new mechanism by which ARF1 regulates cell migration and provide this GTPase as a target for the development of new therapeutics in triple negative breast cancer.

VAV3 mediates resistance to breast cancer endocrine therapy

Introduction

Endocrine therapies targeting cell proliferation and survival mediated by estrogen receptor α (ERα) are among the most effective systemic treatments for ERα-positive breast cancer. However, most tumors initially responsive to these therapies acquire resistance through mechanisms that involve ERα transcriptional regulatory plasticity. Herein we identify VAV3 as a critical component in this process.

Methods

A cell-based chemical compound screen was carried out to identify therapeutic strategies against resistance to endocrine therapy. Binding to ERα was evaluated by molecular docking analyses, an agonist fluoligand assay and short hairpin (sh)RNA–mediated protein depletion. Microarray analyses were performed to identify altered gene expression. Western blot analysis of signaling and proliferation markers, and shRNA-mediated protein depletion in viability and clonogenic assays, were performed to delineate the role of VAV3. Genetic variation in VAV3 was assessed for association with the response to tamoxifen. Immunohistochemical analyses of VAV3 were carried out to determine its association with therapeutic response and different tumor markers. An analysis of gene expression association with drug sensitivity was carried out to identify a potential therapeutic approach based on differential VAV3 expression.

Results

The compound YC-1 was found to comparatively reduce the viability of cell models of acquired resistance. This effect was probably not due to activation of its canonical target (soluble guanylyl cyclase), but instead was likely a result of binding to ERα. VAV3 was selectively reduced upon exposure to YC-1 or ERα depletion, and, accordingly, VAV3 depletion comparatively reduced the viability of cell models of acquired resistance. In the clinical scenario, germline variation in VAV3 was associated with the response to tamoxifen in Japanese breast cancer patients (rs10494071 combined P value = 8.4 × 10⁻⁴). The allele association combined with gene expression analyses indicated that low VAV3 expression predicts better clinical outcome. Conversely, high nuclear VAV3 expression in tumor cells was associated with poorer endocrine therapy response. Based on VAV3 expression levels and the response to erlotinib in cancer cell lines, targeting EGFR signaling may be a promising therapeutic strategy.

Conclusions

This study proposes VAV3 as a biomarker and a rationale for its use as a signaling target to prevent and/or overcome resistance to endocrine therapy in breast cancer.

Apoptosis and autophagy in breast cancer cells following exemestane treatment

Aromatase inhibitors (AIs), which block the conversion of androgens to estrogens, are used for hormone-dependent breast cancer treatment. Exemestane, a steroidal that belongs to the third-generation of AIs, is a mechanism-based inhibitor that binds covalently and irreversibly, inactivating and destabilizing aromatase. Since the biological effects of exemestane in breast cancer cells are not totally understood, its effects on cell viability, cell proliferation and mechanisms of cell death were studied in an ER-positive aromatase-overexpressing breast cancer cell line (MCF-7aro). The effects of 3-methyladenine (3-MA), an inhibitor of autophagy and of ZVAD-FMK, an apoptotic inhibitor, in exemestane treated cells were also investigated. Our results indicate that exemestane induces a strong inhibition in MCF-7aro cell proliferation in a dose- and time-dependent manner, promoting a significant cell cycle arrest in G(0)/G1 or in G(2)/M phases after 3 and 6 days of treatment, respectively. This was accompanied by a decrease in cell viability due to activation of cell death by apoptosis, via mitochondrial pathway and the occurrence of autophagy. Inhibition of autophagy by the autophagic inhibitor, 3-MA, resulted in a reduction of cell viability and activation of caspases. All together the results obtained suggest that exemestane induced mitochondrial-mediated apoptosis and autophagy, which act as a pro-survival process regulating breast cancer cell apoptosis.

At the crossroads: EGFR and PTHrP signaling in cancer-mediated diseases of bone

The epidermal growth factor receptor is a well-established cancer therapeutic target due to its stimulation of proliferation, motility, and resistance to apoptosis. Recently, additional roles for the receptor have been identified in growth of metastases. Similar to development, metastatic spread requires signaling interactions between epithelial-derived tumor cells and mesenchymal derivatives of the microenvironment. This necessitates reactivation of developmental signaling molecules, including the hypercalcemia factor parathyroid hormone-related protein. This review covers the variations of epidermal growth factor receptor signaling in cancers that produce bone metastases, regulation of parathyroid hormone-related protein, and evidence that the two molecules drive cancer-mediated diseases of bone.

Targeted agents to reverse resistance to endocrine therapy in metastatic breast cancer: where are we now and where are we going?

Endocrine therapy is the most important systemic therapy for hormone receptor positive breast cancer; however, some patients with ER+ breast cancer show intrinsic resistance to endocrine therapy, whereas others develop acquired resistance. Preclinical models have shown that endocrine resistance is associated with enhanced expression of membrane growth factor pathways or activation of various intracellular pathways involved in signal transduction and cell survival. Despite encouraging preclinical data, clinical trials investigating the combination of endocrine therapy with trastuzumab or the TKIs gefitinib, erlotinib and lapatinib have yielded varied results. This may be related to some limitations in the studies conducted so far: lack of appropriate patient selection and stratification based on previous endocrine exposure and/or sensitivity; lack of identification of a molecular biomarker; lack of appropriate clinical endpoints in the trial design. More promising results come from clinical studies which have focused on novel agents such as the mTOR inhibitor everolimus. The two randomized trials (BOLERO-2 and TAMRAD) evaluating everolimus±endocrine therapy in a selected subgroup of HR-positive metastatic breast cancer patients have demonstrated a significant improvement in progression free survival for the combination compared to the endocrine therapy alone. The data reported so far show that the combination of target agents with endocrine therapy is effective in overcoming acquired resistance in patients with hormone receptor positive metastatic breast cancer. However, this therapeutic strategy is not yet a standard treatment for this patients. Application of more rigorous trial design, tumor and patient selection criteria will be important to better understand the complexity of endocrine resistance.

A randomized trial of combination anastrozole plus gefitinib and of combination fulvestrant plus gefitinib in the treatment of postmenopausal women with hormone receptor positive metastatic breast cancer

EGFR signalling pathways appear involved in endocrine therapy resistance in breast cancer. This trial estimates the antitumor efficacy and toxicity of the EGFR tyrosine kinase inhibitor gefitinib in combination with anastrozole or fulvestrant in postmenopausal hormone receptor positive breast cancer. Subjects with estrogen receptor and/or PgR positive, metastatic breast cancer were randomized into this phase II study of gefitinib (initial dose was 500 mg orally daily, due to high rate of diarrhea, starting dose was reduced to 250 mg orally daily) with either anastrozole 1 mg daily or fulvestrant 250 mg every 4 weeks. The primary endpoint was clinical benefit (complete responses plus partial responses plus stable disease for 6 months or longer). 141 eligible subjects were enrolled, 72 in the anastrozole plus gefitinib arm, and 69 in the fulvestrant plus gefitinib arm. Anastrozole plus gefitinib had a clinical benefit rate of 44% [95% confidence interval (CI) 33-57%] and fulvestrant plus gefitinib 41% (95% CI 29-53%). Median progression-free survival was 5.3 months (95% CI 3.1-10.4) versus 5.2 months (95% CI 2.9-8.2) for anastrozole plus gefitinib versus fulvestrant plus gefitinib, respectively. Median survival was 30.3 months (95% CI 21.2-38.9+) versus 23.9 months (95% CI 15.4-33.5) for anastrozole plus gefitinib versus fulvestrant plus gefitinib, respectively. In general, the toxicity is greater than expected for single agent endocrine therapy alone. Anastrozole plus gefitinib and fulvestrant plus gefitinib have similar clinical benefit rates in the treatment of estrogen and/or PgR positive metastatic breast cancer, and the rates of response are not clearly superior to gefitinib or endocrine therapy alone. Further studies of EGFR inhibition plus endocrine therapy do not appear warranted, but if performed should include attempts to identify biomarkers predictive of antitumor activity.

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.

Quantitative assays for the measurement of HER1-HER2 heterodimerization and phosphorylation in cell lines and breast tumors: applications for diagnostics and targeted drug mechanism of action

Introduction

Ligand-bound and phosphorylated ErbB/HER heterodimers are potent signaling forms of this receptor family, and quantitative measurements of these active receptors may be predictive of patient response to targeted therapies. Using VeraTag™ technology, we developed and characterized quantitative assays measuring epidermal growth factor (EGF)-dependent increases in activated HER receptors in tumor cell line lysates and formalin-fixed, paraffin-embedded (FFPE) tumor sections. We demonstrated the ability of the assays to quantitatively measure changes in activated HER1 and HER2 receptor levels in cell lines following treatment with 2C4, erlotinib, and lapatinib. We utilized these assays to determine the prevalence and distribution of activated HER1, HER2, and HER1-HER2 heterodimers in 43 HER2-positive breast tumors.

Methods

Assays for activated HER1 and HER2 receptors in FFPE and cell lysate formats were developed using VeraTag™ technology, which requires the proximity of an antibody pair for light-dependent release of a fluorescently labeled tag, followed by capillary electrophoresis-based quantitation.

Results

Ligand-dependent and independent HER1-HER2 heterodimer levels measured by lysate and FFPE VeraTag™ assays trended with HER1 and HER2 expression levels in tumor cell lines, which was confirmed by co-immunoprecipitation. The formation of EGF-dependent HER1-HER2 heterodimers were inhibited by the HER2-targeted monoclonal antibody 2C4 and stabilized by the HER1 tyrosine kinase inhibitor (TKI) erlotinib. EGF-dependent HER1 and HER2 phosphorylation was inhibited by lapatinib and erlotinib. Further, we observed that dominant receptor signaling patterns may switch between HER1-HER1 and HER1-HER2, depending on drug mechanism of action and relative levels of HER receptors. In FFPE breast tumors that expressed both HER1 and HER2, HER1-HER2 heterodimers were detected in 25 to 50% of tumors, depending on detection method. The levels of activated phospho-HER1-HER2 heterodimers correlated with HER1 or HER2 levels in an analysis of 43 HER2-positive breast tumors.

Conclusions

VeraTag™ lysate assays can be used as a tool for understanding the mechanism of action of targeted HER-family inhibitors in the preclinical setting, while VeraTag™ FFPE assays of activated HER receptors combined with total HER2 measurements (HERmark^®) in tumor samples may provide a more accurate prediction of clinical response to both HER1 and HER2 targeted therapies.

Fulvestrant-induced expression of ErbB3 and ErbB4 receptors sensitizes oestrogen receptor-positive breast cancer cells to heregulin β1

Introduction

We have previously reported that induction of epidermal growth factor receptor and ErbB2 in response to antihormonal agents may provide an early mechanism to allow breast cancer cells to evade the growth-inhibitory action of such therapies and ultimately drive resistant cell growth. More recently, the other two members of the ErbB receptor family, ErbB3 and ErbB4, have been implicated in antihormone resistance in breast cancer. In the present study, we have investigated whether induction of ErbB3 and/or ErbB4 may provide an alternative resistance mechanism to antihormonal action in a panel of four oestrogen receptor (ER)-positive breast cancer cell lines.

Methods

MCF-7, T47D, BT474 and MDAMB361 cell lines were exposed to fulvestrant (100 nM) for seven days, and effects on ErbB3/4 expression and signalling, as well as on cell growth, were assessed. Effects of heregulin β1 (HRGβ1) were also examined in the absence and presence of fulvestrant to determine the impact of ER blockade on the capacity of this ErbB3/4 ligand to promote signalling and cell proliferation.

Results

Fulvestrant potently reduced ER expression and transcriptional activity and significantly inhibited growth in MCF-7, T47D, BT474 and MDAMB361 cells. However, alongside this inhibitory activity, fulvestrant also consistently induced protein expression and activity of ErbB3 in MCF-7 and T47D cells and ErbB4 in BT474 and MDAMB361 cell lines. Consequently, fulvestrant treatment sensitised all cell lines to the actions of the ErbB3/4 ligand HRGβ1 with enhanced ErbB3/4-driven signalling activity, reexpression of cyclin D1 and significant increases in cell proliferation being observed when compared to untreated cells. Indeed, in T47D and MDAMB361 HRGβ1 was converted from a ligand having negligible or suppressive growth activity into one that potently promoted cell proliferation. Consequently, fulvestrant-mediated growth inhibition was completely overridden by HRGβ1 in all four cell lines.

Conclusions

These findings suggest that although antihormones such as fulvestrant may have potent acute growth-inhibitory activity in ER-positive breast cancer cells, their ability to induce and sensitise cells to growth factors may serve to reduce and ultimately limit their inhibitory activity.

Vaccination with human anti-trastuzumab anti-idiotype scFv reverses HER2 immunological tolerance and induces tumor immunity in MMTV.f.huHER2(Fo5) mice

Introduction

Novel adjuvant therapies are needed to prevent metastatic relapses in HER2-expressing breast cancer. Here, we tested whether trastuzumab-selected single-chain Fv (scFv) could be used to develop an anti-idiotype-based vaccine to inhibit growth of HER2-positive tumor cells in vitro and in vivo through induction of long-lasting HER-specific immunity.

Methods

BALB/c mice were immunized with anti-trastuzumab anti-idiotype (anti-Id) scFv (scFv40 and scFv69), which mimic human HER2. Their sera were assessed for the presence of HER2-specific Ab1' antibodies and for their ability to reduce viability of SK-OV-3 cells, a HER2-positive cancer cell line, in nude mice. MMTV.f.huHER2(Fo5) transgenic mice were immunized with scFv40 and scFv69 and, then, growth inhibition of spontaneous HER2-positive mammary tumors, humoral response, antibody isotype as well as splenocyte secretion of IL2 and IFN-γ were evaluated.

Results

Adoptively-transferred sera from BALB/c mice immunized with scFv40 and scFv69 contain anti-HER2 Ab1' antibodies that can efficiently inhibit growth of SK-OV-3 cell tumors in nude mice. Similarly, prophylactic vaccination with anti-Id scFv69 fully protects virgin or primiparous FVB-MMTV.f.huHER2(Fo5) females from developing spontaneous mammary tumors. Moreover, such vaccination elicits an anti-HER2 Ab1' immune response together with a scFv69-specific Th1 response with IL2 and IFN-γ cytokine secretion.

Conclusions

Anti-trastuzumab anti-Id scFv69, used as a therapeutic or prophylactic vaccine, protects mice from developing HER2-positive mammary tumors by inducing both anti-HER2 Ab1' antibody production and an anti-HER2 Th2-dependent immune response. These results suggest that scFv69 could be used as an anti-Id-based vaccine for adjuvant therapy of patients with HER2-positive tumors to reverse immunological tolerance to HER2.

Bcl-2 expression and triple negative profile in breast carcinoma

Many biomarkers for breast cancer prognosis have been proposed during the last two decades, among which HER2 and oestrogen receptors are of common use in routine clinical practice. However, in recent years, BCL2 has been recognized as an important prognostic parameter in human breast cancer, although its clinical utility is well established. The aim of this study was to examine the protein expression patterns of BCL2, HER2, oestrogen (ER) and progesterone receptors (PR) and to evaluate their correlation with survival and other prognostic parameters such as tumour size, histological grade and metastasis. We used a retrospective study including 84 Tunisian women with breast cancer. Immunohistochemistry was used to measure protein expression levels of several biomarkers. Association with conventional biopathological factors was analysed by SPSS (version13). The expression rates of BCL2, HER2, ER and PR were, respectively, 69, 62, 58.3 and 51.2%. In univariate analyses, BCL2 was highly correlated with both PR (P < 0.001) and ER (P = 0.006) and also with HER2 expression (P = 0.001). The triple negative profile showed a significant association with SBR (P = 0.016) and BCL2 expression (P = 0.02). In multivariate analyses, a significant association was maintained between BCL2 and both PR and ER (P = 0.02 and P = 0.004, respectively). Survival analysis showed that BCL2 expression was positively correlated with patients survival (P = 0.032). A Bayesian network analysis of all the variables confirmed the high value of BCL2 expression as a predictor of survival. As conclusion, BCL2 expression seems to be a very useful factor that should be in combination with HER2 and ER in breast cancer prognosis.

Inferring predominant pathways in cellular models of breast cancer using limited sample proteomic profiling

Background

Molecularly targeted drugs inhibit aberrant signaling within oncogenic pathways. Identifying the predominant pathways at work within a tumor is a key step towards tailoring therapies to the patient. Clinical samples pose significant challenges for proteomic profiling, an attractive approach for identifying predominant pathways. The objective of this study was to determine if information obtained from a limited sample (i.e., a single gel replicate) can provide insight into the predominant pathways in two well-characterized breast cancer models.

Methods

A comparative proteomic analysis of total cell lysates was obtained from two cellular models of breast cancer, BT474 (HER2+/ER+) and SKBR3 (HER2+/ER-), using two-dimensional electrophoresis and MALDI-TOF mass spectrometry. Protein interaction networks and canonical pathways were extracted from the Ingenuity Pathway Knowledgebase (IPK) based on association with the observed pattern of differentially expressed proteins.

Results

Of the 304 spots that were picked, 167 protein spots were identified. A threshold of 1.5-fold was used to select 62 proteins used in the analysis. IPK analysis suggested that metabolic pathways were highly associated with protein expression in SKBR3 cells while cell motility pathways were highly associated with BT474 cells. Inferred protein networks were confirmed by observing an up-regulation of IGF-1R and profilin in BT474 and up-regulation of Ras and enolase in SKBR3 using western blot.

Conclusion

When interpreted in the context of prior information, our results suggest that the overall patterns of differential protein expression obtained from limited samples can still aid in clinical decision making by providing an estimate of the predominant pathways that underpin cellular phenotype.

The effects of gefitinib in tamoxifen-resistant and hormone-insensitive breast cancer: a phase II study

Estrogen receptor (ER)-positive acquired tamoxifen-resistant (TAM-R) MCF-7 breast cancer cell lines exhibit epidermal growth factor receptor (EGFR) expression/signaling and are growth-inhibited by gefitinib (IRESSA). We examined the effect of gefitinib on ER-positive TAM-R and ER-negative hormone-insensitive breast cancer in a Phase II study. Fifty-four patients with breast cancer [ER-positive/acquired TAM-R (n = 28); ER-negative (n = 26)] received oral gefitinib 500 mg/day. Tumor biopsies were taken pre- (n = 28) and 8 weeks post-treatment (n = 14 matched samples). Gefitinib was well tolerated and the clinical benefit rate (objective response or stable disease >24 weeks) was 33.3% overall (n = 18/54), and 53.6 and 11.5% in ER-positive/TAM-R and ER-negative patients, respectively. Pretreatment ER and progesterone receptor-positivity were associated with response (p < 0.001 and 0.016, respectively) and longer progression-free survival (PFS; p= 0.001 and 0.013, respectively). All patients expressed EGFR, but high pretreatment levels predicted poorer outcome (p = 0.005) and shorter PFS (p = 0.012) with gefitinib. In patients with clinical benefit, reduced Ki67 staining during treatment (p = 0.024) was commonly observed, and those with >10% decline in EGFR phosphorylation demonstrated parallel decreases in ERK1/2 MAPK phosphorylation. Acquired tamoxifen resistance appears in part mediated through EGFR signaling and can be blocked with gefitinib.

Selective regain of egfr gene copies in CD44+/CD24-/low breast cancer cellular model MDA-MB-468

Background

Increased transcription of oncogenes like the epidermal growth factor receptor (EGFR) is frequently caused by amplification of the whole gene or at least of regulatory sequences. Aim of this study was to pinpoint mechanistic parameters occurring during egfr copy number gains leading to a stable EGFR overexpression and high sensitivity to extracellular signalling. A deeper understanding of those marker events might improve early diagnosis of cancer in suspect lesions, early detection of cancer progression and the prediction of egfr targeted therapies.

Methods

The basal-like/stemness type breast cancer cell line subpopulation MDA-MB-468 CD44^high/CD24^-/low, carrying high egfr amplifications, was chosen as a model system in this study. Subclones of the heterogeneous cell line expressing low and high EGF receptor densities were isolated by cell sorting. Genomic profiling was carried out for these by means of SNP array profiling, qPCR and FISH. Cell cycle analysis was performed using the BrdU quenching technique.

Results

Low and high EGFR expressing MDA-MB-468 CD44⁺/CD24^-/low subpopulations separated by cell sorting showed intermediate and high copy numbers of egfr, respectively. However, during cell culture an increase solely for egfr gene copy numbers in the intermediate subpopulation occurred. This shift was based on the formation of new cells which regained egfr gene copies. By two parametric cell cycle analysis clonal effects mediated through growth advantage of cells bearing higher egfr gene copy numbers could most likely be excluded for being the driving force. Subsequently, the detection of a fragile site distal to the egfr gene, sustaining uncapped telomere-less chromosomal ends, the ladder-like structure of the intrachromosomal egfr amplification and a broader range of egfr copy numbers support the assumption that dynamic chromosomal rearrangements, like breakage-fusion-bridge-cycles other than proliferation drive the gain of egfr copies.

Conclusion

Progressive genome modulation in the CD44⁺/CD24^-/low subpopulation of the breast cancer cell line MDA-MB-468 leads to different coexisting subclones. In isolated low-copy cells asymmetric chromosomal segregation leads to new cells with regained solely egfr gene copies. Furthermore, egfr regain resulted in enhanced signal transduction of the MAP-kinase and PI3-kinase pathway. We show here for the first time a dynamic copy number regain in basal-like/stemness cell type breast cancer subpopulations which might explain genetic heterogeneity. Moreover, this process might also be involved in adaptive growth factor receptor intracellular signaling which support survival and migration during cancer development and progression.

Epidermal growth factor receptor expression in breast cancer association with biologic phenotype and clinical outcomes

BACKGROUND

Epidermal growth factor receptor (EGFR) expression is associated with aggressive phenotypes in preclinical breast cancer models, but in clinical studies, EGFR has been inconsistently linked to poor outcome. We hypothesized that EGFR expression in human breast tumors, when centrally and uniformly assessed, is associated with an aggressive phenotype and resistance to systemic therapy.

METHODS

In a database of 47,286 patients with breast cancer, EGFR status was known on 2567 tumors. EGFR levels were measured centrally by ligand binding assay, and tumors with > or =10 fmol/mg were prospectively deemed positive. Clinical and biological features of EGFR-positive and EGFR-negative tumors were compared. Clinical outcomes were assessed by systemic therapy status.

RESULTS

Of 2567 tumors, 475 (18%) were EGFR positive. EGFR-positive tumors were more common in younger and in black women, were larger, had a higher S-phase fraction, and were more likely to be aneuploid. EGFR-positive tumors were more likely to be HER2-positive (26% vs 16%, P < .0001), but less likely to be estrogen receptor-positive (60% vs 88%, P < .0001) or progesterone receptor-positive (26% vs 65%, P < .0001). In multivariate analyses, EGFR expression independently correlated with worse disease-free survival (hazard ratio [HR] = 1.66; 95% confidence interval [CI], 1.4-2.41, P = .007) and overall survival (HR = 1.98, 95% CI, 1.36-2.88, P = .0004) in treated patients, but not in untreated patients.

CONCLUSIONS

EGFR expression is more common in breast tumors in younger and black women. It is associated with lower hormone receptor levels, higher proliferation, genomic instability, and HER2 overexpression. It is correlated with higher risk of relapse in patients receiving adjuvant treatment. Blocking EGFR may improve outcome in selected patients.

EGFRvIII-induced estrogen-independence, tamoxifen-resistance phenotype correlates with PgR expression and modulation of apoptotic molecules in breast cancer

The tumor-specific, ligand-independent, constitutively active epidermal growth factor receptor (EGFR) variant, EGFRvIII, remains understudied in breast cancer. Here, we report that expression of EGFRvIII in the ErbB-2-overexpressing, estrogen-dependent MDA-MB-361 breast cancer cell line resulted in significant estrogen-independent tumor growth in ovariectomized, athymic nude mice in comparison to MDA-MB-361/wt cells. MDA-MB-361/vIII breast cancer cells maintained estrogen-induced tumor growth, but were tamoxifen-resistant in the presence of estrogen, while MDA-MB-361/wt cells had a significant reduction in tumor growth in the presence of estrogen and tamoxifen. Tamoxifen alone did not have a significant effect on EGFRvIII-mediated estrogen-independent tumor growth. Constitutive signaling from the EGFRvIII receptor resulted in an increased activation of both the Akt and MAPK pathways. Compared to estrogen-dependent, tamoxifen-sensitive MCF-7/vIII breast cancer cells, which had unchanged levels of ERalpha, but an increase in progesterone receptor (PgR) in comparison to MCF-7/wt cells, MDA-MB-361/vIII cells had a reduction in ERalpha expression as well as a more pronounced reduction in PgR compared with MDA-MB-361/wt cells. EGFRvIII expression was also significantly associated with an absence of PgR protein in invasive human breast cancer specimens. Alterations of proapoptotic proteins and antiapoptotic proteins were observed in EGFRvIII transfectants. In conclusion, constitutive signaling through EGFRvIII and its downstream effector proteins crosstalks with the ERalpha pathway, resulting in loss of PgR expression and alterations in the apoptotic pathway, which may result in the estrogen-independent, tamoxifen-resistant phenotype conferred to EGFRvIII-expressing breast cancer cells.

Inhibition of histone deacetylase suppresses EGF signaling pathways by destabilizing EGFR mRNA in ER-negative human breast cancer cells

Estrogen receptor alpha (ER)-negative human breast cancer cells frequently overexpress epidermal growth factor receptor (EGFR) and respond poorly to endocrine therapies. Our previous studies demonstrate that histone deacetylation plays a key role in ER gene silencing, and ER expression can be restored with histone deacetylase (HDAC) inhibitors in ER-negative human breast cancer cells. Whether inhibition of HDAC also alters epidermal growth factor (EGF) signaling pathways is not defined. Here we present evidence that reexpression of ER protein by a clinically available HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA or vorinostat), is coupled with loss of EGFR in ER-negative human breast cancer cells. Consistent with this observation, MDA-MB-231 cells, which are ER-negative and overexpress EGFR, that are engineered to express ER show a decrease in EGFR protein expression. Down-regulation of EGFR by SAHA results from attenuation of its mRNA stability. We also confirm that new protein synthesis is required for maintaining EGFR mRNA stability. Further experiments indicate that a decrease in EGFR abolished EGF-initiated signaling pathways including phosphorylated PAK1, p38MAPK and AKT. Thus, SAHA may not only reactivate silenced ER, but also simultaneously deplete EGFR expression. These data suggest that inhibition of HDAC is a promising epigenetic therapy for ER-negative human breast cancer.

E-cadherin mediates the aggregation of breast cancer cells induced by tamoxifen and epidermal growth factor

In the present study, we evaluated the ability of 4-hydroxytamoxifen (OHT) and epidermal growth factor (EGF) to regulate homotypic adhesion in MCF7 breast cancer cells. Our results demonstrate that OHT and EGF activate the E-cadherin promoter, increase E-cadherin mRNA and protein expression and enhance homotypic aggregation of MCF7 cells. Interestingly, an ERalpha and EGFR cross-talk is involved in the E-cadherin expression by OHT and EGF, as demonstrated by knocking down either receptor. On the basis of our findings, the well-established cross-talk between ERalpha and EGFR could be extended to the modulation of E-cadherin expression by OHT and EGF. Thus, the potential ability of tamoxifen to induce cell-cell aggregation may contribute to the biologic response of pharmacologic intervention in patients with breast cancer.

ADP-ribosylation factor 1 controls the activation of the phosphatidylinositol 3-kinase pathway to regulate epidermal growth factor-dependent growth and migration of breast cancer cells

Activation of intracellular signaling pathways by growth factors is one of the major causes of cancer development and progression. Recent studies have demonstrated that monomeric G proteins of the Ras family are key regulators of cell proliferation, migration, and invasion. Using an invasive breast cancer cell lines, we demonstrate that the ADP-ribosylation factor 1 (ARF1), a small GTPase classically associated with the Golgi, is an important regulator of the biological effects induced by epidermal growth factor. Here, we show that this ARF isoform is activated following epidermal growth factor stimulation and that, in MDA-MB-231 cells, ARF1 is found in dynamic plasma membrane ruffles. Inhibition of endogenous ARF1 expression results in the inhibition of breast cancer cell migration and proliferation. The underlying mechanism involves the activation of the phosphatidylinositol 3-kinase pathway. Our data demonstrate that depletion of ARF1 markedly impairs the recruitment of the phosphatidylinositol 3-kinase catalytic subunit (p110alpha) to the plasma membrane, and the association of the regulatory subunit (p85alpha) to the activated receptor. These results uncover a novel molecular mechanism by which ARF1 regulates breast cancer cell growth and invasion during cancer progression.

Development of resistance to targeted therapies transforms the clinically associated molecular profile subtype of breast tumor xenografts

The effectiveness of therapies targeting specific pathways in breast cancer, such as the estrogen receptor or HER2, is limited because many tumors manifest resistance, either de novo or acquired, during the course of treatment. To investigate molecular mechanisms of resistance, we used two xenograft models of estrogen receptor-positive (ER+) breast cancer, one with and one without HER2 overexpression (MCF7/HER2-18 and MCF7 wt, respectively). Mice with established tumors were assigned to the following treatment groups: estrogen supplementation (E2), estrogen deprivation (ED), ED plus tamoxifen (Tam), all with or without the epidermal growth factor receptor tyrosine kinase inhibitor gefitinib (G). Another group received ED plus the antiestrogen fulvestrant (MCF7 wt only). Tumors with acquired or de novo resistance to these endocrine therapies were profiled for gene expression and compared with tumors in the E2 control group. One class of genes underexpressed in endocrine-resistant tumors (relative to E2-treated tumors) were estrogen inducible in vitro and associated with ER+ human breast cancers (luminal subtype). Another class of genes overexpressed in tumors with acquired resistance in both models represented transcriptional targets of HER2 signaling and was associated with ER-/HER2+ human cancers (ERBB2+ subtype). A third class of genes overexpressed in MCF7/HER2-18 tumors exhibiting de novo resistance to tamoxifen was associated with ER+ human cancers but not with estrogen-regulated genes. Thus, in response to various endocrine therapy regimens, these xenograft breast tumors shut down classic estrogen signaling and activate alternative pathways such as HER2 that contribute to treatment resistance. Over time, the molecular phenotype of breast cancer can change.

Expression of EGFR and c-kit is associated with the basal-like phenotype in breast carcinomas of African women

Epidermal growth factor receptor (EGFR) and c-kit are tyrosine kinase growth factor receptors which are frequently expressed in basal-like breast carcinomas, and tyrosine kinase inhibition is now a promising strategy in treatment of breast cancer. The aim of this study was to evaluate the expression of EGFR and c-kit in breast cancer with special focus on the basal-like phenotype (BLP) and other prognostic factors in an African population. We analyzed 65 archival tissues immunohistologically. EGFR and/or c-kit were expressed in 55% of basal-like tumors. Expression of EGFR and/or c-kit was strongly associated with high histologic grade (P=0.001), high nuclear grade (P=0.017), high mitotic counts (P=0.002), ER negativity (P=0.003), PR negativity (P=0.007), and HER2 negativity (P=0.014). EGFR and/or c-kit positive tumors were more likely to express the BLP (OR 9.1, CI 2.6-32.0, P<0.0005) than the negative tumors. In conclusion, there is a high expression of EGFR and/or c-kit in basal-like breast carcinoma in this series from Uganda and their expression is associated with features of poor prognosis. More studies are required to assess the clinical significance of EGFR and c-kit in breast cancer patients in Uganda.

New steroidal aromatase inhibitors: suppression of estrogen-dependent breast cancer cell proliferation and induction of cell death

BACKGROUND

Aromatase, the cytochrome P-450 enzyme (CYP19) responsible for estrogen biosynthesis, is an important target for the treatment of estrogen-dependent breast cancer. In fact, the use of synthetic aromatase inhibitors (AI), which induce suppression of estrogen synthesis, has shown to be an effective alternative to the classical tamoxifen for the treatment of postmenopausal patients with ER-positive breast cancer. New AIs obtained, in our laboratory, by modification of the A and D-rings of the natural substrate of aromatase, compounds 3a and 4a, showed previously to efficiently suppress aromatase activity in placental microsomes. In the present study we have investigated the effects of these compounds on cell proliferation, cell cycle progression and induction of cell death using the estrogen-dependent human breast cancer cell line stably transfected with the aromatase gene, MCF-7 aro cells.

RESULTS

The new steroids inhibit hormone-dependent proliferation of MCF-7aro cells in a time and dose-dependent manner, causing cell cycle arrest in G0/G1 phase and inducing cell death with features of apoptosis and autophagic cell death.

CONCLUSION

Our in vitro studies showed that the two steroidal AIs, 3a and 4a, are potent inhibitors of breast cancer cell proliferation. Moreover, it was also shown that the antiproliferative effects of these two steroids on MCF-7aro cells are mediated by disrupting cell cycle progression, through cell cycle arrest in G0/G1 phase and induction of cell death, being the dominant mechanism autophagic cell death. Our results are important for the elucidation of the cellular effects of steroidal AIs on breast cancer.

Expression of the epidermal growth factor receptor (EGFR) and the phosphorylated EGFR in invasive breast carcinomas

Introduction

Epidermal growth factor receptor (EGFR) is involved in regulating cell growth in breast carcinomas. Its activated form, phosphorylated EGFR (pEGFR), is correlated with poor prognosis in lung cancer, but it has not yet been fully investigated in breast cancer. The aim of this study was to investigate the expressions of EGFR and pEGFR and their correlation with overall and disease-free survival, clinicopathological parameters and biological markers of invasion and angiogenesis (phosphorylated Akt [pAkt], urokinase plasminogen activator receptor [uPAR], matrix metalloproteinase [MMP]-14, vascular endothelial growth factor receptor [VEGFR]-1/Flt-1).

Methods

A three-step immunohistochemical method was applied to paraffin-embedded sections from 154 patients with invasive breast carcinoma in order to detect expressions of the proteins EGFR, pEGFR, oestrogen receptor, progesterone receptor, c-erbB-2, pAkt, VEGFR-1/Flt-1, MMP-14 and uPAR. The results were evaluated statistically using the χ² test. Overall and disease-free survival distribution curves were assessed using the Kaplan-Meier test and log-rank statistics, followed by Cox proportional hazards regression model.

Results

EGFR and pEGFR proteins were immunodetected in the membrane of the malignant cells (11.3% and 35.7%, respectively). EGFR expression was positively correlated with nuclear grade (P = 0.001) and negatively correlated with the hormonal receptor oestrogen receptor (P = 0.005). pEGFR was positively related to the Akt pathway (P = 0.008) and appeared to participate in invasion and metastasis (uPAR, P = 0.049; MMP-14, P = 0.025; VEGFR-1/Flt-1, P = 0.016). Univariate analysis showed that the EGFR/pEGFR phenotype was associated with poor overall survival (P = 0.019), a finding further supported by multivariate analysis (P = 0.013).

Conclusion

These data provide evidence that pEGFR expression is related to angiogenesis (via VEGFR-1/Flt-1, MMP-14 and pAkt pathways) and invasiveness (via uPAR, MMP-14 and pAkt pathways) and that the EGFR/pEGFR phenotype is associated with poor patient survival in invasive breast cancer.

The functional implications of Akt activity and TGF-beta signaling in tamoxifen-resistant breast cancer

Development of acquired resistance to tamoxifen is a major clinical problem during endocrine treatment in estrogen receptor positive breast cancer. Transforming growth factor-beta1 (TGF-beta) has been implicated in tamoxifen-induced cellular signaling in breast cancer, and increased Akt activation is associated with tamoxifen-resistant cell types. We hypothesized that the relationship between TGF-beta and Akt signaling may be involved in the development and progression of tamoxifen resistance. Tamoxifen-resistant (Tam-R) cells were established from parental MCF-7 cells by continuously exposing them to 4-hydroxytamoxifen (4-OHT). Tam-R cells were associated with a decrease in TGF-beta1 secretion, TGF-beta-mediated transcriptional response, and growth inhibitory effects of 4-OHT. Tam-R cells expressed significantly higher levels of phosphorylated Akt and lower levels of phosphorylated Smad 3 in both the absence and presence of 4-OHT when compared to MCF-7 cells treated with 4-OHT. Ectopic expression of constitutively active Akt (Myc-Akt(Myr)) rendered MCF-7 cells resistant to activation by TGF-beta and the growth inhibitory effects of 4-OHT, while over-expression of kinase-dead Akt (Myc-Akt(K179M)) or LY294002 treatment of Tam-R cells enhanced TGF-beta activation and blocked cell growth. These results suggest that suppression of TGF-beta signaling by activated Akt is correlated with the development of tamoxifen resistance in breast cancer.

17beta-estradiol promotes breast cancer cell proliferation-inducing stromal cell-derived factor-1-mediated epidermal growth factor receptor transactivation: reversal by gefitinib pretreatment

The coordinated activity of estrogens and epidermal growth factor receptor (EGFR) family agonists represents the main determinant of breast cancer cell proliferation. Stromal cell-derived factor-1 (SDF-1) enhances extracellular signal-regulated kinases 1 and 2 (ERK1/2) activity via the transactivation of EGFR and 17beta-estradiol (E2) induces SDF-1 production to exert autocrine proliferative effects. On this basis, we evaluated whether the inhibition of the tyrosine kinase (TK) activity of EGFR may control different mitogenic stimuli in breast tumors using the EGFR-TK inhibitor gefitinib to antagonize the proliferation induced by E2 in T47D human breast cancer cells. EGF, E2, and SDF-1 induced a dose-dependent T47D cell proliferation, that being nonadditive suggested the activation of common intracellular pathways. Gefitinib treatment inhibited not only the EGF-dependent proliferation and ERK1/2 activation but also the effects of SDF-1 and E2, suggesting that these activities were mediated by EGFR transactivation. Indeed, both SDF-1 and E2 caused EGFR tyrosine phosphorylation. The molecular link between E2 and SDF-1 proliferative effects was identified because 1,1'-(1,4-phenylenebis(methylene))-bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (AMD3100), a CXCR4 antagonist, inhibited SDF-1- and E2-dependent proliferation and EGFR and ERK1/2 phosphorylation. EGFR transactivation was dependent on c-Src activation. E2 treatment caused a powerful SDF-1 release from T47D cells. Finally, in SKBR3, E2-resistant cells, EGFR was constitutively activated, and AMD3100 reduced EGFR phosphorylation and cell proliferation, whereas HER2-neu was transactivated by SDF-1 in SKBR3 but not in T47D cells. In conclusion, we show that activation of CXCR4 transduces proliferative signals from the E2 receptor to EGFR, whose inhibition is able to revert breast cancer cell proliferation induced by multiple receptor activation.

The emerging role of the LIV-1 subfamily of zinc transporters in breast cancer

Zinc transporter LIV-1 (SLC39A6) is estrogen regulated and present in increased amounts in estrogen receptor-positive breast cancer as well as in tumors that spread to the lymph nodes. The LIV-1 subfamily of ZIP zinc transporters consists of nine human sequences that share considerable homology across transmembrane domains. Many of these sequences have been shown to transport zinc and/or other ions across cell membranes. Increasingly, studies have implicated members of the LIV-1 transporter subfamily in a variety of diseases. We review these studies and report our own investigations of the role in breast cancer of the nine LIV-1 zinc transporters. We have documented the response of these transporters to estrogen and antiestrogens, and also their presence in our models of resistance to antiestrogens. Resistance to antiestrogen drugs such as tamoxifen and fulvestrant often occurs in advanced breast cancer. In these models we observed differential expression of individual LIV-1 family members, which may be related to their observed variable tissue expression. We were unable detect ZIP4, which is known to be expressed in the intestine. HKE4/SLC39A7 had elevated expression in both antiestrogen-resistant cell lines, and ZIP8 had elevated expression in fulvestrant-resistant cells. In addition, we investigated the expression of the nine LIV-1 family members in a clinical breast cancer series. Although a number of different LIV-1 family members showed some association with growth factor receptors, LIV-1 was solely associated with estrogen receptor and a variety of growth factors commonly associated with clinical breast cancer. HKE4, however, did show an association with the marker of cell proliferation Ki67 the spread of breast cancer to lymph nodes.

Prognostic significance of overexpression and phosphorylation of epidermal growth factor receptor (EGFR) and the presence of truncated EGFRvIII in locoregionally advanced breast cancer

PURPOSE

The prognostic value of the epidermal growth factor receptor (EGFR) in breast cancer and more specifically, in patients with locoregionally advanced disease, is still undefined. We hypothesized that EGFR status plays a major prognostic role in this setting, through expression, activation, or the presence of its mutated variant EGFRvIII.

PATIENTS AND METHODS

We reviewed tumor samples of 225 patients treated uniformly in prospective trials of high-dose chemotherapy for four to nine positive axillary nodes, > or = 10 positive nodes, or inflammatory carcinoma, and observed for a median of 9 years (range, 3 to 13 years). We analyzed the effect on outcome of expression of EGFR, phosphorylated EGFR (phospho-EGFR), and EGFRvIII, as studied by immunohistochemistry.

RESULTS

EGFR expression, phospho-EGFR, and mutated EGFRvIII were detected in 43%, 54%, and 4% of the patients, respectively. EGFR expression correlated with negative hormone receptor status, and was associated with significantly worse relapse-free survival (59% v 79%; P < .001) and overall survival (61% v 81%; P = .001) than no expression. There was no association of phospho-EGFR or EGFRvIII with outcome. Multivariate models confirmed the prognostic effect of EGFR independent of other known prognostic variables in this population. The prognostic value of EGFR was most prominent in the human epidermal growth factor receptor 2 (HER-2) -positive and the estrogen receptor/progesterone receptor-negative subgroups.

CONCLUSION

EGFR expression, but not phospho-EGFR or EGFRvIII expression, is an independent adverse prognostic factor in patients with high-risk primary breast cancer, particularly when it is coexpressed with HER-2. Our results suggest the potential benefit of dual EGFR/HER-2 receptor targeting in this setting.

Quantitative measurement of epidermal growth factor receptor is a negative predictive factor for tamoxifen response in hormone receptor positive premenopausal breast cancer

PURPOSE

Although there is evidence for interaction between epidermal growth factor receptor (EGFR) and estrogen receptor (ER), it is still not clear how this affects response to endocrine therapies like tamoxifen. Here we assess the relationship between EGFR expression and tamoxifen response, with a new quantitative technology.

PATIENTS AND METHODS

A tissue microarray was constructed from breast cancer from a cohort of 564 patients enrolled in a randomized clinical trial for adjuvant tamoxifen treatment in early breast cancer, with a median follow-up of 14 years. EGFR expression was measured using automated quantitative analysis, a fluorescence-based method for quantitative analysis of in situ protein expression.

RESULTS

In ER-positive patients, tamoxifen-treated patients with low EGFR expression (n = 113) showed a significant effect by 2 years of adjuvant tamoxifen (P = .01), in contrast to no treatment effect in the EGFR-high group (n = 73, P = .69). The untreated group showed 49% v 57% 10-year recurrence-free survival for EGFR low versus high (P = .466) in the corresponding group of ER-positive patients. A significant beneficial effect of tamoxifen treatment was seen in the EGFR-low group (hazard ratio [HR] = 0.43 (95% CI, 0.22 to 0.84; P = .013) in contrast to no effect in the EGFR-high group (HR = 1.14; 95% CI, 0.59 to 2.22; P = .7) by using a Cox model.

CONCLUSION

This study provides clinical evidence that confirms the basic work that has shown high EGFR can indicate resistance to tamoxifen. It suggests that careful measurement of EGFR protein expression might define a subset of low-stage patients that could benefit from an alternative therapy.