Heregulin-beta1 regulates the estrogen receptor-alpha gene expression and activity via the ErbB2/PI 3-K/Akt pathway

Neuregulin modulates hormone receptor levels in breast cancer through concerted action on multiple signaling pathways

The Neuregulins (NRGs) are growth factors that bind and activate ErbB/HER receptor tyrosine kinases. Some reports have described an interplay between this ligand-receptor system and hormonal receptors in breast cancer. However, the mechanisms by which NRGs regulate hormonal receptor signaling have not been sufficiently described. Here, we show that in breast cancer cells the activation of NRG receptors down-regulated ERα through a double mechanism that included post-transcriptional and transcriptional effects. This regulation required the concerted participation of three signaling routes: the PI3K/AKT/mTOR, ERK1/2, and ERK5 pathways. Moreover, these three routes were also involved in the phosphorylation of ERα at serines 118 and 167, two residues implicated in resistance to endocrine therapies. On the other hand, NRGs conferred resistance to fulvestrant in breast cancer cells and this resistance could be reversed when the three pathways activated by NRGs were simultaneously inhibited. Our results indicate that estrogen receptor-positive (ER+) breast tumors that can have access to NRGs may be resistant to fulvestrant. This resistance could be overcome if strategies to target the three main pathways involved in the interplay between NRG receptors and ERα could be developed.

Investigation of the Antitumor Effects of Tamoxifen and Its Ferrocene-Linked Derivatives on Pancreatic and Breast Cancer Cell Lines

Tamoxifen is a long-known anti-tumor drug, which is the gold standard therapy in estrogen receptor (ER) positive breast cancer patients. According to previous studies, the conjugation of the original tamoxifen molecule with different functional groups can significantly improve its antitumor effect. The purpose of this research was to uncover the molecular mechanisms behind the cytotoxicity of different ferrocene-linked tamoxifen derivates. Tamoxifen and its ferrocene-linked derivatives, T5 and T15 were tested in PANC1, MCF7, and MDA-MB-231 cells, where the incorporation of the ferrocene group improved the cytotoxicity on all cell lines. PANC1, MCF7, and MDA-MB-231 express ERα and GPER1 (G-protein coupled ER 1). However, ERβ is only expressed by MCF7 and MDA-MB-231 cells. Tamoxifen is a known agonist of GPER1, a receptor that can promote tumor progression. Analysis of the protein expression profile showed that while being cytotoxic, tamoxifen elevated the levels of different tumor growth-promoting factors (e.g., Bcl-XL, Survivin, EGFR, Cathepsins, chemokines). On the other hand, the ferrocene-linked derivates were able to lower these proteins. Further analysis showed that the ferrocene-linked derivatives significantly elevated the cellular oxidative stress compared to tamoxifen treatment. In conclusion, we were able to find two molecules possessing better cytotoxicity compared to their unmodified parent molecule while also being able to counter the negative effects of the presence of the GPER1 through the ER-independent mechanism of oxidative stress induction.

Kaempferol, a natural dietary flavonoid, suppresses 17β-estradiol-induced survivin expression and causes apoptotic cell death in endometrial cancer

Endometrioid endometrial carcinoma, commonly known as type 1 endometrial cancer, accounts for >80% of endometrial carcinomas and is dependent on estrogen. We recently reported on the prognostic significance of the BIRC5 survivin gene in endometrial cancer. Estradiol induces survivin expression in estrogen receptor-positive, but not in estrogen receptor-negative, cancer cells. Kaempferol, a bioflavonoid, reportedly inhibits estrogen receptor-α (ERα) in hormone receptor-positive breast cancer cells. However, whether kaempferol-mediated inhibition of ERα suppresses survivin and induces cell death in endometrial cancer remains unclarified. The present study evaluated the antitumor effects of kaempferol on endometrial cancer cells. Cell viability assays, flow cytometry analysis, western blotting and annexin V analyses were used to analyze the antitumor effects of kaempferol. The results demonstrated that kaempferol successfully suppressed the viability of two ER-positive endometrial cancer cell lines, with IC₅₀ values of 83 and 65 µM. In addition, kaempferol induced sub-G1 cell accumulation and apoptotic cell death (P<0.01) in a dose-dependent manner. Treatment of cells with estradiol significantly induced co-expression of nuclear ERα and survivin proteins (P<0.001). Further evaluation revealed that kaempferol causes apoptotic cell death largely by suppressing ERα, survivin and Bcl-2 protein. Therefore, the results of the present study suggested that targeting ERα and survivin with kaempferol may be a novel therapeutic option against endometrial carcinoma.

Neoadjuvant everolimus plus letrozole versus fluorouracil, epirubicin and cyclophosphamide for ER-positive, HER2-negative breast cancer: study protocol for a randomized pilot trial

Background

The response to neoadjuvant chemotherapy (NAC) varies by estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) statuses, with responses being lower in ER-positive, HER2-negative tumors as compared with ER-negative, HER2-positive or triple-negative tumors. Neoadjuvant endocrine therapy (NET) is an attractive alternative to NAC for ER-positive, HER2-negative cancer. However, a prior trial comparing NET with standard NAC in ER-positive tumor showed that the difference of response was not significant. Studies demonstrated that the mTOR inhibitor everolimus could sensitize breast tumors to endocrine therapy. A pilot open-label, randomized trial has been designed to evaluate the feasibility, efficacy and tolerability of neoadjuvant everolimus plus letrozole versus NAC in treating postmenopausal women with ER-positive, HER2-negative breast cancer.

Methods

Forty postmenopausal women with non-metastatic ER-positive, HER2-negative invasive breast cancer with a primary tumor > 2 cm or positive axillary lymph node(s) proved by biopsy will be randomly (1:1) enrolled from Sun Yat-Sen Memorial Hospital to receive neoadjuvant everolimus plus letrozole for 18 weeks or fluorouracil, epirubicin plus cyclophosphamide (FEC) for six cycles before surgery. Primary outcome is the feasibility of the trial. Secondary outcome measures include ultrasound response rate, pathological complete response rate, breast-conserving surgery rate, toxicities, and changes in the percentages of peripheral blood CD4⁺ T cells, CD8⁺ T cells, T helper cells, regulatory T cells, and NK cells.

Discussion

This is the first study to determine the feasibility, efficacy and tolerability of head-to-head neoadjuvant everolimus plus letrozole versus neoadjuvant FEC in treating postmenopausal women with ER-positive, HER2-negative breast cancer. The trial will provide evidence to assess the feasibility of a future multicenter, randomized controlled trial, and will provide valuable clinical data of the immunoregulatory effect of everolimus in breast cancer.

Trial registration

ClinicalTrials.gov registry, ID: NCT02742051. Registered on 7 April 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2228-5) contains supplementary material, which is available to authorized users.

Customizing the therapeutic response of signaling networks to promote antitumor responses by drug combinations

Drug resistance, de novo and acquired, pervades cellular signaling networks (SNs) from one signaling motif to another as a result of cancer progression and/or drug intervention. This resistance is one of the key determinants of efficacy in targeted anti-cancer drug therapy. Although poorly understood, drug resistance is already being addressed in combination therapy by selecting drug targets where SN sensitivity increases due to combination components or as a result of de novo or acquired mutations. Additionally, successive drug combinations have shown low resistance potential. To promote a rational, systematic development of combination therapies, it is necessary to establish the underlying mechanisms that drive the advantages of combination therapies, and design methods to determine drug targets for combination regimens. Based on a joint systems analysis of cellular SN response and its sensitivity to drug action and oncogenic mutations, we describe an in silico method to analyze the targets of drug combinations. Our method explores mechanisms of sensitizing the SN through a combination of two drugs targeting vertical signaling pathways. We propose a paradigm of SN response customization by one drug to both maximize the effect of another drug in combination and promote a robust therapeutic response against oncogenic mutations. The method was applied to customize the response of the ErbB/PI3K/PTEN/AKT pathway by combination of drugs targeting HER2 receptors and proteins in the down-stream pathway. The results of a computational experiment showed that the modification of the SN response from hyperbolic to smooth sigmoid response by manipulation of two drugs in combination leads to greater robustness in therapeutic response against oncogenic mutations determining cancer heterogeneity. The application of this method in drug combination co-development suggests a combined evaluation of inhibition effects together with the capability of drug combinations to suppress resistance mechanisms before they become clinically manifest.

Role of Ki67 in predicting resistance to adjuvant tamoxifen in postmenopausal breast cancer patients

INTRODUCTION

Breast cancer (BC) is a major health problem in Egypt and worldwide. Its prognosis depends not only on tumor stage but also on tumor biology.

AIM

To correlate the expression of Ki67 with the clinical outcomes of early hormone-receptor positive postmenopausal BC patients who are receiving tamoxifen.

METHODS

This cohort study included 70 patients. They were followed up for a minimum of 2 years. Ki67 was assessed on paraffin-embedded blocks using immunohistochemistry methods.

RESULTS

The median Ki67 value was 22.5% (IQR, 10%-50%). Ki67 was significantly higher in patients with HER2 positive tumors compared to HER2 negative tumors. After a median follow up period of 53 months, 22 patients (31%) developed disease recurrence either loco-regional or distant in 5.7% and 30%, respectively. Recurrent patients had significantly higher tumor stage, nodal stage and Ki67 values compared to non-recurrent cases. The 2-, 3- and 5-year overall survival (OS) and disease-free survival (DFS) rates were 100% & 91%, 98% & 84% and 77% & 59%, respectively. DFS was significantly worse with higher TNM stage, lower ER expression and higher Ki67 values. OS was significantly worse in patients with Ki67 values ≥ 30%. Ki67 ≥ 30% was an independent predictor of recurrence, poor DFS and OS.

CONCLUSION

High Ki67 expression is predictive of poor prognosis and of resistance to adjuvant tamoxifen therapy in postmenopausal BC. We recommend considering Ki67 as one of the risk factors that guide adjuvant treatment decisions.

Presurgical (neoadjuvant) endocrine therapy is a useful model to predict response and outcome to endocrine treatment in breast cancer patients

Endocrine therapy of breast cancer has been improved continuously during the last decades. Currently, aromatase inhibitors are dominating treatment algorithms for postmenopausal women with hormone-receptor positive breast cancer while tamoxifen still is the most widely used drug for premenopausal women. Several research tools and study designs have been used to challenge established drugs and develop the field of antihormonal therapy. One pivotal study option has been the observation of clinical responses during presurgical/neoadjuvant endocrine therapy (PSET/NET). This strategy has several major advantages. First, the breast tumor, still present in the patient's breast during therapy, can be followed by clinical observations and radiological measurements and any treatment effect will be immediately registered. Second, tumor biopsies may be obtained before initiation and following therapy allowing intra-patient comparisons. These tumor-biopsies may be used for the evaluation of intra-tumor changes associated with drug treatment. As examples, presurgical breast cancer trials have been used to evaluate intra-tumor estrogen levels during therapy with aromatase inhibitors and also to study mechanisms involved in the adaptation processes to estrogen suppression. Biomarker studies have provided information that may be used for patient selection in the future. Finally, recently published results from presurgical trials testing combinations of classical endocrine drugs and novel targeted therapies have produced promising results.

The BOLERO-2 trial: the addition of everolimus to exemestane in the treatment of postmenopausal hormone receptor-positive advanced breast cancer

The combination of the mTOR inhibitor everolimus with the aromatase inhibitor exemestane was evaluated in the randomized Phase III BOLERO-2 trial. Research has indicated that aberrant signaling through the mTOR pathway is associated with resistance to endocrine therapies. The BOLERO-2 trial examined the effects on progression-free survival of the addition of everolimus to exemestane in a patient population of postmenopausal, hormone receptor-positive, advanced breast cancer. At the interim analysis, the median progression-free survival assessed by local investigators was 6.9 months for everolimus plus exemestane versus 2.8 months for placebo plus exemestane (hazard ratio: 0.43; p < 0.001), and by central assessment was 10.6 versus 4.1 months, respectively (hazard ratio: 0.36; p < 0.001). The everolimus plus exemestane arm showed greater number of grade 3 and 4 adverse events. This study suggests that the addition of everolimus to exemestane is a potential viable treatment option for this patient population.

Advances in the understanding of the structure and function of ER-α36,a novel variant of human estrogen receptor-alpha

Estrogen receptors (ERs) belong to the nuclear receptor superfamily, whose members include ER-α66, ER-α36, ER-α46 and ER-β. Each receptor performs specific functions through binding with a specific ligand, such as estrogen. Recently, ER-α36, a novel variant of human estrogen receptor-alpha (ER-α), was identified and cloned. ER-α36 inhibits, in a dominant-negative manner, the transactivation of both the wild-type ER-α (ER-α66) and ER-β. As a predominantly membrane-based ER, ER-α36 mediates nongenomic estrogen signaling and is involved in the resistance of breast cancer to endocrine therapy, i.e., tamoxifen. This review summarizes recent studies on the structure and function of ER-α36 and the relationship of ER-α36 with cancer, with special emphasis on its function in the resistance of breast cancer to endocrine therapy.

E₂-BSA activates caveolin-1 via PI₃K/ERK1/2 and lysosomal degradation pathway and contributes to EPC proliferation

BACKGROUND

The mechanism that estrogen (E(2)) increases the number of endothelial progenitor cells (EPC) is largely unknown. Here we used E(2)-conjugated bovine serum albumin (E(2)-BSA, membrane impermeable) to investigate whether the membrane estrogen receptor (mER) and its related protein caveolin-1 (CAV-1) are involved in these processes.

METHODS AND RESULTS

E(2)-BSA promoted [(3)H]-thymidine incorporation of EPC through increasing CAV-1 expression via mER (ERα, but not ERβ or GPR30). Both cholesterol depletion and CAV-1 knockdown with use of CAV-1 siRNA significantly attenuated E(2)-BSA-induced [(3)H]-thymidine incorporation. Western blot showed that E(2)-BSA increased membrane CAV-1 protein expression 12h after treatment, whereas mRNA levels of CAV-1 were augmented until 24h after E(2)-BSA treatment. Furthermore, pre-incubated EPC with ICI 182780 (a specific ER antagonist), LY 294002 (a selective PI(3)K inhibitor) or PD 98059 (a specific ERK1/2 inhibitor) before E(2)-BSA inhibited the late-stage effect of E(2)-BSA (≥24 h) on up-regulation of CAV-1 mRNA and protein expression. Pulse chase results demonstrated that E(2)-BSA inhibited lysosome-mediated degradation of CAV-1 protein at the early stage (≤12 h), and then resulted in the increased CAV-1 protein.

CONCLUSION

In the present work we demonstrated that E(2)-BSA promotes EPC proliferation through mER (ERα) in CAV-1-dependent manner: prolonging the stability of CAV-1 protein through quick inhibition of the lysosomal degradation pathway at the early stage (≤12 h) and up-regulating CAV-1 at transcription levels through PI(3)K/ERK1/2 signaling pathway at the late stage (≥24 h). These data indicated that a there is a novel mechanism of E(2)-BSA in the regulation of EPC proliferation through CAV-1.

Phase II randomized study of neoadjuvant everolimus plus letrozole compared with placebo plus letrozole in patients with estrogen receptor-positive breast cancer

PURPOSE

Cross-talk between the estrogen receptor (ER) and the phosphoinositide-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathways is a mechanism of resistance to endocrine therapy, and blockade of both pathways enhances antitumor activity in preclinical models. This study explored whether sensitivity to letrozole was enhanced with the oral mTOR inhibitor, everolimus (RAD001).

PATIENTS AND METHODS

Two hundred seventy postmenopausal women with operable ER-positive breast cancer were randomly assigned to receive 4 months of neoadjuvant treatment with letrozole (2.5 mg/day) and either everolimus (10 mg/day) or placebo. The primary end point was clinical response by palpation. Mandatory biopsies were obtained at baseline and after 2 weeks of treatment (ie, day 15). Samples were assessed for PI3K mutation status (PIK3CA) and for pharmacodynamic changes of Ki67, phospho-S6, cyclin D1, and progesterone receptor (PgR) by immunohistochemistry.

RESULTS

Response rate by clinical palpation in the everolimus arm was higher than that with letrozole alone (ie, placebo; 68.1% v 59.1%), which was statistically significant at the preplanned, one-sided, alpha = 0.1 level (P = .062). Marked reductions in progesterone receptor and cyclin D1 expression occurred in both treatment arms, and dramatic downregulation of phospho-S6 occurred only in the everolimus arm. An antiproliferative response, as defined by a reduction in Ki67 expression to natural logarithm of percentage positive Ki67 of less than 1 at day 15, occurred in 52 (57%) of 91 patients in the everolimus arm and in 25 (30%) of 82 patients in the placebo arm (P < .01). The safety profile was consistent with historical results of everolimus monotherapy; grades 3 to 4 adverse events occurred in 22.6% of patients who received everolimus and in 3.8% of patients who received placebo.

CONCLUSION

Everolimus significantly increased letrozole efficacy in neoadjuvant therapy of patients with ER-positive breast cancer.

Targeting ErbB2 and ErbB3 with a bispecific single-chain Fv enhances targeting selectivity and induces a therapeutic effect in vitro

Inappropriate signalling through the EGFR and ErbB2/HER2 members of the epidermal growth factor family of receptor tyrosine kinases is well recognised as being causally linked to a variety of cancers. Consequently, monoclonal antibodies specific for these receptors have become increasingly important components of effective treatment strategies for cancer. Increasing evidence suggests that ErbB3 plays a critical role in cancer progression and resistance to therapy. We hypothesised that co-targeting the preferred ErbB2/ErbB3 heterodimer with a bispecific single-chain Fv (bs-scFv) antibody would promote increased targeting selectivity over antibodies specific for a single tumour-associated antigen (TAA). In addition, we hypothesised that targeting this important heterodimer could induce a therapeutic effect. Here, we describe the construction and evaluation of the A5-linker-ML3.9 bs-scFv (ALM), an anti-ErbB3/ErbB2 bs-scFv. The A5-linker-ML3.9 bs-scFv exhibits selective targeting of tumour cells in vitro and in vivo that co-express the two target antigens over tumour cells that express only one target antigen or normal cells that express low levels of both antigens. The A5-linker-ML3.9 bs-scFv also exhibits significantly greater in vivo targeting of ErbB2‘+’/ErbB3‘+’ tumours than derivative molecules that contain only one functional arm targeting ErbB2 or ErbB3. Binding of ALM to ErbB2‘+’/ErbB3‘+’ cells mediates inhibition of tumour cell growth in vitro by effectively targeting the therapeutic anti-ErbB3 A5 scFv. This suggests both that ALM could provide the basis for an effective therapeutic agent and that engineered antibodies selected to co-target critical functional pairs of TAAs can enhance the targeting specificity and efficacy of antibody-based cancer therapeutics.

Multi-targeted therapy of cancer by genistein

Soy isoflavones have been identified as dietary components having an important role in reducing the incidence of breast and prostate cancers in Asian countries. Genistein, the predominant isoflavone found in soy products, has been shown to inhibit the carcinogenesis in animal models. There is a growing body of experimental evidence showing that the inhibition of human cancer cell growth by genistein is mediated via the modulation of genes that are related to the control of cell cycle and apoptosis. It has been shown that genistein inhibits the activation of NF-kappaB and Akt signaling pathways, both of which are known to maintain a homeostatic balance between cell survival and apoptosis. Moreover, genistein antagonizes estrogen- and androgen-mediated signaling pathways in the processes of carcinogenesis. Furthermore, genistein has been found to have antioxidant properties, and shown to be a potent inhibitor of angiogenesis and metastasis. Taken together, both in vivo and in vitro studies have clearly shown that genistein, one of the major soy isoflavones is a promising agent for cancer chemoprevention and further suggest that it could be an adjunct to cancer therapy by virtue of its effects on reversing radioresistance and chemoresistance. In this review, we attempt to provide evidence for these preventive and therapeutic effects of genistein in a succinct manner highlighting comprehensive state-of-the-art knowledge regarding its multi-targeted biological and molecular effects in cancer cells.

Her2 and Progesterone Receptor Status Are Not Predictive of Response to Fulvestrant Treatment

PURPOSE

It has been hypothesized that response to endocrine therapy for breast cancer depends on Her2 and progesterone receptor status, grading, and tumor proliferation rate. In this study, we evaluated factors that are potentially predictive of response and time to progression in patients treated with fulvestrant.

EXPERIMENTAL DESIGN

One hundred fifty-five patients were included and followed prospectively. Patients received fulvestrant at standard dose by i.m. injection. Response was evaluated every 3 months using International Union Against Cancer criteria. Time to progression and overall survival were estimated with the Kaplan-Meier product limit method. A multivariate analysis was done to evaluate factors potentially influencing response and time to progression.

RESULTS

We observed a partial response in 19 patients (12.3%), stable disease > or =6 months in 56 patients (36.1%), stable disease >3 months but <6 months in 7 patients (4.5%), and progressive disease in 73 patients (47.1%). Median time to progression was 5 months, and median overall survival was 27 months. Probability of achieving clinical benefit was significantly associated with a low proliferation rate (P = 0.015), nonvisceral metastatic sites (P = 0.023), and first-line therapy (P = 0.023). First-line therapy was also associated with prolonged time to progression (P = 0.003).

CONCLUSIONS

Response rate and time to progression are shown to be independent of Her2 status, grading, and progesterone receptor status. This is probably caused by the unique mechanism of action associated with fulvestrant: Due to receptor down-regulation, it blocks nuclear, cytoplasmatic, and membrane-bound estrogen receptor. Therefore, it seems to inhibit the cross-talk between growth factor receptor signaling and estrogen receptor in a more effective manner.

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Advanced concepts in estrogen receptor biology and breast cancer endocrine resistance: implicated role of growth factor signaling and estrogen receptor coregulators

Estrogen receptor (ER), mediating estrogen-signaling stimuli, is a dominant regulator and a key therapeutic target in breast cancer etiology and progression. Endocrine therapy, blocking the ER pathway, is one of the most important systemic therapies in breast cancer management, but de novo and acquired resistance is still a major clinical problem. New research highlights the role of both genomic and nongenomic ER activities and their intimate molecular crosstalk with growth factor receptor and other signaling kinase pathways in endocrine resistance. These signaling pathways, when overexpressed and/or hyperactivated, can modulate both activities of ER, resulting in endocrine resistance. Thus, these signal transduction receptors and signaling molecules may serve as both predictive markers and novel therapeutic targets to circumvent endocrine resistance. Compelling experimental and clinical evidence suggest that the epidermal growth factor/HER2/neu receptor (EGFR/HER2) pathway might play a distinct role in endocrine resistance, and especially in resistance to selective estrogen receptor modulators (SERMs) such as tamoxifen. Results from preclinical studies of treatment combinations with various endocrine therapy drugs together with several potent anti-EGFR/HER2 inhibitors are very promising, and clinical trials to see whether this new strategy is effective in patients are now ongoing.

Cross-talk between ER and HER2 in breast carcinoma

In tumors in which estrogen receptor (ER) and growth factor signaling pathways are simultaneously active, there is a bidirectional cross-talk that results in a positive feedback cycle of cell survival and proliferation stimuli. Beside the postulated inverse correlation between ER and HER2 (human epidermal growth factor receptor 2) as a consequence of repressive feedback signaling loop, there are also other mechanisms regarding ER-HER2 interactions. It seems that MAPK (mitogen-activated protein kinase) pathway has a central role in synergistic action between ER and HER2 in normal mammary gland development, as well in the breast cancer. MAPK pathway is hyperstimulated in cells that overexpress HER2 as a consequence of HER2 gene amplification. In ER+ tumors, MAPK phosphorylates and activates either ER itself or ER coregulators, enhancing the transcriptional activation potential of ER. ER and HER2 signaling could interact on multiple levels (genomic or non-genomic) and therefore might induce reduced ER expression or might increase ER function. Based on our own research, dominant effect of postulated cross-talk was not related to HER2-induced reduced expression of ER (no difference in quantitative levels of ER in ER+ tumors regarding their HER2 status and no difference in progression-free time between ER+HER2- and ER+HER2+ patients) as presented. The importance of understanding ER-HER2 cross-talk is not only because of its significance in breast cancer progression, but because it seems to be fundamental factor in endocrine resistance that can improve treatment strategies, especially targeting MAPK pathway. .

Modulation of signal transduction by tea catechins and related phytochemicals

Epidemiologic studies in human populations and experimental studies in rodents provide evidence that green tea and its constituents can inhibit both the development and growth of tumors at a variety of tissue sites. In addition, EGCG, a major biologically active component of green tea, inhibits growth and induces apoptosis in a variety of cancer cell lines. The purpose of this paper is to review evidence that these effects are mediated, at least in part, through inhibition of the activity of specific receptor tyrosine kinases (RTKs) and related downstream pathways of signal transduction. We also review evidence indicating that the antitumor effects of the related polyphenolic phytochemicals resveratrol, genistein, curcumin, and capsaicin are exerted via similar mechanisms. Some of these agents (EGCG, genistein, and curcumin) appear to directly target specific RTKs, and all of these compounds cause inhibition of the activity of the transcription factors AP-1 and NF-kappaB, thus inhibiting cell proliferation and enhancing apoptosis. Critical areas of future investigation include: (1) identification of the direct molecular target(s) of EGCG and related polyphenolic compounds in cells; (2) the in vivo metabolism and bioavailability of these compounds; (3) the ancillary effects of these compounds on tumor-stromal interactions; (4) the development of synergistic combinations with other antitumor agents to enhance efficacy in cancer prevention and therapy, and also minimize potential toxicities.

Induction of heat shock proteins by heregulin beta1 leads to protection from apoptosis and anchorage-independent growth

Elevation of heat shock protein (HSP) levels is widespread in cancer and predicts a poor prognosis and resistance to therapy. We show that HSP elevation in tumor cells can be induced by the highly malignant factor heregulin beta1 (HRGbeta1), which induces HSP expression through heat shock transcription factor 1 (HSF1). Inactivation of the hsf1 gene prevents HSP induction by HRGbeta1. HSP expression is induced through a cascade response initiated by HRGbeta1 binding to c-erbB receptors on the cell surface and which leads to the inhibition of intracellular HSF1 antagonist glycogen synthase kinase 3. HSF1 activated by this pathway plays a key role in the protection of cells from apoptosis and the mediation of anchorage independent growth by HRGbeta1, indicating a role for HSF1 in this tumorigenic pathway.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

Activation of the Akt/mammalian target of rapamycin/4E-BP1 pathway by ErbB2 overexpression predicts tumor progression in breast cancers

The Akt/mammalian target of rapamycin (mTOR)/4E-BP1 pathway is considered to be a central regulator of protein synthesis, involving the regulation of cell proliferation, differentiation, and survival. The inhibitors of mTOR as anticancer reagents are undergoing active evaluation in various malignancies including breast cancer. However, the activation status of the Akt/mTOR/4E-BP1 pathway and its potential roles in breast cancers remain unknown. Thus, we examined 165 invasive breast cancers with specific antibodies for the phosphorylation of Akt, mTOR, and 4E-BP1 by immunohistochemistry and compared them with normal breast epithelium, fibroadenoma, intraductal hyperplasia, and ductal carcinoma in situ. We discovered that the phosphorylation of Akt, mTOR, and 4E-BP1 increased progressively from normal breast epithelium to hyperplasia and abnormal hyperplasia to tumor invasion. Phosphorylated Akt, mTOR, and 4E-BP1 were positively associated with ErbB2 overexpression. Survival analysis showed that phosphorylation of each of these three markers was associated with poor disease-free survival independently. In vitro, we further confirmed the causal relationship between ErbB2 overexpression and mTOR activation, which was associated with enhanced invasive ability and sensitivity to a mTOR inhibitor, rapamycin. Our results, for the first time, demonstrate the following: (a) high levels of phosphorylation of Akt, mTOR, and 4E-BP1 in breast cancers, indicating activation of the Akt/mTOR/4E-BP1 pathway in breast cancer development and progression; (b) a link between ErbB2 and the Akt/mTOR/4E-BP1 pathway in breast cancers in vitro and in vivo, indicating the possible role of Akt/mTOR activation in ErbB2-mediated breast cancer progression; and (c) a potential role for this pathway in predicting the prognosis of patients with breast cancer, especially those treated with mTOR inhibitors.

Selective hormone-dependent repression of estrogen receptor beta by a p38-activated ErbB2/ErbB3 pathway

Deregulated signaling of ErbB2 receptor tyrosine kinase is often associated with hormone resistance in estrogen receptor alpha (ERalpha)-positive breast cancers, establishing a relationship between ErbB2 and ERalpha pathways. Although ERalpha and ERbeta are expressed in many breast cancer cells, the response of ERbeta to ErbB2 signaling is less well defined. In the present study, we demonstrate that ERbeta activity can be modulated by ErbB2 signaling in ER-expressing breast cancer cells. The estrogen-dependent transcriptional activity of ERbeta was altered in a manner similar to ERalpha by either activation of ErbB2/ErbB3 signaling by growth factor heregulin beta or expression of a constitutively active mutant of ErbB2. However, as opposed to ERalpha, the p38 MAPK pathway was found to be involved in liganded ERbeta repression activity by ErbB2 signaling and in regulating estrogen-responsive promoter occupancy by ERbeta. The repression in ERbeta response to hormone was dependent upon its AF-1 domain which includes serines 106 and 124, two phosphorylation target sites for Erk that we previously showed to be involved in SRC-1 recruitment to ERbeta. Substitution of these two serines by aspartic acid residues abolished the repression of ERbeta by activated ErbB2/ErbB3. Moreover, expression of SRC-1 also relieved the inhibition of ERbeta in heregulin-treated cells. Our study demonstrates a functional coupling between ERbeta and ErbB receptors and outlines the differential role of the AF-1 region in the regulation of the estrogen-dependent cell growth and activity of both estrogen receptors in response to growth factor signaling.

Blocking anti-apoptosis as a strategy for cancer chemotherapy: NF-kappaB as a target

Critical processes underlying cancers must be better understood to develop strategies for treatment and prevention. A chemotherapeutic strategy is proposed that is based upon re-establishment, with a drug, of nullified programmed cell death (apoptosis) in cancer cells, which to survive have mutated to block apoptosis. A chemotherapy that is specific against tumors implanted in mice demonstrated the feasibility of this principle. This therapy is specific because it affects a process unique to cancer cells. It also has the advantage of killing these cells, in contrast to reversibly blocking their proliferation. The anti-apoptotic transcription factor NF-kappaB provides a potential therapeutic target in estrogen receptor negative (ER-) breast cancers that over-express the epidermal growth factor family of receptors (EGFR). Further investigations of the pathways utilize dominant negative protein inhibitory peptide, and small inhibitory RNAs (siRNAs) to block the production of relevant enzymes.

Estradiol abrogates apoptosis in breast cancer cells through inactivation of BAD: Ras-dependent nongenomic pathways requiring signaling through ERK and Akt

Estrogens such as 17-beta estradiol (E(2)) play a critical role in sporadic breast cancer progression and decrease apoptosis in breast cancer cells. Our studies using estrogen receptor-positive MCF7 cells show that E(2) abrogates apoptosis possibly through phosphorylation/inactivation of the proapoptotic protein BAD, which was rapidly phosphorylated at S112 and S136. Inhibition of BAD protein expression with specific antisense oligonucleotides reduced the effectiveness of tumor necrosis factor-alpha, H(2)O(2), and serum starvation in causing apoptosis. Furthermore, the ability of E(2) to prevent tumor necrosis factor-alpha-induced apoptosis was blocked by overexpression of the BAD S112A/S136A mutant but not the wild-type BAD. BAD S112A/S136A, which lacks phosphorylation sites for p90(RSK1) and Akt, was not phosphorylated in response to E(2) in vitro(.) E(2) treatment rapidly activated phosphatidylinositol 3-kinase (PI-3K)/Akt and p90(RSK1) to an extent similar to insulin-like growth factor-1 treatment. In agreement with p90(RSK1) activation, E(2) also rapidly activated extracellular signal-regulated kinase, and this activity was down-regulated by chemical and biological inhibition of PI-3K suggestive of cross talk between signaling pathways responding to E(2). Dominant negative Ras blocked E(2)-induced BAD phosphorylation and the Raf-activator RasV12T35S induced BAD phosphorylation as well as enhanced E(2)-induced phosphorylation at S112. Chemical inhibition of PI-3K and mitogen-activated protein kinase kinase 1 inhibited E(2)-induced BAD phosphorylation at S112 and S136 and expression of dominant negative Ras-induced apoptosis in proliferating cells. Together, these data demonstrate a new nongenomic mechanism by which E(2) prevents apoptosis.

Tamoxifen and tamoxifen ethyl bromide induce apoptosis in acutely damaged mammary epithelial cells through modulation of AKT activity

Normal human mammary epithelial cells (HMECs), unlike estrogen receptor-positive (ER+) breast cancers, typically express low nuclear levels of ER (ER-'poor'). We previously demonstrated that 1.0 microM tamoxifen (Tam) induced apoptosis in ER-'poor' HMECs acutely transduced with human papillomavirus-16 E6 (HMEC-E6) through a rapid mitochondrial signaling pathway. Here, we show that plasma membrane-associated E2-binding sites initiate the rapid apoptotic effects of Tam in HMEC-E6 cells through modulation of AKT activity. At equimolar concentrations, Tam and tamoxifen ethyl bromide (QTam), a membrane impermeant analog of Tam, rapidly induced apoptosis in HMEC-E6 cells associated with an even more rapid decrease in phosphorylation of AKT at serine-473. Treatment of HMEC-E6 cells with 1.0 microM QTam resulted in a 50% decrease in mitochondrial transmembrane potential, sequential activation of caspase-9 and -3, and a 90% decrease in AKT Ser-473 phosphorylation. The effects of both Tam and QTam were blocked by expression of constitutively active AKT (myristoylated AKT or AKT-Thr308Asp/Ser473Asp). These data indicate that Tam and QTam induce apoptosis in HMEC-E6 cells through a plasma membrane-activated AKT-signaling pathway that results in (1) decreased AKT phosphorylation at Ser-473, (2) mitochondrial membrane depolarization, and (3) activated caspase-9 and -3.

Cross-talk between estrogen receptor and growth factor pathways as a molecular target for overcoming endocrine resistance

Introduced more than 100 years ago, endocrine therapy is still the most important systemic therapy for all stages of estrogen receptor (ER) -positive breast tumors. A major clinical problem limiting the usefulness of this therapy is tumor resistance, either de novo or acquired during the course of the treatment. Relatively new discoveries emphasize the complexity of ER signaling and its multiple regulatory interactions with growth factor and other kinase signaling pathways. Both genomic (nuclear) and nongenomic (membrane and cytoplasmic) ER activities contribute to this intimate cross-talk, which is probably a fundamental factor in endocrine resistance. New targeted therapies, especially against the epidermal growth factor receptor/HER-2 pathway, should be carefully evaluated in more (bio)logical strategies to enable them to be exploited appropriately. A strategy of combining endocrine therapy (particularly tamoxifen) with these inhibitors, to circumvent de novo and acquired resistance, will be discussed. We will also emphasize open questions and future challenges in the dynamic research field of molecular ER biology from the endocrine therapy perspective.

Expression of ErbB2 enhances radiation-induced NF-kappaB activation

Her-2/neu (ErbB2) oncogene, the second member of the epidermal growth factor receptor (EGFR) family, encodes a transmembrane tyrosine kinase receptor in Her-2-positive tumors. Accumulating evidences demonstrate that signaling networks activated by EGFR and transcription factor NF-kappaB are associated with cell response to ionizing radiation (IR). The present study shows that overexpression of ErbB2 enhanced NF-kappaB activation induced by IR in human breast carcinoma MCF-7 cells transfected with ErbB2 genes (MCF-7/ErbB2). Stable transfection of dominant-negative mutant IkappaB (MCF-7/ErbB2/mIkappaB) or treatment with anti-ErbB2 antibody, Herceptin, inhibited NF-kappaB activation and radiosensitized MCF-7/ErbB2 cells. Consistent with NF-kappaB regulation, basal and IR-induced Akt, a kinase downstream of ErbB2, was activated in MCF-7/ErbB2 cells and inhibited by Herceptin. To identify specific genes affected by ErbB2-mediated NF-kappaB activation, a group of IR-responsive elements Cyclin B1, Cyclin D1, Bcl-2, Bcl/XL, BAD and BAX were evaluated. Basal levels of prosurvival elements Cyclin B1, Cyclin D1, Bcl-2 and Bcl/XL but not apoptotic BAD and BAX were upregulated in MCF-7/ErbB2 cells with striking enhancements in Bcl-2 and Bcl/XL. IR further induced Cyclin B1 and Cyclin D1 expression that was reduced by Herceptin. Bcl-2 kept a high steady level after Herceptin+IR treatment and, in contrast to control MCF-7/Vector cells, Bcl/XL was inhibited in MCF-7/ErbB2 cells by Herceptin+IR treatment. However, all four prosurvival proteins were downregulated by inhibition of NF-kappaB in MCF-7/ErbB2/mIkappaB cells. These results thus provide evidence suggesting that overexpression of ErbB2 is able to enhance NF-kappaB response to IR, and that a specific prosurvival network downstream of NF-kappaB is triggered by treatments using anti-ErbB2 antibody combined with radiation.

Classifying the estrogen receptor status of breast cancers by expression profiles reveals a poor prognosis subpopulation exhibiting high expression of the ERBB2 receptor

Recent work using expression profiling to computationally predict the estrogen receptor (ER) status of breast tumors has revealed that certain tumors are characterized by a high prediction uncertainty ('low-confidence'). We analyzed these 'low-confidence' tumors and determined that their 'uncertain' prediction status arises as a result of widespread perturbations in multiple genes whose expression is important for ER subtype discrimination. Patients with 'low-confidence' ER+ tumors exhibited a significantly worse overall survival (P=0.03) and shorter time to distant metastasis (P=0.004) compared with their 'high-confidence' ER+ counterparts, indicating that the 'high-' and 'low-confidence' binary distinction is clinically meaningful. We then discovered that elevated expression of the ERBB2 receptor is significantly correlated with a breast tumor exhibiting a 'low-confidence' prediction, and this association was subsequently validated across multiple independently derived breast cancer expression datasets employing a variety of different array technologies and patient populations. Although ERBB2 signaling has been proposed to inhibit the transcriptional activity of ER, a large proportion of the perturbed genes in the 'low-confidence'/ERBB2+ samples are not known to be estrogen responsive, and a recently described bioinformatic algorithm (DEREF) was used to demonstrate the absence of potential estrogen-response elements (EREs) in their promoters. We propose that a significant portion of ERBB2's effects on ER+ breast tumors may involve ER-independent mechanisms of gene activation, which may contribute to the clinically aggressive behavior of the 'low-confidence' breast tumor subtype.

Effect of estradiol on estrogen receptor-alpha gene expression and activity can be modulated by the ErbB2/PI 3-K/Akt pathway

Epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and heregulin-beta1 (HRG-beta1), can modulate the expression and activity of the estrogen receptor-alpha (ER-alpha) via the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway in the ER-alpha-positive breast cancer cell line, MCF-7. Estradiol can also rapidly activate PI 3-K/Akt in these cells (nongenomic effect). The recent study examines whether Akt is involved in the ER-alpha regulation by estradiol (genomic effect). Stable transfection of parental MCF-7 cells with a dominant-negative Akt mutant, as well as the PI 3-K inhibitors wortmannin and LY 294,002, blocked the effect of estradiol on ER-alpha expression and activity by 70-80 and 55-63%, respectively. Stable transfection of MCF-7 cells with a constitutively active Akt mimicked the effect of estradiol. The changes in ER-alpha expression and activity were abrogated in response to estradiol by an arginine to cysteine mutation in the pleckstrin homology (PH) domain of Akt (R25C), suggesting the involvement of this amino acid in the interaction between Akt and ER-alpha. Experiments employing selective ErbB inhibitors demonstrate that the effect of estradiol on ER-alpha expression and activity is mediated by ErbB2 and not by EGFR. Moreover, anchorage-dependent and -independent growth assays, cell cycle and membrane ruffling analyses showed that Akt exerts estrogen-like activity on cell growth and membrane ruffling and that a selective ErbB2 inhibitor, but not anti-ErbB2 antibodies directed to the extracellular domain, can block these effects. In the presence of constitutively active Akt, tamoxifen only partially inhibits cell growth. In contrast, in cells stably transfected with either a dominant-negative Akt or with R25C-Akt, as well as in parental cells in the presence of a selective ErbB2 inhibitor, the effect of estradiol on anchorage-dependent and -independent cell growth was inhibited by 50-75 and 100%, respectively. Dominant-negative Akt inhibited membrane ruffling by 54%; however, R25C-Akt did not have any effect, suggesting that kinase activity plays an important role in this process. Scatchard analysis demonstrated a 67% reduction in estrogen-binding capacity in cells transfected with constitutively active Akt. No change in binding affinity of estradiol to the receptor was observed upon transfection with either Akt mutant. Taken together, our results suggest that estradiol treatment results in binding to membrane ER-alpha and interaction with a heterodimer containing ErbB2, leading to tyrosine phosphorylation. This results in the activation of PI 3-K and Akt. Akt, in turn, may interact with nuclear ER-alpha, altering its expression and activity.

Gonadotropin and steroid hormones stimulate proliferation of the rat ovarian surface epithelium

The ovarian surface epithelium (OSE) is a single layer of flattened or cuboidal cells covering the ovary. Ninety percent of all human ovarian malignancies arise from this layer of cells. Incessant ovulation, hyperovulation induced by infertility treatment, and hormone replacement therapy have been suggested as risk factors for ovarian cancer. In this study, two groups of rats, with and without surgically induced injury to the ovary, were treated with 17beta-estradiol, pregnant mare's serum gonadotropin (PMSG), human chorionic gonadotropin (hCG), or the combination PMSG/hCG, and the proliferative response of the OSE cells was measured using bromodeoxyuridne (BrdU) and (3)H-thymidine. All hormones, alone or in combination with ovarian surgery, were found to increase significantly the rate of proliferation of the rat OSE. These data demonstrate that hormones associated with infertility treatments and hormone replacement therapy, as well as injury- or ovulation-induced rupture of the ovarian surface, stimulate the rat OSE, and hence could have a role in the development of ovarian cancer via proliferation-associated mutagenesis, or alternatively, by promoting the rapid selection of OSE cells with accumulated mutations.