A role for glial cell derived neurotrophic factor induced expression by inflammatory cytokines and RET/GFR alpha 1 receptor up-regulation in breast cancer

Targeting the receptor tyrosine kinase RET in combination with aromatase inhibitors in ER positive breast cancer xenografts

The majority of breast cancers are estrogen receptor positive (ER+). Blockade of estrogen biosynthesis by aromatase inhibitors (AIs) is the first-line endocrine therapy for post-menopausal women with ER+ breast cancers. However, AI resistance remains a major challenge. We have demonstrated previously that increased GDNF/RET signaling in ER+ breast cancers promotes AI resistance. Here we investigated the efficacy of different small molecule RET kinase inhibitors, sunitinib, cabozantinib, NVP-BBT594 and NVP-AST487, and the potential of combining a RET inhibitor with the AI letrozole in ER+ breast cancers. The most effective inhibitor identified, NVP-AST487, suppressed GDNF-stimulated RET downstream signaling and 3D tumor spheroid growth. Ovariectomized mice were inoculated with ER+ aromatase-overexpressing MCF7-AROM1 cells and treated with letrozole, NVP-AST487 or the two drugs in combination. Surprisingly, the three treatment regimens showed similar efficacy in impairing MCF7-AROM1 tumor growth in vivo. However in vitro, NVP-AST487 was superior to letrozole in inhibiting the GDNF-induced motility and tumor spheroid growth of MCF7-AROM1 cells and required in combination with letrozole to inhibit GDNF-induced motility in BT474-AROM3 aromatase expressing cells. These data indicate that inhibiting RET is as effective as the current therapeutic regimen of AI therapy but that a combination treatment may delay cancer cell dissemination and metastasis.

RET-mediated modulation of tumor microenvironment and immune response in multiple endocrine neoplasia type 2 (MEN2)

Medullary thyroid carcinomas (MTC) arise from thyroid parafollicular, calcitonin-producing C-cells and can occur either as sporadic or as hereditary diseases in the context of familial syndromes, including multiple endocrine neoplasia 2A (MEN2A), multiple endocrine neoplasia 2B (MEN2B) and familial MTC (FMTC). In a large fraction of sporadic cases, and virtually in all inherited cases of MTC, activating point mutations of the RET proto-oncogene are found. RET encodes for a receptor tyrosine kinase protein endowed with transforming potential on thyroid parafollicular cells. As in other cancer types, microenvironmental factors play a critical role in MTC. Tumor-associated extracellular matrix, stromal cells and immune cells interact and influence the behavior of cancer cells both in a tumor-promoting and in a tumor-suppressing manner. Several studies have shown that, besides the neoplastic transformation of thyroid C-cells, a profound modification of tumor microenvironment has been associated to the RET FMTC/MEN2-associated oncoproteins. They influence the surrounding stroma, activating cancer-associated fibroblasts (CAFs), promoting cancer-associated inflammation and suppressing anti-cancer immune response. These mechanisms might be exploited to develop innovative anti-cancer therapies and novel prognostic tools in the context of familial, RET-associated MTC.

Breast Cancer Cell Apoptosis is Synergistically Induced by Curcumin, Trastuzumab, and Glutathione Peroxidase-1 but Robustly Inhibited by Glial Cell Line-Derived Neurotrophic Factor

We hypothesized that synergy between curcumin (CURC), trastuzumab (TZMB), and glutathione peroxidase-1 (GPX-1) accelerates breast cancer (BC) cell apoptosis which is inhibited by glial cell line-derived neurotrophic factor (GDNF). We measured survival of BC cell lines treated or cotreated with CURC and TZMB, and then with GDNF, before measuring expression levels of growth and apoptosis genes. These experiments were also repeated on SKBR3 cells transiently expressing GPX-1. CURC+TZMB cotreatment induced BC cell apoptosis more significantly than single treatment. GDNF highly inhibited CURC+TZMB toxicity and restored survival. Ectopic overexpression of GPX-1 per se induced SKBR3 cell death that was accelerated upon CURC+TZMB cotreatment. This substantial death induction was inhibited by GDNF more robustly than in single-treated cells. All these changes correlated with changes in expression levels of key molecules and were further confirmed by flow cytometry and correlation analysis. Our data indicate apoptotic induction is jointly shaped in BC cells by CURC, TZMB, and GPX-1 which correlates directly with their tripartite synergism and inversely with GDNF progrowth effects. In light of the active presence of GDNF in tumor microenvironment and necessity to overcome drug resistance, our findings can help in designing combined therapeutic strategies with implications for challenging TZMB resistance in BC.

The GDNF Family: A Role in Cancer?

The glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) comprising of GDNF, neurturin, artemin, and persephin plays an important role in the development and maintenance of the central and peripheral nervous system, renal morphogenesis, and spermatogenesis. Here we review our current understanding of GFL biology, and supported by recent progress in the area, we examine their emerging role in endocrine-related and other non-hormone-dependent solid neoplasms. The ability of GFLs to elicit actions that resemble those perturbed in an oncogenic phenotype, alongside mounting evidence of GFL involvement in tumor progression, presents novel opportunities for therapeutic intervention.

An Anti-GDNF Family Receptor Alpha 1 (GFRA1) Antibody-Drug Conjugate for the Treatment of Hormone Receptor-Positive Breast Cancer

Luminal A (hormone receptor-positive) breast cancer constitutes 70% of total breast cancer patients. In an attempt to develop a targeted therapeutic for this cancer indication, we have identified and characterized Glial cell line-Derived Neurotrophic Factor (GDNF) Family Receptor Alpha 1 (GFRA1) antibody-drug conjugates (ADC) using a cleavable valine-citrulline-MMAE (vcMMAE) linker-payload. RNAseq and IHC analysis confirmed the abundant expression of GFRA1 in luminal A breast cancer tissues, whereas minimal or no expression was observed in most normal tissues. Anti-GFRA-vcMMAE ADC internalized to the lysosomes and exhibited target-dependent killing of GFRA1-expressing cells both in vitro and in vivo The ADCs using humanized anti-GFRA1 antibodies displayed robust therapeutic activity in clinically relevant cell line-derived (MCF7 and KPL-1) tumor xenograft models. The lead anti-GFRA1 ADC cross-reacts with rodent and cynomolgus monkey GFRA1 antigen and showed optimal pharmacokinetic properties in both species. These properties subsequently enabled a target-dependent toxicity study in rats. Anti-GFRA1 ADC is well tolerated in rats, as seen with other vcMMAE linker-payload based ADCs. Overall, these data suggest that anti-GFRA1-vcMMAE ADC may provide a targeted therapeutic opportunity for luminal A breast cancer patients. Mol Cancer Ther; 17(3); 638-49. ©2017 AACR.

Mechanisms that drive inflammatory tumor microenvironment, tumor heterogeneity, and metastatic progression

Treatment of cancer metastasis has been largely ineffective. It is paramount to understand the mechanisms underlying the metastatic process, of which the tumor microenvironment is an indispensable participant. What are the critical cellular and molecular players at the primary tumor site where metastatic cascade initiates? How is tumor-associated inflammation regulated? How do altered vasculatures contribute to metastasis? What is the dynamic nature or heterogeneity of primary tumors and what are the challenges to catch a moving target? This review summarizes recent progress, mechanistic understanding, and options for metastasis-targeted therapy.

Long Non Coding RNA Expression Intersecting Cancer and Spermatogenesis: A Systematic Review

Background: Numerous similarities have been noted between gametogenic and tumorigenic programs in features such as global hypomethylation, immune evasion, immortalization, meiosis induction, and migration. In addition, aberrant expression of testis specific genes has been detected in various cancers which has led to categorization of these genes as “cancer-testis genes”. Most of the examples identified in this category are protein encoding. However, recent studies have revealed that non-coding RNAs, including long non coding RNAs (lncRNAs), may have essential regulatory roles in telomere biology, chromatin dynamics, modulation of gene expression and genome structural organization. All of these functions are implicated in both gametogenic and tumorigenic programs. Methods: In the present study, we conducted a computerized search of the MEDLINE/PUBMED and Embase databases with the key words lncRNA, gametogenesis, testis and cancer. Results: We found a number of lncRNAs with essential roles and notable expression in both gametogenic and cancer tissues. Conclusions: Comparison between cancer tissues and gametogenic tissues has shown that numerous lncRNAs are expressed in both, playing similar roles in processes modulated by signaling pathways such as Wnt/β-catenin and PI3K/AKT/mTOR. Evaluation of expression patterns and functions of these genes should pave the way to discovery of biomarkers for early detection, prognostic assessment and evaluation of therapeutic responses in cancers.

circGFRA1 and GFRA1 act as ceRNAs in triple negative breast cancer by regulating miR-34a

Backgroud

Accumulating evidences indicate that circular RNAs (circRNAs), a class of non-coding RNAs, play important roles in tumorigenesis. However, the function of circRNAs in triple negative breast cancer (TNBC) is largely unknown.

Methods

We performed circRNA microarrays to identify circRNAs that are aberrantly expressed in TNBC cell lines. Expression levels of a significantly upregulated circRNA, circGFRA1, was detected by quantitative real-time PCR (qRT-PCR) in TNBC cell lines and tissues. Kaplan-Meier survival analysis was used to explore the significance of circGFRA1 in clinical prognosis. Then, we examined the functions of circGFRA1 in TNBC by cell proliferation, apoptosis and mouse xenograft assay. In addition, luciferase assay was used to explore the miRNA sponge function of circGFRA1 in TNBC.

Results

Microarray analysis and qRT-PCR verified a circRNA termed circGFRA1 that was upregulated in TNBC. Kaplan-Meier survival analysis showed that upregulated circGFRA1 was correlated with poorer survival. Knockdown of circGFRA1 inhibited proliferation and promoted apoptosis in TNBC. Via luciferase reporter assays, circGFRA1 and GFRA1 was observed to directly bind to miR-34a. Subsequent experiments showed that circGFRA1 and GFRA1 regulated the expression of each other by sponging miR-34a.

Conclusions

Taken together, we conclude that circGFRA1 may function as a competing endogenous RNA (ceRNA) to regulate GFRA1 expression through sponging miR-34a to exert regulatory functions in TNBC. circGFRA1 may be a diagnostic biomarker and potential target for TNBC therapy.

Optimal doses of EGF and GDNF act as biological response modifiers to improve porcine oocyte maturation and quality

It is well documented that both epidermal growth factor (EGF) and glial cell line-derived neurotrophic factor (GDNF) are critical for porcine oocyte maturation, however, little information is known about their mechanism of action in vitro. To gain insight into the mechanisms of action of the optimum doses of EGF and GDNF on porcine oocyte maturation, porcine cumulus–oocyte complexes (COCs) were matured in defined porcine oocyte medium supplemented with EGF, GDNF or a combination of both at varying concentrations (0–100 ng/ml) for 44 h. Nuclear and cytoplasmic maturation were determined in terms of nuclear stage after DNA staining with Hoechst and cortical granule distribution after lectin labeling, respectively. Mature oocytes were subsequently collected for gene expression analysis or subjected to in vitro fertilization and cultured for 7 days. The results showed that EGF and/or GDNF, when administered in a certain dose (50 ng/μl) to the maturation medium, not only effectively improved the synchronization of nuclear and cytoplasmic maturation processes within the oocyte, but enhanced expression of their corresponding receptors in mature oocytes (P < 0.05). Moreover, supplementation with an optimal combination of EGF + GDNF resulted in elevation of TFAM transcripts as well as a decrease of caspase-3 transcripts compared with the other studied groups (P < 0.05). Collectively, our results indicate that treatment of porcine oocytes with specific-dose combinations of EGF and GDNF stimulates oocyte quality and competence by transcriptional modulation of genes involved in oocyte survival and competence.

RET Signaling in Prostate Cancer

Purpose: Large diameter perineural prostate cancer is associated with poor outcomes. GDNF, with its coreceptor GFRα1, binds RET and activates downstream pro-oncogenic signaling. Because both GDNF and GFRα1 are secreted by nerves, we examined the role of RET signaling in prostate cancer.Experimental Design: Expression of RET, GDNF, and/or GFRα1 was assessed. The impact of RET signaling on proliferation, invasion and soft agar colony formation, perineural invasion, and growth in vivo was determined. Cellular signaling downstream of RET was examined by Western blotting.Results: RET is expressed in all prostate cancer cell lines. GFRα1 is only expressed in 22Rv1 cells, which is the only line that responds to exogenous GDNF. In contrast, all cell lines respond to GDNF plus GFRα1. Conditioned medium from dorsal root ganglia contains secreted GFRα1 and promotes transformation-related phenotypes, which can be blocked by anti-GFRα1 antibody. Perineural invasion in the dorsal root ganglion assay is inhibited by anti-GFRα antibody and RET knockdown. In vivo, knockdown of RET inhibits tumor growth. RET signaling activates ERK or AKT signaling depending on context, but phosphorylation of p70S6 kinase is markedly increased in all cases. Knockdown of p70S6 kinase markedly decreases RET induced transformed phenotypes. Finally, RET is expressed in 18% of adenocarcinomas and all three small-cell carcinomas examined.Conclusions: RET promotes transformation associated phenotypes, including perineural invasion in prostate cancer via activation of p70S6 kinase. GFRα1, which is secreted by nerves, is a limiting factor for RET signaling, creating a perineural niche where RET signaling can occur. Clin Cancer Res; 23(16); 4885-96. ©2017 AACR.

Simvastatin down-regulates differential genetic profiles produced by organochlorine mixtures in primary breast cell (HMEC)

Women all over the world are exposed to an unavoidable contamination by organochlorine pesticides and other chemical pollutants. Many of them are considered as xenoestrogens and have been associated with the development and progression of breast cancer. We have demonstrated that the most prevalent pesticide mixtures found in healthy women and in women diagnosed with breast cancer modulates the gene expression in human epithelial mammary cells. Statins are well-known cholesterol-depleting agents acting as inhibitors of cholesterol synthesis. Since the early 1990s, it has been known that statins could be successfully used in cancer therapy, including breast cancer, but the exact mechanism behind anti-tumor activity of the statins remains unclear. In the present study we evaluated the effect of simvastatin in the gene expression pattern induced by realistic organochlorine mixtures found in breast cancer patients. The gene expression of 94 genes related with the cell signaling pathways were assessed. Our results indicate that simvastatin exerts a global down regulating effect on successfully determined genes (78.7%), thus attenuating the effects induced by organochlorine mixtures on the gene profile of human mammary epithelial cells. This effect was more evident on genes whose function is the ATP-binding process (that also were particularly up-regulated by pesticide mixtures). We also found that MERTK (a proto-oncogene which is overexpressed in several malignancies) and PDGFRB (a member of the platelet-derived growth factor family whose expression is high in breast-cancer cells that have become resistant to endocrine therapy) were among the genes with a higher differential regulation by simvastatin. Since resistance to treatment with tyrosine kinase inhibitors is closely related to MERKT, our findings would enhance the possible utility of statins in breast cancer treatment, i.e. improving therapeutic results combining statins with tyrosine Kinase inhibitors.

Expression of NGF, GDNF and MMP-9 in prostate carcinoma

The aim of the present study was to investigate the immunohistochemical expression of NGF, GDNF and MMP-9 in benign prostatic hyperplasia (BPH), high grade prostatic intraepithelial neoplasia (HGPIN) and prostate cancer (PC), and to analyse their association with the clinicopathological parameters in PC cases. Immunohistochemistry was performed on the tissue microarray (TMA) sections of 30 BPH, 40 HGPIN and 121 primary PC tissues. There was a significant difference regarding the expression of NGF and GDNF between PC and HGPIN (p<0.0001; p<0.0001), and PC and BPH (p=0.001; p<0.0001), but not between HGPIN and BPH (p>0.05). Furthermore MMP-9 expression was significantly different among all groups (PC vs. HGPIN, p<0.0001; PC vs. BPH, p<0.0001; HGPIN vs. BPH, p=0.001). NGF, GDNF and MMP-9 expression was significantly stronger in cases with high Gleason score (p<0.0001, p=0.004, p<0.0001 respectively) and pT stage (p=0.046, p=0.004, p=0.001, respectively) in PC cases. All these markers were also associated with perineural, lymphovascular and extraprostatic invasion (p <0.05). In addition, a positive correlation was found between NGF and MMP-9 (p<0.0001, r=0.435), NGF and GDNF (p<0.0001, r=0.634), and GDNF and MMP-9 (p<0.0001, r=0.670) in PC cases. According to our results we suggest an interaction between NGF, GDNF and MMP-9 during the transition to malignancy in PC. Also this interaction may involve in regulating PC cell differentiation, tumor invasion, progression, and the agressiveness of PC.

Upregulation of RET induces perineurial invasion of pancreatic adenocarcinoma

Tumor spread along nerves, a phenomenon known as perineurial invasion, is common in various cancers including pancreatic ductal adenocarcinoma (PDAC). Neural invasion is associated with poor outcome, yet its mechanism remains unclear. Using the transgenic Pdx-1-Cre/KrasG12D /p53R172H (KPC) mouse model, we investigated the mechanism of neural invasion in PDAC. To detect tissue-specific factors that influence neural invasion by cancer cells, we characterized the perineurial microenvironment using a series of bone marrow transplantation (BMT) experiments in transgenic mice expressing single mutations in the Cx3cr1, GDNF and CCR2 genes. Immunolabeling of tumors in KPC mice of different ages and analysis of human cancer specimens revealed that RET expression is upregulated during PDAC tumorigenesis. BMT experiments revealed that BM-derived macrophages expressing the RET ligand GDNF are highly abundant around nerves invaded by cancer. Inhibition of perineurial macrophage recruitment, using the CSF-1R antagonist GW2580 or BMT from CCR2-deficient donors, reduced perineurial invasion. Deletion of GDNF expression by perineurial macrophages, or inhibition of RET with shRNA or a small-molecule inhibitor, reduced perineurial invasion in KPC mice with PDAC. Taken together, our findings show that RET is upregulated during pancreas tumorigenesis and its activation induces cancer perineurial invasion. Trafficking of BM-derived macrophages to the perineurial microenvironment and secretion of GDNF are essential for pancreatic cancer neural spread.

GFRA1 promotes cisplatin-induced chemoresistance in osteosarcoma by inducing autophagy

Recent progress in chemotherapy has significantly increased its efficacy, yet the development of chemoresistance remains a major drawback. In this study, we show that GFRA1/GFRα1 (GDNF family receptor α 1), contributes to cisplatin-induced chemoresistance by regulating autophagy in osteosarcoma. We demonstrate that cisplatin treatment induced GFRA1 expression in human osteosarcoma cells. Induction of GFRA1 expression reduced cisplatin-induced apoptotic cell death and it significantly increased osteosarcoma cell survival via autophagy. GFRA1 regulates AMPK-dependent autophagy by promoting SRC phosphorylation independent of proto-oncogene RET kinase. Cisplatin-resistant osteosarcoma cells showed NFKB1/NFκB-mediated GFRA1 expression. GFRA1 expression promoted tumor formation and growth in mouse xenograft models and inhibition of autophagy in a GFRA1-expressing xenograft mouse model during cisplatin treatment effectively reduced tumor growth and increased survival. In cisplatin-treated patients, treatment period and metastatic status were associated with GFRA1-mediated autophagy. These findings suggest that GFRA1-mediated autophagy is a promising novel target for overcoming cisplatin resistance in osteosarcoma.

RET kinase inhibitors: a review of recent patents (2012-2015)

INTRODUCTION

Tyrosine kinases are involved in the control of several biological processes and have been recognized as hot spots of oncogenic transformation, thus representing a major therapeutic target. Dysregulated activation of RET kinase, either through point mutations or gene fusions, is accountable for a significant fraction of thyroid carcinomas, as well as a minor population of lung cancers. Two drugs are currently available for the treatment of medullary thyroid carcinoma and two additional compounds have been approved for differentiated thyroid carcinoma. Several other molecules are under preclinical and clinical evaluation. Areas covered: This review covers the most recent patent literature (2012-2015) describing compounds with activity against the RET kinase, trying to catch a view of the next generation of potential anti-RET drugs. Expert opinion: RET has been a focus of molecularly targeted efforts for over a decade. However, none of the drugs currently on the clinical stage were specifically developed to hit RET, which was rather an off-target. Besides, only two of four drugs have activity on metastatic medullary carcinoma. Therefore, there is still a need of additional, more potent and more specific RET inhibitors, which will hopefully emerge from the new generation of compounds disclosed in most recent patents.

Mechanisms of cancer dissemination along nerves

The local extension of cancer cells along nerves is a frequent clinical finding for various tumours. Traditionally, nerve invasion was assumed to occur via the path of least resistance; however, recent animal models and human studies have revealed that cancer cells have an innate ability to actively migrate along axons in a mechanism called neural tracking. The tendency of cancer cells to track along nerves is supported by various cell types in the perineural niche that secrete multiple growth factors and chemokines. We propose that the perineural niche should be considered part of the tumour microenvironment, describe the molecular cues that facilitate neural tracking and suggest methods for its inhibition.

Genetic and epigenetic factors affect RET gene expression in breast cancer cell lines and influence survival in patients

Germline and somatic mutations play a crucial role in breast cancer (BC), driving the initiation, progression, response to therapy and outcome of the disease. Hormonal therapy is limited to patients with tumors expressing steroid hormone receptors, such as estrogen receptor (ER), nevertheless resistance often limits its success.The RET gene is known to be involved in neurocristopathies such as Hirschsprung disease and Multiple Endocrine Neoplasia type 2, in the presence of loss-of-function and gain-of-function mutations, respectively. More recently, RET over-expression has emerged as a new player in ER-positive (ER+) BC, and as a potential target to enhance sensitivity and avoid resistance to tamoxifen therapy.Therefore, targeting the RET pathway may lead to new therapies in ER+ BC. To this end, we have investigated the molecular mechanisms which underlie RET overexpression and its possible modulation in two BC cell lines, MCF7 and T47D, showing different RET expression levels. Moreover, we have carried out a pilot association study in 93 ER+ BC patients. Consistent with the adverse role of RET over-expression in BC, increased overall survival was observed in carriers of the variant allele of SNP rs2435357, a RET polymorphism already known to be associated with reduced RET expression.

Preclinical Efficacy and Safety Assessment of an Antibody-Drug Conjugate Targeting the c-RET Proto-Oncogene for Breast Carcinoma

PURPOSE

The RET proto-oncogene has been implicated in breast cancer, and the studies herein describe the preclinical and safety assessment of an anti-RET antibody-drug conjugate (ADC) being developed for the treatment of breast cancer.

EXPERIMENTAL DESIGN

RET protein expression was analyzed in breast tumor samples using tissue microarrays. The fully human anti-RET antibody (Y078) was conjugated to the DM1 and DM4 derivatives of the potent cytotoxic agent maytansine using thioether and disulfide linkers, respectively. The resulting compounds, designated Y078-DM1 and Y078-DM4, were evaluated for antitumor activity using human breast cancer cell lines and established tumor xenograft models. A single-dose, 28-day, safety study of Y078-DM1 was performed in cynomolgus monkeys.

RESULTS

By immunohistochemistry, RET expression was detected in 57% of tumors (1,596 of 2,800 tumor sections) and was most common in HER2-positive and basal breast cancer subtypes. Potent in vitro cytotoxicity was achieved in human breast cancer cell lines that have expression levels comparable with those observed in breast cancer tissue samples. Dose-response studies in xenograft models demonstrated antitumor activity with both weekly and every-3-weeks dosing regimens. In cynomolgus monkeys, a single injection of Y078-DM1 demonstrated dose-dependent, reversible drug-mediated alterations in blood chemistry with evidence of on-target neuropathy.

CONCLUSIONS

RET is broadly expressed in breast cancer specimens and thus represents a potential therapeutic target; Y078-DM1 and Y078-DM4 demonstrated antitumor activity in preclinical models. Optimization of the dosing schedule or an alternate cytotoxic agent with a different mechanism of action may reduce the potential risk of neuropathy. Clin Cancer Res; 21(24); 5552-62. ©2015 AACR.

ESR1 mutations—a mechanism for acquired endocrine resistance in breast cancer

Approximately 70% of breast cancers are oestrogen receptor α (ER) positive, and are, therefore, treated with endocrine therapies. However, about 25% of patients with primary disease and almost all patients with metastases will present with or eventually develop endocrine resistance. Despite the magnitude of this clinical challenge, the mechanisms underlying the development of resistance remain largely unknown. In the past 2 years, several studies unveiled gain-of-function mutations in ESR1, the gene encoding the ER, in approximately 20% of patients with metastatic ER-positive disease who received endocrine therapies, such as tamoxifen and aromatase inhibitors. These mutations are clustered in a 'hotspot' within the ligand-binding domain (LBD) of the ER and lead to ligand-independent ER activity that promotes tumour growth, partial resistance to endocrine therapy, and potentially enhanced metastatic capacity; thus, ER LBD mutations might account for a mechanism of acquired endocrine resistance in a substantial fraction of patients with metastatic disease. In general, the absence of detectable ESR1 mutations in patients with treatment-naive disease, and the correlation between the frequency of patients with tumours harbouring these mutations and the number of endocrine treatments received suggest that, under selective treatment pressure, clonal expansion of rare mutant clones occurs, leading to resistance. Preclinical and clinical development of rationale-based novel therapeutic strategies that inhibit these ER mutants has the potential to substantially improve treatment outcomes. We discuss the contribution of ESR1 mutations to the development of acquired resistance to endocrine therapy, and evaluate how mutated ER can be detected and targeted to overcome resistance and improve patient outcomes.

Thyroid C-Cell Biology and Oncogenic Transformation

The thyroid parafollicular cell, or commonly named "C-cell," functions in serum calcium homeostasis. Elevations in serum calcium trigger release of calcitonin from the C-cell, which in turn functions to inhibit absorption of calcium by the intestine, resorption of bone by the osteoclast, and reabsorption of calcium by renal tubular cells. Oncogenic transformation of the thyroid C-cell is thought to progress through a hyperplastic process prior to malignancy with increasing levels of serum calcitonin serving as a biomarker for tumor burden. The discovery that multiple endocrine neoplasia type 2 is caused by activating mutations of the RET gene serves to highlight the RET-RAS-MAPK signaling pathway in both initiation and progression of medullary thyroid carcinoma (MTC). Thyroid C-cells are known to express RET at high levels relative to most cell types; therefore, aberrant activation of this receptor is targeted primarily to the C-cell, providing one possible cause of tissue-specific oncogenesis. The role of RET signaling in normal C-cell function is unknown though calcitonin gene transcription appears to be sensitive to RET activation. Beyond RET, the modeling of oncogenesis in animals and screening of human tumors for candidate gene mutations have uncovered mutation of RAS family members and inactivation of Rb1 regulatory pathway as potential mediators of C-cell transformation. A growing understanding of how RET interacts with these pathways, both in normal C-cell function and during oncogenic transformation, will help in the development of novel molecular-targeted therapies.

Prognostic significance of artemin and GFRα1 expression in laryngeal squamous cell carcinoma

Artemin (ARTN) has been implicated in the development and progression of several human malignancies. However, the clinical and prognostic significance of ARTN and its receptors has not yet been investigated in human laryngeal squamous cell carcinoma (LSCC). Therefore, in the present study, the protein expression of ARTN and its receptor, namely GFRα1, was determined in 76 LSCC and 26 laryngeal polyp tissue samples using immunohistochemistry. Furthermore, the clinicopathological and prognostic significance of ARTN and GFRα1 expression was analyzed in patients with LSCC. The results revealed that the expression of ARTN and GFRα1 was significantly increased in LSCC compared with polyp tissue samples. Furthermore, the expression of ARTN and GFRα1 was positively associated with pTNM stage in LSCC. Kaplan-Meier survival analyses revealed a strong association between the expression of ARTN or GFRα1 and the survival of patients with LSCC. Correlation analysis demonstrated that the expression of ARTN was significantly correlated with the expression GFRα1. In conclusion, the results demonstrated that ARTN and GFRα1 may be useful predictors of disease progression and outcome in patients with LSCC.

Mechanisms of RET signaling in cancer: current and future implications for targeted therapy

De-regulation of RET signaling by oncogenic mutation, gene rearrangement, overexpression or transcriptional up-regulation is implicated in several human cancers of neuroendocrine and epithelial origin (thyroid, breast, lung). Understanding how RET signaling mechanisms associated with these oncogenic events are deregulated, and their impact in the biological processes driving tumor formation and progression, as well as response to treatment, will be crucial to find and develop better targeted therapeutic strategies. In this review we emphasie the distinct mechanisms of RET signaling in cancer and summarise current knowledge on small molecule inhibitors targeting the tyrosine kinase domain of RET as therapeutic drugs in RET-positive cancers.

RET revisited: expanding the oncogenic portfolio

The RET receptor tyrosine kinase is crucial for normal development but also contributes to pathologies that reflect both the loss and the gain of RET function. Activation of RET occurs via oncogenic mutations in familial and sporadic cancers - most notably, those of the thyroid and the lung. RET has also recently been implicated in the progression of breast and pancreatic tumours, among others, which makes it an attractive target for small-molecule kinase inhibitors as therapeutics. However, the complex roles of RET in homeostasis and survival of neural lineages and in tumour-associated inflammation might also suggest potential long-term pitfalls of broadly targeting RET.

Inhibition of RET increases the efficacy of antiestrogen and is a novel treatment strategy for luminal breast cancer

PURPOSE

Recent findings suggest that combination treatment with antiestrogen and anti-RET may offer a novel treatment strategy in a subset of patients with breast cancer. We investigated the role of RET in potentiating the effects of antiestrogen response and examined whether RET expression predicted the ability for tyrosine kinase inhibitor (TKI) to affect extracellular signal-regulated kinase 1/2 (ERK1/2) activation in primary breast cancer.

EXPERIMENTAL DESIGN

Growth response, ERK1/2 activation, Ki-67, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling were assessed in breast cancer cell lines in vitro and in xenografts with vandetanib and/or tamoxifen. Thirty tumors with matched normal breast tissue were evaluated for RET expression and response to TKI treatment.

RESULTS

Vandetanib potentiated the inhibitory effect of tamoxifen in hormone responsive (P = 0.01) and hormone insensitive (P < 0.001) estrogen receptor α (ERα)-positive breast cancer cells. Vandetanib significantly repressed tumorigenesis of MCF-7 xenografts (P < 0.001), which displayed decreased activation of ERK1/2 and AKT. Vandetanib and tamoxifen reduced the growth of established tumors with a greater effect of dual therapy compared with single agent (P = 0.003), with tamoxifen-reducing proliferative index and vandetanib-inducing apoptosis. In primary breast cancers, RET expression correlated with the ERα-positive subtype. Relative decrease in ERK1/2 phosphorylation with TKI treatment was 42% (P < 0.001) in RET-positive tumors versus 14% (P = ns) in RET-negative tumors.

CONCLUSIONS

Vandetanib potentiated the antigrowth effects of tamoxifen in breast cancer, which was mediated through RET activation. RET predicted response to TKI therapy with minimal effects on ERK1/2 activation in RET-negative tumors. The preclinical data support evaluation of antiestrogen in combination with TKI as a potential treatment strategy for RET-positive luminal breast cancer.

Targeting RET-interleukin-6 crosstalk to impair metastatic dissemination in breast cancer

RET (rearranged during transfection) is a receptor tyrosine kinase overexpressed in a subset of oestrogen receptor (ER)-positive breast cancers whose expression is regulated by ER signalling. The article from the Hynes group has reported for the first time that RET expression can also be regulated by the inflammatory cytokine IL-6. Importantly, RET and IL-6 interact at a functional level to control migration and the metastatic potential of ER-positive breast cancer cells, in a process that is mediated by FAK activation. Further, targeting RET with receptor tyrosine kinase inhibitors was reported to be more effective than endocrine therapies in impairing metastatic dissemination in vivo, thereby indicating a level of RET regulation that is independent of ER.

Enigma prevents Cbl-c-mediated ubiquitination and degradation of RETMEN2A

The Cbl proteins (Cbl, Cbl-b, and Cbl-c) are a highly conserved family of RING finger ubiquitin ligases (E3s) that function as negative regulators of tyrosine kinases in a wide variety of signal transduction pathways. In this study, we identify a new Cbl-c interacting protein, Enigma (PDLIM7). This interaction is specific to Cbl-c as Enigma fails to bind either of its closely related homologues, Cbl and Cbl-b. The binding between Enigma and Cbl-c is mediated through the LIM domains of Enigma as removal of all three LIM domains abrogates this interaction, while only LIM1 is sufficient for binding. Here we show that Cbl-c binds wild-type and MEN2A isoforms of the receptor tyrosine kinase, RET, and that Cbl-c enhances ubiquitination and degradation of activated RET. Enigma blocks Cbl-c-mediated RETMEN2A ubiquitination and degradation. Cbl-c decreased downstream ERK activation by RETMEN2A and co-expression of Enigma blocked the Cbl-c-mediated decrease in ERK activation. Enigma showed no detectable effect on Cbl-c-mediated ubiquitination of activated EGFR suggesting that this effect is specific to RET. Through mapping studies, we show that Cbl-c and Enigma bind RETMEN2A at different residues. However, binding of Enigma to RETMENA prevents Cbl-c recruitment to RETMEN2A. Consistent with these biochemical data, exploratory analyses of breast cancer patients with high expression of RET suggest that high expression of Cbl-c correlates with a good outcome, and high expression of Enigma correlates with a poor outcome. Together, these data demonstrate that Cbl-c can ubiquitinate and downregulate RETMEN2A and implicate Enigma as a positive regulator of RETMEN2A through blocking of Cbl-mediated ubiquitination and degradation.

Central role of RET in thyroid cancer

RET (rearranged during transfection) is a receptor tyrosine kinase involved in the development of neural crest derived cell lineages, kidney, and male germ cells. Different human cancers, including papillary and medullary thyroid carcinomas, lung adenocarcinomas, and myeloproliferative disorders display gain-of-function mutations in RET. Accordingly, RET protein has become a promising molecular target for cancer treatment.

Identification of integrin α3 as a molecular marker of cells undergoing epithelial-mesenchymal transition and of cancer cells with aggressive phenotypes

Epithelial-mesenchymal transition (EMT) is a crucial event in wound healing, tissue repair, and cancer progression in adult tissues. Transforming growth factor (TGF)-β induces EMT in mouse epithelial cells. During prolonged treatment, TGF-β successively induces myofibroblastic differentiation with increased expression of myofibroblast marker proteins, including smooth muscle α actin and calponin. We recently showed that fibroblast growth factor-2 prevented myofibroblastic differentiation induced by TGF-β, and transdifferentiated the cells to those with much more aggressive characteristics (enhanced EMT). To identify the molecular markers specifically expressed in cells undergoing enhanced EMT induced by the combination of TGF-β and fibroblast growth factor-2, we carried out a microarray-based analysis and found that integrin α3 (ITGA3) and Ret were upregulated. Intriguingly, ITGA3 was also overexpressed in breast cancer cells with aggressive phenotypes and its expression was correlated with that of δEF-1, a key regulator of EMT. Moreover, the expression of both genes was downregulated by U0126, a MEK 1/2 inhibitor. Therefore, ITGA3 is a potential marker protein for cells undergoing enhanced EMT and for cancer cells with aggressive phenotypes, which is positively regulated by δEF-1 and the MEK-ERK pathway.

Ret inhibition decreases growth and metastatic potential of estrogen receptor positive breast cancer cells

We show that elevated levels of Ret receptor are found in different sub-types of human breast cancers and that high Ret correlates with decreased metastasis-free survival. The role of Ret in ER+ breast cancer models was explored combining in vitro and in vivo approaches. Our analyses revealed that ligand-induced Ret activation: (i) stimulates migration of breast cancer cells; (ii) rescues cells from anti-proliferative effects of endocrine treatment and (iii) stimulates expression of cytokines in the presence of endocrine agents. Indeed, we uncovered a positive feed-forward loop between the inflammatory cytokine IL6 and Ret that links them at the expression and the functional level. In vivo inhibition of Ret in a metastatic breast cancer model inhibits tumour outgrowth and metastatic potential. Ret inhibition blocks the feed-forward loop by down-regulating Ret levels, as well as decreasing activity of Fak, an integrator of IL6-Ret signalling. Our results suggest that Ret kinase should be considered as a novel therapeutic target in subsets of breast cancer.

GDNF-RET signaling in ER-positive breast cancers is a key determinant of response and resistance to aromatase inhibitors

Most breast cancers at diagnosis are estrogen receptor-positive (ER(+)) and depend on estrogen for growth and survival. Blocking estrogen biosynthesis by aromatase inhibitors has therefore become a first-line endocrine therapy for postmenopausal women with ER(+) breast cancers. Despite providing substantial improvements in patient outcome, aromatase inhibitor resistance remains a major clinical challenge. The receptor tyrosine kinase, RET, and its coreceptor, GFRα1, are upregulated in a subset of ER(+) breast cancers, and the RET ligand, glial-derived neurotrophic factor (GDNF) is upregulated by inflammatory cytokines. Here, we report the findings of a multidisciplinary strategy to address the impact of GDNF-RET signaling in the response to aromatase inhibitor treatment. In breast cancer cells in two-dimensional and three-dimensional culture, GDNF-mediated RET signaling is enhanced in a model of aromatase inhibitor resistance. Furthermore, GDNF-RET signaling promoted the survival of aromatase inhibitor-resistant cells and elicited resistance in aromatase inhibitor-sensitive cells. Both these effects were selectively reverted by the RET kinase inhibitor, NVP-BBT594. Gene expression profiling in ER(+) cancers defined a proliferation-independent GDNF response signature that prognosed poor patient outcome and, more importantly, predicted poor response to aromatase inhibitor treatment with the development of resistance. We validated these findings by showing increased RET protein expression levels in an independent cohort of aromatase inhibitor-resistant patient specimens. Together, our results establish GDNF-RET signaling as a rational therapeutic target to combat or delay the onset of aromatase inhibitor resistance in breast cancer.

Prognostic significance of the expression of GFRα1, GFRα3 and syndecan-3, proteins binding ARTEMIN, in mammary carcinoma

BACKGROUND

Artemin (ARTN) has been implicated in promoting oncogenicity, tumor growth and invasiveness in diverse human malignancies. However, the clinical and prognostic significance of upstream ligand binding components, potentially mediating ARTN oncogenicity, largely remain to be determined.

METHODS

We determined the mRNA and protein expression of three proteins demonstrated to bind ARTN, namely GFRα1, GFRα3 and syndecan-3 (SDC3), in benign breast disease and mammary carcinoma by in situ hybridization and immunohistochemistry, respectively. Their prognostic significance combined with ARTN expression was also investigated in mammary carcinoma.

RESULTS

The expression of GFRα1 and GFRα3, but not SDC3, was significantly increased in mammary carcinoma and positively associated with tumor lymph node metastases, higher clinical stage and HER-2 positivity. Moreover, both GFRα1 and GFRα3 expression were significantly associated with survival outcome of patients with mammary carcinoma by univariate and multivariate analyses, whereas expression of SDC3 was not. Co-expression of ARTN with either GFRα1 or GFRα3, but not SDC3, produced synergistic increases in the odds ratio for both relapse-free and overall survival in patients with mammary carcinoma. Furthermore, significant association of GFRα1 and GFRα3 expression with survival outcome observed herein were restricted to ER negative or HER-2 negative mammary carcinoma.

CONCLUSIONS

The expression of GFRα1 and/or GFRα3, especially when combined with ARTN expression, may be useful predictors of disease progression and outcome in specific subtypes of mammary carcinoma.

Endoneurial macrophages induce perineural invasion of pancreatic cancer cells by secretion of GDNF and activation of RET tyrosine kinase receptor

Perineural invasion of cancer cells (CPNI) is found in most patients with pancreatic adenocarcinomas (PDA), prostate, or head and neck cancers. These patients undergo palliative rather than curative treatment due to dissemination of cancer along nerves, well beyond the extent of any local invasion. Although CPNI is a common source of distant tumor spread and a cause of significant morbidity, its exact mechanism is undefined. Immunohistochemical analysis of specimens excised from patients with PDAs showed a significant increase in the number of endoneurial macrophages (EMΦ) that lie around nerves invaded by cancer compared with normal nerves. Video microscopy and time-lapse analysis revealed that EMΦs are recruited by the tumor cells in response to colony-stimulated factor-1 secreted by invading cancer cells. Conditioned medium (CM) of tumor-activated EMΦs (tEMΦ) induced a 5-fold increase in migration of PDA cells compared with controls. Compared with resting EMΦs, tEMΦs secreted higher levels of glial-derived neurotrophic factor (GDNF), inducing phosphorylation of RET and downstream activation of extracellular signal-regulated kinases (ERK) in PDA cells. Genetic and pharmacologic inhibition of the GDNF receptors GFRA1 and RET abrogated the migratory effect of EMΦ-CM and reduced ERK phosphorylation. In an in vivo CPNI model, CCR2-deficient mice that have reduced macrophage recruitment and activation showed minimal nerve invasion, whereas wild-type mice developed complete sciatic nerve paralysis due to massive CPNI. Taken together, our results identify a paracrine response between EMΦs and PDA cells that orchestrates the formation of cancer nerve invasion.

Loss of pigment epithelium-derived factor: a novel mechanism for the development of endocrine resistance in breast cancer

INTRODUCTION

Despite the benefits of endocrine therapies such as tamoxifen and aromatase inhibitors in treating estrogen receptor (ER) alpha-positive breast cancer, many tumors eventually become resistant. The molecular mechanisms governing resistance remain largely unknown. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that displays broad anti-tumor activity based on dual targeting of the tumor microenvironment (anti-angiogenic action) and the tumor cells (direct anti-tumor action). Recent studies indicate that PEDF expression is significantly reduced in several tumor types, including breast cancer, and that its reduction is associated with disease progression and poor patient outcome. In the current study, we investigated the role of PEDF in the development of endocrine resistance in breast cancer.

METHODS

PEDF mRNA and protein levels were measured in several endocrine-resistant breast cancer cell lines including MCF-7:5C, MCF-7:2A, and BT474 and in endocrine-sensitive cell lines MCF-7, T47D, and ZR-75-1 using real-time PCR and western blot analyses. Tissue microarray analysis and immunohistochemistry were used to assess the PEDF protein level in tamoxifen-resistant breast tumors versus primary tumors. Lentiviruses were used to stably express PEDF in endocrine-resistant breast cancer cell lines to determine their sensitivity to tamoxifen following PEDF re-expression.

RESULTS

We found that PEDF mRNA and protein levels were dramatically reduced in endocrine-resistant MCF-7:5C, MCF-7:2A, and BT474 breast cancer cells compared with endocrine-sensitive MCF-7, T47D, and ZR-75-1 cells, and that loss of PEDF was associated with enhanced expression of pSer167ERα and the receptor tyrosine kinase rearranged during transfection (RET). Importantly, we found that silencing endogenous PEDF in tamoxifen-sensitive MCF-7 and T47D breast cancer cells conferred tamoxifen resistance whereas re-expression of PEDF in endocrine-resistant MCF-7:5C and MCF-7:2A cells restored their sensitivity to tamoxifen in vitro and in vivo through suppression of RET. Lastly, tissue microarray studies revealed that PEDF protein was reduced in ~52.4% of recurrence tumors (31 out of 59 samples) and loss of PEDF was associated with disease progression and poor patient outcome.

CONCLUSION

Overall, these findings suggest that PEDF silencing might be a novel mechanism for the development of endocrine resistance in breast cancer and that PEDF expression might be a predictive marker of endocrine sensitivity.

Expression of the RET proto-oncogene is regulated by TFAP2C in breast cancer independent of the estrogen receptor

BACKGROUND

The RET proto-oncogene is expressed as part of the estrogen receptor (ER) cluster in breast cancer. We sought to determine if TFAP2C regulates Ret expression directly or indirectly through ER.

METHODS

Chromatin immunoprecipitation sequencing (ChIP-Seq) and gel-shift assay were used to identify TFAP2C binding sites in the RET promoter in four breast cancer cell lines. Ret mRNA and protein levels were evaluated in ER-positive and ER-negative breast cancer cell lines after knockdown of TFAP2C. Luciferase expression assay was performed to assess expression from two of the identified sites.

RESULTS

ChIP-Seq identified five main binding peaks for TFAP2C in the RET promoter at -101.5 kb, -50.7 kb, -32.5 kb, +5.0 kb, and +33.6 from the RET transcriptional start site. Binding at three of the AP-2 sites was conserved across all four cell lines, whereas the RET -101.5 and RET +33.6 sites were each found to be unbound by TFAP2C in one cell line. A TFAP2C consensus element was confirmed for all five sites. Knockdown of TFAP2C by siRNA in ER-positive MCF-7 cells resulted in significant down regulation of Ret mRNA compared to nontargeting (NT) siRNA (0.09 vs. 1.0, P < 0.001). Knockdown of TFAP2C in ER-negative MDA-MB-453 cells also led to a significant reduction in Ret mRNA compared to NT siRNA (0.16 vs. 1.0, P < 0.001). In MCF-7 cells, knockdown of TFAP2C abrogated Ret protein expression (0.02 vs. 1.0, P < 0.001) before reduction in ER.

CONCLUSIONS

TFAP2C regulates expression of the RET proto-oncogene through five AP-2 regulatory sites in the RET promoter. Regulation of Ret by TFAP2C occurs independently of ER expression in breast carcinoma.

Using rule-based machine learning for candidate disease gene prioritization and sample classification of cancer gene expression data

Microarray data analysis has been shown to provide an effective tool for studying cancer and genetic diseases. Although classical machine learning techniques have successfully been applied to find informative genes and to predict class labels for new samples, common restrictions of microarray analysis such as small sample sizes, a large attribute space and high noise levels still limit its scientific and clinical applications. Increasing the interpretability of prediction models while retaining a high accuracy would help to exploit the information content in microarray data more effectively. For this purpose, we evaluate our rule-based evolutionary machine learning systems, BioHEL and GAssist, on three public microarray cancer datasets, obtaining simple rule-based models for sample classification. A comparison with other benchmark microarray sample classifiers based on three diverse feature selection algorithms suggests that these evolutionary learning techniques can compete with state-of-the-art methods like support vector machines. The obtained models reach accuracies above 90% in two-level external cross-validation, with the added value of facilitating interpretation by using only combinations of simple if-then-else rules. As a further benefit, a literature mining analysis reveals that prioritizations of informative genes extracted from BioHEL's classification rule sets can outperform gene rankings obtained from a conventional ensemble feature selection in terms of the pointwise mutual information between relevant disease terms and the standardized names of top-ranked genes.

Target points in trastuzumab resistance

Epidermal growth factor (EGF) family of receptors is involved in cell growth and differentiation. The human EGF2 (HER2) lacks natural ligands, and correlation between HER2 levels and carcinogenesis makes the receptor an ideal candidate for targeted therapy in breast cancer. Trastuzumab is a humanized antibody applied against HER2-positive breast tumors in clinic. Metastatic tumors respond well to trastuzumab therapy for the first year, but development of antibody resistance helps the tumors to regrow allowing the disease to progress. Trastuzumab resistance is shaped via a range of intracellular signaling pathways that are interconnected and share in key effector molecules. Identification of a common node central to these resistance pathways could provide an ultimate solution for trastuzumab resistance in breast and other cancers.

Molecular mechanisms of RET receptor-mediated oncogenesis in multiple endocrine neoplasia 2

Multiple endocrine neoplasia type 2 is an inherited cancer syndrome characterized by tumors of thyroid and adrenal tissues. Germline mutations of the REarranged during Transfection (RET) proto-oncogene, leading to its unregulated activation, are the underlying cause of this disease. Multiple endocrine neoplasia type 2 has been a model in clinical cancer genetics, demonstrating how knowledge of the genetic basis can shape the diagnosis and treatment of the disease. Here, we discuss the nature and effects of the most common recurrent mutations of RET found in multiple endocrine neoplasia type 2. Current understanding of the molecular mechanisms of RET mutations and how they alter the structure and function of the RET protein leading to its aberrant activation, and the effects on RET localization and signaling are described.

Hormone receptor and ERBB2 status in gene expression profiles of human breast tumor samples

The occurrence of large publically available repositories of human breast tumor gene expression profiles provides an important resource to discover new breast cancer biomarkers and therapeutic targets. For example, knowledge of the expression of the estrogen and progesterone hormone receptors (ER and PR), and that of the ERBB2 in breast tumor samples enables choice of therapies for the breast cancer patients that express these proteins. Identifying new biomarkers and therapeutic agents affecting the activity of signaling pathways regulated by the hormone receptors or ERBB2 might be accelerated by knowledge of their expression levels in large gene expression profiling data sets. Unfortunately, the status of these receptors is not invariably reported in public databases of breast tumor gene expression profiles. Attempts have been made to employ a single probe set to identify ER, PR and ERBB2 status, but the specificity or sensitivity of their prediction is low. We enquired whether estimation of ER, PR and ERBB2 status of profiled tumor samples could be improved by using multiple probe sets representing these three genes and others with related expression.We used 8 independent datasets of human breast tumor samples to define gene expression signatures comprising 24, 51 and 14 genes predictive of ER, PR and ERBB2 status respectively. These signatures, as demonstrated by sensitivity and specificity measures, reliably identified hormone receptor and ERBB2 expression in breast tumors that had been previously determined using protein and DNA based assays. Our findings demonstrate that gene signatures can be identified which reliably predict the expression status of the estrogen and progesterone hormone receptors and that of ERBB2 in publically available gene expression profiles of breast tumor samples. Using these signatures to query transcript profiles of breast tumor specimens may enable discovery of new biomarkers and therapeutic targets for particular subtypes of breast cancer.

Down-regulation of estrogen receptor-alpha and rearranged during transfection tyrosine kinase is associated with withaferin a-induced apoptosis in MCF-7 breast cancer cells

BACKGROUND

Withaferin A (WA), a naturally occurring withanolide, induces apoptosis in both estrogen-responsive MCF-7 and estrogen-independent MDA-MB-231 breast cancer cell lines with higher sensitivity in MCF-7 cells, but the underlying mechanisms are not well defined. The purpose of this study was to determine the anti-cancer effects of WA in MCF-7 breast cancer cells and explore alterations in estrogen receptor alpha (ERα) and its associated molecules in vitro as novel mechanisms of WA action.

METHODS

The effects of WA on MCF-7 viability and proliferation were evaluated by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and trypan blue exclusion assays. Apoptosis was evaluated by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) flow cytometry and Western blot analysis of poly (ADP-ribose) polymerase (PARP) cleavage. Cell cycle effects were analyzed by PI flow cytometry. Western blotting was also conducted to examine alterations in the expression of ERα and pathways that are associated with ERα function.

RESULTS

WA resulted in growth inhibition and decreased viability in MCF-7 cells with an IC50 of 576 nM for 72 h. It also caused a dose- and time-dependent apoptosis and G2/M cell cycle arrest. WA-induced apoptosis was associated with down-regulation of ERα, REarranged during Transfection (RET) tyrosine kinase, and heat shock factor-1 (HSF1), as well as up-regulation of phosphorylated p38 mitogen-activated protein kinase (phospho-p38 MAPK), p53 and p21 protein expression. Co-treatment with protein synthesis inhibitor cycloheximide or proteasome inhibitor MG132 revealed that depletion of ERα by WA is post-translational, due to proteasome-dependent ERα degradation.

CONCLUSIONS

Taken together, down-regulation of ERα, RET, HSF1 and up-regulation of phospho-p38 MAPK, p53, p21 are involved in the pro-apoptotic and growth-inhibitory effects of WA in MCF-7 breast cancer cells in vitro. Down-regulation of ERα protein levels by WA is caused by proteasome-dependent ERα degradation.

Estrogen receptor (ESR1) mRNA expression and benefit from tamoxifen in the treatment and prevention of estrogen receptor-positive breast cancer

PURPOSE

Several mechanisms have been proposed to explain tamoxifen resistance of estrogen receptor (ER) -positive tumors, but a clinically useful explanation for such resistance has not been described. Because the ER is the treatment target for tamoxifen, a linear association between ER expression levels and the degree of benefit from tamoxifen might be expected. However, such an association has never been demonstrated with conventional clinical ER assays, and the ER is currently used clinically as a dichotomous marker. We used gene expression profiling and ER protein assays to help elucidate molecular mechanism(s) responsible for tamoxifen resistance in breast tumors.

PATIENTS AND METHODS

We performed gene expression profiling of paraffin-embedded tumors from National Surgical Adjuvant Breast and Bowel Project (NSABP) trials that tested the worth of tamoxifen as an adjuvant systemic therapy (B-14) and as a preventive agent (P-1). This was a retrospective subset analysis based on available materials.

RESULTS

In B-14, ESR1 was the strongest linear predictor of tamoxifen benefit among 16 genes examined, including PGR and ERBB2. On the basis of these data, we hypothesized that, in the P-1 trial, a lower level of ESR1 mRNA in the tamoxifen arm was the main difference between the two study arms. Only ESR1 was downregulated by more than two-fold in ER-positive cancer events in the tamoxifen arm (P < .001). Tamoxifen did not prevent ER-positive tumors with low levels of ESR1 expression.

CONCLUSION

These data suggest that low-level expression of ESR1 is a determinant of tamoxifen resistance in ER-positive breast cancer. Strategies should be developed to identify, treat, and prevent such tumors.