Inhibition of androgen receptor and Cdc25A phosphatase as a combination targeted therapy in molecular apocrine breast cancer

Novel Small-Molecule Inhibitor for the Oncogenic Tyrosine Phosphatase SHP2 with Anti-Breast Cancer Cell Effects

The oncogenic property of the Src homology phosphotyrosine phosphatase 2 (SHP2) is well-known, but developing specific inhibitors has been very difficult. Based on our previous reports that showed the importance of acidic residues surrounding SHP2 substrate phosphotyrosines for specific recognition, we have rationally designed and chemically synthesized a small-molecule SHP2 inhibitor named 4,4'-(4'-carboxy)-4-nonyloxy-[1,1'-biphenyl]-3,5-diyl)dibutanoic acid (CNBDA). Molecular modeling predicted that CNBDA packs well into the SHP2 active site and makes extended interactions primarily with positively charged and polar amino acids surrounding the active site. In vitro PTPase assays showed that CNBDA inhibits SHP2 with an IC₅₀ of 5 μM. However, the IC₅₀ of CNBDA toward SHP1, the close structural homologue of SHP2, was 125 μM, suggesting an approximately 25-fold effectiveness against SHP2 than SHP1. Because SHP2 is known for its positive role in breast cancer (BC) cell biology, we tested the effect of SHP2 inhibition with CNBDA in HER2-positive BC cells. Treatment with CNBDA suppressed cell proliferation in 2D culture, anchorage-independent growth in soft agar, and mammosphere (tumorisphere) formation in suspension cultures in a concentration-dependent manner. Furthermore, CNBDA inhibited EGF-induced signaling and expression of HER2 by inhibiting the PTPase activity of SHP2 in BC cells. These findings suggest that CNBDA is a promising anti-SHP2 lead compound with anti-BC cell effects.

Anti-tumor activity of BET inhibitors in androgen-receptor-expressing triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a heterogeneous disease comprising several subtypes. Androgen-receptor (AR) signaling has been targeted by several investigational agents in luminal AR subtype TNBCs. Bromodomain (BRD) and extra-terminal motif (BET) protein inhibitors have been shown to attenuate AR signaling in metastatic castration-resistant prostate cancer and to overcome enzalutamide resistance. We demonstrated potent anti-tumor effects of the BET inhibitor JQ1 against AR-positive TNBC cell lines using cell viability and cell cycle analysis. To reveal the mechanisms of JQ1 effects, multiplex gene expression analysis and immunoblotting assays were used. We examined in vivo effects of JQ1 in a xenograft model of AR expressing TNBC. JQ1 exhibited its anti-proliferative activity by inducing apoptosis and cell cycle arrest. JQ1 activity was not mediated by MYC downregulation. Instead, JQ1 blocked the interactions among the ATPase-family AAA-domain-containing 2 protein (ATAD2), BRD2, BRD4, and AR; effectively suppressing the expression of AR associated targets. In addition, JQ1 showed significant anti-tumor activity in vivo in TNBC xenograft mouse models as a monotherapy and in combination with anti-AR therapy. Taken together, our results showed that the BET inhibitor JQ1 is a promising therapeutic agent for the treatment of AR-positive TNBC.

Androgen receptor: A promising therapeutic target in breast cancer

Breast cancer (BCa) is the second most common cancer worldwide and the most prevalent cancer in women. The majority of BCa cases are positive (+) for the estrogen receptor (ER⁺, 80%) and progesterone receptor (PR⁺, 65%). Estrogen and progesterone hormones are known to be involved in cancer progression, and thus hormonal deprivation is used as an effective treatment for ER⁺PR⁺ BCa subtypes. However, some ER⁺PR⁺ BCa patients develop resistance to such therapies. Meanwhile, chemotherapy is the only available treatment for ER^-PR^- BCa tumors. Another hormone receptor known as the androgen receptor (AR) has also been found to be widely expressed in human breast carcinomas. However, the mechanisms of AR and its endogenous androgen ligands is not well-understood in BCa and its biological role in this hormone-related disease remains unclear. In this review, we aim to address the importance of the AR in BCa diagnosis and prognosis, current AR-targeting approaches in BCa, and the potential for AR-downstream molecules to serve as therapeutic targets.

The cellular and molecular effects of the androgen receptor agonist, Cl-4AS-1, on breast cancer cells

PURPOSE

The androgen receptor (AR) has attracted attention in the treatment of breast cancer. Due to the undesirable side effects of AR agonists, attempts have been undertaken to develop selective AR modulators. One of these compounds is Cl-4AS-1. This study examined this compound more closely at the cellular and molecular levels.

METHODS

Three different breast cancer cell lines were utilized, namely the luminal MCF-7 cells, the molecular apocrine MDA-MB-453 cells, and the triple negative, basal MDA-MB-231 cells.

RESULTS

High and significant concordance between dihydrotestosterone (DHT) and Cl-4AS-1 in regulation of gene expression in MDA-MB-453 cells was found. However, some differences were noted including the expression of AR, which was upregulated by DHT, but not Cl-4AS-1. In addition, both DHT and Cl-4AS-1 caused a similar morphological change and reorganization of the actin structure of MDA-MB-453 cells into a mesenchymal phenotype. Treatment of cells with DHT resulted in induction of proliferation of MCF-7 and MDA-MB-453 cells, but no effect was observed on the growth of MDA-MB-231 cells. On the other hand, increasing doses of Cl-4AS-1 resulted in a dose-dependent inhibition on the growth of the three cell lines. This inhibition was a result of induction of apoptosis whereby Cl-4AS-1 caused a block in entry of cells into the S-phase followed by DNA degradation.

CONCLUSIONS

These results indicate that although Cl-4AS-1 has characteristics of classical AR agonist, it has dissimilar properties that may make it useful in treating breast cancer.

In vitro and in vivo effect of flutamide on steroid hormone secretion in canine and human inflammatory breast cancer cell lines

The aim was to study the effects of flutamide on cell proliferation, in vivo tumour growth and steroid production in canine and human IBC cell lines. IPC-366 and SUM149 cell cultures were exposed to flutamide concentrations for 72 hours. Additionally, IPC-366 and SUM149 xenotransplanted mice were treated subcutaneously with flutamide 3 times a week for 2 weeks. Steroid hormones determination in culture media, serum and tumour homogenates (pregnenolone, progesterone, androstenedione, testosterone, dihydrotestosterone, 17β-oestradiol and oestrone sulphate) were assayed by EIA. in vitro cell proliferation percentages showed a decrease in all flutamide dosages in IPC-366 and SUM149. in vivo flutamide reduced tumour size by 55% to 65%, and metastasis rates decreased. In treated groups, androgen levels in culture media, serum and tumour homogenates were increased as oestrogen levels decreased. These results suggest that flutamide treatment inhibits cell proliferation and promotes tumour reduction by increasing androgen levels and also support future therapy approaches.

C1orf64 is a novel androgen receptor target gene and coregulator that interacts with 14-3-3 protein in breast cancer

This study investigated the network of genes that are co-expressed with androgen receptor (AR) to discover novel AR targets in breast cancer. Bioinformatics analysis of two datasets from breast cancer cell lines resulted in the identification of an AR-gene signature constituted of 98 genes that highly correlated with AR expression. Notably, C1orf64 showed the highest positive correlation with AR across the datasets with a correlation coefficient (CC) of 0.737. In addition, C1orf64 closely correlated with AR expression in primary and metastatic breast tumors and C1orf64 expression was relatively higher in breast tumors with a lower grade and lobular histology. Furthermore, there is a functional interplay between AR and C1orf64 in breast cancer. In this process, AR activation directly represses C1orf64 transcription and C1orf64, in turn, interacts with AR as a corepressor and negatively regulates the AR-mediated induction of prolactin-induced protein (PIP) and AR reporter activity. Moreover, the corepressor effect of C1orf64 results in a reduction of AR binding to PIP promoter. The other aspect of this interplay involves a cross-talk between AR and estrogen receptor (ER) signaling in which C1orf64 silencing intensifies the AR-mediated down-regulation of ER target gene, progesterone receptor. Therefore, the repression of C1orf64 by AR provides an underlying mechanism for the AR inhibitory effects on ER signaling. To elucidate the biochemical mechanisms of C1orf64 function, this study demonstrates that C1orf64 is a phosphothreonine protein that interacts with the chaperone protein 14-3-3. In summary, C1orf64 is a novel AR coregulator and a 14-3-3 binding partner in breast cancer.

Role and regulation of Cdc25A phosphatase in neuron death induced by NGF deprivation or β-amyloid

Neuron death during development and in Alzheimer’s disease (AD) is associated with aberrant regulation/induction of cell cycle proteins. However, the proximal events in this process are unknown. Cell cycle initiation requires dephosphorylation of cyclin-dependent kinases by cell division cycle 25A (Cdc25A). Here, we show that Cdc25A is essential for neuronal death in response to NGF deprivation or β-amyloid (Aβ) treatment and describe the mechanisms by which it is regulated in these paradigms. Cdc25A mRNA, protein and Cdc25A phosphatase activity were induced by NGF deprivation and Aβ treatment. Enhanced Cdc25A expression was also observed in rat brains infused with Aβ and in Aβ-overexpressing AβPPswe-PS1dE9 mice. In cultured neurons Cdc25A inhibition by chemical inhibitors or shRNA prevented cell death and neurite degeneration caused by NGF deprivation or Aβ. Additionally, Cdc25A inhibition diminished distal signaling events including Cdk-dependent elevation of phospho-pRb and subsequent caspase-3 activation. Mechanism studies revealed that Cdc25A induction by NGF deprivation and Aβ is mediated by activation of Forkhead transcription factors that in turn suppress miR-21, a negative regulator of Cdc25A. Our studies thus identify Cdc25A as a required upstream element of the apoptotic cell cycle pathway that is required for neuron death in response to trophic factor deprivation and to Aβ exposure and therefore as a potential target to suppress pathologic neuron death.

Phosphatases and kinases regulating CDC25 activity in the cell cycle: clinical implications of CDC25 overexpression and potential treatment strategies

Alterations in the cell-cycle regulatory genes result in uncontrolled cell proliferation leading to several disease conditions. Cyclin-dependent kinases (CDK) and their regulatory subunit, cyclins, are essential proteins in cell-cycle progression. The activity of CDK is regulated by a series of phosphorylation and dephosphorylation at different amino acid residues. Cell Division Cycle-25 (CDC25) plays an important role in transitions between cell-cycle phases by dephosphorylating and activating CDKs. CDC25B and CDC25C play a major role in G2/M progression, whereas CDC25A assists in G1/S transition. Different isomers of CDC25 expressions are upregulated in various clinicopathological situations. Overexpression of CDC25A deregulates G1/S and G2/M events, including the G2 checkpoint. CDC25B has oncogenic properties. Binding to the 14-3-3 proteins regulates the activity and localization of CDC25B. CDC25C is predominantly a nuclear protein in mammalian cells. At the G2/M transition, mitotic activation of CDC25C protein occurs by its dissociation from 14-3-3 proteins along with its phosphorylation at multiple sites within its N-terminal domain. In this article, we critically reviewed the biology of the activation/deactivation of CDC25 by kinases/phosphatases to maintain the level of CDK-cyclin activities and thus the genomic stability, clinical implications due to dysregulation of CDC25, and potential role of CDC25 inhibitors in diseases.

TOPK is highly expressed in circulating tumor cells, enabling metastasis of prostate cancer

Circulating tumor cells (CTCs) are important for metastasis in prostate cancer. T-LAK cell-originated protein kinase (TOPK) is highly expressed in cancer cells. Herein, we established a xenograft animal model, isolated and cultured the CTCs, and found CTCs have significantly greater migratory capacity than parental cells. TOPK is more highly expressed in the CTCs than in parental cells and is also highly expressed in the metastatic nodules caused by CTCs in mice. Knocking down TOPK decreased the migration of CTCs both in vitro and in vivo. TOPK was modulated by the PI3K/PTEN and ERK pathways during the metastasis of prostate cancer. High levels of TOPK in the tumors of patients were correlated with advanced stages of prostate cancer, especially for high-risk patients of Gleason score≥8, PSA>20ng/ml. In summary, TOPK was speculated to be one of a potential marker and therapeutic target in advanced prostate cancer.

Prolactin-induced protein is required for cell cycle progression in breast cancer

Prolactin-induced protein (PIP) is expressed in the majority of breast cancers and is used for the diagnostic evaluation of this disease as a characteristic biomarker; however, the molecular mechanisms of PIP function in breast cancer have remained largely unknown. In this study, we carried out a comprehensive investigation of PIP function using PIP silencing in a broad group of breast cancer cell lines, analysis of expression microarray data, proteomic analysis using mass spectrometry, and biomarker studies on breast tumors. We demonstrated that PIP is required for the progression through G1 phase, mitosis, and cytokinesis in luminal A, luminal B, and molecular apocrine breast cancer cells. In addition, PIP expression is associated with a transcriptional signature enriched with cell cycle genes and regulates key genes in this process including cyclin D1, cyclin B1, BUB1, and forkhead box M1 (FOXM1). It is notable that defects in mitotic transition and cytokinesis following PIP silencing are accompanied by an increase in aneuploidy of breast cancer cells. Importantly, we have identified novel PIP-binding partners in breast cancer and shown that PIP binds to β-tubulin and is necessary for microtubule polymerization. Furthermore, PIP interacts with actin-binding proteins including Arp2/3 and is needed for inside-out activation of integrin-β1 mediated through talin. This study suggests that PIP is required for cell cycle progression in breast cancer and provides a rationale for exploring PIP inhibition as a therapeutic approach in breast cancer that can potentially target microtubule polymerization.

Coagulation factor VII is regulated by androgen receptor in breast cancer

Androgen receptor (AR) is widely expressed in breast cancer; however, there is limited information on the key molecular functions and gene targets of AR in this disease. In this study, gene expression data from a cohort of 52 breast cancer cell lines was analyzed to identify a network of AR co-expressed genes. A total of 300 genes, which were significantly enriched for cell cycle and metabolic functions, showed absolute correlation coefficients (|CC|) of more than 0.5 with AR expression across the dataset. In this network, a subset of 35 "AR-signature" genes were highly co-expressed with AR (|CC|>0.6) that included transcriptional regulators PATZ1, NFATC4, and SPDEF. Furthermore, gene encoding coagulation factor VII (F7) demonstrated the closest expression pattern with AR (CC=0.716) in the dataset and factor VII protein expression was significantly associated to that of AR in a cohort of 209 breast tumors. Moreover, functional studies demonstrated that AR activation results in the induction of factor VII expression at both transcript and protein levels and AR directly binds to a proximal region of F7 promoter in breast cancer cells. Importantly, AR activation in breast cancer cells induced endogenous factor VII activity to convert factor X to Xa in conjunction with tissue factor. In summary, F7 is a novel AR target gene and AR activation regulates the ectopic expression and activity of factor VII in breast cancer cells. These findings have functional implications in the pathobiology of thromboembolic events and regulation of factor VII/tissue factor signaling in breast cancer.

Prediction of gene-based drug indications using compendia of public gene expression data and PubMed abstracts

The tremendous research effort on diseases and drug discovery has produced a huge amount of important biomedical information which is mostly hidden in the web. In addition, many databases have been created for the purpose of storing enormous amounts of information and high-throughput experiments related to drugs and diseases' effects on genes. Thus, developing an algorithm to integrate biological data from different sources forms one of the greatest challenges in the field of computational biology. Based on our belief that data integration would result in better understanding for the drug mode of action or the disease pathophysiology, we have developed a novel paradigm to integrate data from three major sources in order to predict novel therapeutic drug indications. Microarray data, biomedical text mining data, and gene interaction data have been all integrated to predict ranked lists of genes based on their relevance to a particular drug or disease molecular action. These ranked lists of genes have finally been used as a raw material for building a disease-drug connectivity map based on the enrichment between the up/down tags of a particular disease signature and the ranked lists of drugs. Using this paradigm, we have reported 13% sensitivity improvement in comparison with using microarray or text mining data independently. In addition, our paradigm is able to predict many clinically validated disease-drug associations that could not be captured using microarray or text mining data independently.

Correlation between expression of CDC25A and Doppler ultrasound features in primary hepatocellular carcinoma

AIM: To investigate the expression of cell division cycle 25A (CDC25A) in primary hepatocellular carcinoma (PHC) and to explore its relationship with Doppler ultrasound imaging features.

METHODS: The expression of CDC25A in 86 PHC specimens and matched tumor-adjacent tissue specimens was detected by RT-PCR and Western blot. The imaging features of PHC was analyzed by Doppler ultrasound.

RESULTS: CDC25A was found to be overexpressed in 75.58% (65/86) of PHC cases (P < 0.05). The expression of CDC25A protein was significantly correlated with Doppler ultrasound imaging features including tumor size, blood flow grade, resistance index (RI) and portal vein invasion (all P < 0.05), but not with the number of liver tumor nodes (P > 0.05).

CONCLUSION: CDC25A may play an important role in the development and metastasis of PHC. Detection of CDC25A expression combined with ultrasound imaging may be used clinically for evaluation of treatment response and prognosis in PHC patients.

Phase II trial of bicalutamide in patients with androgen receptor-positive, estrogen receptor-negative metastatic Breast Cancer

PURPOSE

Patients with hormone receptor-negative breast cancer generally do not benefit from endocrine-targeted therapies. However, a subset with androgen receptor (AR) expression is predicted to respond to antiandrogen therapies. This phase II study explored bicalutamide in AR-positive, estrogen receptor (ER), and progesterone receptor (PgR)-negative metastatic breast cancer.

EXPERIMENTAL DESIGN

Tumors from patients with ER/PgR-negative advanced breast cancer were tested centrally for AR [immunohistochemistry (IHC) > 10% nuclear staining considered positive]. If either the primary or a metastatic site was positive, patients were eligible to receive the AR antagonist bicalutamide at a dose of 150 mg daily. Clinical benefit rate (CBR), the primary endpoint, was defined as the total number of patients who show a complete response (CR), partial response (PR), or stable disease (SD) > 6 months; secondary endpoints included progression-free survival (PFS) and toxicity. Correlative studies included measurement of circulating endocrine markers and IHC surrogates for basal-like breast cancer.

RESULTS

Of 424 patients with ER/PgR-negative breast cancer, 12% tested AR-positive. The 6-month CBR was 19% [95% confidence interval (CI), 7%-39%] for bicalutamide. The median PFS was 12 weeks (95% CI, 11-22 weeks). Bicalutamide was well-tolerated with no grade 4/5 treatment-related adverse events observed.

CONCLUSION

AR was expressed in 12% of patients with ER/PgR-negative breast cancer screened for this trial. The CBR of 19% observed with bicalutamide shows proof of principle for the efficacy of minimally toxic androgen blockade in a select group of patients with ER/PgR-negative, AR-positive breast cancer.

The influence of reactive oxygen species on cell cycle progression in mammalian cells

Cell cycle regulation is performed by cyclins and cyclin dependent kinases (CDKs). Recently, it has become clear that reactive oxygen species (ROS) influence the presence and activity of these enzymes and thereby control cell cycle progression. In this review, we first describe the discovery of enzymes specialized in ROS production: the NADPH oxidase (NOX) complexes. This discovery led to the recognition of ROS as essential players in many cellular processes, including cell cycle progression. ROS influence cell cycle progression in a context-dependent manner via phosphorylation and ubiquitination of CDKs and cell cycle regulatory molecules. We show that ROS often regulate ubiquitination via intermediate phosphorylation and that phosphorylation is thus the major regulatory mechanism influenced by ROS. In addition, ROS have recently been shown to be able to activate growth factor receptors. We will illustrate the diverse roles of ROS as mediators in cell cycle regulation by incorporating phosphorylation, ubiquitination and receptor activation in a model of cell cycle regulation involving EGF-receptor activation. We conclude that ROS can no longer be ignored when studying cell cycle progression.

An androgen receptor mutation in the MDA-MB-453 cell line model of molecular apocrine breast cancer compromises receptor activity

Recent evidence indicates that the estrogen receptor-α-negative, androgen receptor (AR)-positive molecular apocrine subtype of breast cancer is driven by AR signaling. The MDA-MB-453 cell line is the prototypical model of this breast cancer subtype; its proliferation is stimulated by androgens such as 5α-dihydrotestosterone (DHT) but inhibited by the progestin medroxyprogesterone acetate (MPA) via AR-mediated mechanisms. We report here that the AR gene in MDA-MB-453 cells contains a G-T transversion in exon 7, resulting in a receptor variant with a glutamine to histidine substitution at amino acid 865 (Q865H) in the ligand binding domain. Compared with wild-type AR, the Q865H variant exhibited reduced sensitivity to DHT and MPA in transactivation assays in MDA-MB-453 and PC-3 cells but did not respond to non-androgenic ligands or receptor antagonists. Ligand binding, molecular modeling, mammalian two-hybrid and immunoblot assays revealed effects of the Q865H mutation on ligand dissociation, AR intramolecular interactions, and receptor stability. Microarray expression profiling demonstrated that DHT and MPA regulate distinct transcriptional programs in MDA-MB-453 cells. Gene Set Enrichment Analysis revealed that DHT- but not MPA-regulated genes were associated with estrogen-responsive transcriptomes from MCF-7 cells and the Wnt signaling pathway. These findings suggest that the divergent proliferative responses of MDA-MB-453 cells to DHT and MPA result from the different genetic programs elicited by these two ligands through the AR-Q865H variant. This work highlights the necessity to characterize additional models of molecular apocrine breast cancer to determine the precise role of AR signaling in this breast cancer subtype.

Prolactin-induced protein mediates cell invasion and regulates integrin signaling in estrogen receptor-negative breast cancer

Introduction

Molecular apocrine is a subtype of estrogen receptor (ER)-negative breast cancer that is characterized by a steroid-response gene signature. We have recently identified a positive feedback loop between androgen receptor (AR) and extracellular signal-regulated kinase (ERK) signaling in this subtype. In this study, we investigated the transcriptional regulation of molecular apocrine genes by the AR-ERK feedback loop.

Methods

The transcriptional effects of AR and ERK inhibition on molecular apocrine genes were assessed in cell lines. The most regulated gene in this process, prolactin-induced protein (PIP), was further studied using immunohistochemistry of breast tumors and xenograft models. The transcriptional regulation of PIP was assessed by luciferase reporter assay and chromatin immunoprecipitation. The functional significance of PIP in cell invasion and viability was assessed using siRNA knockdown experiments and the mechanism of PIP effect on integrin-β1 signaling was studied using immunoblotting and immunoprecipitation.

Results

We found that PIP is the most regulated molecular apocrine gene by the AR-ERK feedback loop and is overexpressed in ER-/AR+ breast tumors. In addition, PIP expression is regulated by AR-ERK signaling in xenograft models. These observations are explained by the fact that PIP is a target gene of the ERK-CREB1 pathway and is also induced by AR activation. Furthermore, we demonstrated that PIP has a significant functional role in maintaining cell invasion and viability of molecular apocrine cells because of a positive regulatory effect on the Integrin-ERK and Integrin-Akt signaling pathways. In fact, PIP-knockdown markedly decreases the phosphorylation of ERK, Akt, and CREB1. Importantly, PIP knockdown leads to a marked reduction of integrin-β1 binding to ILK1 and ErbB2 that can be reversed by the addition of fibronectin fragments.

Conclusions

We have identified a novel feedback loop between PIP and CREB1 mediated through the Integrin signaling pathway. In this process, PIP cleaves fibronectin to release fragments that activate integrin signaling, which in turn increases PIP expression through the ERK-CREB1 pathway. In addition, we demonstrated that PIP expression has a profound effect on cell invasion and the viability of molecular apocrine cells. Therefore, PIP signaling may be a potential therapeutic target in molecular apocrine breast cancer.

Minireview: The androgen receptor in breast tissues: growth inhibitor, tumor suppressor, oncogene?

Androgen receptor (AR) signaling exerts an antiestrogenic, growth-inhibitory influence in normal breast tissue, and this role may be sustained in estrogen receptor α (ERα)-positive luminal breast cancers. Conversely, AR signaling may promote growth of a subset of ERα-negative, AR-positive breast cancers with a molecular apocrine phenotype. Understanding the molecular mechanisms whereby androgens can elicit distinct gene expression programs and opposing proliferative responses in these two breast cancer phenotypes is critical to the development of new therapeutic strategies to target the AR in breast cancer.

Cross-regulation between FOXA1 and ErbB2 signaling in estrogen receptor-negative breast cancer

Molecular apocrine is a subtype of estrogen receptor-negative (ER.) breast cancer, which is characterized by a steroid-response gene signature that includes androgen receptor, FOXA1, and a high frequency of ErbB2 overexpression. In this study, we demonstrate that there is a strong association between the overexpression of FOXA1 and ErbB2 in ER- breast tumors. This has led us to identify a cross-regulation network between FOXA1 and ErbB2 signaling in ER- breast cancer. We present two mechanisms to explain the association between FOXA1 and ErbB2 overexpression in molecular apocrine cells. In one process, ErbB2 signaling genes CREB1 and c-Fos regulate FOXA1 transcription, and in another process, AP2α regulates the expression of both FOXA1 and ErbB2. Moreover, we demonstrate that FOXA1, in turn, regulates the transcription of ErbB2 signaling genes. This includes a core gene signature that is shared across two molecular apocrine cell lines. Importantly, the most upregulated (RELB) and downregulated (PAK1) genes in this signature are direct FOXA1 targets. Our data suggest that FOXA1 acts as a dual-function transcription factor and the repressive function of FOXA1 on RELB can be explained by the recruitment of its binding partner corepressor TLE3. It is notable that a group of FOXA1-regulated genes vary across molecular apocrine cell lines leading to the differences in the functional effects of FOXA1 on extracellular signal-regulated kinase phosphorylation and cell viability between these lines. This study demonstrates that there is a cross-regulation network between FOXA1 and ErbB2 signaling that connects FOXA1 to some of the key signaling pathways in ER-breast cancer.

Inhibition of Cdc25A suppresses hepato-renal cystogenesis in rodent models of polycystic kidney and liver disease

BACKGROUND & AIMS

In polycystic kidney disease and polycystic liver disease (PLD), the normally nonproliferative hepato-renal epithelia acquire a proliferative, cystic phenotype that is linked to overexpression of cell division cycle 25 (Cdc25)A phosphatase and cell-cycle deregulation. We investigated the effects of Cdc25A inhibition in mice and rats via genetic and pharmacologic approaches.

METHODS

Cdc25A(+/-) mice (which have reduced levels of Cdc25A) were cross-bred with polycystic kidney and hepatic disease 1 (Pkhd1(del2/del2)) mice (which have increased levels of Cdc25A and develop hepatic cysts). Cdc25A expression was analyzed in livers of control and polycystic kidney (PCK) rats, control and polycystic kidney 2 (Pkd2(ws25/-)) mice, healthy individuals, and patients with PLD. We examined effects of pharmacologic inhibition of Cdc25A with vitamin K3 (VK3) on the cell cycle, proliferation, and cyst expansion in vitro; hepato-renal cystogenesis in PCK rats and Pkd2(ws25/-)mice; and expression of Cdc25A and the cell-cycle proteins regulated by Cdc25A. We also examined the effects of the Cdc25A inhibitor PM-20 on hepato-renal cystogenesis in Pkd2(ws25/-) mice.

RESULTS

Liver weights and hepatic and fibrotic areas were decreased by 32%-52% in Cdc25A(+/-):Pkhd1(del2/del2) mice, compared with Pkhd1(del2/del2) mice. VK3 altered the cell cycle and reduced proliferation of cultured cholangiocytes by 32%-83% and decreased growth of cultured cysts by 23%-67%. In PCK rats and Pkd2(ws25/-) mice, VK3 reduced liver and kidney weights and hepato-renal cystic and fibrotic areas by 18%-34%. PM-20 decreased hepato-renal cystogenesis in Pkd2(ws25/-) mice by 15%.

CONCLUSIONS

Cdc25A inhibitors block cell-cycle progression and proliferation, reduce liver and kidney weights and cyst growth in animal models of polycystic kidney disease and PLD, and might be developed as therapeutics for these diseases.

A feedback loop between androgen receptor and ERK signaling in estrogen receptor-negative breast cancer

Estrogen receptor (ER)-negative breast cancer is heterogeneous, and the biology of this disease has remained poorly understood. Molecular apocrine is a subtype of ER-negative breast cancer that is characterized by the overexpression of steroid-response genes such as AR and a high rate of ErbB2 amplification. In this study, we have identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in molecular apocrine breast cancer. In this process, AR regulates ERK phosphorylation and kinase activity. In addition, AR inhibition results in the down-regulation of ERK target proteins phospho-RSK1, phospho-Elk-1, and c-Fos using an in vivo molecular apocrine model. Furthermore, we show that AR-mediated induction of ERK requires ErbB2, and AR activity, in turn, regulates ErbB2 expression as an AR target gene. These findings suggest that ErbB2 is an upstream connector between the AR and ERK signaling pathways. Another feature of this feedback loop is an ERK-mediated regulation of AR. In this respect, the inhibition of ERK phosphorylation reduces AR expression and CREB1-mediated transcriptional regulation of AR acts as a downstream connector between the AR and ERK signaling pathways in molecular apocrine cells. Finally, we demonstrate that AR-positive staining is associated with the overexpression of ERK signaling targets phospho-Elk-1 and c-Fos in ER-negative breast tumors, which further supports a cross-regulation between the AR and ERK signaling pathways in molecular apocrine subtype. This study demonstrates an AR-ERK feedback loop in ER-negative breast cancer with significant biologic and therapeutic implications in this disease.

Synergy between inhibitors of androgen receptor and MEK has therapeutic implications in estrogen receptor-negative breast cancer

INTRODUCTION

Estrogen receptor-negative (ER-) breast cancer is a heterogeneous disease with limited therapeutic options. The molecular apocrine subtype constitutes 50% of ER-tumors and is characterized by overexpression of steroid response genes including androgen receptor (AR). We have recently identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in the molecular apocrine subtype. In this feedback loop, AR regulates ERK phosphorylation through the mediation of ErbB2 and, in turn, ERK-CREB1 signaling regulates the transcription of AR in molecular apocrine cells. In this study, we investigated the therapeutic implications of the AR-ERK feedback loop in molecular apocrine breast cancer.

METHODS

We examined a synergy between the AR inhibitor flutamide and the MEK inhibitor CI-1040 in the molecular apocrine cell lines MDA-MB-453, HCC-1954 and HCC-202 using MTT cell viability and annexin V apoptosis assays. Synergy was measured using the combination index (CI) method. Furthermore, we examined in vivo synergy between flutamide and the MEK inhibitor PD0325901 in a xenograft model of the molecular apocrine subtype. The effects of in vivo therapies on tumor growth, cell proliferation and angiogenesis were assessed.

RESULTS

We demonstrate synergistic CI values for combination therapy with flutamide and CI-1040 across three molecular apocrine cell lines at four dose combinations using both cell viability and apoptosis assays. Furthermore, we show in vivo that combination therapy with flutamide and MEK inhibitor PD0325901 has a significantly higher therapeutic efficacy in reducing tumor growth, cellular proliferation and angiogenesis than monotherapy with these agents. Moreover, our data suggested that flutamide and CI-1040 have synergy in trastuzumab resistance models of the molecular apocrine subtype. Notably, the therapeutic effect of combination therapy in trastuzumab-resistant cells was associated with the abrogation of an increased level of ERK phosphorylation that was developed in the process of trastuzumab resistance.

CONCLUSIONS

In this study, we demonstrate in vitro and in vivo synergies between AR and MEK inhibitors in molecular apocrine breast cancer. Furthermore, we show that combination therapy with these inhibitors can overcome trastuzumab resistance in molecular apocrine cells. Therefore, a combination therapy strategy with AR and MEK inhibitors may provide an attractive therapeutic option for the ER-/AR+ subtype of breast cancer.