HER2/neu kinase-dependent modulation of androgen receptor function through effects on DNA binding and stability

Antitumoral action of icaritin in LNCaP prostate cancer cells by regulating PEA3/HER2/AR signaling

Human epidermal growth factor receptor type 2 (HER2) and androgen receptor (AR) are critical factors for prostate cancer (PCa) progression. These factors regulate tumor cell survival and proliferation, and remain as crucial drivers of castration-resistant PCa progression. Icaritin (ICT) is a prenyl flavonoid derived from the Epimedium genus, which has many biological and pharmacological effects. Using androgen-sensitive human prostate carcinoma LNCaP cell lines, we found that 35 μg/ml of ICT could inhibit more than 50% of cell proliferation, induce cell apoptosis, and lead to a strong G1 phase arrest by targeting cyclin-related proteins and suppressing the ability of cell invasion. Moreover, ICT exerts its potent anticancer efficacy by inducing polyomavirus enhancer activator 3 (PEA3) to inhibit the aberrantly activated HER2/AR signaling. In addition, after PEA3 expression was silenced by specific small-interference RNA, we found that both the ICT-inhibited effect on LNCaP cell proliferation and the ICT-induced cell apoptosis rate decreased. These results provide alternative mechanisms for the antitumor actions of ICT, indicating that ICT might be a promising therapeutic agent, as well as a preventive agent, for hormone therapy-resistant PCa.

Androgen Signaling in Prostate Cancer

The androgen-signaling axis plays a pivotal role in the pathogenesis of prostate cancer. Since the landmark discovery by Huggins and Hodges, gonadal depletion of androgens has remained a mainstay of therapy for advanced disease. However, progression to castration-resistant prostate cancer (CRPC) typically follows and is largely the result of restored androgen signaling. Efforts to understand the mechanisms behind CRPC have revealed new insights into dysregulated androgen signaling and intratumoral androgen synthesis, which has ultimately led to the development of several novel androgen receptor (AR)-directed therapies for CRPC. However, emergence of resistance to these newer agents has also galvanized new directions in investigations of prereceptor and postreceptor AR regulation. Here, we review our current understanding of AR signaling as it pertains to the biology and natural history of prostate cancer.

Mechanisms of resistance to systemic therapy in metastatic castration-resistant prostate cancer

Patients with metastatic castration-resistant prostate cancer (mCPRC) now have an unprecedented number of approved treatment options, including chemotherapies (docetaxel, cabazitaxel), androgen receptor (AR)-targeted therapies (enzalutamide, abiraterone), a radioisotope (radium-223) and a cancer vaccine (sipuleucel-T). However, the optimal treatment sequencing pathway is unknown, and this problem is exacerbated by the issues of primary and acquired resistance. This review focuses on mechanisms of resistance to AR-targeted therapies and taxane-based chemotherapy. Patients treated with abiraterone, enzalutamide, docetaxel or cabazitaxel may present with primary resistance, or eventually acquire resistance when on treatment. Multiple resistance mechanisms to AR-targeted agents have been proposed, including: intratumoral androgen production, amplification, mutation, or expression of AR splice variants, increased steroidogenesis, upregulation of signals downstream of the AR, and development of androgen-independent tumor cells. Known mechanisms of resistance to chemotherapy are distinct, and include: tubulin alterations, increased expression of multidrug resistance genes, TMPRSS2-ERG fusion genes, kinesins, cytokines, and components of other signaling pathways, and epithelial-mesenchymal transition. Utilizing this information, biomarkers of resistance/response have the potential to direct treatment decisions. Expression of the AR splice variant AR-V7 may predict resistance to AR-targeted agents, but available biomarker assays are yet to be prospectively validated in the clinic. Ongoing prospective trials are evaluating the sequential use of different drugs, or combination regimens, and the results of these studies, combined with a deeper understanding of mechanisms of primary and acquired resistance to treatment, have the potential to drive future treatment decisions in mCRPC.

AR Signaling and the PI3K Pathway in Prostate Cancer

Prostate cancer is a leading cause of cancer-related death in men worldwide. Aberrant signaling in the androgen pathway is critical in the development and progression of prostate cancer. Despite ongoing reliance on androgen receptor (AR) signaling in castrate resistant disease, in addition to the development of potent androgen targeting drugs, patients invariably develop treatment resistance. Interactions between the AR and PI3K pathways may be a mechanism of treatment resistance and inhibitors of this pathway have been developed with variable success. Herein we outline the role of the PI3K pathway in prostate cancer and, in particular, its association with androgen receptor signaling in the pathogenesis and evolution of prostate cancer, as well as a review of the clinical utility of PI3K targeting.

Role of steroid receptor and coregulator mutations in hormone-dependent cancers

Steroid hormones mediate critical lineage-specific developmental and physiologic responses. They function by binding their cognate receptors, which are transcription factors that drive specific gene expression programs. The requirement of most prostate cancers for androgen and most breast cancers for estrogen has led to the development of endocrine therapies that block the action of these hormones in these tumors. While initial endocrine interventions are successful, resistance to therapy often arises. We will review how steroid receptor-dependent genomic signaling is affected by genetic alterations in endocrine therapy resistance. The detailed understanding of these interactions will not only provide improved treatment options to overcome resistance, but, in the future, will also be the basis for implementing precision cancer medicine approaches.

AR Signaling in Breast Cancer

Androgen receptor (AR, a member of the steroid hormone receptor family) status has become increasingly important as both a prognostic marker and potential therapeutic target in breast cancer. AR is expressed in up to 90% of estrogen receptor (ER) positive breast cancer, and to a lesser degree, human epidermal growth factor 2 (HER2) amplified tumors. In the former, AR signaling has been correlated with a better prognosis given its inhibitory activity in estrogen dependent disease, though conversely has also been shown to increase resistance to anti-estrogen therapies such as tamoxifen. AR blockade can mitigate this resistance, and thus serves as a potential target in ER-positive breast cancer. In HER2 amplified breast cancer, studies are somewhat conflicting, though most show either no effect or are associated with poorer survival. Much of the available data on AR signaling is in triple-negative breast cancer (TNBC), which is an aggressive disease with inferior outcomes comparative to other breast cancer subtypes. At present, there are no approved targeted therapies in TNBC, making study of the AR signaling pathway compelling. Gene expression profiling studies have also identified a luminal androgen receptor (LAR) subtype that is dependent on AR signaling in TNBC. Regardless, there seems to be an association between AR expression and improved outcomes in TNBC. Despite lower pathologic complete response (pCR) rates with neoadjuvant therapy, patients with AR-expressing TNBC have been shown to have a better prognosis than those that are AR-negative. Clinical studies targeting AR have shown somewhat promising results. In this paper we review the literature on the biology of AR in breast cancer and its prognostic and predictive roles. We also present our thoughts on therapeutic strategies.

Unraveling the role of preexisting immunity in prostate cancer patients vaccinated with a HER-2/neu hybrid peptide

Background

Cancer vaccines aim at eliciting not only an immune response against specific tumor antigens, but also at enhancing a preexisting immunity against the tumor. In this context, we recently reported on the levels of preexisting immunity in prostate cancer patients vaccinated with the HER-2 hybrid peptide (AE37), during a phase I clinical trial. The purpose of the current study was to correlate between preexisting immunity to the native HER-2 peptide, AE36, and expression of HLA-A2 and -A24 molecules with the clinical outcome. Additionally, we investigated the ability of the AE37 vaccine to induce an antitumor immune response against other tumor associated antigens, not integrated in the vaccine formulation, with respect to the clinical response.

Methods

We analyzed prostate cancer patients who were vaccinated with the AE37 vaccine [Ii-Key-HER-2/neu_(776–790) hybrid peptide vaccine (AE37), which is a MHC class II long peptide vaccine encompassing MHC class I epitopes, during a phase I clinical trial. Preexisting immunity to the native HER-2/neu_(776–790) (AE36) peptide was assessed by IFNγ response or dermal reaction at the inoculation site. Antigen specificity against other tumor antigens was defined using multimer analysis. Progression free survival (PFS) was considered as the patients’ clinical outcome. Two-tailed Wilcoxon signed rank test at 95 % confidence interval was used for statistical evaluation at different time points and Kaplan–Meier curves with log-rank (Mantel-Cox) test were used for the evaluation of PFS.

Results

Preexisting immunity to AE36, irrespectively of HLA expression, was correlated with longer PFS. Specific CD8⁺ T cell immunity against E75 and PSA_146–151 (HLA-A2 restricted), as well as, PSA_153–161 (HLA-A24 restricted) was detected at relatively high frequencies which were further enhanced during vaccinations. Specific immunity against PSA_153–161 correlated with longer PFS in HLA-A24⁺ patients. However, HLA-A2⁺ patients with high preexisting or vaccine-induced immunity to E75, showed a trend for shorter PFS.

Conclusions

Our data cast doubt on whether preexisting immunity or epitope spreading specific for HLA-class I-restricted peptides can actually predict a favorable clinical outcome. They also impose that preexisting immunity to long vaccine peptides, encompassing both HLA class II and I epitopes should be considered as an important prerequisite for the improvement of future immunotherapeutic protocols.

Protocol ID Code: Generex-06-07

National Organization for Medicines (EOF) ID Code: IS-107-01-06

NEC Study Code: EED107/1/06

EudraCT Number: 2006-003299-37

Date of registration: 07/06/2006

Date of enrolment of the first participant to the trial: Nov 1st, 2007

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-016-0183-4) contains supplementary material, which is available to authorized users.

Adaptive pathways and emerging strategies overcoming treatment resistance in castration resistant prostate cancer

The therapies available for prostate cancer patients whom progress from hormone-sensitive to castration resistant prostate cancer include both systemic drugs, including docetaxel and cabazitaxel, and drugs that inhibit androgen signaling such as enzalutamide and abiraterone. Unfortunately, it is estimated that up to 30% of patients have primary resistance to these treatments and over time even those who initially respond to therapy will eventually develop resistance and their disease will continue to progress regardless of the presence of the drug. Determining the mechanisms involved in the development of resistance to these therapies has been the area of intense study and several adaptive pathways have been uncovered. Androgen receptor (AR) mutations, expression of AR-V7 (or other constitutively active androgen receptor variants), intracrine androgen production and overexpression of androgen synthesis enzymes such as Aldo-Keto Reductase Family 1, Member C3 (AKR1C3) are among the many mechanisms associated with resistance to anti-androgens. In regards to the taxanes, one of the key contributors to drug resistance is increased drug efflux through ATP Binding Cassette Subfamily B Member 1 (ABCB1). Targeting these resistance mechanisms using different strategies has led to various levels of success in overcoming resistance to current therapies. For instance, targeting AR-V7 with niclosamide or AKR1C3 with indomethacin can improve enzalutamide and abiraterone treatment. ABCB1 transport activity can be inhibited by the dietary constituent apigenin and antiandrogens such as bicalutamide which in turn improves response to docetaxel. A more thorough understanding of how drug resistance develops will lead to improved treatment strategies. This review will cover the current knowledge of resistance mechanisms to castration resistant prostate cancer therapies and methods that have been identified which may improve treatment response.

Bioactive natural products for chemoprevention and treatment of castration-resistant prostate cancer

Prostate cancer (PCa), a hormonally-driven cancer, ranks first in incidence and second in cancer related mortality in men in most Western industrialized countries. Androgen and androgen receptor (AR) are the dominant modulators of PCa growth. Over the last two decades multiple advancements in screening, treatment, surveillance and palliative care of PCa have significantly increased quality of life and survival following diagnosis. However, over 20% of patients initially diagnosed with PCa still develop an aggressive and treatment-refractory disease. Prevention or treatment for hormone-refractory PCa using bioactive compounds from marine sponges, mushrooms, and edible plants either as single agents or as adjuvants to existing therapy, has not been clinically successful. Major advancements have been made in the identification, testing and modification of the existing molecular structures of natural products. Additionally, conjugation of these compounds to novel matrices has enhanced their bio-availability; a big step towards bringing natural products to clinical trials. Natural products derived from edible plants (nutraceuticals), and common folk-medicines might offer advantages over synthetic compounds due to their broader range of targets, as compared to mostly single target synthetic anticancer compounds; e.g. kinase inhibitors. The use of synthetic inhibitors or antibodies that target a single aberrant molecule in cancer cells might be in part responsible for emergence of treatment refractory cancers. Nutraceuticals that target AR signaling (epigallocatechin gallate [EGCG], curcumin, and 5α-reductase inhibitors), AR synthesis (ericifolin, capsaicin and others) or AR degradation (betulinic acid, di-indolyl diamine, sulphoraphane, silibinin and others) are prime candidates for use as adjuvant or mono-therapies. Nutraceuticals target multiple pathophysiological mechanisms involved during cancer development and progression and thus have potential to simultaneously inhibit both prostate cancer growth and metastatic progression (e.g., inhibition of angiogenesis, epithelial-mesenchymal transition (EMT) and proliferation). Given their multi-targeting properties along with relatively lower systemic toxicity, these compounds offer significant therapeutic advantages for prevention and treatment of PCa. This review emphasizes the potential application of some of the well-researched natural compounds that target AR for prevention and therapy of PCa.

Integrated and Functional Genomics Analysis Validates the Relevance of the Nuclear Variant ErbB380kDa in Prostate Cancer Progression

The EGF-family of tyrosine-kinase receptors activates cytoplasmic pathways involved in cell proliferation, migration and differentiation in response to specific extracellular ligands. Beside these canonical pathways, the nuclear localization of the ErbB receptors in primary tumours and cancer cell lines led to investigate their role as transcriptional regulators of cancer genes. The nuclear localization of ErbB3 has been reported in various cancer tissues and cell lines but the nuclear functions and the putative correlation with tumour progression and resistance to therapy remain unclear. We first assessed ErbB3 expression in normal and tumour prostate tissues. The nuclear staining was mainly due to an isoform matching the C-terminus domain of the full length ErbB3_185kDa receptor. Nuclear staining was also restricted to cancer cells and was increased in advanced castration-resistant prostate cancer when compared to localized tumours, suggesting it could be involved in the progression of prostate cancer up to the terminal castration-resistant stage. ChIP-on-chip experiments were performed on immortalized and tumour cell lines selected upon characterization of endogenous nuclear expression of an ErbB3_80kDa isoform. Among the 1840 target promoters identified, 26 were selected before ErbB3_80kDa-dependent gene expression was evaluated by real-time quantitative RT-PCR, providing evidence that ErbB3_80kDa exerted transcriptional control on those genes. Some targets are already known to be involved in prostate cancer progression even though no link was previously established with ErbB3 membrane and/or nuclear signalling. Many others, not yet associated with prostate cancer, could provide new therapeutic possibilities for patients expressing ErbB3_80kDa. Detecting ErbB3_80kDa could thus constitute a useful marker of prognosis and response to therapy.

Lemur Tyrosine Kinase 2, a novel target in prostate cancer therapy

Progression from early forms of prostate cancer to castration-resistant disease is associated with an increase in signal transduction activity. The majority of castration-resistance cancers persist in the expression of the androgen receptor (AR), as well as androgen-dependent genes. The AR is regulated not only by it associated steroid hormone, but also by manifold regulatory and signaling molecules, including several kinases. We undertook evaluation of the role of Lemur Tyrosine Kinase 2 (LMTK2) in modulating AR activity, as several Genome Wide Association Studies (GWAS) have shown a marked association of LMTK2 activity with the development of prostate cancer. We confirm that not only is LMTK2 mRNA reduced in prostate cancer tissue, but also LMTK2 protein levels are markedly diminished. Knockdown of LMTK2 protein in prostate cell lines greatly increased the transcription of androgen-responsive genes. In addition, LMTK2 knockdown led to an increase in prostate cancer stem cell populations in LNCaP cells, indicative of increased tumorogenicity. Using multiple approaches, we also demonstrate that LMTK2 interacts with the AR, thus putting LMTK2 as a component of a signaling complex modulating AR activity. Our finding that LMTK2 is a negative regulator of AR activity defines a novel cellular pathway for activation of AR-responsive genes in castrate resistant-prostate cancer. Moreover, pharmacologic manipulation of LMTK2 activity will provide a novel therapeutic target for more effective treatments for patients with castrate-resistant prostate cancer.

Choline Kinase Alpha as an Androgen Receptor Chaperone and Prostate Cancer Therapeutic Target

BACKGROUND

The androgen receptor (AR) is a major drug target in prostate cancer (PCa). We profiled the AR-regulated kinome to identify clinically relevant and druggable effectors of AR signaling.

METHODS

Using genome-wide approaches, we interrogated all AR regulated kinases. Among these, choline kinase alpha (CHKA) expression was evaluated in benign (n = 195), prostatic intraepithelial neoplasia (PIN) (n = 153) and prostate cancer (PCa) lesions (n = 359). We interrogated how CHKA regulates AR signaling using biochemical assays and investigated androgen regulation of CHKA expression in men with PCa, both untreated (n = 20) and treated with an androgen biosynthesis inhibitor degarelix (n = 27). We studied the effect of CHKA inhibition on the PCa transcriptome using RNA sequencing and tested the effect of CHKA inhibition on cell growth, clonogenic survival and invasion. Tumor xenografts (n = 6 per group) were generated in mice using genetically engineered prostate cancer cells with inducible CHKA knockdown. Data were analyzed with χ(2) tests, Cox regression analysis, and Kaplan-Meier methods. All statistical tests were two-sided.

RESULTS

CHKA expression was shown to be androgen regulated in cell lines, xenografts, and human tissue (log fold change from 6.75 to 6.59, P = .002) and was positively associated with tumor stage. CHKA binds directly to the ligand-binding domain (LBD) of AR, enhancing its stability. As such, CHKA is the first kinase identified as an AR chaperone. Inhibition of CHKA repressed the AR transcriptional program including pathways enriched for regulation of protein folding, decreased AR protein levels, and inhibited the growth of PCa cell lines, human PCa explants, and tumor xenografts.

CONCLUSIONS

CHKA can act as an AR chaperone, providing, to our knowledge, the first evidence for kinases as molecular chaperones, making CHKA both a marker of tumor progression and a potential therapeutic target for PCa.

Resistance to Novel Antiandrogen Therapies in Metastatic Castration-Resistant Prostate Cancer

Despite the introduction of novel therapies that maximally decrease androgen-receptor (AR) signaling activity, metastatic castration-resistant prostate cancer (mCRPC) remains a lethal disease. Even though abiraterone and enzalutamide represent breakthroughs in the treatment of mCRPC and have demonstrated significant survival benefits, a significant proportion of patients have primary resistance to these agents and virtually all patients develop secondary resistance. While the mechanisms of resistance to these agents are not fully understood, many hypotheses of AR-dependent and AR-independent mechanisms are emerging, including upregulation of AR and cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17), induction of AR splice variants, AR point mutations, upregulation of glucocorticoid receptor, activation of alternative oncogenic signaling pathways, neuroendocrine transformation, and immune evasion via programmed death-ligand 1 upregulation. The aim of this review is to summarize the most clinically relevant mechanisms of resistance to novel androgen-directed agents, focusing on escape from enzalutamide and abiraterone.

Resistance to Novel Antiandrogen Therapies in Metastatic Castration-Resistant Prostate Cancer

Despite the introduction of novel therapies that maximally decrease androgen-receptor (AR) signaling activity, metastatic castration-resistant prostate cancer (mCRPC) remains a lethal disease. Even though abiraterone and enzalutamide represent breakthroughs in the treatment of mCRPC and have demonstrated significant survival benefits, a significant proportion of patients have primary resistance to these agents and virtually all patients develop secondary resistance. While the mechanisms of resistance to these agents are not fully understood, many hypotheses of AR-dependent and AR-independent mechanisms are emerging, including upregulation of AR and cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17), induction of AR splice variants, AR point mutations, upregulation of glucocorticoid receptor, activation of alternative oncogenic signaling pathways, neuroendocrine transformation, and immune evasion via programmed death-ligand 1 upregulation. The aim of this review is to summarize the most clinically relevant mechanisms of resistance to novel androgen-directed agents, focusing on escape from enzalutamide and abiraterone.

ErbB2 Signaling Increases Androgen Receptor Expression in Abiraterone-Resistant Prostate Cancer

PURPOSE

ErbB2 signaling appears to be increased and may enhance androgen receptor (AR) activity in a subset of patients with castration-resistant prostate cancer (CRPC), but agents targeting ErbB2 have not been effective. This study was undertaken to assess ErbB2 activity in abiraterone-resistant prostate cancer and to determine whether it may contribute to AR signaling in these tumors.

EXPERIMENTAL DESIGN

AR activity and ErbB2 signaling were examined in the radical prostatectomy specimens from a neoadjuvant clinical trial of leuprolide plus abiraterone and in the specimens from abiraterone-resistant CRPC xenograft models. The effect of ErbB2 signaling on AR activity was determined in two CRPC cell lines. Moreover, the effect of combination treatment with abiraterone and an ErbB2 inhibitor was assessed in a CRPC xenograft model.

RESULTS

We found that ErbB2 signaling was elevated in residual tumor following abiraterone treatment in a subset of patients and was associated with higher nuclear AR expression. In xenograft models, we similarly demonstrated that ErbB2 signaling was increased and associated with AR reactivation in abiraterone-resistant tumors. Mechanistically, we show that ErbB2 signaling and subsequent activation of the PI3K/AKT signaling stabilizes AR protein. Furthermore, concomitantly treating CRPC cells with abiraterone and an ErbB2 inhibitor, lapatinib, blocked AR reactivation and suppressed tumor progression.

CONCLUSIONS

ErbB2 signaling is elevated in a subset of patients with abiraterone-resistant prostate cancer and stabilizes AR protein. Combination therapy with abiraterone and ErbB2 antagonists may be effective for treating the subset of CRPC with elevated ErbB2 activity. Clin Cancer Res; 22(14); 3672-82. ©2016 AACR.

Inhibition of the HER2-YB1-AR axis with Lapatinib synergistically enhances Enzalutamide anti-tumor efficacy in castration resistant prostate cancer

Incurable castration-resistant prostate cancer (CRPC) is driven by androgen receptor (AR) activation. Potent therapies that prevent AR signaling, such as Enzalutamide (ENZ), are mainstay treatments for CRPC; however patients eventually progress with ENZ resistant (ENZR) disease. In this study, we investigated one mechanism of ENZ resistance, and tried to improve therapeutic efficiency of ENZ. We found HER2 expression is increased in ENZR tumors and cell lines, and is induced by ENZ treatment of LNCaP cells. ENZ-induced HER2 overexpression was dependent on AKT-YB1 activation and modulated AR activity. HER2 dependent AR activation in LNCaP and ENZR cells was effectively blocked by treatment with the EGFR/HER2 inhibitor Lapatinib, which reduced cell viability and increased apoptosis. Despite efficacy in vitro, in vivo monotherapy with Lapatinib did not prevent ENZR tumor growth. However, combination treatment of Lapatinib with ENZ most effectively induced cell death in LNCaP cells in vitro and was more effective than ENZ alone in preventing tumor growth in an in vivo model of CRPC. These results suggest that while HER2 overexpression and subsequent AR activation is a targetable mechanism of resistance to ENZ, therapy using Lapatinib is only a rational therapeutic approach when used in combination with ENZ in CRPC.

Expression of androgen receptor splice variants in clinical breast cancers

The importance of androgen receptor (AR) signaling is increasingly being recognized in breast cancer, which has elicited clinical trials aimed at assessing the efficacy of androgen deprivation therapy (ADT) for metastatic disease. In prostate cancer, resistance to ADT is frequently associated with the emergence of androgen-independent splice variants of the AR (AR variants, AR-Vs) that lack the LBD and are constitutively active. Women with breast cancer may be prone to a similar phenomenon. Herein, we show that in addition to the prototypical transcript, the AR gene produces a diverse range of AR-V transcripts in primary breast tumors. The most frequently and highly expressed variant was AR-V7 (exons 1/2/3/CE3), which was detectable at the mRNA level in > 50% of all breast cancers and at the protein level in a subset of ERα-negative tumors. Functionally, AR-V7 is a constitutively active and ADT-resistant transcription factor that promotes growth and regulates a transcriptional program distinct from AR in ERα-negative breast cancer cells. Importantly, we provide ex vivo evidence that AR-V7 is upregulated by the AR antagonist enzalutamide in primary breast tumors. These findings have implications for treatment response in the ongoing clinical trials of ADT in breast cancer.

Non-Coding RNAs in Castration-Resistant Prostate Cancer: Regulation of Androgen Receptor Signaling and Cancer Metabolism

Hormone-refractory prostate cancer frequently relapses from therapy and inevitably progresses to a bone-metastatic status with no cure. Understanding of the molecular mechanisms conferring resistance to androgen deprivation therapy has the potential to lead to the discovery of novel therapeutic targets for type of prostate cancer with poor prognosis. Progression to castration-resistant prostate cancer (CRPC) is characterized by aberrant androgen receptor (AR) expression and persistent AR signaling activity. Alterations in metabolic activity regulated by oncogenic pathways, such as c-Myc, were found to promote prostate cancer growth during the development of CRPC. Non-coding RNAs represent a diverse family of regulatory transcripts that drive tumorigenesis of prostate cancer and various other cancers by their hyperactivity or diminished function. A number of studies have examined differentially expressed non-coding RNAs in each stage of prostate cancer. Herein, we highlight the emerging impacts of microRNAs and long non-coding RNAs linked to reactivation of the AR signaling axis and reprogramming of the cellular metabolism in prostate cancer. The translational implications of non-coding RNA research for developing new biomarkers and therapeutic strategies for CRPC are also discussed.

Adaptive responses of androgen receptor signaling in castration-resistant prostate cancer

Prostate Cancer (PCa) is an important age-related disease being the most common cancer malignancy and the second leading cause of cancer mortality in men in Western countries. Initially, PCa progression is androgen receptor (AR)- and androgen-dependent. Eventually advanced PCa reaches the stage of Castration-Resistant Prostate Cancer (CRPC), but remains dependent on AR, which indicates the importance of AR activity also for CRPC. Here, we discuss various pathways that influence the AR activity in CRPC, which indicates an adaptation of the AR signaling in PCa to overcome the treatment of PCa. The adaptation pathways include interferences of the normal regulation of the AR protein level, the expression of AR variants, the crosstalk of the AR with cytokine tyrosine kinases, the Src-Akt-, the MAPK-signaling pathways and AR corepressors. Furthermore, we summarize the current treatment options with regard to the underlying molecular basis of the common adaptation processes of AR signaling that may arise after the treatment with AR antagonists, androgen deprivation therapy (ADT) as well as for CRPC, and point towards novel therapeutic strategies. The understanding of individualized adaptation processes in PCa will lead to individualized treatment options in the future.

A pilot study in prostate cancer patients treated with the AE37 Ii-key-HER-2/neu polypeptide vaccine suggests that HLA-A*24 and HLA-DRB1*11 alleles may be prognostic and predictive biomarkers for clinical benefit

Recently, several types of immunotherapies have been shown to induce encouraging clinical results, though in a restricted number of patients. Consequently, there is a need to identify immune biomarkers to select patients who will benefit from such therapies. Such predictive biomarkers may be also used as surrogates for overall survival (OS). We have recently found correlations between immunologic parameters and clinical outcome in prostate cancer patients who had been vaccinated with a HER-2/neu hybrid polypeptide vaccine (AE37) and received one booster 6 months post-primary vaccinations. Herein, we aimed to expand these retrospective analyses by studying the predictive impact of HLA-A*24 and HLA-DRB1*11 alleles, which are expressed at high frequencies among responders in our vaccinated patients, for clinical and immunological responses to AE37 vaccination. Our data show an increased OS of patients expressing the HLA-DRB1*11 or HLA-A*24 alleles, or both. Vaccine-induced immunological responses, measured as interferon γ (IFN-γ) responses in vitro or delayed-type hypersensitivity reactions in vivo, were also higher in these patients and inversely correlated with suppressor elements. Preexisting (i.e., before vaccinations with AE37) levels of vaccine-specific IFN-γ immunity and plasma TGF-β, among the HLA-A*24 and/or HLA-DRB1*11 positive patients, were strong indicators for immunological responses to AE37 treatment. These data suggest that HLA-DRB1*11 and HLA-A*24 are likely to be predictive factors for immunological and clinical responses to vaccination with AE37, though prospective validation in larger cohorts is needed.

ErbB-2 signaling plays a critical role in regulating androgen-sensitive and castration-resistant androgen receptor-positive prostate cancer cells

While androgen deprivation therapy (ADT) reduces tumor burden, autocrine growth factor loops such as human epidermal growth factor receptor 2 (HER2/ErbB-2/neu) have been proposed to contribute to prostate cancer (PCa) survival and relapse. However, the role of ErbB-2 in regulating androgen-sensitive (AS) and castration-resistant (CR) cell proliferation remains unclear. Here, we determined the role of ErbB-2 in PCa progression and survival under steroid-reduced conditions using two independent PCa cell progression models. In AR-positive androgen-independent (AI) PCa cells that exhibit the CR phenotype, ErbB-2 was constitutively activated, compared to corresponding AS PCa cells. In AS LNCaP C-33 cells, androgen-induced ErbB-2 activation through ERK1/2 mediates PCa cell proliferation. Further, the ErbB-2-specific but not EGFR-specific inhibitor suppresses basal and androgen-stimulated cell proliferation and also blocks ERK1/2 activation. ErbB-2 ectopic expression and cPAcP siRNA transfection of LNCaP C-33 cells each increases ErbB-2 tyrosine phosphorylation, correlating with increased AI PSA secretion and cell proliferation. Conversely, trapping ErbB-2 by transfected endoplasmic reticulum-targeting ScFv5R expression vector abolished DHT-induced LNCaP C-33 cell growth. Moreover, inhibition of ErbB-2 but not EGFR in AI LNCaP C-81 and MDA PCa2b-AI PCa cells significantly abolished AI cell growth. In contrast to androgens via ErbB-2/ERK1/2 signaling in AS PCa cells, the inhibition of ErbB-2 abrogated AI cell proliferation by inhibiting the cell survival protein Akt in those AI cells. These results suggest that ErbB-2 is a prominent player in mediating the ligand-dependent and -independent activation of AR in AS and AI/CR PCa cells respectively for PCa progression and survival.

Gene interference strategies as a new tool for the treatment of prostate cancer

Prostate cancer (PCa) is one of the most common cancer in men. It affects older men and the incidence increases with age; the median age at diagnosis is 67 years. The diagnosis of PCa is essentially based on three tools: digital rectal exam, serum concentration of prostate specific antigen, and transrectal ultrasound-guided biopsy. Currently, the therapeutic treatments of this cancer are different and range from the prostatectomy to hormonal therapy, to radiation therapy, to immunotherapy, and to chemotherapy. However, additional efforts are required in order to find new weapons for the treatment of metastatic setting of disease. The purpose of this review is to highlight new therapeutic strategies based on gene interference; in fact, numerous siRNA and miRNA in the therapeutic treatment of PCa are reported below.

Recepteur d'origine nantais (RON), more than a kinase: Role in castrate-resistant prostate cancer

Prostate cancer (PCA) is the second leading cause of cancer-related deaths in men in the United States. It is natural for a hormone-driven malignancy such as prostate cancer that androgen deprivation therapy (ADT) would be the preferred treatment for clinical disease management. However, after initial treatment response a vast majority of patients develop metastatic castrate-resistant prostate cancer (CRPC), which is fatal. While great headway has been made to understand the possible mechanisms that drive castrate-resistant disease, a bonafide cure remains elusive. Reactivation of androgen receptor (AR) signaling partly contributes to the emergence of CRPC. Here we briefly examine some of the known mechanisms of AR reactivation including intratumoral synthesis of androgens, modulation of AR coregulators, and AR variants with constitutive activity as well as activation of receptor tyrosine kinases. We primarily focus on the emerging dual function of the receptor tyrosine kinase (recepteur d'origine nantais; RON) as a traditional tyrosine kinase and transcription factor. We further discuss activation of RON as an alternate mechanism in the development of CRPC and available therapeutic approaches for clinical management of CRPC by combined inhibition of RON and AR.

Targeting the adaptive molecular landscape of castration-resistant prostate cancer

Castration and androgen receptor (AR) pathway inhibitors induce profound and sustained responses in advanced prostate cancer. However, the inevitable recurrence is associated with reactivation of the AR and progression to a more aggressive phenotype termed castration-resistant prostate cancer (CRPC). AR reactivation can occur directly through genomic modification of the AR gene, or indirectly via co-factor and co-chaperone deregulation. This mechanistic heterogeneity is further complicated by the stress-driven induction of a myriad of overlapping cellular survival pathways. In this review, we describe the heterogeneous and evolvable molecular landscape of CRPC and explore recent successes and failures of therapeutic strategies designed to target AR reactivation and adaptive survival pathways. We also discuss exciting areas of burgeoning anti-tumour research, and their potential to improve the survival and management of patients with CRPC.

The ErbB3-binding protein EBP1 modulates lapatinib sensitivity in prostate cancer cells

Although ErbB receptors have been implicated in prostate cancer progression, ErbB-directed drugs have not proven effective for prostate cancer treatment. The ErbB3-binding protein EBP1 affects both ErbB2 and androgen receptor signaling, two components of the response to ErbB-targeted therapies. We therefore examined the effects of EBP1 expression on the response to the ErbB1/2 tyrosine kinase inhibitor lapatinib. We found a negative correlation between endogenous EBP1 levels and lapatinib sensitivity in prostate cancer cell lines. We then overexpressed or inhibited expression of EBP1. Silencing EBP1 expression increased lapatinib sensitivity and overexpression of EBP1 increased resistance in androgen-containing media. Androgen depletion resulted in an increased sensitivity of androgen-dependent EBP1 expressing cells to lapatinib, but did not affect the lapatinib sensitivity of hormone resistant cells. However, EBP1 silenced cells were still more sensitive to lapatinib than EBP1-expressing cells in the absence of androgens. The increase in sensitivity to lapatinib following EBP1 silencing was associated with increased ErbB2 levels. In addition, lapatinib treatment increased ErbB2 levels in sensitive cells that express low levels of EBP1, but decreased ErbB2 levels in resistant EBP1-expressing cells. In contrast, ErbB3 and phospho ErbB3 levels were not affected by either changes in EBP1 levels or lapatinib treatment. The production of the ErbB3/4 ligand heregulin was increased in EBP1-silenced cells. EBP1-induced changes in AR levels were not associated with changes in lapatinib sensitivity. These studies suggest that the ability of EBP1 to activate ErbB2 signaling pathways results in increased lapatinib sensitivity.

Androgen receptor: structure, role in prostate cancer and drug discovery

Androgens and androgen receptors (AR) play a pivotal role in expression of the male phenotype. Several diseases, such as androgen insensitivity syndrome (AIS) and prostate cancer, are associated with alterations in AR functions. Indeed, androgen blockade by drugs that prevent the production of androgens and/or block the action of the AR inhibits prostate cancer growth. However, resistance to these drugs often occurs after 2–3 years as the patients develop castration-resistant prostate cancer (CRPC). In CRPC, a functional AR remains a key regulator. Early studies focused on the functional domains of the AR and its crucial role in the pathology. The elucidation of the structures of the AR DNA binding domain (DBD) and ligand binding domain (LBD) provides a new framework for understanding the functions of this receptor and leads to the development of rational drug design for the treatment of prostate cancer. An overview of androgen receptor structure and activity, its actions in prostate cancer, and how structural information and high-throughput screening have been or can be used for drug discovery are provided herein.

Precision medicine for prostate cancer

Metastatic castration-resistant prostate cancer remains a lethal disease despite considerable progress in systemic therapy over the past decade. The recent advances in genomic sequencing have improved the molecular classification of prostate cancer. The translation of genomic data into clinically relevant prognostic and predictive biomarkers to guide therapy is still in its infancy and therapies for castration-resistant prostate cancer are still used empirically. We discuss these genomic aberrations in more detail, focusing on androgen receptor signaling, ETS transcription factor gene rearrangements and PTEN loss. The incorporation of this genomic data within early phase clinical trials is evolving and may prove significant in advancing personalized care in prostate cancer.

Enzalutamide for the treatment of prostate cancer: results and implications of the AFFIRM trial

Enzalutamide is a second-generation androgen receptor signaling inhibitor that was approved by the US FDA in 2012 for the treatment of metastatic docetaxel-pretreated castrate-resistant prostate cancer. In preclinical studies, enzalutamide demonstrated higher affinity to the androgen receptor compared with the first-generation androgen receptor inhibitors. In the well-designed Phase III AFFIRM study, enzalutamide treatment showed improved overall survival compared with placebo in addition to improvement of all preplanned secondary parameters. Overall, enzalutamide seemed to be very well tolerated with a favorable side-effect profile, with a lower incidence of grade 3-4 adverse events. A potentially concerning adverse effect was the occurrence of seizures that were reported in approximately 1% of the patients receiving enzalutamide (compared with 0% in the placebo arm). This review will summarize the mechanism of action of enzalutamide, the preclinical and clinical development that led to its approval focusing on the AFFIRM trial results, its safety and efficacy and the ongoing trials, as well as patterns of resistance to this drug in the context of five new drugs approved for the treatment of metastatic castration-resistant prostate cancer. With a changing landscape for these patients, treatment sequencing and best treatment for individual patients remains challenging.

Tyrosine kinase inhibitors in the treatment of prostate cancer: taking the next step in clinical development

INTRODUCTION

Prostate cancer (PCa) is the most frequently diagnosed, non-cutaneous malignancy in Western countries. Until recently, few therapeutic options were available for patients with advanced PCa. Although these treatments may delay progression of disease, none are curative. Therefore, research continues to investigate other treatments for advanced PCa. Tyrosine kinase inhibitors (TKIs) have been extensively studied as a treatment for multiple malignancies and may represent an additional strategy. In addition to limiting cellular proliferation and metastasis, there is also growing interest in using these treatments to impact the bone microenvironment and reduce associated morbidity from PCa.

AREAS COVERED

Several TKIs have been evaluated in the preclinical setting in advanced PCa. Targets reviewed include the epidermal growth factor family, VEGF receptor, c-Src family kinases, platelet-derived growth factor and c-Met.

EXPERT OPINION

Despite strong biological rationale for the use of TKIs therapy for the treatment of PCa, Phase III clinical trials have produced disappointing results. As TKI strategies move forward, the failures of past trials need to be better understood. New approaches with these treatments will also have to take into account modern anti-androgens and a treatment landscape that now includes immunotherapy.

Understanding the mechanisms of androgen deprivation resistance in prostate cancer at the molecular level

CONTEXT

Various molecular mechanisms play a role in the development of resistance to androgen deprivation therapy in castration-resistant prostate cancer (CRPC).

OBJECTIVE

To understand the mechanisms and biological pathways associated with the progression of prostate cancer (PCa) under systemic androgen depletion or administration of the novel antiandrogens abiraterone, enzalutamide, and ARN-509. This review also examines the introduction of novel combinational approaches for patients with CRPC.

EVIDENCE ACQUISITION

PubMed was the data source. Keywords for the search were castrate resistant prostate cancer, abiraterone, enzalutamide resistance mechanisms, resistance to androgen deprivation, AR mutations, amplifications, splice variants, and AR alterations. Papers published before 1990 were excluded from the review, and only English-language papers were included.

EVIDENCE SYNTHESIS

This review summarizes the current literature regarding the mechanisms implicated in the development of CRPC and the acquisition of resistance to novel antiandrogen axis agents. The review focuses on androgen biosynthesis in the tumor microenvironment, androgen receptor (AR) alterations and post-transcriptional modifications, the role of glucocorticoid receptor, and alternative oncogenic signaling that is derepressed on maximum AR inhibition and thus promotes cancer survival and progression.

CONCLUSIONS

The mechanisms implicated in the development of resistance to AR inhibition in PCa are multiple and complex, involving virtually all classes of genomic alteration and leading to a host of selective/adaptive responses. Combinational therapeutic approaches targeting both AR signaling and alternative oncogenic pathways may be reasonable for patients with CRPC.

PATIENT SUMMARY

We looked for mechanisms related to the progression of PCa in patients undergoing hormonal therapy and treatment with novel drugs targeting the AR. Based on recent data, combining maximal AR inhibition with novel agents targeting other tumor-compensatory, non-AR-related pathways may improve the survival and quality of life of patients with castration-resistant PCa.

Interplay between steroid signalling and microRNAs: implications for hormone-dependent cancers

Hormones are key drivers of cancer development. To date, interest has largely been focussed on the classical model of hormonal gene regulation, but there is increasing evidence for a role of hormone signalling pathways in post-translational regulation of gene expression. In particular, a complex and dynamic network of bi-directional interactions with microRNAs (miRs) at all stages of biogenesis and during target gene repression is emerging. miRs, which act mainly by negatively regulating gene expression through association with 3'-UTRs of mRNA species, are increasingly understood to be important in development, normal physiology and pathogenesis. Given recent demonstrations of altered miR profiles in a diverse range of cancers, their ability to function as oncogenes or tumour suppressors, and hormonal regulation of miRs, understanding mechanisms by which miRs are generated and regulated is vitally important. miRs are transcribed by RNA polymerase II and then processed in the nucleus by the Drosha-containing Microprocessor complex and in the cytoplasm by Dicer, before mature miRs are incorporated into the RNA-induced silencing complex. It is increasingly evident that multiple cellular signalling pathways converge upon the miR biogenesis cascade, adding further layers of regulatory complexity to modulate miR maturation. This review summarises recent advances in identification of novel components and regulators of the Microprocessor and Dicer complexes, with particular emphasis on the role of hormone signalling pathways in regulating their activity. Understanding hormone regulation of miR production and how this is perturbed in cancer are critical for the development of miR-based therapeutics and biomarkers.

ACK1 tyrosine kinase interacts with histone demethylase KDM3A to regulate the mammary tumor oncogene HOXA1

Hormone therapy with the selective estrogen-receptor modulator tamoxifen provides a temporary relief for patients with estrogen receptor α (ER)-positive breast cancers. However, a subset of patients exhibiting overexpression of the HER2 receptor tyrosine kinase displays intrinsic resistance to tamoxifen therapy. Therefore, elucidating the mechanisms promoting the estrogen (E2)-independent ER-regulated gene transcription in tamoxifen-resistant breast tumors is essential to identify new therapeutic avenues to overcome drug resistance and ameliorate poor prognosis. The non-receptor tyrosine kinase, ACK1 (also known as TNK2), has emerged as a major integrator of signaling from various receptor tyrosine kinases including HER2. We have uncovered that heregulin-mediated ACK1 activation promoted ER activity in the presence of tamoxifen, which was significantly down-regulated upon ACK1 knockdown or inhibition of ACK1 by small molecule inhibitors, AIM-100 or Dasatinib. We report that ACK1 phosphorylates the ER co-activator, KDM3A, a H3K9 demethylase, at an evolutionary conserved tyrosine 1114 site in a heregulin-dependent manner, even in the presence of tamoxifen. Consistent with this finding, ACK1 activation resulted in a significant decrease in the deposition of dimethyl H3K9 epigenetic marks. Conversely, inhibition of ACK1 by AIM-100 or Dasatinib restored dimethyl H3K9 methylation marks and caused transcriptional suppression of the ER-regulated gene HOXA1. Thus, by its ability to regulate the epigenetic activity of an ER co-activator KDM3A, ACK1 modulates HOXA1 expression in the absence of E2, conferring tamoxifen resistance. These data reveal a novel therapeutic option, suppression of ACK1 signaling by AIM-100 or Dasatinib, to mitigate HOXA1 up-regulation in breast cancer patients displaying tamoxifen resistance.

Breast carcinoma: molecular profiling and updates

The most significant contribution of molecular subtyping of breast carcinomas has been the identification of estrogen-positive and estrogen-negative tumor subtypes, which are 2 distinct entities with differing prognoses and requiring different therapy. Molecular and genetic analyses can provide prognostic information; however, a thorough histopathologic evaluation with an evaluation of predictive biomarkers will provide similar information. Knowledge of genetic alterations in these tumors will help identify novel therapeutic targets, which might have an impact on prognosis. Understanding the progression pathways involved in the transition of in situ carcinoma to invasive carcinoma might lead to efficient risk stratification in these patients.

Beyond androgen deprivation: ancillary integrative strategies for targeting the androgen receptor addiction of prostate cancer

The large majority of clinical prostate cancers remain dependent on androgen receptor (AR) activity for proliferation even as they lose their responsiveness to androgen deprivation or antagonism. AR activity can be maintained in these circumstances by increased AR synthesis--often reflecting increased NF-κB activation; upregulation of signaling pathways that promote AR activity in the absence of androgens; and by emergence of AR mutations or splice variants lacking the ligand-binding domain, which render the AR constitutively active. Drugs targeting the N-terminal transactivating domain of the AR, some of which are now in preclinical development, can be expected to inhibit the activity not only of unmutated ARs but also of the mutant forms and splice variants selected for by androgen deprivation. Concurrent measures that suppress AR synthesis or boost AR turnover could be expected to complement the efficacy of such drugs. A number of nutraceuticals that show efficacy in prostate cancer xenograft models--including polyphenols from pomegranate, grape seed, and green tea, the crucifera metabolite diindolylmethane, and the hormone melatonin--have the potential to suppress AR synthesis via downregulation of NF-κB activity; clinical doses of salicylate may have analogous efficacy. The proteasomal turnover of the AR is abetted by diets with a high ratio of long-chain omega-3 to omega-6 fatty acids, which are beneficial in prostate cancer xenograft models; berberine and sulforaphane, by inhibiting AR's interaction with its chaperone Hsp90, likewise promote AR proteasomal degradation and retard growth of human prostate cancer in nude mice. Hinge region acetylation of the AR is required for optimal transactivational activity, and low micromolar concentrations of the catechin epigallocatechin-3-gallate (EGCG) can inhibit such acetylation--possibly explaining the ability of EGCG administration to suppress androgenic activity and cell proliferation in prostate cancer xenografts. Hence, it is proposed that regimens featuring an N-terminal domain-targeting drug, various nutraceuticals/drugs that downregulate NF-κB activity, and/or supplemental intakes of fish oil, berberine, sulforaphane, and EGCG have potential for blocking proliferation of prostate cancer by targeting its characteristic addiction to androgen receptor activity.

Phospho-kinase profile of triple negative breast cancer and androgen receptor signaling

Background

The androgen receptor (AR) plays a central role in the oncogenesis of different tumors, as is the case in prostate cancer. In triple negative breast cancer (TNBC) a gene expression classification has described different subgroups including a luminal androgen subtype. The AR can be controlled by several mechanisms like the activation of membrane tyrosine kinases and downstream signaling pathways. However little is known in TNBC about how the AR is modulated by these mechanisms and the potential therapeutic strategists to inhibit its expression.

Methods

We used human samples to evaluate the expression of AR by western-blot and phospho-proteomic kinase arrays that recognize membrane tyrosine kinase receptors and downstream mediators. Western-blots in human cell lines were carried out to analyze the expression and activation of individual proteins. Drugs against these kinases in different conditions were used to measure the expression of the androgen receptor. PCR experiments were performed to assess changes in the AR gene after therapeutic modulation of these pathways.

Results

AR is present in a subset of TNBC and its expression correlates with activated membrane receptor kinases-EGFR and PDGFRβ in human samples and cell lines. Inhibition of the PI3K/mTOR pathway in TNBC cell lines decreased notably the expression of the AR. Concomitant administration of the anti-androgen bicalutamide with the EGFR, PDGFRβ and Erk1/2 inhibitors, decreased the amount of AR compared to each agent given alone, and had an additive anti-proliferative effect. Administration of dihydrotestosterone augmented the expression of AR that was not modified by the inhibition of the PI3K/mTOR or Erk1/2 pathways. AR expression was posttranscriptionally regulated by PI3K or Erk1/2 inhibition.

Conclusion

Our results describe the expression of the AR in TNBC as a druggable target and further suggest the combination of bicalutamide with inhibitors of EGFR, PDGFRβ or Erk1/2 for future development.

Androgen receptor and gene network: Micromechanics reassemble the signaling machinery of TMPRSS2-ERG positive prostate cancer cells

Prostate cancer is a gland tumor in the male reproductive system. It is a multifaceted and genomically complex disease. Transmembrane protease, serine 2 and v-ets erythroblastosis virus E26 homolog (TMPRSS2-ERG) gene fusions are the common molecular signature of prostate cancer. Although tremendous advances have been made in unraveling various facets of TMPRSS2-ERG-positive prostate cancer, many research findings must be sequentially collected and re-interpreted. It is important to understand the activation or repression of target genes and proteins in response to various stimuli and the assembly in signal transduction in TMPRSS2-ERG fusion-positive prostate cancer cells. Accordingly, we divide this multi-component review ofprostate cancer cells into several segments: 1) The role of TMPRSS2-ERG fusion in genomic instability and methylated regulation in prostate cancer and normal cells; 2) Signal transduction cascades in TMPRSS2-ERG fusion-positive prostate cancer; 3) Overexpressed genes in TMPRSS2-ERG fusion-positive prostate cancer cells; 4) miRNA mediated regulation of the androgen receptor (AR) and its associated protein network; 5) Quantitative control of ERG in prostate cancer cells; 6) TMPRSS2-ERG encoded protein targeting; In conclusion, we provide a detailed understanding of TMPRSS2-ERG fusion related information in prostate cancer development to provide a rationale for exploring TMPRSS2-ERG fusion-mediated molecular network machinery.

Ligand-independent and tissue-selective androgen receptor inhibition by pyrvinium

Pyrvinium pamoate (PP) is a potent noncompetitive inhibitor of the androgen receptor (AR). Using a novel method of target identification, we demonstrate that AR is a direct target of PP in prostate cancer cells. We demonstrate that PP inhibits AR activity via the highly conserved DNA binding domain (DBD), the only AR inhibitor that functions via this domain. Furthermore, computational modeling predicts that pyrvinium binds at the interface of the DBD dimer and the minor groove of the AR response element. Because PP acts through the DBD, PP is able to inhibit the constitutive activity of AR splice variants, which are thought to contribute to the growth of castration resistant prostate cancer (CRPC). PP also inhibits androgen-independent AR activation by HER2 kinase. The antiandrogen activity of pyrvinium manifests in the ability to inhibit the in vivo growth of CRPC xenografts that express AR splice variants. Interestingly, PP was most potent in cells with endogenous AR expression derived from prostate or bone. PP was able to inhibit several other hormone nuclear receptors (NRs) but not structurally unrelated transcription factors. PP inhibition of other NRs was similarly cell-type selective. Using dual-energy X-ray absorptiometry, we demonstrate that the cell-type specificity of PP manifests in tissue-selective inhibition of AR activity in mice, as PP decreases prostate weight and bone mineral density but does not affect lean body mass. Our results suggest that the noncompetitive AR inhibitor pyrvinium has significant potential to treat CRPC, including cancers driven by ligand-independent AR signaling.

Rapid induction of androgen receptor splice variants by androgen deprivation in prostate cancer

PURPOSE

Mechanisms mediating androgen receptor (AR) reactivation in prostate cancer that progresses after castration (castration-resistant prostate cancer; CRPC) and subsequent treatment with abiraterone (CYP17A1 inhibitor that further suppresses androgen synthesis) remain unclear.

EXPERIMENTAL DESIGN

Prostate cancer xenografts were examined to identify mechanism of progression after castration and abiraterone.

RESULTS

AR reactivation in abiraterone-resistant VCaP xenografts was not associated with restoration of intratumoral androgens or alterations in AR coregulators. In contrast, mRNA encoding full-length AR (AR-FL) and a constitutively active splice variant (AR-V7) were increased compared with xenografts before castration, with an increase in AR-V7 relative to AR-FL. This shift toward AR-V7 was due to a feedback mechanism whereby the androgen-liganded AR stimulates expression of proteins that suppress generation of AR-V7 relative to AR-FL transcripts. However, despite the increases in AR-V7 mRNA, it remained a minor transcript (<1%) relative to AR-FL in resistant VCaP xenografts and CRPC clinical samples. AR-V7 protein expression was similarly low relative to AR-FL in castration-resistant VCaP xenografts and androgen-deprived VCaP cells, but the weak basal AR activity in these latter cells was further repressed by AR-V7 siRNA.

CONCLUSIONS

AR-V7 at these low levels is not adequate to restore AR activity, but its rapid induction after androgen deprivation allows tumors to retain basal AR activity that may be needed for survival until more potent mechanisms emerge to activate AR. Agents targeting AR splice variants may be most effective when used very early in conjunction with therapies targeting the AR ligand-binding domain.

Sex hormone receptor repertoire in breast cancer

Classification of breast cancer as endocrine sensitive, hormone dependent, or estrogen receptor (ER) positive refers singularly to ER α . One of the oldest recognized tumor targets, disruption of ER α -mediated signaling, is believed to be the mechanistic mode of action for all hormonal interventions used in treating this disease. Whereas ER α is widely accepted as the single most important predictive factor (for response to endocrine therapy), the presence of the receptor in tumor cells is also of prognostic value. Even though the clinical relevance of the two other sex hormone receptors, namely, ER β and the androgen receptor remains unclear, two discordant phenomena observed in hormone-dependent breast cancers could be causally related to ER β -mediated effects and androgenic actions. Nonetheless, our understanding of regulatory molecules and resistance mechanisms remains incomplete, further compromising our ability to develop novel therapeutic strategies that could improve disease outcomes. This review focuses on the receptor-mediated actions of the sex hormones in breast cancer.

Mechanisms of androgen receptor activation in castration-resistant prostate cancer

Systemic treatment of advanced prostate cancer is initiated with androgen deprivation therapy by gonadal testosterone depletion. Response durations are variable and tumors nearly always become resistant as castration-resistant prostate cancer (CRPC), which is driven, at least in part, by a continued dependence on the androgen receptor (AR). The proposed mechanisms that underlie AR function in this clinical setting are quite varied. These include intratumoral synthesis of androgens from inactive precursors, increased AR expression, AR activation through tyrosine kinase-dependent signaling, alterations in steroid receptor coactivators, and expression of a truncated AR with constitutive activity. Various pharmacologic interventions have clinically validated some of these mechanisms, such as those that require the AR ligand-binding domain. Clinical studies have failed to validate other mechanisms, and additional mechanisms have yet to be tested in patients with CRPC. Here, we review the mechanisms that elicit AR activity in CRPC, with a particular focus on recent developments.

MicroRNA signature helps distinguish early from late biochemical failure in prostate cancer

PURPOSE

Prostate-specific antigen testing has led to overtreatment of prostate cancer (PCa). Only a small subset of PCa patients will have an aggressive disease that requires intensive therapy, and there is currently no biomarker to predict disease aggressiveness at the time of surgery. MicroRNAs (miRNAs) are reported to be involved in PCa pathogenesis.

METHODS

This study involved 105 participants. For the discovery phase, prostatectomy samples were dichotomized to high-risk (n = 27, biochemical failure <36 months after prostatectomy) and low-risk groups (n = 14, ≥ 36 months without biochemical failure). Expression of 754 mature miRNAs was compared between the 2 groups. Linear regression models were built to accurately predict biochemical failure risk. miRNA mimics were transfected into PCa model cell lines to test effects on proliferation and to deduce responding signaling pathways.

RESULTS

We identified 25 differentially expressed miRNAs between the biochemical failure risk groups. Based on the expression of 2-3 miRNAs, 3 logistic regression models were developed, each with a high positive predictive value. Candidate miRNAs and the best-performing model were also verified on an independent PCa set. miRNA-152, featured in the models, was further investigated by using cell line models and was shown to affect cell proliferation. Predicted interaction between miR-152 and (mRNA)ERBB3 (erythroblastic leukemia viral oncogene homolog 3) was experimentally validated in vitro.

CONCLUSIONS

miRNAs can help to predict biochemical failure risk at the time of prostatectomy.

Androgen receptor phosphorylation at serine 308 and serine 791 predicts enhanced survival in castrate resistant prostate cancer patients

We previously reported that AR phosphorylation at serine 213 was associated with poor outcome and may contribute to prostate cancer development and progression. This study investigates if specific AR phosphorylation sites have differing roles in the progression of hormone naïve prostate cancer (HNPC) to castrate resistant disease (CRPC). A panel of phosphospecific antibodies were employed to study AR phosphorylation in 84 matched HNPC and CRPC tumours. Immunohistochemistry measured Androgen receptor expression phosphorylated at serine residues 94 (pAR⁹⁴), 308 (pAR³⁰⁸), 650(pAR⁶⁵⁰) and 791 (pAR⁷⁹¹). No correlations with clinical parameters were observed for pAR⁹⁴ or pAR⁶⁵⁰ in HNPC or CRPC tumours. In contrast to our previous observation with serine 213, high pAR³⁰⁸ is significantly associated with a longer time to disease specific death (p = 0.011) and high pAR⁷⁹¹ expression significantly associated with a longer time to disease recurrence (p = 0.018) in HNPC tumours and longer time to death from disease recurrence (p = 0.040) in CRPC tumours. This observation in CRPC tumours was attenuated in high apoptotic tumours (p = 0.022) and low proliferating tumours (p = 0.004). These results demonstrate that understanding the differing roles of AR phosphorylation is necessary before this can be exploited as a target for castrate resistant prostate cancer.