NanoLuc Binary Technology as a methodological approach: an important new tool for studying the localization of androgen receptor and androgen receptor splice variant V7 homo and heterodimers.

BACKGROUND: The androgen/androgen receptor (AR)-signaling axis plays a central role in prostate cancer (PCa). Upon androgen-binding the AR dimerizes with another AR, and translocates into the nucleus where the AR-dimer activates/inactivates androgen-dependent genes. Consequently, treatments for PCa are commonly based on androgen deprivation therapy (ADT). The clinical benefits of ADT are only transitory and most tumors develop mechanisms allowing the AR to bypass its need for physiological levels of circulating androgens. Clinical failure of ADT is often characterized by the synthesis of a constitutively active AR splice variant, termed AR-V7. AR-V7 mRNA expression is considered as a resistance mechanism following ADT. AR-V7 no longer needs androgenic stimuli for nuclear entry and/or dimerization. METHODS: Our goal was to mechanistically decipher the interaction between full-length AR (AR-FL) and AR-V7 in AR-null HEK-293 cells using the NanoLuc Binary Technology under androgen stimulation and deprivation conditions. RESULTS: Our data point toward a hypothesis that AR-FL/AR-FL homodimers form in the cytoplasm, whereas AR-V7/AR-V7 homodimers localize in the nucleus. However, after androgen stimulation, all the AR-FL/AR-FL, AR-FL/AR-V7 and AR-V7/AR-V7 dimers were localized in the nucleus. CONCLUSIONS: We showed that AR-FL and AR-V7 form heterodimers that localize to the nucleus, whereas AR-V7/AR-V7 dimers were found to localize in the absence of androgens in the nucleus.

Sildenafil triggers tumor lethality through altered expression of HSP90 and degradation of PKD2.

The repurposing of existing drugs has emerged as an attractive additional strategy to the development of novel compounds in the fight against cancerous diseases. Inhibition of phosphodiesterase 5 (PDE5) has been claimed as a potential approach to target various cancer subtypes in recent years. However, data on the treatment of tumors with PDE5 inhibitors as well as the underlying mechanisms are as yet very scarce. Here, we report that treatment of tumor cells with low concentrations of Sildenafil was associated with decreased cancer cell proliferation and augmented apoptosis in vitro and resulted in impaired tumor growth in vivo. Notably, incubation of cancer cells with Sildenafil was associated with altered expression of HSP90 chaperone followed by degradation of protein kinase D2, a client protein previously reported to be involved in tumor growth. Furthermore, the involvement of low doses of PU-H71, an HSP90 inhibitor currently under clinical evaluation, in combination with low concentrations of Sildenafil, synergistically and negatively impacted on the viability of cancer cells in vivo. Taken together, our study suggests that repurposing of already approved drugs, alone or in combination with oncology-dedicated compounds, may represent a novel cancer therapeutic strategy.

The BET-inhibitor PFI-1 diminishes AR/AR-V7 signaling in prostate cancer cells.

OBJECTIVE: The bromodomain and extra-terminal (BET) family of proteins provides a scaffolding platform for the recruitment and tethering of transcription factors to acetylated chromatin, thereby modulating gene expression. In this study, we evaluated the efficacy of the BET-inhibitor PFI-1 to diminish AR/AR-V7 signaling and proliferation in castration-resistant prostate cancer cells. METHODS: Prostate-specific antigen and androgen receptor (AR) protein were quantified by means of two commercial ELISAs. Transactivation of the AR, AR-V7 and Q641X was determined by reporter gene assays. Cell proliferation was measured using a colorimetric MTT-assay. RESULTS: PFI-1 dose-dependently inhibited transactivation of full-length AR (non- mutated, i.e., wild-type or point-mutated/promiscuous forms) without affecting their cellular protein levels. Moreover, PFI-1 was active against C-terminally truncated constitutively active ARs like AR-V7 and Q641X. Prostate cancer cells exhibiting a transcriptionally active AR-signaling complex (LNCaP, 22Rv1) were more susceptible to the growth-inhibitory effects than the AR-negative PC-3 cells. CONCLUSION: The quinazolinone PFI-1 is a highly efficient inhibitor of AR-signaling-competent prostate cancer cells in vitro. PFI-1 could serve as a lead compound for the development of new therapeutics able to block AR/AR-V7 signaling in advanced prostate cancer.

Inhibition of IGF-1R diminishes transcriptional activity of the androgen receptor and its constitutively active, C-terminally truncated counterparts Q640X and AR-V7.

PURPOSE: Failure of endocrine treatment in castration-resistant prostate cancer (CRPC) is often associated with the emergence of C-terminally truncated androgen receptor variants that function as constitutively active transcription factors (i.e., AR∆LBD). The mechanisms involved in the regulation of AR∆LBD signaling are largely unknown. Since the IGF-1 pathway was repeatedly shown to affect AR function, we studied whether an inhibition of IGF-1R could also affect AR∆LBD signaling. METHODS: Regulation of androgen receptor (AR) and AR∆LBD signaling was analyzed by reporter gene assays, immunoblotting, ELISA and quantitative RT-PCR. RESULTS: Inhibition of IGF-1R with the small-molecule inhibitor NVP-AEW541 reduced the transcriptional activity of the AR and its truncated counterparts Q640X and AR-V7. As shown in Q640X, the inhibition of transcriptional activity was paralleled by a decreased receptor phosphorylation. CONCLUSIONS: Inhibition of IGF-1R leads to a down-regulation of AR∆LBD signaling and provides a rationale for CRPC therapies targeting growth factor receptors.

Androgen receptor aberrations in the era of abiraterone and enzalutamide.

Prostate cancer is the most prevalent non-skin cancer and the second leading cause of cancer death in men of the western world. As growth and differentiation of prostate cancer largely depend on androgens, inhibition of the androgen/androgen receptor signaling axis is the main treatment for locally advanced and/or metastatic tumors. Although first-line androgen deprivation therapies like chemical/surgical castration and/or administration of anti-androgens are able to control the disease for several years, prostate cancer almost invariably recurs as castration-resistant prostate cancer. This stage of the disease is characterized by a sustained AR-signaling despite castrate levels of circulating androgens. Various molecular mechanisms were shown to induce castration resistance. This review will discuss the most recent and relevant experimental findings on AR-signaling in castration-resistant prostate cancer in order to provide a comprehensive interpretation of the clinical behavior of this tumor entity following treatments with abiraterone, enzalutamide, ARN-509 or taxanes.

Corpulence is the crucial factor: association of testosterone and/or obesity with prostate cancer stage.

OBJECTIVES: To evaluate whether low testosterone levels or obesity, or both, are directly associated with tumor stage/grade in patients with clinically localized prostate cancer. METHODS: Preoperative androgen serum levels (total and free testosterone), sex hormone-binding globulin, body mass index and waist circumference were assessed in 510 consecutive European Caucasian men treated with radical prostatectomy. Hormone levels and body mass index/waist circumference were correlated with patient- and tumor-specific characteristics using multivariable logistic regression analysis. RESULTS: Even though we confirmed an inverse correlation between bodyweight and testosterone levels, only overweight - but not low testosterone - was associated with advanced disease and poor differentiation of prostate cancer. Using multivariate analyses, both body mass index ≥30 kg/m(2) and waist circumference >110 cm were associated with high-grade disease (Gleason score ≥8). A waist circumference >110 cm also correlated significantly with lymph node metastasis. CONCLUSIONS: This is the first study showing that obesity, but not low serum testosterone levels, is significantly associated with high grade and metastatic disease in men diagnosed with clinically localized prostate cancer. The present findings suggest that low androgen levels at diagnosis, which used to be held responsible for the development of aggressive prostate cancer, is only an epiphenomenon of obesity rather than the cause of prostate cancer development and/or progression.

Expression of the microtubule-associated protein 2 (MAP2) as a potential independent prognostic marker in prostate cancer.

PURPOSE: Investigation of Microtubuli-associated Protein 2 (MAP2) expression and its clinical relevance in prostate cancer. MATERIAL AND METHODS: MAP2 expression was immunohistochemically analysed on radical prostatectomy specimens using whole block sections (n = 107) and tissue microarrays (TMA; n = 310). The staining intensity was evaluated for carcinoma, benign tissue and prostatic intraepithelial neoplasia. Expression data were correlated with clinicopathological parameters and biochemical recurrence-free survival. Additionally, MAP2 protein expression was quantitatively analysed in the serum of histologically confirmed prostate carcinoma patients and the control group using a commercial enzyme-linked immunosorbent assay. RESULTS: MAP2 staining was significantly stronger in neoplastic tissue than in non-neoplastic prostatic glands, both in whole block sections (p < 0.01) and in TMA sections (p < 0.05). TMA data revealed significantly stronger MAP2 staining in high-grade tumors. Survival analysis showed a significant correlation between strong MAP2 staining in carcinoma and shortened biochemical recurrence-free survival after prostatectomy (p < 0.001). Multivariate Cox regression analysis confirmed MAP2 as an independent predictor for an unfavourable course. Mean MAP2 serum levels for non-PCA vs. PCA patients differed significantly (non-PCA = 164.7 pg/ml vs. PCA = 242.5 pg/ml, p < 0.001). CONCLUSION: The present data support MAP2 as a novel biomarker in PCA specimens. MAP2 is correlated with tumor grade and MAP2 high-expressing PCA is associated with an increased risk of biochemical recurrence after radical prostatectomy. Future studies are necessary to evaluate MAP2 as a valuable immunohistochemical biomarker in preoperative PCA diagnostic procedures, in particular with regard to treatment modalities.

Clinical implications of AGR2 in primary prostate cancer: Results from a large-scale study.

Human anterior gradient-2 (AGR2) has been implicated in carcinogenesis of various solid tumours, but the expression data in prostate cancer are contradictory regarding its prognostic value. The objective of this study is to evaluate the expression of AGR2 in a large prostate cancer cohort and to correlate it with clinicopathological data. AGR2 protein expression was analysed immunohistochemically in 1023 well-characterized prostate cancer samples with a validated antibody. AGR2 expression levels in carcinomas were compared with matched tissue samples of adjacent normal glands. AGR2 expression levels were dichotomized and tested for statistical significance. Increased AGR2 expression was found in 93.5% of prostate cancer cases. AGR2 levels were significantly higher in prostate cancer compared with normal prostate tissue. A gradual loss of AGR2 expression was associated with increasing tumour grade (ISUP), and AGR2 expression is inversely related to patient survival, however, multivariable significance is not achieved. AGR2 is clearly upregulated in the majority of prostate cancer cases, yet a true diagnostic value appears unlikely. In spite of the negative correlation of AGR2 expression with increasing tumour grade, no independent prognostic significance was found in this large-scale study.

High CRP values predict poor survival in patients with penile cancer.

BACKGROUND: High levels of circulating C-reactive protein (CRP) have recently been linked to poor clinical outcome in various malignancies. The aim of this study was to evaluate the prognostic significance of the preoperative serum CRP level in patients with squamous cell carcinoma (SCC) of the penis. METHODS: This retrospective analysis included 79 penile cancer patients with information about their serum CRP value prior to surgery who underwent either radical or partial penectomy at two German high-volume centers (Ulm University Medical Center and Hannover Medical School) between 1990 and 2010. They had a median (mean) follow-up of 23 (32) months. RESULTS: A significantly elevated CRP level (>15 vs. ≤ 15 mg/l) was found more often in patients with an advanced tumor stage (≥pT2) (38.9 vs. 11.6%, p=0.007) and in those with nodal disease at diagnosis (50.0 vs. 14.6%, p=0.007). However, high CRP levels were not associated with tumor differentiation (p=0.53). The Kaplan-Meier 5-year cancer-specific survival (CSS) rate was 38.9% for patients with preoperative CRP levels above 15 mg/l and 84.3% for those with lower levels (p=0.001). Applying multivariate analysis and focusing on the subgroup of patients without metastasis at the time of penile surgery, both advanced local tumor stage (≥pT2; HR 8.8, p=0.041) and an elevated CRP value (>15 mg/l; HR 3.3, p=0.043) were identified as independent predictors of poor clinical outcome in patients with penile cancer. CONCLUSIONS: A high preoperative serum CRP level was associated with poor survival in patients with penile cancer. If larger patient populations confirm its prognostic value, its routine use could enable better risk stratification and risk-adjusted follow-up of patients with SCC of the penis.

Circulating free testosterone is an independent predictor of advanced disease in patients with clinically localized prostate cancer.

PURPOSE: To evaluate the clinical value of the pre-treatment calculated free testosterone (fT), total testosterone (tT), sexual hormone-binding globulin (SHBG) and estradiol (E2) levels as potential predictors of pathological stage and grade in patients with clinically localized prostate cancer. METHODS: Preoperative sex hormone serum levels were prospectively measured in 137 patients who underwent radical prostatectomy at the University Hospital Ulm from February 2011 to February 2012. We related sex hormone levels to clinicopathologic data including tumour stage, Gleason score and prostate specific antigen (PSA). (Non)parametric statistical tests and receiver operating characteristics (ROC) analyses were performed. RESULTS: Preoperative serum fT levels were significantly associated with advanced disease (pT3-4 and/or pN+; p = 0.047) and lymph node involvement (pN+) (p = 0.027). Patients with low (<0.047 µg/l) vs. normal fT values (≥0.047 µg/l) were associated with higher tumour stage (p = 0.049), positive lymph node status (pN+ , p = 0.038) and advance disease (p = 0.016). Moreover, low tT values (≤0.193 µg/l; p = 0.018) and elevated SHBG levels (>48.4 nmol/l, p = 0.043) correlated with a higher Gleason score. Conversely, E2 levels were not associated with tumour stage or grade. Applying multivariate analysis, unlike tT, SHBG, and E2 levels, low fT levels were a significant independent predictor of advanced disease (relative hazard ratio 3.05, p = 0.028). CONCLUSIONS: Low pre-treatment fT levels were significantly associated with tumour stage and extraprostatic tumour spread and might-in addition or combination with PSA-serve as a useful prognostic parameter for prostate cancer patients prior to radical prostatectomy.

JS-K, a glutathione/glutathione S-transferase-activated nitric oxide releasing prodrug inhibits androgen receptor and WNT-signaling in prostate cancer cells.

BACKGROUND: Nitric oxide (NO) and its oxidative reaction products have been repeatedly shown to block steroid receptor function via nitrosation of zinc finger structures in the DNA-binding domain (DBD). In consequence NO-donors could be of special interest for the treatment of deregulated androgen receptor(AR)-signaling in castration resistant prostate cancer (CRPC). METHODS: Prostate cancer (PCa) cells were treated with JS-K, a diazeniumdiolate derivate capable of generating large amounts of intracellular NO following activation by glutathione S-transferase. Generation of NO was determined indirectly by the detection of nitrate in tissue culture medium or by immunodetection of nitrotyrosine in the cytoplasm. Effects of JS-K on intracellular AR-levels were determined by western blotting. AR-dimerization was analyzed by mammalian two hybrid assay, nuclear translocation of the AR was visualized in PCa cells transfected with a green fluorescent AR-Eos fusion protein using fluorescence microscopy. Modulation of AR- and WNT-signalling by JS-K was investigated using reporter gene assays. Tumor cell proliferation following JS-K treatment was measured by MTT-Assay. RESULTS: The NO-releasing compound JS-K was shown to inhibit AR-mediated reporter gene activity in 22Rv1 CRPC cells. Inhibition of AR signaling was neither due to an inhibition of nuclear import nor to a reduction in AR-dimerization. In contrast to previously tested NO-donors, JS-K was able to reduce the intracellular concentration of functional AR. This could be attributed to the generation of extremely high intracellular levels of the free radical NO as demonstrated indirectly by high levels of nitrotyrosine in JS-K treated cells. Moreover, JS-K diminished WNT-signaling in AR-positive 22Rv1 cells. In line with these observations, castration resistant 22Rv1 cells were found to be more susceptible to the growth inhibitory effects of JS-K than the androgen dependent LNCaP which do not exhibit an active WNT-signaling pathway. CONCLUSIONS: Our results suggest that small molecules able to inhibit WNT- and AR-signaling via NO-release represent a promising platform for the development of new compounds for the treatment of CRPC.

NF-κB signaling in prostate cancer: a promising therapeutic target?

Prostate carcinoma (PCa) displays a wide variety of genetic alterations, versatile expression profiles as well as cell surface markers. Despite this heterogeneity, a common treatment for advanced PCa is androgen deprivation therapy (ADT). ADT targets the androgen receptor-a member of the nuclear receptor superfamily-which is required for development and function of the prostate and critical for PCa growth and survival. After an initial regression of the tumor during ADT, a large fraction of tumors progress to so-called castration-resistant prostate carcinoma (CRPca) which is highly resistant toward chemotherapy. The ensuing high mortality rates illustrate the importance of novel therapeutic targets for CRPCa. The transcription factor NF-κB was recently proposed as such a potential target for therapeutic intervention in CRPCa. Although NF-κB is essential for the regulation of innate and adaptive immunity recent data suggest a role of NF-κB in cancer initiation and progression. However, the exact function of NF-κB signaling in PCa is still a matter of debate. Here, we review known roles of NF-κB signaling in PCa and emphasize the crosstalk of NF-κB and androgen receptor signaling. Finally, we discuss potential therapeutic relevance of blocking NF-κB in PCa.

AR-Q640X, a model to study the effects of constitutively active C-terminally truncated AR variants in prostate cancer cells.

PURPOSE: A recently identified mechanism allowing prostate cancer (PCa) cells to grow in the absence of androgens is the expression of constitutively active, C-terminally truncated androgen receptor (AR) variants lacking vast parts of the ligand-binding domain. These AR variants termed ARΔLBD are either products of alternative splicing, point mutations leading to premature stop codons or proteolytic cleavage of the AR. Some controversies exist about the requirement of additional full-length AR for the full transcriptional activity of the ARΔLBD. On basis of a mutated, C-terminally truncated AR termed Q640X, we developed an experimental model for the study of ARΔLBD in PCa cells. METHODS: Activation of AR-dependent promoters was analyzed by reporter gene assays. Dimerization studies were conducted using a mammalian two-hybrid system. RESULTS: Although Q640X/Q640X homodimers were able to induce the expression of certain AR target genes, Q640X/AR heterodimers were necessary to activate the full panel of androgen-dependent genes under androgen-deprived conditions. CONCLUSIONS: The following study supports the hypothesis that castration-resistant prostate cancer (CRPC) cells are able to activate specific androgen-dependent genes by selective modulation of the ratio between ARΔLBD and their putative dimerization partners like the full-length AR or other ARΔLBD in the absence of androgens. The present data suggest that AR-mutant Q640X is a powerful experimental tool for the functional analysis of ARΔLBD in CRPC.

The "Aging Males' Symptoms" Scale (AMS): predictive value for lowered circulating androgens.

BACKGROUND: Symptoms of the "male climacteric" are often at least in part referred to an age-dependent decline of serum androgen levels. Therefore, we evaluated the relationship of climacteric symptoms as assessed by the "Aging Males' Symptoms" (AMS) Questionnaire with circulating androgen levels. METHODS: 146 ambulatory men (age, 27-85 years) were surveyed with the AMS Questionnaire and sampled for serum values of total testosterone (tT) and sexual hormone binding globulin (SHBG). Free testosterone (fT) was calculated from tT and SHBG. A total AMS score ≥37 was considered pathological; the lower limits for tT and fT were set to 8 nmol/l and 180 pmol/l, respectively. RESULTS: A significant deficit in tT and fT was shown in 25 (17.1%) and 34 (24.5%) men, respectively; the AMS Questionnaire showed pathological results for 66 (45.2%) men. In predicting a tT deficit, the AMS Questionnaire rendered a sensitivity of 76% and a specificity of 61.6%, only. However, multiple regression analysis revealed a significant correlation of lowered tT with a pathological somatovegetative and psychological AMS subscore (p = 0.042 and p = 0.01) and a correlation of lowered fT with a pathological sexual subscore (p = 0.039). CONCLUSION: In predicting hypogonadism the AMS Questionnaire in total did not render a sufficient diagnostic efficiency.

Effects of sorafenib on C-terminally truncated androgen receptor variants in human prostate cancer cells.

Recent evidence suggests that the development of castration resistant prostate cancer (CRPCa) is commonly associated with an aberrant, ligand-independent activation of the androgen receptor (AR). A putative mechanism allowing prostate cancer (PCa) cells to grow under low levels of androgens, is the expression of constitutively active, C-terminally truncated AR lacking the AR-ligand binding domain (LBD). Due to the absence of a LBD, these receptors, termed ARΔLBD, are unable to respond to any form of anti-hormonal therapies. In this study we demonstrate that the multikinase inhibitor sorafenib inhibits AR as well as ARΔLBD-signalling in CRPCa cells. This inhibition was paralleled by proteasomal degradation of the AR- and ARΔLBD-molecules. In line with these observations, maximal antiproliferative effects of sorafenib were achieved in AR and ARΔLBD-positive PCa cells. The present findings warrant further investigations on sorafenib as an option for the treatment of advanced AR-positive PCa.

Androgen Receptor Splice Variants Contribute to the Upregulation of DNA Repair in Prostate Cancer.

BACKGROUND: Canonical androgen receptor (AR) signaling regulates a network of DNA repair genes in prostate cancer (PCA). Experimental and clinical evidence indicates that androgen deprivation not only suppresses DNA repair activity but is often synthetically lethal in combination with PARP inhibition. The present study aimed to elucidate the impact of AR splice variants (AR-Vs), occurring in advanced or late-stage PCA, on DNA repair machinery. METHODS: Two hundred and seventy-three tissue samples were analyzed, including primary hormone-naïve PCA, primary metastases, hormone-sensitive PCA on androgen deprivation therapy (ADT) and castration refractory PCA (CRPC group). The transcript levels of the target genes were profiled using the nCounter platform. Experimental support for the findings was gained in AR/AR-V7-expressing LNCaP cells subjected to ionizing radiation. RESULTS: AR-Vs were present in half of hormone-sensitive PCAs on androgen deprivation therapy (ADT) and two-thirds of CRPC samples. The presence of AR-Vs is highly correlated with increased activity in the AR pathway and DNA repair gene expression. In AR-V-expressing CRPC, the DNA repair score increased by 2.5-fold as compared to AR-V-negative samples. Enhanced DNA repair and the deregulation of DNA repair genes by AR-V7 supported the clinical data in a cell line model. CONCLUSIONS: The expression of AR splice variants such as AR-V7 in PCA patients following ADT might be a reason for reduced or absent therapy effects in patients on additional PARP inhibition due to the modulation of DNA repair gene expression. Consequently, AR-Vs should be further studied as predictive biomarkers for therapy response in this setting.

Inhibition of glycogen synthase kinase-3beta promotes nuclear export of the androgen receptor through a CRM1-dependent mechanism in prostate cancer cell lines.

The androgen receptor (AR) is a ligand-dependent transcription factor belonging to the steroid hormone receptor superfamily. Under normal conditions, in the absence of a ligand, the AR is localized to the cytoplasm and is actively transported into the nucleus upon binding of androgens. In advanced prostate cancer (PCa) cell lines, an increased sensitivity to dihydrotestosterone (DHT), enabling the cells to proliferate under sub-physiological levels of androgens, has been associated with increased stability and nuclear localization of the AR. There is experimental evidence that the glycogen synthase kinase-3beta (GSK-3beta), a multifunctional serine/threonine kinase is involved in estrogen and AR stability. As demonstrated in the following study by immunoprecipitation analysis, GSK-3beta binds to the AR forming complexes in the cytoplasm and in the nucleus. Furthermore, inhibition of GSK-3beta activity by pharmacological inhibitors like the maleimide SB216761, the chloromethyl-thienyl-ketone GSK-3 inhibitor VI or the aminopyrazol GSK-3 inhibitor XIII in cells grown in the presence of DHT triggered a rapid nuclear export of endogenous AR as well as of green fluorescent AR-EosFP. The nuclear export of AR following GSK-3beta inhibition could be blocked by leptomycin B suggesting a CRM1-dependent export mechanism. This assumption is supported by the localization of a putative CRM1 binding site at the C-terminus of the AR protein. The results suggest that GSK-3beta is an important element not only in AR stability but also significantly alters nuclear translocation of the AR, thereby modulating the androgenic response of human PCa cells.

Antibody selection influences the detection of AR-V7 in primary prostate cancer.

BACKGROUND: The androgen receptor (AR) splice variant V7 (AR-V7) is an emerging marker to aid clinical decision-making in patients with castration-resistant prostate cancer (CRPC). A number of studies have shown that a subset of patients also express AR-V7 in the primary tumor. These findings have recently been challenged by a study showing that AR-V7 becomes only detectable in CRPC but is virtually absent in castration-naïve prostate cancer. METHODS: Herein, we directly compare the two relevant antibodies used for the immunodetection of AR-V7 in the conflicting studies (clones AG10008 and RM7) in a predominantly high-risk prostate cancer patient cohort with primary tumor specimens assembled in a tissue microarray (TMA). RESULTS: The overall rate of AR-V7 positive TMA cores was comparable (AG10008, 24.9%; RM7, 21%). However, the percentage agreement of identical staining intensities of positive cores was only 7%. In contrast, the percentage agreement of negative cores was 62.8%. In approximately 30% of the cores, the antibodies produced discordant staining intensities. Only one of the two antibody stainings (AG10008) conveyed prognostic information and was associated with a shorter progression-free patient survival. CONCLUSIONS: Our study underscores that nuclear AR-V7 expression can be detected in primary prostate cancer prior to long-term androgen deprivation and castration resistance. There are staining differences between the two antibodies in tumor tissue, for which we currently have no explanation. Clearly, improvements in the detection of functional AR-V7 in prostate cancer are urgently needed.

Detecting predictive androgen receptor modifications in circulating prostate cancer cells.

Molecular modifications of the androgen receptor (AR) can cause resistance to androgen deprivation therapy (ADT) in prostate cancer patients. Since lack of representative tumor samples hinders therapy adjustments according to emerging AR-modifications, we evaluated simultaneous detection of the two most common AR modifications (AR-V7 splice variant and AR point mutations) in circulating tumor cells (CTCs). We devised a single-tube assay to detect AR-V7 splice variants and AR point mutations in CTCs using immunomagnetic cell isolation, followed by quantitative real-time PCR and DNA pyrosequencing. We prospectively investigated 47 patients with PSA progression awaiting therapy switch. Comparison of response to newly administered therapy and CTC-AR-status allowed effect size estimation. Nineteen (51%) of 37 patients with detectable CTCs carried AR-modifications. Seventeen patients carried the AR-V7 splice variant, one harbored a p.T878A point mutation and one harbored both AR-V7 and a p.H875Y mutation. We estimated a positive predictive value for response and non-response to therapy by AR status in CTCs of ~94%. Based on a conservative calculation, we estimated the effect size for molecularly-informed therapy switches for prospective clinical trial planning to ~27%. In summary, the ability to determine key resistance-mediating AR modifications in CTCs has the potential to considerably improve prostate cancer treatment.

Overexpression of nuclear AR-V7 protein in primary prostate cancer is an independent negative prognostic marker in men with high-risk disease receiving adjuvant therapy.

BACKGROUND: Overexpression of the androgen receptor (AR) splice variant 7 (AR-V7) has recently been reported to be associated with resistance to antihormonal therapy. Herein, we address the question whether tumor cells with AR-V7 expression can be detected at the time of radical prostatectomy, that is, before long-term hormonal manipulation and castration resistance, and what the potential prognostic impact on the biochemical recurrence (BCR)-free survival may be. METHODS: An anti-AR-V7 antibody was first validated in a training set of prostate cancer specimens by a comparison of AR-V7 protein to AR-V7 mRNA expression. We then analyzed nuclear AR-V7 protein expression in the primary tumors and lymph node metastases from 163 predominantly high-risk patients (cohort I) as well as the primary tumors from patients of a second, consecutive patient cohort (n = 238, cohort II) not selected for any clinicopathological features. Staining results were correlated to patient characteristics and BCR-free patient survival. RESULTS: High nuclear AR-V7 protein expression was detected in approximately 30%-40% of patients in cohort I and II at the time of radical prostatectomy. High baseline expression of nuclear AR-V7 protein was associated with an unfavorable BCR-free survival in the high-risk patient cohort I but not in the unselected consecutive cohort II. Remarkably, AR-V7 was an independent negative prognostic factor in high-risk prostate cancer patients of cohort I who were selected to receive adjuvant treatment. CONCLUSIONS: Prostate cancer cells with high nuclear AR-V7 protein expression can be detected in a substantial proportion of tumors at the time of radical prostatectomy. The presence of AR-V7-positive tumor cells is associated with an unfavorable prognosis for BCR-free survival in a high-risk patient cohort including a subgroup of patients selected to receive adjuvant therapy, in which AR-V7 was an independent negative prognosticator. Overexpression of nuclear AR-V7 protein hence identifies a subset of tumors with remarkably aggressive growth characteristics among clinically and histologically high-risk patients at the time of radical prostatectomy.