Therapeutic Rationales, Progresses, Failures, and Future Directions for Advanced Prostate Cancer

Androgen Receptor Imaging in the Management of Hormone-Dependent Cancers with Emphasis on Prostate Cancer

Prostate cancer is dependent on the action of steroid hormones on the receptors. Endocrine therapy inhibits hormone production or blocks the receptors, thus providing clinical benefit to many, but not all, oncological patients. It is difficult to predict which patient will benefit from endocrine therapy and which will not. Positron Emission Tomography (PET) imaging of androgen receptors (AR) may provide functional information on the likelihood of endocrine therapy response in individual patients. In this article, we review the utility of [¹⁸F]FDHT-PET imaging in prostate, breast, and other hormone-dependent cancers expressing AR. The methodologies, development, and new possibilities are discussed as well.

Investigation of the regulatory effects of synthesized antisense oligonucleotides on androgen receptor (AR) exon 3 splicing in prostate cancer cells

The Androgen Receptor (AR) gene plays a key role in castration-resistant prostate cancer (CRPC). Controlling the progression of CRPC by inhibiting AR gene expression is one of the core directions for prostate cancer (Pca) drug development. A 23-amino acids retention, named exon 3a, into the DNA binding domain of the splice variant AR23 has been shown to prevent AR from entering the nucleus and restore the sensitivity of cancer cells to related therapies. In this study, we conducted a preliminary investigation of the splicing modulation of the AR gene in order to develop a splice-switching therapy for Pca by promoting exon 3a inclusion. Using mutagenesis-coupled RT-PCR with AR minigene and over-expression of certain splicing factors, we found that serine/arginine-rich (SR) proteins are key factors facilitating the recognition of the 3' splice site of exon 3a (L-3' SS), while the deletion or blocking of the polypyrimidine tract (PPT) region of the original 3' splice site of exon 3 (S-3' SS) could strongly enhance exon 3a splicing without affecting the function of any SR protein. Furthermore, we designed a series of antisense oligonucleotides (ASOs) to screen drug candidates, and ASOs targeting S-3' SS and its PPT region or the exonic region of exon 3 turned out to be most effective in rescuing exon 3a splicing. A dose-response test indicated ASO12 as the lead candidate drug significantly promoting the inclusion of exon 3a to more than 85%. MTT assay confirmed that the cell proliferation was significantly inhibited after ASO treatment. Our results provide the first glance to AR splicing regulation. With several promising therapeutic ASO candidates obtained here, further development of ASO drugs to treat CRPC is strongly encouraged.

The Discovery of BMS-737 as a Potent, CYP17 Lyase-Selective Inhibitor for the Treatment of Castration-Resistant Prostate Cancer

We report herein, the discovery of BMS-737 (compound 33) as a potent, non-steroidal, reversible small molecule inhibitor demonstrating 11-fold selectivity for CYP17 lyase over CYP17 hydroxylase, as well as a clean xenobiotic CYP profile for the treatment of castration-resistant prostate cancer (CRPC). Extensive SAR studies on the initial lead 1 at three different regions of the molecule resulted in the identification of BMS-737, which demonstrated a robust 83% lowering of testosterone without any significant perturbation of the mineralocorticoid and glucocorticoid levels in cynomologous monkeys in a 1-day PK/PD study.

Therapeutic Strategies to Target the Androgen Receptor

The androgen receptor (AR) plays a key role in the maintenance of muscle and bone and the support of male sexual-related functions, as well as in the progression of prostate cancer. Accordingly, AR-targeted therapies have been developed for the treatment of related human diseases and conditions. AR agonists are an important class of drugs in the treatment of bone loss and muscle atrophy. AR antagonists have also been developed for the treatment of prostate cancer, including metastatic castration-resistant prostate cancer (mCRPC). Additionally, selective AR degraders (SARDs) have been reported. More recently, heterobifunctional degrader molecules of AR have been developed, and four such compounds are now in clinical development for the treatment of human prostate cancer. This review attempts to summarize the different types of compounds designed to target AR and the current frontiers of research on this important therapeutic target.

A Pilot Study of Dynamic 18F-DCFPyL PET/CT Imaging of Prostate Adenocarcinoma in High-Risk Primary Prostate Cancer Patients

PURPOSE

The primary aim of this study was to investigate the pharmacokinetics of 18F-DCFPyL, an 18F-labeled PSMA-based ligand, and to explore the utility of early time point positron emission tomography (PET) imaging extracted from PET data to distinguish malignant primary prostate from benign prostate tissue.

PROCEDURES

Ten consecutive patients with biopsy-proven high-risk prostate cancer underwent a dynamic 18F-DCFPyL PET/CT scan of the pelvis for the first 45 min post-injection (p.i.) followed by a static PET/CT at 2 h p.i. 18F-DCFPyL uptake values and kinetics were compared between benign prostate tissue and prostate cancer, including quantitative pharmacokinetic PET parameters extracted from 18F-DCFPyL time activity curves generated from dynamic data using a two-tissue compartment model and Patlak plots.

RESULTS

18F-DCFPyL uptake values were significantly higher in primary prostate tumors than those in benign prostatic hyperplasia (BPH) and normal prostate tissue at 5 min, 30 min, and 120 min p.i. (P = 0.0002), when examining both SUVmax and SUVmean values. The two-tissue compartment model found an overall influx value (Ki) of 0.063 in primary prostate cancer, demonstrating a Ki over 15-fold higher in malignant prostate tissue compared with BPH (Ki = 0.004) and normal prostate tissue (Ki = 0.005) (P = 0.0001).

CONCLUSION

High-risk primary prostate cancer is readily identified on dynamic and static, delayed, 18F-DCFPyL PET images. The tumor-to-background ratio increases over time, with optimal 18F-DCFPyL PET/CT imaging at 120 min p.i. for evaluation of prostate cancer, but not necessarily ideal for clinical application. Primary prostate cancer demonstrates different uptake kinetics in comparison to BPH and normal prostate tissue. The 15-fold difference in Ki between prostate cancer and non-cancer (BPH and normal) tissues translates to an ability to distinguish prostate cancer from normal tissue at time points as early as 5 to 10 min p.i.

Neoadjuvant hormonal therapy before radical prostatectomy in high-risk prostate cancer

Patients with high-risk prostate cancer treated with curative intent are at an increased risk of biochemical recurrence, metastatic progression and cancer-related death compared with patients treated for low-risk or intermediate-risk disease. Thus, these patients often need multimodal therapy to achieve complete disease control. Over the past two decades, multiple studies on the use of neoadjuvant treatment have been performed using conventional androgen deprivation therapy, which comprises luteinizing hormone-releasing hormone agonists or antagonists and/or first-line anti-androgens. However, despite results from these studies demonstrating a reduction in positive surgical margins and tumour volume, no benefit has been observed in hard oncological end points, such as cancer-related death. The introduction of potent androgen receptor signalling inhibitors (ARSIs), such as abiraterone, apalutamide, enzalutamide and darolutamide, has led to a renewed interest in using neoadjuvant hormonal treatment in high-risk prostate cancer. The addition of ARSIs to androgen deprivation therapy has demonstrated substantial survival benefits in the metastatic castration-resistant, non-metastatic castration-resistant and metastatic hormone-sensitive settings. Intuitively, a similar survival effect can be expected when applying ARSIs as a neoadjuvant strategy in high-risk prostate cancer. Most studies on neoadjuvant ARSIs use a pathological end point as a surrogate for long-term oncological outcome. However, no consensus yet exists regarding the ideal definition of pathological response following neoadjuvant hormonal therapy and pathologists might encounter difficulties in determining pathological response in hormonally treated prostate specimens. The neoadjuvant setting also provides opportunities to gain insight into resistance mechanisms against neoadjuvant hormonal therapy and, consequently, to guide personalized therapy.

Alzheimer's Disease, and Breast and Prostate Cancer Research: Translational Failures and the Importance to Monitor Outputs and Impact of Funded Research

Dementia and cancer are becoming increasingly prevalent in Western countries. In the last two decades, research focused on Alzheimer's disease (AD) and cancer, in particular, breast cancer (BC) and prostate cancer (PC), has been substantially funded both in Europe and worldwide. While scientific research outcomes have contributed to increase our understanding of the disease etiopathology, still the prevalence of these chronic degenerative conditions remains very high across the globe. By definition, no model is perfect. In particular, animal models of AD, BC, and PC have been and still are traditionally used in basic/fundamental, translational, and preclinical research to study human disease mechanisms, identify new therapeutic targets, and develop new drugs. However, animals do not adequately model some essential features of human disease; therefore, they are often unable to pave the way to the development of drugs effective in human patients. The rise of new technological tools and models in life science, and the increasing need for multidisciplinary approaches have encouraged many interdisciplinary research initiatives. With considerable funds being invested in biomedical research, it is becoming pivotal to define and apply indicators to monitor the contribution to innovation and impact of funded research. Here, we discuss some of the issues underlying translational failure in AD, BC, and PC research, and describe how indicators could be applied to retrospectively measure outputs and impact of funded biomedical research.

Structural Dynamics of Agonist and Antagonist Binding to the Androgen Receptor

Androgen receptor (AR) is a steroid hormone nuclear receptor which upon binding its endogenous androgenic ligands (agonists), testosterone and dihydrotestosterone (DHT), alters gene transcription, producing a diverse range of biological effects. Antiandrogens, such as the pharmaceuticals bicalutamide and hydroxyflutamide, act as agonists in the absence of androgens and as antagonists in their presence or in high concentration. The atomic level mechanism of action by agonists and antagonists of AR is less well characterized. Therefore, in this study, multiple 1 μs molecular dynamics (MD), docking simulations, and perturbation-response analyses were performed to more fully explore the nature of interaction between agonist or antagonist and AR and the conformational changes induced in the AR upon interaction with different ligands. We characterized the mechanism of the ligand entry/exit and found that helix-12 and nearby structural motifs respond dynamically in that process. Modeling showed that the agonist and antagonist/agonist form a hydrogen bond with Thr877/Asn705 and that this interaction is absent for antagonists. Agonist binding to AR increases the mobility of residues at allosteric sites and coactivator binding sites, while antagonist binding decreases mobility at these important sites. A new site was also identified as a potential surface for allosteric binding. These results shed light on the effect of agonists and antagonists on the structure and dynamics of AR.

Screening of Drug Repositioning Candidates for Castration Resistant Prostate Cancer

Purpose: Most prostate cancers (PCs) initially respond to androgen deprivation therapy (ADT), but eventually many PC patients develop castration resistant PC (CRPC). Currently, available drugs that have been approved for the treatment of CRPC patients are limited. Computational drug repositioning methods using public databases represent a promising and efficient tool for discovering new uses for existing drugs. The purpose of the present study is to predict drug candidates that can treat CRPC using a computational method that integrates publicly available gene expression data of tumors from CRPC patients, drug-induced gene expression data and drug response activity data. Methods: Gene expression data from tumoral and normal or benign prostate tissue samples in CRPC patients were downloaded from the Gene Expression Omnibus (GEO) and differentially expressed genes (DEGs) in CRPC were determined with a meta-signature analysis by a metaDE R package. Additionally, drug activity data were downloaded from the ChEMBL database. Furthermore, the drug-induced gene expression data were downloaded from the LINCS database. The reversal relationship between the CRPC and drug gene expression signatures as the Reverse Gene Expression Scores (RGES) were computed. Drug candidates to treat CRPC were predicted using summarized scores (sRGES). Additionally, synergic effects of drug combinations were predicted with a Target Inhibition interaction using the Minimization and Maximization Averaging (TIMMA) algorithm. Results: The drug candidates of sorafenib, olaparib, elesclomol, tanespimycin, and ponatinib were predicted to be active for the treatment of CRPC. Meanwhile, CRPC-related genes, in this case MYL9, E2F2, APOE, and ZFP36, were identified as having gene expression data that can be reversed by these drugs. Additionally, lenalidomide in combination with pazopanib was predicted to be most potent for CRPC. Conclusion: These findings support the use of a computational reversal gene expression approach to identify new drug and drug combination candidates that can be used to treat CRPC.

ZBTB46, SPDEF, and ETV6: Novel Potential Biomarkers and Therapeutic Targets in Castration-Resistant Prostate Cancer

Prostate cancer (PCa) is the second most common killer among men in Western countries. Targeting androgen receptor (AR) signaling by androgen deprivation therapy (ADT) is the current therapeutic regime for patients newly diagnosed with metastatic PCa. However, most patients relapse and become resistant to ADT, leading to metastatic castration-resistant PCa (CRPC) and eventually death. Several proposed mechanisms have been proposed for CRPC; however, the exact mechanism through which CRPC develops is still unclear. One possible pathway is that the AR remains active in CRPC cases. Therefore, understanding AR signaling networks as primary PCa changes into metastatic CRPC is key to developing future biomarkers and therapeutic strategies for PCa and CRPC. In the current review, we focused on three novel biomarkers (ZBTB46, SPDEF, and ETV6) that were demonstrated to play critical roles in CRPC progression, epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) drug resistance, and the epithelial-to-mesenchymal transition (EMT) for patients treated with ADT or AR inhibition. In addition, we summarize how these potential biomarkers can be used in the clinic for diagnosis and as therapeutic targets of PCa.

Riluzole induces AR degradation via endoplasmic reticulum stress pathway in androgen-dependent and castration-resistant prostate cancer cells

BACKGROUND

Prostate cancer (PCa) is diagnosed at the highest rate of all non-cutaneous male cancers in the United States. The androgen-dependent (AD) transcription factor, androgen receptor (AR), drives PCa-but inhibiting AR or androgen biosynthesis induces remission for only a short time. At which point, patients acquire more aggressive castration-resistant (CR) disease with re-activated AR-dependent signaling. To combat treatment resistance, down-regulating AR protein expression has been considered as a potential treatment strategy for CR-PCa.

METHODS

AD- and CR-PCa cell lines were treated with the well-tolerated FDA-approved oral medicine, riluzole. Expression of full-length or wild-type AR (AR-FL) and constitutively active AR-splice variant 7 (AR-V7) was assessed by immunoblotting. AR-FL/AR-V7 activity was measured using qRT-PCR of AR-target genes. Cytoplasmic [Ca²⁺ ] levels were measured using a fluorescent Ca²⁺ indicator microplate assay. Markers of the endoplasmic reticulum stress (ERS) pathway and autophagy were assessed by immunoblotting. Direct interaction between AR and selective autophagy receptor p62 was demonstrated by co-immunoprecipitation.

RESULTS

We demonstrate that riluzole downregulates AR-FL, mutant ARs, and AR-V7 proteins expression by protein degradation through ERS pathway and selective autophagy. Riluzole also significantly inhibited AR transcription activity by decreasing its target genes expression (PSA, TMPRSS2, and KLK2).

CONCLUSIONS

We provide key mechanistic insights by which riluzole exerts its anti-tumorigenic effects and induces AR protein degradation via ERS pathways. Our findings support the potential utility of riluzole for treatment of PCa.

Downregulation of Pro-Inflammatory and Pro-Angiogenic Pathways in Prostate Cancer Cells by a Polyphenol-Rich Extract from Olive Mill Wastewater

Dietary phytochemicals are particularly attractive for chemoprevention and are able to modulate several signal transduction pathways linked with cancer. Olive oil, a major component of the Mediterranean diet, is an abundant source of phenolic compounds. Olive oil production is associated with the generation of a waste material, termed 'olive mill wastewater' (OMWW) that have been reported to contain water-soluble polyphenols. Prostate cancer (PCa) is considered as an ideal cancer type for chemopreventive approaches, due to its wide incidence but relatively long latency period and progression time. Here, we investigated activities associated with potential preventive properties of a polyphenol-rich olive mill wastewater extract, OMWW (A009), on three in vitro models of PCa. A009 was able to inhibit PCa cell proliferation, adhesion, migration, and invasion. Molecularly, we found that A009 targeted NF-κB and reduced pro-angiogenic growth factor, VEGF, CXCL8, and CXCL12 production. IL-6/STAT3 axis was also regulated by the extract. A009 shows promising properties, and purified hydroxytyrosol (HyT), the major polyphenol component of A009, was also active but not always as effective as A009. Finally, our results support the idea of repositioning a food waste-derived material for nutraceutical employment, with environmental and industrial cost management benefits.

A short peptide reverses the aggressive phenotype of prostate cancer cells

Previous studies have demonstrated that fibroblast growth factor 8b (FGF8b) is up-regulated in a large proportion of prostate cancer patients, and plays a key role in the aggressive progress of prostate cancer. Herein, we investigated the effects of a short peptide derived from the gN helix domain of FGF8b on the metastatic behaviors of prostate cancer cells. The results demonstrated that the synthetic peptide might reverse the effects of FGF8b on cell proliferation, migration and invasion by suppressing the activation of MAPK and Akt signaling cascades, and reducing the expressions of the metastasis-related proteins, resulting in suppression of the aggressive phenotype of the prostate cancer cells. Collectively, these results underline the therapeutic potential of the FGF8b mimic peptide in advanced prostate cancer.

Quercetin inhibits prostate cancer by attenuating cell survival and inhibiting anti-apoptotic pathways

Background

Despite recent advances in diagnosis and treatment, prostate cancer (PCa) remains the leading cause of cancer-related deaths in men. Current treatments offered in the clinics are often toxic and have severe side effects. Hence, to treat and manage PCa, new agents with fewer side effects or having potential to reduce side effects of conventional therapy are needed. In this study, we show anti-cancer effects of quercetin, an abundant bioflavonoid commonly used to treat prostatitis, and defined quercetin-induced cellular and molecular changes leading to PCa cell death.

Methods

Cell viability was assessed using MTT. Cell death mode, mitochondrial outer membrane potential, and oxidative stress levels were determined by flow cytometry using Annexin V-7 AAD dual staining kit, JC-1 dye, and ROS detection kit, respectively. Antibody microarray and western blot were used to delineate the molecular changes induced by quercetin.

Results

PCa cells treated with various concentrations of quercetin showed time- and dose-dependent decrease in cell viability compared to controls, without affecting normal prostate epithelial cells. Quercetin led to apoptotic and necrotic cell death in PCa cells by affecting the mitochondrial integrity and disturbing the ROS homeostasis depending upon the genetic makeup and oxidative status of the cells. LNCaP and PC-3 cells that have an oxidative cellular environment showed ROS quenching after quercetin treatment while DU-145 showed rise in ROS levels despite having a highly reductive environment. Opposing effects of quercetin were also observed on the pro-survival pathways of PCa cells. PCa cells with mutated p53 (DU-145) and increased ROS showed significant reduction in the activation of pro-survival Akt pathway while Raf/MEK were activated in response to quercetin. PC-3 cells lacking p53 and PTEN with reduced ROS levels showed significant activation of Akt and NF-κB pathway. Although some of these changes are commonly associated with oncogenic response, the cumulative effect of these alterations is PCa cell death.

Conclusions

Our results demonstrated quercetin exerts its anti-cancer effects by modulating ROS, Akt, and NF-κB pathways. Quercetin could be used as a chemopreventive option as well as in combination with chemotherapeutic drugs to improve clinical outcomes of PCa patients.

Androgen receptor: a potential therapeutic target for glioblastoma

The median survival time of patients with glioblastoma is still poor (14.6 month), partly due to a lack of effective treatment.

We have observed that androgen receptor (AR) is amplified in glioblastomas at the DNA, RNA and protein levels. The AR gene was amplified in 27% of glioblastoma specimens from men (n=22) and of 38.2% from women (n=21). AR-RNA was overexpressed (>2.5 fold) in 93% (n=30), and AR-protein was induced (>two fold) in 56% of the glioblastomas samples (n=16). Thirty percent of the glioblastomas (n=21) also expressed a constitutively active AR-splice-variant (AR-V7/AR3) lacking the Ligand-Binding-Domain. Following these findings, we examined the effect of pharmacological inhibition of androgen receptor in vitro and in vivo, as well as of genetic silencing of the receptor in glioblastoma cell lines. AR antagonists, induced concentration-dependent death in three glioblastoma cell lines, as well as in two glioma initiating cell lines. Silencing of AR expression by siRNA induced cell death in the three tested glioblastoma cell lines. Enzalutamide given orally to nude mice bearing subcutaneous human glioma xenografts resulted in a 72% reduction in tumor volume (p=0.0027).

The presence of AR-V7/AR3 in glioblastoma, together with the present data showing that genetic silencing of the full length AR in cell lines and pharmacological inhibition of AR, induce GBM cell death in vivo and in vitro, point to the important role of AR in GBM survival and render a potential therapeutic target for this devastating disease.

Incidence and Characterization of Antiandrogen Withdrawal Syndrome After Discontinuation of Treatment With Enzalutamide in Castration-resistant Prostate Cancer

BACKGROUND

Antiandrogen withdrawal syndrome (AAWS), manifested as a prostate-specific antigen (PSA) decline after discontinuation of a first-generation antiandrogen has been well characterized. The objective of the present study was to assess the incidence of AAWS with enzalutamide in men with metastatic castration-resistant prostate cancer.

PATIENTS AND METHODS

Patients from a single-institution cohort with metastatic castration-resistant prostate cancer who had discontinued enzalutamide after PSA or radiographic progression were included. AAWS after enzalutamide was defined as any PSA decline after discontinuation of enzalutamide. The baseline patient, disease, and treatment characteristics were compared between patients with and without AAWS after enzalutamide. Statistical analysis of the baseline characteristics included descriptive statistics using the Wilcoxon rank sum test and the Fisher exact test. The median duration of enzalutamide therapy was compared using the log-rank test, and the progression-free survival of the patients with AAWS was evaluated using the Kaplan-Meier method.

RESULTS

Of 47 eligible patients, 5 experienced AAWS after enzalutamide discontinuation. The PSA response in these 5 patients was 84%, 32%, 17%, 15%, and 15%. The median AAWS response time until subsequent PSA progression was 3.3 months. No patient, disease, or treatment characteristics differed among the patients with and without AAWS after enzalutamide discontinuation.

CONCLUSION

To the best of our knowledge, this is the largest reported cohort documenting the incidence and characterization of AAWS after enzalutamide to date. The AAWS frequency after enzalutamide was low and of short duration. No patient- or disease-related characteristics were associated with AAWS with enzalutamide. The occurrence of AAWS after enzalutamide was not clinically meaningful. Thus, accounting for this phenomenon in clinical practice or trial designs could be unnecessary.

Darolutamide (ODM-201) for the treatment of prostate cancer

INTRODUCTION

Androgen deprivation therapy (ADT) is a mainstay initial treatment for advanced hormone-sensitive prostate cancer (HSPC), but disease progression to castration-resistant prostate cancer (CRPC) invariably occurs when patients do not succumb to another disease or comorbidity. Recognition that the androgen receptor (AR) axis continues to drive disease progression has led to the development of several AR-directed approved agents, including abiraterone acetate and enzalutamide. An investigational agent, darolutamide (ODM-201, BAY-1841788), has completed early-phase clinical trials, and two global phase III trials are currently accruing patients. Areas covered: The unmet clinical need, pharmacokinetics, preclinical development, and clinical efficacy and safety of darolutamide for the treatment of advanced prostate cancer are reviewed. The design of two ongoing phase III trials (ARAMIS and ARASENS) of darolutamide in men with non-metastatic CRPC and metastatic HSPC, respectively, are also discussed. Expert opinion: Darolutamide is an oral, investigational, high-affinity AR antagonist which has activity against known AR mutants that confer resistance to other second-generation antiandrogens, has minimal blood-brain barrier penetration, and does not significantly increase serum testosterone. These features may offer potential advantages over the second-generation antiandrogens. In the phase I/II ARADES trial, darolutamide demonstrated promising antitumor activity and a favorable safety profile in men with metastatic CRPC.

Degarelix versus luteinizing hormone-releasing hormone agonists for the treatment of prostate cancer

INTRODUCTION

Androgen deprivation therapy (ADT) is the mainstay for advanced, hormone-sensitive prostate cancer, and options include surgical castration, luteinizing hormone-releasing hormone (LHRH) agonist, and more recently, gonadotropin releasing hormone (GnRH) antagonist therapy. Our understanding of the mechanisms and adverse effects of ADT has increased substantially, including the class-specific adverse effects of ADT. Areas covered: This review will summarize the pharmacodynamic and pharmacokinetic properties of the GnRH antagonist degarelix and its role in the management of advanced prostate cancer, the clinical evidence supporting its regulatory approval, as well as potential benefits and disadvantages over traditional LHRH agonist therapy. Expert opinion: Degarelix represents a newer class of ADT that results in a rapid and reliable decline in serum testosterone, a quality that makes it particularly advantageous in men presenting with symptomatic, hormone-sensitive prostate cancer. Due to differences in mechanism of action, there is observational data suggesting a potential cardiovascular and even oncologic benefit over traditional LHRH agonist therapy. Further research is ongoing to more clearly define this potential benefit.

Effects of Testosterone on Benign and Malignant Conditions of the Prostate

PURPOSE OF THE REVIEW

This review summarizes the current literature regarding the effects of testosterone therapy (TTh) on common disorders of the prostate.

RECENT FINDINGS

Testosterone therapy has gained credibility over the last several decades as a potentially safe co-treatment modality for men with benign and malignant prostatic conditions. Our understanding of the effects of testosterone on the prostate continues to evolve with ongoing clinical and basic science research. Findings of these studies have reinvigorated the debate over the effects of testosterone on benign and malignant disorders of the prostate, including BPH, chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), and prostate cancer.

SUMMARY

Despite the burgeoning body of data claiming the safety and efficacy of TTh in common prostatic conditions (including BPH, CP/CPPS, and prostate cancer), diligent monitoring, appropriate patient selection, and informed consent are critical until more definitive studies are performed.

High expression of Rab25 contributes to malignant phenotypes and biochemical recurrence in patients with prostate cancer after radical prostatectomy

Background

Ras-related protein 25 (Rab25) functions either as an oncogene or a tumor suppressor with a cancer type-dependent manner. We aimed to investigate clinical significance of Rab25 in prostate cancer (PCa).

Methods

Quantitative real-time polymerase chain reaction, Western blot and immunohistochemistry were respectively performed to detect Rab25 mRNA and protein expression in PCa and adjacent non-cancerous prostate tissues. Receiver-operating characteristic curve analysis was used to evaluate predictive diagnostic value of Rab25. Associations of Rab25 expression with various clinicopathological characteristics and biochemical recurrence-free survival of PCa patients were statistically evaluated. In vitro, PCa cell proliferation was assessed by CCK-8 assay, and the cell migration and invasion activities were evaluated by Transwell assay, following the transfection of Rab25 small interfering RNA.

Results

Ras-related protein 25 mRNA and protein expression in PCa tissues were both significantly higher than adjacent non-cancerous prostate tissues (both P < 0.001). The area under the curve of Rab25 immunoreactive score (IRS) was 0.896 (P < 0.001) with 74.0% sensitivity and 95.0% specificity. High Rab25 IRS was significantly associated with high Gleason score (P = 0.02) and distant metastasis (P = 0.01). PCa patients with high Rab25 IRS had shorter overall and biochemical recurrence-free survivals than those with low Rab25 IRS (both P < 0.001). Cox regression analysis identified Rab25 as an independent biomarker for both overall and biochemical recurrence-free survivals of PCa patients. By exploring its activities in vitro, Rab25 downregulation was found to inhibit PCa cell proliferation, migration and invasion.

Conclusions

High expression of Rab25 may contribute to malignant progression and biochemical recurrence of PCa patients after radical prostatectomy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0411-0) contains supplementary material, which is available to authorized users.

Androgen receptor splice variants and prostate cancer: From bench to bedside

Therapeutic interventions for advanced prostate cancer (PCa) center on inhibiting androgen receptor (AR) and downstream signaling pathways. Resistance to androgen deprivation therapy and/or AR antagonists is inevitable and molecular mechanisms driving castration-resistant PCa (CR-PCa) primarily involve alterations in AR expression and activity. Detailed molecular biology work over the past decade, discussed at length in this review article, has revealed several AR transcripts that result from alternative splicing. These AR splice variants are increased in cell and mouse models of CR-PCa and in CR-PCa tumors. Several AR variants lack the ligand binding domain, but retain their ability to bind DNA and activate transcription-linking constitutive AR function and therapeutic failure. ARV7 is the only variant endogenously detected at the protein level and thus has undergone more thorough molecular characterization. Clinical trials in PCa are currently investigating ARV7 utility as a biomarker and new therapeutics that inhibit ARV7 . Overall, this review will illustrate the historical perspectives of AR splice variant discovery using fundamental molecular biology techniques and how it changed the clinical approach to both therapeutic decisions and strategy. The body of work investigating AR splice variants in PCa represents a true example of translational research from bench to bedside.

Impact of treatment on progression to castration-resistance, metastases, and death in men with localized high-grade prostate cancer

Men with high‐grade prostate cancer (HGPC) are at greatest risk of disease progression. Clinical risk factors associated with castration‐resistant prostate cancer (CRPC), metastases, and prostate cancer‐specific mortality (PCSM) were identified in a contemporary HGPC cohort. Clinical data was collected from men diagnosed with Gleason sum (GS) ≥8 at the Greater Los Angeles Veterans Affairs (GLA‐VA) Healthcare System between 2000 and 2013. Multivariable competing risks regression analyses assessed progression to CRPC, metastases, and PCSM within three treatment strata. The cumulative incidence of disease progression was calculated at 2, 5, and 10‐year time points. Review of 2149 prostate cancer cases yielded 322 with HGPC. Median survival times for cancer‐specific and overall mortality were significantly shorter in men treated with primary androgen deprivation therapy (ADT) (P = 0.0002 and P < 0.0001). Multivariable analyses revealed that clinical stage N1, GS 10, and treatment with primary ADT were significantly associated with increased risk of CRPC, metastases, and PCSM. Significant differences in these outcomes were not observed in men treated with radical prostatectomy (RP) when compared to those treated with radiation therapy combined with short‐term ADT (XRT‐ADT). Ten‐year event rates of progression to CRPC, metastases, and PCSM, for men treated with primary ADT, were 45.5%, 25.4%, and 25.1%, respectively. In conclusion, GS 10 and lymph node involvement, as well as primary ADT treatment in men with HGPC was associated with increased risk of CRPC, metastases, and PCSM. Curative‐intent treatment with RP or XRT‐ADT is associated with reduced progression rates and death in men with HGPC.

Molecular mechanisms underlying resistance to androgen deprivation therapy in prostate cancer

Prostate cancer (PCa) is the most widely diagnosed male cancer in the Western World and while low- and intermediate-risk PCa patients have a variety of treatment options, metastatic patients are limited to androgen deprivation therapy (ADT). This treatment paradigm has been in place for 75 years due to the unique role of androgens in promoting growth of prostatic epithelial cells via the transcription factor androgen receptor (AR) and downstream signaling pathways. Within 2 to 3 years of ADT, disease recurs-at which time, patients are considered to have castration-recurrent PCa (CR-PCa). A universal mechanism by which PCa becomes resistant to ADT has yet to be discovered. In this review article, we discuss underlying molecular mechanisms by which PCa evades ADT. Several major resistance pathways center on androgen signaling, including intratumoral and adrenal androgen production, AR-overexpression and amplification, expression of AR mutants, and constitutively-active AR splice variants. Other ADT resistance mechanisms, including activation of glucocorticoid receptor and impairment of DNA repair pathways are also discussed. New therapies have been approved for treatment of CR-PCa, but increase median survival by only 2-8 months. We discuss possible mechanisms of resistance to these new ADT agents. Finally, the practicality of the application of "precision oncology" to this continuing challenge of therapy resistance in metastatic or CR-PCa is examined. Empirical validation and clinical-based evidence are definitely needed to prove the superiority of "precision" treatment in providing a more targeted approach and curative therapies over the existing practices that are based on biological "cause-and-effect" relationship.

Characterization of fibroblast-free CWR-R1ca castration-recurrent prostate cancer cell line

BACKGROUND

The previously established CWR-R1 cell line has been used as an in vitro model representing castration-recurrent prostate cancer. Microscopic observation of subconfluent cells demonstrated two distinct cellular morphologies: polygonal closely aggregated epithelial cells surrounded by bipolar fibroblastic cells with long processes. This study sought to establish and characterize a fibroblast-free derivative of the CWR-R1 cell line.

METHODS

The CWR-R1ca cell line was established from CWR-R1 cells by removing fibroblasts using multiple cycles of short-term trypsinization, cloning, and pooling single-cell colonies. Authentication of fibroblast-free CWR-R1ca cells was demonstrated by analyzing the expression of cytodifferentiation and prostate-associated markers, DNA and cytogenetic profiling, and growth pattern in the absence or presence of androgen.

RESULTS

CWR-R1ca is an androgen-sensitive cell line that expresses the androgen receptor (AR) and its splice variant 7 and the luminal epithelia markers, CK-8, CK-18, and c-Met. CWR-R1fb fibroblasts isolated from CWR-R1 cells express AR, hepatocyte growth factor-α, and mouse β-actin but not AR-V7 or epithelial markers. Cytogenetic analysis of CWR-R1ca cells revealed a hyperdiploid male with numerical gains in chromosomes 1, 7, 8, 10, 11, and 12, deletion of one chromosome 2 allele, structural abnormalities that include der(1)t(1:4), der(4)t(2:4), der(10)t(4:10), and an unbalanced reciprocal translocation between chromosome 6 and 14. DNA-profiling revealed that CWR-R1ca cells had significant short-tandem repeat marker homology with CWR22Pc and CWR22Rv1 cell lines, which indicated lineage derivation from CWR22 prostate cancer xenografts. CWR-R1ca cells were responsive to the growth stimulatory effects of dihydrotestosterone (DHT) in the femtomolar range.

CONCLUSION

This study establishes CWR-R1ca cells as a fibroblast-free derivative of the castration-recurrent CWR-R1 cell line. Prostate 76:1067-1077, 2016. © 2016 Wiley Periodicals, Inc.

Association of AR-V7 and Prostate-Specific Antigen RNA Levels in Blood with Efficacy of Abiraterone Acetate and Enzalutamide Treatment in Men with Prostate Cancer

PURPOSE

We evaluated the association of PSA and androgen receptor splice variant-7 (AR-V7) transcript levels in patients' blood with time to treatment failure (TTF) and overall survival (OS) with abiraterone acetate and/or enzalutamide treatment in castration-resistant prostate cancer (CRPC) patients.

EXPERIMENTAL DESIGN

RNA levels of AR-V7 and PSA in peripheral blood collected before treatment were quantified using droplet digital-PCR in retrospective cohorts treated with abiraterone acetate (N = 81) or enzalutamide (N = 51) for CRPC. Multivariable Cox regression adjusted for known prognostic factors was used for analyses.

RESULTS

PSA transcripts were detected in 57% of abiraterone acetate-treated patients and in 63% of enzalutamide-treated patients. PSA-positive patients had a shorter TTF than PSA-negative patients [adjusted HR = 2.27 (95% confidence interval (CI) 1.26-4.10) and 2.60 (95% CI, 1.19-5.69); P = 0.006 and 0.017 in abiraterone acetate and enzalutamide cohorts, respectively]. Patients with a higher-AR-V7 transcript level had a shorter TTF with abiraterone acetate and enzalutamide in univariate analysis (median 8.0 months vs. 15.6 months, P = 0.046 in abiraterone acetate-cohort and 3.6 months vs. 5.6 months; P = 0.050 in enzalutamide cohort). In multivariable models, the association with TTF remained significant in the enzalutamide cohort (adjusted HR = 2.02; 95% CI, 1.01-4.05; P = 0.048), but statistically insignificant in the abiraterone acetate cohort. In both cohorts, we observed potential prognostic value of both PSA and AR-V7 RNA expression on OS; patients with detectable PSA transcripts and high AR-V7 predicted the poorest OS.

CONCLUSIONS

PSA and AR-V7 transcripts in blood potentially serve as biomarkers predicting TTF and OS with abiraterone acetate or enzalutamide treatment. If validated prospectively, their detection could be facilitated without isolation of circulating tumor cells. Clin Cancer Res; 23(3); 726-34. ©2016 AACR.