Current and emerging treatments in the management of castration-resistant prostate cancer

Non-steroidal CYP17A1 Inhibitors: Discovery and Assessment

CYP17A1 is an enzyme that plays a major role in steroidogenesis and is critically involved in the biosynthesis of steroid hormones. Therefore, it remains an attractive target in several serious hormone-dependent cancer diseases, such as prostate cancer and breast cancer. The medicinal chemistry community has been committed to the discovery and development of CYP17A1 inhibitors for many years, particularly for the treatment of castration-resistant prostate cancer. The current Perspective reflects upon the discovery and evaluation of non-steroidal CYP17A1 inhibitors from a medicinal chemistry angle. Emphasis is placed on the structural aspects of the target, key learnings from the presented chemotypes, and design guidelines for future inhibitors.

The Role of ERα and ERβ in Castration-Resistant Prostate Cancer and Current Therapeutic Approaches

Castration-resistant prostate cancer, or CRPC, is an aggressive stage of prostate cancer (PCa) in which PCa cells invade nearby or other parts of the body. When a patient with PCa goes through androgen deprivation therapy (ADT) and the cancer comes back or worsens, this is called CRPC. Instead of androgen-dependent signalling, recent studies show the involvement of the estrogen pathway through the regulation of estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) in CRPC development. Reduced levels of testosterone due to ADT lead to low ERβ functionality in inhibiting the proliferation of PCa cells. Additionally, ERα, which possesses androgen independence, continues to promote the proliferation of PCa cells. The functions of ERα and ERβ in controlling PCa progression have been studied, but further research is needed to elucidate their roles in promoting CRPC. Finding new ways to treat the disease and stop it from becoming worse will require a clear understanding of the molecular processes that can lead to CRPC. The current review summarizes the underlying processes involving ERα and ERβ in developing CRPC, including castration-resistant mechanisms after ADT and available medication modification in mitigating CRPC progression, with the goal of directing future research and treatment.

SRC Kinase-Mediated Tyrosine Phosphorylation of TUBB3 Regulates Its Stability and Mitotic Spindle Dynamics in Prostate Cancer Cells

Tubulin is an integral part of the cytoskeleton and plays a pivotal role in cellular signaling, maintenance, and division. β-tubulin is also the molecular target for taxane compounds such as docetaxel (DTX) and cabazitaxel (CTX), both first-line treatments for several solid cancers. Increased expression of Class III β-tubulin (TUBB3), a primarily neural isoform of β-tubulin, correlates with taxane resistance and poor prognosis. Although tyrosine kinase c-Src has been implicated to phosphorylate β-tubulins during both hematopoietic and neural differentiation, the mechanisms by which Src modulates tubulins functions are still poorly understood. Here, we report, for the first time, that TUBB3 is phosphorylated at Tyrosine 340 (Y340) by c-SRC in prostate cancer cells. We also showed that Y340 phosphorylation regulates TUBB3 protein stability and subcellular localization. Furthermore, we demonstrated that inhibition of SRC kinase activity compromises spindle stability in mitotic cells, at least partly due to the lack of TUBB3 Y340 phosphorylation. Given the importance of TUBB3 as a clinical biomarker of poor prognosis and drug resistance, characterization of TUBB3 posttranslational regulation could potentially serve as new biomarkers for disease recurrence and/or treatment failure.

Molecular and metabolic imaging of castration-resistant prostate cancer: state of art and future prospects

Prostate cancer (PCa) represents the most common tumor in male and one of the most relevant causes of death in Western countries. Androgen deprivation therapy (ADT) constitutes a widely used approach in advanced PCa. When PCa progresses in spite of ADT and castrate levels of testosterone, the severe clinical condition termed as metastatic castration-resistant prostate cancer (mCRPC) takes place. The only approach to mCRPC has been represented by chemotherapy with taxanes for many years. Nevertheless, recently introduced treatments such as 2nd generation antiandrogens (i.e. enzalutamide and abiraterone), cell immunotherapy with sipuleucel-T or targeted alpha therapy with 223Ra-dichloride, have dramatically changed mCRPC prognosis. These novel therapies call for an unmet need for imaging biomarkers suitable for patients' pre-treatment stratification and response assessment. In this scenario, nuclear medicine can provide several metabolic and molecular probes for investigating pathological processes at a cellular and sub-cellular level. The aim of this paper is to review the most relevant findings of the literature published to date on this topic, giving particular emphasis to the pros and cons of each tracer and also covering future prospects for defining personalized therapeutic approaches.

B lymphoma Moloney murine leukemia virus insertion region 1: An oncogenic mediator in prostate cancer

B lymphoma Moloney murine leukemia virus insertion region 1 (BMI1), a core member of polycomb repressive complex 1 (PRC1), has been intensely investigated in the field of cancer epigenetics for decades. Widely known as a critical regulator in cellular physiology, BMI1 is essential in self-renewal and differentiation in different lineages of stem cells. BMI1 also plays a significant role in cancer etiology for its involvement in pathological progress such as epithelial–mesenchymal transition (EMT) and cancer stem cell maintenance, propagation, and differentiation. Importantly, overexpression of BMI1 is predictive for drug resistance, tumor recurrence, and eventual therapy failure of various cancer subtypes, which renders the pharmacological targeting at BMI1 as a novel and promising therapeutic approach. The study on prostate cancer, a prevalent hormone-related cancer among men, has promoted enormous research advancements in cancer genetics and epigenetics. This review summarizes the role of BMI1 as an oncogenic and epigenetic regulator in tumor initiation, progression, and relapse of prostate cancer.

The Prospect of Identifying Resistance Mechanisms for Castrate-Resistant Prostate Cancer Using Circulating Tumor Cells: Is Epithelial-to-Mesenchymal Transition a Key Player?

Prostate cancer (PCa) is initially driven by excessive androgen receptor (AR) signaling with androgen deprivation therapy (ADT) being a major therapeutic approach to its treatment. However, the development of drug resistance is a significant limitation on the effectiveness of both first-line and more recently developed second-line ADTs. There is a need then to study AR signaling within the context of other oncogenic signaling pathways that likely mediate this resistance. This review focuses on interactions between AR signaling, the well-known phosphatidylinositol-3-kinase/AKT pathway, and an emerging mediator of these pathways, the Hippo/YAP1 axis in metastatic castrate-resistant PCa, and their involvement in the regulation of epithelial-mesenchymal transition (EMT), a feature of disease progression and ADT resistance. Analysis of these pathways in circulating tumor cells (CTCs) may provide an opportunity to evaluate their utility as biomarkers and address their importance in the development of resistance to current ADT with potential to guide future therapies.

DNA Methylation-Based Testing in Liquid Biopsies as Detection and Prognostic Biomarkers for the Four Major Cancer Types

Lung, breast, colorectal, and prostate cancers are the most incident worldwide. Optimal population-based cancer screening methods remain an unmet need, since cancer detection at early stages increases the prospects of successful and curative treatment, leading to a lower incidence of recurrences. Moreover, the current parameters for cancer patients' stratification have been associated with divergent outcomes. Therefore, new biomarkers that could aid in cancer detection and prognosis, preferably detected by minimally invasive methods are of major importance. Aberrant DNA methylation is an early event in cancer development and may be detected in circulating cell-free DNA (ccfDNA), constituting a valuable cancer biomarker. Furthermore, DNA methylation is a stable alteration that can be easily and rapidly quantified by methylation-specific PCR methods. Thus, the main goal of this review is to provide an overview of the most important studies that report methylation biomarkers for the detection and prognosis of the four major cancers after a critical analysis of the available literature. DNA methylation-based biomarkers show promise for cancer detection and management, with some studies describing a "PanCancer" detection approach for the simultaneous detection of several cancer types. Nonetheless, DNA methylation biomarkers still lack large-scale validation, precluding implementation in clinical practice.

Galeterone and The Next Generation Galeterone Analogs, VNPP414 and VNPP433-3β Exert Potent Therapeutic Effects in Castration-/Drug-Resistant Prostate Cancer Preclinical Models In Vitro and In Vivo

These studies compared the efficacies of our clinical agent galeterone (Gal) and the FDA-approved prostate cancer drug, enzalutamide (ENZ) with two lead next generation galeterone analogs (NGGAs), VNPP414 and VNPP433-3β, using prostate cancer (PC) in vitro and in vivo models. Antitumor activities of orally administered agents were also assessed in CWR22Rv1 tumor-bearing mice. We demonstrated that Gal and NGGAs degraded AR/AR-V7 and Mnk1/2; blocked cell cycle progression and proliferation of human PC cells; induced apoptosis; inhibited cell migration, invasion, and putative stem cell markers; and reversed the expression of epithelial-to-mesenchymal transition (EMT). In addition, Gal/NGGAs (alone or in combination) also inhibited the growth of ENZ-, docetaxel-, and mitoxantrone-resistant human PC cell lines. The NGGAs exhibited improved pharmacokinetic profiles over Gal in mice. Importantly, in vivo testing showed that VNPP433-3β (at 7.53-fold lower equimolar dose than Gal) markedly suppressed (84% vs. Gal, 47%; p < 0.01) the growth of castration-resistant PC (CRPC) CWR22Rv1 xenograft tumors, with no apparent host toxicity. ENZ was ineffective in this CRPC xenograft model. In summary, our findings show that targeting AR/AR-V7 and Mnk1/2 for degradation represents an effective therapeutic strategy for PC/CRPC treatment and supports further development of VNPP433-3β towards clinical investigation.

Molecular signaling involving intrinsically disordered proteins in prostate cancer

Investigations on cellular protein interaction networks (PINs) reveal that proteins that constitute hubs in a PIN are notably enriched in Intrinsically Disordered Proteins (IDPs) compared to proteins that constitute edges, highlighting the role of IDPs in signaling pathways. Most IDPs rapidly undergo disorder-to-order transitions upon binding to their biological targets to perform their function. Conformational dynamics enables IDPs to be versatile and to interact with a broad range of interactors under normal physiological conditions where their expression is tightly modulated. IDPs are involved in many cellular processes such as cellular signaling, transcriptional regulation, and splicing; thus, their high-specificity/low-affinity interactions play crucial roles in many human diseases including cancer. Prostate cancer (PCa) is one of the leading causes of cancer-related mortality in men worldwide. Therefore, identifying molecular mechanisms of the oncogenic signaling pathways that are involved in prostate carcinogenesis is crucial. In this review, we focus on the aspects of cellular pathways leading to PCa in which IDPs exert a primary role.

Galeterone and VNPT55 induce proteasomal degradation of AR/AR-V7, induce significant apoptosis via cytochrome c release and suppress growth of castration resistant prostate cancer xenografts in vivo

Galeterone (Gal) is a first-in-class multi-target oral small molecule that will soon enter pivotal phase III clinical trials in castration resistant prostate cancer (CRPC) patients. Gal disrupts androgen receptor (AR) signaling via inhibition of CYP17, AR antagonism and AR degradation. Resistance to current therapy is attributed to up-regulation of full-length AR (fAR), splice variants AR (AR-Vs) and AR mutations. The effects of gal and VNPT55 were analyzed on f-AR and AR-Vs (AR-V7/ARv567es) in LNCaP, CWR22Rv1 and DU145 (transfected with AR-Vs) human PC cells in vitro and CRPC tumor xenografts. Galeterone/VNPT55 decreased fAR/AR-V7 mRNA levels and implicates Mdm2/CHIP enhanced ubiquitination of posttranslational modified receptors, targeting them for proteasomal degradation. Gal and VNPT55 also induced significant apoptosis in PC cells via increased Bax/Bcl2 ratio, cytochrome-c release with concomitant cleavage of caspase 3 and PARP. More importantly, gal and VNPT55 exhibited strong in vivo anti-CRPC activities, with no apparent host toxicities. This study demonstrate that gal and VNPT55 utilize cell-based mechanisms to deplete both fAR and AR-Vs. Importantly, the preclinical activity profiles, including profound apoptotic induction and inhibition of CRPC xenografts suggest that these agents offer considerable promise as new therapeutics for patients with CRPC and those resistant to current therapy.

Current Patterns of Management of Advanced Prostate Cancer in Routine Clinical Practice in Spain

Objective. To describe urologists' practice patterns when managing patients with advanced prostate cancer (PCa) in Spain. Methods. This was an observational study conducted by 120 urologists using retrospective data of advanced PCa patients attending hospitals and outpatient centers. Results. Urologists evaluated a total of 375 patients (mean age: 75 years; ECOG 0-1: 77%; mean serum PSA levels at study entry: 50.5 ng/Ml). Approximately 50% of patients had bone metastases, and 60.6% experienced pain as the main symptom of progressive disease. Primary androgen deprivation therapy (ADT) use was 99.7%, with continuous ADT as the dominant strategy (91.9%). After failure of initial ADT, antiandrogen withdrawal was the next method most commonly used in 57% of patients. Choice of secondary hormonal treatment was made mostly by urologists (96%), who continued to monitor patients. Patient follow-up after chemotherapy and supportive care were mainly done in urology units, although responsibility was shared with medical oncologists and radiologists. Conclusion. The urologists' attitudes towards management of PCa in the routine practice in Spain show the urologist as an integral component even when patients progress to advanced stages of the disease.

Disease Progression/Clinical Outcome Model for Castration-Resistant Prostate Cancer in Patients Treated With Eribulin

Frameworks that associate cancer dynamic disease progression models with parametric survival models for clinical outcome have recently been proposed to support decision making in early clinical development. Here we developed such a disease progression clinical outcome model for castration-resistant prostate cancer (CRPC) using historical phase II data of the anticancer agent eribulin. Disease progression was captured using the dynamics of prostate-specific antigen (PSA). For clinical outcome, overall survival (OS) was used. The model for PSA dynamics comprised parameters for baseline PSA (23.2 ng/ml, relative standard error (RSE) 16.5%), growth rate (0.00879 day(-1), RSE 12.6%), drug effect (0.241 µg·h·l(-1) day(-1), RSE 32.6%), and resistance development (0.0113 day(-1), RSE 44.3%). OS was modeled according to a Weibull distribution. Predictors for survival included model-predicted PSA time to nadir (TTN), PSA growth rate, Eastern Cooperative Oncology Group (ECOG) score, and baseline PSA. The developed framework can be considered to support informative design and analysis of drugs developed for CRPC.

Maintenance of androgen receptor inactivation by S-nitrosylation

Antiandrogens target ligand-binding domain of androgen receptor (AR) and are used as first-line therapeutics to treat patients diagnosed with locally advanced and metastatic prostate cancer. Although initially beneficial as judged with actual tumor mass shrinkage, this therapy invariably fails and the cancer reappears as castration-resistant disease. Here, we report that increased intracellular nitric oxide (NO) levels lead to growth inhibition of both androgen-dependent and castration-resistant prostate tumors through a mechanism that involves AR function inactivation by S-nitrosylation of a single C601 residue present in the DNA-binding domain. AR S-nitrosylation does not impact its subcellular distribution but attenuates its ability to bind AR-responsive elements in promoter region of target genes. Mechanistically, AR is transnitrosylated by its partner HSP90 protein. Ubiquitous small-molecule NO donors promote the AR S-nitrosylation and inhibit growth of castration-resistant prostate tumors. These findings reveal a new mechanism of regulating AR function and suggest that sequential targeting of distinct domains of AR may extend therapeutic efficacy for patients with advanced prostate cancer.

Vaccines for pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) remains a highly lethal disease; new therapeutic modalities are urgently needed. A number of immunotherapies tested in preclinical models have shown promise. Early-phase clinical trials have demonstrated evidence of immune activation that in some cases correlates with clinical response. Moreover, recent evidence delineates the intricate role of inflammation in PDA, even at its earliest stages. Pancreatic ductal adenocarcinoma is thus ripe for immunotherapy; however, significant challenges remain before success can be realized. Future studies will need to focus on the discovery of novel PDA antigens and the identification of the multiple immune suppressive pathways within the PDA tumor microenvironment that inhibit an effective PDA-targeted immune response. Technologies are now available to rapidly advance discovery. Rapid translation of new discoveries into scientifically driven clinical trials testing combinations of immune agents will likely continue to shift the procarcinogenic tumor environment toward the most potent anticancer response.

EZH2, an epigenetic driver of prostate cancer

The histone methyltransferase EZH2 has been in the limelight of the field of cancer epigenetics for a decade now since it was first discovered to exhibit an elevated expression in metastatic prostate cancer. It persists to attract much scientific attention due to its important role in the process of cancer development and its potential of being an effective therapeutic target. Thus here we review the dysregulation of EZH2 in prostate cancer, its function, upstream regulators, downstream effectors, and current status of EZH2-targeting approaches. This review therefore provides a comprehensive overview of EZH2 in the context of prostate cancer.

Radium-223 for the treatment of prostate cancer

INTRODUCTION

Bone metastases cause significant morbidity and mortality in castration-resistant prostate cancer (CRPC). Until recently, treatment options have been limited, but now six drugs are known to extend life expectancy, with docetaxel the current standard first-line cytotoxic therapy. Phase III studies have also shown a survival advantage for sipuleucel-T, cabazitaxel, abiraterone, enzalutamide and radium-223 . Radium-223 is unique among these agents, as the only bone-directed therapy shown to prolong survival in CRPC.

AREAS COVERED

This review covers the current standard of care for CRPC and recent drug developments that have demonstrated a survival benefit. It focuses on bone-directed therapies, in particular radium-223, the first-in-class alpha-emitting radionuclide and discusses the pivotal studies to date. A PubMed search using the keywords below was performed.

EXPERT OPINION

Radium-223 is set to become a new standard of care for the treatment of bony metastatic CRPC. It improves both survival and quality of life, delays skeletal events and is well tolerated. Its optimal use in the evolving treatment strategies for men with CRPC and bone metastases is yet to be determined.