The biology of castration-resistant prostate cancer

Two calix[4]pyrroles as potential therapeutics for castration-resistant prostate cancer

Macrocyclic compounds meso-(p-acetamidophenyl)-calix[4]pyrrole and meso-(m-acetamidophenyl)-calix[4]pyrrole have previously been reported to exhibit cytotoxic properties towards lung cancer cells. Here, we report pre-clinical in vitro and in vivo studies showing that these calixpyrrole derivatives can inhibit cell growth in both PC3 and DU145 prostatic cancer cell lines. We explored the impact of these compounds on programmed cell death, as well as their ability to inhibit cellular invasion. In this study we have demonstrated the safety of these macrocyclic compounds by cytotoxicity tests on ex-vivo human peripheral blood mononuclear cells (PBMCs), and by in vivo subcutaneous administration. Preliminary in vivo tests demonstrated no hepato-, no nephro- and no genotoxicity in Balb/c mice compared to controls treated with cisplatin. These findings suggest these calixpyrroles might be novel therapeutic tools for the treatment of prostate cancer and of particular interest for the treatment of androgen-independent castration-resistant prostate cancer.

The Transcription Factors Zeb1 and Snail Induce Cell Malignancy and Cancer Stem Cell Phenotype in Prostate Cells, Increasing Androgen Synthesis Capacity and Therapy Resistance

Prostate cancer (PCa) incidence has increased during the last decades, becoming one of the leading causes of death by cancer in men worldwide. During an extended period of prostate cancer, malignant cells are androgen-sensitive being testosterone the main responsible for tumor growth. Accordingly, treatments blocking production and action of testosterone are mostly used. However, during disease progression, PCa cells become androgen insensitive producing a castration-resistant stage with a worse prognosis. Overcoming castration-resistant prostate cancer (CRPC) has become a great challenge in the management of this disease. In the search for molecular pathways leading to therapy resistance, the epithelial-mesenchymal transition (EMT), and particularly the transcription factors zinc finger E-box-binding homeobox 1 (Zeb1) and zinc finger protein SNAI1 (Snail), master genes of the EMT, have shown to have pivotal roles. Also, the discovery that cancer stem cells (CSCs) can be generated de novo from their non-CSCs counterpart has led to the question whereas these EMT transcription factors could be implicated in this dynamic conversion between non-CSC and CSC. In this review, we analyze evidence supporting the idea that Zeb1 and Snail induce cell malignancy and cancer stem cell phenotype in prostate cells, increasing androgen synthesis capacity and therapy resistance.

Natural Product-Based Studies for the Management of Castration-Resistant Prostate Cancer: Computational to Clinical Studies

Background: With prostate cancer being the fifth-greatest cause of cancer mortality in 2020, there is a dire need to expand the available treatment options. Castration-resistant prostate cancer (CRPC) progresses despite androgen depletion therapy. The mechanisms of resistance are yet to be fully discovered. However, it is hypothesized that androgens depletion enables androgen-independent cells to proliferate and recolonize the tumor. Objectives: Natural bioactive compounds from edible plants and herbal remedies might potentially address this need. This review compiles the available cheminformatics-based studies and the translational studies regarding the use of natural products to manage CRPC. Methods: PubMed and Google Scholar searches for preclinical studies were performed, while ClinicalTrials.gov and PubMed were searched for clinical updates. Studies that were not in English and not available as full text were excluded. The period of literature covered was from 1985 to the present. Results and Conclusion: Our analysis suggested that natural compounds exert beneficial effects due to their broad-spectrum molecular disease-associated targets. In vitro and in vivo studies revealed several bioactive compounds, including rutaecarpine, berberine, curcumin, other flavonoids, pentacyclic triterpenoids, and steroid-based phytochemicals. Molecular modeling tools, including machine and deep learning, have made the analysis more comprehensive. Preclinical and clinical studies on resveratrol, soy isoflavone, lycopene, quercetin, and gossypol have further validated the translational potential of the natural products in the management of prostate cancer.

Oxidative stress and redox signaling in CRPC progression: therapeutic potential of clinically-tested Nrf2-activators

Androgen deprivation therapy (ADT) is the mainstay regimen in patients with androgen-dependent prostate cancer (PCa). However, the selection of androgen-independent cancer cells leads to castrate resistant prostate cancer (CRPC). The aggressive phenotype of CRPC cells underscores the need to elucidate mechanisms and therapeutic strategies to suppress CRPC outgrowth. Despite ADT, the activation of androgen receptor (AR) transcription factor continues via crosstalk with parallel signaling pathways. Understanding of how these signaling cascades are initiated and amplified post-ADT is lacking. Hormone deprivation can increase oxidative stress and the resultant reactive oxygen species (ROS) may activate both AR and non-AR signaling. Moreover, ROS-induced inflammatory cytokines may further amplify these redox signaling pathways to augment AR function. However, clinical trials using ROS quenching small molecule antioxidants have not suppressed CRPC progression, suggesting that more potent and persistent suppression of redox signaling in CRPC cells will be needed. The transcription factor Nrf2 increases the expression of numerous antioxidant enzymes and downregulates the function of inflammatory transcription factors, e.g., nuclear factor kappa B. We documented that Nrf2 overexpression can suppress AR-mediated transcription in CRPC cell lines. Furthermore, two Nrf2 activating agents, sulforaphane (a phytochemical) and bardoxolone-methyl (a drug in clinical trial) suppress AR levels and sensitize CRPC cells to anti-androgens. These observations implicate the benefits of potent Nrf2-activators to suppress the lethal signaling cascades that lead to CRPC outgrowth. This review article will address the redox signaling networks that augment AR signaling during PCa progression to CRPC, and the possible utility of Nrf2-activating agents as an adjunct to ADT.

Signaling Pathways That Control Apoptosis in Prostate Cancer

Prostate cancer is the second most common malignancy and the fifth leading cancer-caused death in men worldwide. Therapies that target the androgen receptor axis induce apoptosis in normal prostates and provide temporary relief for advanced disease, yet prostate cancer that acquired androgen independence (so called castration-resistant prostate cancer, CRPC) invariably progresses to lethal disease. There is accumulating evidence that androgen receptor signaling do not regulate apoptosis and proliferation in prostate epithelial cells in a cell-autonomous fashion. Instead, androgen receptor activation in stroma compartments induces expression of unknown paracrine factors that maintain homeostasis of the prostate epithelium. This paradigm calls for new studies to identify paracrine factors and signaling pathways that control the survival of normal epithelial cells and to determine which apoptosis regulatory molecules are targeted by these pathways. This review summarizes the recent progress in understanding the mechanism of apoptosis induced by androgen ablation in prostate epithelial cells with emphasis on the roles of BCL-2 family proteins and "druggable" signaling pathways that control these proteins. A summary of the clinical trials of inhibitors of anti-apoptotic signaling pathways is also provided. Evidently, better knowledge of the apoptosis regulation in prostate epithelial cells is needed to understand mechanisms of androgen-independence and implement life-extending therapies for CRPC.

Efficacy of docetaxel combined carboplatin for the treatment of patients with castration-resistant prostate cancer: A protocol of systematic review and meta-analysis

BACKGROUND

A numerous published studies have reported that docetaxel combined carboplatin (DC) has been utilized for the treatment of patients with castration-resistant prostate cancer (CRPC). However, there are still contradictory results. Therefore, this systematic review and meta-analysis will explore the efficacy and safety of DC for the treatment of patients with CRPC.

METHODS

We will systematically and comprehensively search MEDLINE, EMBASE, Cochrane Library, Web of Science, CINAHL, WANGFANG, CBM, and CNKI from the beginning up to the March 1, 2020, regardless language and publication time. We will consider randomized controlled trials that evaluated the efficacy and safety of DC for the treatment of patients with CRPC. The treatment effects of all dichotomous data will be estimated as risk ratio and 95% confidence intervals (CIs), and that of continuous outcomes will be calculated as standardized mean difference or mean difference and 95% CIs. Methodological quality will be appraised by Cochrane risk of bias tool, and quality of evidence will be identified by Grading of Recommendations Assessment Development and Evaluation. Statistical analysis will be undertaken by RevMan 5.3 software.

RESULTS

This study will systematically explore the efficacy and safety of DC for the treatment of patients with CRPC.

CONCLUSION

This study may provide helpful evidence to determine whether DC is an effective treatment for patients with CRPC or not.

SYSTEMATIC REVIEW REGISTRATION

INPLASY202040076.

Aggressive prostate cancer phenotype and genome-wide association studies: where are we now?

The majority of prostate cancer (PCa) is indolent, however, a percentage of patients are initially diagnosed with metastatic disease, for which there is a worse prognosis. There is a lack of biomarkers to identify men at greater risk for developing aggressive PCa. Genome-wide association studies (GWAS) scan the genome to search associations of SNPs with specific traits, like cancer. To date, eight GWAS have resulted in the reporting of 16 SNPs associated with aggressive PCa (p < 5.00 × 10^-2). Still, validation studies need to be conducted to confirm the obtained results as GWAS can generate false-positive results. Furthermore, post-GWAS studies provide a better understanding of the functional consequences.

The JNK inhibitor AS602801 Synergizes with Enzalutamide to Kill Prostate Cancer Cells In Vitro and In Vivo and Inhibit Androgen Receptor Expression

In our previous study, we observed that androgen deprivation therapy (ADT) may induce a compensatory increase in MAPK or JNK signaling. Here, we tested the effects of the MEK inhibitors PD0325901 and GSK1120212, ERK1/2 inhibitor GDC-0994, and the JNK inhibitor AS602801 alone and in combination with the AR inhibitor enzalutamide (ENZ) in androgen-sensitive LNCaP cells and androgen-resistant C4-2 and 22Rv1 cells. Enzalutamide combined with AS602801 synergistically killed LNCaP, C4-2, and 22Rv1 cells, and decreased migration and invasion of LNCaP and C4-2 cells. We studied the combination of enzalutamide with AS602801 in vivo using luciferase labeled LNCaP xenografts, and observed that combination of ENZ with AS602801 significantly suppressed tumor growth compared with either drug alone. Importantly, combination therapy resulted in dramatic loss of AR mRNA and protein. Surprisingly, mechanistic studies and Nanostring data suggest that AS602801 likely activates JNK signaling to induce apoptosis. Since AS602801 had sufficient safety and toxicity profile to advance from Phase I to Phase II in clinical trials, repurposing of this compound may represent an opportunity for rapid translation for clinical therapy of CRPC patients.

Lutetium-177 prostate-specific membrane antigen (PSMA) theranostics: practical nuances and intricacies

Theranostic principles utilize a molecular biomarker specific for a tumor target, initially for imaging to assess target expression and, if deemed suitable, for targeted therapy. This presents an exciting opportunity for a highly personalized treatment strategy in the era of precision medicine. Prostate-specific membrane antigen (PSMA) theranostics has attracted increasing attention as a promising targeted treatment in metastatic prostate cancer (PC). ¹⁷⁷Lu-DOTA-PSMA-617 (¹⁷⁷Lu-PSMA-617) is a PSMA-targeted small molecule with favorable properties and is the most extensively investigated PSMA radioligand for radionuclide therapy (RNT) in PC. Since 2014 multiple retrospective studies and more recently a phase II prospective study demonstrated safety and impressive efficacy of ¹⁷⁷Lu-PSMA RNT. The evidence generated by these trials led to two currently underway randomized trials in metastatic castrate-resistant PC: TheraP (NCT03392428) and VISION (NCT03511664). While we wait for these pivotal trials to read out, nuclear medicine physicians, medical oncologists, radiation oncologists, and urologists are facing a steep learning curve to master the intricacies and nuances of this novel therapeutic strategy. This review article aims to share and discuss the evolving experience in practical aspects of PSMA theranostics.

Reversibility of castration resistance status after Radium-223 dichloride treatment: clinical evidence and review of the literature

In the history of prostate cancer, some of the patients progressed to castration-resistant prostate cancer (CRPC) stage and, although new drugs and treatment protocols have been introduced, CRPC presents poor prognosis. This review is focused on biological mechanisms, underlying CRPC described in scientific literature in order to explain the reversion of resistance to castration. We present the case of a 73-year-old man, affected by bone metastatic CRPC, early treated with Radium-223 with a complete response. After 15 months from Radium-223 treatment, prostate-specific antigen increased with radiological progression. Androgen deprivation therapy was again performed and was effective, despite previous CRPC condition and no known mechanisms that may explain the reversion of this condition. Therefore, to our knowledge, he is the unique described case of the reversion of resistance to castration. Nevertheless, promising aspects may be lack of intrametastatic production of androgen or the suppression of bypass androgen receptor signaling pathways. Furthermore, the cytotoxic action of Radium-223 on cancer stem cell (CSC), due to surrounding clones with high-bone turnover, or the immune response that underlying the abscopal effect, may also modulate the reversion of CRPC after Radium-223. If confirmed by multicenter trials, the reversion of CRPC may impact on the management of prostate cancer.

Novel Method for Structure-Activity Relationship of Aptamer Sequences for Human Prostate Cancer

Prostate cancer (PCa) is one of the most common malignancies in men and seriously threatens men's health. Developing aptamer probes for PCa cells is of great significance for early diagnosis and treatment of PCa. This paper reports a classification model for SELEX-based aptamers, which were obtained with PCa cell line PCa-3M-1E8 (highly metastatic tumor cell) as target cells and PCa cell line PCa-3M-2B4 (low metastatic tumor cell) as control cells. On the basis of the SELEX principle, 100 oligonucleotide sequences from the 3rd round of SELEX were defined as low affinity and specificity aptamers, and 100 sequences from the 11th round were set as high affinity and specificity aptamers. Seven molecular descriptors were used for the classification model, which were calculated from amino acid sequences translated from DNA aptamer sequences with DNAMAN software. The classification model based on binary logical regression analysis has prediction accuracies, sensitivity, and specificity of about 80% for both the training set and test set. Therefore, it is feasible to calculate molecular descriptors from amino acid sequence translated from DNA aptamer sequences and develop a classification model for PCa cell line PCa-3M-1E8.

Molecular and cellular mechanisms of castration resistant prostate cancer

With increases in the mortality rate and number of patients with prostate cancer (PCa), PCa, particularly the advanced and metastatic disease, has been the focus of a number of studies globally. Over the past seven decades, androgen deprivation therapy has been the primary therapeutic option for patients with advanced PCa; however, the majority of patients developed a poor prognosis stage of castration resistant prostate cancer (CRPC), which eventually led to mortality. Due to CRPC being incurable, laboratory investigations and clinical studies focusing on CRPC have been conducted worldwide. Clarification of the molecular pathways that may lead to CRPC is important for discovering novel therapeutic strategies to delay or reverse the progression of disease. A sustained androgen receptor (AR) signal is still regarded as the main cause of CRPC. Increasing number of studies have proposed different potential mechanisms that cause CRPC, and this has led to the development of novel agents targeting the AR-dependent pathway or AR-independent signaling. In the present review, the major underlying mechanisms causing CRPC, including several major categories of AR-dependent mechanisms, AR bypass signaling, AR-independent mechanisms and other important hypotheses (including the functions of autophagy, PCa stem cell and microRNAs in CRPC progression), are summarized with retrospective pre-clinical or clinical trials to guide future research and therapy.

Selection and characterization of DNA aptamer for metastatic prostate cancer recognition and tissue imaging

Prostate cancer (PCa) is the second leading cause of death and most prevalent cancer in men. The absence of curative options for castration-resistant metastatic prostate cancer and biomarkers able to discriminate between indolent and aggressive tumors contribute to these statistics. In this study, a DNA aptamer termed DML-7 was successfully selected against human PCa cell line DU145 by using the cell-based systematic evolution of ligands by exponential enrichment (SELEX) method. The selected aptamer DML-7 was found to internalize into target cells in a temperature-dependent manner and exhibit high binding affinity for target cells with dissociation constants in the nanomolar range. Binding analysis further revealed that DML-7 only binds to DU145 and PC-3 cells with metastatic potential, but not to LNCaP or 22Rv1 cells with low or nonmetastatic potential, demonstrating that DML-7 has excellent selectivity for the recognition of the metastatic PCa cells. Clinical tissue imaging further confirmed these results. Therefore, both high binding affinity and specificity to metastatic PCa cells and tissues afford DML-7 with the potential for development into a novel tool for diagnosis and targeted drug delivery against metastatic prostate cancer.

Diagnostic, prognostic and predictive value of cell-free miRNAs in prostate cancer: a systematic review

Prostate cancer, the second most frequently diagnosed cancer in males worldwide, is estimated to be diagnosed in 1.1 million men per year. Introduction of PSA testing substantially improved early detection of prostate cancer, however it also led to overdiagnosis and subsequent overtreatment of patients with an indolent disease. Treatment outcome and management of prostate cancer could be improved by the development of non-invasive biomarker assays that aid in increasing the sensitivity and specificity of prostate cancer screening, help to distinguish aggressive from indolent disease and guide therapeutic decisions. Prostate cancer cells release miRNAs into the bloodstream, where they exist incorporated into ribonucleoprotein complexes or extracellular vesicles. Later, cell-free miRNAs have been found in various other biofluids. The initial RNA sequencing studies suggested that most of the circulating cell-free miRNAs in healthy individuals are derived from blood cells, while specific disease-associated miRNA signatures may appear in the circulation of patients affected with various diseases, including cancer. This raised a hope that cell-free miRNAs may serve as non-invasive biomarkers for prostate cancer. Indeed, a number of cell-free miRNAs that potentially may serve as diagnostic, prognostic or predictive biomarkers have been discovered in blood or other biofluids of prostate cancer patients and need to be validated in appropriately designed longitudinal studies and clinical trials. In this review, we systematically summarise studies investigating cell-free miRNAs in biofluids of prostate cancer patients and discuss the utility of the identified biomarkers in various clinical scenarios. Furthermore, we discuss the possible mechanisms of miRNA release into biofluids and outline the biological questions and technical challenges that have arisen from these studies.

Registered report: the androgen receptor induces a distinct transcriptional program in castration-resistant prostate cancer in man

The Prostate Cancer Foundation-Movember Foundation Reproducibility Initiative (PCFMFRI) seeks to address growing concerns about reproducibility in scientific research by conducting replications of recent papers in the field of prostate cancer. This Registered Report describes the proposed replication plan of key experiments from “The Androgen Receptor Induces a Distinct Transcriptional Program in Castration-Resistant Prostate Cancer in Man” by Sharma and colleagues (2013), published in Cancer Cell in 2013. Of thousands of targets for the androgen receptor (AR), the authors elucidated a subset of 16 core genes that were consistently downregulated with castration and re-emerged with castration resistance. These 16 AR binding sites were distinct from those observed in cells in culture. The authors suggested that cellular context can have dramatic effects on downstream transcriptional regulation of AR binding sites. The present study will attempt to replicate Fig. 7C by comparing gene expression of the 16 core genes identified by Sharma and colleagues in xenograft tumor tissue compared to androgen treated LNCaP cells in vitro. The Prostate Cancer Foundation-Movember Foundation Reproducibility Initiative is a collaboration between the Prostate Cancer Foundation, the Movember Initiative, and Science Exchange, and the results of the replications will be published by PeerJ.