Dissecting the roles of the androgen receptor in prostate cancer from molecular perspectives

Cytotoxic N-Methylpretrichodermamide B Reveals Anticancer Activity and Inhibits P-Glycoprotein in Drug-Resistant Prostate Cancer Cells

N-methylpretrichodermamide B (NB) is a biologically active epidithiodiketopiperazine isolated from several strains of the algae-derived fungus Penicillium sp. Recently, we reported the first data on its activity in human cancer cells lines in vitro. Here, we investigated the activity, selectivity, and mechanism of action of NB in human prostate cancer cell lines, including drug-resistant subtypes. NB did not reveal cross-resistance to docetaxel in the PC3-DR cell line model and was highly active in hormone-independent 22Rv1 cells. NB-induced cell death was stipulated by externalization of phosphatidylserine and activation of caspase-3. Moreover, inhibition of caspase activity by z-VAD(OMe)-fmk did not affect NB cytotoxicity, suggesting a caspase-independent cell death induced by NB. The compound has a moderate p-glycoprotein (p-gp) substrate-like affinity and can simultaneously inhibit p-gp at nanomolar concentrations. Therefore, NB resensitized p-gp-overexpressing PC3-DR cells to docetaxel. A kinome profiling of the NB-treated cells revealed, among other things, an induction of mitogen-activated protein kinases JNK1/2 and p38. Further functional analysis confirmed an activation of both kinases and indicated a prosurvival role of this biological event in the cellular response to the treatment. Overall, NB holds promising anticancer potential and further structure-activity relationship studies and structural optimization are needed in order to improve its biological properties.

The T850D Phosphomimetic Mutation in the Androgen Receptor Ligand Binding Domain Enhances Recruitment at Activation Function 2

Several key functions of the androgen receptor (AR) such as hormone recognition and co-regulator recruitment converge in the ligand binding domain (LBD). Loss- or gain-of-function of the AR contributes to pathologies such as the androgen insensitivity syndrome and prostate cancer. Here, we describe a gain-of-function mutation of the surface-exposed threonine at position 850, located at the amino-terminus of Helix 10 (H10) in the AR LBD. Since T850 phosphorylation was reported to affect AR function, we created the phosphomimetic mutation T850D. The AR T850D variant has a 1.5- to 2-fold increased transcriptional activity with no effect on ligand affinity. In the androgen responsive LNCaP cell line grown in medium with low androgen levels, we observed a growth advantage for cells in which the endogenous AR was replaced by AR T850D. Despite the distance to the AF2 site, the AR T850D LBD displayed an increased affinity for coactivator peptides as well as the ²³FQNLF²⁷ motif of AR itself. Molecular Dynamics simulations confirm allosteric transmission of the T850D mutation towards the AF2 site via extended hydrogen bond formation between coactivator peptide and AF2 site. This mechanistic study thus confirms the gain-of-function character of T850D and T850 phosphorylation for AR activity and reveals details of the allosteric communications within the LBD.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 4: Experimental Treatments in Pre-Clinical Studies (Cell Lines and Mouse Models)

In prostate cancer (PC), the PD-1/PD-L1 axis regulates various signaling pathways and it is influenced by extracellular factors. Pre-clinical experimental studies investigating the effects of various treatments (alone or combined) may discover how to overcome the immunotherapy-resistance in PC-patients. We performed a systematic literature review (PRISMA guidelines) to delineate the landscape of pre-clinical studies (including cell lines and mouse models) that tested treatments with effects on PD-L1 signaling in PC. NF-kB, MEK, JAK, or STAT inhibitors on human/mouse, primary/metastatic PC-cell lines variably down-modulated PD-L1-expression, reducing chemoresistance and tumor cell migration. If PC-cells were co-cultured with NK, CD8+ T-cells or CAR-T cells, the immune cell cytotoxicity increased when PD-L1 was downregulated (opposite effects for PD-L1 upregulation). In mouse models, radiotherapy, CDK4/6-inhibitors, and RB deletion induced PD-L1-upregulation, causing PC-immune-evasion. Epigenetic drugs may reduce PD-L1 expression. In some PC experimental models, blocking only the PD-1/PD-L1 pathway had limited efficacy in reducing the tumor growth. Anti-tumor effects could be increased by combining the PD-1/PD-L1 blockade with other approaches (inhibitors of tyrosine kinase, PI3K/mTOR or JAK/STAT3 pathways, p300/CBP; anti-RANKL and/or anti-CTLA-4 antibodies; cytokines; nitroxoline; DNA/cell vaccines; radiotherapy/Radium-223).

Molecular Characterization of Prostate Cancers in the Precision Medicine Era

Prostate cancer (PCa) therapy has been recently revolutionized by the approval of new therapeutic agents in the metastatic setting. However, the optimal therapeutic strategy in such patients should be individualized in the light of prognostic and predictive molecular factors, which have been recently studied: androgen receptor (AR) alterations, PTEN-PI3K-AKT pathway deregulation, homologous recombination deficiency (HRD), mismatch repair deficiency (MMRd), and tumor microenvironment (TME) modifications. In this review, we highlighted the clinical impact of prognostic and predictive molecular factors in PCa patients' outcomes, identifying biologically distinct subtypes. We further analyzed the relevant methods to detect these factors, both on tissue, i.e., immunohistochemistry (IHC) and molecular tests, and blood, i.e., analysis of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA). Moreover, we discussed the main pros and cons of such techniques, depicting their present and future roles in PCa management, throughout the precision medicine era.

miRNAs and androgen deprivation therapy for prostate cancer

Androgen deprivation therapy (ADT) is mainly used for the treatment of advanced, metastatic or recurrent prostate cancer (PCa). However, patients progress to ADT resistance and castration-resistant prostate cancer (CRPC) with a poor prognosis. Reliable validated markers of ADT resistance with proven clinical utility are necessary for timely correction of the therapy as well as for improvement of patient quality of life. MiRNAs involved in the ADT response and CRPC development via multiple mechanisms may act as biomarkers for patient outcomes. Available data on miRNAs associated with the ADT response (resistance and sensitivity) are summarized and analyzed in the manuscript, including analyses using bioinformatics resources. Molecular targets of miRNAs, as well as reciprocal relations between miRNAs and their targets, were studied using different databases. Special attention was dedicated to the mechanisms of ADT resistance and CRPC development, including testosterone, PI3K-AKT, VEGF pathways and associated genes. Several different approaches can be used to search for miRNAs associated with the ADT response, each of which focuses on the associated set of miRNAs - potential markers of ADT. The intersection of these approaches and combined analysis allowed us to select the most promising miRNA markers of the ADT response. Meta-analysis of the current data indicated that the selected 5 miRNAs (miRNAs - 125b, miR-21, miR-23b, miR-27b and miR-221) and 14 genes are involved in the regulation of key processes of CRPC development and represent the most promising predictors of the ADT response, further demonstrating their potential in combination therapy for advanced PCa.

Efficacy and Mechanism of Action of Marine Alkaloid 3,10-Dibromofascaplysin in Drug-Resistant Prostate Cancer Cells

Efficacy and mechanism of action of marine alkaloid 3,10-dibromofascaplysin (DBF) were investigated in human prostate cancer (PCa) cells harboring different levels of drug resistance. Anticancer activity was observed across all cell lines examined without signs of cross-resistance to androgen receptor targeting agents (ARTA) or taxane based chemotherapy. Kinome analysis followed by functional investigation identified JNK1/2 to be one of the molecular targets of DBF in 22Rv1 cells. In contrast, no activation of p38 and ERK1/2 MAPKs was observed. Inhibition of the drug-induced JNK1/2 activation or of the basal p38 activity resulted in increased cytotoxicity of DBF, whereas an active ERK1/2 was identified to be important for anticancer activity of the alkaloid. Synergistic effects of DBF were observed in combination with PARP-inhibitor olaparib most likely due to the induction of ROS production by the marine alkaloid. In addition, DBF intensified effects of platinum-based drugs cisplatin and carboplatin, and taxane derivatives docetaxel and cabazitaxel. Finally, DBF inhibited AR-signaling and resensitized AR-V7-positive 22Rv1 prostate cancer cells to enzalutamide, presumably due to AR-V7 down-regulation. These findings propose DBF to be a promising novel drug candidate for the treatment of human PCa regardless of resistance to standard therapy.

Marine alkaloid monanchoxymycalin C: a new specific activator of JNK1/2 kinase with anticancer properties

Monanchoxymycalin C (MomC) is a new marine pentacyclic guanidine alkaloid, recently isolated from marine sponge Monanchora pulchra by us. Here, anticancer activity and mechanism of action was investigated for the first time using a human prostate cancer (PCa) model. MomC was active in all PCa cell lines at low micromolar concentrations and induced an unusual caspase-independent, non-apoptotic cell death. Kinase activity screening identified activation of mitogen-activated protein kinase (MAPK) c-Jun N-terminal protein kinase (JNK1/2) to be one of the primary molecular mechanism of MomC anticancer activity. Functional assays demonstrated a specific and selective JNK1/2 activation prior to the induction of other cell death related processes. Inhibition of JNK1/2 by pretreatment with the JNK-inhibitor SP600125 antagonized cytotoxic activity of the marine compound. MomC caused an upregulation of cytotoxic ROS. However, in contrast to other ROS-inducing agents, co-treatment with PARP-inhibitor olaparib revealed antagonistic effects indicating an active PARP to be necessary for MomC activity. Interestingly, although no direct regulation of p38 and ERK1/2 were detected, active p38 kinase was required for MomC efficacy, while the inhibition of ERK1/2 increased its cytotoxicity. In conclusion, MomC shows promising activity against PCa, which is exerted via JNK1/2 activation and non-apoptotic cell death.

LncRNA GAS5 participates in the regulation of dexamethasone on androgen receptor -negative and -positive prostate cancer cell proliferation

BACKGROUND

Androgen receptor (AR) and long non-coding RNAs (lncRNA) play important roles in the initiation and progression of prostate cancer (PCa). The present study was designed to investigate whether lncRNA growth arrest-specific 5 (GAS5) is involved in the regulation of dexamethasone on the proliferation of AR⁺ PCa and AR^- PCa cell lines.

METHODS

Cell proliferation and cell cycle distribution were assessed using MTT assay and flow cytometry, respectively. GAS5 expression was examined by quantitative real-time PCR. AR protein level was examined by Western blot. RNA immunoprecipitation and RNA pull-down were performed to analyze the binding of GAS5 to AR.

RESULTS

In AR^- PCa cell line PC3, dexamethasone upregulated GAS5 expression, induced cell cycle arrest in the G0/G1 phase and inhibited cell proliferation, which were enhanced by GAS5 overexpression and attenuated by GAS5 silencing. However, in AR⁺ PCa cell line 22Rv1, dexamethasone had no obvious effects on GAS5 expression, cell cycle distribution and cell proliferation. AR was localized in the cytoplasm and bound to GAS5, counteracting the proliferation-inhibitory effect of GAS5.

CONCLUSION

Taken together, GAS5 participates in the regulation of dexamethasone on the proliferation of AR⁺ PCa and AR^- PCa cell lines.

Clinicopathological and prognostic significance of androgen receptor overexpression in colorectal cancer. Experience from Al-Madinah Al-Munawarah, Saudi Arabia

Objectives:

To examine the androgen receptor (AR) status in colorectal cancer (CRC) patients by the immunohistochemical method and to correlate the findings with all available clinicopathological parameters of prognostic significance.

Methods:

Archival tumor samples were studied using immunohistochemistry for AR expression in 324 patients with CRC. Patients were diagnosed at the Pathology Department at a tertiary care Hospital, Al-Madinah Al-Munawarah, Saudi Arabia, between January 2006 and December 2017.

Results:

There is a complete lack of AR expression in normal colonic mucosa; however, AR was expressed in 16 cases (40%) of colorectal adenoma. In CRC, AR expression was high in 118 cases (36.4%). There were no significant correlations between AR expression and gender, age, tumor histologic type, and tumor location. However, AR expression revealed a significant correlation with tumor size (p=0.026), tumor differentiation (p=0.047), American Joint Committee on Cancer (AJCC) staging (p=0.043), lymph node positivity (p=0.018), lymphovascular invasion (p=0.018), and distant metastasis (p=0.049). In univariate Kaplan-Meier survival analysis, there was a significant (p=0.002) difference in overall survival between AR positive and negative tumors in favor of the latter. In multivariate (COX) models, high AR expression (p=0.002), AJCC (p<0.001), and lymphovascular invasion (p<0.001) were the only significant independent prognostic indicators of overall survival in CRC.

Conlusion:

Our study showed that the patients with higher AR expression had a significantly poorer survival rate, AR expression had the potential to be a prognostic marker of CRC.

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.

Androgen-targeted therapy in men with prostate cancer: evolving practice and future considerations

Background

Androgen deprivation therapy (ADT) is foundational in the management of advanced prostate cancer (PCa) and has benefitted from a recent explosion in scientific advances. These include approval of new therapies that suppress testosterone (T) levels or inactivate its function, improvements in diagnostic and assay technologies, identification of lower therapeutic targets for T, discovery of the relevance of germline genetic mutations and identification of the benefits of sequential and combination therapies.

Methods

This review discusses the clinical profiles of the most up-to-date options for ADT, best practices for managing patients with advanced PCa and future directions in therapy.

Results and conclusions

Modern assay technologies reveal that bilateral orchiectomy results in a serum T level of approximately 15 ng/dL as compared to the historical definition of castration of T < 50 ng/dL. Evidence shows that lowering T levels to <20 ng/dL improves patient survival and delays disease progression. Routine monitoring of T in addition to prostate-specific antigen throughout treatment is important to ensure continuing efficacy of T suppression. New drugs that inhibit androgen signaling in combination with traditional ADT suppress T activity to near zero and have significantly improved patient survival. When personalizing ADT regimens physicians should consider a number of factors including initiation and duration of ADT, monitoring of T levels and PSA, the possibility of switching monotherapies if a patient does not achieve adequate T suppression, and consideration of intermittent vs. continuous ADT according to patients’ lifestyles, comorbidities, risk factors and tolerance to treatment.

Nuclear loss and cytoplasmic expression of androgen receptor in penile carcinomas: role as a driver event and as a prognosis factor

Androgen receptor (AR) is a member of the steroid and nuclear family receptor that acts as transcription factor. AR signaling plays pivotal role in the development and progression of prostate cancer. However, the role of AR in penile cancer (PeCa) is poorly explored. Our previous molecular studies unveiled frequent AR mRNA loss in PeCa, which was further predicted as a major driver alteration in this neoplasm. Herein, we assessed the AR protein expression in 59 usual PeCa tissues and 42 surrounding normal tissues (SNT) by immunohistochemistry using a tissue microarray. In a paired analysis, we found a total absence of nuclear AR expression in PeCa while 95.2% of SNT samples presented strong nuclear AR expression (P < 0.001). Interestingly, 17 of 42 PeCa presented weak or moderate cytoplasmic AR staining, contrasting with 5 of 42 SNT (P = 0.008). Increased levels of AR cytoplasmic expression were related with poor prognosis features including advanced clinical staging (P = 0.044), compromised surgical margins (P = 0.005), and pathological inguinal node status (P = 0.047). Furthermore, AR cytoplasmic expression was also related with shorter overall survival (P = 0.032). In conclusion, the frequent loss of nuclear AR protein levels suggests a potential function in PeCa development. Based on this result, the androgen deprivation therapy is not indicated for PeCa patients. In addition, the AR cytoplasmic expression found in a significant number of cases (40.5%) showed prognostic value and pathways activated by the non-genomic AR signaling may represent a promising therapeutic strategy.

Androgen receptor reverts dexamethasone‑induced inhibition of prostate cancer cell proliferation and migration

The aim of the present study was to determine the role of androgen receptor in the effect of dexamethasone on cell proliferation and migration of multiple prostate cancer cells. The prostate cancer cell lines LNCaP, 22Rv1, C4-2 and PC3 were cultured in vitro. For glucocorticoid-induced experiments, the cells were transferred and cultured in RPMI-1640 medium with 10% charcoal-stripped serum from RPMI-1640 medium with 10% fetal bovine serum for at least 24 h. The effects of dexamethasone on the proliferation and migration of various cell lines were analyzed by MTT and migration assays. Dexamethasone exhibited no effect on LNCaP, C4-2 and 22Rv1 cell lines, but suppressed proliferation of glucocorticoid receptor (GR)⁺ androgen receptor (AR)⁻ PC3 cell line. Dexamethasone suppressed PC3 cell migration, and did not affect migration of PC3-AR9 cells. Dexamethasone positively or negatively regulated proliferation of various prostate cancer cells based on AR and GR expression profiles. The data presented in the present study indicates that androgen receptor reverts the dexamethasone-induced inhibition of prostate cancer cell proliferation and migration.