What is the pathophysiology of a hormone-resistant prostate tumour?

Comprehensive genomics in androgen receptor-dependent castration-resistant prostate cancer identifies an adaptation pathway mediated by opioid receptor kappa 1

Castration resistance is a lethal form of treatment failure of prostate cancer (PCa) and is associated with ligand-independent activation of the androgen receptor (AR). It is only partially understood how the AR mediates survival and castration-resistant growth of PCa upon androgen deprivation. We investigated integrative genomics using a patient-derived xenograft model recapitulating acquired, AR-dependent castration-resistant PCa (CRPC). Sequencing of chromatin immunoprecipitation using an anti-AR antibody (AR-ChIP seq) revealed distinct profiles of AR binding site (ARBS) in androgen-dependent and castration-resistant xenograft tumors compared with those previously reported based on human PCa cells or tumor tissues. An integrative genetic analysis identified several AR-target genes associated with CRPC progression including OPRK1, which harbors ARBS and was upregulated upon androgen deprivation. Loss of function of OPRK1 retarded the acquisition of castration resistance and inhibited castration-resistant growth of PCa both in vitro and in vivo. Immunohistochemical analysis showed that expression of OPRK1, a G protein-coupled receptor, was upregulated in human prostate cancer tissues after preoperative androgen derivation or CRPC progression. These data suggest that OPRK1 is involved in post-castration survival and cellular adaptation process toward castration-resistant progression of PCa, accelerating the clinical implementation of ORPK1-targeting therapy in the management of this lethal disease.

Through comparative genomics using PDX models of androgen-dependent (AD) and androgen-resistant (AR) tumors, Makino et al. identify opioid receptor kappa 1 (OPRK1) as being associated with castration-resistance. Loss of OPRK1 function delays castration-resistance and inhibits castration-resistant growth of prostate cancer cells in culture and in vivo, suggesting OPRK1 as a therapeutic target.

[EFFECT OF NEW ANDROGEN RECEPTOR AXIS-TARGETED AGENTS ON SURVIVAL OF CASTRATION-RESISTANT PROSTATE CANCER]

(Background)The real world's effect of new androgen receptor axis-targeted agents (ARATs) on survival of castration-resistant prostate cancer (CRPC) remains unclear in Japan. (Aims)The primary aim was to determine the clinical benefit of ARATs on survival of CRPC patients. The secondary aim was to evaluate predictive factors affecting the survival of CRPC patients. (Patients and results)Among 236 patients treated with androgen deprivation therapy (ADT), 68 patients developed CRPC; two groups of 34 patients were treated with ARATs (A cases) or conventional ADT (V cases). In a median follow-up of 61.5 months, 20 A and 22 V cases died of cancer. Median survival time (MST) from diagnosis was 99 and 66 months for A and V cases, respectively, and MST from CRPC to death were 50.5 and 44.5 months, respectively. There were no significant differences between both cases. The hazard ratio for death from diagnosis or CRPC progression of the A cases to V cases was 0.711; 95% confidence interval (CI), 0.371 to 1.362; P = 0.3037, or 0.805; 95% CI, 0.434 to 1.491; P=0.4899, respectively. Multivariable analysis revealed that a unique and significant independent prognostic factor from diagnosis was time to CRPC. (Conclusions)In this small retrospective study, we could not determine the clinical benefit of new ARATs compared with conventional ADT on survival of CRPC patients, and a unique and significant independent prognostic factor from diagnosis was time to CRPC. We need to validate these results in a future multi-institutional study.

Loss of Fibroblast-Dependent Androgen Receptor Activation in Prostate Cancer Cells is Involved in the Mechanism of Acquired Resistance to Castration

Loss of androgen receptor (AR) dependency in prostate cancer (PCa) cells is associated with progression to castration-resistant prostate cancer (CRPC). The tumor stroma is enriched in fibroblasts that secrete AR-activating factors. To investigate the roles of fibroblasts in AR activation under androgen deprivation, we used three sublines of androgen-sensitive LNCaP cells (E9 and F10 cells: low androgen sensitivity; and AIDL cells: androgen insensitivity) and original fibroblasts derived from patients with PCa. We performed in vivo experiments using three sublines of LNCaP cells and original fibroblasts to form homotypic tumors. The volume of tumors derived from E9 cells plus fibroblasts was reduced following androgen deprivation therapy (ADT), whereas that of F10 or AIDL cells plus fibroblasts was increased even after ADT. In tumors derived from E9 cells plus fibroblasts, serum prostate-specific antigen (PSA) decreased rapidly after ADT, but was still detectable. In contrast, serum PSA was increased even in F10 cells inoculated alone. In indirect cocultures with fibroblasts, PSA production was increased in E9 cells. Epidermal growth factor treatment stimulated Akt and p44/42 mitogen-activated protein kinase phosphorylation in E9 cells. Notably, AR splice variant 7 was detected in F10 cells. Overall, we found that fibroblast-secreted AR-activating factors modulated AR signaling in E9 cells after ADT and loss of fibroblast-dependent AR activation in F10 cells may be responsible for CRPC progression.

The effect of additional chemotherapy on high-risk prostate cancer: a systematic review and meta-analysis

OBJECTIVE

The role of additional chemotherapy in the treatment of high-risk prostate cancer (PCa) remains a controversy. This meta-analysis aimed to investigate the effect of additional chemotherapy on high-risk PCa.

METHODS

Randomized controlled trials (RCTs) about additional chemotherapy for high-risk PCa were searched in PubMed, MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. We extracted HRs of overall survival (OS) and progression-free survival (PFS) for each trial and performed the meta-analysis using Review Manager 5.3.

RESULTS

Eight RCTs involving 4,007 patients were included. Data from four trials, which could collect OS, showed that additional chemotherapy could not significantly improve the OS in patients with high-risk PCa (HR: 0.93; 95% CI: 0.79-1.09; P=0.37). However, the pooled analysis suggested significantly longer PFS in high-risk PCa patients treated with additional chemotherapy (HR: 0.81; 95% CI: 0.74-0.90; P<0.0001). The meta-analysis showed additional chemotherapy to androgen-deprivation therapy improved PFS (HR: 0.82; 95% CI: 0.74-0.91; P=0.0002). Greater improvement in PFS was found in high-risk PCa patients treated with additional docetaxel-based chemotherapy (HR: 0.73; 95% CI: 0.64-0.83; P<0.00001). No prolonged PFS was observed in high-risk PCa patients with non-docetaxel-based chemotherapy (HR: 0.97; 95% CI: 0.83-1.14; P=0.74).

CONCLUSION

Additional chemotherapy, especially docetaxel-based chemotherapy, could significantly improve the PFS in high-risk PCa patients. More evidence about the effect of additional chemotherapy on OS is needed. Further investigations in PCa should also focus on the suitable population for chemotherapy as well as optimal use of chemotherapy.

Antiandrogen withdrawal syndrome (AAWS) in the treatment of patients with prostate cancer

Antiandrogen withdrawal syndrome is an unpredictable event diagnosed in patients with hormone-sensitive prostate cancer treated with combined androgen blockade therapy. It is defined by prostate-specific antigen value reduction, occasionally associated with a radiological response, that occurs 4-6 weeks after first-generation antiandrogen therapy discontinuation. New-generation hormonal therapies, such as enzalutamide and abiraterone acetate, improved the overall survival in patients with metastatic castration-resistant prostate cancer, and recent trials have also shown the efficacy of abiraterone in hormone-sensitive disease. In the last few years, several case reports and retrospective studies suggested that the withdrawal syndrome may also occur with these new drugs. This review summarizes literature data and hypothesis about the biological rationale underlying the syndrome and its potential clinical relevance, focusing mainly on new-generation hormonal therapies. Several in vitro studies suggest that androgen receptor gain-of-function mutations are involved in this syndrome, shifting the antiandrogen activity from antagonist to agonist. Several different drug-specific point mutations have been reported. The association of the withdrawal syndrome for enzalutamide and abiraterone needs confirmation by additional investigations. However, new-generation hormonal therapies being increasingly used in all stages of disease, more patients may experience the syndrome when stopping the treatment at the time of disease progression, although the clinical relevance of this phenomenon in the management of metastatic castration-resistant prostate cancer remains to be defined.

Understanding prostate-specific antigen dynamics in monitoring metastatic castration-resistant prostate cancer: implications for clinical practice

Availability of novel hormonal therapies as well as docetaxel and cabazitaxel treatment for metastatic castration-resistant prostate cancer (CRPC) has changed the outlook for this group of patients with improvements in progression-free survival and overall survival. Physicians often diagnose the progression of prostate cancer using serum prostate-specific antigen (PSA). However, serum PSA is not always correlated with the clinical status in CRPC. To evaluate the PSA dynamics with greater precision, understanding of the control of PSA and of the mechanisms of development of CRPC is needed. Moreover, it is necessary to use new hormonal therapies with an appropriate timing to optimally improve the prognosis and the QOL of the patients. In the present review, we ascertain the PSA dynamics and the mechanisms of the development of CRPC to assist in optimal utilization of the new treatments for mCRPC.

Enzalutamide inhibits proliferation of gemcitabine-resistant bladder cancer cells with increased androgen receptor expression

Advanced bladder cancer is treated mainly with gemcitabine and cisplatin, but most patients eventually become resistance. Androgen receptor (AR) signaling has been implicated in bladder cancer as well as other types of cancer including prostate cancer. In this study, we investigated the expression and role of AR in gemcitabine-resistant bladder cancer cells and also the potential of enzalutamide, an AR inhibitor, as a therapeutic for the chemoresistance. First of all, we established gemcitabine-resistant T24 cells (T24GR) from T24 bladder cancer cells and performed gene expression profiling. Microarray analysis revealed upregulation of AR expression in T24GR cells compared with T24 cells. AR mRNA and protein expression was confirmed to be increased in T24GR cells, respectively, by quantitative RT-PCR and western blot analysis, which was associated with more potent AR transcriptional activity as measured by luciferase reporter assay. The copy number of AR gene in T24GR cells determined by PCR was twice as many as that of T24 cells. AR silencing by siRNA transfection resulted in inhibition of proliferation of T24GR cells. Cell culture in charcoal-stripped serum and treatment with enzalutamide inhibited growth of T24GR cells, which was accompanied by cell cycle arrest. AR transcriptional activity was found to be reduced in T24GR cells by enzalutamide treatment. Lastly, enzalutamide also inhibited cell proliferation of HTB5 bladder cancer cells that express AR and possess intrinsic resistance to gemcitabine. Our results suggest that enzalutamide may have the potential to treat patients with advanced gemcitabine-resistant bladder cancer with increased AR expression.

Efficacy, quality of life, and safety of cabazitaxel in Canadian metastatic castration-resistant prostate cancer patients treated or not with prior abiraterone

INTRODUCTION

In the TROPIC study, cabazitaxel improved overall survival in abiraterone-naïve metastatic castration-resistant prostate cancer (mCRPC) patients post-docetaxel. To evaluate cabazitaxel in routine clinical practice, an international, single-arm trial was conducted. Efficacy, safety, and quality of life (QoL) data were collected from Canadian patients enrolled. Overall survival and progression-free survival were not collected as part of this study. Importantly, prior abiraterone use was obtained and its impact on clinical parameters was examined.

METHODS

Sixty-one patients from nine Canadian centres were enrolled, with prior abiraterone use known for 60 patients. Prostate-specific antigen (PSA) response rate, safety, and impact on QoL life were analyzed as a function of prior abiraterone use.

RESULTS

Overall, 92% of patients were ECOG 0/1, 88% had bone metastases, and 25% visceral metastases. Patients treated without prior abiraterone (NoPriorAbi) (n=35, 58%) and with prior abiraterone (PriorAbi) (n=25, 42%) had similar baseline characteristics, except for age and prior cumulative docetaxel dose. Median number of cabazitaxel cycles received was similar between groups (NoPriorAbi=6, PriorAbi=7), as was PSA response rate (NoPriorAbi=36.4%, PriorAbi=45.0%, p=0.54). Almost one-third (31%) of patients received prophylactic granulocyte colony-stimulating factors. Most frequent Grade 3/4 toxicities were neutropenia (14.8%); anemia, febrile neutropenia, fatigue (each at 9.8%); and diarrhea (8.2%). No treatment-related adverse event leading to death was observed. QoL and pain were improved with no difference seen between groups. Treatment discontinuation was mainly due to disease progression (45.9%) and adverse events (32.8%).

CONCLUSIONS

In routine clinical practice, cabazitaxel's risk-benefit ratio in mCRPC patients previously treated with docetaxel seems to be maintained independent of prior abiraterone use.

Epidermal growth factor induces p38 MAPK-dependent G0/G1-to-S transition in prostate cancer cells upon androgen deprivation conditions

Epidermal growth factor (EGF) is thought to contribute to the emergence of castration-resistant (CR) prostate tumors by inducing proliferation of cancer cells despite the low levels of circulating androgens achieved by androgen deprivation therapy. We show that, in LNCaP cells, androgen deprivation induces arrest in the G0/G1 cell cycle phase, and that EGF partially rescues this arrest without affecting cell death. Inhibition of p38 MAPK, but not MEK or IKK-β, completely abrogates the EGF-induced proliferation of LNCaP cells in androgen-depleted medium, and decreases the fraction of G0/G1-arrested cells. Our results suggest that EGF enables prostate cancer cells to overcome the growth restriction imposed by androgen deprivation by stimulating G0/G1-to-S transition via p38 MAPK. These results suggest the potential of developing therapies for advanced prostate cancer that block the G0/G1 to S transition, such as by targeting p38 MAPK, or that aim to induce apoptosis in G0/G1-arrested cancer cells.

Adaptive responses of androgen receptor signaling in castration-resistant prostate cancer

Prostate Cancer (PCa) is an important age-related disease being the most common cancer malignancy and the second leading cause of cancer mortality in men in Western countries. Initially, PCa progression is androgen receptor (AR)- and androgen-dependent. Eventually advanced PCa reaches the stage of Castration-Resistant Prostate Cancer (CRPC), but remains dependent on AR, which indicates the importance of AR activity also for CRPC. Here, we discuss various pathways that influence the AR activity in CRPC, which indicates an adaptation of the AR signaling in PCa to overcome the treatment of PCa. The adaptation pathways include interferences of the normal regulation of the AR protein level, the expression of AR variants, the crosstalk of the AR with cytokine tyrosine kinases, the Src-Akt-, the MAPK-signaling pathways and AR corepressors. Furthermore, we summarize the current treatment options with regard to the underlying molecular basis of the common adaptation processes of AR signaling that may arise after the treatment with AR antagonists, androgen deprivation therapy (ADT) as well as for CRPC, and point towards novel therapeutic strategies. The understanding of individualized adaptation processes in PCa will lead to individualized treatment options in the future.

Androgen receptors beyond prostate cancer: an old marker as a new target

Androgen receptors (ARs) play a critical role in the development of prostate cancer. Targeting ARs results in important salutary effects in this malignancy. Despite mounting evidence that ARs also participate in the pathogenesis and/or progression of diverse tumors, exploring the impact of hormonal manipulation of these receptors has not been widely pursued beyond prostate cancer. This review describes patterns of AR expression in a spectrum of cancers, and the potential to exploit this knowledge in the clinical therapeutic setting.

TGF-β1 mediates the radiation response of prostate cancer

Radiotherapy is the main treatment modality for prostate cancer. This study investigated the role of TGF-β1 in biological sequelae and tumor regrowth following irradiation, which are critical for the clinical radiation response of prostate cancer. Human and murine prostate cancer cell lines, and corresponding hormone-refractory (HR) cells, were used to examine the radiation response by clonogenic assays in vitro and tumor growth delay in vivo. Biological changes after irradiation, including cell death and tumor regrowth, were examined by experimental manipulation of TGF-β1 signaling. The correlations among tumor radiation responses, TGF-β1 levels, and regulatory T cells (Tregs) recruitment were also evaluated using animal experiments. HR prostate cancer cells appeared more radioresistant and had higher expression of TGF-β1 compared to hormone-sensitive (HS) cells. TGF-β1 expression was positively linked to irradiation and radioresistance, as demonstrated by in vitro and in vivo experiments. Inhibition of TGF-β1 increased tumor inhibition and DNA damage after irradiation. When mice were irradiated with a sub-lethal dose, the regrowth of irradiated tumors was significantly correlated with TGF-β1 levels and Tregs accumulation in vivo. Furthermore, blocking TGF-β1 clearly attenuated Tregs accumulation and tumor regrowth following treatment. These data demonstrate that TGF-β1 is important in determining the radiation response of prostate cancer, including tumor cell killing and the tumor microenvironment. Therefore, concurrent treatment with a TGF-β1 inhibitor is a potential therapeutic strategy for increasing the radiation response of prostate cancer, particularly for more aggressive or HR cancer cells.

KEY MESSAGE

• HR prostate cancer cells appeared more radioresistant and had higher expression of TGF-β1. • TGF-β1 was positively linked to the radiation resistance of prostate cancer. • Tumor regrowth following irradiation was significantly correlated with TGF-β1 and Tregs levels. • Blocking TGF-β1 significantly attenuated RT-induced DNA repair and Tregs. • TGF-β1 inhibitor increases the radiation response of HR cancer cells.

Post genome-wide association studies functional characterization of prostate cancer risk loci

Background

Over the last decade, genome-wide association studies (GWAS) have discovered many risk associated single nucleotide polymorphisms (SNPs) of prostate cancer (PCa). However, the majority of the associated PCa SNPs, including those in linkage disequilibrium (LD) blocks, are generally not located in protein coding regions. The systematical investigation of the functional roles of these SNPs, especially the non-coding SNPs, becomes very necessary and helpful to the understanding of the molecular mechanism of PCa.

Results

In this work, we proposed a comprehensive framework at network level to integrate the SNP annotation, target gene assignment, gene ontology (GO) classification, pathway enrichment analysis and regulatory network reconstruction to illustrate the molecular functions of PCa associated SNPs. By LD expansion, we first identified 1828 LD SNPs using 49 reported GWAS SNPs as a start. We carefully annotated these 1828 LD SNPs via either UCSC known genes, UCSC regulation elements, or expression Quantitative Trait Loci (eQTL) data. As a result, we found 1154 SNPs were functionally annotated and obtained 205 unique PCa genes for further enrichment analysis. The enriched GO biological processes and pathways were found mainly related to regulation of cell death, apoptosis, cell proliferation, and metabolic process, which have been proved essential to cancer development. We constructed PCa genes specific transcription regulatory networks, finding several important genetic regulators for PCa, such as IGF-1/IGF-2 receptors, SP1, CREB1, and androgen receptor (AR).

Conclusions

A comprehensive framework was proposed for integrative and systematic analysis of PCa SNPs, the analysis can provide essential information for the understanding of the regulatory function of GWAS SNPs in PCa, and will facilitate the discovery of novel candidate biomarkers for diagnosis and prognosis of PCa.

Taxane mechanisms of action: potential implications for treatment sequencing in metastatic castration-resistant prostate cancer

CONTEXT

In the past few years, there has been a rapid increase in the number of therapies available to treat metastatic castration-resistant prostate cancer (mCRPC). Currently, approved treatments consist of the taxane class of cytotoxic drugs and androgen-targeted therapies. The challenge for clinicians is to decide the best sequence in which to give these therapies to provide the greatest benefit to their patients.

OBJECTIVE

To review recent research into the mechanism of action of taxanes in prostate cancer (PCa) cells and the clinical evidence for an interaction between taxanes and androgen-targeted therapies. The implications of these findings for clinical practice are discussed.

EVIDENCE ACQUISITION

A nonsystematic review of the relevant medical literature between 2004 and the present, in combination with clinical trial data reported at oncology meetings during 2012, was undertaken. Our perspective, focussing on the potential implications for sequencing of therapies for mCRPC, is provided.

EVIDENCE SYNTHESIS

Taxanes are shown to interact with androgen signalling in PCa cells at both the cytoplasmic level (via microtubules) and the nuclear level, affecting transcriptional regulators of androgen-responsive gene expression. Data from clinical trials suggest that androgen deprivation can potentially decrease the efficacy of taxanes in treating PCa.

CONCLUSIONS

These findings have important implications for clinical practice, and there is an urgent need for strong clinical data to support a recommendation for an optimal sequence of therapies.

Non-metastatic CRPC and asymptomatic metastatic CRPC: which treatment for which patient?

The introduction of early PSa-based diagnosis has profoundly impacted the epidemiology of castration-resistant prostate cancer (CRPC). Many patients enter the disease at an early stage when the only sign of resistance to androgen deprivation therapy (ADT) is a progressive elevation of prostate-specific antigen (PSA). This created a very heterogeneous population of non-metastatic (M0) CRPC. PSa kinetics is the most powerful indicator of aggressiveness in that population and can be used to trigger imaging investigation and enrollment in clinical trials. Several registered and near to come treatments have not been tested in that population but in men with more advanced metastatic and often symptomatic disease. Several agents have been investigated to delay the onset of the first bone metastasis but only one, denosumab, has reached its end-point. Because CRPC remains largely driven by the androgen receptor (AR), physicians have relied on second-line hormonal manipulations to delay the progression of the disease, including first generation antiandrogens, adrenal synthesis inhibitors, steroids and estrogens. The data however are mostly limited to phase II trials.

PSA lo and behold: prostate cancer stem cells

Human prostate cancers contain multiple cell populations marked by varying levels of the differentiation marker prostate-specific antigen (PSA). In this issue of Cell Stem Cell, Qin et al. (2012) show that PSA(-/lo) cells are enriched for cells with tumor-initiating characteristics and may participate in resistance to androgen-ablative therapies.