Role of targeted therapy in the treatment of advanced prostate cancer

Extranuclear partners of androgen receptor: at the crossroads of proliferation, migration, and neuritogenesis

In this review, we focus on the role played by the protein partners of ligand-activated extranuclear androgen receptor (AR) in the final effects of hormone action, such as proliferation, migration, and neuritogenesis. The choice of AR partner, at least in part, depends on cell type. Androgen-activated receptor directly associates with cytoplasmic Src tyrosine kinase in epithelial cells, whereas in mesenchymal and neuronal cells, it prevalently interacts with filamin A. In the former, proliferation represents the final hormonal outcome, whereas in the latter, either migration or neuritogenesis, respectively, occurs. Furthermore, AR partner filamin A is replaced with Src when mesenchymal cells are stimulated with very low androgen concentrations. Consequently, the migratory effect is replaced by mitogenesis. Use of peptides that prevent receptor/partner assembly abolishes the effects that are dependent on their association and offers new therapeutic approaches to AR-related diseases. Perturbation of migration is often associated with metastatic spreading in cancer. In turn, cell cycle aberration causes tumors to grow faster, whereas toxic signaling triggers neurodegenerative events in the CNS. Here, we provide examples of new tools that interfere in rapid androgen effects, including migration, proliferation, and neuronal differentiation, together with their potential therapeutic applications in AR-dependent diseases-mainly prostate cancer and neurodegenerative disorders.-Castoria, G., Auricchio, F., Migliaccio, A. Extranuclear partners of androgen receptor: at the crossroads of proliferation, migration, and neuritogenesis.

PC-1/PrLZ confers resistance to rapamycin in prostate cancer cells through increased 4E-BP1 stability

An important strategy for improving advanced PCa treatment is targeted therapies combined with chemotherapy. PC-1, a prostate Leucine Zipper gene (PrLZ), is specifically expressed in prostate tissue as an androgen-induced gene and is up-regulated in advanced PCa. Recent work confirmed that PC-1 expression promotes PCa growth and androgen-independent progression. However, how this occurs and whether this can be used as a biomarker is uncertain. Here, we report that PC-1 overexpression confers PCa cells resistance to rapamycin treatment by antagonizing rapamycin-induced cytostasis and autophagy (rapamycin-sensitivity was observed in PC-1-deficient (shPC-1) C4-2 cells). Analysis of the mTOR pathway in PCa cells with PC-1 overexpressed and depressed revealed that eukaryotic initiation factor 4E-binding protein 1(4E-BP1) was highly regulated by PC-1. Immunohistochemistry assays indicated that 4E-BP1 up-regulation correlates with increased PC-1 expression in human prostate tumors and in PCa cells. Furthermore, PC-1 interacts directly with 4E-BP1 and stabilizes 4E-BP1 protein via inhibition of its ubiquitination and proteasomal degradation. Thus, PC-1 is a novel regulator of 4E-BP1 and our work suggests a potential mechanism through which PC-1 enhances PCa cell survival and malignant progression and increases chemoresistance. Thus, the PC-1-4E-BP1 interaction may represent a therapeutic target for treating advanced PCa.

The RANKL-RANK Story

Receptor activator of nuclear factor x03BA;B (RANK) and its ligand (RANKL) have originally been described for their key roles in bone metabolism and the immune system. Subsequently, it has been shown that the RANKL-RANK system is critical in the formation of mammary epithelia in lactating females and the thermoregulation of the central nervous system. RANKL and RANK are under the tight control of the female sex hormones estradiol and progesterone. A reduction of the circulating female sex hormones leading to an increase in RANKL-RANK signaling is the leading cause of osteoporosis in postmenopausal women. Denosumab, a human monoclonal anti-RANKL antibody, has been approved for the treatment of postmenopausal osteoporosis, where it is showing great promise. In addition, RANKL-RANK signaling also plays a critical role in other bone pathologies, bone metastasis or hormone-driven breast cancer. This review will highlight some of the functions of RANKL-RANK in bone turnover, the immune system and brain with a focus on the regulatory role of the female sex hormones.

The antitumor lignan Nortrachelogenin sensitizes prostate cancer cells to TRAIL-induced cell death by inhibition of the Akt pathway and growth factor signaling

Prostate cancer cells frequently develop resistance toward androgen-deprivation and chemotherapy. To identify new approaches to treat androgen-dependent prostate cancer, we have performed a structure-activity analysis of lignan polyphenols for cancer cell specific sensitization to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a death ligand that has ability to induce tumor-specific cell death. In this study, we report that the lignan nortrachelogenin (NTG) is the most efficient of the 27 tested lignan compounds in sensitizing prostate cancer cells to TRAIL-induced apoptosis. Importantly, pretreatment with NTG does not sensitize a non-malignant prostate cell line to TRAIL-induced cell death. The structural comparison of lignans reveals that the dibenzylbutyrolactone skeleton is required for the apoptosis-sensitizing activity, while substitutions at the aromatic rings do not seem to play a critical role in this lignan function. Our study also characterizes the cellular effects and molecular mechanisms involved in NTG anticancer activity. We previously reported that specific lignans inhibit the Akt survival-signaling pathway in concert with TRAIL sensitization. While NTG is also shown to be a effective inhibitor of Akt signaling, in this study we further demonstrate that NTG potently inhibits tyrosine kinase (RTK) activation in response to growth factors, such as insulin and insulin-like growth factor I (IGF-I). Our results identify NTG as a novel agent for prostate cancer therapy with ability to inhibit Akt membrane localization and activity as well as the activation of growth factor receptors (GFRs), thereby efficiently synergizing with TRAIL exposure.

Targeted agents in second-line bladder cancer therapy

The treatment of metastasized urothelial cancer has been evolving in recent years. In particular, in the second-line setting after the failure of platinum-containing therapy, options are few and besides vinflunine, the recently approved standard in Europe, well-designed highly selective clinical trials may be possible alternatives for patients in this palliative situation. However, targeted therapy approaches have not achieved the same results in urothelial cancer as for instance in renal cell carcinoma. Many of the new targeted drugs have been investigated as single agents in phase II clinical trials without convincing oncologic outcome. This review aims to highlight the most relevant clinical studies examining targeted agents in the second-line setting of metastasized transitional carcinoma of the urothelium.

Small interfering RNA targeting HMGN5 induces apoptosis via modulation of a mitochondrial pathway and Bcl-2 family proteins in prostate cancer cells

We investigated the importance of HMGN5, a nuclear protein that binds to nucleosomes, unfolds chromatin, and affects transcription, in the LNCaP prostate cancer cell line. We also examined the molecular mechanisms that promote apoptosis of LNCaP cells after infection with small interfering RNA (siRNA) targeting HMGN5 (siRNA-HMGN5). The androgen-dependent LNCaP human prostate cancer cells were infected with siRNA-HMGN5. Apoptosis was detected using the Annexin V-PE/7-AAD double staining and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assays. Mitochondrial membrane potential was measured by JC-1 staining. HMGN5 and GAPDH mRNA expression were determined using real-time PCR. Bcl-2 and other apoptosis-related protein levels were determined by Western blot analysis. Caspase activity was measured by cleavage of the caspase substrate. Infection with siRNA targeting HMGN5 efficiently and specifically reduced the HMGN5 expression in LNCaP cells. The downregulation of HMGN5 induced remarkable apoptosis of LNCaP cells and resulted in the reduction of mitochondrial membrane potential. The induction of cell apoptosis was accompanied by the upregulation of Bax, the Bax/Bcl-2 ratio and the activation of caspase3. The HMGN5-targeted siRNA was effective in downregulating the expression of HMGN5 in androgen-dependent prostate cancer cells and inducing cell apoptosis via the regulation of a caspase-related mitochondrial pathway and Bcl-2 family proteins. This study suggests that HMGN5 may be a potential molecular target with therapeutic relevance for the treatment of prostate cancer.

Alternol exerts prostate-selective antitumor effects through modulations of the AMPK signaling pathway

BACKGROUND

Alternol is an original compound purified from the fermentation products of Alternaria alternata var. monosporus, a microorganism from the bark of the yew tree. It has been reported that Alternol can inhibit proliferation of mouse leukemia cells and human gastric carcinoma cells, the aim of this study was to investigate the effects of Alternol on prostate cancer cells in comparison to prostate cells.

METHODS

The MTT assay was utilized to assess cell viability. Cell cycle was analyzed by flow cytometry with propidium iodide staining. Protein expression levels were examined by Western blotting.

RESULTS

Alternol treatment resulted in a significant decrease in the viability of prostate cancer cells but had lesser effects on prostate cells. Alternol inhibited AMP-activated protein kinase (AMPK) phosphorylation in prostate cancer C4-2 cells but stimulated AMPK phosphorylation in prostate RWPE-1 cells. Inhibition of p27 phosphorylation was observed in C4-2 cells whereas a promotion of p27 phosphorylation was seen in RWPE-1 cells. Alternol treatment resulted in a profound increase in the LC3II/LC3I protein ratio in RWPE-1 cells but not in C4-2 cells. A dose-dependent down-regulation of Bcl-2 protein was detected in C4-2 cells but not in RWPE-1 cells. Pretreatment of cells with Compound C (AMPK inhibitor) before Alternol treatment abolished the selective antitumor effect of Alternol.

CONCLUSIONS

These results reveal for the first time that Alternol exerts a selective antitumor effect on prostate cancer cells when compared with RWPE-1 prostate epithelial cells. In addition, the AMPK signaling pathway is responsible for the selective antitumor effects of Alternol.

[EAU guidelines on prostate cancer. Part II: treatment of advanced, relapsing, and castration-resistant prostate cancer]

OBJECTIVES

Our aim is to present a summary of the 2010 version of the European Association of Urology (EAU) guidelines on the treatment of advanced, relapsing, and castration-resistant prostate cancer (CRPC).

METHODS

The working panel performed a literature review of the new data emerging from 2007 to 2010. The guidelines were updated, and the levels of evidence (LEs) and/or grades of recommendation (GR) were added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews.

RESULTS

Luteinising hormone-releasing hormone (LHRH) agonists are the standard of care in metastatic prostate cancer (PCa). Although LHRH antagonists decrease testosterone without any testosterone surge, their clinical benefit remains to be determined. Complete androgen blockade has a small survival benefit of about 5%. Intermittent androgen deprivation (IAD) results in equivalent oncologic efficacy when compared with continuous androgen-deprivation therapy (ADT) in well-selected populations. In locally advanced and metastatic PCa, early ADT does not result in a significant survival advantage when compared with delayed ADT. Relapse after local therapy is defined by prostate-specific antigen (PSA) values > 0.2 ng/ml following radical prostatectomy (RP) and > 2 ng/ml above the nadir after radiation therapy (RT). Therapy for PSA relapse after RP includes salvage RT at PSA levels < 0.5 ng/ml and salvage RP or cryosurgical ablation of the prostate in radiation failures. Endorectal magnetic resonance imaging and 11C-choline positron emission tomography/computed tomography (CT) are of limited importance if the PSA is < 2.5 ng/ml; bone scans and CT can be omitted unless PSA is >20 ng/ml. Follow-up after ADT should include screening for the metabolic syndrome and an analysis of PSA and testosterone levels. Treatment of castration-resistant prostate cancer (CRPC) includes second-line hormonal therapy, novel agents, and chemotherapy with docetaxel at 75 mg/m(2) every 3 wk. Cabazitaxel as a second-line therapy for relapse after docetaxel might become a future option. Zoledronic acid and denusomab can be used in men with CRPC and osseous metastases to prevent skeletal-related complications.

CONCLUSION

The knowledge in the field of advanced, metastatic, and CRPC is rapidly changing. These EAU guidelines on PCa summarise the most recent findings and put them into clinical practice. A full version is available at the EAU office or online at www.uroweb.org.

Molecular Validation of PACE4 as a Target in Prostate Cancer

Prostate cancer remains the single most prevalent cancer in men. Standard therapies are still limited and include androgen ablation that initially causes tumor regression. However, tumor cells eventually relapse and develop into a hormone-refractory prostate cancer. One of the current challenges in this disease is to define new therapeutic targets, which have been virtually unchanged in the past 30 years. Recent studies have suggested that the family of enzymes known as the proprotein convertases (PCs) is involved in various types of cancers and their progression. The present study examined PC expression in prostate cancer and validates one PC, namely PACE4, as a target. The evidence includes the observed high expression of PACE4 in all different clinical stages of human prostate tumor tissues. Gene silencing studies targeting PACE4 in the DU145 prostate cancer cell line produced cells (cell line 4-2) with slower proliferation rates, reduced clonogenic activity, and inability to grow as xenografts in nude mice. Gene expression and proteomic profiling of the 4-2 cell line reveals an increased expression of known cancer-related genes (e.g., GJA1, CD44, IGFBP6) that are downregulated in prostate cancer. Similarly, cancer genes whose expression is decreased in the 4-2 cell line were upregulated in prostate cancer (e.g., MUC1, IL6). The direct role of PACE4 in prostate cancer is most likely through the upregulated processing of growth factors or through the aberrant processing of growth factors leading to sustained cancer progression, suggesting that PACE4 holds a central role in prostate cancer.

Emerging therapies in metastatic bone pain

INTRODUCTION

Current treatment for metastatic bone pain is mainly palliative. Recent insights into the molecular mechanisms involved in bone metastases have led to the identification of promising therapeutic targets. This review offers an update of preclinical and clinical data on new drugs for metastatic bone pain.

AREAS COVERED

Biphosphonates are the gold standard of bone-targeted therapy in bone metastases, for their anti-resorptive and analgesic effects. New drugs aim at breaking the 'vicious cycle' of bone metastatic disease, due to the bidirectional interaction between cancer cells and bone microenvironment. Osteoprotegerin, RANK/RANKL interaction, cathepsin K, the Wnt/beta-catenin pathway and sclerostin are emerging targets for modulation of cancer-induced bone desorption. Other promising targets are those expressed in cancer cells that metastasize to bone, including Src, nerve growth factor, endothelin A, TGF-beta and CXCR4. Interesting therapeutic options include targets on nociceptors that innervate the bone, such as TPRV1, Trk and cannabinoid receptors.

EXPERT OPINION

Emerging therapies promise, in the next 10 years, a significant expansion in the array of therapeutic options for bone metastases. Most of these drugs are still in an early phase of development. Further clinical trials are needed to support the evidence of their efficacy and tolerability profile.

Induction of in vitro and in vivo NK cell cytotoxicity using high-avidity immunoligands targeting prostate-specific membrane antigen in prostate carcinoma

Cancer that might develop as host natural killer (NK) cells fail to detect ligands for their activating NK receptors. Immunoligands represent promising immunotherapeutic tools to overcome this deficit. These are fusion proteins containing a single-chain antibody fragment (scFv) to target an available tumor antigen and ULBP2 to activate host NK cells by targeting the activatory receptor NKG2D. Prostate-specific membrane antigen (PSMA) is an integral non-shed type 2 membrane protein that is highly and specifically expressed on prostate epithelial cells and strongly upregulated in prostate cancer. Here, we compare the impact of various anti-PSMA immunoligand formats on the therapeutic efficacy against prostate carcinoma cells by activating NK cells via NKG2D. Shortening of the linker separating the heavy and light chain antibody domain leads to the formation of dimers, trimers, and higher molecular mass oligomers. NK cells are most efficiently activated by multimeric immunoligands, thus showing an altered cytokine release pattern. The high avidity format is also superior in in vitro NK-mediated tumor cell targeting as shown in cytotoxicity assays. Finally, the efficacy of a multimeric immunoligand is shown in a prostate carcinoma mouse xenograft model showing a strong activity against advanced established tumors.

Pharmacokinetics and tolerability of zibotentan (ZD4054) in subjects with hepatic or renal impairment: two open-label comparative studies

BACKGROUND

Zibotentan (ZD4054) is a specific endothelin A (ETA) receptor antagonist being investigated for the treatment of prostate cancer. As zibotentan is eliminated by renal and metabolic routes, clearance may be reduced in patients with hepatic or renal impairment, leading to greater drug exposure.

METHODS

Open-label studies investigated the PK and tolerability of zibotentan in subjects with hepatic or renal impairment, compared with those with normal organ function. In the hepatic and renal studies, respectively, subjects were divided into categories using Child-Pugh classification or 24-hour urine creatinine clearance (mild, moderate, or severe impairment and normal function). Each subject received a single oral dose of zibotentan 10 mg and PK sampling was undertaken. Within the hepatic study, AUC and Cmax were expressed as the ratio of geometric means and 90% CI for each impairment group compared with the normal function group. The possibility that hepatic impairment had a clinically relevant effect on exposure was considered if the upper 90% CI for the ratio exceeded 2. In the renal study, AUC, Cmax and t1/2 were analyzed using linear regression fitting effects for creatinine clearance and age.

RESULTS

In the hepatic and renal studies respectively, 32 subjects (eight per group) and 48 subjects received treatment (n = 18 normal, n = 12 mild, n = 9 moderate, n = 9 severe). Zibotentan Cmax was not significantly affected by hepatic or renal impairment. Compared with the normal function group, zibotentan AUC was 40% (1.40; 90% CI 0.91-2.17), 45% (1.45; 90% CI 0.94-2.24) and 190% (2.90; 90% CI 1.88-4.49) higher in subjects with mild, moderate and severe hepatic impairment, respectively, and 66% (1.66; 90% CI 1.38-1.99), 89% (1.89; 90% CI 1.50-2.39) and 117% (2.17; 90% CI 1.64-2.86) higher in subjects with mild, moderate and severe renal impairment, respectively. In both studies mean t1/2 increased and zibotentan clearance decreased with the degree of impairment. Headache was the most common AE in all groups.

CONCLUSIONS

Zibotentan absorption was unchanged, however, exposure was higher in subjects with hepatic or renal impairment due to slower clearance. This increased exposure did not result in differences in the range or severity of AEs observed.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00672581 and AstraZeneca study number D4320C00016 (renal trial; conducted in Germany).

Denosumab versus zoledronic acid for treatment of bone metastases in men with castration-resistant prostate cancer: a randomised, double-blind study

BACKGROUND

Bone metastases are a major burden in men with advanced prostate cancer. We compared denosumab, a human monoclonal antibody against RANKL, with zoledronic acid for prevention of skeletal-related events in men with bone metastases from castration-resistant prostate cancer.

METHODS

In this phase 3 study, men with castration-resistant prostate cancer and no previous exposure to intravenous bisphosphonate were enrolled from 342 centres in 39 countries. An interactive voice response system was used to assign patients (1:1 ratio), according to a computer-generated randomisation sequence, to receive 120 mg subcutaneous denosumab plus intravenous placebo, or 4 mg intravenous zoledronic acid plus subcutaneous placebo, every 4 weeks until the primary analysis cutoff date. Randomisation was stratified by previous skeletal-related event, prostate-specific antigen concentration, and chemotherapy for prostate cancer within 6 weeks before randomisation. Supplemental calcium and vitamin D were strongly recommended. Patients, study staff, and investigators were masked to treatment assignment. The primary endpoint was time to first on-study skeletal-related event (pathological fracture, radiation therapy, surgery to bone, or spinal cord compression), and was assessed for non-inferiority. The same outcome was further assessed for superiority as a secondary endpoint. Efficacy analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00321620, and has been completed.

FINDINGS

1904 patients were randomised, of whom 950 assigned to denosumab and 951 assigned to receive zoledronic acid were eligible for the efficacy analysis. Median duration on study at primary analysis cutoff date was 12·2 months (IQR 5·9-18·5) for patients on denosumab and 11·2 months (IQR 5·6-17·4) for those on zoledronic acid. Median time to first on-study skeletal-related event was 20·7 months (95% CI 18·8-24·9) with denosumab compared with 17·1 months (15·0-19·4) with zoledronic acid (hazard ratio 0·82, 95% CI 0·71-0·95; p = 0·0002 for non-inferiority; p = 0·008 for superiority). Adverse events were recorded in 916 patients (97%) on denosumab and 918 patients (97%) on zoledronic acid, and serious adverse events were recorded in 594 patients (63%) on denosumab and 568 patients (60%) on zoledronic acid. More events of hypocalcaemia occurred in the denosumab group (121 [13%]) than in the zoledronic acid group (55 [6%]; p<0·0001). Osteonecrosis of the jaw occurred infrequently (22 [2%] vs 12 [1%]; p = 0·09).

INTERPRETATION

Denosumab was better than zoledronic acid for prevention of skeletal-related events, and potentially represents a novel treatment option in men with bone metastases from castration-resistant prostate cancer.

FUNDING

Amgen.

EAU guidelines on prostate cancer. Part II: Treatment of advanced, relapsing, and castration-resistant prostate cancer

OBJECTIVES

Our aim is to present a summary of the 2010 version of the European Association of Urology (EAU) guidelines on the treatment of advanced, relapsing, and castration-resistant prostate cancer (CRPC).

METHODS

The working panel performed a literature review of the new data emerging from 2007 to 2010. The guidelines were updated, and the levels of evidence (LEs) and/or grades of recommendation (GR) were added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews.

RESULTS

Luteinising hormone-releasing hormone (LHRH) agonists are the standard of care in metastatic prostate cancer (PCa). Although LHRH antagonists decrease testosterone without any testosterone surge, their clinical benefit remains to be determined. Complete androgen blockade has a small survival benefit of about 5%. Intermittent androgen deprivation (IAD) results in equivalent oncologic efficacy when compared with continuous androgen-deprivation therapy (ADT) in well-selected populations. In locally advanced and metastatic PCa, early ADT does not result in a significant survival advantage when compared with delayed ADT. Relapse after local therapy is defined by prostate-specific antigen (PSA) values >0.2 ng/ml following radical prostatectomy (RP) and >2 ng/ml above the nadir after radiation therapy (RT). Therapy for PSA relapse after RP includes salvage RT at PSA levels <0.5 ng/ml and salvage RP or cryosurgical ablation of the prostate in radiation failures. Endorectal magnetic resonance imaging and (11)C-choline positron emission tomography/computed tomography (CT) are of limited importance if the PSA is <2.5 ng/ml; bone scans and CT can be omitted unless PSA is >20 ng/ml. Follow-up after ADT should include screening for the metabolic syndrome and an analysis of PSA and testosterone levels. Treatment of castration-resistant prostate cancer (CRPC) includes second-line hormonal therapy, novel agents, and chemotherapy with docetaxel at 75 mg/m(2) every 3 wk. Cabazitaxel as a second-line therapy for relapse after docetaxel might become a future option. Zoledronic acid and denusomab can be used in men with CRPC and osseous metastases to prevent skeletal-related complications.

CONCLUSION

The knowledge in the field of advanced, metastatic, and CRPC is rapidly changing. These EAU guidelines on PCa summarise the most recent findings and put them into clinical practice. A full version is available at the EAU office or online at www.uroweb.org.

Steroid signaling activation and intracellular localization of sex steroid receptors

In addition to stimulating gene transcription, sex steroids trigger rapid, non-genomic responses in the extra-nuclear compartment of target cells. These events take place within seconds or minutes after hormone administration and do not require transcriptional activity of sex steroid receptors. Depending on cell systems, activation of extra-nuclear signaling pathways by sex steroids fosters cell cycle progression, prevents apoptosis, leads to epigenetic modifications and increases cell migration through cytoskeleton changes. These findings have raised the question of intracellular localization of sex steroid receptors mediating these responses. During the past years, increasing evidence has shown that classical sex steroid receptors localized in the extra-nuclear compartment or close to membranes of target cells induce these events. The emerging picture is that a process of bidirectional control between signaling activation and sex steroid receptor localization regulates the outcome of hormonal responses in target cells. This mechanism ensures cell cycle progression in estradiol-treated breast cancer cells, and its derangement might occur in progression of human proliferative diseases. These findings will be reviewed here together with unexpected examples of the relationship between sex steroid receptor localization, signaling activation and biological responses in target cells. We apologize to scientists whose reports are not mentioned or extensively discussed owing to space limitations.