Therapeutic options for hormone-refractory prostate cancer in 2007

Regulation of SPDEF expression by DNA methylation in advanced prostate cancer

Introduction

Prostate cancer (PCa) presents a significant health challenge in men, with a substantial number of deaths attributed to metastatic castration resistant PCa (mCRPC). Moreover, African American men experience disproportionately high mortality rates due to PCa. This study delves into the pivotal role of SPDEF, a prostate specific Ets transcription factor, and its regulation by DNA methylation in the context of PCa progression.

Methods

We performed Epigenetic reprogramming using daily treatment with non-toxic dose of 5Aza-2-deoxycytidine (5Aza-dC) for two weeks to assess its impact on PDEF expression in prostate cancer cells. Next, we conducted functional studies on reprogrammed cells, including cell migration (wound-healing assay), invasion (Boyden-Chamber test), and proliferation (MTT assay) to comprehensively evaluate the consequences of altered PDEF expression. We used bisulfite sequencing (BSP) to examine DNA methylation at SPDEF promoter. Simultaneously, we utilized siRNA-mediated targeting of key DNMTs (DNMT1, DNMT3A, and DNMT3B) to elucidate their specific role in regulating PDEF. We measured mRNA and protein expressions using qRT-PCR and immune-blotting techniques, respectively.

Results

In this report, we observed that: a) there is a gradual decrease in SPDEF expression with a concomitant increase in methylated CpG sites within the SPDEF gene during prostate cancer progression from lower to higher Gleason grade; b) Expression of DNMT's (DNMT1, 3a and 3b) is increased during prostate cancer progression, and there is an inverse correlation between SPDEF and DNMT expression; c) SPDEF levels are decreased in RC77/T, a line of PCa cells from African American origin similar to PC3 and DU145 cells (CRPC cells), as compared to LNCaP cells , a line of androgen dependent cells,; d) the 5' CpG island of SPDEF gene are hypermethylated in SPDEF-negative CRPC ( PC3, DU145 and RC77/T) cell lines but the same regions are hypomethylated in SPDEF-positive castrate sensitive (LNCaP) cell line ; (e) expression of SPDEF in PCa cells lacking SPDEF decreases cell migration and invasion, but has no significant effect on cell proliferation, and; (f) treatment with the demethylating agent, 5-aza-2'-deoxycytidine, or silencing of the DNMT's by siRNA, partially restores SPDEF expression in SPDEF-negative PCa cell lines, and decreases cell migration and invasion.

Discussion

These results indicate hypermethylation is a prevalent mechanism for decreasing SPDEF expression during prostate cancer progression. The data demonstrate that loss of SPDEF expression in prostate cancer cells, a critical step in cellular plasticity, results from a potentially reversible process of aberrant DNA methylation. These studies suggest DMNT activity as a potential therapeutic vulnerability that can be exploited for limiting cellular plasticity, tumor progression, and therapy resistance in prostate cancer.

A study of gene expression by RNA-seq in patients with prostate cancer and in patients with Parkinson disease: an example of inverse comorbidity

BACKGROUND

Prostate cancer (PCa) is one of the leading causes of death in Western countries. Environmental and genetic factors play a pivotal role in PCa etiology. Timely identification of the genetic causes is useful for an early diagnosis. Parkinson's disease (PD) is the most frequent neurodegenerative movement disorder; it is associated with the presence of Lewy bodies and genetic factors are involved in its pathogenesis. Several studies have indicated that the expression of target genes in patients with PD is inversely related to cancer development; this phenomenon has been named "inverse comorbidity". The present study was undertaken to evaluate whether a genetic dysregulation occurs in opposite directions in patients with PD or PCa.

METHODS AND RESULTS

In the present study, next-generation sequencing transcriptome analysis was used to assess whether a genetic dysregulation in opposite directions occurs in patients with PD or PCa. The genes SLC30A1, ADO, SRGAP2C, and TBC1D12 resulted up-regulated in patients with PD compared to healthy donors as controls and down-regulated in patients with PCa compared with the same control group.

CONCLUSIONS

These results support the hypothesis of the presence of inverse comorbidity between PD and PCa.

1α,25-Dihydroxyvitamin D3 synergistically enhances anticancer effects of ginsenoside Rh2 in human prostate cancer cells

1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃, commonly known as calcitriol), the most active metabolite of vitamin D₃, and ginsenoside Rh2 can regulate cellular differentiation and proliferation proteins. The purpose of the present study was to assess the effect of 1,25(OH)₂D₃ on the anticancer activities of Rh2 in human prostate cancer cells such as androgen-dependent LNCaP and androgen-independent C4-2 in vitro. The effects of treatment with 1,25(OH)₂D₃ or Rh2, either alone or in combination, on prostate cancer cells were evaluated through tetrazolium-based cell viability assay, BrdU cell proliferation rate estimation assay, and Western blot protein expression analyses of nuclear receptors (androgen receptor and vitamin D receptors) and apoptotic proteins (Bcl-2, Bax, and Caspase 3). The Combination Indices (CI) and Dose Reduction Indices (DRI) of 1,25(OH)₂D₃ and Rh2 were calculated to determine synergistic anticancer activity using Calcusyn software (Biosoft, Cambridge, UK). The cell viability assay data indicate that Rh2 treatment alone inhibited cell viability in a concentration-dependent manner and the addition of 10 nM 1,25(OH)₂D₃ to Rh2 significantly enhanced its ability to reduce cell viability up to 80 % in both the cell lines. Similarly, addition of 10 nM 1,25(OH)₂D₃ to Rh2 significantly lowered its IC₅₀ values for cell proliferation from the range of 32-65 μM to 14-8 μM in LNCaP and C4-2 cells. In addition, protein expression analyses indicated that the combined treatment with Rh2 and 1,25(OH)₂D₃ led to greater downregulation of androgen receptor expression compared to single agent exposure. Similarly, the presence of 1,25(OH)₂D₃ synergistically increased the pro-apoptotic actions of Rh2 in both the cell lines. Overall, 1,25(OH)₂D₃ augments the Rh2-mediated anticancer effects through stimulating apoptosis and reduced cell proliferation which suggests that synergism of this combination may lead to potential lower need of the active vitamin D₃ and limited toxicity from it.

Nemo-like kinase as a negative regulator of nuclear receptor Nurr1 gene transcription in prostate cancer

Background

Nurr1, a member of the orphan receptor family, plays an important role in several types of cancer. Our previous work demonstrated that increased expression of Nurr1 plays a significant role in the initiation and progression of prostate cancer (PCa), though the mechanisms for regulation of Nurr1 expression remain unknown. In this study, we investigated the hypothesis that Nemo-like kinase (NLK) is a key regulator of Nurr1 expression in PCa.

Methods

Immunohistochemistry and Western blot analysis were used to evaluate levels of NLK and Nurr1 in prostatic tissues and cell lines. The effects of overexpression or knockdown of Nurr1 were evaluated in PCa cells through use of PCR, Western blots and promoter reporter assays. The role of Nurr1 promoter cis element was studied by creation of two mutant Nurr1 promoter luciferase constructs, one with a mutated NF-κB binding site and one with a mutated CREB binding site. In addition, three specific inhibitors were used to investigate the roles of these proteins in transcriptional activation of Nurr1, including BAY 11–7082 (NF-κB inhibitor), KG-501 (CREB inhibitor) and ICG-001 (CREB binding protein, CBP, inhibitor). The function of CBP in NLK-mediated regulation of Nurr1 expression was investigated using immunofluorescence, co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation assays (ChIPs).

Results

NLK expression was inversely correlated with Nurr1 expression in prostate cancer tissues and cell lines. Overexpression of NLK suppressed Nurr1 promoter activity, leading to downregulation of Nurr1 expression. In contrast, knockdown of NLK demonstrated opposite results, leading to upregulation of Nurr1. When compared with the wild-type Nurr1 promoter, mutation of NF-κB- and CREB-binding sites of the Nurr1 promoter region significantly reduced the upregulation of Nurr1 induced by knockdown of NLK in LNCaP cells; treatment with inhibitors of CREB, CBP and NF-κB led to similar results. We also found that NLK directly interacts with CBP, that knockdown of NLK significantly increases the recruitment of CBP to both NF-κB- and CREB-binding sites, and that regulation of NLK on Nurr1 expression is abrogated by knockdown of CBP.

Conclusions

Our results suggest that NLK inhibits transcriptional activation of Nurr1 gene by impeding CBP’s role as a co-activator of NF-κB and CREB in prostate cancer.

Calcitriol in Combination Therapy for Prostate Cancer: Pharmacokinetic and Pharmacodynamic Interactions

Epidemiological studies indicate that vitamin D insufficiency could have an etiological role in prostate cancer. In addition, calcitriol, used in combination with currently available drugs, has the potential to potentiate their anticancer effects or act synergistically by inhibiting distinct mechanisms involved in prostate cancer growth. Clinical data have not yet provided sufficient evidence to demonstrate benefit of vitamin D due to the limited and underpowered studies that have been published to date. Here, we review the preclinical and clinical studies that describe the activity of calcitriol, applied either alone or in combination and assessed the mechanistic basis of pharmacodynamic and pharmacokinetic interactions with calcitriol. Important considerations for calcitriol use in combination therapy with respect to safety and clinical outcomes have been discussed. Many of these combinations have therapeutic potential for the treatment of several cancer types and it is anticipated that future clinical research will put emphasis on well‑designed clinical trials to establish efficacy.

CXCR4 pharmacogical inhibition reduces bone and soft tissue metastatic burden by affecting tumor growth and tumorigenic potential in prostate cancer preclinical models

BACKGROUND

The majority of prostate cancer (Pca) patient morbidity can be attributed to bone metastatic events, which poses a significant clinical obstacle. Therefore, a better understanding of this phenomenon is imperative and might help to develop novel therapeutic strategies. Stromal cell-derived factor 1α (SDF-1α) and its receptor CXCR4 have been implicated as regulators of bone resorption and bone metastatic development, suggesting that agents able to suppress this signaling pathway may be used as pharmacological treatments. In this study we studied if two CXCR4 receptor antagonists, Plerixafor and CTE9908, may affect bone metastatic disease induced by Pca in preclinical experimental models

METHODS

To verify the hypothesis that CXCR4 inhibition affects Pca metastatic disease, selective CXCR4 compounds, Plerixafor, and CTE9908, were tested in preclinical models known to generate bone lesions. Additionally, the expression levels of CXCR4 and SDF-1α were analyzed in a number of human tissues derived from primary tumors, lymph-nodes and osseous metastases of Pca as well as in a wide panel of human Pca cell lines to non-tumorigenic and tumorigenic phenotype.

RESULTS

Bone-derived Pca cells express higher CXCR4 levels than other Pca cell lines. This differential expression was also observed in human Pca samples. In vitro evidence supports the hypothesis that factors produced by bone microenvironment differentially sustain CXCR4 and SDF1-α expression with respect to prostate microenvironment determining increased efficacy toward Plerixafor. The use of SDF1-α neutralizing antibodies greatly reduced the increase of CXCR4 expression in cells co-cultured with bone stromal cells (BMSc) and to a lesser extent in cells co-cultured with prostate stromal cells (HPSc) and partially reduced SDF1-α Plerixafor efficacy. SDF-1α induced tumor cell migration and invasion, as well as MMP-9, MMP-2, and uPA expression, which were reduced by Plerixafor. The incidence of X-ray detectable bone lesions was significantly reduced following Plerixafor and CTE9908 treatment Kaplan-Meier probability plots showed a significant improvement in the overall survival of mice treated with Plerixafor and CTE9908. The reduced intra-osseous growth of PC3 and PCb2 tumor cells after intratibial injection, as a result of Plerixafor and CTE9908 treatment, correlated with decreased osteolysis and serum levels of both mTRAP and type I collagen fragments (CTX), which were significantly lower with respect to controls.

CONCLUSIONS

Our report provides novel information on the potential activity of CXCR4 inhibitors on the formation and progression of Pca bone and soft tissue metastases and supports a biological rationale for the use of these inhibitors in men at high risk to develop clinically evident bone lesions.

Mcl-1 protects prostate cancer cells from cell death mediated by chemotherapy-induced DNA damage

The anti-apoptotic protein Mcl-1 is highly expressed in castration-resistant prostate cancer (CRPC), resulting in resistance to apoptosis and association with poor prognosis. Although predominantly localized in the cytoplasm, there is evidence that Mcl-1 exhibits nuclear localization where it is thought to protect against DNA damage-induced cell death. The role of Mcl-1 in mediating resistance to chemotherapy-induced DNA damage in prostate cancer (PCa) is not known. We show in human PCa cell lines and in TRAMP, a transgenic mouse model of PCa, that the combination of the antimitotic agent ENMD-1198 (analog of 2-methoxyestradiol) with betulinic acid (BA, increases proteotoxic stress) targets Mcl-1 by increasing its proteasomal degradation, resulting in increased γH2AX (DNA damage) and apoptotic/necrotic cell death. Knockdown of Mcl-1 in CRPC cells leads to elevated γH2AX, DNA strand breaks, and cell death after treatment with 1198 + BA- or doxorubicin. Additional knockdowns in PC3 cells suggests that cytoplasmic Mcl-1 protects against DNA damage by blocking the mitochondrial release of apoptosis-inducing factor and thereby preventing its nuclear translocation and subsequent interaction with the cyclophilin A endonuclease. Overall, our results suggest that chemotherapeutic agents that target Mcl-1 will promote cell death in response to DNA damage, particularly in CRPC.

Exosomes secreted under hypoxia enhance invasiveness and stemness of prostate cancer cells by targeting adherens junction molecules

Hypoxic conditions in prostate cancer (PCA) are associated with poor prognosis; however, precise mechanism/s through which hypoxia promotes malignant phenotype remains unclear. Here, we analyzed the role of exosomes from hypoxic PCA cells in enhancing the invasiveness and stemness of naïve PCA cells, as well as in promoting cancer-associated fibroblast (CAF) phenotype in prostate stromal cells (PrSC). Human PCA LNCaP and PC3 cells were exposed to hypoxic (1% O2 ) or normoxic (21% O2 ) conditions, and exosomes secreted under hypoxic (Exo(Hypoxic) ) and normoxic (Exo(Normoxic) ) conditions were isolated from conditioned media. Nanoparticle tracking analysis revealed that Exo(Hypoxic) have smaller average size as compared to Exo(Normoxic) . Immunoblotting results showed a higher level of tetraspanins (CD63 and CD81), heat shock proteins (HSP90 and HSP70), and Annexin II in Exo(Hypoxic) compared to Exo(Normoxic) . Co-culturing with Exo(Hypoxic) increased the invasiveness and motility of naïve LNCaP and PC3 cells, respectively. Exo(Hypoxic) also promoted prostasphere formation by both LNCaP and PC3 cells, and enhanced α-SMA (a CAF biomarker) expression in PrSC. Compared to Exo(Normoxic) , Exo(Hypoxic) showed higher metalloproteinases activity and increased level of diverse signaling molecules (TGF-β2, TNF1α, IL6, TSG101, Akt, ILK1, and β-catenin). Furthermore, proteome analysis revealed a higher number of proteins in Exo(Hypoxic) (160 proteins) compared to Exo(Normoxic) (62 proteins), primarily associated with the remodeling of epithelial adherens junction pathway. Importantly, Exo(Hypoxic) targeted the expression of adherens junction proteins in naïve PC3 cells. These findings suggest that Exo(Hypoxic) are loaded with unique proteins that could enhance invasiveness, stemness, and induce microenvironment changes; thereby, promoting PCA aggressiveness.

Changes of protein expression in prostate cancer having lost its androgen sensitivity

OBJECTIVE

The majority of prostate cancers require androgen hormones for growth, and androgen ablation is an important part of the systemic treatment of advanced prostate cancer. Nevertheless, most of these cancers eventually relapse as they become less sensitive to androgen ablation and anti-androgen treatment. Elucidating the molecular events that are responsible for the conversion of androgen-sensitive cancers to androgen-refractory tumors may reveal new therapeutic opportunities.

METHODS

In the present study, we investigated nine androgen-sensitive and nine androgen-refractory prostate cancer samples to evaluate the expression levels of 10 selected proteins that have been implicated in oncogenesis and cancer progression.

RESULTS

Our immunohistochemical data show that three of the investigated proteins (i.e., minichromosome maintenance-2, methylguanine-DNA methyltransferase, and androgen receptor) are expressed at significantly different levels in the androgen-refractory cancer samples than in the androgen-sensitive tumors, whereas the expression levels of the seven other studied proteins (i.e., β-catenin, p27, p21, p16, Ki67, hypoxia-inducible factor 1 alpha, and geminin) are not significantly different regarding the two groups.

CONCLUSIONS

Our data suggest that the increased expression of minichromosome maintenance-2 and decreased expression of methylguanine-DNA methyltransferase related to androgen receptor are indicative of the androgen-refractory stage in prostate cancer. Further studies are required to determine whether these expression changes play a causative role in the transition of androgen-sensitive to androgen-refractory prostate cancer.

Atelocollagen-mediated intravenous siRNA delivery specific to tumor tissues orthotopically xenografted in prostates of nude mice and its anticancer effects

Successful short interfering RNA (siRNA)-based therapy for cancers depends on functional siRNA delivery specific to tumors. In our previous report, we have shown systemic siRNA delivery specific to human prostate cancer cell line PC-3 subcutaneous tumors in nude mice by atelocollagen, a collagen derivative, for formulating a complex with siRNA. We used an siRNA for human Bcl-xL as a model target. In the present study, we examined the antitumor effect on PC-3 orthotopic tumors in nude mice, as these tumors resemble the human clinical situation. The systemic intravenous administration of the complex (siRNA, 50 μg/shot) significantly reduced Bcl-xL expression and induced apoptosis in the tumors, and suppressed their growth. Liver metastasis was also inhibited in the orthotopic model. We successfully showed tumor-specific accumulation of the siRNA by Cy3-labeled siRNA and the direct quantification of the siRNA via reverse-phase high-performance liquid chromatography. The tumor-specific delivery was achieved by the enhanced permeability and retention effect, which is characteristic of macromolecular drugs. The high expression of vascular endothelial growth factor-A in the tumors provided adequate conditions to promote the permeability in the tumors, and to finally form the enhanced permeability and retention effect. In conclusion, our siRNA delivery is specific to the PC-3 orthotopic tumors in nude mice, and is practically feasible to treat tumors.

Multiple roles for UDP-glucuronosyltransferase (UGT)2B15 and UGT2B17 enzymes in androgen metabolism and prostate cancer evolution

In the prostate, approximately 50% of androgens are from adrenal steroids, mainly dehydroepiandrosterone (DHEA), its sulfate and androstenedione. These compounds are converted first into testosterone, and then into the active hormone dihydrotestosterone (DHT). After having activated the androgen receptor (AR), DHT is reduced into androstane-3α-DIOL (3α-DIOL) and androsterone (ADT), which are subsequently converted into 2 inactive and easily excretable metabolites: 3α-DIOL-17glucuronide (3α-DIOL-17G) and ADT-3glucuronide (ADT-3G). The formation of these last derivatives through the glucuronidation reaction involves 2 UDP-glucuronosyltransferase (UGT) enzymes, namely UGT2B15 and UGT2B17. The present review article aims at providing a comprehensive view of the physiological and pharmacological importance of these 2 enzymes for the control of androgen homeostasis. We will resume: (i) how UGT2B15 and UGT2B17 contribute to androgen elimination; (ii) how their glucuronidation capacity influences the androgen signaling pathway in prostate cells; (iii) how they contribute to the anti-proliferative properties of AR antagonists in prostate cancer cells; and (iv) how AR and its spliced variants regulate the UGT2B15 and/or UGT2B17 genes expression. Finally, whether the unexploited AR-UGT axis could serve as a prognostic maker or a pharmacological target for novel therapeutics in the treatment of prostate cancer is also discussed. This article is part of a special issue entitled 'Essential role of DHEA'.

SNAI1 is critical for the aggressiveness of prostate cancer cells with low E-cadherin

BACKGROUND

A better molecular understanding of prostate carcinogenesis is warranted to devise novel targeted preventive and therapeutic strategies against prostate cancer (PCA), a major cause of mortality among men. Here, we examined the role of two epithelial-to-mesenchymal transition (EMT) regulators, the adherens junction protein E-cadherin and its transcriptional repressor SNAI1, in regulating the aggressiveness of PCA cells.

METHODS

The growth rate of human prostate carcinoma PC3 cells with stable knock-down of E-cadherin (ShEC-PC3) and respective control cells (Sh-PC3) was compared in MTT and clonogenic assays in cell culture and in nude mouse xenograft model in vivo. Stemness of ShEC-PC3 and Sh-PC3 cells was analyzed in prostasphere assay. Western blotting and immunohistochemistry (IHC) were used to study protein expression changes following E-cadherin and SNAI1 knock-down. Small interfering RNA (siRNA) technique was employed to knock- down SNAI1 protein expression in ShEC-PC3 cells.

RESULTS

ShEC-PC3 cells exerted higher proliferation rate both in cell culture and in athymic nude mice compared to Sh-PC3 cells. ShEC-PC3 cells also formed larger and a significantly higher number of prostaspheres suggesting an increase in the stem cell-like population with E-cadherin knock-down. Also, ShEC-PC3 prostaspheres disintegration, in the presence of serum and attachment, generated a bigger mass of proliferating cells as compared to Sh-PC3 prostaspheres. Immunoblotting/IHC analyses showed that E-cadherin knock-down increases the expression of regulators/biomarkers for stemness (CD44, cleaved Notch1 and Egr-1) and EMT (Vimentin, pSrc-tyr416, Integrin β3, β-catenin, and NF-κB) in cell culture and xenograft tissues. The expression of several bone metastasis related molecules namely CXCR4, uPA, RANKL and RunX2 was also increased in ShEC-PC3 cells. Importantly, we observed a remarkable increase in SNAI1 expression in cytoplasmic and nuclear fractions, prostaspheres and xenograft tissues of ShEC-PC3 cells. Furthermore, SNAI1 knock-down by specific siRNA strongly inhibited the prostasphere formation, clonogenicity and invasiveness, and decreased the level of pSrc-tyr416, total Src and CD44 in ShEC-PC3 cells. Characterization of RWPE-1, WPE1-NA22, WPE1-NB14 and DU-145 cells further confirmed that low E-cadherin is associated with higher SNAI1 expression and prostasphere formation.

CONCLUSIONS

Together, these results suggest that E-cadherin loss promotes SNAI1 expression that controls the aggressiveness of PCA cells.

ABT-737, a small molecule Bcl-2/Bcl-xL antagonist, increases antimitotic-mediated apoptosis in human prostate cancer cells

Castration-resistant prostate cancer (CRPC) expresses high levels of the anti-apoptotic proteins Bcl-2, Bcl-xL and Mcl-1, resulting in resistance to apoptosis and association with poor prognosis. Docetaxel, an antimitotic drug that is the first-line treatment strategy for CRPC, is known to provide a small survival benefit. However, docetaxel chemotherapy alone is not enough to counteract the high levels of Bcl-2/Bcl-xL/Mcl-1 present in CRPC. ABT-737 is a small molecule that binds to Bcl-2/Bcl-xL (but not Mcl-1) with high affinity and disrupts their interaction with pro-apoptotic Bax/Bak, thus enhancing apoptosis. Our results indicate that ABT-737 can sensitize androgen-dependent LNCaP and CRPC PC3 cells to docetaxel- and to the novel antimitotic ENMD-1198-mediated caspase-dependent apoptosis. CRPC DU145 cells, however, are more resistant to ABT-737 because they are Bax null and not because they express the highest levels of anti-apoptotic Mcl-1 (associated with ABT-737 resistance). Knockdown of Bax or Bak in LNCaP indicates that ABT-737-induced antimitotic enhancement of apoptosis is more dependent on the levels of Bax than Bak. Furthermore, we find that the ability of docetaxel to increase cyclin B1/Cdk1-mediated phosphorylation of Bcl-2/Bcl-xL and decrease Mcl-1 is required for ABT-737 to enhance apoptosis in PC3 cells, as determined by addition of Cdk1 inhibitor purvalanol A and expression of shRNA specific for cyclin B1. Overall, our data suggests that the high levels of anti-apoptotic proteins in Bax-expressing CRPC cells can be overcome by targeting Bcl-2/Bcl-xL with ABT-737 and Mcl-1 with antimitotics.

Nuclear receptors and endobiotics glucuronidation: the good, the bad, and the UGT

The recent progresses in molecular biology and pharmacology approaches allowed the characterization of a series of nuclear receptors (NRs) as efficient regulators of uridine diphosphate glucuronosyltransferase (UGT) genes activity. These regulatory processes ensure an optimized UGT expression in response to specific endo- and/or exogenous stimuli. Many of these NRs are activated by endobiotics that also are substrates for UGTs. Thus, by activating their receptors, these endogenous substances control their own conjugation, leading to the concept that glucuronidation is an important part of feed-forward/feedback mechanisms by which bioactive molecules control their own concentrations. On the other hand, numerous studies have established the pharmacological relevance of NR-UGT regulatory pathways in the response to therapeutic ligands. The present review article aims at providing a comprehensive view of the physiological and pharmacological importance of the NR regulation of the expression and activity of endobiotics-conjugating UGT enzymes. Selected examples will illustrate how the organism profits from the feed-forward/feedback mechanisms involving NR-UGT pathways, but also how such regulatory processes are involved in the initiation and/or progression of several pathological situations. Finally, we will discuss how the present pharmacopeia involves NR-dependent regulation of endobiotics glucuronidation, and whether the unexploited NR-UGT axes could serve as pharmacological targets for novel therapeutics to restore endobiotics homeostasis.

Chemokines and chemokine receptors as promoters of prostate cancer growth and progression

Prostate cancer (CaP) is estimated to be first in incidence among cancers, with more than 240,000 new cases in 2012 in the United States. Chemokines and their receptors provide survival, proliferation, and invasion characteristics to CaP cells in both primary sites of cancer and metastatic locations. The emerging data demonstrate that many chemokines and their receptors are involved in the multistep process of CaP, leading to metastasis, and, further, that these factors act cooperatively to enhance other mechanisms of tumor cell survival, growth, and metastasis. Changes of chemokine receptor cohorts may be necessary to activate tumor-promoting signals. Chemokine receptors can activate downstream effectors, such as mitogen-activated protein kinases, by complex mechanisms of ligand-dependent activation of cryptic growth factors; guanosine triphosphate-binding, protein-coupled activation of survival kinases; or transactivation of other receptors such as ErbB family members. We describe vanguard research in which more than the classic view of chemokine receptor biology was clarified. Control of chemokines and inhibition of their receptor activation may add critical tools to reduce tumor growth, especially in chemo-hormonal refractory CaP that is both currently incurable and the most aggressive form of the disease, accounting for most of the more than 28,000 annual deaths.

Trefoil factor 1 suppression of E-CADHERIN enhances prostate carcinoma cell invasiveness and metastasis

Metastasis is the primary mediator of prostate cancer (PCA) lethality and poses a significant clinical obstacle. The identification of factors involved in the metastasis of PCA is imperative. We demonstrate herein that trefoil factor 1 (TFF1) promotes PCA cell migration and invasion in vitro and metastasis in vivo. The capacity of TFF1 to enhance cell migration/invasion is mediated by transcriptional repression of E-CADHERIN. Consideration of targeted inhibition of TFF1 to prevent metastasis of prostate carcinoma is warranted.

CD49f is an efficient marker of monolayer- and spheroid colony-forming cells of the benign and malignant human prostate

Stem cells may play a role in the development and maintenance of proliferative diseases of the prostate such as prostate cancer and benign prostatic hyperplasia. Cell membrane protein markers, CD49f, CD133 and CD44, have been shown to identify putative prostate stem cells, but a lack of consensus exists with regards to the most efficient marker(s) for stem-like cell identification. This study aimed to determine whether previously reported markers had equal capacity to select monolayer and spheroid colony-forming cells (CFCs), which were used as surrogate readouts of stem-like cells, and to characterize the expression of CD49f, CD44 and CD133 by flow cytometry and immunohistochemistry.

In benign prostate cells, CD49f+, CD44+, and CD133+ cells represented 5.6±3.1%, 28.2±4.1% and 0.10±0.06% of total cells. Both monolayer- and spheroid-CFCs existed at a frequency of approximately 0.5% of total cells. CD49f+, CD44+, and CD133+ subpopulations differed significantly in their ability to select benign CFCs. The highest recovery of CFCs was achieved by CD49f+ selection (98%), whereas CD44+ or CD133+ selection led to poor CFC-recovery (17% and 3%, respectively). For the first time, we show highly efficient recovery of CFCs from advanced prostate cancer by CD49f+, but not by CD44+ or CD133+ selection. Furthermore, CD133 expression (AC133 clone) could not be detected in benign prostate cells by either immunohistochemistry or flow cytometry. We conclude that CD49f, but not previously described stem cell markers CD133 and CD44, to be optimal for selection of monolayer- and spheroid-CFCs in the benign and malignant prostate.

Claudin-4-targeted therapy using Clostridium perfringens enterotoxin for prostate cancer

BACKGROUND

Clostridium perfringens enterotoxin (CPE) triggers lysis of epithelial cells through binding to tight-junction proteins claudin-3 (Cldn3) and Cldn4, which are over-expressed in prostate cancer. We investigated the potential of Cldn-targeted therapy using CPE.

METHODS

We investigated the expression levels and subcellular localization of Cldn3 and Cldn4 in primary human prostate cancer tissues, human prostate cancer cell lines (22Rv1, DU145, and PC3) and normal human prostate epithelial cells (PrECs). Cytotoxic effects of CPE on these cells were examined by colorimetric assay. We studied whether knockdown of Cldn3 and/or Cldn4 expression using RNA interference influenced CPE-mediated cytotoxicity. The therapeutic effect of CPE was evaluated in PC3 xenografts in athymic mice.

RESULTS

Cldn4 and Cldn3 were expressed in primary human prostate cancer tissues, 22Rv1, DU145, and PC3. Cldn4 protein was expressed in PrEC. Cldn4 was distributed along whole cell membranes of the cancer cell lines, whereas it was localized at tight junctions in PrEC. CPE-mediated cytotoxicity was greatly detected in PC3, but was hardly detectable in PrEC. Reduced expression of Cldn4, but not Cldn3, led to remarkable decreases of cytotoxicity in both PC3 and 22Rv1. The injection of CPE around PC3 xenografts significantly suppressed tumor growth.

CONCLUSION

CPE-mediated cytotoxicity was observed in human prostate cancer cell lines, but barely detected in normal human PrECs. The cytotoxic effect depended not only on the expression level of Cldn4 protein but also on its subcellular localization. These results suggest that Cldn4-targeted therapy using CPE may be a new treatment for prostate cancer.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.

Role of E-cadherin in antimigratory and antiinvasive efficacy of silibinin in prostate cancer cells

The epithelial-to-mesenchymal transition (EMT) in prostate cancer (PCA) cells is considered prerequisite for acquiring migratory/invasive phenotype, and subsequent metastasis. We hypothesized that promoting the E-cadherin expression in PCA cells by using nontoxic phytochemicals, like silibinin, would prevent EMT and consequently invasiveness. Our results showed that silibinin treatment (5-90 μmol/L) significantly inhibits migratory and invasive potential of advance human PCA PC3, PC3MM2, and C4-2B cells in in vitro assays. Importantly, the antimigratory/antiinvasive efficacy of silibinin was not due to its cytotoxicity toward PCA cells. Molecular analyses showed that silibinin increases E-cadherin level that was localized mainly at cellular membrane as evidenced by subcellular fractional and confocal analyses in PC3 cells, which might be responsible for morphologically observed shift toward epithelial character. Silibinin also decreased the levels of Slug, Snail, phospho-Akt(ser(473)), nuclear β-catenin, phospho-Src(tyr(419)) and Hakai; together they play an important role in regulating E-cadherin expression/function and EMT. Similar silibinin effects on E-cadherin, β-catenin, phospho-Src(tyr(419)), and Hakai levels were also observed in PC3MM2 and C4-2B PCA cells. Selective Src inhibition by dasatinib also showed increased E-cadherin expression in PC3 cells suggesting a possible involvement of Src inhibition in silibinin-caused increase in E-cadherin level. Additional studies in PC3 cells with stable knock-down of E-cadherin expression revealed that antimigratory/antiinvasive efficacy of silibinin is in-part dependent on E-cadherin expression. Together, our results showing antimigratory/antiinvasive effects of silibinin and associated mechanisms suggest that silibinin should be tested further in clinically relevant animal models toward exploiting its potential benefits against metastatic PCA.

Transcription factor Stat5 knockdown enhances androgen receptor degradation and delays castration-resistant prostate cancer progression in vivo

Signal transducer and activator of transcription 5 (Stat5) plays an important role in the transition of prostate cancer (PCa) to its castrate-resistant state. Pharmacologic targeting of Stat5 is a rational approach to delay castrate-resistant progression, in part, because Stat5 cooperates with the androgen receptor (AR) to promote PCa progression. Immunostaining of tissue microarrays was used to correlate Stat5 expression with Gleason grade and to characterize changes in treatment-naive and androgen-deprived human PCa. Potency of a Stat5 antisense oligonucleotide (ASO) on Stat5 knockdown, cell growth, and apoptosis was assessed in LNCaP, C4-2, and DU145 cells. Effects of Stat5 knockdown on AR activity and stability was assessed using a PSA transactivation-luciferase assay and cyclohexamide plus MG132 treatment, respectively. LNCaP tumor-bearing mice were castrated and randomly assigned to treatment with Stat5-ASO or controls. Here, we show that the frequency of Stat5 expression is significantly increased in high Gleason grade as well as in hormone-treated PCa. Also, specific knockdown of Stat5 with ASO abrogates androgen-induced AR nuclear translocation and PSA transactivation despite R1881 stimulation. Moreover, Stat5 knockdown destabilizes AR, which leads to AR degradation via the proteasome. Shown for the first time as a preclinical proof-of-principle, Stat5 knockdown with Stat5-ASO significantly delays CRPC tumor progression in vivo. Thereby, we are able to recapitulate our in vitro results by reducing serum PSA and expression levels of target proteins in the xenograft tumors.

Antimetastatic efficacy of silibinin: molecular mechanisms and therapeutic potential against cancer

Cancer is a major health problem around the world. Research efforts in the last few decades have been successful in providing better and effective treatments against both early stage and localized cancer, but clinical options against advanced metastatic stage/s of cancer remain limited. The high morbidity and mortality in most of the cancers are attributed to their metastatic spread to distant organs. Due to its extreme clinical relevance, metastasis has been extensively studied and is now understood as a highly complex biological event that involves multiple steps including acquisition of invasiveness by cancer cells, intravasation into circulatory system, survival in the circulation, arrest in microvasculature, extravasation, and growth at distant organs. The increasing understanding of molecular underpinnings of these events has provided excellent opportunity to target metastasis especially through nontoxic and biologically effective nutraceuticals. Silibinin, a popular dietary supplement isolated from milk thistle seed extracts, is one such natural agent that has shown biological efficacy through pleiotropic mechanisms against a variety of cancers and is currently in clinical trials. Recent preclinical studies have also shown strong efficacy of silibinin to target cancer cell's migratory and invasive characteristics as well as their ability to metastasize to distant organs. Detailed mechanistic analyses revealed that silibinin targets signaling molecules involved in the regulation of epithelial-to-mesenchymal transition, proteases activation, adhesion, motility, invasiveness as well as the supportive tumor-microenvironment components, thereby inhibiting metastasis. Overall, the long history of human use, remarkable nontoxicity, and preclinical efficacy strongly favor the clinical use of silibinin against advanced metastatic cancers.

NF-kappaB activation enhances cell death by antimitotic drugs in human prostate cancer cells

Background

NF-κB is a transcription factor that promotes inhibition of apoptosis and resistance to chemotherapy. It is commonly believed that inhibition of NF-κB activity can increase sensitivity of cancer cells to chemotherapy. However, there is evidence that NF-κB activation can sensitize cells to apoptosis and that inhibition of NF-κB results in resistance to chemotherapy. In prostate cancer, it is not clear in the different cell types (androgen-dependent and castration-resistant) if activation or inhibition of NF-κB is required for stimulation of apoptosis by chemotherapy.

Results

Our data indicate that the response of prostate cancer (PC) cells to the antimitotic drugs docetaxel (Doc) and 2-methoxyestradiol (2ME2) is dependent on the levels of NF-κB activity. In androgen-dependent LNCaP cells, Doc and 2ME2 treatment increased the low basal NF-κB activity, as determined by Western blot analysis of phospho-IκBα/p65, NF-κB promoter reporter assays, and p65 localization. Treatment of LNCaP cells with parthenolide, a pharmacologic inhibitor of NF-κB, or introduction of dominant-negative IκBα, or an shRNA specific for p65, a component of the NF-κB heterodimer, blocked apoptosis induced by Doc and 2ME2. In castration-resistant DU145 and PC3 cells, Doc and 2ME2 had little effect on the high basal NF-κB activity and addition of parthenolide did not enhance cell death. However, the combination of Doc or 2ME2 with betulinic acid (BA), a triterpenoid that activates NF-κB, stimulated apoptosis in LNCaP and non-apoptotic cell death in DU145 and PC3 cells. Increased sensitivity to cell death mediated by the Doc or 2ME2 + BA combination is likely due to increased NF-κB activity.

Conclusions

Our data suggest that the combination of antimitotic drugs with NF-κB inhibitors will have antagonistic effects in a common type of PC cell typical of LNCaP. However, combination strategies utilizing antimitotic drugs with BA, an activator of NF-κB, will universally enhance cell death in PC cells, notably in the aggressive, castration-resistant variety that does not respond to conventional therapies.

A phase I clinical study of high dose ketoconazole plus weekly docetaxel for metastatic castration resistant prostate cancer

PURPOSE

This phase I study of high dose ketoconazole and docetaxel was designed against castration resistant prostate cancer to determine the maximum tolerated doses, side effects, and pharmacokinetic interaction of co-administered docetaxel and ketoconazole.

MATERIALS AND METHODS

Patients with metastatic castration resistant prostate cancer received weekly docetaxel for 3 of every 4 weeks plus daily ketoconazole. Pharmacokinetic studies were performed on day 1 (docetaxel alone) and day 16 (after ketoconazole).

RESULTS

The study enrolled 42 patients at 9 different dose levels. The combination regimens investigated included docetaxel weekly, increasing from 5 to 43 mg/m(2), with starting doses of 600, 800 or 1,200 mg ketoconazole daily. Decreases in prostate specific antigen of 50% or greater were seen in 62% of patients. Of 25 patients with soft tissue disease 7 (28%) had a partial response. Median overall survival was 22.8 months and was significantly greater in docetaxel naïve patients than in patients pretreated with docetaxel (36.8 vs 10.3 months, p = 0.0001). The most frequently observed adverse events were anemia, edema, fatigue, diarrhea, nausea, sensory neuropathy and elevated liver function tests. The fractional change in docetaxel clearance correlated significantly with ketoconazole exposure (p <0.01). Concomitant ketoconazole increased docetaxel exposure 2.6-fold with 1,200 mg daily, 1.6-fold with 800 mg daily and approximately 1.3 to 1.5-fold with 600 mg daily.

CONCLUSIONS

Combination regimens using 600 mg ketoconazole daily were fairly well tolerated and the maximum tolerated dose of docetaxel was 32 mg/m(2). Results suggest that the combination has significant antitumor activity in castration resistant prostate cancer. The long survival in the docetaxel naïve cohort warrants additional, larger trials of docetaxel with ketoconazole or possibly CYP17A1 inhibitors such as abiraterone.

KLK5 gene expression is severely upregulated in androgen-independent prostate cancer cells after treatment with the chemotherapeutic agents docetaxel and mitoxantrone

Kallikrein-related peptidases (KLKs), includingKLK5, have been proposed as promising biomarkers for prostate cancer diagnosis and prognosis. In the present study, we report that distinct augmentations (up to 6.4-fold) ofKLK5mRNA expressional levels, calculated via quantitative real-time PCR, occur after treatment of DU145 cells with appropriate concentrations, determined by the MTT method, of docetaxel and mitoxantrone. Our data reveal the endogenous need of prostate cancer cells for modifiedKLK5expression to cope with the administration of chemotherapeutic drugs. Furthermore, it is proposed that the expression profile ofKLK5could serve as a putative biomarker for monitoring the treatment response in hormone refractory prostate cancer patients.

CXC receptor-1 silencing inhibits androgen-independent prostate cancer

The CXC receptor-1 (CXCR1) is a coreceptor for interleukin-8 (IL-8) and is expressed on both normal and tumor cells. The function of CXCR1 in prostate cancer was investigated by silencing its expression, using RNA interference. We established stable cell colonies of PC-3 cells, depleted of CXCR1, using lentiviral plasmids (pLK0.1puro) generating small hairpin RNA (shRNA) against CXCR1 mRNA. Stable shRNA transfectants (PLK1-PLK5) that express significantly reduced CXCR1 mRNA (>or=90% down) and protein (>or=43% down) or vector-only transfectants (PC-3V) were characterized. PLK cells showed reduced cell proliferation (down, >or=66%), due to cell cycle arrest at G(1)-S phase, decreases in Cyclin D1, CDK4, phosphorylated Rb, and extracellular signal-regulated kinase 1/2 levels compared with those in PC-3V cells. CXCR1 depletion lead to increases in spontaneous apoptosis by mitochondria-mediated intrinsic mechanism and increases in proapoptotic proteins (BAD, 40%; BAX, 12%), but decreases in antiapoptotic proteins (BCL2, down 38%; BCL(xL), 20%). PLK2 cells grew as slow-growing tumors (decrease of 54%), compared with that of PC3V tumors in athymic mice. Ex vivo analyses of PLK2 tumor tissues showed reduced expression of Cyclin D1 and vascular endothelial growth factor, and increased apoptosis activity. Other IL-8-expressing prostate cancer cell lines also exhibited similar phenotypes when CXCR1 was depleted by CXCR1 shRNA transfection. In contrast to these cells, CXCR1 depletion had little effect on IL-8 ligand-deficient LNCaP cells. RNA interference rescue using mutated CXCR1 plasmids reversed the silencing effect of PLK2, thus demonstrating the specificity of phenotypic alteration by CXCR1 shRNA. These studies establish that CXCR1 promotes IL-8-mediated tumor growth.

Hyaluronic acid and HYAL-1 in prostate biopsy specimens: predictors of biochemical recurrence

PURPOSE

Molecular markers could aid prostate specific antigen, biopsy Gleason sum and clinical stage to provide accurate information on prostate cancer progression. HYAL-1 hyaluronidase and hyaluronic acid staining in prostatectomy specimens predicts biochemical recurrence. We examined whether hyaluronic acid and HYAL-1 staining in biopsy specimens predicts biochemical recurrence and correlates with staining in matched prostatectomy specimens.

MATERIALS AND METHODS

Biopsy and prostatectomy specimens were obtained from 61 patients with clinically localized prostate cancer from multiple centers, including 23 with (group 1) and 38 without (group 2) biochemical recurrence. Mean followup was 103.1 months. Biotinylated hyaluronic acid binding protein and anti-HYAL-1 antibody were used for hyaluronic acid and HYAL-1 staining, respectively. Staining was graded between 0 and 300 depending on staining intensity and area.

RESULTS

HYAL-1 and hyaluronic acid were expressed in tumor cells and stroma, respectively. In biopsy specimens HYAL-1 and hyaluronic acid expression was higher in group 1 than in group 2 (203.9 and 182.1 vs 48.8 and 87.0, respectively, p <0.0001). On univariate analysis hyaluronic acid, HYAL-1, biopsy Gleason and prostate specific antigen significantly predicted biochemical recurrence (p <0.001). On multivariate analysis only HYAL-1 staining independently predicted recurrence with an accuracy of 81.8% (p <0.001). In prostatectomy specimens only HYAL-1 staining correlated with staining in biopsy specimens (Spearman rho = 0.72, p = 0.0002) and predicted biochemical recurrence.

CONCLUSIONS

To our knowledge this is the first report that HYAL-1 staining in biopsy specimens is an independent predictor of biochemical recurrence. This may be useful when selecting treatment.

Depletion of intrinsic expression of Interleukin-8 in prostate cancer cells causes cell cycle arrest, spontaneous apoptosis and increases the efficacy of chemotherapeutic drugs

Background

The progression of all cancers is characterized by increased-cell proliferation and decreased-apoptosis. The androgen-independent prostate cancer (AIPC) is the terminal stage of the disease. Many chemokines and cytokines are suspects to cause this increased tumor cell survival that ultimately leads to resistance to therapy and demise of the host. The AIPC cells, but not androgen-responsive cells, constitutively express abundant amount of the pro-inflammatory chemokine, Interleukin-8 (IL-8). The mechanism of IL-8 mediated survival and therapeutic resistance in AIPC cells is unclear at present. The purpose of this report is to show the pervasive role of IL-8 in malignant progression of androgen-independent prostate cancer (AIPC) and to provide a potential new therapeutic avenue, using RNA interference.

Results

The functional consequence of IL-8 depletion in AIPC cells was investigated by RNA interference in two IL-8 secreting AIPC cell lines, PC-3 and DU145. The non-IL-8 secreting LNCaP and LAPC-4 cells served as controls. Cells were transfected with RISC-free siRNA (control) or validated-pool of IL-8 siRNA. Transfection with 50 nM IL-8 siRNA caused >95% depletion of IL-8 mRNA and >92% decrease in IL-8 protein. This reduction in IL-8 led to cell cycle arrest at G₁/S boundary and decreases in cell cycle-regulated proteins: Cyclin D1 and Cyclin B1 (both decreased >50%) and inhibition of ERK1/2 activity by >50%. Further, the spontaneous apoptosis was increased by >43% in IL-8 depleted cells, evidenced by increases in caspase-9 activation and cleaved-PARP. IL-8 depletion caused significant decreases in anti-apoptotic proteins, BCL-2, BCL-xL due to decrease in both mRNA and post-translational stability, and increased levels of pro-apoptotic BAX and BAD proteins. More significantly, depletion of intracellular IL-8 increased the cytotoxic activity of multiple chemotherapeutic drugs. Specifically, the cytotoxicity of Docetaxel, Staurosporine and Rapamycin increased significantly (>40% at IC₅₀ dose) in IL-8 depleted cells as compared to that in C-siRNA transfected cells.

Conclusion

These results show the pervasive role of IL-8 in promoting tumor cell survival, and resistance to cytotoxic drugs, regardless of the cytotoxic mechanism of antiproliferative drugs, and point to potential therapeutic significance of IL-8 depletion in men with AIPC.

Expression of the Bcl-2 protein BAD promotes prostate cancer growth

BAD, a pro-apoptotic protein of the Bcl-2 family, has recently been identified as an integrator of several anti-apoptotic signaling pathways in prostate cancer cells. Thus, activation of EGFR, GPCRs or PI3K pathway leads to BAD phosphorylation and inhibition of apoptosis. Increased levels of BAD in prostate carcinomas have also been reported. It appears contradictory that instead of limiting expression of pro-apoptotic protein, prostate cancer cells choose to increase BAD levels while keeping it under tight phosphorylation control. Analysis of the effect of BAD on prostate cancer xenografts has shown that increased BAD expression enhances tumor growth, while knockdown of BAD expression by shRNA inhibits tumor growth. Tissue culture experiments demonstrated that increased BAD expression stimulates proliferation of prostate cancer cells. These results suggest that increased expression of BAD provides a proliferative advantage to prostate tumors, while BAD dephosphorylation increases sensitivity of prostate cancer cells to apoptosis. Combination of proliferative and apoptotic properties prompts prostate cancer cells to be "addicted" to increased levels of phosphorylated BAD. Thus, kinases that phosphorylate BAD are plausible therapeutic targets; while monitoring BAD phosphorylation could be used to predict tumor response to treatments.

Somatostatin analog lanreotide in the treatment of castration-resistant prostate cancer (CRPC)

Prostate cancer is a common disease affecting males. Despite initial sensitivity to hormone treatment, prostate cancer eventually progresses to a castration-resistant stage (CRPC), which carries an ominous prognosis. Lanreotide is a long-acting somatostatin analog with the same properties with the native peptide. It has been shown to be highly efficacious in treating various hypersecretoty disorders and tumors. Lanreotide has been administered to patients with CRPC within a novel treatment concept, with the aim of targeting not only cancer cells but also various factors secreted in the tumor cell milieu that confer protection from apoptosis. Within this concept, lanreotide has been administered as part of the "antisurvival factor therapy" in combination with dexamethasone and a gonadotropin releasing hormone (GnRH) analog. It has also been given combined with oestrogens in patients with CRPC. The so far published series have documented a clinical response in many patients treated along with significant improvement in parameters related to quality of life. In view of these promising results, large-scale, randomized, controlled trials are warranted to clearly define the exact role of lanreotide and other somatostatin analogs in the treatment of patients with CRPC.

Silibinin inhibits established prostate tumor growth, progression, invasion, and metastasis and suppresses tumor angiogenesis and epithelial-mesenchymal transition in transgenic adenocarcinoma of the mouse prostate model mice

PURPOSE

The chronic nature of prostate cancer growth and progression leading to metastasis provides a large window for intervention. Herein, for the first time, we investigated the effect and associated mechanisms of silibinin phosphatidylcholine (silybin-phytosome) on established prostate tumors in transgenic adenocarcinoma of the mouse prostate (TRAMP) model.

EXPERIMENTAL DESIGN

Twenty-week-old TRAMP male mice having palpable prostate tumor were fed with control or 0.5% and 1%, w/w, silybin-phytosome diets for 11 weeks and then sacrificed.

RESULTS

Dietary silibinin inhibited the growth of prostate tumors (up to 60%, P < 0.001) and suppressed tumor progression from prostatic intraepithelial neoplasia to differentiated adenocarcinoma and poorly differentiated adenocarcinoma, with a complete absence of poorly differentiated adenocarcinoma at higher doses. It also inhibited the incidence of tumor invasion of seminal vesicle (up to 81%, P < 0.001) with complete absence of distant metastasis. Silibinin moderately inhibited tumor cell proliferation and induced apoptosis, but strongly suppressed tumor microvessel density (up to 60%, P < 0.001), vascular endothelial growth factor, and vascular endothelial growth factor receptor-2 expression. Antibody array analysis of plasma showed a decrease in the circulatory levels of vascular endothelial growth factor and basic fibroblast growth factor. Decreased levels of matrix metalloproteinases (MMP), snail-1, and vimentin, and an increased level of E-cadherin were also observed, indicating the anti-epithelial-mesenchymal transition effect of silibinin in tumors.

CONCLUSIONS

Overall, silibinin treatment of TRAMP mice bearing prostate tumor inhibited tumor growth, progression, local invasion, and distant metastasis involving suppression of tumor angiogenesis and epithelial-mesenchymal transition. These findings would have greater relevance for the ongoing phase II clinical trial with silibinin-phytosome in prostate cancer patients.

p21/Cip1 and p27/Kip1 Are essential molecular targets of inositol hexaphosphate for its antitumor efficacy against prostate cancer

Inositol hexaphosphate (IP6) causes G(1) arrest and increases cyclin-dependent kinase inhibitors p21/Cip1 and p27/Kip1 protein levels in human prostate cancer (PCa) DU145 cells lacking functional p53. However, whether cyclin-dependent kinase inhibitor I induction by IP6 plays any role in its antitumor efficacy is unknown. Herein, we observed that either p21 or p27 knockdown by small interfering RNA has no considerable effect on IP6-induced G(1) arrest, growth inhibition, and death in DU145 cells; however, the simultaneous knockdown of both p21 and p27 reversed the effects of IP6. To further confirm these findings both in vitro and in vivo, we generated DU145 cell variants with knockdown levels of p21 (DU-p21), p27 (DU-p27), or both (DU-p21+p27) via retroviral transduction of respective short hairpin RNAs. Knocking down p21 or p27 individually did not alter IP6-caused cell growth inhibition and G(1) arrest; however, their simultaneous ablation completely reversed the effects of IP6. In tumor xenograft studies, IP6 (2% w/v, in drinking water) caused a comparable reduction in tumor volume (40-46%) and tumor cell proliferation (26-28%) in DU-EV (control), DU-p21, and DU-p27 tumors but lost most of its effect in DU-p21+p27 tumors. IP6-caused apoptosis also occurred in a Cip/Kip-dependent manner because DU-p21+p27 cells were completely resistant to IP6-induced apoptosis both in cell culture and xenograft. Together, these results provide evidence, for the first time, of the critical role of p21 and p27 in mediating the anticancer efficacy of IP6, and suggest their redundant role in the antiproliferative and proapoptotic effects of IP6 in p53-lacking human PCa cells, both in vitro and in vivo.

[Management of metastatic androgeno-independent prostate cancer]

After first line hormonal therapy (agonist LHRH), metastasic prostate cancer becomes androgen independent in a period of 18 months on average. After this period and after having verified the castration by blood testosterone level, a few options are possible: either inhibit adrenal androgens by maximum androgen blockage (+anti androgens) or by specific adrenal androgen inhibitors. It is also possible to use estrogen or, in a few cases, to propose chemotherapy.

Cyclin D1 repressor domain mediates proliferation and survival in prostate cancer

Regulation of the androgen receptor (AR) is critical to prostate cancer (PCa) development; therefore, AR is the first line therapeutic target for disseminated tumors. Cell cycle dependent accumulation of cyclin D1 negatively modulates the transcriptional regulation of the AR through discrete, CDK4-independent mechanisms. The transcriptional co-repressor function of cyclin D1 resides within a defined motif termed ther repressor domain (RD), and it was hypothesized that this motif could be utilized as a platform to develop new strategies for blocking AR function. Here, we demonstrate that expression of the RD peptide is sufficient to disrupt AR transcriptional activation of multiple, prostate-specific AR target genes. Importantly, these actions are sufficient to specifically inhibit S-phase progression in AR-positive PCa cells, but not in AR-negative cells or tested AR-positive cells of other lineages. As expected, impaired cell cycle progression resulted in a suppression of cell doubling. Additionally, cell death was observed in AR-positive cells that maintain androgen dependence and in a subset of castrate-resistant PCa cells, dependent on Akt activation status. Lastly, the ability of RD to cooperate with existing hormone therapies was examined, which revealed that RD enhanced the cellular response to an AR antagonist. Together, these data demonstrate that RD is sufficient to disrupt AR-dependent transcriptional and proliferative responses in PCa, and can enhance efficacy of AR antagonists, thus establishing the impetus for development of RD-based mimetics.

Identification of molecular targets in urologic oncology

OBJECTIVES

Molecular targets in cancer diagnosis and therapy have come to the fore of the oncology field in the last decade. Their identification is rooted in basic science investigation and enhanced knowledge in the fields of genetics, biochemistry, molecular and tumor biology, and pathology among others.

METHODS

A medical literature search in English using MEDLINE/PUBMed was performed on the topics of molecular targets, targeted therapy, and biomarkers in the areas of bladder, prostate, and renal cancers. This information was analyzed and combined with the author's personal knowledge in the identification and development of molecular targets. Data is included from the author's laboratory regarding examples of target development and clinical translation.

RESULTS

Molecular targets are often biomarkers; either prognostic ones that reflect the natural history of the cancer or predictive ones that reflect the impact of a therapy. Molecular targets in urologic cancer may arise from four sources: the host, the tumor, as a result of a treatment, or associated with a specific disease stage. Understanding the continuum of targets through the progression of a urologic cancer is central to the translational applications of diagnostics, individualized medicine and targeted therapeutics. Urologists are most familiar with targeted therapy in renal cancer with the introduction of tyrosine kinase inhibitors. Yet, herein are examples of biomarkers and targets across the spectrum of urologic tumors, stages and treatments.

CONCLUSIONS

Identification of events, signals, and pathways in urologic cancer are opportunities to develop biomarkers and targets for diagnosis and treatment.

The antitumor activity of an anti-CD54 antibody in SCID mice xenografted with human breast, prostate, non-small cell lung, and pancreatic tumor cell lines

We have previously described the development and testing of a monoclonal anti-human CD54 antibody (UV3) in SCID mice xenografted with human multiple myeloma, lymphoma, and melanoma cell lines. In all 3 cases, UV3 was highly effective at slowing the growth of tumors and/or prolonging survival. Since CD54 (ICAM-1) is up-regulated on many different types of cancer cells, we have now investigated the anti-tumor activity of UV3 in several other CD54(+) epithelial tumors. A panel of 16 human breast, prostate, non-small cell (NSC) lung, and pancreatic tumor cell lines was examined for reactivity with UV3, and 13 were positive. A representative CD54(+) cell line from each cancer was grown subcutaneously in SCID mice. Once the tumors were established, UV3 was administered using different dose regimens. UV3 slowed the growth of all 4 tumors, although it was not curative. When UV3 or gemcitabine were administered to SCID mice xenografted with a NSC lung tumor cell line or a pancreatic tumor cell line, UV3 was as effective as the chemotherapy alone. When gemcitabine and UV3 were administered together, the best anti-tumor responses were observed. UV3 has been chimerized (cUV3) and both toxicology studies and clinical trials are planned to assess the safety and activity of cUV3 in patients with one or more of these tumors.

Minireview: regulation of prostatic stem cells by stromal niche in health and disease

The isolation and characterization of prostatic stem cells has received significant attention in the last few years based on the belief that aberrant regulation of adult stem cells leads to prostate disease including cancer. The nature of the perturbations in stem cell regulation remains largely unknown. Although adult stem cells are can be governed by autonomous regulatory mechanisms, the stromal niche environment also provides essential cues to direct directing differentiation decisions and can lead to aberrant proliferation and/or differentiation. Elegant tissue recombination experiments, pioneered by Gerald Cunha and colleagues, provided evidence that quiescent epithelial tissues containing adult stem cells were capable of altered differentiation in response to inductive and instructive mesenchyme. In more recent times, it has been demonstrated that embryonic mesenchyme is sufficiently powerful to direct the differentiation of embryonic stem cells into mature prostate or bladder. In addition, prostatic tumor stroma provides another unique niche or microenvironment for stem cell differentiation that is distinct to normal stroma. This review highlights the importance of the appropriate selection of the stromal cell niche for tissue regeneration and implies plasticity of adult stem cells that is dictated by the tissue microenvironment.

Specific targeting of prostate cancer cells in vitro by the suicide gene/prodrug system, uracil phosphoribosyltransferase/5-fluorouracil, under the control of prostate-specific membrane antigen promoter/enhancer

This study was designed to investigate the prostate cancer-specific tumoricidal effect of the suicide gene, Escherichia coli uracil phosphoribosyltransferase (UPRT), driven by the human prostate-specific membrane antigen promoter/enhancer (PSMA(E/P)) in vitro. When transfected with PSMA(E/P)-EGFP (enhanced green fluorescence protein) (a plasmid construct with the green fluorescence protein gene driven by the PSMA(E/P)), only the androgen-responsive and PSMA-positive prostate cancer cell line, LNCaP, expressed GFP, indicating the specificity of the PSMA(E/P) activity in androgen-sensitive and PSMA-positive prostate cancer cells. Taking advantage of this prostate cancer-specific property of PSMA(E/P), we successfully introduced bacterial UPRT into LNCaP cells where the tumoricidal effect of 5-fluorouracil (5-FU) was significantly increased when compared with the cells without the exogenous UPRT. We conclude that the efficacy of 5-FU-based chemotherapy in prostate cancers can be significantly improved by targeted expression of the suicide gene UPRT under the control of PSMA(E/P).

Therapeutic dendritic cell vaccine preparation using tumor RNA transfection: a promising approach for the treatment of prostate cancer

BACKGROUND

Early prostate adenocarcinoma can be diagnosed through seric prostate-specific antigen (PSA) screenings. However, a fraction of patients progress to an incurable metastatic disease. Therefore, novel therapies for treating these patients are extremely desirable. Therapeutic vaccines based on Dendritic Cells (DCs) carrying tumor antigens have emerged as a promising strategy to initiate an immune response against tumor cells. These vaccines can be prepared using different methodologies, such as the application of tumor mRNA described in this work.

METHODS

Mature and immature DCs were obtained in vitro by adding specific cytokines to monocyte cell cultures. RNA extracted from prostate tumor lineage (LNCAP) was introduced into these cells by electroporation and co-incubation. Transfection success was measured by immunocytochemistry of the PSA expression level in DCs.

RESULTS

Cell surface markers, including CD14, CD80, CD86, CCR7, CD11c, and CD1a, confirmed mature and immature DC phenotypes. Both cell maturation stages were successfully used for RNA introduction as shown by PSA characterization.

CONCLUSION

Our data support the use of mature and immature DCs for vaccine preparation with either RNA electroporation or RNA co-incubation. The highest efficiency, however, was observed when RNA was delivered by electroporation into mature DCs. Due to in vitro RNA transcription, this method allows small tumors to be used for DC vaccine preparation; it is therefore a promising approach for the treatment of metastatic prostate cancer.