Growth Of Androgen-independent Prostate Cancer Research Articles

Physalins A and B Inhibit Androgen-Independent Prostate Cancer Cell Growth through Activation of Cell Apoptosis and Downregulation of Androgen Receptor Expression

Androgen deprivation therapy is a common treatment strategy for advanced prostate cancer. Though effective initially, the tumor often progresses to androgen independent stage in most patients eventually after a period of remission. One of the key factors of development of resistance is reflected in expression of androgen receptor (AR). In this study, we showed that two natural compounds, physalins A and B, both secosteriods from Physalisalkekengi var. franchetii, significantly inhibited the growth of two androgen-independent cell lines CWR22Rv1 and C42B, induced apoptosis via c-Jun N-terminal kinase (JNK) and/or extracellular signal-regulated kinase (ERK) activation, and decreased AR expression. In addition, physalins A and B down-regulated the expression of prostate specific antigen (PSA) in C42B cells which is a target gene of AR. Our results suggest that physalin A and B might be useful agents in preventing the growth of androgen-independent prostate cancer (AI-PCa).

Inhibition of Aberrant Androgen Receptor Induction of Prostate Specific Antigen Gene Expression, Cell Proliferation and Tumor Growth by 17α-Estradiol in Prostate Cancer

Androgen independent prostate cancer growth and metastasis are a major cause of prostate cancer death. Aberrant androgen receptor activation due to androgen receptor mutation is an important mechanism of androgen independence. We determined the effectiveness and mechanism of 17α-estradiol (Sigma®) in blocking aberrant androgen receptor activation due to androgen receptor mutation. We used LNCaP and MDA Pca-2b prostatic tumor cells (ATCC®) containing a mutated androgen receptor and WT estrogen receptor β to test 17α-estradiol inhibition of aberrant androgen receptor activation of prostate specific antigen gene expression and cell growth. Cotransfection analysis was used to further elucidate the mechanism of 17α-estradiol action. Xenograft animals with an LNCaP prostate tumor were prepared to study the in vivo effect of 17α-estradiol on tumor growth inhibition. In LNCaP cells 17α-estradiol produced a dose dependent inhibition of cyproterone acetate (Sigma) or dihydrotestosterone induced prostate specific antigen gene expression. In MDA Pca-2b cells 17α-estradiol inhibited cortisol (Sigma) induced prostate specific antigen expression and blocked dihydrotestosterone and cortisol induced cell proliferation in LNCaP and MDA Pca-2b cells, respectively. Cotransfection analysis showed that 17α-estradiol inhibition of aberrant androgen receptor activation of prostate specific antigen gene expression was medicated via estrogen receptors. In xenograft mice with LNCaP prostate cancer 17α-estradiol but not 17β-estradiol (Sigma) significantly inhibited tumor growth, although each estrogen tended to decrease tumor growth. Results suggest that 17α-estradiol with less classic estrogenic activity is a potential therapeutic agent for androgen independent prostate cancer due to androgen receptor mutation.

Molecular Oncogenesis of Prostate Adenocarcinoma: Role of the Human Epidermal Growth Factor Receptor 2 (HER-2/neu)

The potential mechanisms involving the genesis and growth of androgen-independent prostate cancer include super-expression of the androgen receptor (AR), in an attempt to compensate for the low androgenic plasma levels and mutations of this specific receptor, which could determine resistance to anti-androgenic therapy. However, most advanced prostate tumors have no mutations or amplifications of the AR, suggesting a potential role of non-androgenic growth factors, including epidermal growth factor (EGF), transforming growth factor alpha, insulin-like growth factor (IGF-1) and fibroblast growth factor. More specifically, these factors, and their receptors like EGFR (HER-1) and HER-2/neu, through paracrine and autocrine mechanisms, may contribute to the proliferation and growth of prostate cancer.

Abstract 1710: Epigenetic repression of regulator of G-protein signaling 2 promotes prostate cancer progression

Abstract Prostate cancer is the most common cancer in American men and acquisition of androgen independence by prostate cancer is the key problem causing prostate cancer progression to highly aggressive form of cancer, leaving limited modalities in its treatment. Recent studies suggest that G protein-coupled receptor (GPCR)-stimulated androgen-independent activation of androgen receptor (AR) contributes to development of androgen independence. We previously reported that RGS2, an inhibitor of GPCR signaling, inhibits androgen-independent AR activation in prostate cancer cells (Cao et al., (2006) Oncogene, 25: 3719-3734). Here, we report that RGS2 protein expression was significantly reduced in human prostate cancer specimens compared to adjacent normal prostate tissues. Interestingly, RGS2 repression in androgen-independent prostate cancer cells and human prostate cancer specimens is not simply due to the loss of the RGS2 gene. Instead, methylation-specific PCR analysis and bisulfite sequencing indicated that methylation of the RGS2 gene promoter correlates with RGS2 down-regulation in prostate cancer cells and human prostate cancer specimens. Hypermethylation of the RGS2 gene promoter abolished its promoter activity and suppressed RGS2 gene expression. Conversely, the DNA methyltransferase inhibitor, 5-aza-2’-deoxycytidine induced re-expression of RGS2 in androgen-independent prostate cancer cells via demethylation of the RGS2 promoter to inhibit androgen-independent prostate cancer growth. Furthermore, ectopic re-expression of RGS2 in androgen-independent prostate cancer cells by RGS2-adenovirus infection suppressed tumorigenicity and growth of xenografts in castrated nude mice. Taken together, our results suggest that RGS2 repression due to hypermethylation of its promoter could unmask a latent pathway for AR activation by various GPCRs, thus contributing to prostate cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1710.

94 THE CXCL12/CXCR4 INFLAMMATORY AXIS PROMOTES ANDROGEN-INDEPENDENT GROWTH IN PROSTATE CANCER CELLS

You have accessJournal of UrologyProstate Cancer: Basic Research I1 Apr 201094 THE CXCL12/CXCR4 INFLAMMATORY AXIS PROMOTES ANDROGEN-INDEPENDENT GROWTH IN PROSTATE CANCER CELLS Sathish Kasina, and Jill Macoska Sathish KasinaSathish Kasina More articles by this author , and Jill MacoskaJill Macoska More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.143AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The activation of G protein coupled receptors (GPCRs) has been implicated in the growth of hormone-independent prostate tumors. Interactions between the inflammation-associated GPCR, CXCR4, and its ligand, the CXCL12 chemokine, have been shown to mediate gene transcription and cellular proliferation in both malignant and benign prostate epithelial cells, as well as motility/invasiveness in malignant cells. In this report, we investigated whether CXCL12/CXCR4 interactions might mediate prostate cancer cell proliferation through androgen-independent functional transactivation of the AR. METHODS The effect of exogenous synthetic androgen, R1881, or CXCL12 on prostate specific antigen (PSA) gene transcript and protein levels was determined by qRT-PCR, immunoblot, and ELISA assays. R1881- or CXCL12-stimulated expression of a reporter gene construct carrying the PSA promoter was determined by luciferase assay. Nuclear translocation of AR was determined by immunoblot and by immunofluorescence analysis. Inhibitor experiments utilized the androgen antagonist, casodex at 10uM, MEK-1 inhibitor, U0126 at 10uM, and PI3kinase inhibitors, LY294002 and wortmanin at 10uM and 1uM respectively, or vehicle (0.1% DMSO), the CXCR4 inhibitor, AMD3100 at 10uM, or the CXCR2 inhibitor, repertaxin at 10uM. RESULTS The results of these studies show that endogenous transcription of the AR-regulated PSA gene and expression of PSA promoter-driven luciferase was enhanced in prostate epithelial cells stimulated with R1881 or CXCL12. PSA protein secretion was significantly higher for cells treated with R1881 or CXCL12, and was greatly reduced upon pre-treatment with the AR inhibitor, Casodex, the CXCR4 inhibitor, AMD3100, or the PI3K inhibitors LY294002 or wortmannin prior to R1881 or CXCL12 treatment. Both R1881- and CXCL12-treated cells exhibited nuclear accumulation and phosphorylation of AR at Ser210, as well as AR-dependent proliferative responses. CONCLUSIONS These studies identify the inflammatory chemokine, CXCL12, as a novel, non-steroidal growth factor that promotes the growth of androgen-dependent prostate epithelial cells in the absence of steroid hormones. These findings support the development of novel therapeutics targeting the CXCL12/CXCR4 inflammatory axis as an ancillary to those targeting the androgen/AR axis to effectively treat hormone refractory prostate tumors. Ann Arbor, MI© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e39 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Sathish Kasina More articles by this author Jill Macoska More articles by this author Expand All Advertisement Advertisement PDF DownloadLoading ...

The molecular mechanism of Vav3 oncogene on upregulation of androgen receptor activity in prostate cancer cells

Our previous studies revealed that Vav3 oncogene is overexpressed in human prostate cancer, enhances androgen receptor (AR)-mediated signaling, and may play a role in prostate cancer development and progression. The purpose of this study was to determine the molecular mechanisms responsible for AR activation by Vav3. We found that interaction between N-terminus and C-terminus of AR is essential for its elevated activity stimulated by Vav3. The DH and PH domains of Vav3 are involved in direct interaction with AR. Both cytoplasmic and nuclear levels of AR and Vav3 are elevated and their nuclear localization is further stimulated by DHT in androgen-independent LNCaP-AI cells relative to their parental androgen-dependent LNCaP cells. Vav3 is colocalized with AR, phospho(P)-Akt, and HER2 with a short term stimulation by EGF and DHT. PI3K inhibitor LY294002 blocks colocalization of Vav3 with P-Akt. Consistently, EGF and DHT stimulate Vav3 and AR interaction and enhance PI3K-Akt signaling. Mutation of tyrosines to phenylalanines in the acidic domain or deletion of the SH2 and SH3 domains significantly enhances Vav3 ability for AR activation, while deletion of the DH domain abolishes this activity. Given that an elevated interaction of Vav3 with AR, P-Akt, and HER2 in both cytoplasm and nucleus upon the short-term of DHT stimulation, our data suggest that Vav3 may enhance non-genomic AR activity via PI3K-Akt signaling in addition to AR transcriptional activity and further support a role in androgen-independent growth in prostate cancer.

Pomegranate extract inhibits androgen-independent prostate cancer growth through a nuclear factor-κB-dependent mechanism

Constitutive nuclear factor-kappaB (NF-kappaB) activation is observed in androgen-independent prostate cancer and represents a predictor for biochemical recurrence after radical prostatectomy. Dietary agents such as pomegranate extract (PE) have received increasing attention as potential agents to prevent the onset or progression of many malignancies, including prostate cancer. Here, we show that PE inhibited NF-kappaB and cell viability of prostate cancer cell lines in a dose-dependent fashion in vitro. Importantly, maximal PE-induced apoptosis was dependent on PE-mediated NF-kappaB blockade. In the LAPC4 xenograft model, PE delayed the emergence of LAPC4 androgen-independent xenografts in castrated mice through an inhibition of proliferation and induction of apoptosis. Moreover, the observed increase in NF-kappaB activity during the transition from androgen dependence to androgen independence in the LAPC4 xenograft model was abrogated by PE. Our study represents the first description of PE as a promising dietary agent for the prevention of the emergence of androgen independence that is driven in part by heightened NF-kappaB activity.

Relationship between Glucocorticoid Receptor Signal Pathway and Androgen-Independent Prostate Cancer

Objective: To study the role of the glucocorticoid receptor (GR) signal pathway and downstream cytokine interleukin-6 (IL-6) in androgen-independent growth of prostate cancer (PC). Methods: The human androgen-dependent PC (ADPC) cell line LNCaP and androgen-independent PC (AIPC) cell line DU145 were cultured in vitro. Immunocytochemistry was used to examine the expression of the androgen receptor (AR), GR, HSP90 and IL-6. The GR antagonist RU486 was used to treat cultured cells, and the effects of RU486 on the proliferation of both cell lines were analyzed by MTT assay. Expression of HSP90 and IL-6 mRNA and protein was assessed by RT-PCR and Western blots, respectively. Results: LNCaP cells were AR-positive and GR-negative, whereas DU145 cells were GR-positive and AR-negative. The expression of HSP90 and IL-6 in DU145 cells were significantly stronger than that in LNCaP cells (p < 0.01). RU486 had no obvious effects on the growth of LNCaP cells, but exerted a significant time- and dose-dependent growth inhibition on DU145 cells at doses as low as 0.1 µmol/l. RU486 treatment of DU145 cells also resulted in a dose-dependent decrease in the expression of HSP90 and IL-6 mRNA and protein. Conclusions: The GR signal pathway may be the main survival pathway for DU145 cells. Abnormal hyperactivation of the GR signal pathway and its promoting the expression of HSP90 and IL-6 contribute to the progression of ADPC to AIPC after androgen ablation.

AN S296R MUTATION IN THE HUMAN ANDROGEN RECEPTOR CAUSES ACTIVATION OF THE RECEPTOR BY NON-ANDROGENIC STEROIDS AND STRONGER INHIBITION BY THE NUCLEAR RECEPTOR COREPRESSOR N-coR

Mutation of the androgen receptor (AR) is believed to contribute to androgen-independent growth of prostate cancer. In the present study, we examined the functional changes associated with the novel somatic mutation S296R in the N-terminal domain of the AR identified from one recurrent prostate cancer sample. The results indicate that the S296R mutation does not differ obviously from the wild-type AR in its ability to bind the synthetic androgen methyltrienolone, or in its transcriptional activity induced by dihydrotestosterone (DHT) in the absence or presence of the overexpression of coactivators (steroid receptor coactivator-1, transcription intermediary factor-2, cAMP response element-binding protein-binding protein and p300). However, S296R was found to differ from wild-type AR in that its transcriptional activity could be activated by high concentrations (1 micromol/L) of 17beta-oestradiol and progesterone and its transactivity induced by DHT was more obviously inhibited by overexpression of the nuclear receptor corepressor N-coR in CV-1 cells. These findings indicate that a point mutation (S296R) in the N-terminal domain of the AR can decrease the ligand specificity of the AR and alter the interaction between S296R and the corepressor N-coR.

Effect of a Prodrug of the Green Tea Polyphenol (-)-Epigallocatechin-3-Gallate on the Growth of Androgen-Independent Prostate Cancer In Vivo

Epigallocatechin-3-gallate (EGCG) is the major and most potent polyphenol compound of green tea that has been shown to have anticancer effects against various types of cancers. In this study, in addition to the EGCG compound, a synthetic derivative, the peracetate of EGCG (EGCG-P), was used to investigate the inhibitory effects on growth of androgen-independent prostate cancer in vivo. The advantage of EGCG-P is that it may act as a prodrug, leading to higher bioavailability than EGCG itself. The aim of our study was to compare the differences between EGCG and EGCG-P on their inhibitory effect on androgen-independent prostate cancer, CWR22R, xenograft model in nude mice. The mice were administrated daily with solvent dimethyl sulfoxide, EGCG, and EGCG-P separately through intraperitoneal injection for 20 days. Tumor volume and body weight of nude mice were recorded daily. Serum prostate-specific antigen (PSA) levels were also measured before and after the treatment. The effects of both EGCG and EGCG-P on tumor cell proliferation were assessed by immunohistochemical (IHC) method using antibodies against Ki-67 and proliferating cell nuclear antigen. The apoptotic effect was evaluated by IHC against B-cell non-Hodgkin lymphoma-2 and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay by in situ apoptosis detection kit. Moreover, the potential suppression of angiogenesis by EGCG and EGCG-P on prostate cancer was examined by IHC against CD31. Our results revealed that treatment of EGCG and EGCG-P compounds suppressed the growth of CWR22R xenografts without causing any detectable side effects in nude mice. The suppression of growth of the tumor was correlated with the decrease of serum PSA level together with the reduction in tumor angiogenesis and an increase in apoptosis on prostate cancer cells. The results showed that treatment of EGCG and EGCG-P inhibited tumor growth and angiogenesis while promoting apoptosis of the prostate cancer cells in vivo. Our results suggest that EGCG-P may be a more stable and useful compound for increasing the therapeutic anticancer effects in androgen-independent prostate cancer.

In Vivo Evaluation of AT-101 (R-(—)-Gossypol Acetic Acid) in Androgen-Independent Growth of VCaP Prostate Cancer Cells in Combination with Surgical Castration

PURPOSE: Upregulation of Bcl-2 family members is a well-established mechanism in the development of androgen-independent prostate cancer. Inhibition of the antiapoptotic proteins Bcl-2 and Mcl-1 may delay the transition to androgen-independent growth. EXPERIMENTAL DESIGN: We have established a prostate cancer model with VCaP prostate cancer cells in vivo to study the transition to androgen independence. Here, we investigated the efficacy of AT-101 (R-(—)-gossypol acetic acid; a pan small molecule inhibitor of Bcl-2, BCI-xL, Mcl-1) in combination with surgical castration to delay the onset of androgen-independent growth in vivo. RESULTS: AT-101 (15 mg/kg, per os (p.o.) 5 days/week) in combination with surgical castration delayed the onset of androgen-independent prostate cancer growth in vivo. In addition, we demonstrate the induction of caspase-9- and caspase-3-dependent induction of apoptosis following AT-101 treatment in vitro which was accompanied by an AT-101-induced downregulation of Bcl-2 and Mcl-1 mRNA and protein expression. CONCLUSIONS: We conclude that AT-101 in combination with surgical castration delays the onset of androgen-independent prostate cancer in vivo by disrupting the antiapoptotic activity of BCl-2 upregulation during the transition to androgen independence. Further studies are needed to define the mechanism of action by which AT-101 attenuates the expression of Bcl-2 and Mcl-1 and to characterize the potential for AT-101 in combination with hormone therapy.

Interleukin‐4 stimulates androgen‐independent growth in LNCaP human prostate cancer cells

Clinical data showed that the levels of interleukin-4 (IL-4) are significantly elevated in serum of patients with ablation resistant prostate cancer. Previous studies demonstrated that IL-4 enhances androgen receptor (AR) activation mediated by NF-kappaB in the absence or in the very low levels of androgen in prostate cancer cells. In this study, the role of IL-4 in promoting the growth of androgen-independent prostate cancer cells was examined. LNCaP cells were transfected with a full-length IL-4 cDNA and stable clones expressing IL-4 were selected. The growth of LNCaP cells expressing IL-4 was analyzed in vitro and in vivo both in the presence and absence of androgen. Overexpression of IL-4 enhances the growth of androgen-sensitive LNCaP cells in culture media containing charcoal-stripped FBS condition (CS-FBC), and increases the sensitivity of LNCaP cells in response to androgen stimulation. The DHT-mediated cell growth could not be blocked by bicalutamide in IL-4 overexpressing LNCaP cells, but can be neutralized by bicalutamide in parental LNCaP and neo control cells. Furthermore, overexpression of IL-4 stimulates tumor growth of androgen-sensitive LNCaP cells both in intact and castrated male mice. Overexpression of IL-4 increases the sensitivity of androgen-sensitive LNCaP prostate cancer cells in response to androgen stimulation and enhances the growth of LNCaP cells both in the presence and absence of androgen in vitro and in vivo. These studies suggest that IL-4 plays an important role in promoting androgen-independent prostate cancer growth.

Interleukin-8 Is a Molecular Determinant of Androgen Independence and Progression in Prostate Cancer

The proinflammatory chemokine interleukin-8 (IL-8) is undetectable in androgen-responsive prostate cancer cells (e.g., LNCaP and LAPC-4), but it is highly expressed in androgen-independent metastatic cells, such as PC-3. In this report, we show IL-8 functions in androgen independence, chemoresistance, tumor growth, and angiogenesis. We stably transfected LNCaP and LAPC-4 cells with IL-8 cDNA and selected IL-8-secreting (IL8-S) transfectants. The IL8-S transfectants that secreted IL-8 at levels similar to that secreted by PC-3 cells (100-170 ng/10(6) cells) were characterized. Continuous or transient exposure of LNCaP and LAPC-4 cells to IL-8 reduced their dependence on androgen for growth and decreased sensitivity (>3.5x) to an antiandrogen. IL-8-induced cell proliferation was mediated through CXCR1 and was independent of androgen receptor (AR). Quantitative PCR, immunoblotting, and transfection studies showed that IL8-S cells or IL-8-treated LAPC-4 cells exhibit a 2- to 3-fold reduction in PSA and AR levels, when compared with vector transfectants. IL8-S cells expressed 2- to 3-fold higher levels of phospho-EGFR, src, Akt, and nuclear factor kappaB (NF-kappaB) and showed increased survival when treated with docetaxel. This increase was blocked by NF-kappaB and src inhibitors, but not by an Akt inhibitor. IL8-S transfectants displayed a 3- to 5-fold increased motility, invasion, matrix metalloproteinase-9 and vascular endothelial growth factor production. LNCaP IL8-S cells grew rapidly as tumors, with increased microvessel density and abnormal tumor vasculature when compared with the tumors derived from their vector-transfected counterparts. Therefore, IL-8 is a molecular determinant of androgen-independent prostate cancer growth and progression.

Establishment and characterization of androgen‐independent human prostate cancer cell lines, LN‐REC4 and LNCaP‐SF, from LNCaP

To investigate the mechanisms of androgen-independent growth in prostate cancer (PCa), we established two PCa cell lines, LN-REC4 and LNCaP-SF, from the androgen-dependent PCa cell line, LNCaP. LN-Pre and LN-REC4 cells were generated from LNCaP tumors grown on intact and castrated severe combined immunodeficient (SCID) mouse, respectively. After we cultured LNCaP cells under a steroid-free conditions for 6 months in vitro, LNCaP-SF cells were established. To show the character of LN-REC4 and LNCaP-SF cells, androgen sensitivity was investigated through examination of growth rate, and prostate-specific antigen (PSA), androgen receptor (AR), p21, p27, and cyclin D1 expression were examined by reverse transcription-polymerase chain reaction (RT-PCR). Angiogenesis assay in vitro was carried out using conditioned medium. To examine the expression level of vascular endothelial growth factor (VEGF), RT-PCR and enzyme-linked immunosorbent assay were also done. LN-REC4 cells proliferated better than LNCaP cells in castrated mice and did well irrespective of castration, although responsiveness for androgen of LN-REC4 cells attenuated less than that of LNCaP cells in vitro. LNCaP-SF cells in castrated mice proliferated more rapidly than in normal mice. The PSA expression in LNCaP-SF cells was still induced by androgen. Expression of AR, p21, p27 and cyclin D1 were not changed in LN-REC4 and LNCaP-SF cells. Angiogenesis assay showed that both cells stimulated angiogenesis. LN-REC4 induced VEGF more than LNCaP and LN-Pre cells. However, expression of VEGF per cell in LNCaP-SF was lower than LNCaP cells, suggesting that other factors might be involved in angiogenesis. These cell lines might be a useful tool for researching androgen-independent growth and treatments of recurred PCa.

Glucocorticoids suppress tumor angiogenesis and in vivo growth of prostate cancer cells: Yano A, Fujii Y, Iwai A, Kageyama Y, Kihara K, Department of Urology, Tokyo Medical and Dental University, Yushima, Tokyo, Japan

Purpose Glucocorticoids, such as prednisone, hydrocortisone, and dexamethasone, are known to produce some clinical benefit for patients with hormone-refractory prostate cancer (HRPC). However, the underlying mechanisms by which glucocorticoids affect HRPC growth are not well established as yet. Here, we hypothesize that the therapeutic effect of glucocorticoids on HRPC can be attributed to a direct inhibition of angiogenesis through the glucocorticoid receptor by down-regulating two major angiogenic factors, vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8). Experimental Design The effects of dexamethasone on VEGF and IL-8 expression and cell proliferation were examined using DU145, which expresses glucocorticoid receptor. The effects of dexamethasone on DU145 xenografts were determined by analyzing VEGF and IL-8 gene expression, microvessel density, and tumor volume. Results Dexamethasone significantly down-regulated VEGF and IL-8 gene expression by 50% (P Conclusion Glucocorticoids suppressed androgen-independent prostate cancer growth possibly due to the inhibition of tumor-associated angiogenesis by decreasing VEGF and IL-8 production directly through glucocorticoid receptor in vivo.

Glucocorticoids Suppress Tumor Angiogenesis and In vivo Growth of Prostate Cancer Cells

Glucocorticoids, such as prednisone, hydrocortisone, and dexamethasone, are known to produce some clinical benefit for patients with hormone-refractory prostate cancer (HRPC). However, the underlying mechanisms by which glucocorticoids affect HRPC growth are not well established as yet. Here, we hypothesize that the therapeutic effect of glucocorticoids on HRPC can be attributed to a direct inhibition of angiogenesis through the glucocorticoid receptor by down-regulating two major angiogenic factors, vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8). The effects of dexamethasone on VEGF and IL-8 expression and cell proliferation were examined using DU145, which expresses glucocorticoid receptor. The effects of dexamethasone on DU145 xenografts were determined by analyzing VEGF and IL-8 gene expression, microvessel density, and tumor volume. Dexamethasone significantly down-regulated VEGF and IL-8 gene expression by 50% (P < 0.001) and 89% (P < 0.001), respectively, and decreased VEGF and IL-8 protein production by 55% (P < 0.001) and 74% (P < 0.001), respectively, under normoxic condition. Similarly, hydrocortisone down-regulated VEGF and IL-8 gene expression. The effects of dexamethasone were completely reversed by the glucocorticoid receptor antagonist RU486. Even under hypoxia-like conditions, dexamethasone inhibited VEGF and IL-8 expression. In DU145 xenografts, dexamethasone significantly decreased tumor volume and microvessel density and down-regulated VEGF and IL-8 gene expression, whereas dexamethasone did not affect the in vitro proliferation of the cells. Glucocorticoids suppressed androgen-independent prostate cancer growth possibly due to the inhibition of tumor-associated angiogenesis by decreasing VEGF and IL-8 production directly through glucocorticoid receptor in vivo.

PLZF regulates Pbx1 transcription and Pbx1–HoxC8 complex leads to androgen-independent prostate cancer proliferation

Promyelocytic leukemia zinc finger (PLZF) protein, a transcriptional repressor and negative regulator of the cell cycle, has been characterized as a prostatic androgen-responsive gene. DU145 cells show androgen-independent growth and lack PLZF gene expression. We analyzed PLZF-regulating genes by DNA microarray using DU145 cells infected with LacZ- or PLZF-carrying adenoviruses. DNA microarray revealed that Pbx1 is a prominent suppressed gene in PLZF-overexpressing DU145 cells. Androgen receptor (AR)-expressing DU145 cells recovered androgen-dependent PLZF expression and subsequent repression of Pbx1 expression. Immunoprecipitation of Pbx1 in DU145 cells revealed a Pbx1-HoxC8 heterocomplex. siRNAs for Pbx1 and HoxC8 knocked downexpression of each, and this suppressed androgen-independent cell growth. Double knockdown of both Pbx1 and HoxC8 suppressed cell growth much more significantly. Androgen-independent cell line DU145 cells lack PLZF gene expression, resulting in the upregulation of Pbx1 and HoxC8 expression. The Pbx1-HoxC8 heterocomplex may lead to androgen-independent growth in prostate cancer.

New perspective in the management of neuroendocrine differentiation in prostate adenocarcinoma

In this review, we will present some of the information that is known about neuroendocrine (NE) cells and differentiation in the prostate. We will then speculate on the potential role that NE differentiation in prostate carcinoma may play and how this differentiation may be clinically analysed and treated. The androgen-independent growth of prostate cancer can be caused by different mechanisms; one of these is receptor-specific paracrine or autocrine growth modulation of human prostatic cancer cells by neuropeptides secreted by NE cells. Our results affirm that different methods of androgen deprivation can influence the serum chromogranin A (CgA) levels to different extents in prostate cancer. In particular, bicalutamide produces a significantly lower increase in serum CgA compared with castration therapy. In the light of other evidence that supports a significant relationship between serum CgA levels, tissue CgA expression and NE activity, we hypothesise that bicalutamide may reduce the risk of NE cell hyperactivation in prostate cancer. It is important to determine whether increases in CgA levels and NE cell activation are associated with progression towards hormone-independent prostate cancer. We recently proposed as therapy of NE activation in hormone-independent prostate cancer, a combination of oestrogens and somatostatin analogues. The combination of ethinyl estradiol and lanreotide had a favourable toxicity profile, offered objective and symptomatic responses in patients with limited treatment options and refractoriness to conventional hormonal therapy strategies and, in particular, offered a median overall survival that was superior to the 10-month median survival in patients with hormone refractory disease. This combination therapy also sustains the novel concept in cancer treatment in which therapies may target not only cancer cells but also its microenvironment in combination, which can confer protection from apoptosis.

PI3K-Akt signaling is involved in the regulation of p21WAF/CIP expression and androgen-independent growth in prostate cancer cells

The purpose of this study is to investigate the role of PI3K-Akt signaling in prostate cancer cell growth and androgen receptor (AR)-mediated gene expression. Androgen-dependent LNCaP cells and their androgen-independent counterpart, LNCaP-AI cells, were used. We found that PI3K-Akt signaling is elevated in LNCaP-AI cells compared to that in LNCaP cells and is involved in androgen-independent growth. More importantly, PI3K-Akt signaling enhances AR activity and is involved in the induction of AR target genes, such as p21(WAF/CIP), a gene with anti-apoptosis activity and associated with androgen-independent growth in human prostate cancer. A receptor tyrosine kinase inhibitor also inhibits the PI3K-Akt signaling and compromises AR activity and cell growth. These findings suggest that the PI3K-Akt cell growth survival pathway and its downstream-regulated gene, p21(WAF/CIP), are targets for developing novel therapies against prostate cancer, especially those androgen-independent diseases.

Interleukin-17 Receptor-Like Gene Is a Novel Antiapoptotic Gene Highly Expressed in Androgen-Independent Prostate Cancer

We have recently identified a new gene, interleukin-17 receptor-like (IL-17RL), which is expressed in normal prostate and prostate cancer. This investigation is focused on the role of IL-17RL in prostate cancer. We found that IL-17RL was expressed at significantly higher levels in several androgen-independent prostate cancer cell lines (PC3, DU145, cds1, cds2, and cds3) and tumors compared with the androgen-dependent cell lines (LNCaP and MLC-SV40) and tumors. In an in vivo model of human prostate tumor growth in nude mice (CWR22 xenograft model), IL-17RL expression in tumors was induced by androgen deprivation. The relapsed androgen-independent tumors expressed higher levels of IL-17RL compared with the androgen-dependent tumors. Overexpression of IL-17RL in tumor necrosis factor alpha (TNFalpha)-sensitive LNCaP cells inhibited TNFalpha-induced apoptosis by blocking activation of caspase-3 downstream to caspase-2 and caspase-8. Reciprocally, knocking down IL-17RL expression by small interfering RNA induced apoptosis in all the prostate cancer cell lines studied. Taken together, these results show that IL-17RL is a novel antiapoptotic gene, which may confer partially the property of androgen-independent growth of prostate cancer by promoting cell survival. Thus, IL-17RL is a potential therapeutic target in the treatment of prostate cancer.