Role of androgen receptor in the progression of human prostate tumor cells to androgen independence and insensitivity

Updates on Overcoming Bicalutamide Resistance: A Glimpse into Resistance to a Novel Antiandrogen

The standard androgen deprivation therapy for advanced prostate cancer includes the use of bicalutamide, which is a well-known antagonist of androgen receptors. Despite numerous benefits of the drugs in prostate cancer treatment, there is always a risk of developing a resistant phenotype, which paves the way for a more aggressive and low-survival type of prostate cancer. Over the years, many studies have investigated the candidate mechanisms of such resistance and have managed to find possible therapeutic solutions. In this Review, we shed light on the heterogeneous dynamics of progression to resistance against bicalutamide treatment, referring to the most recent studies and the approaches that have been so far discussed. This Review tries to offer a deep and comprehensive understanding about how the resistant cells become sensitive to the drug and what corresponding pathways lead to an appropriate solution for the antiandrogen resistance challenge.

Rooibos suppresses proliferation of castration-resistant prostate cancer cells via inhibition of Akt signaling

BACKGROUND

Androgen ablation therapy is the primary treatment for metastatic prostate cancer (PCa). However, the majority of PCa patients receiving the androgen deprivation therapy develop recurrent castration-resistant prostate cancer (CRPC) within two years. Chemotherapies show little effect on prolonging survival of CRPC patients and new treatments are needed. Previous studies reported that the extracts from rooibos (Aspalathus linearis) exhibit chemopreventive properties in some cancer models, including skin, liver and oesophagus cancers in animals. We therefore investigate if extracts from rooibos can suppress the proliferation of CRPC cells.

PURPOSE

We investigated whether an aspalathin-rich green rooibos extract (GRT™; 12.78 g aspalathin/100 g extract) demonstrates anti-cancer activity against CRPC cells.

METHODS

High performance liquid chromatography (HPLC) was used to profile the major flavonoids in GRT. Hoechst-dye proliferation assay, 3,4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide (MTT) viability assay and flow cytometry assay were used to explore the effects of GRT on the proliferation and cell cycle progression of CRPC cells. Comet assay was used to survey whether GRT induces apoptosis in CRPC cells. LNCaP 104-R1 xenograft nude mice model was used to determine the inhibitory effect of GRT on CRPC tumors in vivo. Micro-Western Array (MWA) and Western blot analysis were carried out to unravel the underlying molecular mechanism.

RESULTS

GRT contained aspalathin as the most abundant flavonoid. GRT suppressed the proliferation and survival of LNCaP 104-R1, LNCaP FGC and PC-3 PCa cells. Flow cytometry analysis showed that GRT decreased the population of PCa cells in S phase but increased the cell population in G2/M phase. Comet assay confirmed that GRT induced apoptosis in LNCaP 104-R1 cells. Gavage of 400 mg/kg GRT suppressed LNCaP 104-R1 xenografts in castrated nude mice. MWA and Western blot analysis indicated that GRT treatment suppressed Akt1, phospho-Akt Ser473, Cdc2, Bcl-2, TRAF4 and Aven, but increased activated Caspase 3, cytochrome c, and p27^Kip1. Overexpression of Akt rescued the suppressive effects of GRT on CRPC cells. Co-treatment of GRT with Bcl-2 inhibitor ABT-737, PI3K inhibitor LY294002 and Akt inhibitor GSK 690693 exhibited additive inhibitory effect on proliferation of CRPC cells.

CONCLUSIONS

GRT suppresses the proliferation of CRPC cells via inhibition of Akt signaling.

Caffeic acid phenethyl ester suppresses androgen receptor signaling and stability via inhibition of phosphorylation on Ser81 and Ser213

Background

Androgen receptor (AR) plays important role in the development, progression, and metastasis of prostate cancer (PCa). Caffeic acid phenethyl ester (CAPE) is the main component of honey bee propolis. We determined if CAPE affects the signaling and stability of AR in PCa cells.

Methods

Effects of CAPE on AR transcriptional activity and localization were determined by reporter gene assay and immunofluorescent microscopy. Western blotting, fluorescent polarization, computer simulation, and animal experiment were performed to investigate the molecular mechanism how CAPE reduces the stability of AR.

Results

CAPE treatment dose-dependently suppressed the transcriptional activity of AR as well as the protein levels of AR and its target gene PSA. Cyclohexamide treatment revealed that androgen stabilized AR protein, but AR stability was diminished by CAPE. Fluorescence microscopy demonstrated that androgen promoted the nucleus translocation of AR in PCa cells, while treatment with CAPE reduced protein level of AR in both nucleus and cytoplasm. CAPE treatment suppressed the phosphorylation of Ser81 and Ser213 on AR, which regulates the stability of AR. CDK1 and AKT are the kinases phosphorylating Ser81 and Ser213 on AR, respectively. CAPE treatment significantly reduced the protein level and activity of CDK1 and AKT in PCa cells. Overexpression of CDK1 or AKT rescued the AR protein level under CAPE treatment.

Conclusions

Our results suggested that CAPE treatment reduced AR stability and AR transcriptional activity in PCa cells, implying the possibility of using CAPE as a treatment for advanced PCa.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0404-9) contains supplementary material, which is available to authorized users.

Regulation of the Antioxidant Response by MyoD Transcriptional Coactivator in Castration-resistant Prostate Cancer Cells

OBJECTIVE

To reveal the potential role of the basic helix-loop-helix myogenic transcription regulator MyoD in the regulation of castration-resistant prostate cancer.

METHODS

Expression level of MyoD was assessed in prostate cancer tissues using quantitative reverse transcription polymerase chain reaction and immunohistochemistry and in experimentally induced castration-resistant LNCaP/R cells using quantitative reverse transcription polymerase chain reaction and immunoblotting. Effect of MyoD knockdown on LNCaP/R cell progression was determined by assessing cell proliferation, apoptosis, and colony formation rate. The effect of MyoD knockdown on the oxidative stress state in PC3 cells was determined by assessing antioxidant response gene expression and glutathione synthetase-to-glutathione ratio. Finally, the functional link between the nuclear factor erythroid-derived 2-related factor 1 (NRF1) and the regulation of antioxidant response element-driven transcription by MyoD was studied at both molecular and functional levels.

RESULTS

MyoD expression was significantly upregulated in hormone-refractory prostate cancer tissues and in experimentally induced castration-resistant LNCaP/R cells, and MyoD knockdown effectively impaired LNCaP/R cell proliferation and promoted apoptosis under androgen-depleted condition. Moreover, MyoD enhanced the glutathione production and protected against oxidative stress by positively regulating a cluster of antioxidant genes known to be the downstream targets of NRF1. Mechanistically, MyoD could augment the antioxidant response element-driven transcription in an NRF1-dependent manner, and the stimulatory effect of MyoD on the antioxidant response was substantially compromised in the presence of NRF1 small interfering RNA treatment.

CONCLUSION

We have identified an unexpected collaboration between MyoD and NRF1 under androgen-depleted condition, which may serve as an important adaptive mechanism during the pathogenesis of castration-resistant prostate cancer.

PC-1 works in conjunction with E3 ligase CHIP to regulate androgen receptor stability and activity

The androgen receptor (AR) is not only a ligand-dependent transcription factor, but also functions as a licensing factor, a component of DNA replication, which is degraded during mitosis. Furthermore, the deregulation of AR activity is involved in the initiation of prostate cancer and contributes to castration resistant prostate cancer (CRPC). While AR degradation is known to occur primarily through a proteasome-mediated pathway, very little is known about how this process is regulated, especially in M phase. PC-1 is an androgen-responsive factor and expresses specificity in prostate cancer, with higher expression noted at G2/M. In this study, PC-1 was shown to interact with AR and E3 ligase CHIP (Carboxy-terminus of Hsc70 Interacting Protein) and to enhance AR/CHIP interactions, thereby decreasing AR stability. Moreover, PC-1 was found to act in conjunction with CHIP in the decreasing of AR via ubiquitination, with the subsequent degradation predominantly occurring during M phase. PC-1 was also found to repress AR transcriptional activity in androgen-dependent and androgen-independent prostate cancer cells and attenuate the growth inhibition of AR. In conclusion, these findings should provide new clues regarding the modulation of AR turnover and activity via PC-1 and reveals an essential role of PC-1 in AR signaling.

Saurolactam Inhibits Proliferation, Migration, and Invasion of Human Osteosarcoma Cells

Osteosarcoma is a common type of malignant bone tumor with features of osteoid formation or osteolytic lesions of bone. New therapeutic approaches are urgently needed since it lacks response to chemotherapeutic treatments. Saurolactam, a natural compound isolated from the aerial portions of Saururus chinensis, was reported to have an anti-inflammatory activity. Here, we demonstrate that saurolactam shows anti-cancer activity against human osteosarcoma cells. Saurolactam treatment inhibited proliferation of human osteosarcoma cell lines MG-63 and HOS and decreased colony formation in soft agar in a dose-dependent manner. Intraperitoneal administration of saurolactam at 25 mg/kg of body weight for 21 days dramatically inhibited the growth of MG-63 xenografts in nude mice. Flow cytometric analysis indicated that saurolactam treatment (20 μM) led to G1 cell cycle arrest and induced apoptosis in these two cell lines. Western analysis suggested that saurolactam treatment resulted in a reduction of Akt/PKB, phospho-Ser473-Akt, c-Myc, and S-phase kinase-associated protein 2 (Skp2) in MG-63 and HOS osteosarcoma cells. Akt overexpression significantly abolished saurolactam-induced decrease in protein and phosphorylation levels of Akt, c-Myc, and Skp2 protein levels, implying that Akt inactivation was a causal mediator of saurolactam-induced inhibition of c-Myc and Skp2. Moreover, Skp2 overexpression in MG-63 cells partly abolished the growth inhibition induced by saurolactam. Saurolactam treatment repressed migration and invasion ability, and Skp2 overexpression significantly blocked these inhibitory effects of saurolactam in MG-63 Cells. The present study indicates that saurolactam might represent a new promising agent to improve osteosarcoma treatment.

Caffeic acid phenethyl ester induced cell cycle arrest and growth inhibition in androgen-independent prostate cancer cells via regulation of Skp2, p53, p21Cip1 and p27Kip1

Prostate cancer (PCa) patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant prostate cancer (CRPC) within 1–3 years. Treatment with caffeic acid phenethyl ester (CAPE) suppressed cell survival and proliferation via induction of G1 or G2/M cell cycle arrest in LNCaP 104-R1, DU-145, 22Rv1, and C4–2 CRPC cells. CAPE treatment also inhibited soft agar colony formation and retarded nude mice xenograft growth of LNCaP 104-R1 cells. We identified that CAPE treatment significantly reduced protein abundance of Skp2, Cdk2, Cdk4, Cdk7, Rb, phospho-Rb S807/811, cyclin A, cyclin D1, cyclin H, E2F1, c-Myc, SGK, phospho-p70S6kinase T421/S424, phospho-mTOR Ser2481, phospho-GSK3α Ser21, but induced p21^Cip1, p27^Kip1, ATF4, cyclin E, p53, TRIB3, phospho-p53 (Ser6, Ser33, Ser46, Ser392), phospho-p38 MAPK Thr180/Tyr182, Chk1, Chk2, phospho-ATM S1981, phospho-ATR S428, and phospho-p90RSK Ser380. CAPE treatment decreased Skp2 and Akt1 protein expression in LNCaP 104-R1 tumors as compared to control group. Overexpression of Skp2, or siRNA knockdown of p21^Cip1, p27^Kip1, or p53 blocked suppressive effect of CAPE treatment. Co-treatment of CAPE with PI3K inhibitor LY294002 or Bcl-2 inhibitor ABT737 showed synergistic suppressive effects. Our finding suggested that CAPE treatment induced cell cycle arrest and growth inhibition in CRPC cells via regulation of Skp2, p53, p21^Cip1, and p27^Kip1.

KPT-330, a potent and selective exportin-1 (XPO-1) inhibitor, shows antitumor effects modulating the expression of cyclin D1 and survivin [corrected] in prostate cancer models

BACKGROUND AND AIMS

Increased expression of Chromosome Region Maintenance (CRM-1)/exportin-1 (XPO-1) has been correlated with poor prognosis in several aggressive tumors, making it an interesting therapeutic target. Selective Inhibitor of Nuclear Export (SINE) compounds bind to XPO-1 and block its ability to export cargo proteins. Here, we investigated the effects of a new class of SINE compounds in models of prostate cancer.

MATERIAL AND METHODS

We evaluated the expression of XPO-1 in human prostate cancer tissues and cell lines. Next, six SINE (KPT-127, KPT-185, KPT-205, KPT-225, KPT-251 and KPT-330) compounds having different potency with broad-spectrum, tumor-selective cytotoxicity, tolerability and pharmacokinetic profiles were tested in a panel of prostate cancer cells representing distinct differentiation/progression states of disease and genotypes. Two SINE candidates for clinical trials (KPT-251 and KPT-330) were also tested in vivo in three cell models of aggressive prostate cancer engrafted in male nude mice.

RESULTS AND CONCLUSIONS

XPO-1 is overexpressed in prostate cancer compared to normal or hyperplastic tissues. Increased XPO-1 expression, mainly in the nuclear compartment, was associated with increased Gleason score and bone metastatic potential supporting the use of SINEs in advanced prostate cancer. SINE compounds inhibited proliferation and promoted apoptosis of tumor cells, but did not affect immortalized non-transformed prostate epithelial cells. Nuclei from SINE treated cells showed increased protein localization of XPO-1, survivin and cyclin D1 followed by degradation of these proteins leading to cell cycle arrest and apoptosis. Oral administration of KPT-251 and KPT-330 in PC3, DU145 and 22rv1 tumor-bearing nude mice reduced tumor cell proliferation, angiogenesis and induced apoptosis. Our results provide supportive evidence for the therapeutic use of SINE compounds in advanced/castration resistant prostate cancers and warrants further clinical investigation.

Genome-wide analysis of androgen receptor binding sites in prostate cancer cells

The transformation of prostate cancer from an androgen-dependent state to an androgen-independent state is a lethal progression. Alterations in transcriptional programs are the basis of prostate cancer deterioration. The androgen receptor (AR), a member of the nuclear hormone receptor superfamily, mediates prostate cancer progression by functioning primarily through the ligand-activated transcription of target genes. Therefore, a detailed map of AR-regulated genes and AR genomic binding sites is required for hormone-naive and castration-resistant prostate cancer. Through the use of chromatin immunoprecipitation in combination with direct sequencing, 4,143 AR binding sites were defined in the LNCaP androgen-sensitive prostate cancer cell line. Using the same method, 2,380 AR binding regions were identified in the LNCaP-AI long-term androgen-deprived cell line. Approximately 8.5% (354/4,143) of the binding regions were mapped to within 2 kb of the transcription start site (TSS) in the LNCaP cells, while ∼12.6% (299/2,380) were mapped to within 2 kb of the TSS in the LNCaP-AI cells. In total, the study mapped 2,796 genes in LNCaP cells and 1,854 genes in LNCaP-AI cells. The cell lines shared 789 mutual genes. In addition, gene ontology (GO) analysis of the genes revealed that there was a notable overlap between the GO terms in the LNCaP cells and LNCaP-AI cells. However, GO terms within the biological process domain that were only observed in the LNCaP-AI cells included the reproduction process, death, immune system process, multi-organism process, pigmentation and viral reproduction. The major genes in the different GO terms were TNFAIP8, RTN4, APP and SYNE1. Through analyzing the AR binding sites in the two cell types, the present study aimed to map potential AR-regulated genes, identify their associated transcription factors and provide a new perspective on the biological processes in the development of prostate cancer. The results provided a valuable data set that furthered the understanding of the genome-wide analysis of AR binding sites in prostate cancer cells, which may be exploited for the development of novel prostate cancer therapeutic strategies.

Identification and functional analysis of a novel tryptophyllin peptide from the skin of the red-eye leaf frog, Agalychnis callidryas

Amphibian skin has proved repeatedly to be a largely untapped source of bioactive peptides and this is especially true of members of the Phyllomedusinae subfamily of frogs native to South and Central America. Tryptophyllins are a group of peptides mainly found in the skin of members of this genus. In this study, a novel tryptophyllin (TPH) type 3 peptide, named AcT-3, has been isolated and structurally-characterised from the skin secretion and lyophilised skin extract of the red-eye leaf frog, Agalychnis callidryas. The peptide was identified in and purified from the skin secretion by reverse-phase HPLC. MALDI-TOF mass spectrometry and MS/MS fragmentation sequencing established its primary structure as: pGlu-Gly-Lys-Pro-Tyr-Trp-Pro-Pro-Pro-Phe-Leu-Pro-Glu, with a non-protonated molecular mass of 1538.19Da. The mature peptide possessed the canonical N-terminal pGlu residue that arises from post-translational modification of a Gln residue. The deduced open-reading frame consisted of 63 amino acid residues encoding a highly-conserved signal peptide of approximately 22 amino acid residues, an intervening acidic spacer peptide domain, a single AcT-3 encoding domain and a C terminal processing site. A synthetic replicate of AcT-3 was found to antagonise the effect of BK on rat tail artery smooth muscle and to contract the intestinal smooth muscle preparations. It was also found that AcT-3 could dose-dependently inhibit the proliferation of human prostate cancer cell lines after 72h incubation.

Androgen suppresses the proliferation of androgen receptor-positive castration-resistant prostate cancer cells via inhibition of Cdk2, CyclinA, and Skp2

The majority of prostate cancer (PCa) patient receiving androgen ablation therapy eventually develop castration-resistant prostate cancer (CRPC). We previously reported that androgen treatment suppresses Skp2 and c-Myc through androgen receptor (AR) and induced G1 cell cycle arrest in androgen-independent LNCaP 104-R2 cells, a late stage CRPC cell line model. However, the mechanism of androgenic regulation of Skp2 in CRPC cells was not fully understood. In this study, we investigated the androgenic regulation of Skp2 in two AR-positive CRPC cell line models, the LNCaP 104-R1 and PC-3^AR Cells. The former one is an early stage androgen-independent LNCaP cells, while the later one is PC-3 cells re-expressing either wild type AR or mutant LNCaP AR. Proliferation of LNCaP 104-R1 and PC-3^AR cells is not dependent on but is suppressed by androgen. We observed in this study that androgen treatment reduced protein expression of Cdk2, Cdk7, Cyclin A, cyclin H, Skp2, c-Myc, and E2F-1; lessened phosphorylation of Thr14, Tyr15, and Thr160 on Cdk2; decreased activity of Cdk2; induced protein level of p27^Kip1; and caused G1 cell cycle arrest in LNCaP 104-R1 cells and PC-3^AR cells. Overexpression of Skp2 protein in LNCaP 104-R1 or PC-3^AR cells partially blocked accumulation of p27^Kip1 and increased Cdk2 activity under androgen treatment, which partially blocked the androgenic suppressive effects on proliferation and cell cycle. Analyzing on-line gene array data of 214 normal and PCa samples indicated that gene expression of Skp2, Cdk2, and cyclin A positively correlates to each other, while Cdk7 negatively correlates to these genes. These observations suggested that androgen suppresses the proliferation of CRPC cells partially through inhibition of Cyclin A, Cdk2, and Skp2.

MicroRNA expressions associated with progression of prostate cancer cells to antiandrogen therapy resistance

Background

Development of resistance to androgen deprivation therapy (ADT) is a major obstacle for the management of advanced prostate cancer. Therapies with androgen receptor (AR) antagonists and androgen withdrawal initially regress tumors but development of compensatory mechanisms including AR bypass signaling leads to re-growth of tumors. MicroRNAs (miRNAs) are small regulatory RNAs that are involved in maintenance of cell homeostasis but are often altered in tumor cells.

Results

In this study, we determined the association of genome wide miRNA expression (1113 unique miRNAs) with development of resistance to ADT. We used androgen sensitive prostate cancer cells that progressed to ADT and AR antagonist Casodex (CDX) resistance upon androgen withdrawal and treatment with CDX. Validation of expression of a subset of 100 miRNAs led to identification of 43 miRNAs that are significantly altered during progression of cells to treatment resistance. We also show a correlation of altered expression of 10 proteins targeted by some of these miRNAs in these cells.

Conclusions

We conclude that dynamic alterations in miRNA expression occur early on during androgen deprivation therapy, and androgen receptor blockade. The cumulative effect of these altered miRNA expression profiles is the temporal modulation of multiple signaling pathways promoting survival and acquisition of resistance. These early events are driving the transition to castration resistance and cannot be studied in already developed CRPC cell lines or tissues. Furthermore our results can be used a prognostic marker of cancers with a potential to be resistant to ADT.

Difference in protein expression profile and chemotherapy drugs response of different progression stages of LNCaP sublines and other human prostate cancer cells

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, 80-90% of the patients who receive androgen ablation therapy ultimately develop recurrent tumors in 12-33 months after treatment with a median overall survival time of 1-2 years after relapse. LNCaP is a commonly used cell line established from a human lymph node metastatic lesion of prostatic adenocarcinoma. We previously established two relapsed androgen receptor (AR)-rich androgen-independent LNCaP sublines 104-R1 (androgen depleted for 12 months) and 104-R2 cells (androgen depleted for 24 months) from AR-positive androgen-dependent LNCaP 104-S cells. LNCaP 104-R1 and 104-R2 mimics the AR-positive hormone-refractory relapsed tumors in patients receiving androgen ablation therapy. Androgen treatment stimulates proliferation of 104-S cells, but causes growth inhibition and G1 cell cycle arrest in 104-R1 and 104-R2 cells. We investigated the protein expression profile difference between LNCaP 104-S vs. LNCaP 104-R1, 104-R2, PC-3, and DU-145 cells as well as examined the sensitivity of these prostate cancer cells to different chemotherapy drugs and small molecule inhibitors. Compared to 104-S cells, 104-R1 and 104-R2 cells express higher protein levels of AR, PSA, c-Myc, Skp2, BCL-2, P53, p-MDM2 S166, Rb, and p-Rb S807/811. The 104-R1 and 104-R2 cells express higher ratio of p-Akt S473/Akt, p-EGFR/EGFR, and p-Src/Src, but lower ratio of p-ERK/ERK than 104-S cells. PC-3 and DU-145 cells express higher c-Myc, Skp2, Akt, Akt1, and phospho-EGFR but less phospho-Akt and phospho-ERK. Overexpression of Skp2 increased resistance of LNCaP cells to chemotherapy drugs. Paclitaxel, androgen, and inhibitors for PI3K/Akt, EGFR, Src, or Bcl-2 seem to be potential choices for treatment of advanced prostate cancers. Our study provides rationale for targeting Akt, EGFR, Src, Bcl-2, and AR signaling as a treatment for AR-positive relapsed prostate tumors after hormone therapy.

Cholestane-3β, 5α, 6β-triol suppresses proliferation, migration, and invasion of human prostate cancer cells

Oxysterols are oxidation products of cholesterol. Cholestane-3β, 5α, 6β-triol (abbreviated as triol) is one of the most abundant and active oxysterols. Here, we report that triol exhibits anti-cancer activity against human prostate cancer cells. Treatment of cells with triol dose-dependently suppressed proliferation of LNCaP CDXR-3, DU-145, and PC-3 human prostate cancer cells and reduced colony formation in soft agar. Oral administration of triol at 20 mg/kg daily for three weeks significantly retarded the growth of PC-3 xenografts in nude mice. Flow cytometric analysis revealed that triol treatment at 10–40 µM caused G1 cell cycle arrest while the TUNEL assay indicated that triol treatment at 20–40 µM induced apoptosis in all three cell lines. Micro-Western Arrays and traditional Western blotting methods indicated that triol treatment resulted in reduced expression of Akt1, phospho-Akt Ser473, phospho-Akt Thr308, PDK1, c-Myc, and Skp2 protein levels as well as accumulation of the cell cycle inhibitor p27^Kip. Triol treatment also resulted in reduced Akt1 protein expression in PC-3 xenografts. Overexpression of Skp2 in PC-3 cells partially rescued the growth inhibition caused by triol. Triol treatment suppressed migration and invasion of DU-145, PC-3, and CDXR-3 cells. The expression levels of proteins associated with epithelial-mesenchymal transition as well as focal adhesion kinase were affected by triol treatment in these cells. Triol treatment caused increased expression of E-cadherin protein levels but decreased expression of N-cadherin, vimentin, Slug, FAK, phospho-FAK Ser722, and phospho-FAK Tyr861 protein levels. Confocal laser microscopy revealed redistribution of β-actin and α-tubulin at the periphery of the CDXR-3 and DU-145 cells. Our observations suggest that triol may represent a promising therapeutic agent for advanced metastatic prostate cancer.

Caffeic acid phenethyl ester suppresses proliferation and survival of TW2.6 human oral cancer cells via inhibition of Akt signaling

Caffeic acid phenethyl ester (CAPE) is a bioactive component extracted from honeybee hive propolis. Our observations indicated that CAPE treatment suppressed cell proliferation and colony formation of TW2.6 human oral squamous cell carcinoma (OSCC) cells dose-dependently. CAPE treatment decreased G1 phase cell population, increased G2/M phase cell population, and induced apoptosis in TW2.6 cells. Treatment with CAPE decreased protein abundance of Akt, Akt1, Akt2, Akt3, phospho-Akt Ser473, phospho-Akt Thr 308, GSK3β, FOXO1, FOXO3a, phospho-FOXO1 Thr24, phospho-FoxO3a Thr32, NF-κB, phospho-NF-κB Ser536, Rb, phospho-Rb Ser807/811, Skp2, and cyclin D1, but increased cell cycle inhibitor p27^Kip. Overexpression of Akt1 or Akt2 in TW2.6 cells rescued growth inhibition caused by CAPE treatment. Co-treating TW2.6 cells with CAPE and 5-fluorouracil, a commonly used chemotherapeutic drug for oral cancers, exhibited additive cell proliferation inhibition. Our study suggested that administration of CAPE is a potential adjuvant therapy for patients with OSCC oral cancer.

Caffeic Acid phenethyl ester as a potential treatment for advanced prostate cancer targeting akt signaling

Prostate cancer is the fifth most common cancer overall in the world. Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, most prostate cancer patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant tumors within 1–3 years after treatment. The median overall survival time is 1–2 years after tumor relapse. Chemotherapy shows little effect on prolonging survival for patients with metastatic hormone-refractory prostate cancer. More than 80% of prostate tumors acquire mutation or deletion of tumor suppressor phosphatase and tensin homolog (PTEN), a negative regulator of PI3K/Akt signaling, indicating that inhibition of PI3K/Akt might be a potential therapy for advanced prostate tumors. Caffeic acid phenethyl ester (CAPE) is a strong antioxidant extracted from honeybee hive propolis. CAPE is a well-known NF-κB inhibitor. CAPE has been used in folk medicine as a potent anti-inflammatory agent. Recent studies indicate that CAPE treatment suppresses tumor growth and Akt signaling in human prostate cancer cells. We discuss the potential of using CAPE as a treatment for patients with advanced prostate cancer targeting Akt signaling pathway in this review article.

Does changing androgen receptor status during prostate cancer development impact upon cholesterol homeostasis?

BACKGROUND

Recent evidence associates prostate cancer with high cholesterol levels, with cholesterol being an important raw material for cell-growth. Within the cell, cholesterol homeostasis is maintained by two master transcription factors: sterol-regulatory element-binding protein 2 (SREBP-2) and liver X receptor (LXR). We previously showed that the androgen receptor, a major player in prostate cell physiology, toggles these transcription factors to promote cholesterol accumulation. Given that prostate cancer therapy targets the androgen receptor, selecting for cells with altered androgen receptor activity, how would this affect SREBP-2 and LXR activity? Using a novel prostate cancer progression model, we explored how this crosstalk between the androgen receptor and cholesterol homeostasis changes during prostate cancer development.

METHODOLOGY/PRINCIPAL FINDINGS

Firstly, we characterised our progression model, which involved 1) culturing LNCaP cells at physiological testosterone levels to generate androgen-tolerant LNCaP-305 cells, and 2) culturing LNCaP-305 with the anti-androgen casodex to generate castration-resistant LNCaP-364 cells. This progression was accompanied by upregulated androgen receptor expression, typically seen clinically, and a reduction in androgen receptor activity. Although this influenced how SREBP-2 and LXR target genes responded to androgen treatment, cellular cholesterol levels and their response to changing sterol status was similar in all LNCaP sub-lines.

CONCLUSION/SIGNIFICANCE

Overall cholesterol homeostasis is unaffected by changing androgen receptor activity in prostate cancer cells. This does not negate the relationship between androgens and cholesterol homeostasis, but rather suggests that other factors compensate for altered androgen receptor activity. Given that cholesterol regulation is maintained during progression, this supports the growing idea that cholesterol metabolism is a suitable target for prostate cancer.

Androgen receptor primes prostate cancer cells to apoptosis through down-regulation of basal p21 expression

The androgen receptor (AR) for the male hormone androgen plays an important role in regulation of cell survival or death depending on the nature of cellular context and extracellular stimuli. The pro-survival function of AR is mediated mainly by transcriptional regulation of its target genes. By contrast, the pro-death function of AR can be transcription-dependent or -independent, although the underlying mechanism of the latter is incompletely understood. Here we report that, in androgen-independent prostate cancer cells, AR promotes UV-induced apoptosis through down-regulation of basal expression of p21 independently of its transcriptional activity. Down-regulation of basal p21 expression depends on AR N-terminal interacting protein PIRH2, an E3 ligase for proteasomal degradation of p53. Silencing of PIRH2 up-regulates p53, which in turn activates p21 transcription. Consistent with this, knockdown of PIRH2 suppresses UV-induced AR-dependent apoptosis. Our data suggest that AR primes androgen-independent prostate cancer cells to DNA damage-induced apoptosis through the PIRH2-p53-p21 axis.

Caffeic acid phenethyl ester suppresses the proliferation of human prostate cancer cells through inhibition of p70S6K and Akt signaling networks

Caffeic acid phenethyl ester (CAPE) is a bioactive component derived from honeybee hive propolis. CAPE has been shown to have antimitogenic, anticarcinogenic, and other beneficial medicinal properties. Many of its effects have been shown to be mediated through its inhibition of NF-κB signaling pathways. We took a systematic approach to uncover the effects of CAPE from hours to days on the signaling networks in human prostate cancer cells. We observed that CAPE dosage dependently suppressed the proliferation of LNCaP, DU-145, and PC-3 human prostate cancer cells. Administration of CAPE by gavage significantly inhibited the tumor growth of LNCaP xenografts in nude mice. Using LNCaP cells as a model system, we examined the effect of CAPE on gene expression, protein signaling, and transcriptional regulatory networks using micro-Western arrays and PCR arrays. We built a model of the impact of CAPE on cell signaling which suggested that it acted through inhibition of Akt-related protein signaling networks. Overexpression of Akt1 or c-Myc, a downstream target of Akt signaling, significantly blocked the antiproliferative effects of CAPE. In summary, our results suggest that CAPE administration may be useful as an adjuvant therapy for prostate and potentially other types of cancers that are driven by the p70S6K and Akt signaling networks.

Quantitative mathematical modeling of PSA dynamics of prostate cancer patients treated with intermittent androgen suppression

If a mathematical model is to be used in the diagnosis, treatment, or prognosis of a disease, it must describe the inherent quantitative dynamics of the state. An ideal candidate disease is prostate cancer owing to the fact that it is characterized by an excellent biomarker, prostate-specific antigen (PSA), and also by a predictable response to treatment in the form of androgen suppression therapy. Despite a high initial response rate, the cancer will often relapse to a state of androgen independence which no longer responds to manipulations of the hormonal environment. In this paper, we present relevant background information and a quantitative mathematical model that potentially can be used in the optimal management of patients to cope with biochemical relapse as indicated by a rising PSA.

Androgens as therapy for androgen receptor-positive castration-resistant prostate cancer

Prostate cancer is the most frequently diagnosed non-cutaneous tumor of men in Western countries. While surgery is often successful for organ-confined prostate cancer, androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, this therapy is associated with several undesired side-effects, including increased risk of cardiovascular diseases. Shortening the period of androgen ablation therapy may benefit prostate cancer patients. Intermittent Androgen Deprivation therapy improves quality of life, reduces toxicity and medical costs, and delays disease progression in some patients. Cell culture and xenograft studies using androgen receptor (AR)-positive castration-resistant human prostate cancers cells (LNCaP, ARCaP, and PC-3 cells over-expressing AR) suggest that androgens may suppress the growth of AR-rich prostate cancer cells. Androgens cause growth inhibition and G1 cell cycle arrest in these cells by regulating c-Myc, Skp2, and p27Kip via AR. Higher dosages of testosterone cause greater growth inhibition of relapsed tumors. Manipulating androgen/AR signaling may therefore be a potential therapy for AR-positive advanced prostate cancer.

Androgen suppresses proliferation of castration-resistant LNCaP 104-R2 prostate cancer cells through androgen receptor, Skp2, and c-Myc

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, this therapy is associated with several undesired side-effects, including increased risk of cardiovascular diseases. To study if termination of long-term androgen ablation and restoration of testosterone levels could suppress the growth of relapsed hormone-refractory prostate tumors, we implanted testosterone pellets in castrated nude mice carrying androgen receptor (AR)-positive LNCaP 104-R2 cells, which relapsed from androgen-dependent LNCaP 104-S cells after long-term androgen deprivation. 104-R2 tumor xenografts regressed after testosterone pellets were implanted. Of 33 tumors, 24 adapted to elevation of testosterone level and relapsed as androgen-insensitive tumors. Relapsed tumors (R2Ad) expressed less AR and prostate-specific antigen. We then studied the molecular mechanism underlying the androgenic regulation of prostate cancer cell proliferation. Androgen suppresses proliferation of 104-R2 by inducing G(1) cell cycle arrest through reduction of S-phase kinase-associated protein 2 (Skp2) and c-Myc, and induction of p27(Kip1). 104-R2 cells adapted to androgen treatment and the adapted cells, R2Ad, were androgen-insensitive cells with a slower growth rate and low protein level of AR, high levels of c-Myc and Skp2, and low levels of p27(Kip1). Nuclear AR and prostate-specific antigen expression is present in 104-R2 cells but not R2Ad cells when androgen is absent. Overexpression of AR in R2Ad cells regenerated an androgen-repressed phenotype; knockdown of AR in 104-R2 cells generated an androgen-insensitive phenotype. Overexpression of Skp2 and c-Myc in 104-R2 cells blocked the growth inhibition caused by androgens. We concluded that androgens cause growth inhibition in LNCaP 104-R2 prostate cancer cells through AR, Skp2, and c-Myc.

Leptin signaling and apoptotic effects in human prostate cancer cell lines

BACKGROUND

Prostate cancer (PCa) progression is often associated with transactivation of the androgen receptor (AR) by endogenous hormones/growth factors. One such factor affecting growth, proliferation, and apoptostis (pro-/anti-) in various cancers is the adipokine leptin. This research studied leptin-induced signaling and apoptosis in androgen sensitive (LNCaP, PC3/AR) and insensitive (PC3, DU145) PCa cell lines.

METHODS

Signaling was studied by immunoblotting in cells overexpressing leptin receptors (LRb), Janus kinase 2 (JAK2), and kinase negative-HER2-YFP cDNAs. Apoptosis was measured by immunoblotting of apoptotic proteins and by Hoechst staining of condensed DNA.

RESULTS

Leptin rapidly induced activation of JAK2, STAT3, and MAPK (ERK1/2) signaling cascades; it may also induce HER2 transactivation via leptin-induced phospho-JAK2. Leptin was then shown to exert clear pro-apoptotic effects, increasing levels of caspase 3, cleavage of its substrate, poly (ADP-ribose) polymerase (PARP) to cleaved PARP(89) , levels of CK 18, a cytoskeletal protein formed during apoptosis, and DNA condensation. Kinase inhibitors indicated that leptin-induced apoptosis is probably mediated by balanced activation of JAK2/STAT3, p38 MAPK, and PKC pathways in PCa cells. A human leptin mutein LRb antagonist, L39A/D40A/F41A, fully inhibited leptin-induced phosphorylation of JAK2, ERK1/2, and Akt/PKB, and partially abrogated effects on apoptotic proteins. In LNCaP and PC3/AR cells, leptin increased AR protein levels in correlation with raised apoptotic markers. Thus, AR may mediate, at least partly, the leptin-induced apoptotic response.

CONCLUSIONS

Leptin can clearly induce apoptosis in human PCa cell lines. These findings could lead to development of new leptin agonists with enhanced pro-apoptotic effects and targeted for use in human PCa.

Mathematical modelling of prostate cancer growth and its application to hormone therapy

Hormone therapy in the form of androgen deprivation is a major treatment for advanced prostate cancer. However, if such therapy is overly prolonged, tumour cells may become resistant to this treatment and result in recurrent fatal disease. Long-term hormone deprivation also is associated with side effects poorly tolerated by patients. In contrast, intermittent hormone therapy with alternating on- and off-treatment periods is a possible clinical strategy to delay progression to hormone-refractory disease with the advantage of reduced side effects during the off-treatment periods. In this paper, we first overview previous studies on mathematical modelling of prostate tumour growth under intermittent hormone therapy. The model is categorized into a hybrid dynamical system because switching between on-treatment and off-treatment intervals is treated in addition to continuous dynamics of tumour growth. Next, we present an extended model of stochastic differential equations and examine how well the model is able to capture the characteristics of authentic serum prostate-specific antigen (PSA) data. We also highlight recent advances in time-series analysis and prediction of changes in serum PSA concentrations. Finally, we discuss practical issues to be considered towards establishment of mathematical model-based tailor-made medicine, which defines how to realize personalized hormone therapy for individual patients based on monitored serum PSA levels.

Proteasomal degradation unleashes the pro-death activity of androgen receptor

Androgen receptor (AR) is able to promote stress-induced cell death independently of its transcription activity in androgen-independent prostate cancer cells. Yet, the underlying mechanism is incompletely understood. Here, we report that stress-induced proteasomal degradation of AR contributes to its pro-death activity. Upon exposure to ultraviolet light and staurosporine, AR underwent proteasomal degradation. Blockade of AR degradation significantly suppressed stress-induced apoptosis in androgen-independent prostate cancer cells. Ectopic expression of the AR N-terminal (AR-N) domain, which lacks DNA- and ligand-binding abilities, led to cell death without any additional death stimuli. Truncation analysis revealed that AR-N domain contains several sub-domains that regulate the pro-death activity of AR, specifically the first 105 amino acids, which function as a minimal pro-death domain acting upstream of caspases. The pro-apoptotic activity of AR N-terminal fragments was suppressed by ectopic expression of Bcl-2 or selected caspase inhibitors. Thus, our results reveal a novel mechanism by which AR promotes stress-induced cell death in androgen-independent prostate cancer cells.

The role of PI 3-kinase p110beta in AKT signally, cell survival, and proliferation in human prostate cancer cells

BACKGROUND

Class IA PI 3-kinases produce phosphatidylinositol (3,4,5)-trisphosphate (PIP3). PIP3 is bound by AKT which facilities its activation by PDK1. Activated AKT promotes cell survival and stimulates cell proliferation. Class IA PI 3-kinases are heterodimers consisting of a regulatory subunit p85 and a catalytic subunit p110. The p110alpha isoform has been shown to be mutated in a number of tumor types. A number of recent studies suggest that the p110beta isoform may be functionally relevant in prostate cancer. In this study we extend this work to include the examination of the expression and functional properties of p110alpha and p110beta in three different prostate cancer cell lines, DU145, LNCaP, PC3, as well as the non-tumorigenic but immortalized RWPE1 prostate epithelial cell line.

METHODS

Western blot analysis was used to measure protein expression and quantitative real-time PCR was used to measure mRNA levels. After targeted knockdown using isoform-specific siRNAs to reduce PI 3-kinase p110alpha or p110beta isoform expression, we measured downstream signally events such as phosphorylation of AKT, ERK 1/2, PDK, and FOXO, as well as biological consequences such as changes in apoptosis, and alterations in cell cycle progression.

RESULTS

In all three prostate cancer cell lines examined, targeted knockdown of p110beta, and not p110alpha, resulted in significantly reduced AKT, PDK, and FOXO phosphorylation. While knockdown of either p110 isoform resulted in an increase in apoptosis and a cell cycle arrest in G1 in the remaining non-apoptotic cells, these effects were much more pronounced with knockdown of p110beta.

CONCLUSIONS

Our results support the concept that p110beta appears to be the predominant functional class I PI 3-kinase isoform in prostate cancer cells.

Prolonged treatment with bicalutamide induces androgen receptor overexpression and androgen hypersensitivity

BACKGROUND

Various hormone refractory prostate cancer cell models have been established with androgen depletion and have helped to clarify the mechanism for the transition into androgen-depletion independent status. However, the mechanism of bicalutamide resistance remains unclear because few cell models have been generated.

METHODS

We generated a bicalutamide-resistant subline, LNCaP-BC2, from LNCaP after prolonged treatment with bicalutamide. Androgen and/or bicalutamide responsiveness for proliferation and prostate-specific antigen (PSA) secretion were examined in vitro and in vivo. Testosterone and dihydrotestosterone (DHT) levels in xenografted tumors were analyzed by liquid chromatography-tandem mass spectrometry. Androgen receptor (AR) gene mutation and amplification and AR and pAR(210) expression were determined.

RESULTS

LNCaP-BC2 did not grow in an androgen-depleted medium and proliferation was stimulated in a tenfold lower concentration of androgen than that of LNCaP. LNCaP-BC2 grew in castrated male mice, and the DHT level in grafted LNCaP-BC2 tumors was 7.7-fold lower than in LNCaP tumors. Bicalutamide stimulated LNCaP-BC2 proliferation and PSA secretion in vitro and the antitumor activity of bicalutamide against LNCaP-BC2 was weaker than that of LNCaP in vivo. Additional AR mutation and AR gene amplification were not detected in LNCaP-BC2, but AR and pAR(210) expression and PSA secretion in LNCaP-BC2 were higher than in LNCaP.

CONCLUSIONS

Bicalutamide-resistant LNCaP-BC2 exhibited AR overexpression and hypersensitivity to low levels of androgen. Our data suggests that AR overexpression is a significant mechanism of bicalutamide resistance similar to resistance from chronic androgen depletion. In addition, pAR(210) overexpression could be a potential mechanism for hypersensitivity to low androgen in LNCaP-BC2.

Establishment and characterization of an androgen receptor-dependent, androgen-independent human prostate cancer cell line, LNCaP-CS10

BACKGROUND

Hormone refractoriness is a lethal event for advanced prostate cancer patients, but the mechanisms of the disease are not well elucidated, especially for the so-called "outlaw" pathways of androgen receptor (AR)-dependent, androgen-independent hormone-refractory prostate cancer.

METHODS

Androgen-dependent prostate cancer LNCaP cells were treated with bicalutamide under an androgen-depleted condition to obtain refractory cells. In the obtained cell line, LNCaP-CS10, we analyzed the effects of androgen and bicalutamide on cell growth and prostate-specific antigen (PSA) production. In addition, AR gene mutation, AR expression levels, and AR subcellular localizations were analyzed.

RESULTS

In LNCaP-CS10, cell growth and PSA production were found under an androgen-depleted condition and were induced by both R1881 and bicalutamide. Knocking down AR by siRNAs did suppress the growth and PSA production of LNCaP-CS10 cells in the androgen-depleted condition. In comparison to LNCaP, amplification or additional new mutations were not found in the AR genes, but AR nuclear translocation induced by bicalutamide was identified in the LNCaP-CS10 cells. The growth and PSA production of xenografted LNCaP-CS10 tumors, which secrete PSA not only in non-castrated SCID mice but also in castrated SCID mice, were not inhibited by bicalutamide.

CONCLUSIONS

We have generated a bicalutamide-resistant and androgen-independent prostate cancer cell line, LNCaP-CS10, with outlaw activation both in vitro and in vivo. The LNCaP-CS10 cell line is beneficial for elucidating outlaw pathway mechanisms and evaluating the efficacy of new therapeutics for hormone-refractory prostate cancer.

Androgen via p21 inhibits tumor necrosis factor alpha-induced JNK activation and apoptosis

The male hormone androgen is a growth/survival factor for its target tissues or organs. Yet, the underlying mechanism is incompletely understood. Here, we report that androgen via p21 inhibits tumor necrosis factor alpha-induced JNK activation and apoptosis. Inhibition by androgen requires the transcription activity of androgen receptor (AR) and de novo protein synthesis. Androgen.AR induces expression of p21 that in turn inhibits tumor necrosis factor alpha-induced JNK and apoptosis. Furthermore, genetic interruption of p21 alleles abolishes the inhibition by androgen. Our results reveal a novel cross-talk between androgen x AR and JNK, thereby providing a molecular mechanism underlying the survival function of androgen.

Up-regulation of Bcl-2 is required for the progression of prostate cancer cells from an androgen-dependent to an androgen-independent growth stage

Bcl-2 is an anti-apoptotic oncoprotein and its protein levels are inversely correlated with prognosis in many cancers. However, the role of Bcl-2 in the progression of prostate cancer is not clear. Here we report that Bcl-2 is required for the progression of LNCaP prostate cancer cells from an androgen-dependent to an androgen-independent growth stage. The mRNA and protein levels of Bcl-2 are significantly increased in androgen-independent prostate cancer cells. shRNA-mediated gene silencing of Bcl-2 in androgen-independent prostate cancer cells promotes UV-induced apoptosis and suppresses the growth of prostate tumors in vivo. Growing androgen-dependent cells under androgen-deprivation conditions results in formation of androgen-independent colonies; and the transition from androgen-dependent to androgen-independent growth is blocked by ectopic expression of the Bcl-2 antagonist Bax or Bcl-2 shRNA. Thus, our results demonstrate that Bcl-2 is not only critical for the survival of androgen-independent prostate cancer cells, but is also required for the progression of prostate cancer cells from an androgen-dependent to an androgen-independent growth stage.

Suppression of androgen receptor signaling and prostate specific antigen expression by (-)-epigallocatechin-3-gallate in different progression stages of LNCaP prostate cancer cells

The green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), inhibits the development and progression of prostate cancer in TRAMP mice and in men. We examined the effects of EGCG on LNCaP human prostate cancer sublines 104-S, 104-R1 and R1Ad representing different progression stages of prostate cancer. EGCG suppressed cell proliferation, prostate specific antigen (PSA) expression, and AR transcriptional activity in the different LNCaP sublines. Intraperitoneal administration of EGCG also suppressed the growth of relapsing R1Ad tumors and decreased tumor-derived serum PSA. Effects of EGCG on tumor PSA expression have the potential to affect accurate monitoring of patient tumor burden by serum PSA measurements.

Androgen inhibits the growth of carcinoma cell lines established from prostate cancer xenografts that escape androgen treatment

Most prostate cancers escape endocrine therapy by diverse mechanisms. One of them might be growth repression by androgen. We reported that androgen represses the growth in culture of MOP cells (a sub-line of LNCaP cells) and that of MOP cell xenografts, although tumor growth becomes androgen-independent (AI). Here we explore whether AI tumors contain androgen-responsive cells. ME carcinoma cells were established from AI tumors. The responses to androgen were examined by cell counting, DAPI labeling, flow cytometry, PSA immunoassay and tumor size follow-up. Androgen receptors (AR) were analyzed by western blotting and DNA sequencing. The pattern of responses of these cells to androgen was compared to that of MOP cells and that of JAC cells established from LNCaP-like MOP cells. R1881, a synthetic androgen: (1) repressed the growth of all the six ME cell lines obtained, MOP and JAC cells, (2) augmented the secretion of PSA, (3) induced spectacular cell bubbling/fragmentation and (4) blocked the cell cycle and induced a modest increase of apoptosis. All the androgen-repressed cells expressed the same level of mutated AR as LNCaP cells. In nude mice, the growth of ME-2 cell xenografts displayed transient androgen repression similar to that of MOP cells. In culture neither fibroblasts nor extra-cellular matrix altered the effects of R1881 on cell proliferation. These results demonstrate that androgen-independent tumors contain androgen-responsive cells. The apparent discrepancy between the responses to androgen of tumors and those of carcinoma cells in culture suggests that microenvironmental factors contribute to the androgen responsiveness of tumor cells in vivo. These modifications, albeit unspecified, could be suitable targets for restoring the androgen responsiveness of AI tumors.

Longitudinal analysis of androgen deprivation of prostate cancer cells identifies pathways to androgen independence

BACKGROUND

Following androgen ablation therapy, the majority of prostate cancer patients develop treatment resistance with a median time of 18-24 months to disease progression.

METHODS

To identify molecular targets that promote prostate cancer cell survival and contribute to androgen independence, we evaluated changes in LNCaP cell gene expression during 12 months of androgen deprivation. At time points reflecting critical growth and phenotypic changes, we performed Affymetrix expression array analysis to examine the effects of androgen deprivation during the acute response, during the period of apparent quiescence, and following the emergence of a highly proliferative, androgen-independent prostate cancer cell phenotype (LNCaP-AI).

RESULTS

We discovered alterations in gene expression for molecules associated with promoting prostate cancer cell growth and survival, and regulating cell cycle progression and apoptosis. Additionally, expression of AR co-regulators, adrenal androgen metabolizing enzymes, and markers of neuroendocrine disease were significantly altered.

CONCLUSIONS

These findings contribute greatly to our understanding of androgen-independent prostate cancer. The value of this longitudinal approach lies in the ability to examine gene expression changes throughout the adaptive response to androgen deprivation; it provides a more dynamic illustration of genes which contribute to disease progression in addition to specific genes which constitute an androgen-independent phenotype.

Antisense MDM2 enhances the response of androgen insensitive human prostate cancer cells to androgen deprivation in vitro and in vivo

BACKGROUND

Antisense MDM2 oligonucleotide (AS-MDM2) sensitizes androgen sensitive LNCaP cells to androgen deprivation (AD) in vitro and in vivo. In this study, we investigated the effects of AS-MDM2 combined with AD on androgen resistant LNCaP (LNCaP-Res) and moderately androgen resistant bcl-2 overexpressing LNCaP (LNCaP-BST) cells.

METHODS

The LNCaP-Res cell line was generated by culturing LNCaP cells in medium containing charcoal-stripped serum for more than 1 year. Apoptosis was quantified in vitro by Annexin V staining and caspase 3 + 7 activity. For the in vivo studies, orthotopic tumor growth was monitored by magnetic resonance imaging (MRI). AS-MDM2 and the mismatch control were given by i.p. injection at doses of 25 mg/kg per day, 5 days/week for 15 days.

RESULTS

LNCaP-Res cells expressed high levels of androgen receptor (AR) and bcl-2, and displayed no growth inhibition to AD. AS-MDM2 caused significant reductions in MDM2 and AR expression, and increases in p53 and p21 expression in both cell lines. AS-MDM2 + AD resulted in the highest levels of apoptosis in vitro and tumor growth inhibition in vivo in both cell lines; although, these effects were less pronounced in LNCaP-BST cells.

CONCLUSIONS

AS-MDM2 + AD enhanced apoptotic cell death in vitro and tumor growth inhibition in vivo in androgen resistant cell lines. The action of AS-MDM2 + AD was influenced somewhat by bcl-2 expression as an isolated change (LNCaP-BST cells), but not when accompanied by other molecular changes associated with androgen insensitivity (LNCaP-Res cells). MDM2 knockdown has promise for the treatment of men with early hormone refractory disease.

Prostate cancer cells tolerate a narrow range of androgen receptor expression and activity

BACKGROUND

The precise role of androgen receptor (AR) in the normal development of prostate and the progression of prostate cancer (CaP) remains controversial. While AR expression and activity is associated with growth arrest and differentiation of normal prostate cells, it is maintained in CaP cells that are characterized by continued proliferation. Our objective was to determine the importance of AR signaling for survival and growth of CaP cells, particularly those with a hormone-refractory phenotype.

METHOD

AR expression was modulated in androgen-sensitive (AS) and androgen-insensitive (AI) CaP cells using RNAi and cDNA transduction. Resulting changes in AR transcriptional activity and cell growth were quantified.

RESULTS

Interference with AR expression in both AS and AI CaP cells by shRNA transduction demonstrated a direct correlation between residual AR expression and cell viability. CaP cells lacking AR expression undergo apoptosis several days after AR down-regulation. This delayed response suggests that AR regulates apoptosis likely through an indirect mechanism. Overexpression of AR or hyper-stimulation of AR with high levels of androgen was also poorly tolerated by CaP cells. Cells with elevated AR had a growth disadvantage due to G1 cell cycle arrest and induction of p21 and GADD45 expression.

CONCLUSIONS

CaP cells expressing endogenous AR are sensitive to both increases and decreases in AR expression levels and activity. AR in CaP cells is delicately regulated to provide a balance between cell death and continued proliferation. Thus, both approaches, inhibition and over-stimulation of AR activity, may have therapeutic value for treatment of prostate cancer.

Combination treatment of prostate cancer cell lines with bioactive soy isoflavones and perifosine causes increased growth arrest and/or apoptosis

PURPOSE

To determine whether targeting the androgen receptor (AR) and Akt pathways using a combination of genistein combined polysaccharide (GCP) and perifosine is more effective at inducing growth arrest/apoptosis in prostate cancer cells compared with treatment with GCP or perifosine as single agents.

EXPERIMENTAL DESIGN

The effect of GCP and perifosine treatment was assessed in five prostate cancer cell lines: LNCaP (androgen sensitive), LNCaP-R273H, C4-2, Cds1, and PC3 (androgen insensitive). A clonogenic assay assessed the long-term effects on cell growth and survival. Flow cytometry and Western blot analysis of poly(ADP)ribose polymerase cleavage were used to assess short-term effects. Preliminary studies to investigate mechanism of action included Western blot for P-Akt, Akt, P-p70S6K, p70S6K, p53, and p21; prostate-specific antigen analysis; and the use of myristoylated Akt and AR-specific small interfering RNA.

RESULTS

Combination treatment with GCP and perifosine caused a decrease in clonogenic potential in all cell lines. In short-term assays, growth arrest was observed in the majority of cell lines, as well as increased inhibition of Akt activity and induction of p21 expression. Increased apoptosis was only observed in LNCaP. Knockdown of AR caused a further increase in apoptosis.

CONCLUSION

Combination treatment with GCP and perifosine targets the Akt pathway in the majority of the prostate cancer cell lines and causes increased inhibition of cell growth and clonogenicity. In LNCaP, combination treatment targets both the Akt and AR pathways and causes increased apoptosis. These data warrant clinical validation in prostate cancer patients.

Therapeutic potential of CDK inhibitor NU2058 in androgen-independent prostate cancer

Antiandrogens are initially effective in controlling prostate cancer (CaP), the second most common cancer in men, but resistance, associated with the loss of androgen-regulated cell cycle control, is a major problem. At present there is no effective treatment for androgen-independent prostate cancer (AIPC). Cellular proliferation is driven by cyclin-dependent kinases (CDKs) with kinase inhibitors (for example, p27) applying the breaks. We present the first investigation of the therapeutic potential of CDK inhibitors, using the guanine-based CDK inhibitor NU2058 (CDK2 IC(50)=17 microM, CDK1 IC(50)=26 microM), in comparison with the antiandrogen bicalutamide (Casodex) in AIPC cells. A panel of AIPC cells was found to be resistant to Casodex-induced growth inhibition, but with the exception of PC3 (GI(50)=38 microM) and CWR22Rv1 (GI(50)=46 microM) showed similar sensitivity to NU2058 (GI(50)=10-17 microM) compared to androgen-sensitive LNCaP cells (GI(50)=15 microM). In LNCaP cells and their Casodex-resistant derivative, LNCaP-cdxR, growth inhibition by NU2058 was accompanied by a concentration-dependent increase in p27 levels, reduced CDK2 activity and pRb phosphorylation, a decrease in early gene expression and G1 cell cycle phase arrest in both cell lines. In response to Casodex, there were similar observations in LNCaP cells (GI(50)=6+/-3 microM Casodex) but not in LNCaP-cdxR cells (GI(50)=24+/-5 microM Casodex).

The liver X receptor agonist T0901317 acts as androgen receptor antagonist in human prostate cancer cells

T0901317 is a potent non-steroidal synthetic liver X receptor (LXR) agonist. T0901317 blocked androgenic stimulation of the proliferation of androgen-dependent LNCaP 104-S cells and androgenic suppression of the proliferation of androgen-independent LNCaP 104-R2 cells, inhibited the transcriptional activation of an androgen-dependent reporter gene by androgen, and suppressed gene and protein expression of prostate specific antigen (PSA), a target gene of androgen receptor (AR) without affecting gene and protein expression of AR. T0901317 also inhibited binding of a radiolabeled androgen to AR, but inhibition was much weaker compared to the effect of the antiandrogens, bicalutamide and hydroxyflutamide. The LXR agonist T0901317, therefore, acts as an antiandrogen in human prostate cancer cells.

Modulation of liver X receptor signaling as novel therapy for prostate cancer

Liver X receptors (LXRs) are important regulators of cholesterol, fatty acid, and glucose homeostasis. LXR agonists are effective for treatment of murine models of atherosclerosis, diabetes, and Alzheimer's disease. Recently we observed that LXR agonists suppressed proliferation of prostate and breast cancer cells in vitro and treatment of mice with the LXR agonist T0901317 suppressed the growth of prostate tumor xenografts. LXR agonists appear to cause G1 cell cycle arrest in cells by reducing expression of Skp2 and inducing the accumulation of p27(Kip). T0901317 induced expression of ATP-binding cassette transporter A1 (ABCA1) and delayed the progression of androgen-dependent human prostate tumor xenografts towards androgen-independency in mice. Phytosterols, the plant equivalent of mammalian cholesterol, have recently been shown to be agonists for LXRs. beta-Sitosterol and campesterol, the two most common phytosterols, suppressed proliferation of prostate and breast cancer cells. The anticancer activity of phytosterols may be due to LXR signaling. This review examines the potential use of LXR signaling as a therapeutic target in prostate and other cancers.

Androgen axis in prostate cancer

Endocrine therapy for advanced prostate cancer is based on androgen ablation or blockade of the androgen receptor (AR). AR action in prostate cancer has been investigated in a number of cell lines, their derivatives, and transgenic animals. AR expression is heterogenous in prostate cancer in vivo; it could be detected in most primary tumors and their metastases. However, some cells lack the AR because of epigenetic changes in the gene promoter. AR expression increases after chronic androgen ablation in vitro. In several xenografts, AR upregulation is the most consistent change identified during progression towards therapy resistance. In contrast, the AR pathway may be by-passed during chronic treatment with a nonsteroidal anti-androgen. AR sensitivity in prostate cancer increases as a result of activation of the Ras/mitogen-activated protein kinase pathway. One of the major difficulties in endocrine therapy for prostate cancer is acquisition of agonistic properties of AR antagonists observed in the presence of mutated AR. Enhancement of AR function by associated coactivator proteins has been extensively investigated. Cofactors SRC-1, RAC3, p300/CBP, TIF-2, and Tip60 are upregulated in advanced prostate cancer. Most studies on ligand-independent activation of the AR are focused on Her-2/neu and interleukin-6 (IL-6). On the basis of studies that showed overexpression and activation of the AR in advanced prostate cancer, it was suggested that novel therapies that reduce AR expression will provide a benefit to patients. There is experimental evidence showing that prostate tumor growth in vitro and in vivo is inhibited following administration of chemopreventive drugs or antisense oligonucleotides that downregulate AR mRNA and protein expression.

Inhibition of tumor growth and progression of LNCaP prostate cancer cells in athymic mice by androgen and liver X receptor agonist

Androgen-dependent human LNCaP 104-S tumor xenografts progressed to androgen-independent relapsed tumors (104-Rrel) in athymic mice after castration. The growth of 104-Rrel tumors was suppressed by testosterone. However, 104-Rrel tumors adapted to androgen and regrew as androgen-stimulated 104-Radp tumors. Androgen receptor expression in tumors and serum prostate-specific antigen increased during progression from 104-S to 104-Rrel but decreased during transition from 104-Rrel to 104-Radp. Expression of genes related to liver X receptor (LXR) signaling changed during progression. LXRalpha, LXRbeta, ATP-binding cassette transporter A1 (ABCA1), and sterol 27-hydroxylase decreased during progression from 104-S to 104-Rrel. These coordinated changes in LXR signaling in mice during progression are consistent with our previous findings that reduction of ABCA1 gene expression stimulates proliferation of LNCaP cells. To test if attenuation of LXR signaling may enhance prostate cancer progression from an androgen-dependent state to an androgen-independent state, castrated mice carrying 104-S tumors were given the synthetic LXR agonist T0901317 by gavage. T0901317 delayed progression from 104-S to 104-Rrel tumors. Based on our in vivo model, androgen is beneficial for the treatment of androgen-independent androgen receptor-rich prostate cancer and modulation of LXR signaling may be a potentially useful therapy for prostate cancer.

Molecular markers in the diagnosis of prostate cancer

The genetic alterations leading to prostate cancer are gradually being discovered. A wide variety of genes have been associated with prostate cancer development as well as tumor progression. Knowledge of gene polymorphisms associated with disease aid in the understanding of important pathways involved in this process and may result in the near future in clinical applications. Urinary molecular markers will soon be available to aid in the decision of repeat prostate biopsies. Recent findings suggest the importance of androgen signaling in disease development and progression. The further understanding of interaction of inflammation, diet, and genetic predisposition will improve risk stratification in the near future.

Requirement of androgen-dependent activation of protein kinase Czeta for androgen-dependent cell proliferation in LNCaP Cells and its roles in transition to androgen-independent cells

A cell line that we designed, AILNCaP, proliferated in androgen-depleted medium after emerging from long-term androgen-depleted cultures of an androgen-sensitive prostate cancer cell line, LNCaP. Using this cell line as a model of progression to androgen independence, we demonstrated that the activity of the mammalian target of rapamycin/p70 S6 kinase transduction pathway is down-regulated after androgen depletion in LNCaP, whereas its activation is related to transition of this cell line to androgen-independent proliferation. Kinase activity of protein kinase Czeta is regulated by androgen stimulation in LNCaP cells, whereas it is activated constitutively in AILNCaP cells under androgen-depleted conditions. Treatment with a protein kinase Czeta pseudosubstrate inhibitor reduced p70 S6 kinase activity and cell proliferation in both cell lines. We identified that both protein kinase Czeta and p70 S6 kinase were associated in LNCaP cells and this association was enhanced by the androgen stimulation. We examined the expression of phospho-protein kinase Czeta and phospho-p70 S6 kinase in hormone-naive prostate cancer specimens and found that the expression of both kinases was correlated with each other in those specimens. Significant correlation was observed between the expression of both kinases and Ki67 expression. Most of the prostate cancer cells that survived after prior hormonal treatment also expressed both kinases. This is the first report that shows the significance of this pathway for both androgen-dependent and -independent cell proliferation in prostate cancer. Our data suggest that protein kinase Czeta/mammalian target of rapamycin/S6 kinase pathway plays an important role for the transition of androgen-dependent to androgen-independent prostate cancer cells.