Multiple estrogen function in human prostate cancer cells

Urinary estrogen metabolites and prostate cancer risk: a pilot study

BACKGROUND

The high incidence of and few identified risk factors for prostate cancer underscore the need to further evaluate markers of prostate carcinogenesis. The aim of this pilot study was to evaluate urinary estrogen metabolites as a biomarker of prostate cancer risk.

METHODS

Using a liquid chromatography-tandem mass spectrometry method, urinary concentrations of 15 estrogen metabolites were determined in 77 prostate cancer cases, 77 healthy controls, and 37 subjects who had no evidence of prostate cancer after a prostate biopsy.

RESULTS

We observed an inverse association between the urinary 16-ketoestradiol (16-KE2) and 17-epiestriol (17-epiE3)--metabolites with high estrogenic activity--and prostate cancer risk. Men in the lowest quartile of 16-KE2, had a 4.6-fold risk of prostate cancer (OR=4.62, 95% CI=1.34-15.99), compared with those in the highest quartile.

CONCLUSIONS

We observed modest differences in estrogen metabolite concentrations between prostate cancer patients and subjects without cancer. Larger studies with both androgen and estrogen measurements are needed to confirm these results to clarify further whether estrogen metabolites are independent biomarkers for prostate cancer risk and whether androgen/estrogen imbalance influences prostate cancer risk.

Promoter methylation in prostate cancer and its application for the early detection of prostate cancer using serum and urine samples

Prostate cancer is the second most common cancer and the second leading cause of cancer death in men. However, prostate cancer can be effectively treated and cured, if it is diagnosed in its early stages when the tumor is still confined to the prostate. Combined with the digital rectal examination, the PSA test has been widely used to detect prostate cancer. But, the PSA screening method for early detection of prostate cancer is not reliable due to the high prevalence of false positive and false negative results. Epigenetic alterations including hypermethylation of gene promoters are believed to be the early events in neoplastic progression and thus these methylated genes can serve as biomarkers for the detection of cancer from clinical specimens. This review discusses DNA methylation of several gene promoters during prostate carcinogenesis and evaluates the usefulness of monitoring methylated DNA sequences, such as GSTP1, RASSF1A, RARβ2 and galectin-3, for early detection of prostate cancer in tissue biopsies, serum and urine.

Prostate cancer epigenetics: a review on gene regulation

Prostate cancer is the most common cancer in men in western countries, and its incidence is increasing steadily worldwide. Molecular changes including both genetic and epigenetic events underlying the development and progression of this disease are still not well understood. Epigenetic events are involved in gene regulation and occur through different mechanisms such as DNA methylation and histone modifications. Both DNA methylation and histone modifications affect gene regulation and play important roles either independently or by interaction in tumor initiation and progression. This review will discuss the genes associated with epigenetic alterations in prostate cancer progression: their regulation and importance as possible markers for the disease.

Human prostate cancer cells and xenografts are targeted and destroyed through luteinizing hormone releasing hormone receptors

BACKGROUND

A conjugate of a lytic peptide, hecate, and a 15-amino acid segment of the beta-chain of chorionic gonadotropin (CG) destroyed human prostate xenografts in nude mice by targeting LH receptors. Since these xenografts also express LHRH receptors, we prepared a LHRH-hecate conjugate and tested its ability to destroy PC-3 cells in vitro and in vivo.

MATERIALS AND METHODS

LHRH-hecate was added to cultures of PC-3, BRF 41 T, DU145, and LNCaP cells in the presence and absence of steroids. PC-3 xenografts were established in nude male mice, which were treated with LHRH-hecate.

RESULTS

Injections of LHRH-hecate resulted in tumor growth arrest and marked reduction of tumor burden (62.2 mg/g body weight in saline controls vs. 10.5 mg/g body weight in treated mice; P < 0.0001); unconjugated LHRH and hecate had no effect on tumor burden and tumor viability (48.5 mg/g body weight in LHRH treated animals vs. 63.2 mg/g body weight in hecate treated mice). Marked tumor necrosis occurred in conjugate treated mice. Removal of steroids from the culture media decreased the sensitivity of LNCaP and PC-3 cells to the LHRH-hecate; adding estrogen restored the sensitivity.

CONCLUSIONS

LHRH-hecate may be effective in treating hormone dependent and independent prostate cancers.

Measurement of endogenous estrogens: analytical challenges and recent advances

Recent developments in the analysis of endogenous estrogens (including both free and conjugated estrogens) are reviewed. Largely due to urging by some cancer researchers, new demands are now being placed on such measurements in terms of sensitivity, throughput, multi-analyte detection and accuracy. Especially high sensitivity is required for detecting estrogens in serum from postmenopausal women, children and men, where concentrations at the low pg/ml level are encountered, and one would prefer to test much less than 1 ml of serum. Aside from throughput, meeting all of these demands may be beyond the reach of immunoassay, the method that has created and continues to dominate this field. Both HPLC and GC versions of mass spectrometry are emerging that have some potential to improve the testing of physiological samples for endogenous estrogens. The following topics are covered in this review: related analyses (e.g. detection of estrogens in environmental samples such as water, where 1-1 samples can be collected to provide ng amounts of estrogens); structure and metabolism of estrogens; biological actions (with an emphasis on their role in cancer); immunoassays; HPLC with electrochemical detection; GC-ECD; and various forms of mass spectrometry.

Estradiol metabolism and malignant disease

Endogenous estradiol metabolism results in metabolic products that are still capable of exerting various biological, partially estrogen-antagonistic actions. This indicates that the effects of estradiol in carcinogenesis may depend on individual variations of metabolic breakdown of estradiol. The aim of this paper is to review and discuss the available data relating to stimulatory and inhibitory properties of estradiol metabolites on carcinogenesis. Results of main D-ring metabolites and main A-ring metabolites are presented. There are indications that the endogenous production of growth influencing estradiol metabolites may be elevated in neoplasias. Some results in this respect are available for stimulating tumor growth for the D-ring metabolite 16-hydroxyestrone and the A-ring metabolites 4-hydroxyestrone and 4-hydroxyestradiol. Inhibitory effects exist for the A-ring metabolite 2-methoxyestradiol (2-ME). So far, only a few metabolites have been studied closely for their influence on carcinogenesis. There is also a dearth of data on the intracellular metabolism of estradiol in neoplastic tissues. Knowledge of the metabolites may reveal new approaches to diagnosis and treatment of malignant diseases. 2-ME has already shown actions in pharmacological dosages which led already to a first trial to prove its suitability for treating human breast cancer.

Signaling through estrogen receptors modulates telomerase activity in human prostate cancer

Sex steroid hormone receptors play a central role in all stages of prostate cancer. Here, we tested whether estrogen receptor (ER) signaling contributes to telomerase activation, an early event in prostate tumorigenesis. Following 17beta-estradiol (E(2)) treatment, both mRNA encoding the catalytic subunit of human telomerase (hTERT) and telomerase activity were promptly induced in human prostate normal epithelial cells, fresh explants from benign prostate hyperplasia, and prostate cancer explants and cell lines. Reporter expression studies and in vivo chromatin immunoprecipitation assays revealed E(2)-dependent hTERT promoter induction and showed that both ERalpha and ERbeta bound this sequence. Crucially, addition of the anti-estrogen 4-hydroxytamoxifen caused a differential recruitment in vivo of ERalpha and ERbeta onto the hTERT promoter and inhibited telomerase activity. Treatment with the aromatase inhibitor letrozole, which prevented testosterone-mediated interaction between ER and the hTERT estrogen response element, resulted in a negative regulation of telomerase activity. Thus, intracellular conversion of androgens to estrogens may contribute to the etiopathogenesis of prostate cancer. Given the present evidence for direct control of hTERT gene expression and telomerase activity in the prostate by the ER, we suggest that this transcriptional regulator represents a possible therapeutic target in prostate cancer.

Regulation of cell-to-cell communication in non-tumorigenic and malignant human prostate epithelial cells

BACKGROUND

Gap-junction-mediated intercellular communication (GJIC) is required for normal development and tissue homeostasis. However, the role of GJIC in human prostate carcinogenesis and progression remains ill-defined.

METHODS

The ability of hormones, anti-hormones, and the anti-hypertensive drug, forskolin, to restore GJIC in non-tumorigenic (RWPE-1 and PWR-1E) and malignant (RWPE-2, LNCaP, DU-145) human prostate epithelial cell lines, was examined by Scrape-Loading/Dye Transfer (SL/DT) and Fluorescence Recovery After Photobleaching (FRAP) methods using an Ultima laser cytometer.

RESULTS

Results from both assays show that PWR-1E, RWPE-2, LNCaP, and DU-145 cells have weak or absent GJIC activity. However, the non-tumorigenic RWPE-1 cells showed restoration of some GJIC (nearly 10%) after 1 hr in the FRAP assay. Forskolin and estrone, which increase intracellular cAMP levels, induced a significant and consistent increase (2.8- and 4.4-fold, respectively) in cell-to-cell communication only in the non-tumorigenic RWPE-1 cells. Furthermore, estrone induced a two-fold increase in connexin 43 (Cx43) and a 30% decrease in Cx32 expression, while forskolin caused a 50% reduction in Cx32 with no effect on Cx43 expression in RWPE-1 cells.

CONCLUSIONS

These data suggest that agents that increase Cx43:Cx32 ratio may be used to restore GJIC in junctionally-deficient, non-tumorigenic immortalized cells, thus providing insights into potential mechanisms responsible for the multistep carcinogenesis in the human prostate.

CpG hypermethylation of the promoter region inactivates the estrogen receptor-beta gene in patients with prostate carcinoma

BACKGROUND

The down-regulation of the estrogen receptor-beta (ERbeta) gene is associated with several malignancies, including prostate carcinoma. The purpose of the current study was to investigate the mechanisms of ERbeta inactivation through the analysis of CpG methylation of the promoter region of ERbeta gene.

METHODS

ERbeta protein expression was examined by immunohistochemistry in 23 cases of human prostate carcinoma and 40 cases of benign prostatic hyperplasia (BPH). DNA was extracted from these tissues and processed for sodium bisulfite genomic sequencing. The percentage of methylation of CpG sites in the promoter region of ERbeta (-376 to -117), which contains 19 CpG sites, was determined from genomic sequencing data. The prostate carcinoma cell lines DU145 and ND1 were treated with the demethylating agent 5-AZAC and ERbeta mRNA expression was analyzed by reverse transcriptase-polymerase chain reaction.

RESULTS

In BPH tissues, ERbeta protein expression was found mainly in epithelial cells. ERbeta protein expression was lacking in 83% of prostate carcinoma samples (19 of 23 samples) whereas all cases of BPH (40 of 40) demonstrated expression of ERbeta protein. The mechanism of inactivation of the ERbeta gene in prostate carcinoma was CpG methylation because the degree of methylation at all CpG sites within the promoter region between -376 and -117 was higher in prostate carcinoma samples compared with BPH tissues. Nine of 19 CpG sites within the promoter region of ERbeta displayed significant differences in methylation between prostate carcinoma and BPH samples. The prostate carcinoma cell lines appeared to lack ERbeta expression. However, 5-AZAC treatment restored ERbeta expression in those cell lines, suggesting that methylation inactivates the ERbeta gene in prostate carcinoma.

CONCLUSIONS

The results of the current study demonstrate, for what we believe to be the first time, that the inactivation of the ERbeta gene in prostate carcinoma occurs through CpG methylation of the promoter region of this gene.

Targeted destruction of androgen-sensitive and -insensitive prostate cancer cells and xenografts through luteinizing hormone receptors

BACKGROUND

We have prepared a conjugate of a lytic peptide (hecate) and a 15-amino acid segment of the beta-chain of LH to test the concept that this conjugate will target cancer cells expressing LH receptors.

METHODS

Hecate-betaLH was added in vitro to cultures of Chinese hamster ovary (CHO) cells with and without LH receptors and to prostate cancer cells in the presence or absence of steroids, follicle-stimulating hormone (FSH), epidermal growth factor (EGF), or betaLH. PC-3 xenografts were established in male athymic nude mice and treated once a week for 3 weeks with hecate-betaLH via the lateral tail vein.

RESULTS

The conjugate showed concentration-dependent toxicity for the following prostate cancer cell lines: BRF 41 T>DU145>PC-3>LNCaP, according to their LH receptor capacities. Steroid removal reduced sensitivity to the drug in a reversible manner. Hecate-betaLH reduced the tumor burden in the nude mice from 60 to 12.5 mg/g body weight.

CONCLUSIONS

We conclude that the hecate-betaLH conjugate selectively kills androgen-dependent and-independent prostate cancer cells both in vivo and in vitro; its toxicity depends on the number of LH receptor sites present.

Differential effects on growth, cell cycle arrest, and induction of apoptosis by resveratrol in human prostate cancer cell lines

Epidemiologic studies have suggested that nutrition plays an important role in carcinogenesis and that 30% of cancer morbidity and mortality can potentially be prevented with proper adjustment of diets. Resveratrol, a polyphenol present in red wines and a variety of human foods, has recently been reported to exhibit chemopreventive properties when tested in a mouse skin cancer model system. In this study, we investigated the effects of resveratrol on growth, induction of apoptosis, and modulation of prostate-specific gene expression using cultured prostate cancer cells that mimic the initial (hormone-sensitive) and advanced (hormone-refractory) stages of prostate carcinoma. Androgen-responsive LNCaP and androgen-nonresponsive DU-145, PC-3, and JCA-1 human prostate cancer cells were cultured with different concentrations of resveratrol (2. 5 x 10(-5)-10(-7) M). Cell growth, cell cycle distribution, and apoptosis were determined. Addition of 2.5 x 10(-5) M resveratrol led to a substantial decrease in growth of LNCaP and in PC-3 and DU-145 cells, but only had a modest inhibitory effect on proliferation of JCA-1 cells. Flow cytometric analysis showed resveratrol to partially disrupt G1/S transition in all three androgen-nonresponsive cell lines, but had no effect in the androgen-responsive LNCaP cells. In difference to the androgen-nonresponsive prostate cancer cells however, resveratrol causes a significant percentage of LNCaP cells to undergo apoptosis and significantly lowers both intracellular and secreted prostate-specific antigen (PSA) levels without affecting the expression of the androgen receptor (AR). These results suggest that resveratrol negatively modulates prostate cancer cell growth, by affecting mitogenesis as well as inducing apoptosis, in a prostate cell-type-specific manner. Resveratrol also regulates PSA gene expression by an AR-independent mechanism.

Hormonal interactions in human prostate tumor LNCaP cells

Melatonin, the hormone secreted by the pineal gland at night, has recently been found to attenuate growth and viability of benign human prostate epithelial cells. Estradiol suppressed these responses by efflecting a protein kinase C mediated inactivation of melatonin receptors. In the present study, the effects of melatonin on growth and viability of the human androgen-sensitive prostatic tumor cell line-LNCaP and the influence of estradiol on these responses were explored. Melatonin inhibited 3H-thymidine incorporation into LNCaP cells at physiological concentrations. This response decayed within 24 h. The inactivation of the response slowed down in the presence of the protein kinase C inhibitor GF-109203X. Estradiol also inhibited 3H-thymidine incorporation and its effects were additive to those of melatonin. Suppression of DNA content was observed in cells treated for 2 days with melatonin (0.1 nM); this suppression was maintained for longer periods in the presence than in the absence of estradiol. In addition, estradiol and melatonin slightly and additively decreased cell viability. These results demonstrate for the first time a direct interaction of melatonin with androgen-sensitive prostate tumor cells leading to attenuation of cell growth. They also show that unlike in benign prostate epithelial cells, estrogen attenuates LNCaP cell growth and supports rather than inactivates melatonin's action.