In vivo and in vitro effects of androgen on fibroblast growth factor-2 concentrations in the human prostate

Negative regulation of NEP expression by hypoxia

BACKGROUND

Neutral endopeptidase (NEP) is a transmembrane cell surface peptidase present on prostatic epithelial cells that catalytically inactivates small peptide substrates. Neutral endopeptidase loss is associated with prostate cancer growth, progression, and increased angiogenesis. We examined whether NEP expression is regulated by hypoxia, frequently encountered in the tumor microenvironment.

METHODS

NEP expression was compared in prostate cancer cell lines cultured in normoxic and hypoxic conditions. The NEP activity, protein levels, and mRNA levels were determined using enzyme assay, Western blotting and q-PCR analysis, respectively. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay (ChIP) was used to confirm the negative regulation of NEP at the transcriptional level by hypoxia responsive elements (HREs).

RESULTS

The results indicate that NEP expression was inhibited under hypoxic conditions in the NEP positive LNCaP, C4-2, and 22RV1 cells and human umbilical vascular endothelial (HUVEC) cells. NEP regulation appeared to be predominantly at the transcriptional level as NEP mRNA expression significantly reduced with hypoxia, concordant with the kinetics of protein levels, and NEP enzyme activity. A search of the NEP gene sequence revealed three putative HREs upstream of the NEP promoter. Two of the HREs demonstrated a specific reduction of shift in the presence of cobalt chloride; specificity of the binding sites was confirmed by ChIP.

CONCLUSIONS

Our data indicate a novel mechanism where hypoxia negatively regulates the tumor suppressor function of NEP in prostate cancer. The negative regulation of NEP is mediated by binding of the HIF1-α protein binding to the HREs present upstream of the NEP promoter.

Expression of basic fibroblast growth factor and its receptors FGFR1 and FGFR2 in human benign prostatic hyperplasia treated with finasteride

BACKGROUND

The development of benign prostatic hyperplasia (BPH) is an androgen-dependent process which may be mediated by a number of locally produced growth factors. One of these, the basic fibroblast growth factor (bFGF or FGF2), has a mitogenic effect on prostatic stroma. High expression levels of bFGF have been reported in BPH. FGFR1 and FGFR2 receptors, that exhibit affinity for bFGF, have been identified in normal and hyperplastic prostate. Finasteride, a 5alpha-reductase inhibitor, is an effective drug in the treatment of BPH, inducing regressive changes in the prostate of treated patients, even though its mechanisms of action are not yet completely elucidated. This study was designed to assess the effects of finasteride on the expression levels of bFGF, FGFR1, and FGFR2 in patients with BPH.

METHODS

The expression levels of bFGF, FGFR1, and FGFR2 in 9 patients with prostatic hyperplasia treated with finasteride were assessed by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) analysis of mRNA expression and were compared with those of 9 control patients with untreated BPH.

RESULTS

Immunohistochemistry showed strong bFGF immunoreactivity in the prostatic stroma of untreated patients, this being somewhat weaker in the epithelium. In treated patients, epithelial immunoreactivity was practically negative, and a considerable reduction in stromal immunoreactivity was seen. These findings were also confirmed by RT-PCR. FGFR1 showed a weak immunoreactivity in the stroma and in basal epithelial cells. FGFR1 showed a weak immunoreactivity in the stroma and in basal epithelial cells. FGFR2 exhibited strong stromal immunoreactivity, becoming weaker in the basal epithelium. No differences were seen in the expression of both receptors between the groups of treated and untreated patients.

CONCLUSIONS

A marked reduction in bFGF levels is seen in BPH treated with finasteride in comparison to untreated BPH. In our opinion, finasteride may act as a negative regulator of bFGF expression, counteracting the role of bFGF in the development of BPH.

Elevated expression of FGF-2 does not cause prostate cancer progression in LNCaP cells

BACKGROUND

Androgen-independent (AI) prostate cancer (CaP) resulting from progression of disease is untreatable. Such progression may relate to upregulation and autocrinicity of growth factor expression. We studied one candidate growth factor, basic fibroblast growth factor (FGF-2).

METHODS

LNCaP cells made autocrine for FGF-2 by stable transfection with FGF-2 were examined for cancer progression, measured by 1) altered response to androgen, 2) ability to grow more quickly when cocultured with bone cells in vitro or to form tumors when coinoculated with bone cells in vivo, or 3) increase in metastatic ability.

RESULTS

Stably transfected lines differed in FGF-2 protein expression. LNCaP-HF (high production of FGF-2) expressed more FGF-2 than LNCaP-LF (low production of FGF-2); controls were negative. In vitro, compared with LNCaPs, LNCaP-HF cells showed a slightly increased growth rate, reduced proliferation in response to androgen but not to estrogen or progesterone, and a decreased proliferative response to epidermal growth factor (EGF) and FGF-2. Although giving a slightly faster take rate, LNCaP-HF cells without Matrigel only formed small, fast-regressing tumors in male nude mice, and with Matrigel, did not differ from LNCaPs in growth rate or tumor size. No metastases occurred. No tumors grew in females. Mixed growth of FGF-2 transfectants with human fetal osteoblasts failed to cross-stimulate in vitro, or to allow tumor formation in vivo.

CONCLUSIONS

Although FGF-2 is overexpressed in AI CaPs, our experiments show that upregulation of FGF-2 expression is not sufficient to cause androgen independence, tumorigenicity, or metastases production (i.e., prostate cancer progression) in LNCaP cells.

Three-dimensional cultures of prostatic cells: tissue models for the development of novel anti-cancer therapies

This review addresses the application of three-dimensional cultures of prostatic cells to the development of novel anti-cancer therapies. A variety of therapeutic agents to combat prostate cancer are currently under development. These include cytotoxins, differentiation agents and, more recently, genetically modified tumor vaccines. Three-dimensional cultures of prostatic cells are increasingly used in preclinical research in the design of new therapies and in the development of delivery strategies for these treatments. These tissue-like structures more realistically model the structural architecture and differentiated function of the human prostate than a cellular monolayer. In doing so, three-dimensional cultures produce an in vivo-like response to therapeutic agents. Advances in tissue engineering have improved the variety, fidelity and quantity of these prostate models. To date, they have been applied to estimate the dose of new drug therapies, evaluate drug penetration into solid tumors, assess the effectiveness of drug combinations, and develop tumor vaccines.

New sensitive discovery histoculture model for growth-inhibition studies in prostate cancer and BPH

BACKGROUND

A new, total-immersion three-dimensional histoculture (TIH) method was developed to evaluate growth of tissue containing a mixture of benign prostate hyperplasia (BPH) and prostate cancer in vitro.

METHODS

Efficacy of inhibitors, such as genistein, was determined by measuring 3H-thymidine incorporation per microgram protein. Inhibitory effects obtained in TIH were compared to those in sponge-gel supported histoculture (SSH).

RESULTS

3H-thymidine incorporation was 2-5-fold higher in tissue cultured in TIH than in SSH. The average inhibition by genistein at a concentration of 18 JIM was 73% in TIH, vs. 31% in SSH. TIH also appeared to be more sensitive, since the lowest concentration of genistein that significantly inhibited growth of BPH mixed with prostate cancer tissue was 2.3 IJM, while in SSH the lowest concentration was 9.2 F,M. Although the within-assay coefficient of variation (CV) was similar for both TIH and SSH, the between-assay CV was better in TIH.

CONCLUSIONS

These data suggest that TIH can be used as a discovery model for screening and evaluating inhibitors of prostate tissue growth in vitro.

Production and oestrogen regulation of FGF1 in normal and cancer breast cells

To investigate the relationship between the FGF1 oestrogen regulation and the normal/cancer status of breast cells, we have studied FGF1 17beta-oestradiol regulation in normal, transformed and cancerous cells. Normal (NMEC), transformed (HBL-100) and cancerous (MCF-7, MDA-MB-231) human mammary epithelial cells express different levels of FGF1 mRNAs. Western blot analysis allowed us to characterize FGF1 as an 18 kDa form of this polypeptide. Using a neutralizing anti-FGF1 antibody we demonstrated that FGF1 is secreted by all mammary cells studied and stimulates their proliferation in an autocrine manner. We have examined the regulation of FGF1 mRNAs in response to 17beta-oestradiol. FGF1 mRNAs were upregulated in hormone-dependent NMEC but was not upregulated either in hormone-sensitive HBL-100 cells or in the hormone-dependent cancerous cell line MCF-7. However, enzyme linked immunosorbent assay indicated an increase of FGF1 protein in NMEC, HBL-100 and MCF-7 cells. We have also examined the 17beta-oestradiol regulation of the four alternatively spliced FGF1 mRNAs: 1.A, 1.B, 1. C and 1.D. Only 1.B transcripts were downregulated by 17beta-oestradiol in normal cells. These results show that 17beta-oestradiol regulates FGF1 mRNAs in a cell-specific manner, and that this regulation may be transcriptional or translational depending on cell phenotype. The specificity of oestradiol effects was checked using its receptor antagonist tamoxifen.

Growth factor involvement in progression of prostate cancer

Understanding how the regulation of growth factor pathways alters during prostate cancer (PC) progression may enable researchers to develop targeted therapeutic strategies for advanced disease. PC progression involves the shifting of cells from androgen-dependent growth to an androgen-independent state, sometimes with the loss or mutation of the androgen receptors in PC cells. Both autocrine and paracrine pathways are up-regulated in androgen-independent tumors and may replace androgens as primary growth stimulatory factors in cancer progression. Our discussion focuses on growth factor families that maintain homeostasis between epithelial and stromal cells in the normal prostate and that undergo changes as PC progresses, often making stromal cells redundant. These growth factors include fibroblast growth factor, insulin-like growth factors, epidermal growth factor, transforming growth factor α, retinoic acid, vitamin D3, and the transforming growth factor β families. We review their role in normal prostate development and in cancer progression, using evidence from clinical specimens and models of PC cell growth.

Genistein inhibits the growth of human-patient BPH and prostate cancer in histoculture

BACKGROUND

There is strong epidemiological evidence that prostate disease is significantly less prevalent in the Orient, where the intake of soy products is very high, than in the United States. We therefore undertook a study of the effects of genistein, a major component of soy, on growth of human-patient benign prostatic hypertrophy (BPH) and prostate cancer tissue in three-dimensional collagen gel-supported histoculture.

METHODS

Surgical specimens of human BPH and cancer were histocultured for 5 days to study the effects of genistein on growth, as measured by inhibition of 3H-thymidine incorporation per microgram protein on day 5.

RESULTS

Genistein in doses of 1.25-10 micrograms/ml decreased the growth of BPH tissue in histoculture in a dose-dependent manner, with little additional effect at higher doses. Prostate cancer tissue in histoculture was similarly inhibited by these doses of genistein.

CONCLUSIONS

Genistein decreases the growth of both BPH and prostate cancer tissue in histoculture. The data suggest that genistein has potential as a therapeutic agent for BPH and prostate cancer.

Differences in prostate and adipose tissue basic fibroblast growth factor: analysis of preliminary results

OBJECTIVES

Basic fibroblast growth factor (bFGF or FGF-2) is mitogenic to human prostate epithelial and stromal cells, and it is reported to be elevated in the serum and urine of patients with various cancers, including prostate cancer. Obesity, with increased body fat, is a risk factor for prostate cancer through unknown mechanisms. Because adipose tissue is a source of FGF-2, we determined the quantity and quality of activity of FGF-2 in omental adipose tissue and compared it with normal and cancerous prostate tissues.

METHODS

Using heparin-Sepharose chromatography, we extracted proteins from human omental adipose tissue, adenocarcinoma of the prostate, and benign prostatic hypertrophic (BPH) tissues. Each of the mitogenic proteins eluted with NaCl concentrations between 1.4 M and 1.8 M, similar to control FGF-2. Using FGF-2 antisera (which inhibited the mitogenic activity of the proteins), we performed Western blot analysis to confirm their homology to FGF-2. We also assessed recovery, mitogenicity, and angiogenicity of each of the proteins using thymidine incorporation into human umbilical vein endothelial cells and the chorioallantoic membrane assay.

RESULTS

There was greater recovery of FGF-2 from omental adipose tissue compared with cancerous or BPH homogenates (40 micrograms [2.0 micrograms/g] versus 25 micrograms [1.25 micrograms/g] and 20 micrograms [1.0 microgram/g], respectively). Moreover. FGF-2 from adipose tissue had greater mitogenic activity (96.2% versus 74.8% and 54%; P < 0.05) and a greater angiogenic activity (5.1 vessels versus 2.9 and 1.8 vessels; P < 0.05) on the chorioallantoic assay.

CONCLUSIONS

We suggest that human omental adipose tissue FGF-2 may demonstrate greater mitogenic and angiogenic activity than either BPH or prostate cancer tissue FGF-2. It is not known whether FGF-2 from adipose tissue qualitatively or quantitatively may underlie the relationship between obesity and prostate cancer.

Regulation of prostatic growth and function by peptide growth factors

Polypeptide growth factors are positive and negative regulators of prostatic growth and function. Expression and biological effects of epidermal growth factor (EGF), transforming growth factors (TGFs) alpha and beta, fibroblast growth factors (FGFs), and insulin-like growth factors (IGFs) in the prostate have been extensively studied. EGF and TGF alpha, which share the same receptor, are strong mitogens for prostatic epithelial and stromal cells. Their paracrine mode of action in normal tissue and early-stage tumors is apparently altered towards an autocrine stimulation in hormone-independent tumors, which gain the ability to produce TGF alpha by themselves. TGF beta has a dual role in the regulation of prostatic growth. It inhibits growth of prostatic epithelial cells in culture and mediates programmed cell death after androgen withdrawal. However, advanced prostatic carcinomas become insensitive to the inhibitory effect of TGF beta. Several members of the FGF family have been identified in the prostate. They are mainly or exclusively expressed in the stromal cells, and stimulate the epithelial cells. In the rat Dunning tumor model, progression is accompanied by distinct changes in the expression of FGFs and their receptors. In the hyperplastic tissue, basic FGF (bFGF) is accumulated. This growth factor is also a potent angiogenic inducer, expression of which may determine the metastatic capability of a tumor. IGFs are paracrine growth stimulators in the normal and hyperplastic prostate. It is still under consideration whether prostatic cancer cells gain the ability to produce IGF-I by themselves and thus shift to an autocrine mode of IGF-I stimulation. Growth factors also interact with the androgen-signaling pathway. IGF-I in particular, other growth factors as well, can activate the androgen receptor.