Effects of hydroxyflutamide in the medial preoptic area or lateral septum on reproductive behaviors in male rats

We examined whether androgen receptors in the medial preoptic area (MPOA) and lateral septum (LS) are required for the expression of copulation and sexual motivation. Castrated males received testosterone-filled silastic capsules to restore behavior, and were implanted with the antiandrogen hydroxyflutamide (OHF) or blank cannulae. One group was implanted in either the anteroventral MPOA or LS (ANT group). Another group was implanted in the posterodorsal MPOA or LS (POST group). Copulation was tested on days 2, 6, 10, and 14 of OHF exposure; partner preference, a measure of sexual motivation, was tested on day 15. The results showed that sexual behavior was significantly suppressed by OHF in the MPOA of the ANT group, but not the POST group. However, sexual motivation was significantly reduced by OHF in the MPOA of the POST group, but not the ANT group. In the LS, OHF had no effect on sexual behavior and partner preference regardless of implant site. The data suggest site specificity within the MPOA for androgen receptor activation of male reproductive behaviors.

Activation of mitogen-activated protein kinase pathway by the antiandrogen hydroxyflutamide in androgen receptor-negative prostate cancer cells

Whereas hydroxyflutamide (HF) has been used as an antiandrogen to block androgen-stimulated prostate tumor growth, the antiandrogen withdrawal syndrome that allows antiandrogens to stimulate prostate tumor growth still occurs in many patients treated with androgen ablation therapy. This was previously explained by mutations in the androgen receptor (AR) and/or modulation from AR coregulators, so that HF becomes an AR agonist. Using immunohistochemical analysis, we analyzed four prostate cancer patients undergoing androgen ablation therapy with flutamide and compared their phospho-extracellular signal-regulated kinase 1/2 levels in prostate cancer biopsies before receiving HF and after experiencing disease progression while taking HF. We found a significant increase of activated mitogen-activated protein (MAP) kinase in prostate tumors from patients receiving HF during androgen ablation therapy. In vitro studies showed that HF induced a rapid activation of the Ras/MAP kinase pathway in human prostate cancer DU145 cells which lack the AR, as well as in PC-3AR2 and CWR22 cells which express the AR. Cycloheximide failed to inhibit this activation, but both AG1478, an inhibitor of the epidermal growth factor receptor (EGF-R), and an EGF-R-neutralizing antibody blocked this HF-mediated activation of MAP kinase, which suggests that the activation of Ras/MAP kinase by HF is a membrane-initiated, non-AR-mediated, and nongenomic action. The consequence of this activation may result in increasing cell proliferation and cyclin D1 expression. This raises a concern for using HF in the complete-androgen-ablation therapy in prostate cancer treatment and provides a possible pathway that might contribute to the HF withdrawal syndrome.

Nerve growth factor induces the re-expression of functional androgen receptors and p75(NGFR) in the androgen-insensitive prostate cancer cell line DU145

BACKGROUND

One of the paracrine/autocrine factors regulating prostate growth and differentiation is nerve growth factor (NGF). The role of NGF and its receptors in the prostate, however, remains controversial. We have shown that NGF treatment of human prostate cancer cell lines reduced their tumorigenicity, both in vitro and in vivo.

OBJECTIVE

To investigate the involvement of NGF as a differentiation factor in prostate cancer cells.

DESIGN

We exposed the androgen-independent/androgen receptor (AR)-negative prostate cancer cell line DU145 to NGF to study whether this neurotrophin could revert DU145 cells to a less malignant phenotype.

METHODS

DU145 cells were treated with NGF, then ARs and NGF receptor p75(NGFR) expression and telomerase activity were studied. Finally, we investigated whether re-expression of ARs could restore the androgen sensitivity in this cell line.

RESULTS AND CONCLUSIONS

NGF treatment induced a reversion of DU145 cells to a less malignant phenotype, characterized by the re-expression of ARs and p75(NGFR) NGF receptors. Re-expression of ARs restored the androgen sensitivity, as suggested by the fact that exposure to dihydrotestosterone stimulated the growth of NGF-treated DU145 cells. This effect was blocked by androgen antagonist drugs, such as hydroxyflutamide and cyproterone acetate, which also induced apoptotic death of NGF-treated cells. The hypothesis that a differentiation pathway is activated by exogenous NGF in DU145 cells is also supported by findings indicating that NGF-treated DU145 cells expressed a low telomerase activity, as a result of a decrease in human telomerase reverse transcriptase transcription.

[Sex-difference on flutamide metabolism in rat liver microsomal cytochrome P450 1A2]

AIM

To assess the sex-difference on flutamide metabolism in rat liver microsomes useing rat cytochrome P450, 1A2, inhibitory monoclonal antibody.

METHODS

Liver microsomes were prepared from male or female rats. Protein concentration and total cytochrome P450 content were determined. Incubation mixture included liver microsomes (1.0 nmol.L-1), reduced form of nicotinamide adenine dinucleotide phosphate (NADPH, 0.1 nmol.L-1), CYP1A2 (1:400) and flutamide (2 mg.L-1). The incubation time was 30 min. The concentration of flutamide and its major metabolite 2-hydroxyflutamide were analyzed by reverse high-performance liquid chromatography. The mobile phase was a mixture of methanol-acetonitrile-water-diethylether (40:20:35:1) with methyltestosterone as internal standard. The detection wavelength was 234 nm. The reaction mixture was extracted with acetic ether 4 mL. Sex-difference on flutamide metabolism was expressed as the difference between the concentration ratio of 2-hydroxyflutamide to flutamide in male and female rat liver microsomes.

RESULTS

The recoveries of flutamide and 2-hydroxyflutamide for the proposed method were more than 75%. The formation of 2-hydroxyflutamide from flutamide was inhibited by CYP1A2 antibodies (1:400) in male and female rat liver microsome for 30 min of incubation time, but the inhibition of flutamide metabolism in female rat was stronger than that in male. The concentration ratios of 2-hydroxyflutamide to flutamide were (1.5 +/- 0.6) and (0.9 +/- 0.4) in male and female rat liver microsomes, respectively (P < 0.01).

CONCLUSION

The results indicate that the activity of male rat CYP1A2 is higher than that of the female rat. There is difference in sex-related rate of flutamide metabolism in rat liver microsomes.

Pure antiandrogens disrupt the recruitment of coactivator GRIP1 to colocalize with androgen receptor in nuclei

We have used confocal microscopy to elucidate the effects of antiandrogens on nuclear localization of the androgen receptor (AR) with its transcriptional coactivator GRIP1. We show that the agonist-activated AR recruits GRIP1 to colocalize with the receptor in the nucleoplasm. By contrast, AR complexed to the antiandrogens hydroxyflutamide and bicalutamide fails to influence nuclear distribution of GRIP1. Likewise, the non-steroidal antiandrogens prevent the agonist-induced AR-GRIP1 colocalization from occurring. Androgen antagonists affect nuclear redistribution of AR-GRIP1 in a fashion that parallels their effects on the transcriptional activity of AR, in that the pure antagonists block GRIP1-dependent activation of AR function, whereas the mixed antagonist/agonist cyproterone acetate promotes both AR-driven redistribution of GRIP1 and activation of AR by GRIP1.

Acquisition of agonistic properties of nonsteroidal antiandrogens after treatment with oncostatin M in prostate cancer cells

PURPOSE

Interleukin-6 (IL-6), a proinflammatory cytokine the serum andtissue levels of which are elevated in prostate cancer patients, activates the androgen receptor (AR) in a ligand-independent and synergistic manner. Oncostatin M (OSM) is an IL-6 type cytokine that regulates the growth of prostate cancer cells in a paracrine fashion. The present study was designed to investigate the regulation of AR expression and function by OSM, as well as the efficacy of the nonsteroidal antiandrogens hydroxyflutamide and bicalutamide in the inhibition of AR-mediated signal transduction.

EXPERIMENTAL DESIGN

Expression of the OSM receptor-beta in the prostate cancer cell lines LNCaP, PC-3, and DU-145 was investigated by reverse transcription-PCR. DU-145 and PC-3 cells were cotransfected with an androgen-responsive gene and AR cDNA. Reporter gene activity was measured after treatment with androgen and/or OSM in the absence or presence of antiandrogens or protein kinase inhibitors. AR expression after OSM treatment was assessed by Western blot.

RESULTS

OSM receptor-beta expression was higher in DU-145 and PC-3 than in LNCaP cells. OSM caused ligand-independent activation of the AR in DU-145 cells, and the maximal activation was 62% of that induced by the synthetic androgen methyltrienolone. In the presence of OSM, hydroxyflutamide behaved as an AR agonist. Bicalutamide down-regulated AR activation caused by OSM only at a concentration of 1 microM. The inhibitor of the protein kinase A signaling pathway PKI and dn signal transducers and activators of transcription (STAT) 3 showed no effect on AR activation by OSM. The inhibitor of the MAPK pathway, PD 98059, caused only a minor down-regulation of OSM-induced reporter gene activity. OSM did not change AR expression in DU-145 cells transfected with AR cDNA.

CONCLUSIONS

OSM is a member of the IL-6 family of cytokines, which causes ligand-independent activation of the AR without altering receptor expression. In contrast to AR activation by IL-6, nonsteroidal AR antagonists act as agonists in the presence of OSM. This may be attributable to recruitment of different intermediary signal transduction proteins by OSM and IL-6, respectively. The acquisition of agonistic properties of AR blockers in the presence of OSM might compromise use of these drugs in prostate cancer treatment.

Stabilization of androgen receptor protein is induced by agonist, not by antagonists

The action of nuclear receptor ligands in target tissues is specified mainly by the expression levels of their cognate nuclear receptors. The expression levels of these receptors are controlled through transcriptional and post-transcriptional events. Among post-transcriptional events, the effect of ligand on nuclear receptor protein turnover still remains largely unknown. Therefore, we studied the effects of agonist and antagonists on the turnover of the human androgen receptor (hAR) protein in stably transformed Chinese hamster ovary cells expressing exogenous hAR. Western blot analysis showed that the most potent androgen, dihydrotestosterone (DHT), stabilizes hAR with the induction of the transactivation function of hAR. However, this androgen-induced stabilization of hAR protein was abrogated by well-known androgen antagonists, hydroxyflutamide and bicalutamide (BIC), with inhibition of the transactivation function of hAR. Thus, the present study suggests that androgen antagonists exert their effects through, at least in part, abrogating the agonist-induced stabilization of hAR protein as well as blocking the ligand-induced transactivation function of hAR.

Androgens protect against apolipoprotein E4-induced cognitive deficits

Compared with apolipoprotein (apo) E2 and E3, apoE4 increases the risk of Alzheimer's disease (AD), but it remains unknown how apoE4 affects neuronal function. ApoE4 interacts with female gender, further increasing the risk of AD and decreasing treatment response. Female mice are also more susceptible to apoE4-induced impairments of spatial learning and memory than male mice. To assess the role of sex steroids in this process, we studied mice deficient in mouse apoE (Apoe(-/-)) and expressing human apoE4 or apoE3 in the brain at comparable levels. Even brief periods of androgen treatment improved the memory deficits of female apoE4 mice. Female apoE3 mice had no memory deficits and did not benefit from the treatment. ApoE4 male mice, which performed normally in a water-maze test at baseline, developed prominent deficits in spatial learning and memory after blockade of androgen receptors (ARs), whereas apoE3 male mice did not. Untreated apoE4 mice had significantly lower cytosolic AR levels in the neocortex than wild-type, Apoe(-/-), and apoE3 mice. Improved memory in androgen-treated female apoE4 mice was associated with increased cytosolic AR levels. Our findings suggest that apoE4 contributes to cognitive decline by reducing AR levels in the brain, and that stimulating AR-dependent pathways can reverse apoE4-induced cognitive deficits.

Cytotoxicity of flutamide and 2-hydroxyflutamide and their effects on CYP1A2 mRNA in primary rat hepatocytes

AIM

To compare the cytotoxicity of flutamide and its active metabolite 2-hydroxyflutamide and their effects on cytochrome P-450 1A2 mRNA in primary rat hepatocytes.

METHODS

After the isolation of hepatocytes a nd t he primary incubation for 4 h, flutamide and 2-hydroxyflutamide were added respectively to the medium at the concentration of 10, 20, and 50 mg/L and incubated for 8 h. Cytotoxicity of hepatocytes was assessed by Trypan blue exclusion, lactate dehydrogenase (LDH) leakage, percentage of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) release, and reduced glutathione (GSH). The effect of flutamide and 2-flutamide on the CYP1A2 mRNA level was further analyzed by Northern blot.

RESULTS

After incubation for 8 h, cell viability was observed by Trypan blue exclusion. The increase of ALT and AST activity and the decrease of glutathione content were also noted at 10, 20, and 50 mg/L of flutamide and 50 mg/L of 2-hydroxyflutamide as compared with normal rat hepatocytes. Induction of CYP1A 2 mRNA were 2-, 5-, and 7.5-fold at 10, 20, and 50 mg/L of flutamide and 3.5-fold at 50 mg/L of 2-hydroxyflutamide.

CONCLUSION

Cytotoxicity of flutamide and its effect on CYP1A2 mRNA were stronger than those of its active metabolite 2-hydroxyflutamide in primary rat hepatocytes.

The amino terminus of the human AR is target for corepressor action and antihormone agonism

Antiandrogens inhibit the ligand-induced transactivation by the androgen receptor (AR) and have a widespread use in the treatment of prostate cancer but their mode of action is not fully understood. Here we show that the ability of the antiandrogen cyproterone acetate (CPA) to inhibit transactivation by the human AR (hAR) involves the corepressor SMRT (silencing mediator for retinoic acid and thyroid hormone receptor). We detect binding of SMRT to hAR when treating with the antiandrogen CPA, but not with the antihormones casodex or hydroxyflutamide. Interestingly, we find that SMRT binds to the N terminus of the hAR. Thereby, SMRT modulates the activity of hAR in receptor-negative CV1 cells. In addition, we have used receptor point mutants that exhibit normal transactivation potential and unchanged partial agonistic activity when treated with CPA, but lack both SMRT binding and SMRT-mediated inhibition of CPA-bound AR. This indicates that mechanisms involved in hAR-mediated transactivation are distinct from antihormone-induced receptor inactivation. Furthermore, we show that treatment of transfected cells with a cAMP analog or coexpression of the catalytic subunit of PKA, known to activate hAR, inhibits the binding of SMRT to the AR. This suggests that the association of SMRT with hAR is regulated at the level of cross-talk mechanisms and that ligand-independent receptor activation is due to corepressor dissociation. Taken together, we provide novel insights in AR regulation, antihormone action, and functional nuclear receptor-corepressor interaction.

Development of two androgen receptor assays using adenoviral transduction of MMTV-luc reporter and/or hAR for endocrine screening

The discovery of xenobiotics that interfere with androgen activity has highlighted the need to assess chemicals for their ability to modulate dihydrotestosterone (DHT)-receptor binding. Previous test systems have used cells transfected with plasmid containing a reporter gene. Here we report the use of transduction for gene delivery and assessment of the modulation of DHT-induced gene activation. Transduction, the ability of replication-defective viruses to deliver biologically competent genes, is a well understood biological process, which has been utilized to repair defective genes in humans as well as to express exogenous genes in rodent models. Human breast carcinoma cells (MDA-MB-453) containing endogenous copies of the androgen (hAR) and glucocorticoid (GR) receptors were transduced with replication-defective human adenovirus type 5 containing the luciferase (Luc) reporter gene driven by the AR- and GR-responsive glucocorticoid-inducible hormone response element found with the mammary tumor virus LTR (Ad/MLUC7). In a second set of experiments, CV-1 cells were transduced as above with MMTV-luc and also hAR. Cells were subcultured in 96-well plates, transduced with virus, exposed to chemicals, incubated for 48 h, lysed, and assayed for luciferase. Luc gene expression was induced in a dose-dependent manner by DHT, estradiol, and dexamethasone (MDA only) and inhibited by AR antagonist hydroxyflutamide (OHF), hydroxy-DDE, HPTE (2,2-bis(p-hydroxyphenyl)-1,1, 1-trichloroethane), a methoxychlor metabolite, and M1 and M2 (vinclozolin metabolites). The transduced cells responded to AR agonists and antagonists as predicted from our other studies, with a very robust and reproducible response. Over all replicates, 0.1 nM DHT induced luc expression by about 45-fold in CV-1 cells (intra-assay CV = 20%) and 1micromolar OHF inhibited DHT by about 80%. In the transduced MDA cells, 0.1 nM DHT induced luc by about 24-fold (intra-assay CV = 33%), which was inhibited by OHF by about 85%. DHT-induced luciferase activity peaked in both cell lines between 1 and 100 nM, displaying about 64- and 115-fold maximal induction in the CV-1 and MDA 453 cells, respectively. For agonists, a two-fold induction of luc over media control was statistically significant. For AR antagonists, a 25-30% inhibition of DHT-induced luc expression was typically statistically significant. Comparing the two assays, the transduced CV-1 cells were slightly more sensitive to AR-mediated responses, but the transduced MDA 453 cells were more responsive to GR agonists. In summary, these assays correctly identified the endocrine activity of all chemicals examined and displayed sensitivity with a relatively low variability and a high-fold induction over background. Adenovirus transduction for EDC screening has the potential to be employed in a high-throughput mode, and could easily be applied to other cell lines and utilized to deliver other receptors and reporter genes.

Use of the probasin promoter ARR2PB to express Bax in androgen receptor-positive prostate cancer cells

BACKGROUND

Adenovirus-mediated overexpression of the apoptosis-inducing protein Bax can induce apoptosis in prostate cancer cell lines. Constitutive overexpression of Bax could result in unwanted apoptosis in every site of accidental Bax accumulation in vivo. Therefore, we developed an adenoviral construct (Av-ARR2PB-Bax) in which the probasin promoter, modified to contain two androgen response elements, drives Bax expression. This promoter would be expected to limit expression of Bax to cells expressing the androgen receptor.

METHODS

A variety of androgen receptor (AR)-positive and -negative cell lines of prostatic or nonprostatic origin were infected with Av-ARR2PB-Bax or a control virus, Av-ARR2PB-CAT, in which the same promoter drives expression of the chloramphenicol acetyl transferase-reporter gene. Bax expression and apoptosis in vitro were assessed by western blot analysis. Tumor size and apoptosis in vivo were assessed after four weekly injections of Av-ARR2PB-Bax or Av-ARR2PB-CAT into subcutaneous LNCaP xenografts growing in uncastrated male mice. All statistical tests were two-sided.

RESULTS

Bax was overexpressed in an androgen-dependent way in AR-positive cell lines of prostatic origin but not in AR-positive cells of nonprostatic origin or in AR-negative cell lines of either prostatic or nonprostatic origin. The androgen dihydrotestosterone activated apoptosis in LNCaP cells infected with Av-ARR2PB-Bax but not in those infected with Av-ARR2PB-CAT. Av-ARR2PB-Bax-injected LNCaP xenograft tumors decreased in tumor size from 34.1 mm3 (95% confidence interval [CI] = 25.1 mm3 to 43.1 mm3) to 24.6 mm3 (95% CI = -2.5 mm3 to 51.7 mm3), but the difference was not statistically significant (P =.5). Tumors injected with Av-ARR2PB-CAT increased in size, from 28.9 mm3 (95% CI = 12.7 mm3 to 45.1 mm3) to 206 mm3 (95% CI = 122 mm3 to 290 mm3) (P =.002) and contained statistically significant more apoptotic cells (23.3% [95% CI = 21.1% to 25.6%] versus 9.5% [95% CI = 8.0% to 11.1]) (P<.001).

CONCLUSIONS

Av-ARR2PB-Bax induces androgen-dependent therapeutic apoptosis in vitro and in vivo by activating apoptosis in AR-positive cells derived specifically from prostatic epithelium and does not affect nonprostatic cells.

Determination of 2-hydroxyflutamide in human plasma by high-performance liquid chromatography and its application to pharmacokinetic studies

Flutamide is a potent antiandrogen used for the treatment of prostatic cancer. Flutamide undergoes extensive first-pass metabolism to the pharmacologically active metabolite 2-hydroxyflutamide. A simple, sensitive, precise, accurate and specific HPLC method, using carbamazepine as the internal standard, for the determination of 2-hydroxyflutamide in human plasma was developed and validated. After addition of the internal standard, the analytes were isolated from human plasma by liquid-liquid extraction. The method was linear in the 25 to 1,000 ng/ml concentration range (r>0.999). Recovery for 2-hydroxyflutamide was greater than 91.4% and for internal standard was 93.6%. The limit of quantitation was 25 ng/ml. Inter-batch precision, expressed as the relative standard deviation (RSD), ranged from 4.3 to 7.9%, and accuracy was better than 93.9%. Analysis of 2-hydroxyflutamide concentrations in plasma samples from 16 healthy volunteers following oral administration of 250 mg of flutamide provided the following pharmacokinetic data (mean+/-SD): Cmax, 776 +/- 400 ng/ml; AUC(0-infinity), 5,368 +/- 2,689 ng h/ml; AUC(0-t) 5,005 +/- 2,605 ng h/ml; Tmax 2.6 +/- 1.6 h; elimination half-life, 5.2 +/- 2.0 h.

The Subnuclear Three-dimensional Image Analysis of Androgen Receptor Fused to Green Fluorescence Protein

To establish the novel approach in order to distinguish the transcriptionally active androgen receptor (AR) from the transcriptionally inactive AR, we performed the three-dimensional construction of confocal microscopic images of intranuclear AR. This method clearly distinguished the subnuclear localization of transcriptionally active AR tagged with green fluorescent protein (AR-GFP) from the transcriptionally inactive AR-GFP. Transcriptionally active AR-GFP mainly produced 250-400 fluorescence foci in the boundary region between euchromatin and heterochromatin. Although the AR-GFP bound to such antiandrogens as hydroxyflutamide or bicalutamide translocated to the nucleus, they homogeneously spread throughout the nucleus without producing any fluorescence foci. Antiandrogenic environmental disrupting chemicals, such as 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, vinclozolin, or nitrofen, also disrupted the intranuclear fluorescence foci. A point mutation (T877A) resulted in the loss of ligand specificity in AR-GFP. Even in this mutant receptor, agonists, such as dihydrotestosterone, hydroxyflutamide, or progesterone, produced the fluorescence foci in the nucleus, whereas the transcriptionally inactive mutant binding bicalutamide was observed to be spread homogeneously in the nucleus. Taken together, our findings suggest that, after nuclear translocation, AR is possibly located in the specific region in the nucleus while demonstrating clustering tightly depending on the agonist-induced transactivation competence.

Dexamethasone blocks antioestrogen- and oxidant-induced death of pituitary tumour cells

The oestrogen receptor is fundamental to the growth and survival of the rat pituitary tumour cell line, GH(3). Our previous studies have shown that antioestrogens such as RU 58668 and ZM 182780 will reduce the rate of cell division and also induce cell death. Death of these cells in response to antioestrogen treatment appears to be due to a heightened sensitivity to reactive oxygen species (ROS). As part of a study to determine the cross-talk between steroid receptor systems in these cells, we have observed that the glucocorticoid, dexamethasone (Dex), inhibits antioestrogen-induced cell death. Cell death induced by H(2)O(2) is enhanced by ZM 182780 and this effect is also blocked by Dex. As apoptotic cell death in a number of systems involves an early loss of mitochondrial membrane potential (DeltaPsi(m)), we have performed detailed studies on the time-course of DeltaPsi(m) loss in relation to the loss in cell membrane function. These studies have indicated that a loss of DeltaPsi(m) parallels a loss of cell membrane function - this is more characteristic of necrosis than of apoptosis. From microscopic observations of these cells in response to H(2)O(2), it has been noted that early cell membrane blebbing, induced by H(2)O(2), is blocked in the presence of ZM 182780. Cell membrane blebbing can precede necrosis as well as apoptosis and it is thought to involve cytoskeletal changes, for which localised glycolytic reactions provide ATP. These observations, together with those showing that removal of glucose, but not inhibition of mitochondrial function, enhances ROS-induced cell death, prompted studies on the glycolytic pathway. As a strong candidate mechanism, it would appear that, via an effect on one of the rate-limiting glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase, Dex is able to overcome the antioestrogen-enhanced loss of glycolytic function following exposure of cells to ROS. This report contributes to the growing body of evidence showing that glucocorticoids provide a survival advantage to both normal and tumour cell types.

Homology Modeling Using Multiple Molecular Dynamics Simulations and Docking Studies of the Human Androgen Receptor Ligand Binding Domain Bound to Testosterone and Nonsteroidal Ligands†

To facilitate the rational design of novel and more potent androgen receptor ligands, three-dimensional models for the human androgen receptor ligand binding domain bound to testosterone have been developed. These models of the androgen receptor were based on the crystal structure of the highly homologous human progesterone receptor ligand binding domain. The homology modeled androgen receptor was refined using unrestrained multiple molecular dynamics simulations in explicit solvent. Key H-bonding partners with the 17-hydroxy group and 3-keto group of testosterone are Asn705 and Thr877, and Gln711 and Arg752, respectively. These models show the presence of a unique unoccupied cavity within the androgen receptor binding pocket which may be valuable in the development of novel selective androgen receptor ligands. A qualitative analysis of amino acid mutations within the hAR binding pocket that affect ligand binding are consistent with these androgen receptor models. In addition to testosterone, the binding modes of several hydroxyflutamide-like nonsteroidal ligands for the androgen receptor are investigated using flexible docking with FlexX followed by refinement of the initial complexes with molecular dynamics simulations. These docking studies indicate that Asn705 is an important determinant in binding hydroxyflutamide and its derivatives by participating in H-bond interactions with the alpha-hydroxy moiety of these ligands. In addition, the nitro functionality mimics the 3-keto group of the natural ligand testosterone and is involved in H-bonding interactions with Gln711 and Arg752. From these docking studies, we suggest a mechanism for the enantioselective binding of chiral hydroxyflutamide derivatives and expand upon the previously reported structure-activity relationship for hydroxyflutamide and its derivatives.

Testosterone inhibits osteoclast formation stimulated by parathyroid hormone through androgen receptor

Androgens play an important role in the regulation of bone metabolism in animals and humans. The present study was performed to investigate whether androgens would affect osteoclast formation stimulated by parathyroid hormone (PTH) in mouse bone cell cultures and its mechanism. Testosterone as well as alpha-dihydrotestosterone (DHT) concentration-dependently inhibited osteoclast formation induced by PTH-(1-34). 10(-8) M ICI 182780, an estrogen receptor inhibitor, did not affect PTH-induced osteoclast formation antagonized by 10(-8) M testosterone, although it completely antagonized the effects of 10(-8) M 17beta-estradiol. Moreover, 3 microM 4-androsten-4-ol-3,17-dione, an aromatase inhibitor, did not affect PTH-induced osteoclast formation antagonized by testosterone. Hydroxyflutamide, an androgen receptor antagonist, concentration-dependently antagonized the inhibitory effects of testosterone as well as DHT on PTH-stimulated osteoclast formation. In conclusion, the present study first demonstrated that testosterone inhibited osteoclast formation stimulated by PTH through the androgen receptor, but not through the production of intrinsic estrogen in mouse bone cell cultures.

Androgen-induced cell growth and c-myc expression in human non-transformed epithelial prostatic cells in primary culture

We assessed androgen-induced cell growth and c-myc expression in human non-transformed epithelial prostatic (HNTEP) cells in primary culture. Prostatic tissue was obtained from 48 retropubic prostatectomy patients (age: 61-77years) with benign prostatic hyperplasia (malignant tumors excluded). HNTEP cells were treated with testosterone or DHT, alone or in association with hydroxyflutamide. DHT action on c-myc mRNA was examined using Northern blots and RT-PCR. RT-PCR also was used to verify if HNTEP cells expressed the androgen receptor gene. Cell proliferation was assessed on days 3 and 6. Testosterone (2 x 10(-11) M) and DHT (10(-13)M) caused a significant increase (P < 0.05) in cell proliferation on both days. Addition of hydroxyflutamide (10(-6) M) to DHT abolished cell proliferation. HNTEP cells expressed androgen receptor (AR) gene and the treatment with DHT increased AR mRNA levels. C-myc expression was maximal at 30 min and 1 h with DHT (10(-13) M). C-myc seems to play a key role in the control of hormone responsiveness and cell proliferation in epithelial prostatic cells. The detection of androgen receptor gene expression and the increase in this expression with the addition of androgen shows that the HTNEP cells maintain functional characteristics and hormone dependence, and that they are a fruitful in vitro model for studying steroid hormone action mechanisms.

Mutations at the boundary of the hinge and ligand binding domain of the androgen receptor confer increased transactivation function

The androgen receptor (AR), a member of the steroid receptor superfamily of nuclear transcription factors, mediates androgen signaling in diverse target tissues. Here we report AR gene mutations identified in human prostate cancer and the autochthonous transgenic adenocarcinoma of the mouse prostate model that colocate to residues (668)QPIF(671) at the boundary of the hinge and ligand-binding domain, resulting in receptors that exhibit 2- to 4-fold increased activity compared with wild-type AR in response to dihydrotestosterone, estradiol, progesterone, adrenal androgens, and the AR antagonist, hydroxyflutamide, without an apparent effect on receptor levels, ligand binding kinetics, or DNA binding. The expression of these or similar variants could explain the emergence of hormone refractory disease in a subset of patients. Homology modeling indicates that amino acid residues (668)QPIF(671) form a ridge bordering a potential protein-protein interaction surface. The naturally occurring AR gene mutations reported in this study result in decreased hydrophobicity of this surface, suggesting that altered receptor-protein interaction mediates the precocious activity of the AR variants.

Characterization of androgen receptors in a well-differentiated endometrial adenocarcinoma cell line (Ishikawa)

Androgen receptors (AR) have been identified in the human endometrium, but their role in endometrial function and development towards endometrial receptivity remains poorly understood. In an effort to study the regulation and possible function in endometrial epithelium, we utilized the well-differentiated endometrial adenocarcinoma cell line, Ishikawa, as a model system. This cell line has proven to be stable, hormonally responsive, contains both estrogen and progesterone receptors, and has been shown to express endometrial proteins in a hormone responsive manner. In the present study, we demonstrate that Ishikawa cells also express AR, based on immunohistochemical staining, radioactive binding studies, RT-PCR and Northern blot analysis. The expression of AR is induced in Ishikawa cells by estrogens, similar to that reported for normal endometrium. Further, using an estrogen-responsive gene that has been characterized in this cell line, alkaline phosphatase, we show that androgens act as antiestrogens in diethylstilbestrol (DES) treated cells, inhibiting enzymatic activity in a dose-dependent manner. These data support a physiologic role for AR in the endometrium. Elevations in endometrial AR in certain clinical situations such as polycystic ovarian syndrome (PCOS) may amplify the effects of androgens on the endometrium leading to suspected defects in uterine receptivity, higher than expected infertility and high miscarriage rates observed in patients with this disorder.

Mechanical strain stimulates osteoblast proliferation through the estrogen receptor in males as well as females

Mechanical strain, testosterone, and estrogen all stimulate proliferation of primary cultures of male rat long bone (LOB)-derived osteoblast-like cells as determined by [3H]thymidine incorporation. The maximum proliferative effect of a single period of mechanical strain (3400 microepsilon, 1 Hz, and 600 cycles) is additional to that of testosterone (10(-8) M) or estrogen (10(-8) M). The cells' proliferative response to strain is abolished both by concentrations of tamoxifen that cause proliferation (10(-8) M) and by those that have no effect (10(-6) M). Strain-related proliferation also is reduced by the estrogen antagonist ICI 182,780 (10(-8) M) but is unaffected by the androgen receptor antagonist hydroxyflutamide (10(-7) M). Tamoxifen, ICI 182,780, and the aromatase inhibitor 4-dihydroandrostenedione, at concentrations that have no effect on basal proliferation, significantly reduce the proliferative effect of the aromatizable androgen testosterone but not that of the nonaromatizable androgen 5alpha-dihydrotestosterone. Hydroxyflutamide, at a concentration that has no effect on basal proliferation (10(-7) M), eliminates the proliferative effect of 5alpha-dihydro-testosterone but had no significant effect on that caused by testosterone. Proliferation associated with strain is blocked by neutralizing antibody to insulin-like growth factor II (IGF-II) but not by antibody to IGF-I. Proliferation associated with testosterone is blocked by neutralizing antibody to IGF-I but is unaffected by antibody to IGF-II. These data suggest that in rat osteoblast-like cells from males, as from females, strain-related proliferation is mediated through the estrogen receptor (ER) in a manner that does not compete with estrogen but that can be blocked by ER modulators. Proliferation associated with testosterone appears to follow its aromatization to estrogen and is mediated through the ER, whereas proliferation associated with 5alpha-dihydrotestosterone is mediated by the androgen receptor. Strain-related proliferation in males, as in females, is mediated by IGF-II, whereas proliferation associated with estrogen and testosterone is mediated by IGF-I.

Effects of antiandrogens on chromatin remodeling and transcription of the integrated mouse mammary tumor virus promoter

Inhibition of the ligand-activated androgen receptor (AR) by antiandrogens plays an important role in the treatment of various hyperandrogenic disorders including prostate cancer. However, the molecular mechanisms of antiandrogen activity in vivo remain unclear. In this study we analyzed the effects of cyproterone acetate (CPA), flutamide (F), and hydroxyflutamide (OHF) on transcriptional activation and chromatin remodeling of the genomically integrated mouse mammary tumor virus (MMTV) promoter. This promoter has provided an excellent model system to study the impact of steroid hormones on transcriptional activation in the context of a defined chromatin structure. The MMTV hormone response element is positioned on a phased nucleosome, which becomes remodeled in response to steroids. We utilized this model system in mouse L-cell fibroblasts that contain a stably integrated MMTV promoter. In these cells, dihydrotestosterone (DHT) induced a large increase of AR protein levels that correlated with transcriptional activation and chromatin remodeling of the MMTV promoter. Coadministration of DHT and CPA or DHT and OHF in these cells inhibited the increase of AR levels, which resulted in a strong blockage of transcriptional activation and chromatin remodeling of the MMTV promoter. In contrast, F had no significant influence on these activities. We conclude that a major portion of the antiandrogenic effects of CPA and OHF in vivo are mediated by the reduction of AR levels.

Nonsteroidal progestins and antiprogestins related to flutamide

From the dual progestin/antiandrogenic properties of certain synthetic steroids (e.g. cyproterone acetate), it was apparent that the progesterone (P) and androgen (A) receptors must have some common ligand binding features. The nonsteroidal antiandrogen (aA) hydroxyflutamide was therefore considered a possible starting point for medicinal chemistry aimed at antiprogestin (aP) activity. Various modifications to the side chain and aryl ring substituents of flutamide yielded both P and aP activity, but always coupled with varying degrees of A or aA activity. Mineralocorticoid activity was present in some structures, but glucocorticoid and antiglucorticoid activities were not detected. Species (rat, rabbit and monkey) and chiral differences presented formidable difficulties in developing simple structure activity patterns, and low ( < 1%) in vitro uterine receptor binding belied in vivo potency of some aPs. One of the most active aPs, ZM172406, the R enantiomer of ZM150271, N-(3-chloro-4-cyanophenyl)-3,3, 3-trifluoro-2-hydroxy-2-methylpropanamide, had comparable oral potency to mifepristone in rats and monkeys. The racemate ZM150271 was an effective abortifacient during early pregnancy in pigtailed monkeys (3 x 10 mg/kg) but less effective in cynomolgus monkeys. One of the most active progestins (Pn), ZM182345, N-(4-nitro-3-trifluoromethylphenyl)-4-phenyl-2-hydroxy-2-trifluoromet hyl-pentanamide, was at least as potent as P in rats and rabbits but also possessed A activity.

Rapid androgen actions on calcium signaling in rat sertoli cells and two human prostatic cell lines: similar biphasic responses between 1 picomolar and 100 nanomolar concentrations

Androgen-induced calcium fluxes and gap junctional intercellular communication (GJIC) were studied in three different cell types. A transient (2-3 min duration) increase in intracellular calcium levels was observed within 20-30 sec of androgen addition, which was followed by a plateau phase with steroid concentrations higher than 1 nM. The kinetics of the calcium responses were similar in immature rat Sertoli cells, which contain normal nuclear receptors; the human prostatic tumor cell line, LNCaP, which contains a mutated nuclear receptor; and the human prostatic cell line, PC3, which does not contain a nuclear receptor. The human A431 tumor cell line did not respond to androgens. Concentrations of testosterone and the synthetic androgen, R1881, between 1-1000 pM induced transient calcium increases with ED(50) values near 1 pM and 1 nM, whereas dihydrotestosterone (DHT) was not active at these concentrations. At concentrations higher than 1 nM, testosterone, R1881, and DHT were equipotent in stimulating an increase in calcium that lasted for more than 10 min, with ED(50) values between 5 and 20 nM. Testosterone covalently bound to albumin was also active, whereas 11 related androstane compounds as well as progesterone and estradiol-17beta were inactive at 1000 nM. The calcium response induced by the three androgens (10 nM) was abolished in all cell types by hydroxyflutamide (1000 nM) and finasteride (1000 nM), but not by cyproterone acetate (1000 nM). The calcium response was also abolished in the absence of extracellular calcium and strongly inhibited by the presence of verapamil. Exposure of the responsive cells to brief (150-sec) pulses of androgens generated calcium responses that were similar to those after continuous exposure. After exposure of Sertoli cells for only 30 sec to 100 nM testosterone, the calcium response lasted for at least 50 min. Although nuclear binding of androgens could be demonstrated, there was no evidence for tight binding to the plasma membrane under similar conditions. When protein synthesis was inhibited, an enhancement of GJIC between rat Sertoli cells, but not between LNCaP cells or PC3 cells, was observed within 15 min of the addition of 10 nM testosterone. Because nuclear androgens are not present in PC3 cells and many functional properties of the responsive system are different from the nuclear receptor in all three cell types, we postulate the existence of an alternative cell surface receptor system with biphasic response characteristics (high and low affinity). The calcium signals are probably coupled to the regulation of gap junctional efficiency between Sertoli cells. The low-affinity receptors may convey complementary androgen signals at elevated local levels such as in the testis, when nuclear receptors are (over)saturated.

Specific recognition of androgens by their nuclear receptor. A structure-function study

Androgens, like progestins, are 3-ketosteroids with structural differences restricted to the 17beta substituent in the steroid D-ring. To better understand the specific recognition of ligands by the human androgen receptor (hAR), a homology model of the ligand-binding domain (LBD) was constructed based on the progesterone receptor LBD crystal structure. Several mutants of residues potentially involved in the specific recognition of ligands in the hAR were constructed and tested for their ability to bind agonists. Their transactivation capacity in response to agonist (R1881) and antagonists (cyproterone acetate, hydroxyflutamide, and ICI 176344) was also measured. Substitution of His(874) by alanine, only marginally impairs the ligand-binding and transactivation capacity of the hAR receptor. In contrast, mutations of Thr(877) and, to a greater extent, Asn(705) perturb ligand recognition, alter transactivation efficiency, and broaden receptor specificity. Interestingly, the N705A mutant acquires progesterone receptor (PR) properties for agonist ligands but, unlike wild type AR and PR, loses the capacity to repress transactivation with nonsteroidal antagonists. Models of the hAR.LBD complexes with several ligands are presented, which suggests new directions for drug design.

Down-regulation of transforming growth factor beta receptors by androgen in ovarian cancer cells

Steroid hormones have been implicated in the etiology and/or progression of epithelial ovarian cancer. As ovarian surface epithelial cells are growth inhibited by transforming growth factor beta (TGF-beta), we tested whether steroid hormones could regulate the expression of TGF-beta1 or its receptors in ovarian cancer cells, as assessed by quantitative reverse transcription-PCR. Treatment of ovarian cancer HEY cells with 500 nM 5alpha-dihydrotestosterone (DHT), but not estradiol-17beta or progesterone, for 60 h down-regulated the expression of mRNA for TGF-beta receptors I and II (TbetaR-I and TbetaR-II), betaglycan, and endoglin but had no effect on TGF-beta1 mRNA levels. Androgen receptor (AR) mRNA expression in HEY cells was compared to other ovarian cancer cell lines. OVCAR-3 cells expressed AR mRNA levels similar to that of androgen-responsive LNCaP prostate cancer cells, whereas SKOV-3 and HEY cells expressed only 3 and 0.01%, respectively. Western blot analysis and saturation binding assays confirmed the expression of AR protein in these three cell lines, but at the limit of detection in SKOV-3 and HEY cells. Treatment of SKOV-3 and HEY cells for 24 h with 1-50 nM DHT resulted in a dose-dependent down-regulation of TbetaR-II mRNA. The AR antagonist hydroxyflutamide did not reverse the effect of DHT on SKOV-3 cells but by itself down-regulated TbetaR-II mRNA. This apparent androgen-mimetic action of hydroxyflutamide and the ability of SKOV-3 and HEY cells to respond to DHT may be due to their expression of AR-associating protein 70, an AR co-activator reported to amplify AR transactivation and to result in agonist activity of AR antagonists. DHT was able to reverse TGF-beta1 growth-inhibitory action in SKOV-3 cells and in a primary culture of ovarian cancer cells derived from ascites. Thus, androgens may promote ovarian cancer progression in part by decreasing TGF-beta receptor levels, thereby allowing ovarian cancer cells to escape TGF-beta1 growth inhibition.

Isolation and characterization of the androgen receptor mutants with divergent transcriptional activity in response to hydroxyflutamide

A yeast genetic screening was developed to isolate androgen receptor (AR) mutants with divergent transactivation characteristics in response to hydroxyflutamide (HF), an active metabolite of flutamide used for prostate cancer treatment. Two mutants carrying the substitution C685Y or E708K were isolated and characterized. Substitution of C685Y for wild-type AR (wtAR) rendered the receptor supersensitive to androgenic activity from HF and female hormones such as 17beta-estradiol (E2) and progesterone (P). Similar effects were observed in the AR mutant, named T876AAR, isolated from LNCaP cells. Surprisingly, we found that C685YAR7, but not T876AAR7, could be activated by casodex (bicalutamide), a nonsteroidal pure antiandrogen, with an induction fold 3- to 5-fold times higher than that for wild type or T876AAR. By contrast, although replacement of E708K for wtAR showed little effect on dihydrotestosterone-mediated transactivation, E708KAR lost its transcriptional response from many other ligands. The effects of ligands on E708KAR could be controlled at the DNA-binding level owing to the finding of a significant decrease in the DNA-binding ability once E708KAR was bound to HF, E2, or P. Together, these results suggest that C685YAR can be a novel tool for assaying the androgenic activity from antiandrogens, and the mechanism revealed from E708KAR could provide a possible explanation for the partial androgen insensitivity syndrome in men with a natural E708KAR mutation.

Androgen receptor expression is greater in macrophages from male than from female donors. A sex difference with implications for atherogenesis

BACKGROUND

Male sex is an independent risk factor for the extent and severity of atherosclerosis. The influence of androgens on foam cell formation, a key event in atherogenesis, has not yet been investigated.

METHODS AND RESULTS

Primary human monocytes were allowed to differentiate into macrophages. RNA was then extracted from healthy male-donor (n=8) and premenopausal female-donor (n=8) macrophages, and message for the androgen receptor (AR) was examined by RT-PCR. There was a significantly higher level of AR mRNA in macrophages isolated from men than in those from women (0.64+/-0.06 versus 0.15+/-0.02 amol/microgram total RNA; P<0.001). AR mRNA levels were similar in macrophages from postmenopausal and premenopausal women (P=0.16). The functional consequence of this sex difference was then explored. Lipid-loading studies were performed on male (n=9) macrophages treated with the androgen dihydrotestosterone (DHT) and/or the AR antagonist hydroxyflutamide. These showed that DHT caused a dose-dependent and receptor-mediated increase in macrophage cholesteryl ester content (109+/-10%, 117+/-3%, and 120+/-4% for 4, 40, and 400 nmol/L DHT, respectively, as a percentage of control, P=0.002; 95+/-8% for DHT with hydroxyflutamide, P=0.58 versus controls). By contrast, there was no significant effect of androgen on lipid loading in female-donor macrophages (P>0.2 versus controls).

CONCLUSIONS

Sex differences in androgen-mediated macrophage lipid loading may contribute to the greater prevalence and severity of atherosclerosis in men.

7alpha-methyl-19-nortestosterone, a synthetic androgen with high potency: structure-activity comparisons with other androgens

CNNT. There was a good correlation between bioactivity and binding affinity to AR for the 7alpha-substituted androgens compared to T. In contrast, relative to their binding affinity to AR, the androgenic potency of DHT and 19-NT was lower compared to T. The reason for the lower in vivo androgenic activity of 19-NT is attributable to its enzymatic conversion to 5alpha-reduced-19-NT in the prostate. In the case of DHT, the lower bioactivity could be attributed to its faster metabolic clearance rate relative to T. The correlation was further investigated in vitro by co-transfection of rat ARcDNA expression plasmid and a reporter plasmid encoding the chloramphenicol acetyl transferase (CAT) gene driven by an androgen inducible promoter into CV-1 cells. All the androgens led to a dose-dependent increase in the CAT activity. MENT was found to be the most potent followed by DHT, 19-NT, T, and CNNT. The specificity of the androgenic response was confirmed by its inhibition with hydroxyflutamide, an antiandrogen. Thus, there was a good correlation between binding affinity and in vitro bioactivity in the transient transfection assay for the androgens. This suggests that the in vivo bioactivity of androgens could be influenced not only by binding affinity to receptors but also by factors such as absorption, binding to serum proteins and metabolism. However, the high potency of MENT is primarily related to its higher affinity to AR.

Domain requirements of DnaJ-like (Hsp40) molecular chaperones in the activation of a steroid hormone receptor

DnaJ-like proteins function in association with Hsp70 molecular chaperones to facilitate protein folding. We previously demonstrated that a yeast DnaJ-like protein, Ydj1p, was important for activation of heterologously expressed steroid hormone receptors (Caplan, A. J., Langley, E., Wilson, E. M., and Vidal, J. (1995) J. Biol. Chem. 270, 5251-5257). In the present study, we analyzed Ydj1p function by assaying hormone binding to the human androgen receptor (AR) heterologously expressed in yeast. We analyzed hormone binding in strains that were wild type or deleted for the YDJ1 gene. In the deletion mutant, the AR did not bind hormone to the same extent as the wild type. Introduction of mutant forms of Ydj1p to the deletion strain revealed that the J-domain is necessary but not sufficient for Ydj1p action, and that other domains of the protein are also functionally important. Of three human DnaJ-like proteins introduced into the deletion mutant, only Hdj2, which displays full domain conservation with Ydj1p, suppressed the hormone binding defect of the deletion mutant. By comparison of the domains shared by these three human proteins, and with mutants of Ydj1p that were functional, it was deduced that the cysteine-rich zinc binding domain is important for Hdj2/Ydj1p action in hormone receptor function. A model for the mechanism of DnaJ-like protein action is discussed.

Differential induction of androgen receptor transactivation by different androgen receptor coactivators in human prostate cancer DU145 cells

Recently identified androgen receptor (AR) coactivators were used in this study to determine whether the specificity of sex hormones and antiandrogens could be modulated at the coactivator level. We found that ARA70 is the best coactivator to confer the androgenic activity on 17beta-estradiol. Only ARA70 and ARA55 could increase significantly the androgenic activity of hydroxyflutamide, a widely used antiand rogen for the treatment of prostate cancer. None of the AR coactivators we tested could significantly confer androgenic activity on progesterone and glucocorticoid at their physiological concentrations (1-10nM). We also found that ARA70, ARA55, and ARA54, but not steroid receptor coactivator-1 (SRC-1) and Rb, could significantly enhance the delta5-androstenediol-mediated AR transactivation. Furthermore, in comparing the relative specificity of these coactivators to AR in DU145 cells, our results suggested that ARA70 has a relatively higher specificity and that SRC-1 can enhance almost equally well many other steroid receptors. Finally, our data demonstrated that AR itself and some select AR coactivators such as ARA70 or ARA54 could, respectively, interact with CBP and p300/CBP-associated factors that have histone acetyl-transferase activity for assisting chromatin remodeling. Together, our data suggest that the specificity of sex hormones and antiandrogens can be modulated by some selective AR coactivators. These findings may not only help us to better understand the specificity of the sex hormones and antiandrogens, but also facilitate the development of better antiandrogens to fight the androgen-related diseases, such as prostate cancer.

Androgen and epidermal growth factor down-regulate cyclin-dependent kinase inhibitor p27Kip1 and costimulate proliferation of MDA PCa 2a and MDA PCa 2b prostate cancer cells

Low levels of p27Kip1 in primary prostate cancer specimens have been shown to be associated with higher rates of disease recurrence and poor rates of disease-free survival in patients with localized disease. In this study, we provide the first direct evidence showing that dihydrotestosterone (DHT), a major proliferation regulator of prostate cancer, can down-regulate p27Kip1 and stimulate cyclin-dependent kinase-2 (CDK2) activity in established prostate cancer cell lines. We investigated the cooperative effects of DHT and epidermal growth factor (EGF) on the proliferation of androgen-responsive MDA PCa 2a and MDA PCa 2b prostate cancer cells. DHT and EGF each stimulated proliferation of these cells, but exposure of the cells to DHT and EGF together stimulated greater proliferation. Stimulation of cell proliferation by DHT and/or EGF was associated with increased CDK2 activity and a decreased level of p27Kip1. There seems to be a positive feedback stimulation loop between androgen-induced gene transcription and EGF-stimulated signal transduction, as one could stimulate the synthesis of the receptors for the other. Dual blockade of androgen receptor function with the antiandrogen hydroxyflutamide and EGF receptor superfamily-mediated signal transduction with the anti-EGF receptor monoclonal antibody C225 and the anti-HER2 receptor monoclonal antibody Herceptin significantly enhanced growth inhibition of the MDA PCa 2a cells. Our results demonstrate the importance of counteracting both androgen receptors and EGF receptors in the development of novel therapies for prostate cancer.

The anti-androgen hydroxyflutamide and androgens inhibit interleukin-6 production by an androgen-responsive human osteoblastic cell line

While androgens clearly have significant skeletal effects, the paracrine mediators of androgen action on bone are at present unclear. Interleukin-6 (IL-6) is a candidate cytokine that is produced by osteoblastic lineage cells and promotes osteoclastogenesis and bone resorption. Here, we assessed constitutive as well as IL-1beta- and tumor necrosis factor-alpha (TNF-alpha)-stimulated IL-6 mRNA expression by Northern analysis and protein secretion by immunoassay in a human androgen-responsive osteoblastic cell line (hFOB/AR-6) which contains approximately 4000 androgen receptors (ARs)/nucleus. Treatment with 5alpha-dihydrotestosterone (DHT) dose-dependently inhibited constitutive and TNF-alpha/IL-1beta-stimulated IL-6 mRNA steady-state levels in hFOB/AR-6 cells by 70-80% at 10-7 M. In addition, testosterone also suppressed TNF-alpha/IL-1beta-stimulated IL-6 mRNA levels by 57%, while the adrenal androgen dehydroepiandrosterone had no effect. Of note, the specific AR antagonist, hydroxyflutamide, also inhibited IL-6 mRNA levels by 70%. Consistent with the Northern analyses, treatment with 5alpha-DHT, testosterone, and hydroxyflutamide also inhibited IL-6 protein production by 79%, 62%, and 71%, respectively (p < 0.001), while these agents had no effect on IL-6 soluble receptor levels. Finally, we demonstrated that hydroxyflutamide treatment of hFOB/AR-6 cells markedly inhibited the activation and binding of NF-kappaB (a known stimulator of IL-6 gene transcription) to its response element, thus providing a potential mechanism for its effect on IL-6 production by osteoblasts. These data are consistent with the hypothesis that suppression of osteoblast IL-6 production by androgens may mediate, at least in part, the antiresorptive effects of androgens on bone. Moreover, our findings also indicate that hydroxyflutamide, which is a known AR antagonist in most tissues, may function as a selective AR modulator for effects on IL-6 production by osteoblasts.

Regulation of GCDFP-15 expression in human mammary cancer cells

Gross cystic disease fluid protein 15 (GCDFP-15) is a major protein component of benign breast gross cysts. It is also found in approximately 50% of all breast cancer specimens. Androgen receptor (AR) mediated regulation of GCDFP-15 expression was investigated in the AR-positive human mammary cancer cell lines MFM-223 and ZR-75-1. Proliferation of MFM-223 and ZR-75-1 cells is inhibited by androgens. Ten nM 5alpha-dihydrotestosterone stimulated the expression of GCDFP-15 mRNA in MFM-223 (ca. 3-fold) and ZR-75-1 cancer cells (ca. 30-fold) as well as the secretion of GCDFP-15 into the culture medium. Competition experiments with DHT and the antiandrogens hydroxyflutamide and casodex confirmed the involvement of the AR in the regulation of GCDFP-15. Both antiandrogens inhibited GCDFP-15 mRNA expression even in the absence of DHT. AR mRNA was down-regulated in MFM-223 and ZR-75-1 cells (80 and 20% of the control, respectively) during incubation with DHT. Our data demonstrate the effective inhibition of GCDFP-15 expression by pure antiandrogens.

Pharmacokinetics of 2-hydroxyflutamide, a major metabolite of flutamide, in normal and CCl4-poisoned rats

AIM

To study the pharmacokinetics of 2-hydroxyflutamide (HF), a major active metabolite of flutamide (Flu), in normal and CCl4-poisoned rats.

METHODS

Normal and CCl4-poisoned rats were given i.g. HF 25 mg.kg-1. HF concentrations of plasma were determined by HPLC with YWG C 18 column, Flu was used as an internal standard. The mobile phase was composed of methanol: water = 3:2 (vol), and absorbance was measured at lambda 295 nm.

RESULTS

HF elimination was inhibited in CCl4-poisoned rats compared with normal rats. K decreased from (0.11 +/- 0.05) to (0.05 +/- 0.01) h-1 (P < 0.01), T1/2 was prolonged from (6.8 +/- 1.9) to (14 +/- 4) h (P < 0.01), Cl decreased from (0.18 +/- 0.06) to (0.12 +/- 0.02) L.kg-1.h-1 (P < 0.05), AUC increased from (149 +/- 47) to (226 +/- 54) mg.L-1.h (P < 0.05).

CONCLUSION

This HPLC assay was sensitive and precise, and the elimination of HF was inhibited due to CCl4 poisoning.

Phosphorylation/dephosphorylation of androgen receptor as a determinant of androgen agonistic or antagonistic activity

Protein phosphorylation/dephosphorylation is an important posttranslational modification that plays a critical role in signal transduction. The androgen receptor (AR) is under such control. We demonstrate that androgen receptor phosphorylation determines whether or not AR ligands perform as agonists or antagonists in LNCaP cells. Androgen receptor ligands (such as dihydrotestosterone and beta-estradiol) stimulate receptor expression and phosphorylation and, as a result, they act as agonists or partial agonists. In contrast, agents such as bicalutamide and estramustine inhibit the receptor phosphorylation and act as antagonists. This model is supported by gene expression and transactivation assays. Significant increases in levels of both mRNA and protein of prostate-specific antigen (PSA), a natural AR target gene, occur following the treatment of LNCaP cells with DHT, beta-estradiol, or hydroxyflutamide. In contrast, exposure of LNCaP cells to bicalutamide or estramustine results in a sharp decrease of PSA expression. Agonistic or antagonistic effect of these compounds on PSA expression parallels the level of phosphorylated, but not dephosphorylated androgen receptors. These agonistic or antagonistic effects are also observed in HeLa cells transfected with wild-type AR expression plasmid (pAR0) and AR-driven luciferase expression plasmid GRE-tk-LUC in the presence of different groups of AR blockers. Our data indicate that the functional status of androgen receptors is strongly correlated with the phosphorylation status of the receptors, and that the phosphorylated androgen receptor is the form of the receptor transcriptionally active in regulation. Thus the androgen receptor phosphorylation/dephosphorylation may serve as a new molecular target for screening androgen antagonists for the treatment of prostate cancer.

From HER2/Neu signal cascade to androgen receptor and its coactivators: a novel pathway by induction of androgen target genes through MAP kinase in prostate cancer cells

Overexpression of the HER2/Neu protooncogene has been linked to the progression of breast cancer. Here we demonstrate that the growth of prostate cancer LNCaP cells can also be increased by the stable transfection of HER2/Neu. Using AG879, a HER2/Neu inhibitor, and PD98059, a MAP kinase inhibitor, as well as MAP kinase phosphatase-1 (MPK-1), in the transfection assay, we found that HER2/Neu could induce prostate-specific antigen (PSA), a marker for the progression of prostate cancer, through the MAP kinase pathway at a low androgen level. Reporter assays and mammalian two-hybrid assays further suggest this HER2/Neu-induced androgen receptor (AR) transactivation may function through the promotion of interaction between AR and AR coactivators, such as ARA70. Furthermore, we found this HER2/Neu --> MAP kinase --> AR-ARAs --> PSA pathway could not be blocked completely by hydroxyflutamide, an antiandrogen used in the treatment of prostate cancer. Together, these data provide a novel pathway from HER2/Neu to AR transactivation, and they may represent one of the reasons for the PSA re-elevation and hormone resistance during androgen ablation therapy in prostate cancer patients.

5,6 Dihydro-5'-azacytidine (DHAC) restores androgen responsiveness in androgen-insensitive prostate cancer cells

INTRODUCTION

The androgen resistance of some prostate cancer patients may be due to transcriptional inactivation of the androgen receptor (AR) gene catalyzed by cytosine DNA methyltransferase.

MATERIALS AND METHODS

To determine if an inhibitor of cytosine DNA methyltransferase, 5,6-dihydro-5'-azacytidine (DHAC), can restore the androgen sensitivity in androgen-insensitive human prostate carcinoma cell lines in vitro, we cultured androgen-insensitive (PC3, DU-145, and TSUPrl) and androgen-responsive (LNCaP) cells with subcytotoxic concentrations (< or = IC50) of DHAC for 14 days followed by exposure to dihydrotestosterone (DHT) or to hydroxyflutamide for 7 days.

RESULTS AND CONCLUSIONS

Only DHAC-treated DU-145 cells showed growth stimulation by 10(-11) to 10(-9) M DHT and a partial inhibition by 10(-5) and 10(-6) M hydroxyflutamide. However, since DU-145 is the only cell line tested that is known to have a hypermethylated AR promoter, the observed effects may be due to a partial demethylation of the AR by DHAC. Our data provide an evidence that cytosine DNA methyltransferase inhibitors can restore androgen responsiveness in androgen-refractory tumor cells, which are then sensitive to growth inhibition by antiandrogens.

Androgens regulate bone resorption activity of isolated osteoclasts in vitro

For many years it has been recognized that sex steroids have profound effects on bone metabolism. The current perception is that estrogen decreases bone resorption and androgen increases bone deposition. To investigate the potential for androgens to directly modulate bone resorption, we have examined avian osteoclast and human and mouse osteoclast-like cells for androgen responsiveness. There was a dose-dependent decrease in resorption activity in response to alpha-dihydrotestosterone (alpha-DHT), beta-DHT, testosterone, or the synthetic androgen RU1881. This decrease was blocked by cotreatment with the specific androgen antagonist hydroxyflutamide. Further examination of avian osteoclasts revealed that the cells exhibited specific and saturable nuclear binding of tritiated RU1881 and that alpha-DHT stimulated the activity of the androgen response element as measured by using a chloramphenicol acetyltransferase reporter plasmid. In addition, avian osteoclasts responded to androgen treatment with elevated production and secretion of transforming growth factor beta, a well documented response to androgen exposure in other cell systems. Treatment with either alpha-DHT or beta-DHT for 24 hours resulted in a significant dose-dependent decrease in secretion of cathepsin B and tartrate-resistant acid phosphatase. This response to beta-DHT, a stereoisomer of alpha-DHT that is inactive in other androgen receptor-dependent systems, supports the hypothesis that the osteoclast androgen receptor has unusual ligand-binding properties. Taken together, these results confirm the presence of functional androgen receptors in these cells and support the conclusion that osteoclasts are able to respond directly to androgens in vitro and thus are potential androgen target cells in vivo.

Pharmacokinetics of flutamide in patients with renal insufficiency

AIMS

The aim of this study was to determine the pharmacokinetic parameters of flutamide, a nonsteroidal antiandrogenic compound, and its pharmacologically active metabolite, hydroxyflutamide, in renal insufficiency. Haemodialysis (HD) clearance of flutamide and hydroxyflutamide was also determined.

METHODS

Pharmacokinetic parameters were assessed for flutamide and hydroxyflutamide in 26 male subjects with normal renal function (creatinine clearance by 24 h urine collection, CLcr, greater than 80 ml min(-1) 1.73 m(-2); n=6) or reduced renal function; CLcr=50-80 (n=7), 30-49 (n=3), 5-29 (n=4), and <5 ml min(-1) 1.73 m(-2)-HD (n=6), following a single, oral 250 mg flutamide dose. Subjects undergoing HD received a second 250 mg dose of flutamide 4 h prior to HD; blood and dialysate were collected during HD to determine dialysability of flutamide and hydroxyflutamide.

RESULTS

Cmax, tmax, AUC, t1/2, and renal clearance of flutamide and hydroxyflutamide did not differ between groups. Less than 1% of the dose appeared in dialysate as hydroxyflutamide. No serious adverse events were observed.

CONCLUSIONS

Renal function did not affect flutamide nor hydroxyflutamide disposition. HD did not alter hydroxyflutamide pharmacokinetics. Dosing adjustments for renal impairment or HD are not indicated for flutamide.

Androgens down-regulate bcl-2 protooncogene expression in ZR-75-1 human breast cancer cells

Although a large proportion of primary human breast cancers express the androgen receptor, and treatment with androgens exerts beneficial effects in women with breast cancer, the role and especially the mechanism of action of androgens in breast cancer development and growth are not well understood. The potential effect of androgens on bcl-2 protooncogene expression was investigated in a human breast cancer cell line whose proliferation is known to be inhibited by androgens. The estrogen-responsive ZR-75-1 cells were grown in the presence or absence of 5alpha-dihydrotestosterone (DHT), alone or in combination with 17beta-estradiol. DHT caused a marked down-regulation of Bcl-2 protein and messenger RNA levels in both the presence and absence of 17beta-estradiol. The inhibitory effect of DHT was completely prevented by coincubation with the pure antiandrogen hydroxyflutamide. The present data indicate that androgens can down-regulate bcl-2 protooncogene levels via an androgen receptor-mediated mechanism, thus providing a novel mechanism for their known inhibitory effect on breast cancer cell growth.

Evidence for androgen receptor gene expression and growth inhibitory effect of dihydrotestosterone on human adrenocortical cells

Evidence for the expression of the canonic androgen receptor (AR) in human adrenal cortex has not been provided so far. The aim of the present study was to demonstrate the expression of the AR gene in normal and neoplastic adrenocortical human tissues and in the human adrenocortical cancer cell line, NCI-H295, and then to evaluate the effect of dihydrotestosterone (DHT) on human adrenocortical cell growth. An AR cDNA fragment with the expected size of 262 bp was detected by using reverse transcription (RT)-PCR in normal and neoplastic adrenocortical human tissues and in the neoplastic cell line, demonstrating that the gene for AR is indeed expressed in human adrenal cells. In the human adrenocortical cancer cell line NCI-H295, DHT at physiological concentrations produced a significant reduction in cell proliferation and inhibition of colony formation in soft agar. The inhibitory effect on adrenocortical cell growth was evident after both 24 and 48 h of treatment. The antiandrogens, cyproterone acetate and hydroxyflutamide, were capable of reversing the effects exerted by DHT. The androgen-induced growth inhibitory effect was also detected in primary culture of three non-functioning adrenocortical adenomas. These findings show that the canonic AR is present in human adrenocortical cells and that androgens may have a role in the adrenal cortex by reducing cell proliferation.

Effects of gonadal and adrenal androgens in a novel androgen-responsive human osteoblastic cell line

While androgens have important skeletal effects, the mechanism(s) of androgen action on bone remain unclear. Current osteoblast models to study androgen effects have several limitations, including the presence of heterogeneous cell populations. In this study, we examined the effects of androgens on the proliferation and differentiation of a novel human fetal osteoblastic cell line (hFOB/AR-6) that expresses a mature osteoblast phenotype and a physiological number (approximately 4,000/nucleus) of androgen receptors (AR). Treatment with 5alpha-dihydrotestosterone (5alpha-DHT) inhibited the proliferation of hFOB/AR-6 cells in a dose-dependent fashion, while it had no effect on the proliferation of hFOB cells, which express low levels of AR (<200/nucleus). In hFOB/AR-6 cells, co-treatment with the specific AR antagonist, hydroxyflutamide abolished 5alpha-DHT-induced growth inhibition. Steady-state levels of transforming growth factor-beta1 (TGF-beta1) and TGF-beta-induced early gene (TIEG) mRNA decreased after treatment of hFOB/AR-6 cells with 5alpha-DHT, suggesting a role for the TGF-beta1-TIEG pathway in mediating 5alpha-DHT-induced growth inhibition of hFOB/AR-6 cells. In support of this, co-treatment of hFOB/AR-6 cells with TGF-beta1 (40 pg/ml) reversed the 5alpha-DHT-induced growth inhibition, whereas TGF-beta1 alone at this dose had no effect on hFOB/AR-6 cell proliferation. Furthermore, treatment of hFOB/AR-6 cells with 5alpha-DHT and testosterone (10(-8) M) inhibited basal and 1,25-(OH)2D3-induced alkaline phosphatase (ALP) activity and type I collagen synthesis without affecting osteocalcin production. Thus, in this fetal osteoblast cell line expressing a physiological number of AR, androgens decrease proliferation and the expression of markers associated with osteoblast differentiation. These studies suggest that the potential anabolic effect of androgens on bone may not be mediated at the level of the mature osteoblast.

Phorbol ester causes ligand-independent activation of the androgen receptor

We have examined the human androgen receptor (hAR) for its ability to activate AR-dependent transcription of a transgene in a ligand-independent manner. The transcriptional activity was determined by analysis of chloramphenicol acetyltransferase (CAT) activity in T47D cells cotransfected with a plasmid expressing the hAR and a natural AR-regulated promoter (the MVDP androgen-dependent enhancer) ligated to the reporter CAT gene. In this study, the effects of the protein kinase C (PKC) activator 12-O-tetradecanoyphorbol-13 acetate (TPA) on AR activity were tested. We demonstrated that in the absence of androgen, TPA enhanced AR-mediated transactivation by 10-12-fold. This effect was specific of the PKC pathway since stimulation to the PKA pathway did not activate the unliganded AR. This ligand-independent pathway can function through another androgen-regulated promoter as shown by the use of the mouse mammary tumor virus MMTV-CAT reporter. The human glucocorticoid receptor (hGR) and the rabbit progesterone receptor (rPR) could not be activated by TPA, indicating that the effects are not universal for steroid receptors. A reporter plasmid containing the MVDP androgen response element (ARE) in front of the thymidine kinase promoter ligated to the CAT gene was activated by DHT but not by TPA, indicating that the context of the natural promoter is critical for ligand-independent activation of the AR. Exogenous c-jun enhanced transcriptional activation by the AR in a ligand-dependent manner, but had no effect in the absence of DHT. Base pair substitutions in both AR-binding (5'-TGTTCT-3' to 5'-TTTTTT-3') and NF1-binding (5'-GTGGCTG-3' to 5'-GTTTTTG-3') sites resulted in a loss of TPA responsiveness. Our results suggest that ligand-independent activation of the AR by TPA results from interaction of unliganded AR with other proteins in the transcription machinery.

Delta5-androstenediol is a natural hormone with androgenic activity in human prostate cancer cells

It is known that androst-5-ene-3beta,17beta-diol (Adiol), a precursor of testosterone (T), can activate estrogen target genes. The androgenic activity of Adiol itself, however, is poorly understood. Using a transient transfection assay, we here demonstrate in human prostate cancer cells that Adiol can activate androgen receptor (AR) target genes in the presence of AR, and that AR coactivator ARA70 can further enhance this Adiol-induced AR transcriptional activity. In contrast to this finding, an active metabolite of dehydroepiandrosterone, 7-oxo-dehydroepiandrosterone, does not activate AR target gene in the absence or presence of ARA70. Thin layer chromatography analysis reveals that T, dihydrotestosterone, and 17beta-estradiol are undetectable in human prostate cancer DU145 cells after treatment with Adiol. Additionally, a proteolysis assay shows that a distinct ligand-receptor conformational difference exists between T-AR and Adiol-AR. Together, the above findings and the fact that T, but not Adiol, can induce transcriptional activity in a mutant AR (mtAR708), suggest that, without being metabolized into T, Adiol itself may represent a natural hormone with androgenic activity in human prostate cancer cells. Because two potent antiandrogens, hydroxyflutamide (Eulexin), and bicalutamide (casodex), that are widely used for the treatment of prostate cancer, fail to block Adiol-mediated induction of AR transcriptional activity in prostate cancer cells, the effectiveness of so-called "total androgen blockage," a standard treatment for prostate cancer, may need to be reevaluated.

Inhibition of androgen receptor-dependent transcriptional activity by DDT isomers and methoxychlor in HepG2 human hepatoma cells

Recent reports have raised new concerns that chemicals in our environment may disrupt normal reproduction and development through inhibition of androgen receptor function. This heightened concern has also increased our need for methods that allow us to characterize chemical interaction with the androgen receptor. In this report we describe an androgen receptor assay that utilizes the HepG2 human hepatoma cell line transiently transfected with the human androgen receptor and an androgen-responsive reporter. We used this assay to characterize the interaction with the androgen receptor of several steroidal and nonsteroidal chemicals, including isomers of DDT and methoxychlor. Chemicals were tested either in the absence (for determining agonist activity) or presence of 10(-7) M dihydrotestosterone (for determining antagonist activity). Testosterone and dihydrotestosterone were equally potent agonists in this assay. Estradiol and progesterone displayed partial agonist/antagonist activity. Flutamide was a complete agonist, whereas its hydroxylated metabolite, hydroxyflutamide, only partially antagonized and displayed some agonist activity at 10(-6) M and above. o,p'-DDT, o,p'-DDE, o,p'-DDD, p,p'-DDT, p,p'-DDE, and p, p'-DDD all behaved as antagonists at concentrations above 10(-6) M. p,p'-DDE also showed some agonist activity at 10(-5) M. Methoxychlor was only weakly antagonistic while its hydroxylated metabolite, HPTE, was approximately 10-fold more potent. Our results demonstrate that the HepG2 assay is a sensitive and specific method for detecting chemical interaction with the androgen receptor. This reporter gene assay, which we have used to characterize interaction with both the estrogen and androgen receptors, coupled with more extensive in vivo studies, should be useful for determining the role of multiple steroid receptors in the mechanism of action of endocrine active chemicals.

Promotion of agonist activity of antiandrogens by the androgen receptor coactivator, ARA70, in human prostate cancer DU145 cells

Although hormone therapy with antiandrogens has been widely used for the treatment of prostate cancer, some antiandrogens may act as androgen receptor (AR) agonists that may result in antiandrogen withdrawal syndrome. The molecular mechanism of this agonist response, however, remains unclear. Using mammalian two-hybrid assay, we report that antiandrogens, hydroxyflutamide, bicalutamide (casodex), cyproterone acetate, and RU58841, and other compounds such as genistein and RU486, can promote the interaction between AR and its coactivator, ARA70, in a dose-dependent manner. The chloramphenicol acetyltransferase assay further demonstrates that these antiandrogens and related compounds significantly enhance the AR transcriptional activity by cotransfection of AR and ARA70 in a 1:3 ratio into human prostate cancer DU145 cells. Our results suggest that the agonist activity of antiandrogens might occur with the proper interaction of AR and ARA70 in DU145 cells. These findings may provide a good model to develop better antiandrogens without agonist activity.

The role of transforming growth factor-beta1, -beta2, and -beta3 in androgen-responsive growth of NRP-152 rat prostatic epithelial cells

We have investigated the role of autocrine/paracrine TGF-beta secretion in the regulation of cell growth by androgens as demonstrated by its inhibition by two androgen response modifiers; the nonsteroidal antiandrogen hydroxyflutamide (OHF), believed to act by inhibiting androgen binding to androgen receptors, or finasteride, an inhibitor of 5alpha-reductase, the enzyme necessary for the conversion of testosterone to 5alpha-dihydrotestosterone (DHT), using the nontumorigenic rat prostatic epithelial cell line NRP-152. Growth of these cells was stimulated three- to sixfold over control by either testosterone or DHT under serum-free culture conditions. This was accompanied by a two- to threefold decrease in the secretion rate of TGF-beta1, -beta2, and -beta3. Finasteride reversed the ability of testosterone but not DHT to stimulate growth and downregulate expression of TGF-beta1, -beta2, and -beta3 in a dose-dependent fashion, suggesting that this activity of testosterone required its conversion to DHT. OHF antagonized the stimulatory effects of DHT on NRP-152 cell growth but could reverse the inhibitory effects of DHT only on TGF-beta2 and TGF-beta3 and not TGF-beta1 secretion. This suggests that either TGF-beta1 regulation by DHT or the androgen antagonism of OHF occurs independent of androgen receptor binding. Neutralizing antibodies to TGF-beta (pantropic and isoform-specific) were able to block the ability of finasteride to antagonize the effects of testosterone nearly completely while only partially inhibiting the antiandrogenic effects of OHF. Thus, the ability of androgens to stimulate growth of NRP-152 cells involves the downregulation of the production of TGF-beta1, -beta2, and -beta3 in addition to other growth-stimulatory mechanisms.

Regulation of gonadotropin-releasing hormone (GnRH) gene expression by 5alpha-dihydrotestosterone in GnRH-secreting GT1-7 hypothalamic neurons

Hypothalamic GnRH secretory neurons are precisely regulated by circulating gonadal steroids. However, the question of whether these cells are directly responsive to steroid hormones remains a central and controversial issue in reproductive science. In the present study, we demonstrate the expression of androgen receptor (AR) in a mouse hypothalamic GnRH-secreting cell line, GT1-7. AR messenger RNA was detected by Northern blot analysis of 10 microg total cellular RNA. Western blot analysis revealed a 110K AR immunoreactive band, and saturation binding analysis confirmed the presence of a high affinity low capacity androgen binding entity (Kd = 0.06 nM; Bmax = 12.4 fmol/mg protein). In addition, GT1-7 cells were found to express ARA70, an AR-specific coactivator that has been reported to enhance transactivational activity of the AR. GT1-7 cells transiently transfected with an androgen responsive MMTV-luciferase reporter construct displayed a 4.2-fold induction of luciferase reporter gene activity by 1 nM 5alpha-dihydrotestosterone (DHT), further demonstrating the presence of a functional AR. Treatment of GT1-7 cells with 1 or 10 nM DHT resulted in approximately 55% reduction in GnRH messenger RNA measured at 24 and 36 h after treatment. This repression was completely blocked by hydroxyflutamide, an AR antagonist. These results provide the first demonstration that androgen acts directly through an AR-mediated pathway to repress GnRH gene expression in hypothalamic GnRH-secreting neurons.

Pharmacokinetics of flutamide and its metabolite 2-hydroxyflutamide in normal and hepatic injury rats

AIM

To develop a new HPLC assay to study the pharmacokinetics of flutamide (Flu) and its active metabolite 2-hydroxyflutamide (HF) in rats.

METHODS

Normal or hepatic injury rats were given i.g. Flu 50 mg.kg-1. Reverse phase HPLC was developed with a mu-Bondapak C 18 column. Internal standard was methyltestosterone. The mobile phase was a mixture of methanol:acetonitrile:water:diethyl ether = 40:20:35:1 (vol). Absorbance was measured at lambda 234 nm.

RESULTS

The pharmacokinetic parameters of Flu were as follows: in normal rats, K = 0.62 +/- 0.16 h-1, Cl = 6.0 +/- 1.0 L.kg-1.h-1, AUC = 8.6 +/- 1.3 mg.L-1.h, Cmax = 2.4 +/- 0.7 mg.L-1; in hepatic injury rats, K = 0.16 +/- 0.03 h-1, Cl = 0.63 +/- 0.29 L.kg-1.h-1, AUC = 100 +/- 44 mg.L-1.h, Cmax = 6.7 +/- 2.8 mg.L-1. The pharmacokinetic parameters of HF were as follows: in normal rats, K(m) = 0.07 +/- 0.01 h-1, AUC = 219 +/- 22 mg.L-1.h, Cmax = 8.6 +/- 0.6 mg.L-1; in hepatic injury rats, K(m) = 0.05 +/- 0.01 h-1, AUC = 170 +/- 42 mg.L-1.h, Cmax = 3.8 +/- 0.8 mg.L-1. There were significant differences between the parameters of normal and hepatic injury rats (P < 0.01) except AUC of HF (P > 0.05).

CONCLUSION

This HPLC assay was sensitive and precise, and the elimination of Flu and HF was inhibited significantly due to hepatic injury.