Selective retention of dihydrotestosterone by prostatic nuclei

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Relative potency of testosterone and dihydrotestosterone in preventing atrophy and apoptosis in the prostate of the castrated rat

Although dihydrotestosterone (DHT) is the principal androgen in the prostate, testosterone can also act as an androgen in this tissue. To determine the relative potencies of testosterone and DHT in preventing prostate regression, castrated rats were implanted for 4 d with varying doses of testosterone in the presence or absence of the 5alpha-reductase inhibitor finasteride. In the absence of finasteride, testosterone in the prostate is converted to DHT, creating an intraprostatic DHT dose response. In the presence of finasteride, this conversion is blocked, and an intraprostatic testosterone dose response is achieved. DHT was 2.4 times more potent than testosterone at maintaining normal prostate weight and duct lumen mass, a measure of epithelial cell function. The two androgens were equipotent at preventing DNA fragementation and expression of testosterone-repressed prostate message, two measures of apoptosis (cell death). The intraprostatic testosterone concentration that results from finasteride treatment in rats is sufficient to inhibit apoptosis but will not maintain normal epithelial cell activity. In conclusion, whereas DHT is more potent than testosterone at stimulating prostate epithelial cell function as measured by ductal mass, the two androgens are equipotent at preventing prostate cell death after castration. These results explain why finasteride causes prostate involution in the rat with minimal evidence of prostate cell death.

Human prostate tumor growth in athymic mice: inhibition by androgens and stimulation by finasteride

When the human prostate cancer cell line, LNCaP 104-S, the growth of which is stimulated by physiological levels of androgen, is cultured in androgen-depleted medium for > 100 passages, the cells, now called LNCaP 104-R2, are proliferatively repressed by low concentrations of androgens. LNCaP 104-R2 cells formed tumors in castrated male athymic nude mice. Testosterone propionate (TP) treatment prevented LNCaP 104-R2 tumor growth and caused regression of established tumors in these mice. Such a tumor-suppressive effect was not observed with tumors derived from LNCaP 104-S cells or androgen receptor-negative human prostate cancer PC-3 cells. 5 alpha-Dihydrotestosterone, but not 5 beta-dihydrotestosterone, 17 beta-estradiol, or medroxyprogesterone acetate, also inhibited LNCaP 104-R2 tumor growth. Removal of TP or implantation of finasteride, a 5 alpha-reductase inhibitor, in nude mice bearing TP implants resulted in the regrowth of LNCaP 104-R2 tumors. Within 1 week after TP implantation, LNCaP 104-R2 tumors exhibited massive necrosis with severe hemorrhage. Three weeks later, these tumors showed fibrosis with infiltration of chronic inflammatory cells and scattered carcinoma cells exhibiting degeneration. TP treatment of mice with LNCaP 104-R2 tumors reduced tumor androgen receptor and c-myc mRNA levels but increased prostate-specific antigen in serum- and prostate-specific antigen mRNA in tumors. Although androgen ablation has been the standard treatment for metastatic prostate cancer for > 50 years, our study shows that androgen supplementation therapy may be beneficial for treatment of certain types of human prostate cancer and that the use of 5 alpha-reductase inhibitors, such as finasteride or anti-androgens, in the general treatment of metastatic prostate cancer may require careful assessment.

Cloning and characterization of a specific coactivator, ARA70, for the androgen receptor in human prostate cells

The androgen receptor (AR) is a member of the steroid receptor superfamily that plays an important role in male sexual differentiation and prostate cell proliferation. Mutations or abnormal expression of AR in prostate cancer can play a key role in the process that changes prostate cancer from androgen-dependent to an androgen-independent stage. Using a yeast two-hybrid system, we were able to isolate a ligand-dependent AR-associated protein (ARA70), which functions as an activator to enhance AR transcriptional activity 10-fold in the presence of 10(-10) M dihydrotestosterone or 10(-9) M testosterone, but not 10(-6) M hydroxyflutamide in human prostate cancer DU145 cells. Our data further indicated that ARA70 Will only slightly induce the transcriptional activity of other steroid receptors such as estrogen receptor, glucocorticoid receptor, and progesterone receptor in DU145 cells. Together, these data suggest that AR may need a specific coactivator(s) such as ARA70 for optimal androgen activity.

Vinyl fluoride as a mimic of the "intermediate' enol form in the 5 alpha-reductase transformation: synthesis and in vitro activity of (N-1',1'-dimethylethyl)-3-haloandrost-3,5-diene-17 beta-carboxamides

(N-1',1'-Dimethylethyl)-3-haloandrost-3,5-diene-17 beta-carboxamides (9-11) and the methyl ester 8 were prepared from 3-chloro/bromoandrost-3,5-diene-17 beta-carboxylic chloride/bromide (6/7), which were obtained from pregnenolone. In comparison with finasteride and 4-MA, compounds 8-11 showed very weak inhibitory activity ( < or = 10% inhibition) on human type I 5 alpha-reductase (transfected 293 cells) at 100 and 1000 nM concentrations. Against the type II enzyme, chloro compounds 8 and 9, and bromo 10 had no effect at 100 nM concentration, however, they were weak inhibitors of the type II (6.0% < inhibition < 30%) at a higher concentration. The best activity (IC50 = 480 nM) was observed with the 3-vinyl fluoride analogue 11.

Oestrogen formation from androstenedione in human bone

BACKGROUND AND OBJECTIVE

Peripheral aromatization of testosterone and androstenedione is the principal source for circulating oestrogens in men and in castrated and post-menopausal women. Since human bone is a target organ for androgens and oestrogens, aromatase activity was assessed in human spongiosa obtained from patients who were undergoing orthopaedic surgery.

DESIGN AND PATIENTS

In initial experiments for assessing aromatization, oestrogen formation from 1,2,6,7-3H-androstenedione was compared with the release of tritiated water from 1 beta-3H-androstenedione. Since the rates of enzyme activity were similar with the two methods, rates of oestrogen formation were determined under standardized conditions with the tritiated water generation technique in bone specimens obtained from 4 men and 11 post-menopausal women.

RESULTS

The apparent Km of the aromatase ranged between 6 and 50 nM (20.4 +/- 3.9; mean +/- SEM), values in the range of those reported for human placental microsomes. The maximum velocity (Vmax) of the aromatase activity ranged between 0.14 and 1.23 nmol/g DNA/h.

CONCLUSIONS

Oestrogens formed in human bone may play a physiological role in steroid hormone action in this tissue.

The enzyme and inhibitors of 4-ene-3-oxosteroid 5 alpha-oxidoreductase

Since evidence of 5 alpha-reductase activity in rabbit liver homogenate was discovered in 1954, the presence of this enzyme has been demonstrated in many other organs and tissues of mammalian species. 5 alpha-Reductase selectively transforms a 4-ene-3-oxosteroid (e.g., testosterone) irreversibly to the corresponding 5 alpha-3-oxosteroid (e.g., 5 alpha-dihydrotestosterone) in the presence of NADPH as an essential coenzyme at an optimal pH. However, excessive production of 5 alpha-dihydrotestosterone is the major cause of many androgen-related disorders, such as prostate cancer, benign prostatic hyperplasia, acne, female hirsutism, and male pattern baldness; therefore, inhibition of androgenic action by 5 alpha-reductase inhibitors is a logical treatment. During the past two decades, research has focused on understanding the biological functions and effects of 5 alpha-reductase and its 5 alpha-reduced metabolites: purification of the enzyme, substrates, and metabolites; characterization of their physical, chemical, and biochemical properties; analysis of the amino acid sequence of the enzyme; synthesis of various classes of molecules as potential inhibitors; and examination of the biological activity of the inhibitors in vitro and/or in vivo. This review summarizes the biochemical studies on this enzyme, suggests the mechanisms of action of the enzyme or inhibitors, and discusses the chemistry necessary for the preparation, structure-activity relationships, and in vitro and/or in vivo data obtained from the evaluation of nonsteroidal and steroidal compounds that have been tested as inhibitors of 5 alpha-reductase. In particular, IC50 and Ki values for relevant compounds will be compared according to molecular class. This review could function as a comprehensive working reference of what research has been accomplished so far and what problems remain to be solved in the future for those engaged in this interesting field.

5 alpha-Reductase type 1 is localized to the outer nuclear membrane

The subcellular distribution of the two isozymes of 5 alpha-reductase has been controversial. To resolve this issue which could provide clues about the respective functions of the two isozymes, two antisera were generated, one which was specific for the Type 1 5 alpha-reductase and one which recognized both isozymes. In COS cells transfected separately with the Type 1 or Type 2 cDNA, both isozymes were detected on Western blots at an M(r) of 26,000. Subfractionation of the COS cells resulted in the partitioning of both isozymes between the crude nuclear and cytosolic fractions, while cytoimmunofluorescence localized both reductases to the nuclear periphery. In rat liver homogenate, the 5 alpha-reductase was also detected at M(r) 26,000. The 5 alpha-reductase immunoreactivity was increased after castration of the animals with no further effect when castrated animals were treated with androgens. Although the rat liver expresses only the Type 1 5 alpha-reductase, the 5 alpha-reductase was distributed about equally between crude nuclear and cytosolic subfractions; this distribution could be shifted to the cytosolic fractions with harsher homogenization procedures. Further extensive subfractionation and extraction studies identified the rat liver Type 1 5 alpha-reductase as an integral membrane protein present in the outer nuclear membrane of the nuclear envelope and in rough endoplasmic reticulum. Thus, the subfractionation and cytoimmunofluorescence studies are consistent with the localization of the Type 1 5 alpha-reductase to the outer nuclear membrane of the nuclear envelope which is continuous with and indistinguishable from the endoplasmic reticulum. This study is the first to localize rat liver Type 1 5 alpha-reductase to the nuclear envelope to which the prostatic 5 alpha-reductase activity previously had been localized. We conclude that, contrary to previous tissue distribution studies, but consistent with investigations in transfected cells, both isozymes are similarly localized to the nuclear periphery.

FK143, a novel nonsteroidal inhibitor of steroid 5 alpha-reductase: (2) In vivo effects on rat and dog prostates

FK143 is a nonsteroidal new inhibitor of steroid 5 alpha-reductase, an enzyme which converts testosterone into 5 alpha-dihydrotestosterone (DHT). We studied in vivo effects of FK143 on rat and dog prostates. FK143 was orally administered to mature male rats for 14 days. At doses above 1 mg/kg, FK143 significantly reduced the wet weights of the ventral prostate and seminal vesicle, but showed no effects on those of the epididymis, testis, and adrenal. Growth of ventral prostate and seminal vesicle was induced by the subcutaneous injection of testosterone propionate (TP) in the castrated young rats and was reduced by FK143 administration at doses above 3.2 mg/kg, while growth induced by 5 alpha-dihydrotestosterone propionate (DHTP) was not affected. FK143 had no binding affinity for the rat androgen receptor. FK143 showed neither estrogenic and antiestrogenic effects on the rat uterus nor androgenic effect on the rat prostate. Concentration of testosterone and DHT in the rat and dog prostates were measured by GC-MS, and administration of 10 mg/kg of FK143 significantly reduced the intraprostatic concentration of DHT. These results indicate that FK143 reduced the prostate growth by inhibiting 5 alpha-reductase activities in the prostates.

FK143, a novel nonsteroidal inhibitor of steroid 5 alpha-reductase: (1) In vitro effects on human and animal prostatic enzymes

Steroid 5 alpha-reductase is an enzyme which converts testosterone into 5 alpha-dihydrotestosterone (DHT) and is implicated in the pathogenesis of benign prostatic hyperplasia (BPH) in men. We studied in vitro effects of FK143, a nonsteroidal new compound, on 5 alpha-reductase in human and animal prostates. Prostates were obtained from Wistar rats, Beagle dogs, and Cynomolgus monkeys as well as prostatic tissue from BPH patients obtained by the prostatectomy. Nuclear membrane fraction of prostates showed pH dependent 5 alpha-reductase activities, and inhibitory effects of drugs were assayed at pH 6.5. FK143 inhibited human prostatic 5 alpha-reductase in a dose-dependent manner with an IC50 of 1.9 nM and also inhibited animal 5 alpha-reductases with similar IC50 values. FK143 inhibited human and rat 5 alpha-reductases in a noncompetitive fashion while finasteride, a steroidal 5 alpha-reductase inhibitor, showed competitive inhibition. The affinities of FK143 for the human 5 alpha-reductase is constant at pH 5 and 6.5. No inhibitory effects were shown to other oxidoreductases. These results indicate that FK143 is a new type of potent and selective 5 alpha-reductase inhibitor.

Comparison of the effects of new specific azasteroid inhibitors of steroid 5 alpha-reductase on canine hyperplastic prostate: suppression of prostatic DHT correlated with prostate regression

Four new azasteroid inhibitors of steroid 5 alpha-reductase were compared to the benchmark compound finasteride, each at a dose level of 1 mg/kg/day, as well to placebo and to castration, in seven groups of mature male beagle dogs with enlarged prostates. Prostate volumes were measured repetitively by a volume MRI method over 15 weeks of treatment. The study probed the obverse of the familiar relation between DHT and prostate growth, and provides the first documentation of a tight negative correlation between prostate regression and the prostatic concentration of DHT across a range of treatment regimens (r = -0.982). In this first direct comparison study of structure vs. in vivo activity for several azasteroids in the dog model of BPH, relative efficacy for induction of shrinkage of the dog prostate did not correlate at all with the inhibitor's relative activity against the dog 5 alpha-reductase in vitro. On the basis of the relative IC50 values it would not have been predicted that, at the dose tested, the analogue MK-434 (17 beta-benzoyl-4-aza-5 alpha-androst-1-en-3-one) was distinguished from the other inhibitors with respect to the induction of faster and more complete regression (69%) as well as greater reduction in prostatic DHT (95%), both of which approached the castrated dog levels of 75% prostatic shrinkage and > 98% reduction in DHT. Treatment with any one of the five azasteroids induced two- to five-fold increases in prostatic testosterone. However, total androgen was conserved at the placebo control level. Despite the differences noted, each azasteroid tested induced a highly significant decrease in prostatic volume that correlated tightly with a decreased prostatic DHT level in canine spontaneous BPH.

Establishment and characterization of an immortalized but non-transformed human prostate epithelial cell line: BPH-1

This report describes the development and characterization of an epithelial cell line (BPH-1) from human prostate tissue obtained by transurethral resection. Primary epithelial cell cultures were immortalized with SV40 large T antigen. One of the isolated clones was designated BPH-1. These cells have a cobblestone appearance in monolayer culture and are non-tumorigenic in nude mice following subcutaneous injection or subrenal capsule grafting. They express the SV40 large T antigen and exhibit increased levels of p53, as determined by immunocytochemistry. Cytogenetic analysis by G-banding demonstrated an aneuploid karyotype with a modal chromosome number of 76 (range 71 to 79, n = 28) and 6 to 8 marker chromosomes. Some structurally rearranged chromosomes were observed, but the Y chromosome was normal. The expressed cytokeratin profile was consistent with a prostatic luminal epithelial cell. This profile was the same as that of primary prostatic epithelial cultures from which the BPH-1 cells were derived. In serum-free culture in plastic dishes epidermal growth factor (EGF), transforming growth factor (TGF)-alpha, fibroblast growth factor (FGF) 1 (aFGF), and FGF 7 (KGF) induced increased proliferation in these cells whereas FGF 2 (bFGF), TGF-beta 1, and TGF-beta 2 inhibited proliferative activity. Testosterone had no direct effect on the proliferative rate of BPH-1 cells. 5 alpha-Reductase, 3 alpha-hydroxysteroid oxidoreductase, and 17 beta-hydroxy-steroid oxidoreductase activities were detected in BPH-1 cells. Expression of androgen receptors and the secretory markers, prostate specific antigen and prostatic acid phosphatase, were not detectable by immunocytochemistry, biochemical assay, or RT-PCR analysis.

Picogram determination of finasteride in human plasma and semen by high-performance liquid chromatography with atmospheric-pressure chemical-ionization tandem mass spectrometry

A method based on high-performance liquid chromatography (HPLC) with atmospheric-pressure positive-ion chemical ionization (APCI)-tandem mass spectrometric (MS-MS) detection for the determination of finasteride (MK-906, I) in human plasma and semen has been developed. The drug and internal standard (II) were extracted from biological matrices using a single solid-phase cyano cartridge. The eluent from the cartridge was injected directly onto the a 33 x 4.6 mm I.D. C18, 3-microns column coupled with a base deactivated C18 20 x 4.6 mm I.D., 5-microns guard column. The column eluate was passed into the corona discharge APCI source by means of a heated nebulizer interface. The analyte and its internal standard were detected using multiple reaction monitoring (MRM) mode for enhanced selectivity and sensitivity. The chromatographic run time was 3 min, and the method had sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing finasteride at concentration of 0.2 ng/ml. The assay methodology confirms the versatility of APCI-MS-MS detection, combined with HPLC, for the quantitation of selected drugs in the sub-ng/ml range in biological fluids.

Androgen and estrogen sulfotransferases of the rat liver: physiological function, molecular cloning, and in vitro expression

Cloning of the androgen and estrogen sulfotransferases has allowed studies on their spatiotemporal regulation and physiological function. These two enzymes appear to be involved in regulating target cell sensitivity for the androgenic and estrogenic steroids. Recombinant androgen sulfotransferase produced in insect Sf9 cells through a baculoviral expression vector is capable of transferring the sulfate from PAPS (phosphoadenosine phosphosulfate) to 3 alpha, 3 beta, 17 alpha, and 17 beta hydroxyl groups of a number of steroid substrates indicating a broad range of substrate specificity.

A rapid and specific assay, based on liquid chromatography-atmospheric pressure chemical ionization mass spectrometry, for the determination of MK-434 (a 5 alpha-reductase inhibitor) and its metabolites in plasma

MK-434 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography-mass spectrometry (LC-MS) has been developed for the determination of this compound in plasma. The analyte was isolated from plasma by solid-phase extraction on a C18 cartridge. A related substance, L-654,066, was used as the internal standard. Extracts were separated on a 5-cm C18-reversed-phase high performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion MS-MS mode. The method had sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples containing MK-434 and its two principal metabolites at concentrations in the range 0.5-50 ng ml-1. The chromatographic run time was < 5 min.

Effects of 4-MAPC, a 5 alpha-reductase inhibitor, and cyproterone acetate on regrowth of the rat ventral prostate

Inhibitors of 5 alpha-reductase activity cause less involution of the rat ventral prostate (VP) than does castration. Studies were conducted in adult Sprague Dawley rats to evaluate the effects of a potent 5 alpha-reductase inhibitor, 4-MAPC, and the antiandrogen, cyproterone acetate (CA), on DNA synthesis and apoptosis. In experiment 1, VP weight fell 33%, 53%, and 83%, and DNA per ventral prostate was reduced 24%, 46%, and 71%, by 4-MAPC, CA, and castration, respectively. In experiment 2, adult rats were castrated, and the VP involuted for 7 days prior to 3 daily injections of testosterone propionate (TP; 1 mg/kg/d) +/- 10 mg/kg/d of 4-MAPC or CA. 3H-thymidine incorporation into VP DNA was increased in castrated animals treated with TP, and 4-MAPC and CA reduced uptake. In experiment 3, animals were treated for 14 days with the same protocol as that used in experiment 2. VP weight was increased in all animals treated with TP when compared with castration, and was reduced by both 4-MAPC and CA. DNA in rats treated with TP was similar to that in intact animals. DNA was not reduced by 4-MAPC, but was reduced by CA. The mRNA for TRPM-2, a marker of apoptosis, was increased only in untreated castrated rats. It appears that CA has a greater inhibitory effect than 4-MAPC on DNA synthesis. A major reason why castration reduces DNA more than either 4-MAPC or CA is that neither of these agents was able to increase programmed cell death to the degree seen with castration.

Androgen metabolism in men receiving finasteride before prostatectomy

Oral administration of finasteride, a 5 alpha-reductase inhibitor, affects intraprostatic androgens by suppressing dihydrotestosterone and increasing testosterone. This study was designed to determine the correlation of these effects of finasteride with changes in serum dihydrotestosterone, testosterone and androstanediol glucuronide. In a double blind, placebo-controlled study, 27 men with symptomatic benign prostatic hyperplasia were treated with placebo or 1 or 5 mg. per day finasteride for 6 to 8 weeks before transurethral resection of the prostate. There was no significant change in serum testosterone in any group, or in serum dihydrotestosterone or androstanediol glucuronide in the placebo group. There was a decrease in serum dihydrotestosterone by 66 +/- 4% and 70 +/- 8% (p = 0.32), and of serum androstanediol glucuronide by 78 +/- 3% and 86 +/- 3% (p = 0.012) in the 1 and 5 mg. finasteride groups, respectively. Intraprostatic dihydrotestosterone in the placebo group decreased from 18.6 +/- 1.4 nmol./kg. to 3.8 +/- 1.0 nmol./kg. and 1.7 +/- 0.7 nmol./kg. with 1 mg. and 5 mg. finasteride, respectively (p = 0.049 between 1 mg. and 5 mg. finasteride). Intraprostatic testosterone in the placebo group increased from 1.1 +/- 0.2 nmol./kg. to 7.6 +/- 1.0 nmol./kg. and 8.3 +/- 0.7 nmol./kg. with 1 mg. and 5 mg. finasteride, respectively (no significant difference between 1 mg. and 5 mg. finasteride). Serum and intraprostatic dihydrotestosterone correlated (p = 0.002). There was no correlation between intraprostatic dihydrotestosterone and serum androstanediol glucuronide. We conclude that 5 mg. of finasteride cause greater inhibition of intraprostatic 5 alpha-reductase than 1 mg. and that serum dihydrotestosterone is a better marker of intraprostatic dihydrotestosterone than androstanediol glucuronide.

Expression of 5 alpha-reductase in bacteria as a trp E fusion protein and its use in the production of antibodies for immunocytochemical localization of 5 alpha-reductase

A cDNA encoding a full-length rat 5 alpha-reductase was isolated using female rat liver mRNA and the polymerase chain reaction, and fused to the Escherichia coli trp E gene in a pATH expression vector. The trp E-5 alpha-reductase fusion protein expressed in bacteria and a synthetic oligopeptide corresponding to the C-terminus of rat 5 alpha-reductase were used as antigens to produce rabbit polyclonal antibodies to 5 alpha-reductase. Antibodies to the 5 alpha-reductase portion of the fusion protein and to the peptide were purified by affinity chromatography. Antibodies against the 5 alpha-reductase fusion protein reacted with a single component of rat liver microsomes with M(r) 26,000 on Western blots, consistent with the size of 5 alpha-reductase predicted from its cDNA, and with a M(r) 23,000 component on Western blots of detergent extracts of rat ventral prostate nuclei; other rat ventral prostate cellular fractions (mitochondrial, microsomal, cytosol) bound little or no antibody. Antibody against the synthetic peptide reacted with a M(r) 26,000 component of rat liver microsomes as well as with several components in various cellular fractions of rat ventral prostate. With anti-5 alpha-reductase fusion protein antibodies, specific immunocytochemical staining was observed in the epithelial cell nuclei of the rat ventral prostate, seminal vesicle, epididymis and other accessory sex glands. This nuclear staining was specific, since antibodies from non-immunized rabbits did not give nuclear staining and preincubation of the anti-5 alpha-reductase fusion protein antibodies with the trp E-5 alpha-reductase fusion protein eliminated nuclear staining. Incubation of antibodies with trp E (without the 5 alpha-reductase fusion) had no effect on nuclear staining. Specific staining was not detected in the cytoplasm of these epithelial cells. Little or no specific staining was observed in stromal cells in these rat tissues. Human prostate was also immunocytochemically stained with this antibody. Specific staining was found in both epithelial and stromal cell nuclei.

Rapid increase in the number of androgen receptors following electrical stimulation of the rat muscle

The changes in the number of androgen receptors in rat gastrocnemius muscle following muscle contraction caused by electrical stimulation were investigated. The gastrocnemius muscle of one leg, which was selected at random for each rat, was stimulated with needle type electrodes, e.g. for 2 s at 10 V and 100 Hz, with 5-s intervals. The contralateral leg was left unstimulated as a control. One set consisted of ten such stimuli, followed by 5-min rest. Three sets every 2 days caused a statistically significant increase in muscle mass, the increase being about 2.5% after the 3rd day of stimulation, 4.4% after the 5th day, 5.9% after the 13th day and 8.3% after the 27th day compared with each control muscle (P < 0.001 in each case). The protein content also increased but the water content did not change. Stimulation over 4 weeks induced an increase in the area of the cross-section of the muscle fibres to about 30% more than that of the control muscles, though the total muscle fibre numbers were slightly, but significantly, reduced. Electromechanical properties supported the development of the muscle by stimulation, because the maximal isometric tetanic force and peak twitch force markedly increased in the stimulated muscle. The androgen receptors in the muscle cytosol fraction were determined by means of a binding assay involving [3H]methyltrienolone, which is an analogue of testosterone, the number having rapidly increased in the stimulated leg, when compared with that in the control leg, by about 25% after the 3rd day. The increase then slowed down, reaching a plateau after the 5th-day of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of androstenedione-induced stimulation of androgen-sensitive parameters in the rat prostate by combination of Flutamide and 4-MA

In order to mimic the human situation in which adrenal steroid precursors are converted to the active androgen dihydrotestosterone (DHT) in prostatic tissue, we have used castrated rats supplemented with the precursor steroid androstenedione (delta 4-dione) released from Silastic implants. While it is well known that the action of DHT can be partially neutralized by antiandrogens which compete for binding to the androgen receptor, we have used 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one (4-MA), an inhibitor of 5 alpha-reductase, the enzyme which converts testosterone into DHT, in order to decrease intraprostatic DHT levels and thus facilitate the action of the antiandrogen. Animals were treated for 7 days with Flutamide (FLU, 2 mg) or 4-MA (4 mg) injected subcutaneously, twice daily, alone or in combination. 4-MA administered alone caused a 54% inhibition of delta 4-dione-stimulated ventral prostate weight while FLU exerted a 74% inhibitory effect and 4-MA+FLU further improved inhibition to 81%. We then measured, by in situ hybridization, the levels of prostatic mRNAs encoding the C1 and C3 components of the prostatic binding protein (PBP) which are highly specific and sensitive markers of androgen action. PBP-C3 mRNA levels fell by 95% following castration while treatment with delta 4-dione completely reversed the effect of castration. Administration of FLU or 4-MA independently caused 33% and 10% decreases, respectively, of PBP-C3 mRNA levels stimulated by delta 4-dione while the combination of both compounds further inhibited PBP-C3 mRNA levels to reach a 55% inhibition. Similar effects were observed on PBP-C1 mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and selective inhibition of an isozyme of steroid 5 alpha-reductase in human scalp

Steroid 5 alpha-reductase (EC 1.3.1.22) catalyzes the reduction of testosterone to dihydrotestosterone. The 5 alpha-reductase found in human scalp has been compared with the enzyme found in prostate. The scalp reductase has a broad pH optimum centered at pH 7.0. This is distinctly different from the pH optimum of 5.5 observed with the prostatic form of the enzyme. These enzymes also differ in the Km for testosterone, which is 25-fold higher for the scalp reductase. The most significant difference between the two enzymes is their affinity for inhibitors. Two 4-azasteroids and a 3-carboxyandrostadiene are potent inhibitors of the prostatic reductase but are weak inhibitors of the scalp reductase. In contrast, several N-4-methylazasteroids are good inhibitors of the scalp reductase. These findings support a proposal that different isozymes of 5 alpha-reductase may exist in scalp and prostate. The scalp reductase was also compared to 5 alpha-reductase 1, one of the two enzymes recently cloned from human prostate [Andersson, S. & Russell, D. W. (1990) Proc. Natl. Acad. Sci. USA 87, 3640-3644; and Andersson, S., Berman, D. M., Jenkins, E. P. & Russell, D. W. (1991) Nature (London) 354, 159-161]. The characteristics of the cloned reductase 1 are comparable to those of the scalp reductase.

Finasteride in the treatment of benign prostatic hyperplasia. A urodynamic evaluation

A group of 69 men with bladder outflow obstruction due to benign prostatic hyperplasia (BPH) were treated in a double-blind, placebo-controlled study with finasteride (Proscar, MK-906), a 5-alpha reductase inhibitor, 5 mg or 10 mg/day or placebo for 3 months; subsequently, 20 patients received finasteride 5 mg/day for a further 9 months in an open extension study. In treated patients dihydrotestosterone declined by over 60%, remaining unchanged with placebo. Symptom scores fell significantly in all 3 groups. Mean maximum flow rates fell slightly in placebo-treated patients but improved by 1.5 ml/s in the 10 mg group and by 3.3 ml/s in the 5 mg group. After 1 year's treatment, the reduction in symptom score and increase in flow rate were well maintained; the mean prostate volume was reduced by 14% and prostatic specific antigen declined by 28%. It was concluded that finasteride shows some efficacy in the treatment of BPH, with minimal toxicity, but 12 months of therapy or longer may be necessary to achieve maximal effect.

Determination of L-654,066, a new 5 alpha-reductase inhibitor in plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

L-654,066 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography/mass spectrometry has been developed for the determination of this drug candidate in plasma. The analyte was isolated from plasma by solid-phase extraction on a C-18 cartridge. A related substance, L-683,838, was used as the internal standard. Extracts were chromatographed on a 5 cm C18 reverse-phase high-performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion tandem mode. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing L-654,066 at concentrations in the range 0.5-20 ng ml-1. The chromatographic run time is less than 2 min.

Partial purification of 3 alpha- and 3 beta-hydroxysteroid dehydrogenases from human hyperplastic prostate. Comparison between the two enzymes

3 alpha-Hydroxysteroid dehydrogenase (3 alpha-HSD) activity has been purified to homogeneity, the enzyme is a monomer with a Mw of 32,000 Da. 3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) activity has been partially purified and has an apparent Mw of 30,000 Da. Both enzymes have the same cofactor requirements, optimal pH. However, 3 beta-HSD appeared to be an integral protein dependent on protein environment for its activity while 3 alpha-HSD activity is a protein more loosely associated to membranes.

17 beta-acylurea derivatives of 4-azasteroids as inhibitors of testosterone 5 alpha-reductase

A series of 17 beta-acylurea-4-aza-5 alpha-androstan-3-one derivatives has been assayed in vitro as inhibitors of testosterone 5 alpha-reductase, using the particulate fraction of human hyperplastic prostate and rat prostate as enzyme sources. The most active derivatives were 1-[4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carbonyl]- 1,3-dicyclohexylurea (compound 1) and 1-[4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carbonyl]- 1,3-diisopropylurea (compound 3) which demonstrated IC50 values of 41 and 55 nM for the human enzyme and of 83 and 53 nM for the rat enzyme, respectively. Neither compound showed any relevant binding affinity to the rat prostate androgen receptor (IC50 of approximately 100 and 84 microM). When given orally in immature castrated rats together with subcutaneous testosterone propionate (TP) for 7 consecutive days, compound 3 (laboratory code FCE 26073), at 3 mg/kg/day, significantly decreased the ventral prostate growth promoting effect of TP by 40-50%, whereas compound 1 was ineffective up to the dose of 10 mg/kg/day.

Endocrine treatment of benign prostatic hypertrophy: current concepts

To summarize the endocrine approach for the treatment of BPH: much clinical data have accumulated over the past forty years. Until recently, scientists and physicians mainly concentrated on the reduction of androgens as a possible solution. We have come a long way from surgical castration, through the administration of hormones such as estrogen and progesterone, gonadotropin-releasing hormone agonists to the inhibition of an enzymatic reaction reducing testosterone to DHT--the now recognized active intracellular androgen metabolite. Recently, the role of estrogens has been emphasized with the finding that stromal hyperplasia is the main change occurring in BPH. Lately, research has been initiated to examine the clinical effect aromatase inhibitors would have in the treatment of human BPH. Since there is enough evidence that both the epithelial and stromal components of the human prostate undergo hyperplasia in BPH, and individuals vary with respect to their relative epithelial/stromal components, both structures would have to be reduced for therapy to be successful. Therefore, the combination of an antiandrogenic and antiestrogenic effect is theoretically promising. Indeed, prostates of beagles shrunken after treatment with an aromatase inhibitor, further decreased in weight after additional treatment with cyproterone acetate, an antiandrogen. We are now approaching the stage where these "antihormones" are both enzyme inhibitors with actually no side effects that preclude the use of the earlier generation's "antihormonal" hormonal drugs. Furthermore, it has recently been reported that the aromatase inhibitor, 4-hydroxy-androstenedione also inhibits human prostatic 5-alpha reductase, at least in vitro. The in vivo relevance of this finding awaits further classification. Thus, a good hormonal treatment that will be both scientifically sound, and clinically safe and effective, seems feasible in the near future. Two main factors have encouraged our interest and research into methods of inhibiting prostatic growth or reducing its obstructive symptomatology: the enormous cost of prostatic operations for outlet obstruction secondary to BPH, and the natural aging process of the population accompanied by deteriorated health precluding anesthesia and prostatic surgery. Medical treatment of BPH has to result in symptomatic improvement, elimination of residual urine, and improvement of flow to be considered successful. These are usually accomplished by surgery and results at least as good as those obtained by operation should be aimed at, if medical treatment is to replace surgery. Although indications for surgery and outcome of operations are well-defined, this is not the case when alternatives to prostatectomy are chosen.(ABSTRACT TRUNCATED AT 400 WORDS)

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Growth factors, endocrine aspects and hormonal treatment in hepatocellular carcinoma--an overview

Several clinical observations suggest that hepatocellular carcinoma (HCC or "hepatoma") may be a hormone-dependent tumour; the apparent relation to anabolic steroids and oral contraceptive preparations, and the striking male predominance particularly among patients with cirrhosis. In many animal models thyroid hormones, prolactin and testosterone stimulate tumour growth, and the latter may enhance the progression of chemically-induced hyperplastic nodules to frank malignancy. In animals and humans, both oestrogen and androgen receptors have been reported in normal and malignant liver tissue though some of the evidence is conflicting and the amounts detected vary widely. From a therapeutic standpoint, we failed to show any advantage from the addition of tamoxifen to adriamycin, in a controlled trial although other workers have, more recently, reported prolonged survival using tamoxifen alone. About 20% of HCC patients receiving the antiandrogen cyproterone acetate showed a clinical response.

Progesterone metabolism by major salivary glands of rat--II. Parotid gland

The metabolism of [4-14C]progesterone in the parotid salivary glands of nonpregnant female, pregnant female and male rats were investigated in vitro. The metabolic activity of the male rats was significantly lower than in either of the female groups. The pregnant group was metabolically more active than the nonpregnant female group, but his differences was not statistically significant. I homogenates and soluble fractions the main metabolite was 20-alpha-hydroxy- 4-pregnen-3-one in female rats. In male rats the main metabolites were 20-alpha-hydroxy-4- pregnen-3-one and 3-alpha-hydroxy-5-alpha-pregnan-20-one in homogenates and 20-alpha-hydroxy-4- pregnen-3-one in soluble fractions. In the microsomal fractions of both sexes polar compounds predominated. The results indicated the presence of at least the following progesterone metabolizing enzymes in art parotid salivary glands; 3-alpha-, 3-beta-, 20-alpha- and 20-beta-hydroxysteroid dehydrogenase, 5-alpha-and 5-beta-steroid hydrogenase and 17-alpha-steroid hydroxylase activities. Ind the homogenates and soluble fractions of female rats 20-alpha-hydroxysteroid dehydrogenase activity was significantly higher than in males.

Prostate long-term epithelial cell lines. Biological and biochemical features

This review reports studies on long-term prostate cell lines using multiple experimental approaches. The main goal was to investigate the metabolism of testosterone (T) through in vitro conversion rates. Extensive studies were also carried out on growth curves, tritiated thymidine incorporation, and morphometry by either hormone-responsive or hormone-unresponsive, normal and neoplastic human (PC3 and DU-145) and canine (CAPE and CPA) cell lines. All of them were characterized for their content of both soluble and nuclear androgen receptors. Receptor studies at site I binding in both soluble and nuclear fractions were carried out to establish the hormone sensitivity status of cells. In two prostate epithelial cells, steroid metabolic conversions in vitro show predominantly an oxidative metabolism of T, forming mainly androstenedione. Conversion rates were greater than 50% in the first 24 hours and still higher after 72 hours. At the same time and under exactly the same experimental conditions, the other cells showed metabolic pathways in which reductive metabolism prevails, dihydrotestosterone (DHT) being the prevalent metabolite. Different metabolic patterns of steroids of several cell lines relate to the hormone sensitivity status of the cells; steroid receptor-endowed cells are maintaining higher levels of unconverted precursor than are receptor-empty cells. In fact, hormone-sensitive cells, such as cancer canine CPA and human DU-145, produced DHT early through slowly converting T. On the contrary, unresponsive cells such as human cancer cells PC3 and normal canine CAPE quickly metabolize T, but DHT formation was not observed. These significant differences between cells are highly reproducible provided the proportion between cell number and molar concentration of precursors is constant. Differences we observe cannot be attributed to different experimental conditions. Cell viability, extraction efficiency, and all other parameters used for monitoring cell growth kinetics do not substantiate these reported significant differences in metabolic abilities of cells. The divergent steroid metabolic pathway we observe in different prostate long-term cells appears to be an intrinsic, consistent, highly reproducible property of each cell line.

Inhibitors of steroid 5 alpha-reductase in benign prostatic hyperplasia, male pattern baldness and acne

Benign prostatic hyperplasia is an androgen-dependent disease which afflicts a large percentage of males over the age of fifty, and is usually treated by surgery. Dihydrotestosterone, a 5 alpha-reduced metabolite of testosterone, has been implicated as a causative factor in the progression of the disease, largely through the clinical study of males who are genetically deficient in the dihydrotestosterone-producing enzyme, steroid 5 alpha-reductase. As a result, inhibition of this enzyme has become a pharmacological strategy for the treatment of benign prostatic hyperplasia as well as other dihydrotestosterone-related disorders such as acne and male pattern baldness. In this review, Brian Metcalf and colleagues focus on the chemical and kinetic mechanisms of steroid 5 alpha-reductase, and known inhibitors of this enzyme, and discuss the rationale behind the design of a mechanistically distinct class of steroid 5 alpha-reductase inhibitors.

Non-michaelian behavior of 5 alpha-reductase in human prostate

An in-depth analysis of the kinetics of 5 alpha-reductase in human prostatic tissue gave findings inconsistent with the claim that the enzyme is michaelian. In both hyperplastic and malignant tissue, the time-course of the conversion of testosterone (T) into dihydrotestosterone (DHT) was non-linear under conditions ensuring less than 15% conversion of substrate and cofactor. An initial rapid phase of conversion was followed by a long steady-state phase. This time-dependent change in conversion rate was not due to enzyme denaturation, fast inhibition by substrate or product effects. It resulted from a true slow transient kinetic process induced in the reactive enzyme by the substrates. Under our experimental conditions at pH 5.5, 5 alpha-reductase appeared to undergo a conformational change from an initially highly reactive form to a less reactive form. Since this "hysteretic" behavior was correlated with apparently negative cooperativity in enzyme kinetics, we postulate that, as previously described for other key metabolic enzymes, regulation of 5 alpha-reductase activity in the prostate depends on the molecular flexibility of the enzyme and on changes in the cooperativity of different enzyme forms over time. This original non-michaelian behavior may explain the conflicting kinetics reported so far in the literature for this enzyme. The clinical implications of 5 alpha-reductase hysteresis and its involvement in the damping of DHT production within the prostate are discussed.

The effect of several sex steroid hormones on the growth rate of three Morris hepatoma tumor lines

Morris hepatoma 44, whose growth is sensitive to thyroid hormones and prolactin, contains specific receptors for these hormones. In the present experiments, male Buffalo rats bearing Morris hepatoma 7787 were studied to determine the effects of several sex steroid hormones. Castration 1 week postimplantation inhibited tumor growth relative to controls (-53%). Replacement with testosterone propionate (1 mg per day s.c. injection) restored tumor growth to control levels, whereas administration of testosterone (2 mg per day s.c. injection) to castrated controls resulted in significant stimulation. Testosterone administered to control animals at a dose of 1 mg per day stimulated tumor growth (62%), whereas 2 mg per day failed to do so. Progesterone (4-pregnon-3,20-dione) at doses of 125 or 250 micrograms per day (Silastic implants) had no effect on tumor growth, whereas 500 micrograms per day stimulated tumor growth relative to controls. Estrogen (17 beta-estradiol) at doses of 6, 12, or 24 micrograms per day (Silastic implants) did not influence tumor growth. Cytoplasmic testosterone receptors have been demonstrated in tumors (2.2 +/- 0.8 fmoles per mg cytoplasm), although specific cytoplasmic estrogen and progesterone receptors could not be identified in this model. In female rats bearing either Morris hepatoma 44, 7787 or 5123-D, testosterone markedly stimulated tumor growth (226, 328 and 58%, respectively, relative to controls). In conclusion, although Morris hepatoma 7787 appears to be androgen (testosterone) dependent and contains cytoplastic androgen receptors, it lacks specific cytoplasmic receptors for estrogen and progesterone and is not influenced by these hormones except at very high doses of progesterone.

Androgen and estrogen receptors in hepatocellular carcinoma and the surrounding liver in women

Androgen receptors (AR) and estrogen receptors (ER) were consecutively assayed for hepatocellular carcinoma (HCC) and the surrounding liver was removed surgically from 19 female patients. Patient age ranged from 43 to 79 years, with an average of 61 +/- 9 years. All patients had underlying liver disease (liver cirrhosis in 16, liver fibrosis in two, and chronic hepatitis in one). Seven (37%) of 19 HCC had AR ranging from 2.3 to 82.6 fmol/mg of cytosol protein. The AR titer was higher in the HCC than in the liver in these cases. Three cases also had ER. ER existed in seven (37%) tumors (range, 2.4 to 25.6 fmol/mg of protein). AR and ER were detected in 11 (65%) and ten (58%) of 17 nonneoplastic liver tissues, respectively. Serum alpha-fetoprotein (AFP) level, hepatitis B virus markers, or histopathologic types of HCC had no correlation with the presence or absence of AR or ER and their titers. Also, there was no correlation between the AR and ER positivities. Further studies are mandatory to determine the genuine role of sex hormone receptors in the development and growth of HCC in humans.

Structural analysis of complementary DNA and amino acid sequences of human and rat androgen receptors

Structural analysis of cDNAs for human and rat androgen receptors (ARs) indicates that the amino-terminal regions of ARs are rich in oligo- and poly(amino acid) motifs as in some homeotic genes. The human AR has a long stretch of repeated glycines, whereas rat AR has a long stretch of glutamines. There is a considerable sequence similarity among ARs and the receptors for glucocorticoids, progestins, and mineralocorticoids within the steroid-binding domains. The cysteine-rich DNA-binding domains are well conserved. Translation of mRNA transcribed from AR cDNAs yielded 94- and 76-kDa proteins and smaller forms that bind to DNA and have high affinity toward androgens. These rat or human ARs were recognized by human autoantibodies to natural ARs. Molecular hybridization studies, using AR cDNAs as probes, indicated that the ventral prostate and other male accessory organs are rich in AR mRNA and that the production of AR mRNA in the target organs may be autoregulated by androgens.

Anti-androgens in gynaecological practice

Hirsutism and acne in women are common distressing problems. Unwanted hair growth, acne and seborrhoea result from the action of androgens on the skin. Such effects depend not only on increased androgen production by the ovary or adrenal gland but also on the bioavailability of androgen to peripheral tissues. This in turn is related to transport of androgens in plasma by specific binding proteins and to peripheral metabolism of testosterone and androstenedione to their more potent 5 alpha-reduced derivatives. An effective anti-androgen is one which blocks the androgen receptor-mediated actions of testosterone and DHT on skin. CPA, the treatment of choice in the UK, is a potent androgen receptor-blocking steroid which also has progestational properties. When combined with ethinyloestradiol it also suppresses ovarian function, thus reducing androgen production, and provides effective contraception.

Inhibition of steroid 5 alpha-reductase and its effects on testosterone hydroxylation by rat liver microsomal cytochrome P-450

It has been shown previously that liver microsomal steroid 5 alpha-reductase activity increases with age in female but not male rats, which coincides with a female-specific, age-dependent decline in the cytochrome P-450-dependent oxidation of testosterone to 1 beta-, 2 alpha-, 2 beta-, 6 alpha-, 6 beta-, 7 alpha-, 15 beta-, 16 alpha-, 16 beta-, and 18-hydroxytestosterone and androstenedione. To determine whether the increase in steroid 5 alpha-reductase activity is responsible for the decrease in testosterone oxidation, we have examined the effects of the steroid 5 alpha-reductase inhibitor, 4-MA (17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one), on the pathways of testosterone oxidation catalyzed by rat liver microsomes. We have also determined which hydroxytestosterone metabolites are substrates for steroid 5 alpha-reductase. At concentrations of 0.1 to 10 microM, 4-MA completely inhibited steroid 5 alpha-reductase activity without inhibiting the pathways of testosterone oxidation catalyzed by liver microsomes from rats of different age and sex, and from rats induced with phenobarbital or pregnenolone-16 alpha-carbonitrile. 4-MA (10 microM) had little or no effect on the oxidation of testosterone catalyzed by liver microsomes from mature male rats (which have low steroid 5 alpha-reductase activity). In contrast, the hydroxylated testosterone metabolites formed by liver microsomes from mature female rats (which have high steroid 5 alpha-reductase activity) accumulated to a much greater extent in the presence of 4-MA. Evidence is presented that 4-MA increases the accumulation of hydroxytestosterones by two mechanisms. First, 4-MA inhibited the 5 alpha-reduction of those metabolites (such as 6 beta-hydroxytestosterone) that were found to be excellent substrates for steroid 5 alpha-reductase. In the absence of 4-MA, these metabolites eventually disappeared from incubations containing liver microsomes from mature female rats. Second, 4-MA inhibited the formation of 5 alpha-dihydrotestosterone, which otherwise competed with testosterone for oxidation by cytochrome P-450. This second mechanism explains why 4-MA increased the accumulation of metabolites (such as 7 alpha-hydroxytestosterone) that were found to be poor substrates for steroid 5 alpha-reductase. Despite its marked effect on the accumulation of hydroxylated testosterone metabolites, 4-MA had no effect on their initial rate of formation by liver microsomes from either male or female rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Biosynthesis of catalytically active rat testosterone 5 alpha-reductase in microinjected Xenopus oocytes: evidence for tissue-specific differences in translatable mRNA

The enzyme 4-ene-3-ketosteroid-5 alpha-oxidoreductase [5 alpha-reductase; 3-oxo-5 alpha-steroid delta 4-dehydrogenase, 3-oxo-5 alpha-steroid: (acceptor) delta 4-oxidoreductase, EC 1.3.99.5] plays a key role in androgen-dependent target tissues, where it catalyzes the conversion of testosterone to the biologically active dihydrotestosterone. The regulation of 5 alpha-reductase expression has not been studied at the molecular level as the enzyme is a membrane protein that is labile in cell-free homogenates. We developed a sensitive bioassay of the enzyme activity expressed in Xenopus oocytes microinjected with rat liver and prostate mRNA. After microinjection, incubation of intact oocytes in the presence of [3H]testosterone revealed the in ovo appearance of active 5 alpha-reductase. Polyadenylated RNA was fractionated by sucrose gradient centrifugation, and the enzymatic activity was shown to be encoded by a 1600- to 2000-base-pair fraction of hepatic poly(A)+ RNA. 5 alpha-Reductase mRNA was most efficiently translated when up to 80 ng of RNA was injected per oocyte. In the injected oocytes, 5 alpha-reductase mRNA was found to be a short-lived molecule (t1/2 = 2 hr), whereas its in ovo translatable 5 alpha-reductase protein exhibited stable enzymatic activity for over 40 hr. Moreover, the levels of translatable tissue-specific 5 alpha-reductase mRNAs as monitored in the Xenopus oocytes correlated with the variable 5 alpha-reductase activities in female rat liver, male rat liver, and prostate homogenates; the ratio of their specific activities was of 2500:630:1, respectively. Altogether, these results provide supporting evidence in favor of the transcriptional control of 5 alpha-reductase expression in rat tissues.

Human hepatocellular carcinoma tumor xenografts. Their androgen-receptor status and growth responses to castration

Castrated or sham-operated male athymic mice were inoculated with cells from the human hepatocellular carcinoma cell line PLC/PRF/5. There were no significant differences between the two groups with respect to the number of animals developing tumors, the time to tumor development, or the subsequent rate of increase in either tumor base area or mouse serum alpha-fetoprotein concentration. Androgen receptors were assayed in nuclei obtained from three separate liver cancer cell lines and from normal adult human liver. Similar concentrations, ranging from 235 to 550 fmol/mg DNA, of nuclear androgen receptors were detected in all tissues. Low percentages of androgen receptors were retained on DNA-cellulose. Although the presence of receptors implies the potential for metabolic effects of androgens in normal and malignant liver, our in vivo studies suggest that castration does not alter significantly the growth of liver cancer xenografts in athymic mice.

Flutamide and other antiandrogens in the treatment of advanced prostatic carcinoma

The various clinical trials suggest that the qualitative and quantitative responses of patients with Stage D prostatic carcinoma to antiandrogens are similar to those achieved with conventional endocrine therapy. These antiandrogens appear generally safe and many avoid the increased risks of cardiovascular or thromboembolic complications seen with estrogen therapy. Further, flutamide appears to have a lesser adverse effect on libido and sexual potency than do alternative therapies. Antiandrogens offer an alternative mode of therapy for previously untreated patients with advanced prostatic cancer but have produced no convincing benefits in hormonally refractory patients.