Discovery of a novel hybrid from finasteride and epristeride as 5α-reductase inhibitor.

Finasteride and epristeride both inhibit 5α-reductase with high potency via competitive and non-competitive mechanism, respectively. A new hybrid of finasteride and epristeride was designed as a new 5α-reductase inhibitor based on combination principles in medicinal chemistry. Human 5ß-reductase was chosen as a plausible surrogate of 5α-reductase type II and the results indicate that although the hybrid compound possesses the main bulk of epristeride, its inhibitory mechanism is same as of finasteride. The hybrid turned out to be a potent 5α-reductase inhibitor in low IC(50) ranges.

5alpha-dihydrotestosterone (DHT) retards wound closure by inhibiting re-epithelialization.

The ongoing search for explanations as to why elderly males heal acute skin wounds more slowly than do their female counterparts (and are more strongly disposed to conditions of chronic ulceration) has identified endogenous oestrogens and androgens as being respectively enhancers and inhibitors of repair. We previously demonstrated that blocking the conversion of testosterone to 5alpha-dihydrotestosterone (DHT) limits its ability to impair healing, suggesting that DHT is a more potent inhibitor of repair than is testosterone. The present study aimed to delineate the central mechanisms by which androgens delay repair. Whilst the contractile properties of neither rat wounds in vivo nor fibroblast-impregnated collagenous discs in vitro appeared to be influenced by androgen manipulations, the global blockade of DHT biosynthesis markedly accelerated re-epithelialization of incisional and excisional wounds and reduced local expression of beta-catenin, a key inhibitor of repair. Moreover, DHT retarded the in vitro migration of epidermal keratinocytes following scratch wounding. By contrast, it failed to influence the migratory and proliferative properties of dermal fibroblasts, suggesting that its primary inhibitory effect is upon re-epithelialization. These novel findings may be of particular significance in the context of chronic ulceration, for which being male is a key risk factor.

Anabolic effects of testosterone are preserved during inhibition of 5alpha-reductase.

At replacement doses, testosterone produces only modest increases in muscle strength and bone mineral density in older hypogonadal men. Although higher doses of testosterone are more anabolic, there is concern over increased adverse effects, notably prostate enlargement. We tested a novel strategy for obtaining robust anabolic effects without prostate enlargement. Orchiectomized (ORX) male rats were treated for 56 days with 1.0 mg testosterone/day, with and without 0.75 mg/day of the 5alpha-reductase inhibitor MK-434. Testosterone administration elevated the prostate dihydrotestosterone concentration and caused prostate enlargement. Both effects were inhibited by MK-434. ORX produced a catabolic state manifested in reduced food intake, blunted weight gain, reduced hemoglobin concentration, decreased kidney mass, and increased bone resorption, and in the proximal tibia there was both decreased cancellous bone volume and a decreased number of trabeculae. In soleus and extensor digitorum longus muscles, ORX reduced both the percentage of type I muscle fibers and the cross-sectional area of type 1 and 2 fibers. Testosterone administration caused a number of anabolic effects, including increases in food intake, hemoglobin concentration, and grip strength, and reversed the catabolic effects of ORX on bone. Testosterone administration also partially reversed ORX-induced changes in muscle fibers. In contrast to the prostate effects of testosterone, the effects on muscle, bone, and hemoglobin concentration were not blocked by MK-434. Our study demonstrates that the effects of testosterone on muscle and bone can be separated from the prostate effects and provides a testable strategy for combating sarcopenia and osteopenia in older hypogonadal men.

Doping-control analysis of the 5alpha-reductase inhibitor finasteride: determination of its influence on urinary steroid profiles and detection of its major urinary metabolite.

5alpha-Reductase inhibitors such as finasteride are prohibited in sports according to the World Anti-Doping Agency. This class of drugs is used therapeutically to treat benign prostatic hyperplasia, as well as male baldness, by decreasing 5alpha-reductase activity. Accordingly, metabolic pathways of endogenous as well as synthetic steroids are influenced, which complicates the evaluation of steroid profiles in sports drug testing. The possibility of manipulating steroid excretion profiles and, presumably, to mask steroid abuse was investigated in 5 administration studies with use of finasteride at different doses, with and without coadministration of 19-norandrostenedione. The evaluation of urinary steroid profiles demonstrated the intense effect of finasteride on numerous crucial analytical parameters, in particular the production of 5alpha-steroids such as androsterone and 5alpha-androstane-3alpha,17beta-diol, which was significantly reduced. In addition, the excretion of the main metabolite of norandrostenedione, norandrosterone, was significantly suppressed, by up to 84%, in elimination studies. For doping-control analysis the use of 5alpha-reductase inhibitors causes considerable problems because steroid profile parameters, which are commonly considered stable, are highly affected and complicate the detection of steroid abuse. In addition, the suppression of production and renal excretion of 5alpha-steroids such as 19-norandrosterone generated from anabolic agents such as 19-norandrostenedione may lead to false-negative doping-control results, because urine specimens are reported positive only when a threshold level of 2 ng/mL is exceeded. Finally, a method for the determination of the major urinary metabolite of finasteride (carboxy-finasteride) in routine doping-control screening with use of liquid chromatography-tandem mass spectrometry is described, allowing the detection of carboxy-finasteride for up to 94 hours in urine specimens collected after an oral administration of 5 mg of finasteride.

Inhibition of 5alpha-reductase blocks prostate effects of testosterone without blocking anabolic effects.

We studied the effect of the 5alpha-reductase inhibitor MK-434 on responses to testosterone (T) in orchiectomized (ORX) male Brown Norway (BN) rats aged 13 mo. At 4 wk after ORX or sham surgery, a second surgery was performed to implant pellets delivering 1 mg T/day or placebo pellets. During the second 4 wk of the study, rats received injections of MK-434 (0.75 mg/day) or vehicle injections. Treatment with T elevated serum T to 75% above that for sham animals (P = 0.002) and did not affect serum dihydrotestosterone (DHT) or serum estradiol. T treatment also caused an elevation of prostate T and a marked elevation of prostate DHT. During the second half of the study, ORX rats lost an average of 18.86 +/- 4.62 g body wt. T completely prevented weight loss, and the effect was not inhibited by MK-434 (P < 0.001). ORX produced a nonsignificant trend toward a small (5%) decrease in the mass of the gastrocnemius muscle (P = 0.0819). This trend was also reversed by T, and the effect of T was not blocked by MK-434. T caused a significant 16% decrease in subcutaneous fat that was not blocked by MK-434 (P < 0.05). Finally, T caused a 65% decrease in urine excretion of deoxypyridinoline, a marker of bone resorption, and again the effect was not blocked by MK-434 (P < 0.0001). In contrast, T caused a greater than fivefold increase in prostate mass, and the effect was almost completely blocked by MK-434 (P < 0.0001). This study demonstrates that 5alpha-reductase inhibitors may block the undesirable effects of T on the prostate, without blocking the desirable anabolic effects of T on muscle, bone, and fat.

Reduced progesterone metabolites are not critical for plus-maze performance of lactating female rats.

Lactation has been associated with anxiolysis in several tests of anxiety. These observations, considered together with observations that progesterone and its 5alpha-reduced metabolites are anxiolytic in cycling, nonlactating females, raised the question of whether the changes in anxiety-related behaviors that accompany lactation are driven by reduced progesterone metabolites. Lactating female rats were tested on the plus-maze on postpartum days 2 or 7, and demonstrated enhanced open-arm performance relative to cycling, nonlactating females. Hormonal analysis indicated that while serum levels of both progesterone and its 3alpha,5alpha-reduced metabolite were increased in lactating females, the turnover of progesterone to the metabolite was markedly reduced during lactation. Furthermore, treatment with a 5alpha-reductase inhibitor for 3 days prior to testing potentiated the open-arm performance in lactating females, implying that enhanced open-arm performance was not mediated by the reduction of progesterone or other steroids. Additionally, analysis of GABA(A) receptor function indicated that parturition and lactation did not alter the sensitivity of the receptor to GABA or to modulation by reduced steroids. The mechanisms driving enhanced plus-maze behavior in lactating females appear to differ from mechanisms identified in nonlactating females.

Brain androgen-inducible aromatase is critical for adolescent organization of environment-specific social interaction in male rats.

Previous observations have indicated that specific behavioral responses to anxiogenic stimuli emerge over adolescent development in male rats and that gonadal androgens during puberty are essential for this emergence. The objective of the current study was to evaluate mechanisms via which androgens might be organizing the brain during adolescence for appropriate mature adaptive responses. Male rats were exposed to fadrozole (an aromatase inhibitor, 5 mg/kg), flutamide (an androgen receptor antagonist, 10 mg/kg), or MK-434 (a 5 alpha-reductase inhibitor, 10 mg/kg) from day 29 to 60 and tested for environment-specific social interaction (SI) at 60 days of age. The emergence of adult-typical SI was impaired by exposure to the aromatase inhibitor and to the antiandrogen, whereas exposure to the 5 alpha-reductase inhibitor was without effect. Peripheral indices of drug effects indicated that the respective mechanisms had been altered by the different compounds. These results suggest that testosterone induction of aromatase is critical for the organization of mature SI behavior in male rats over adolescent development.

Effect of early treatment of prostate cancer with the 5alpha-reductase inhibitor turosteride in Dunning R3327 prostatic carcinoma in rats.

BACKGROUND: Turosteride, a selective 5alpha-reductase inhibitor, was reported to be effective in inhibiting the growth of established tumors in the Dunning R3327 rat prostatic carcinoma model. We evaluated the preventive effect of turosteride when administered during the latency period in this prostatic tumor model. METHODS: Turosteride was given orally, 6 days a week for 10-15 weeks, starting at different times: 1) 5 weeks after tumor implantation, when tumors were not yet palpable, or 2) 1 day after tumor implantation. In each experiment, one group of animals was castrated on the first treatment day. RESULTS: When treatment started 5 weeks after tumor implantation, neither turosteride (at 50 and 200 mg/kg/day) nor castration reduced tumor incidence (91-100%). Tumor growth was reduced in groups treated with the highest dose of turosteride and in castrated rats. When treatment started 1 day after tumor implantation, castration resulted in a 62% tumor incidence compared to 100% in controls, while turosteride at 200 mg/kg/day was not effective in reducing tumor incidence. However, as in the previous experiment, the compound was highly effective in reducing tumor growth. CONCLUSIONS: The antitumor activity profile of turosteride seems not to be related to the timing of treatment. Given either 5 weeks or 1 day after tumor implantation, the compound did not reduce tumor take, while it maintained effective tumor growth-inhibiting activity in both cases.

Mechanism based representation of the active site of 5 alpha-reductase (5AR).

In the present study, we have attempted to determine a detailed representation of the 5 alpha-Reductase (5AR) active site involving the elucidation of the transition state for the steroid delta 4 reduction reaction (the 'NADPH-substrate' complex), onto which steroidal and non-steroidal inhibitors were superimposed. We conclude that: (i) there is a requirement for groups to mimic the steroid substrate A-ring; (ii) the area about C(3), C(4), C(5) and C(6) of T appears to be sterically hindered, and; (iii) the area of the active site about the C(17) of the steroid substrate does not possess hydrogen bonding groups and is not restricted.

The effects of progesterone, 4,16-androstadien-3-one and MK-434 on the kinetics of pig testis microsomal testosterone-4-ene-5alpha-reductase activity.

The enzyme 3-oxo-steroid: NADP+ 4-oxidoreductase (EC 1.3.1.22; 5alpha-reductase) was assayed in testicular microsomes of pigs of 3, 20 and 24 weeks of age. The activity was very low in 3-week-old animals and approximately 10-fold higher in 5- and 6-month-old pigs. The pH optimum was 6.3 in 6-month-old animals, 5.7 in 5-month-old animals, but could not be reliably determined in 3-week-old animals. The kinetic parameters for 5alpha-reductase in testis microsomes from 6-month-old animals were; K((m)(app)), 8.0 micromol/l, V((max)(app)), 6.7 nmoles/90 min/mg protein. Progesterone was a competitive inhibitor of testosterone 5alpha-reduction with an apparent K((i)(app)) of 0.86 micromol/l. However, 4,16-androstadien-3-one (dienone), which undergoes 5alpha-reduction in the biosynthesis of the pheromonally active 16-androstenes, was a comparatively poor inhibitor with a K((i)(app)) of 4.9 micromol/l. Similarly, MK434, which is a selective inhibitor of the human type 2 5alpha-reductase, but which inhibits both types 1 and 2 in the rat, was also a poor competitive inhibitor of testosterone 5alpha-reductase in the pig testis (K((i)(app)), 3.1 micromol/l). It would appear from these studies that the pig testis microsomal 5alpha-reductase corresponds to a type 1 isozyme that is not capable of reducing dienone other than under conditions where the dienone concentration would be in considerable excess of testosterone. It is, therefore, probable that substrate-specific 5alpha-reductases exist in the pig testis for the 5alpha-reduction of testosterone and dienone.

A putative 5 alpha-reductase inhibitor demasculinizes portions of the zebra finch song system.

One model of the sexual differentiation of the zebra finch song system holds that both major metabolites of testosterone, dihydrotestosterone (DHT) and estradiol (E2), act together to masculinize the song system. To test this model, we administered a putative inhibitor of 5 alpha-reductase (MK-434) to decrease the synthesis of DHT from testosterone (T) in hatchling zebra finches. We tested MK-434's inhibition of 5 alpha-reductase, 5 beta-reductase, and aromatase in vivo and in vitro. In vivo, MK-434 significantly inhibited 5 alpha-reductase activity but also reduced the activities of 5 beta-reductase and aromatase. In vitro, MK-434 was extremely effective in inhibiting 5 alpha-reductase in the rat prostate but only slightly inhibited 5 alpha-reductase in the zebra finch telencephalon, where it also reduced aromatase and 5 beta-reductase activities. These results suggest that MK-434 might differentially influence the availability of androgenic and estrogenic substrates, depending on the relative abundance of these enzymes in brain. MK-434 demasculinized (decreased) the number and decreased the density of RA neurons but did not significantly affect any other sexually dimorphic aspect of the song system, including the volumes of RA, HVC, and Area X; the size of neural somata in IMAN, HVC, and RA; and the number of neurons in HVC and IMAN. The differential influence of MK-434 on sexually dimorphic characteristics suggests that the various sexually dimorphic characteristics of the song system (1) are sensitive to different hormones, depending on the characteristic; or (2) have different sensitivities to hormone levels, some being easily affected by slightly reduced hormone levels whereas others are not; or (3) have markedly different critical periods depending on the characteristic. Regardless of the reason(s) for differential effects on the sexually dimorphic characteristics of the song system, the data clearly suggest that steroid hormones play a role in the normal masculine development of the song system.

Effect of turosteride, a 5 alpha-reductase inhibitor, on the Dunning R3327 rat prostatic carcinoma.

BACKGROUND: Turosteride (FCE 26073) is a new, potent, and selective 5 alpha-reductase inhibitor. We have investigated its effect on tumor growth, organ weight, and serum hormone levels in rats bearing the androgen sensitive Dunning R3327 prostatic carcinoma. METHODS: Animals with tumor diameters of 0.5-1.5 cm were treated for 9 weeks with turosteride (50 and 200 mg/kg/day, 6 days a week, orally), flutamide (25 mg/kg/day, 6 days a week, orally), and leuprolide (300 micrograms/rat, every 3 weeks, subcutaneously) or they were castrated. RESULTS: Turosteride was ineffective at the dose of 50 mg/kg/day, whereas at 200 mg/kg/ day it significantly decreased tumor growth by 45%. Flutamide and leuprolide were highly effective in reducing tumor growth (70 and 77%), although their effect was slightly lower than that of castration (85%). A significant reduction of ventral prostate weight occurred in rats treated with turosteride at 50 and 200 mg/kg/day (53% and 60%). In contrast to leuprolide and castration, the inhibitory effect of turosteride on tumor growth and prostate weight was not associated to any decrease in serum testosterone. CONCLUSIONS: Turosteride has antitumor activity on Dunning prostatic tumor growth and its role in prostatic cancer treatment is worthy of further investigation.

Determination of turosteride, a new inhibitor of 5 alpha-reductase, in human plasma by high-performance liquid chromatography with ultraviolet detection.

A sensitive and specific HPLC method for the determination of turosteride in human plasma was developed and validated. Turosteride was extracted from plasma with diethyl ether. Further purifications of the fraction extracted were performed sequentially by solid-phase extraction using a CN cartridge and by liquid-liquid partition between n-hexane and acetonitrile. Finally the acetonitrile solution containing the test compound was evaporated to dryness and the residue dissolved in the mobile phase, then injected onto the HPLC system. The chromatographic separation was performed isocratically by a reversed-phase column filled with ODS using a water-acetonitrile-methanol mixture. The eluate was monitored at 210 nm. No peak interfering with that of turosteride was observed when blank human plasma was assayed. Linearity was obtained in the turosteride concentration range of 5-1000 ng/ml plasma. Six calibration curves in plasma prepared and run on six different days showed correlation coefficients higher than 0.99 and good reproducibility of the slope (C.V. = 4.3%). The intra-day precision, evaluated at three concentrations (in the low, mid and high range of the standard curve) and expressed as C.V., ranged from 0.81 to 13.25%. The inter-day precision evaluated at the same concentrations was better than 10.7%. The inter-day accuracy evaluated in the same samples and expressed as the ratio of found/added amount of turosteride ranged from 97.66 to 98.38%. The limit of quantitation was 5 ng/ml plasma. The HPLC method described was successfully employed for the determination of turosteride in plasma samples obtained during a phase I clinical trial with the test compound.

Synthesis of 4,17-diazasteroid inhibitors of human 5 alpha-reductase.

The synthesis of the 17-aza isomer of finasteride is described. With the side chain amide group of the compound existing in the Z configuration the structure is similar to one of the two favored conformations of finasteride. A series of 4,17-diazasteroids was assayed against the isoenzymes of human 5 alpha-reductase.

CGP 53153: a new potent inhibitor of 5alpha-reductase.

CGP 53153 (N-2-(cyano-2-propyl)-3-oxo-4-aza-5alpha-androst-1-ene-17beta-carb oxamide) is a steroidal inhibitor of 5alpha-reductase, the enzyme which effects the conversion of testosterone (T) to 5alpha-dihydrotestosterone (DHT). In vitro, CGP 53153 competitively inhibited rat microsomal 5alpha-reductase from prostate by 50% (IC50) at a concentration of 36nM compared to the reference compound finasteride which inhibited 5alpha-reductase with an IC50 of 11 nM in the same system. In vivo, inhibition of 5alpha-reductase activity was characterized in three different test systems. Inhibition of 5alpha-reductase activity was first assessed in a standard test designed to compare directly the potency of different 5alpha-reductase inhibitors. This test assesses potency through the inhibition of prostate growth in juvenile castrate male rats treated with a standard dose of T-propionate (1 mg/kg, s.c.) and a 5alpha-reductase inhibitor administered orally at various doses for 4 days. CGP 53153 and finasteride significantly reduced T-propionate-mediated prostate growth by about 25% (ED25) compared to T-propionate-treated controls at oral doses of 0.01 and 0.1 mg/kg, respectively. Second, the effects on prostate weight were studied in normal adult male rats treated orally once daily for 14 days with 1, 3 and 10 mg/kg CGP 53153 and with 10 mg/kg finasteride. CGP 53153 significantly reduced prostate weight at 3 and 10 mg/kg by 31% and 37%, respectively, compared to vehicle-treated controls, whereas the dose of 10 mg/kg finasteride did not significantly reduce prostate weight. Third, the effects on prostate volume were studied in normal 6-9-year-old male dogs treated orally once daily with 5 mg/kg CGP 53153 and with 5 mg/kg finasteride for 12 weeks. Prostate volume was monitored with magnetic resonance imaging every 2 weeks beginning 6 weeks before start of the treatment with 5alpha-reductase inhibitors and ending after a recovery period of 8 weeks after termination of treatment. Treatment for 12 weeks with both CGP 53153 and finasteride was equally effective in reducing prostate volume by more than 70% in individual dogs. Anti-androgenic potency of CGP 53153 and finasteride was assessed in juvenile castrate male rats treated with DHT-propionate (1 mg/kg, s.c.) and a 5alpha-reductase inhibitor (p.o.) for 4 days. Neither CGP 53153 nor finasteride given at a dose of 10 mg/kg had any significant effect on DHT-propionate-mediated prostate growth, whereas the reference anti-androgen flutamide given at a dose of 10 mg/kg reduced prostate weight to levels comparable to those seen in untreated castrate animals. For CGP 53153, the dose of 10 mg/kg is 1000-fold higher than the ED25 for 5alpha-reductase inhibition in vivo. In conclusion, both CGP 53153 and finasteride are potent inhibitors of the rat 5alpha-reductase enzyme system in vitro without showing any anti-androgenic effects in vivo. Both CGP 53153 and finasteride were equally potent in reducing prostate volume in aged male dogs, whereas in rats, CGP 53153 is up to 10 times more potent than finasteride in reducing prostate weight as shown in two different rat models.

Human prostatic steroid 5 alpha-reductase isoforms--a comparative study of selective inhibitors.

The present study describes the independent expression of the type 1 and 2 isoforms of human 5 alpha-reductase in the baculovirus-directed insect cell expression system and the selectivity of their inhibition. The catalytic properties and kinetic parameters of the recombinant isozymes were consistent with published data. The type 1 isoform displayed a neutral (range 6-8) pH optimum and the type 2 isoform an acidic (5-6) pH optimum. The type 2 isoform had higher affinity for testosterone than did the type 1 isoform (Km = 0.5 and 2.9 microM, respectively). Finasteride and turosteride were selective inhibitors of the type 2 isoform (Ki (type 2) = 7.3 and 21.7 nM compared to Ki (type 1) = 108 and 330 nM, respectively). 4-MA and the lipido-sterol extract of Serenoa repens (LSESr) markedly inhibited both isozymes (Ki (type 1) = 8.4 nM and 7.2 micrograms/ml, respectively; Ki (type 2) = 7.4 nM and 4.9 micrograms/ml, respectively). The three azasteroids were competitive inhibitors vs substrate, whereas LSESr displayed non-competitive inhibition of the type 1 isozyme and uncompetitive inhibition of the type 2 isozyme. These observations suggest that the lipid component of LSESr might be responsible for its inhibitory effect by modulating the membrane environment of 5 alpha-reductase. Partially purified recombinant 5 alpha-reductase type 1 activity was preserved by the presence of lipids indicating that lipids can exert either stimulatory or inhibitory effects on human 5 alpha-reductase.

Quantitative evaluation of glandular and stromal compartments in hyperplastic dog prostates: effect of 5-alpha reductase inhibitors.

The objective of this study was to determine the effects of 2 different 5-alpha reductase inhibitors (finasteride and MK-0434) on the glandular and stromal compartments of hyperplastic canine prostates. In this study, dogs received 1 of the 2 compounds orally, at a dose of 1 mg/kg/day for 16 weeks; control dogs received a placebo. The morphological changes in the glandular and stromal compartments in the prostate were quantitated by a point-counting method on Masson's trichrome-stained sections. Treatment with 5-alpha reductase inhibitors resulted in significant (P < or = 0.05) decreases in mean prostatic volumes, microscopic evidence of prostatic atrophy, and significant (P < or = 0.05) decreases in the absolute volumes of the prostatic glandular and stromal compartments compared to controls. In finasteride-treated dogs, the mean percent change from baseline was: epithelium, -52; lumens, -58; fibrovascular stroma, -41; and smooth muscle, -29. In MK-0434-treated dogs, the mean percent change from baseline was: epithelium, -77; lumens, -58; fibrovascular stroma, -38; and smooth muscle, -42. The effect on the glandular compartment in dogs treated with MK-0434 was slightly greater than in dogs treated with finasteride; however, the effect on the stroma was similar. These results clearly demonstrate that inhibition of 5-alpha reductase enzyme activity affects growth and maintenance of both glandular and stromal compartments of dog hyperplastic prostates. It is likely that the decrease in size of the prostate in finasteride-treated (Proscar) men is due to shrinkage of both glandular and stromal compartments.

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.

Feedback regulation of gonadotropins by androgens in rats: is 5 alpha-reduction involved?

The action of testosterone (T) on the sex accessory organs, such as ventral prostate (VP) and seminal vesicles (SV) is amplified by its 5 alpha-reduction to dihydrotestosterone (DHT). This does not happen in the case of muscle (levator ani, LA) which contains little or no 5 alpha-reductase activity. It has been suggested that the regulation of gonadotropins by T may also be mediated by its 5 alpha-reduced metabolites. We investigated this question by utilizing two types of androgens: (1) T and 17 alpha-methyl-testosterone (17MT), whose potency increases following 5 alpha-reduction; and (2) 19-nortestosterone (NT) and 17 alpha-methyl-19-nortestosterone (17MNT) whose potency decreases following 5 alpha-reduction. Castrated rats were used to investigate the ability of these androgens to stimulate VP, and SV (androgenic action) and LA growth (anabolic action) and to suppress the post-castration rise in LH levels. In addition, modification of these actions by a 5 alpha-reductase inhibitor (5 alpha-RI) was studied. Compared to T, NT was approximately 5 times less potent in stimulating VP and SV. By contrast, it was twice as potent as T in stimulating LA growth. Similarly, 17MNT was 5 times less androgenic but twice as anabolic as 17MT. The antigonadotropic potency of both the 19-nor compounds was 2-3 times greater than that of their respective 19-methylated parent compounds. The similarity in their anabolic and antigonadotropic potency suggested that 5 alpha-reduction is not a factor in their antigonadotropic action. This was confirmed by the use of the 5 alpha-RI. Treatment of rats receiving the androgens with 5 alpha-RI showed that it decreases the androgenic activity of T and 17MT while it increases the androgenic activity of NT and 17 MNT. In all cases the anabolic activity and the antigonadotropic potency remained unchanged. It is concluded that the regulation of pituitary gonadotropin secretion by T does not depend upon its 5 alpha-reduction to DHT.

Biotransformation of finasteride (MK-0906) by Selenastrum capricornutum (green algae).

Finasteride (MK-0906), a drug used for the treatment of benign prostatic hyperplasia, is a highly specific inhibitor of steroid 5 alpha-reductase, an enzyme that converts testosterone (T) to dihydrotestosterone (DHT) in animals and humans. In a study to evaluate the effect of finasteride on the growth of green alga, Selenastrum capricornutum, the parent drug was not detected by HPLC in the posttreatment (14 day) samples, suggesting complete biotransformation. Thermospray LC/MS, followed by NMR analysis, indicated that the major algal metabolite was 11 alpha-hydroxy-finasteride. This metabolite has negligible in vitro bioactivity against human prostatic 5 alpha-reductase; its potency is only 2% that of finasteride. The primary metabolite of finasteride produced by the green alga involved a biotransformation not previously observed in mammalian and human studies. The green alga effectively deactivates the drug, thereby mitigating any potential environmental impact.