4-pregnene-3-one-20 beta-carboxaldehyde: a potent inhibitor of 17 alpha-hydroxylase/C17,20-lyase and of 5 alpha-reductase

New benzothieno[2,3-c]pyridines as non-steroidal CYP17 inhibitors: design, synthesis, anticancer screening, apoptosis induction, and in silico ADME profile studies

A series of [1]benzothieno[2,3-c]pyridines was synthesised. Most compounds were chosen by NCI-USA to evaluate their anticancer activity. Compounds 5a-c showed prominent growth inhibition against most cell lines. 5c was selected at five dose concentration levels. It exhibited potent broad-spectrum anticancer activity with a GI50 of 4 nM-37 µM. Cytotoxicity of 5a-c was further evaluated against prostate, renal, and breast cancer cell lines. 5c showed double and quadruple the activity of staurosporine and abiraterone, respectively, against the PC-3 cell line with IC50 2.08 µM. The possible mechanism of anti-prostate cancer was explored via measuring the CYP17 enzyme activity in mice prostate cancer models compared to abiraterone. The results revealed that 5c suppressed the CYP17 enzyme to 15.80 nM. Moreover, it was found to be equipotent to abiraterone in testosterone production. Cell cycle analysis and apoptosis were performed. Additionally, the ADME profile of compound 5c demonstrated both good oral bioavailability and metabolic stability.

Discovery of novel 1,2,3,4-tetrahydrobenzo[4, 5]thieno[2, 3-c]pyridine derivatives as potent and selective CYP17 inhibitors

The inhibition of CYP17 to block androgen biosynthesis is a well validated strategy for the treatment of prostate cancer. Herein we reported the design, synthesis and structure-activity relationship (SAR) study for a series of novel 1,2,3,4- tetrahydrobenzo[4,5]thieno[2,3-c]pyridine derivatives. Some analogs demonstrated a potent inhibition to both rat and human CYP17 protein and reduced testosterone production in human H295R cell line. Some analogs also showed high selectivity against other CYP enzymes such as 3A4, 1A2, 2C9, 2C19 and 2D6, which may limit side effects due to drug-drug interactions. Among these analogs, the most potent compound 9c showed 1.5 fold more potent against rat and human CYP17 protein than that of abiraterone (IC₅₀ = 16 nM and 20 nM vs. 25 nM and 36 nM respectively). In NCI-H295R cells, the inhibitory effect of compound 9c on testosterone production (52± 2%) was also more potent than that of abiraterone (74± 15%) at the concentration of 1 μM. Further, it was shown that 9c reduced plasma testosterone level in a dose-dependent manner in Sprague-Dawley rats. Thus, analog 9c maybe a potential agent used for the treatment of prostate cancer.

Steroidal 5α-reductase and 17α-hydroxylase/17,20-lyase (CYP17) inhibitors useful in the treatment of prostatic diseases

The role of steroidal inhibitors of androgen biosynthesis as potential weapons in the treatment of prostatic diseases, such as benign prostatic hyperplasia and prostatic cancer will be reviewed. Two enzymes have been targeted in the development of inhibitors that potentially could be useful in the management of such conditions. 5α-Reductase is primarily of interest in benign prostatic disease, though some role in the chemoprevention of prostatic carcinoma have been considered, whereas the 17α-hydroxylase/17,20-lyase (CYP17) enzyme is of interest in the treatment of malignant disease. An overview of the main achievements obtained during the past years will be presented, however special focus will be made on steroidal molecules that reached clinical trials or have been commercially launched. Relevant examples of such drugs are finasteride, dutasteride, abiraterone acetate and galeterone (TOK-001, formerly known as VN/124-1). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Neighboring group participation. Part 15. Stereoselective synthesis of some steroidal tetrahydrooxazin-2-ones, as novel presumed inhibitors of human 5alpha-reductase

During the alkaline methanolysis of 3beta-acetoxy-21-chloromethyl-pregn-5-ene-20beta-N-phenylurethane, and its p-substituted phenyl derivatives, cyclization occurs, in the course of which 17beta-[3-(N-phenyl)tetrahydrooxazin-2-on-6-yl]androst-5-en-3beta-ol and its p-substituted phenyl derivatives are formed. The cyclization takes place with (N(-)-6) neighboring group participation. Oppenauer oxidation of the 3beta-hydroxy-exo-heterocyclic steroids yielded the corresponding delta4-3-ketosteroids. The structures of the new compounds were proved by IR, 1H and 13C NMR spectroscopy, using up-to-date measuring techniques such as 2D-COSY, HMQC, and HMBC. The inhibitory effects (CI50) of the delta4-3-ketosteroids on 5alpha-reductase were studied.

In vitro and in vivo models for the evaluation of potent inhibitors of male rat 17alpha-hydroxylase/C17,20-lyase

The C(17,20)-lyase is a key enzyme in the biosynthesis of androgens by both the testes and adrenals. A complete inhibition of this enzyme would provide an alternative means of androgen suppression for the treatment of prostatic cancers. In the present study, the inhibitory effects of new non-steroidal compounds were tested in vitro on rat C(17,20)-lyase versus abiraterone, a reference steroidal inhibitor. Their activities were also evaluated in vivo on plasma testosterone (T) and luteinizing hormone (LH) levels and on testes, adrenals, seminal vesicles (SV) and ventral prostate (VP) weights after 3 days of oral treatment to adult male rats (50mg/kg per day p.o.). Inhibition in the nanomolar range was obtained with TX 977, the lead racemate product in this series, and optimization is ongoing based on a slight dissociation observed between its two diastereoisomers, TX 1196-11 (S) and TX 1197-11 (R). These non-steroidal compounds (including YM 55208, a reference competitor) proved to be more active in vivo than abiraterone acetate in this model, but the observed impact on adrenal weight suggests that the specificity of lyase inhibition versus corticosteroid biosynthesis deserves further investigations with this new class of potentially useful agents for the treatment of androgen-dependent prostate cancer.

Novel steroidal vinyl fluorides as inhibitors of steroid C17(20) lyase

20-fluoro-17(20)-pregnenolone derivatives were designed as enol mimics of pregnenolone. All of the targeted, novel fluoroolefins were potent inhibitors of C17(20) lyase.

Inhibition of CYP 17, a new strategy for the treatment of prostate cancer

Androgens are growth factors for approximately 80 percent of all prostate cancers. Suppressing androgen biosynthesis is therefore an important therapeutic strategy in order to inhibit tumor growth. Unfortunately, the drugs currently applied to lower androgen levels only affect testicular androgen production. Since androgens are also synthesized in the adrenal glands, tumor stimulation cannot be blocked completely. A new therapeutic target, CYP 17 (P450 17, 17alpha-hydroxylase-C17, C20 lyase), is likely to improve this situation. CYP 17 is a P450 enzyme and catalyzes the last step of androgen biosynthesis in both testes and adrenals. Inhibition of this enzyme will therefore result in a complete block of androgen production. This paper gives an overview of the current situation in this novel field of drug research and focuses on the development of steroidal and non-steroidal inhibitors of CYP 17.

Anti-tumour effects and pharmacokinetic profile of 17-(5'-isoxazolyl)androsta-4,16-dien-3-one (L-39) in mice: an inhibitor of androgen synthesis

17-(5'-Isoxazolyl)androsta-4,16-dien-3-one (L-39), a novel androstene derivative, was synthesized and evaluated in vitro and in vivo. L-39 showed potent and non-competitive inhibition of human testicular microsomal 17alpha-hydroxylase/C(17,20)-lyase with an IC50 value of 59 nM and Ki of 22 nM. L-39 also showed potent and competitive inhibition of 5alpha-reductase in human prostatic microsomes with IC50 and Ki values of 33 and 28 nM respectively. L-39 (5 microM) has also been shown to manifest anti-androgenic activity in cultures of human prostate cancer cell lines (LNCaP) by preventing the labelled synthetic androgen R1881 (5 nM) from binding to the androgen receptors. Androgen-dependent human prostate cancer xenografts (PC-82) were grown in nude mice and the effects of L-39 (50 mg kg(-1) day(-1)) on tumour growth and prostate-specific antigen (PSA) levels were determined after 28 days. L-39 significantly (P < 0.01) diminished tumour growth and wet weights to a similar extent as castration or flutamide treatment. L-39 also significantly (P < 0.01) reduced serum PSA levels by more than 80% in the mice bearing human prostate cancer xenografts. Pharmacokinetic studies were also conducted in male Balb/c mice. After subcutaneous administration of a single bolus dose, L-39 was rapidly absorbed into the systemic circulation. Peak plasma levels occurred at 0.75 h and then declined with a t(1/2) of 1.51 h. The bioavailability of L-39 after subcutaneous administration was 28.5%. These results demonstrate that L-39 is a potent inhibitor of androgen synthesis and is effective in reducing the growth of human prostate cancer xenografts in nude mice. Although improvements in the bioavailability are necessary, L-39 is a potential lead compound with this profile as an inhibitor of prostate cancer growth.

Effects of novel 17-azolyl compounds on androgen synthesis in vitro and in vivo

17-Azolyl steroids were synthesized and evaluated as inhibitors of androgen synthesis in vitro and in vivo. Several of the novel compounds exhibit potent noncompetitive inhibition of human 17alpha-hydroxylase/C17,20-lyase with IC50 values ranging from 7 to 90 nM, and Ki values from 1.2 to 41 nM. VN/85-1 and VN/108-1 were the most potent inhibitors against this enzyme with IC50 value of 8 nM (Ki of 1.2 nM) and 7 nM (Ki of 1.9 nM), respectively. VN/107-1, VN/108-1 and VN/109-1 also showed moderate inhibition of 5alpha-reductase in human prostatic microsomes. Normal adult male rats were treated with these novel 17-azolyl steroidal compounds at a dose level of 50 mg/kg, s.c., for 14 consecutive days, sacrificed 1-2 h after the last administered dose and blood, prostate and other tissues were collected. The organs were weighed and tissue concentrations of testosterone (T) and dihydrotestosterone (DHT) were measured. Tissue T levels were significantly (p<0.05) lower in rats treated with the novel 17-azolyl steroids by more than 50% compared to the control group. Similarly, the concentration of DHT in the serum and prostates was significantly (p<0.05) diminished in rats treated with the 17-azolyl steroids by 39-80% compared to the control group. Furthermore, the wet weights of the prostates and seminal vesicles were significantly (p<0.05) reduced by several of the novel steroids. Although only one dose was evaluated in these studies, VN/85-1 was the most effective compound and reduced prostatic androgen levels by more than 80% and the wet weights of the prostate and seminal vesicles in rats by about 50%. These findings suggest that these novel compounds may provide useful leads for the research and development of suitable agents for the treatment of androgen dependent prostate cancer.

Inhibition of androgen synthesis in human testicular and prostatic microsomes and in male rats by novel steroidal compounds

The C(17,20)-lyase and 5alpha-reductase are key enzymes in the biosynthesis of androgens. The effects of novel steroidal compounds were evaluated as inhibitors against both human C(17,20)-lyase and 5alpha-reductase in vitro. The concentrations of testosterone (T) and dihydrotestosterone (DHT) in the prostate, testis and serum and changes in the tissue weights were also determined in rats treated with the novel inhibitors. L-12 and L-26 showed potent inhibition of human testicular C(17,20)-lyase with IC50 values of 50 and 25 nM, respectively. L-12, L-38, and I-47 showed moderate inhibition of human testicular C(17,20)-lyase with IC50 values of 75, 108, and 70 nM, respectively similar to ketoconazole (78 nM). Interestingly, L-6, L-26, and L-38 also showed some inhibitory activity against 5alpha-reductase with IC50 values of 75, 125, and 377 nM, respectively. Finasteride, an inhibitor of 5alpha-reductase had an IC50 value of 33 nM. However, ketoconazole did not inhibit 5alpha-reductase nor did finasteride inhibit C(17,20)-lyase. Treatment of normal male rats with several of these novel inhibitors (50 mg/kg x day, s.c., for 14 consecutive days) caused about 45-91% decrease in serum, testicular and prostatic T concentration. Similarly, serum and prostatic DHT concentration were significantly decreased in rats treated with these novel compounds by 50-90% compared with controls. Surgical castration caused almost complete elimination of circulating T and DHT concentration in rat tissues. L-6 and L-12 were the most effective and reduced the wet weight of the prostate by 50%. Although future improvements in their bioavailability are necessary, these novel steroidal compounds show promise as potential agents for reducing T and DHT levels in patients with androgen dependent diseases.

Some 1-[(benzofuran-2-yl)methyl]imidazoles as inhibitors of 17 alpha-hydroxylase: 17, 20-lyase (P450 17) and their specificity patterns

Four 1-[(benzofuran-2-yl)methyl]imidazoles (1-4) have been evaluated as in-vitro inhibitors of human testicular and bovine adrenal microsomal 17 alpha-hydroxylase: 17,20-lyase (P450 17) as potential anti-prostatic agents. Their specificity towards other steroidogenic and liver enzymes has been compared with that of ketoconazole. All four compounds were inhibitors of the testicular enzyme (2, IC50 (concentration resulting in 50% inhibition) 0.185 microM; 4, IC50 0.18 microM) but less potent than ketoconazole (IC50 0.03 microM). Towards bovine adrenal enzyme 2 and 4 were 35- and 31-fold more potent than ketoconazole (IC50 = 39.8 microM). Compound 2 is a useful lead compound but although less potent than ketoconazole towards P450SCC and P450 11 beta, but not P450C21, at the enhanced dose required for equivalent effects in-vivo on P450 17 it is likely that cortisol and aldosterone production will be affected to a greater extent than with ketoconazole.

Synthesis and in vitro activity of some epimeric 20 alpha-hydroxy, 20-oxime and aziridine pregnene derivatives as inhibitors of human 17 alpha-hydroxylase/C17,20-lyase and 5 alpha-reductase

Some epimeric 20-hydroxy, 20-oxime, 16 alpha, 17 alpha-, 17,20- and 20,21-aziridine derivatives of progesterone were synthesized and evaluated as inhibitors of human 17 alpha-hydroxylase/C17,20-lyase (P450(17) alpha) and 5 alpha-reductase (5 alpha-R). The reduction of 16-dehydropregenolone acetate (3a) was reinvestigated. NaBH4 in the presence of CeCl3 gave better stereo-selectivity for 20 beta-ol [20 alpha/20 beta-OH (4 alpha/4 beta) = 1/2.7] than LTBAH or the Meerwein-Pondroff method reported; reduction with Zn in HOAc formed exclusively 20 alpha-ol (4 alpha b). The 20 alpha- and 20 beta-hydroxy-4,16-pregnadien-3-one (9 alpha) and (9 beta) were synthesized from the alcohols 4 alpha b and 4 beta b. Several 20-oxime pregnadienes and 16 alpha, 17 alpha-, 17,20- and 20,21-aziridinyl-5-pregnene derivatives were also synthesized. LiAlH4 reduction of the 16-en-20-oxime (12b) yielded 20 (R)-(13a) and 20(S)-17 alpha,20-aziridine (13b) and 20(R)-17 beta,20-aziridine (14a). Several compounds inhibited the human P450(17) alpha with greater potency than ketoconzole. The 5 alpha-R enzyme assay showed that while (9 alpha) did not have any activity, (9 beta) and (3b) were potent 5 alpha-reductase (IC50 = 21 and 31 nM) inhibitors with activities similar to finasteride. The 20-oximes (17a) and (17b) were potent dual inhibitors for both 5 alpha-R (IC50 = 63 and 115 nM, compared to 33 nM for finasteride) and P450(17) alpha (IC50 = 43 and 25 nM, compared to 78 nM for ketoconazole).

Synthesis of novel 21-trifluoropregnane steroids: inhibitors of 17 alpha-hydroxylase/17,20-lyase (17 alpha-lyase)

Novel 21-trifluoropregnenolone (6), 21-trifluoroprogesterone (7) and related compounds 4a and 8 have been synthesized in high yields from 3 beta-acetoxyandrost-5-ene-17 beta-carbaldehyde (3). The key reaction was the conversion of 3 into the 21-trifluoromethyl-20-alcohol as a diastereomeric mixture (4) by trifluoromethyltrimethylsilane (TMS-CF3) in the presence of tetrabutylammonium fluoride (TBAF). All compounds, including 6 and 7, were unambiguously characterized by IR, 1H and 19F NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. On this basis, we concluded that the only report of an earlier synthesis of 6 and 7 is erroneous. Enzyme inhibition studies showed that 20 xi-hydroxy-21-trifluoropregn-4-en-3-one (8) is a potent inhibitor (IC50 value = 0.6 microM) of rat 17 alpha-hydroxylase/17,20-lyase.

20-amino and 20,21-aziridinyl pregnene steroids: development of potent inhibitors of 17 alpha-hydroxylase/C17,20-lyase (P450 17)

In the search for potent inhibitors of P450 17, the key enzyme of androgen biosynthesis, the 20,21-aziridinyl- and 20-aminopregnene steroids 1-11 were synthesized and tested toward rat testicular P450 17. Only the aziridinyl-substituted pregnenolones (1 and 2) and progesterones (3 and 4), respectively, showed inhibitory activity, which strongly depends on C20 stereochemistry. The most active compound 1 [20(S)-20,21-aziridinylpregn-5-en-3 beta-ol; IC50 0.21 microM, progesterone 25 microM; Ki = 1.7 nM, K(m) progesterone = 7.0 microM] is the strongest inhibitor of rat P450 17 described so far. Using UV-vis difference spectroscopy, complexation of the aziridinyl nitrogen to the heme iron, Fe3+, of P450 17 was observed, which could not be reversed by high concentrations of substrate. Preincubation of the enzyme with 1 in the absence and presence of NADPH followed by charcoal treatment results in a strong decrease of enzyme activity within 30 s. However, a recovery of enzyme activity was observed: 90 min after charcoal treatment 75% of the activity was restored.

Kinetic analysis of duodenal and testicular cytochrome P450c17 in the rat

In the adult rat, the duodenal tissue of both sexes can convert progesterone to 17alpha-hydroxyprogesterone, androstenedione and testosterone. The transition from C21 to C19 steroids is apparently controlled by the same cytochrome P450c17 expressed in the testis, which catalyzes both 17alpha-hydroxylation and C-17,20 bond scission at a single bifunctional active site. The kinetic parameters of this enzyme were measured at the steady state for both reactions using [1,2-3H]progesterone and [1,2-3H]17alpha-hydroxyprogesterone as substrates. In the testis and male and female duodena, the Km values for progesterone 17alpha-hydroxylation were 14.2, 23.8 and 23.2 nM, whereas the Vmax values were 105, 3.5 and 3.1 pmol/mg protein/min, respectively. With respect to C-17,20 lyase activity, the Km values for exogenous 17alpha-hydroxyprogesterone were 525, 675 and 637 nM, whereas the Vmax values were 283, 7.8 and 7.8 pmol/mg protein/min, respectively. However, when the Km values were calculated with respect to intermediate 17alpha-hydroxyprogesterone formed from progesterone, they were similar to the Km values for 17alpha-hydroxylase, being 15, 31.4 and 24.8 nM, whereas the Vmax values were 26.3, 2 and 1.8 pmol/mg protein/min, respectively. The similarity of Km values is due to the fact that the relative androgen formation efficiency (bond scission events/total 17alpha-hydroxylation events ratio) was remarkably constant in both testicular and duodenal incubates, irrespective of progesterone concentration. Efficiency values were 2-fold higher in duodenal tissue (0.54) than in testis (0.25). Estradiol-17beta inhibited 17alpha-hydroxylation but not bond scission on intermediate 17alpha-hydroxyprogesterone, because it did not affect the efficiency value. Rat duodenal P450c17 has the same substrate affinity, a lower specific activity and a higher androgen formation efficiency than testicular P450c17.

P450-dependent enzymes as targets for prostate cancer therapy

Metastatic prostate adenocarcinoma is a leading cause of cancer-related deaths among men. First line treatment is primarily aimed at blocking the synthesis and action of androgens. As primary endocrine treatment, androgen deprivation is usually achieved by orchidectomy or LHRH analogues, frequently combined with androgen receptor antagonists in order to block the residual adrenal androgens. However, nearly all the patients will eventually relapse. Available or potential second line therapies include, among others, alternative endocrine manipulations and chemotherapy. Cytochrome P450-dependent enzymes are involved in the synthesis and/or degradation of many endogenous compounds, such as steroids and retinoic acid. Some of these enzymes represent suitable targets for the treatment of prostate cancer. In first line therapy, inhibitors of the P450-dependent 17,20-lyase may achieve a maximal androgen ablation with a single drug treatment. Ketoconazole at high dose blocks both testicular and adrenal androgen biosynthesis but its side-effects, mainly gastric discomfort, limit its widespread use. A series of newly synthesized, more selective, steroidal 17,20-lyase inhibitors related to 17-(3-pyridyl)androsta-5,16-dien-3beta-ol, may open new perspectives in this field. In prostate cancer patients who relapse after surgical or medical castration, therapies aiming at suppressing the remaining adrenal androgen biosynthesis (ketoconazole) or producing a medical adrenalectomy (aminoglutethimide+hydrocortisone) have been used, but are becoming obsolete with the generalization of maximal androgen blockade in first line treatment. The role of inhibition of aromatase in prostate cancer therapy, which was postulated for aminoglutethimide, could not be confirmed by the use of more selective aromatase inhibitors, such as formestane. An alternative approach is represented by liarozole fumarate (LIA), a compound that blocks the P450-dependent catabolism of retinoic acid (RA). In vitro, it enhances the antiproliferative and differentiation effects of RA in cell lines that express RA metabolism, such as F9 teratocarcinoma and MCF-7 breast carcinoma cells. In vivo, monotherapy with LIA increases RA plasma levels and, to a greater extent, endogenous tissue RA levels leading to retinoid-mimetic effects. In the rat Dunning prostate cancer models, it inhibits the growth of androgen-independent as well as androgen-dependent carcinomas relapsing after castration. Concurrently, changes in the pattern of cytokeratins characteristic of increased differentiation were observed. Early clinical trials show that LIA, in second or third line therapy in metastatic prostate cancer, induces PSA responses in about 30% of unselected patients. In some patients regression of soft tissue metastasis ha been observed. In a subgroup of patients, an important relief of metastatic bone pain was also noted.

Inhibition of androgen synthesis by 22-hydroximino-23,24-bisnor-4-cholen-3-one

The 22-hydroximino-23,24-bisnor-4-cholen-3-one (22-oxime) was synthesized and evaluated as an inhibitor of 17 alpha-hydroxylase/C17,20-lyase in rat testicular microsomes and the 5 alpha-reducatase of human prostatic microsomes from patients with benign prostatic hypertrophy. The 22-oxime demonstrated moderate inhibition for the 17 alpha-hydroxylase (Ki 74 nM vs. Km 29 nM) with progesterone as substrate and potent inhibition (Ki 18 nM vs. Km 76 nM) for the C17,20-lyase activity with 17 alpha-hydroxyprogesterone as substrate. Further investigation of this enzyme with progesterone as substrate demonstrated the inhibition occurred mainly at the 17 alpha-hydroxylation step of the progesterone substrate. The 22-oxime also demonstrated potent and competitive inhibition of 5 alpha-reductase in human prostatic microsomes (Ki 1.4 nM vs. Km 14 nM). When adult male rats were injected subcutaneously (sc) daily with 22-oxime (50 mg/kg/day) for 21 days, the concentrations of serum and testicular testosterone were significantly reduced by 65% and 59%, respectively, in comparison to vehicle-treated controls. Furthermore, both testosterone and DHT concentrations in rat prostatic tissue were significantly decreased by 60% and 44% compared to control tissue. Serum LH concentrations were unchanged in the 22-oxime-treated group compared to the control group. This indicates that the reduction in androgen concentrations in animals treated with this compound is not due to its influence on pituitary feedback mechanisms which result in reduced LH secretion. These results suggest that 22-oxime is effective in reducing androgen synthesis through the inhibition of 17 alpha-hydroxylase, C17,20-lyase, and 5 alpha-reductase both in vitro and in vivo.

Pharmacology of novel steroidal inhibitors of cytochrome P450(17) alpha (17 alpha-hydroxylase/C17-20 lyase)

Medical or surgical castration for the treatment of prostatic cancers prevents androgen production by the testes, but not by the adrenals. Inhibition of the key enzyme for androgen biosynthesis, cytochrome P450(17) alpha, could prevent androgen production from both sources. The in vivo effects of 17-(3-pyridyl)androsta-5,16-dien-3 beta-ol (CB7598) and 17-(3-pyridyl)androsta-5,16-dien-3-one (CB7627), novel potent steroidal inhibitors of this enzyme, on WHT mice were compared with those of castration and two clinically active compounds, ketoconazole and flutamide. Flutamide and surgical castration caused significant reductions in the weights of the ventral prostate and seminal vesicles. CB7598, in its 3 beta-O-acetate form (CB7630), and CB7627 caused significant reductions in the weights of the ventral prostate, seminal vesicles, kidneys and testes when administered once daily for 2 weeks. Ketoconazole, given on the same schedule, caused no reductions. Plasma testosterone was reduced to < or = 0.1 nM by CB7630, despite a 3- to 4-fold increase in the plasma level of luteinizing hormone. Adrenal weights were unchanged following treatment with CB7630 or CB7627 but were markedly increased following ketoconazole, indicating no inhibition of corticosterone production by these steroidal compounds. These results indicate that CB7598, CB7630 or CB7627 may be useful in the treatment of hormone-dependent prostatic cancers.