Pharmacology, pharmacokinetics, and metabolism of acetothiolutamide, a novel nonsteroidal agonist for the androgen receptor

Medicinal Use of Testosterone and Related Steroids Revisited

Testosterone derivatives and related compounds (such as anabolic-androgenic steroids—AAS) are frequently misused by athletes (both professional and amateur) wishing to promote muscle development and strength or to cover AAS misuse. Even though these agents are vastly regarded as abusive material, they have important pharmacological activities that cannot be easily replaced by other drugs and have therapeutic potential in a range of conditions (e.g., wasting syndromes, severe burns, muscle and bone injuries, anemia, hereditary angioedema). Testosterone and related steroids have been in some countries treated as controlled substances, which may affect the availability of these agents for patients who need them for therapeutic reasons in a given country. Although these agents are currently regarded as rather older generation drugs and their use may lead to serious side-effects, they still have medicinal value as androgenic, anabolic, and even anti-androgenic agents. This review summarizes and revisits the medicinal use of compounds based on the structure and biological activity of testosterone, with examples of specific compounds. Additionally, some of the newer androgenic-anabolic compounds are discussed such as selective androgen receptor modulators, the efficacy/adverse-effect profiles of which have not been sufficiently established and which may pose a greater risk than conventional androgenic-anabolic agents.

Synthesis, biological evaluation and X-ray analysis of bicalutamide sulfoxide analogues for the potential treatment of prostate cancer

The androgen receptor (AR) is a pivotal target for the treatment of prostate cancer (PC) even when the disease progresses toward androgen-independent or castration-resistant forms. In this study, a series of sulfoxide derivatives were prepared and their antiproliferative activity evaluated in vitro against four different human prostate cancer cell lines (22Rv1, DU-145, LNCaP and VCap). Bicalutamide and enzalutamide were used as positive controls. Compound 28 displayed significant enhancement in anticancer activity across the four PC cell lines with IC₅₀ = 9.09 - 31.11 µM compared to the positive controls: bicalutamide (IC₅₀ = 45.20 -51.61 µM) and enzalutamide (IC₅₀ = 11.47 - 53.04 µM). Sulfoxide derivatives of bicalutamide were prepared efficiently from the corresponding sulfides using only one equivalent of mCPBA, limiting the reaction time to 15-30 min and maintaining the temperature at 0 °C. Interestingly, three pairs of sulfoxide diastereomers were separated and NMR comparison of their diastereotopic methylene (CH₂) group is presented. X-ray diffraction crystal structure analysis provided relative configuration assignment at the chiral sulfur and carbon centres. Molecular modelling study of the four diastereoisomers of compound 28 is described.

Preclinical pharmacology of FL442, a novel nonsteroidal androgen receptor modulator

The preclinical profiles of two most potent compounds of our recently published cycloalkane[d]isoxazole pharmacophore-based androgen receptor (AR) modulators, FL442 (4-(3a,4,5,6,7,7a-hexahydro-benzo[d]isoxazol-3-yl)-2-(trifluoromethyl)benzonitrile) and its nitro analog FL425 (3-(4-nitro-3-(trifluoromethyl)phenyl)-3a,4,5,6,7,7a-hexahydrobenzo[d]isoxazole), were explored to evaluate their druggability for the treatment of AR dependent prostate cancer. The studies revealed that both compounds are selective to AR over other closely related steroid hormone receptors and that FL442 exhibits equal inhibition efficiency towards the androgen-responsive LNCaP prostate cancer cell line as the most widely used antiandrogen bicalutamide and the more recently discovered enzalutamide. Notably, FL442 maintains antiandrogenic activity with enzalutamide-activated AR mutant F876L. In contrast to bicalutamide, FL442 does not stimulate the VCaP prostate cancer cells which express elevated levels of the AR. Distribution analyses showed that [(14)CN]FL442 accumulates strongly in the mouse prostate. In spite of its low plasma concentration obtained by intraperitoneal administration, FL442 significantly inhibited LNCaP xenograft tumor growth. These findings provide a preclinical proof for FL442 as a promising AR targeted candidate for a further optimization.

Trafficking of drug candidates relevant for sports drug testing: detection of non-approved therapeutics categorized as anabolic and gene doping agents in products distributed via the Internet

Identifying the use of non-approved drugs by cheating athletes has been a great challenge for doping control laboratories. This is due to the additional complexities associated with identifying relatively unknown and uncharacterized compounds and their metabolites as opposed to known and well-studied therapeutics. In 2010, the prohibited drug candidates and gene doping substances AICAR and GW1516, together with the selective androgen receptor modulator (SARM) MK-2866 were obtained by the Cologne Doping Control Laboratory from Internet suppliers and their structure, quantity, and formulation elucidated. All three compounds proved authentic as determined by liquid chromatography-high resolution/high accuracy (tandem) mass spectrometry and comparison to reference material. While AICAR was provided as a colourless powder in 100 mg aliquots, GW1516 was obtained as an orange/yellow suspension in water/glycerol (150 mg/ml), and MK-2866 (25 mg/ml) was shipped dissolved in polyethylene glycol (PEG) 300. In all cases, the quantified amounts were considerably lower than indicated on the label. The substances were delivered via courier, with packaging identifying them as containing 'amino acids' and 'green tea extract', arguably to circumvent customs control. Although all of the substances were declared 'for research only', their potential misuse in illicit performance-enhancement cannot be excluded; moreover sports drug testing authorities should be aware of the facile availability of black market copies of these drug candidates.

Nonsteroidal selective androgen receptor modulators enhance female sexual motivation

Women experience a decline in estrogen and androgen levels after natural or surgically induced menopause, effects that are associated with a loss of sexual desire and bone mineral density. Studies in our laboratories have shown the beneficial effects of selective androgen receptor modulators (SARMs) in the treatment of osteoporosis and muscle wasting in animal models. A series of S-3-(phenoxy)-2-hydroxy-2-methyl-N-(4-cyano-3-trifluoromethyl-phenyl)-propionamide analogs was synthesized to evaluate the effects of B-ring substitutions on in vitro and in vivo pharmacologic activity, especially female sexual motivation. The androgen receptor (AR) relative binding affinities ranged from 0.1 to 26.5% (relative to dihydrotestosterone) and demonstrated a range of agonist activity at 100 nM. In vivo pharmacologic activity was first assessed by using male rats. Structural modifications to the B-ring significantly affected the selectivity of the SARMs, demonstrating that single-atom substitutions can dramatically and unexpectedly influence activity in androgenic (i.e., prostate) and anabolic (i.e., muscle) tissues. (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro,4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide (S-23) displayed full agonist activity in androgenic and anabolic tissues; however, the remaining SARMs were more prostate-sparing, selectively maintaining the size of the levator ani muscle in castrated rats. The partner-preference paradigm was used to evaluate the effects of SARMs on female sexual motivation. With the exception of two four-halo substituted analogs, the SARMs increased sexual motivation in ovariectomized rats, with potency and efficacy comparable with testosterone propionate. These results indicate that the AR is important in regulating female libido given the nonaromatizable nature of SARMs and it could be a superior alternative to steroidal testosterone preparations in the treatment of hypoactive sexual desire disorder.

[Myoanabolic steroids and selective androgen receptor modulators: mechanism of action and perspectives]

Interest in anabolic steroids has been renewed in the last decade with the discovery of tissue-selective androgen receptor modulators exhibiting high myotropic and small androgenic activity. An explanation put forward by us in 1982 for the mechanism of the preferential myotropic effect of nandrolone (19-nortestosterone) exploits the fundamental difference between the 5alpha-reductase concentrations in skeletal muscle and androgenic target tissue. In androgenic tissue, testosterone is converted to the more potent 5alpha-dihydrotestosterone whereas nandrolone is converted to a less potent derivative. As 5alpha-reduction is negligible in skeletal muscle, this explains why nandrolone shows a greater myotropic to androgenic ratio when compared with testosterone. Anabolic steroids that do not undergo 5alpha-reduction exert myotropic-androgenic dissociation because their effect in androgenic tissues is not amplified by 5alpha-reduction. Tissue selectivity by receptor modulators may be achieved by inducing specific conformational changes of the androgen receptor that affect its interaction with transcriptional coregulators. Anabolic activity is mediated by the stimulation of ribosomal RNA synthesis therefore regulation of this synthesis by anabolic steroids would deserve detailed studies.

Selective androgen receptor modulators in preclinical and clinical development

Androgen receptor (AR) plays a critical role in the function of several organs including primary and accessory sexual organs, skeletal muscle, and bone, making it a desirable therapeutic target. Selective androgen receptor modulators (SARMs) bind to the AR and demonstrate osteo- and myo-anabolic activity; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents produce less of a growth effect on prostate and other secondary sexual organs. SARMs provide therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, or end-stage renal disease, osteoporosis, frailty, and hypogonadism. This review summarizes the current standing of research and development of SARMs, crystallography of AR with SARMs, plausible mechanisms for their action and the potential therapeutic indications for this emerging class of drugs.

Structure-activity relationships of synthetic progestins in a yeast-based in vitro androgen bioassay

The recent identification of tetrahydrogestrinone (THG), a non-marketed designer androgen used for sports doping but previously undetectable by established mass spectrometry-based urine drug screens, and its production by a facile chemical modification of gestrinone has raised concerns about the risks of developing designer androgens from numerous marketed progestins. We therefore have used yeast-based in vitro androgen and progesterone bioassays to conduct a structure-activity study assessing the intrinsic androgenic potential of commercially available progestins and their derivatives, to identify those compounds or structures with the highest risk of forming a basis for such misapplication. Progestins had a wide range of androgenic bioactivity that was not reliably predicted for individual steroids by their progestin bioactivity. 17alpha-Hydroxyprogesterone and 19-norprogesterone derivatives with their bulky 17beta-substituents were strong progestins but generally weak androgens. 17alpha-Ethynylated derivatives of testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone such as gestrinone, ethisterone, norethisterone and norgestrel had the most significant intrinsic androgenicity of all the commercially marketed progestins. Facile chemical modification of the 17alpha-ethynyl group of each of these progestins produces 17alpha-methyl, ethyl and allyl derivatives, including THG and norbolethone, which further enhanced androgenic bioactivity. Thus by using the rapid and sensitive yeast bioassay we have screened a comprehensive set of progestins and associated structures and identified the ethynylated testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone derivatives as possessing the highest risk for abuse and potential for conversion to still more potent androgens. By contrast, modern progestins such as progesterone, 17alpha-hydroxyprogesterone and 19-norprogesterone derivatives had minimal androgenic bioactivity and pose low risk.

Pharmacological characterization of AC-262536, a novel selective androgen receptor modulator

Because of the limitations and liabilities of current testosterone therapies, non-steroidal tissue-selective androgen receptor modulators may provide a clinically meaningful advance in therapy. Using a functional cell-based assay AC-262536 was identified as a potent and selective AR ligand, with partial agonist activity relative to the natural androgen testosterone. A 2-week chronic study in castrated male rats indicated that AC-262536 significantly improves anabolic parameters in these animals, especially in stimulating the growth of the levator ani and in suppressing elevated LH levels. In sharp contrast to testosterone, AC-262536 has weak androgenic effects, as measured by prostate and seminal vesicle weights. Thus, AC-262536 represents a novel class of selective androgen receptor modulators (SARMs) with beneficial anabolic effects.

In Vivo Metabolism and Final Disposition of a Novel Nonsteroidal Androgen in Rats and Dogs

Compound S-4 (S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide) is a novel nonsteroidal androgen agonist that mimics many of the beneficial pharmacologic effects of testosterone with lesser effects on the prostate. S-4 demonstrated high androgen receptor binding affinity as well as anabolic specificity during in vivo pharmacologic studies in rats, identifying it as the first member of a new class of selective androgen receptor modulators. The purpose of these studies was to determine the pharmacokinetics and metabolism of S-4 in dogs. S-4 showed linear pharmacokinetics after both intravenous (i.v.) and oral (p.o.) administrations at pharmacologically relevant doses, with a mean clearance of 4.6 ml/min/kg and a mean half-life of about 200 min. It is interesting that dose-dependent oral bioavailability was seen. However, at pharmacologically relevant doses, the oral bioavailability of S-4 was 91%. Species differences were observed in S-4 metabolism; the major metabolic pathway for S-4 in dogs was deacetylation of the B-ring acetamide group and reduction of the A-ring nitro group, whereas the major metabolic pathway for S-4 in rats was hydrolysis on the amide bond and reduction of the A-ring nitro group. In addition, oxidative metabolites and phase II metabolites were identified in both rats and dogs. These studies demonstrate that S-4 maintains its promising pharmacokinetic properties in dogs (i.e., high oral bioavailability and linear kinetics) and is largely eliminated via hepatic metabolism by both phase I and phase II enzymes.

Synthesis of oxazolidinedione derived bicalutamide analogs

The synthesis of chiral oxazolidinedione derived bicalutamide analogs has been discussed.

Pharmacokinetics and metabolism of a selective androgen receptor modulator in rats: implication of molecular properties and intensive metabolic profile to investigate ideal pharmacokinetic characteristics of a propanamide in preclinical study

S-1 [3-(4-fluorophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide] is one member of a series of potent selective androgen receptor modulators (SARMs) that are being explored and developed for androgen-dependent diseases. Recent studies showed that S-1 holds great promise as a novel therapeutic agent for benign hyperplasia [W. Gao, J. D. Kearbey, V. A. Nair, K. Chung, A. F. Parlow, D. D. Miller, and J. T. Dalton (2004) Endocrinology 145:5420-5428]. We examined the pharmacokinetics and metabolism of S-1 in rats as a component of our preclinical development of this compound and continued interest in structure-activation relationships for SARM action. Forty male Sprague-Dawley rats were randomly assigned to treatment groups and received either an i.v. or a p.o. dose of S-1 at a dose level of 0.1, 1, 10, or 30 mg/kg. S-1 demonstrated a low clearance (range, 3.6-5.2 ml/min/kg), a moderate volume of distribution (range, 1460-1560 ml/kg), and a terminal half-life ranging from 3.6 to 5.2 h after i.v. doses. The oral bioavailability of S-1 ranged from 55% to 60%. Forty phase I and phase II metabolites of S-1 were identified in the urine and feces of male Sprague-Dawley rats dosed at 50 mg/kg via the i.v. route. The two major urinary metabolites of S-1 were a carboxylic acid and a sulfate-conjugate of 4-nitro-3-trifluoromethylphenylamine. Phase I metabolites arising from A-ring nitro reduction to an aromatic amine and B-ring hydroxylation were also identified in the urinary and fecal samples of rats. Furthermore, a variety of phase II metabolites through sulfation, glucuronidation, and methylation were also found. These studies demonstrate that S-1 is rapidly absorbed, slowly cleared, moderately distributed, and extensively metabolized in rats.

In vitro and in vivo structure-activity relationships of novel androgen receptor ligands with multiple substituents in the B-ring

We recently reported two nonsteroidal androgen receptor (AR) ligands that demonstrate tissue-selective pharmacological activity, identifying these S-3-(phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide analogs as the first members of a new class of drugs known as selective androgen receptor modulators. The purpose of these studies was to explore additional structure-activity relationships of selective androgen receptor modulators to enhance their AR binding affinity, AR-mediated transcriptional activation, and in vivo pharmacological activity. The AR binding affinity (K(i)) of 29 novel synthetic AR ligands was determined by a radioligand competitive binding assay and ranged from 1.0-51 nM. Compounds with electron-withdrawing substituents at the para- and meta-positions of the B-ring demonstrated the highest AR binding affinity. The AR-mediated transcriptional activation was determined using a cotransfection assay in CV-1 cells. Most compounds with two substituents in the B-ring maintained or improved their functional activity in vitro. However, compounds with three halogen substituents exhibited significant regioselectivity. Fifteen compounds were selected to examine their pharmacological activity in castrated rats. In vivo pharmacological activity and selectivity were significantly changed by structural modification in the B-ring. Compounds with halogen groups at the para- and meta-positions of the B-ring displayed the highest pharmacological activity. Incorporating substituents at the ortho-position of the B-ring resulted in poor pharmacological activity. In vitro and in vivo agonist activities were partially correlated. In conclusion, novel selective androgen receptor modulators with improved in vivo pharmacological activity can be designed and synthesized based on the structure-activity relationship identified in these studies.

Characterization of the in vitro metabolism of selective androgen receptor modulator using human, rat, and dog liver enzyme preparations

Compound S4 [S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide] is a novel nonsteroidal selective androgen receptor modulator that demonstrates tissue-selective androgenic and anabolic effects. The purpose of this in vitro study was to identify the phase I metabolites, potential species differences in metabolism, and the cytochromes P450 (P450s) involved in the phase I metabolism of S4 using 14C-S4, recombinant P450s, and other liver enzyme preparations from human, rat, and dog. The major phase I metabolism pathways of S4 in humans were identified as deacetylation of the B-ring acetamide group, hydrolysis of the amide bond, reduction of the A-ring nitro group, and oxidation of the aromatic rings, with deacetylation being the predominant pathway observed with most of the enzyme preparations tested. Among the major human P450 enzymes tested, CYP3A4 appeared to be one of the major phase I enzymes that could be responsible for the phase I metabolism of S4 [Km = 16.1 microM, Vmax = 1.6 pmol/(pmol x min)] in humans and mainly catalyzed the deacetylation, hydrolysis, and oxidation of S4. In humans, the cytosolic enzymes mainly catalyzed the hydrolysis reaction, whereas the microsomal enzymes primarily catalyzed the deacetylation reactions. Similar phase I metabolic profiles were observed in rats and dogs as well, except that the amide bond hydrolysis seemed to occur more rapidly in rats. In summary, these results showed that the major phase I reaction of S4 in human, rat, and dog is acetamide group deacetylation.

Interspecies differences in pharmacokinetics and metabolism of S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethylphenyl)-propionamide: the role of N-acetyltransferase

N-Acetyltransferase (NAT) is one of the major phase II enzymes involved in drug metabolism. Both species differences and polymorphism are observed in NAT expression. During the preclinical development of a novel selective androgen receptor modulator, S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide (S4), we also observed species differences in S4 metabolism due to the interaction between the deacetylation metabolite M1 and NAT, which converted M1 back to S4 both in vitro and in vivo. During incubation with human liver cytosol or rat liver S9 fraction in the presence of acetyl-CoA, more than 50% of M1 (2 microM) was converted back to S4, but this conversion was not observed in the incubation with dog liver S9 fraction or human liver microsome. In vivo pharmacokinetic experiments showed that M1 could be rapidly converted back to S4 in rats, but a similar conversion was not observed in dogs. When S4 was administered, the formation of M1 was only observed in dogs due to the absence of NAT expression. Simultaneous fitting of the concentration-time profiles of both S4 and M1 showed that more than 50% of S4 was deacetylated to M1 in dogs after i.v. administration of S4, whereas more than 80% of M1 was converted to S4 in rats after i.v. administration of M1. Considering the polymorphism in NAT expression, the interaction between M1 and NAT may raise concerns for drug-drug interactions during clinical applications of S4. The observed species differences suggested that interspecies scaling might not be applicable for predicting the metabolism and disposition of S4 in humans.

Synthesis of irreversibly binding bicalutamide analogs for imaging studies

A new synthetic methodology for preparing radioactive androgen receptor binding compounds in order to determine receptor-ligands interactions has been developed.

The Para Substituent of S-3-(Phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamides Is a Major Structural Determinant of in Vivo Disposition and Activity of Selective Androgen Receptor Modulators

Selective androgen receptor modulators (SARMs) have many potential therapeutic applications, including male hypogonadism, osteoporosis, muscle-wasting diseases, sexual libido, and contraception. A series of S-3-(phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamides bearing a four-halogen substituent in the B-ring that displayed in vivo activity were identified in our previous study. Interestingly, in vivo pharmacological activity was not correlated with in vitro androgen receptor (AR) binding affinity. In this study, analysis of the area under the concentration-time curve-response relationship demonstrated that the discrepancy between in vitro and in vivo pharmacological activity of these halogen-substituted SARMs was due to differences in systemic exposure rather than intrinsic pharmacological activity. Studies also suggested that two simple criteria (i.e., Ki < 10 nM and lower in vivo clearance) could be used to identify efficacious and potent SARMs. We tested this hypothesis using a series of four compounds incorporating either a nitro or cyano substituent at the para-position of the A- and B-aromatic rings. The S-3-(4-nitrophenoxy) and S-3-(4-cyanophenoxy) 2-hydroxy-2-methyl-N-(4-nitro-3-trifluromethylphenyl) propionamides (S-19 and S-20, respectively) and S-3-(4-nitrophenoxy) and S-3-(4-cyanophenoxy) 2-hydroxy-2-methyl-N-(4-cyano-3-trifluromethylphenyl) propionamides (S-21 and S-22, respectively) demonstrated high AR binding affinity, with Ki values ranging from 2.0 to 3.8 nM. Pharmacokinetic studies of selected compounds showed that the in vivo clearance of S-22 was the slowest followed sequentially by S-20, S-21, and S-19. The dose-response relationships for S-22 showed that S-22 exerted efficacious and selective activity in anabolic tissues at dose rates as low as 0.03 mg/day, indicative of the high potency of this compound in anabolic tissue (relative potency 4.41) and its potential for clinical use in androgen deficiency-related disorders.

Discovery and therapeutic promise of selective androgen receptor modulators

Androgens are essential for male development and the maintenance of male secondary characteristics, such as bone mass, muscle mass, body composition, and spermatogenesis. The main disadvantages of steroidal androgens are their undesirable physicochemical and pharmacokinetic properties. The recent discovery of nonsteroidal selective androgen receptor modulators (SARMs) provides a promising alternative for testosterone replacement therapies with advantages including oral bioavailability, flexibility of structural modification, androgen receptor specificity, tissue selectivity, and the lack of steroid-related side effects.

Comparison of the pharmacological effects of a novel selective androgen receptor modulator, the 5alpha-reductase inhibitor finasteride, and the antiandrogen hydroxyflutamide in intact rats: new approach for benign prostate hyperplasia

Tissue-selective androgen receptor modulators (SARMs) demonstrate tissue selectivity in both castrated and intact male rats, behaving as partial agonists in androgenic tissues (i.e. prostate and seminal vesicle), but full agonists in anabolic tissues (i.e. levator ani muscle). The partial agonist activity of SARMs (compounds S-1 and S-4) in the prostate of intact rats suggested that SARM could be used for androgen suppression in the treatment of benign prostate hyperplasia (BPH). This study was designed to explore the mechanisms of action of SARM and to characterize the tissue selectivity of S-1 in intact male rats compared with that of hydroxyflutamide (antiandrogen) and finasteride (5alpha-reductase inhibitor), two major drugs used for androgen suppression treatment of BPH. In intact male rats, S-1 (5, 10, and 25 mg/kg) selectively decreased the prostate weight with similar efficacy to finasteride (5 mg/kg), without affecting the levator ani muscle or increasing the plasma levels of testosterone, LH, and FSH. Hydroxyflutamide (0.5, 1, 5, 10, and 25 mg/kg), however, decreased both the prostate and levator ani muscle weights without any selectivity and increased plasma hormone levels in a dose-dependent manner. Furthermore, S-1 and S-4 showed very weak inhibitory effects toward transiently expressed type I and II human 5alpha-reductase (Ki, >20 microm) during in vitro assays. Therefore, although S-1 and finasteride showed very similar suppressive effects in the prostate of intact male rats, they decreased prostate size via different mechanisms of action. S-1 simply worked as androgen receptor partial agonist, whereas finasteride inhibited prostatic 5alpha-reductase. These studies indicate that SARMs may demonstrate clinical utility as single agent or combination therapy for BPH.

Favorable effects of weak acids on negative-ion electrospray ionization mass spectrometry

Despite widespread use in pharmacokinetic, drug metabolism, and pesticide residue studies, little is known about the factors governing response during reversed-phase liquid chromatography coupled with negative-ion electrospray ionization (ESI(-)) mass spectrometry. We examined the effects of various mobile-phase modifiers on the ESI(-) response of four selective androgen receptor modulators using a postcolumn infusion system. Acetic, propionic, and butyric acid improved the ESI(-) responses of analytes to varying extents at low concentrations. Formic acid suppressed ionization, as did neutral salts (ammonium formate, ammonium acetate) and bases (ammonium hydroxide, triethylamine) under most conditions. Two modifiers (2,2,2-trifluoroethanol, formaldehyde) that produce anions with high gas-phase proton affinity increased ESI(-) responses. However, the concentrations of these modifiers required to enhance ESI(-) response were higher than that of acidic modifiers, which is a phenomenon likely related to their low pK(a) values. 2,2,2-Trifluoroethanol increased response of more hydrophobic compounds but decreased response of a more hydrophilic compound. Formaldehyde improved response of all the compounds, especially the hydrophilic compound with lower surface activity. In summary, these results suggest that an ideal ESI(-) modifier should provide cations that can be easily electrochemically reduced and produce anions with small molecular volume and high gas-phase proton affinity.

A selective androgen receptor modulator for hormonal male contraception

The recent discovery of nonsteroidal selective androgen receptor modulators (SARMs) provides a promising alternative for testosterone replacement therapies, including hormonal male contraception. The identification of an orally bioavailable SARM with the ability to mimic the central and peripheral androgenic and anabolic effects of testosterone would represent an important step toward the "male pill". We characterized the in vitro and in vivo pharmacologic activity of (S)-3-(4-chloro-3-fluorophenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethylphenyl)propionamide (C-6), a novel SARM developed in our laboratories. C-6 was identified as an androgen receptor (AR) agonist with high AR binding affinity (K(i) = 4.9 nM). C-6 showed tissue-selective pharmacologic activity with higher anabolic activity than androgenic activity in male rats. The doses required to maintain the weight of the prostate, seminal vesicles, and levator ani muscle to half the size of the maximum effects (i.e., ED(50)) were 0.78 +/- 0.06, 0.88 +/- 0.1, and 0.17 +/- 0.04 mg/day, respectively. As opposed to other SARMs, gonadotropin levels in C-6-treated groups were significantly lower than control values. C-6 also significantly decreased serum testosterone concentration in intact rats after 2 weeks of treatment. Marked suppression of spermatogenesis was observed after 10 weeks of treatment with C-6 in intact male rats. Pharmacokinetic studies of C-6 in male rats revealed that C-6 was well absorbed after oral administration (bioavailability 76%), with a long (6.3 h) half-life at a dose of 10 mg/kg. These studies show that C-6 mimicked the in vivo pharmacologic and endocrine effects of testosterone while maintaining the oral bioavailability and tissue-selective actions of nonsteroidal SARMs.

A ligand-based approach to identify quantitative structure-activity relationships for the androgen receptor

We examined the three-dimensional quantitative structure-activity relationship (QSAR) of a group of endogenous and synthetic compounds for the androgen receptor (AR) using comparative molecular field analysis (CoMFA). The goal of these studies was to identify structural features necessary for high binding affinity and optimization of selective androgen receptor modulators (SARMs). A homology model of the AR was used as a scaffold to align six lead compounds that served as templates for alignment of the remaining 116 structures prior to CoMFA modeling. The conventional r(2) and cross-validated q(2) relating observed and predicted relative binding affinity (RBA) were 0.949 and 0.593, respectively. Comparison of predicted and observed RBA for a test set of 10 compounds resulted in an r(2) of 0.954, demonstrating the excellent predictive ability of the model. These integrated homology modeling and CoMFA studies identified critical amino acids for SARM interactions and provided QSAR data as the basis for mechanistic studies of AR structure, function, and design of optimized SARMs.

Design, synthesis, and biological characterization of metabolically stable selective androgen receptor modulators

A series of nonsteroidal ligands were synthesized as second-generation agonists for the androgen receptor (AR). These ligands were designed to eliminate metabolic sites identified in one of our first-generation AR agonists, which was inactive in vivo due to its rapid metabolism to inactive constituents. The binding affinity of these compounds was evaluated using AR isolated from rat ventral prostate. These second-generation compounds bound the AR in a high affinity and stereoselective manner, with K(i) values ranging from about 4 to 130 nM. The ability of these ligands to stimulate AR-mediated transcriptional activation was examined in cells transfected with the human AR and a hormone-dependent luciferase reporter gene. Although some compounds were unable to stimulate AR-mediated transcription, several demonstrated activity similar to that of dihydrotestosterone (DHT, an endogenous steroidal ligand for the AR). We also evaluated the in vivo pharmacologic activity of selected compounds in castrated male rats. Three compounds were identified as selective androgen receptor modulators (SARMs), exhibiting significant anabolic activity while having only moderate to minimal androgenic activity in vivo.

Pharmacodynamics of selective androgen receptor modulators

The present study aimed to identify selective androgen receptor modulators (SARMs) with in vivo pharmacological activity. We examined the in vitro and in vivo pharmacological activity of four chiral, nonsteroidal SARMs synthesized in our laboratories. In the in vitro assays, these compounds demonstrated moderate to high androgen receptor (AR) binding affinity, with K(i) values ranging from 4 to 37 nM, and three of the compounds efficaciously stimulated AR-mediated reporter gene expression. The compounds were then administered subcutaneously to castrated rats to appraise their in vivo pharmacological activity. Androgenic activity was evaluated by the ability of these compounds to maintain the weights of prostate and seminal vesicle, whereas levator ani muscle weight was used as a measure of anabolic activity. The maximal response (E(max)) and dose for half-maximal effect (ED(50)) were determined for each compound and compared with that observed for testosterone propionate (TP). Compounds S-1 and S-4 demonstrated in vivo androgenic and anabolic activity, whereas compounds S-2 and S-3 did not. The activities of S-1 and S-4 were tissue-selective in that both compounds stimulated the anabolic organs more than the androgenic organs. These two compounds were less potent and efficacious than TP in androgenic activity, but their anabolic activity was similar to or greater than that of TP. Neither S-1 nor S-4 caused significant luteinizing hormone or follicle stimulating hormone suppression at doses near the ED(50) value. Thus, compounds S-1 and S-4 were identified as SARMs with potent and tissue-selective in vivo pharmacological activity, and represent the first members of a new class of SARMs with selective anabolic effects.