Synthesis of potent, substituted carbazoles as selective androgen receptor modulators (SARMs)

The synthesis and in vitro binding affinity for a novel series of potent androgen receptor modulators is described. One of the more potent compounds (17, RAD35010) was further characterized in vivo where it restored levator ani weight in castrated male rats to near sham level while having no significant effect on prostate weight.     

Design and synthesis of tricyclic tetrahydroquinolines as a new series of nonsteroidal selective androgen receptor modulators (SARMs)

Some tricyclic tetrahydroquinolines (THQs) were found to have the potential of a new series of nonsteroidal selective androgen receptor modulators (SARMs). Compound 5b was first designed and synthesized under our hypothesis based on a four-point pharmacophoric requirement of the 3-carbonyl, 18-methyl, 17-hydroxyl, and 13-quaternary carbon groups of dihydrotestosterone (DHT). It was revealed that this compound exhibits not only a strong androgen receptor (AR) agonistic activity (EC₅₀ = 9.2 nM) but also the highest selectivity in binding affinity to AR among the steroid hormone receptors. Furthermore, this compound showed a weak virilizing effect with retention of the desired anabolic effect as compared with DHT in vivo.     

Novel, non-steroidal, selective androgen receptor modulators (SARMs) with anabolic activity in bone and muscle and improved safety profile

A novel approach to the treatment of osteoporosis in men, and possibly women, is the development of selective androgen receptor modulators (SARMs) that can stimulate formation of new bone with substantially diminished proliferative activity in the prostate, as well as reduced virilizing activity in women. Over the last several years, we have developed a program to discover and develop novel, non-steroidal, orally-active selective androgen receptor modulators (SARMs) that provide improved therapeutic benefits and reduce risk and side effects. In recent studies, we have used a skeletally mature orchiectomized (ORX) male rat as an animal model of male hypogonadism for assessing the efficacy of LGD2226, a nonsteroidal, non-aromatizable, and non-5alpha-reducible SARM. We assessed the activity of LGD2226 on bone turnover, bone mass and bone strength, and also evaluated the effects exerted on classic androgen-dependent targets, such as prostate, seminal vesicles and muscle. A substantial loss of bone density was observed in ORX animals, and this loss was prevented by SARMs, as well as standard androgens. Biochemical markers of bone turnover revealed an early increase of bone resorption in androgen-deficient rats that was repressed in ORX animals treated with the oral SARM, LGD2226, during a 4-month treatment period. Differences in architectural properties and bone strength were detected by histomorphometric and mechanical analyses, demonstrating beneficial effects of LGD2226 on bone quality in androgen-deficient rats. Histomorphometric analysis of cortical bone revealed distinct anabolic activity of LGD2226 in periosteal bone. LGD2226 was able to prevent bone loss and maintain bone quality in ORX rats by stimulating bone formation, while also inhibiting bone turnover. LGD2226 also exerted anabolic activity on the levator ani muscle. Taken together, these results suggest that orally-active, non-steroidal SARMs may be useful therapeutics for both muscle and bone in elderly hypogonadal men through their anabolic activities. Since SARMs both prevent bone loss, and also stimulate formation of new bone, they may have significant advantages relative to currently used anti-resorptive therapies. Coupled with their activity in muscle and their ability to maintain or restore libido, they offer new therapeutic approaches for male and female hormone replacement.     

Synthesis of potent and tissue-selective androgen receptor modulators (SARMs): 2-(2,2,2)-Trifluoroethyl-benzimidazole scaffold

The synthesis and in vivo SAR of 2-(2,2,2)-trifluoroethyl-benzimidazoles are described. Prostate antagonism and/or levator ani agonism can be modulated by varying the substitution at the 2-position of 5,6-dichloro-benzimidazoles. Potent androgen agonists on the muscle were discovered that strongly bind to the androgen receptor (2-17 nM) and show potent in vivo efficacy (0.03-0.11 mg/day). True SARMs showing both prostate antagonism and levator ani agonism were revealed.     

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.     

Tetrahydroquinoline-based selective estrogen receptor modulators (SERMs)

A new series of estrogen receptor ligands based on a 6-hydroxy-tetrahydroquinoline scaffold is described, in addition to their binding affinity and functional activity in MCF-7 cells. Several 1,2-disubstituted tetrahydroquinolines bearing a basic side chain were shown to be high affinity ligands and antagonists in the MCF-7 proliferation assay. Compounds lacking the basic side chain were agonists in the MCF-7 assay.     

The androgen receptor (AR) in syndromes of androgen insensitivity and in prostate cancer

The actions of androgens, principally testosterone and 5alpha-dihydrotestosterone, are mediated by a specific receptor protein, the androgen receptor (AR), which is encoded by a single-copy gene located on the human X-chromosome. This receptor protein is a prototypical member of the nuclear receptor family and modulates a range of processes during embryogenesis and in the adult. During embryogenesis, normal AR function is critical to the development of the male phenotype and defects of the AR cause a range of phenotypic abnormalities of male sexual development. Complete loss of AR function has been traced to a number of distinct types of genetic events, including abnormalities of mRNA splicing, the introduction of premature termination codons, and amino acid substitution mutations. An interesting subset of mutations is that in which the AR is completely undetectable using sensitive immunoassays. In all instances, these functional abnormalities are associated with a phenotype of complete androgen insensitivity (complete testicular feminization). By contrast, partial defects of AR function are almost invariably caused by amino acid substitutions within the DNA- and hormone-binding domains of the receptor protein. Such partial defects of receptor function may be caused by changes in either receptor function or receptor abundance.The alterations of AR function and expression that have been characterized in clinical prostatic cancers and in prostate cancer cell lines differ in several important respects. A number of studies have documented the emergence of considerable heterogeneity of AR expression at early stages in the development of prostate cancer. Despite these early changes of AR expression, a substantial body of information suggests that the AR is expressed in advanced forms of prostate cancer, in some cases as the result of amplification events. While infrequent in localized tumors, mutations of the AR have been identified in a number of advanced prostatic cancers and in some instances appear to alter the ligand specificity of the AR. Finally, it appears that other signaling pathways can act to influence AR function.     

Serendipitous discovery of novel imidazolopyrazole scaffold as selective androgen receptor modulators

A novel imidazolopyrazole derivative has been fortuitously discovered as potent selective androgen receptor modulator with in vivo efficacy.     

Synthesis and SAR of novel hydantoin derivatives as selective androgen receptor modulators

A novel series of hydantoin derivatives were identified by in vivo studies as tissue selective androgen receptor modulators. SAR around this series revealed that the function of the ligand could be altered by minor structural modification.     

Facile radiosynthesis of new carbon-11-labeled propanamide derivatives as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging

The androgen receptor (AR) is an attractive target for the treatment and molecular imaging of prostate cancer. New carbon-11-labeled propanamide derivatives were first designed and synthesized as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging using the biomedical imaging technique positron emission tomography (PET). The target tracers, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-[¹¹C]methoxyphenoxy)-2-methylpropanamide ([¹¹C]8a), (S)-2-hydroxy-3-(2-[¹¹C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([¹¹C]8e), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2-methylpropanamide ([¹¹C]8c) and (S)-2-hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([¹¹C]8g), were prepared by O-[¹¹C]methylation of their corresponding precursors, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methylpropanamide (9a), (S)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (9b), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methylpropanamide (9c) and (S)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (9d), with [¹¹C]CH₃OTf under basic conditions and isolated by a simplified C-18 solid-phase extraction (SPE) method in 55 ± 5% (n = 5) radiochemical yields based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 277.5 ± 92.5 GBq/μmol (n = 5).     

Alterations of androgen receptor in prostate cancer

The significance of androgens in the development of prostate cancer has been known for more than half century. During the last decade, a lot of effort has been put to study the significance of the specific nuclear receptor of the hormone, androgen receptor (AR). It has been suggested that polymorphisms, especially the length of CAG repeat in exon 1 of the gene, are associated with the risk of prostate cancer. However, not all studies have confirmed the association. Most surprisingly, it has now become clear that prostate carcinomas emerging during the androgen withdrawal therapy (i.e. hormone-refractory tumors) are capable of reactivating the AR-mediated signalling despite of the low levels of androgens. In addition, it has been shown that AR gene itself is genetically targeted. One-third of the hormone-refractory prostate carcinomas contains amplification of the gene. In addition, 10-30% of prostate carcinomas treated by antiandrogens acquire point mutation in the AR gene. The genetic alterations in AR indicate that receptor should be considered as putative treatment target. Evidently, the currently available antiandrogens are not capable to abolish the AR-mediated signalling efficiently enough.     

Novel selective androgen receptor modulators: SAR studies on 6-bisalkylamino-2-quinolinones

A series of selective androgen receptor modulators (SARMs) with a wide spectrum of receptor modulating activities was developed based on optimization of the 4-substituted 6-bisalkylamino-2-quinolinones (3). Significance of the trifluoromethyl group on the side chains and its interactions with amino acid residues within the androgen receptor (AR) ligand binding domain are discussed. A representative analog (9) was tested orally in a rodent model of hypogonadism and demonstrated desirable tissue selectivity.     

Effect of B-ring substitution pattern on binding mode of propionamide selective androgen receptor modulators

Selective androgen receptor modulators (SARMs) are essentially prostate sparing androgens, which provide therapeutic potential in osteoporosis, male hormone replacement, and muscle wasting. Herein we report crystal structures of the androgen receptor (AR) ligand-binding domain (LBD) complexed to a series of potent synthetic nonsteroidal SARMs with a substituted pendant arene referred to as the B-ring. We found that hydrophilic B-ring para-substituted analogs exhibit an additional region of hydrogen bonding not seen with steroidal compounds and that multiple halogen substitutions affect the B-ring conformation and aromatic interactions with Trp741. This information elucidates interactions important for high AR binding affinity and provides new insight for structure-based drug design.     

Calpain-mediated androgen receptor breakdown in apoptotic prostate cancer cells

Since androgen receptor (AR) plays an important role in prostate cancer development and progression, androgen-ablation has been the frontline therapy for treatment of advanced prostate cancer even though it is rarely curative. A curative strategy should involve functional and structural elimination of AR from prostate cancer cells. We have previously reported that apoptosis induced by medicinal proteasome-inhibitory compound celastrol is associated with a decrease in AR protein levels. However celastrol-stimulated events contributing to this AR decrease have not been elucidated. Here, we report that a variety of chemotherapeutic agents, including proteasome inhibitors, a topoisomerase inhibitor, DNA-damaging agents and docetaxel that cause cell death, decrease AR levels in LNCaP prostate cancer cells. This decrease in AR protein levels was not due to the suppression of AR mRNA expression in these cells. We observed that a proteolytic activity residing in cytosol of prostate cancer cells is responsible for AR breakdown and that this proteolytic activity was stimulated upon induction of apoptosis. Interestingly, proteasome inhibitor celastrol- and chemotherapeutic drug VP-16-stimulated AR breakdown was attenuated by calpain inhibitors calpastatin and N-acetyl-L-leucyl-L-leucyl-L-methioninal. Furthermore, AR proteolytic activity pulled down by calmodulin-agarose beads from celastrol-treated PC-3 cells showed immunoreactivity to a calpain antibody. Taken together, these results demonstrate calpain involvement in proteasome inhibitor-induced AR breakdown, and suggest that AR degradation is intrinsic to the induction of apoptosis in prostate cancer cells.     

The androgen receptor: a potential target for therapy of prostate cancer

The androgen receptor plays a pivotal role in the prostate. Its primary function is to provide responsive gene products for differentiation and growth, but under abnormal conditions it contributes to the development of prostate cancer. The goal of this review is to elucidate the molecular functions of the androgen receptor and its role in prostate cancer. Initially the function of the androgen receptor will be described. Next, the clinical diagnosis, epidemiological impact, and treatments of androgen-dependent and -independent prostate cancer will be discussed. Finally we will examine how the mechanism of androgen action has played a role in the translation of new therapies and how this may influence future treatment modalities of prostate cancer.