Mechanism of antiandrogen action: Conformational changes of the receptor

doi:10.1016/0303-7207(94)90112-0

Molecular and Cellular Endocrinology

Volume 102, Issues 1–2, June 1994, Pages R1-R5

https://doi.org/10.1016/0303-7207(94)90112-0 Get rights and content

Abstract

Androgen receptor mRNA was translated in vitro, and androgen- and antiandrogen-bound receptor complexes were studied using limited proteolytic digestion by trypsin. Partial proteolysis of androgen-bound receptor protein resulted in a 29-kDa proteolysis-resisting fragment, whereas antiandrogen binding stabilised a 35-kDa fragment. Both fragments contain the entire ligand binding domain, and the 35-kDa fragment extended into the hinge region of the receptor. Several antiandrogens show agonistic properties for a mutated androgen receptor (LNCaP cell variant); trypsin digestion of antiandrogen-bound mutated receptor also resulted in a 29-kDa fragment. Our results point to an important difference between antiandrogens and antagonists of other steroid hormone receptors. Antiandrogens result in protection of both the hinge region and C-terminus of the androgen receptor against proteolytic attack, whereas other studies showed that antiestrogens and antiprogestagens expose the C-terminal end of the ligand binding domain of their respective receptors to protease. Differences in conformation of the hinge region distinguish androgen-bound from antiandrogen-bound receptor complexes, which represents an important feature of antiandrogen action.

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Cited by (56)

Disruptors of Androgen Action and Synthesis
2021, Endocrine Disruption and Human Health
Various environmental chemicals have been found to exert antiandrogenic effects in exposed animals, and there is a concern that such compounds may also result in adverse effects in humans. Attempts to elucidate potential mechanisms of antiandrogenic action require knowledge of the functions of androgens in the body and the various ways in which environmental chemicals may disrupt these functions. Environmental antiandrogens may compete with the endogenous androgens testosterone and dihydrotestosterone (DHT) for the androgen receptor (AR), thus blocking its intracellular signaling pathway, which is responsible for the majority of androgenic functions. Other disruptions of androgen function may be caused by inhibition of androgen biosynthesis via catalytic inhibition of key steroidogenic enzymes. Two important enzymes that can be targets for environmental chemicals are cytochrome P450 17-mediated steroid 17α-hydroxylase/17,20-lyase and steroid 5α-reductase activity, which are responsible for the production of the precursor C19-steroids dehydroepiandrosterone (DHEA) and androstenedione, and the conversion of testosterone to its more potent androgenic metabolite DHT, respectively. Various environmental chemicals, most notably pesticides, such as the DDT metabolite p,p-DDE, and fungicides, such as vinclozolin, procymidone, and prochloraz, have been identified to act via several of these antiandrogenic mechanisms to cause reproductive malformations in male rats exposed either in utero or in adult life. In addition to in vivo models to screen for proandrogenic or antiandrogenic compounds (rodent Hershberger assay), several in vitro cell bioassays have been developed for the rapid, mechanism-based screening of disruptors of androgen action either at the level of AR signaling (LNCaP human prostate cancer cells or various reporter-gene systems) or at the level of steroidogenesis (H295R human adrenocortical carcinoma cells). Interestingly, very few, if any, environmental chemicals have been found to act as androgen mimics, in contrast to the many compounds found to act as estrogens in the environment. The consequences of human exposure to environmental levels of antiandrogens remains unclear.
Therapeutic targeting of the androgen receptor (AR) and AR variants in prostate cancer
2020, Asian Journal of Urology
Citation Excerpt :
The reason why the AR-LBD crystal structure could not be resolved and what is unique about the AR-LBD that prevents its structural elucidation, remains important unanswered questions. The only information that is currently available comes from limited trypsinization studies and cofactor-interaction profiling that indicate that the AR conformation in the presence of agonists and antagonists is distinct [79,80]. Similar to the other hormone receptor LBD domains, AR-LBD is also comprised of an α-helical structure.
Prostate cancer (PCa) accounted for over 300 000 deaths world-wide in 2018. Most of the PCa deaths occurred due to the aggressive castration-resistant PCa (CRPC). Since the androgen receptor (AR) and its ligands contribute to the continued growth of androgen-dependent PCa (ADPCa) and CRPC, AR has become a well-characterized and pivotal therapeutic-target. Although AR signaling was identified as therapeutic-target in PCa over five-decades ago, there remains several practical issues such as lack of antagonist-bound AR crystal structure, stabilization of the AR in the presence of agonists due to N-terminus and C-terminus interaction, unfavorable large-molecule accommodation of the ligand-binding domain (LBD), and generation of AR splice variants that lack the LBD that impede the discovery of highly potent fail-safe drugs. This review summarizes the AR-signaling pathway targeted therapeutics currently used in PCa and the approaches that could be used in future AR-targeted drug development of potent next-generation molecules. The review also outlines the discovery of molecules that bind to domains other than the LBD and those that inhibit both the full length and splice variant of ARs.
Reproductive and nonreproductive actions of testosterone
2018, Encyclopedia of Endocrine Diseases
Testosterone is an important regulator of male sexual differentiation, reproductive and nonreproductive behaviors, development of secondary sex characteristics, spermatogenesis, muscle and bone mass, erythropoiesis, and metabolism. Testosterone may exert its biologic effects directly by itself or indirectly through its conversion to its two major metabolites: 5α dihydrotestosterone (DHT) and estradiol 17β. The beneficial effects of testosterone on bone resorption, high-density lipoprotein cholesterol, atherosclerosis progression, sexual desire, and fat mass require its conversion by CYP19A1 (aromatase) to estradiol 17β. Conversion of testosterone to DHT by a family of steroid 5α-reductase enzymes is obligatory for mediating its effects on the differentiation of the urogenital sinus and the genital tubercle. Testosterone׳s conversion to DHT also is believed to mediate its effects on hair growth, scalp hair loss, prostate growth, and acne; however, it is not clear whether this conversion is obligatory for mediating its effects on the prostate, skin, and the hair follicle. Testosterone׳s conversion to DHT is not required for testosterone׳s effects on muscle and bone, plasma lipids, and erythropoiesis.
Design, synthesis and biological evaluation of novel 5-oxo-2-thioxoimidazolidine derivatives as potent androgen receptor antagonists
2015, European Journal of Medicinal Chemistry
Citation Excerpt :
In many cases the resistance is strongly associated with the pull of point mutations occurred predominantly in androgen binding site leading to the aberrant receptor up-regulation and higher sensitivity rather than down-regulation and relaxation upon antiandrogen therapy. It should be noted that AR agonists and AR antagonists share different modes of action towards the related transcriptional machinery inducing the “closed” and “open” conformations of AR-H12 helix [17–19]. Therefore, even minor modifications in the structure of a small molecule AR ligand can lead to dramatic alterations in the receptor–ligand interaction thereby providing opposite pharmacological responses.
A series of novel highly active androgen receptor (AR) antagonists containing spiro-4-(5-oxo-3-phenyl-2-thioxoimidazolidin-1-yl)-2-(trifluoromethyl)benzonitrile core was designed based on the SAR studies available from the reported AR antagonists and in silico modeling. Within the series, compound (R)-6 (ONC1–13B) and its related analogues, including its active N-dealkylated metabolite, were found to be the most potent molecules with the target activity (IC₅₀, androgen-sensitive human PCa LNCaP cells) in the range of 59–80 nM (inhibition of PSA production). The disclosed hits were at least two times more active than bicalutamide, nilutamide and enzalutamide within the performed assay. Several compounds were classified as partial agonists. Hit-compounds demonstrated benefit pharmacokinetic profiles in rats. Comparative SAR and 3D molecular docking studies were performed for the hit compounds elucidating the observed differences in the binding potency.
Disruptors of Androgen Action and Synthesis
2015, Endocrine Disruption and Human Health
Various environmental chemicals have been found to exert antiandrogenic effects in exposed animals and there is a concern that such compounds may also result in adverse effects in humans. Attempts to elucidate potential mechanisms of antiandrogenic action require knowledge of the functions of androgens in the body and the various ways in which environmental chemicals may disrupt these functions. Environmental antiandrogens may compete with the endogenous androgens testosterone and dihydrotestosterone (DHT) for the androgen receptor (AR), thus blocking its intracellular signaling pathway, which is responsible for the majority of androgenic functions. Other disruptions of androgen function may be caused by inhibition of androgen biosynthesis via catalytic inhibition of key steroidogenic enzymes. Two important enzymes that can be targets for environmental chemicals are cytochrome P450 17-mediated steroid 17α-hydroxylase/17,20-lyase and steroid 5α-reductase activity, which are responsible for the production of the precursor C19-steroids dehydroepiandrosterone (DHEA) and androstenedione, and the conversion of testosterone to its more potent androgenic metabolite DHT, respectively. Various environmental chemicals, most notably pesticides, such as the DDT metabolite p,p-DDE, and fungicides, such as vinclozolin, procymidone, and prochloraz, have been identified to act via several of these antiandrogenic mechanisms to cause reproductive malformations in male rats exposed either in utero or in adult life. In addition to in vivo models to screen for proandrogenic or antiandrogenic compounds (rodent Hershberger assay), several in vitro cell bioassays have been developed for the rapid, mechanism-based screening of disruptors of androgen action either at the level of AR signaling (LNCaP human prostate cancer cells or various reporter-gene systems) or at the level of steroidogenesis (H295R human adrenocortical carcinoma cells). Interestingly, very few if any environmental chemicals have been found to act as androgen mimics, in contrast to the many compounds found to act as estrogens in the environment. The consequences of human exposure to environmental levels of antiandrogens remains unclear.
Evolution of prostatic normal cell to hormonodependent-hormonoindependent prostatic cancerous cell
2008, Medecine Nucleaire
La glande prostatique est androgénodépendante. L’implication des androgènes dans le développement, la fonction et la pathologie de la glande prostatique (hypertrophie bénigne ou HBP, cancer), peut être examinée de deux manières : Soit au travers de données directes, issues des modèles expérimentaux (in vitro–in vivo) ou de l’analyse biologique des tissus prostatiques humains normaux et pathologiques qui permettent de décrire les mécanismes moléculaires, cellulaires et tissulaires mis en jeu ; soit au travers de données indirectes issues des études épidémiologiques et cliniques, de suppression, ou supplémentation androgénique décrivant l’impact sur la glande prostatique. Sur le plan expérimental, il est généralement admis que la croissance de la prostate est régulée par les androgènes (testostérone et ses métabolites actifs). Un niveau approprié de testostérone circulante est nécessaire pour maintenir la croissance, le développement, la différenciation et la fonction de la glande prostatique. L’orchidectomie bilatérale induit la mort cellulaire programmée (apoptose) et l’involution de la glande ; l’administration de testostérone exogène est alors capable d’induire la croissance prostatique jusqu’au niveau normal. Il en va de même lorsqu’on traite un animal impubère. La réponse de la prostate à la testostérone exogène ne produit donc pas une croissance au-delà du volume normal qui est maintenu par l’équilibre entre prolifération et mort cellulaire en présence de niveaux physiologiques d’androgènes. L’étude des mécanismes de régulation de la croissance prostatique donne une justification fondamentale aux traitements médicamenteux et hormonaux utilisés par les urologues dans le traitement de l’HBP du cancer de prostate. Dans le cadre du déficit androgénique lié à l’âge (DALA), il persiste un doute sur une action potentiellement néfaste du traitement androgénique substitutif sur la prostate.
The prostatic gland is androgen-dependent. The role of androgens in the development, function and pathology of the prostatic gland (benign hypertrophy or cancer) derives from: direct evidence, resulting from experimental models (in vitro–in vivo) or from the biological analysis of normal and pathological human prostatic tissues. These data make it possible to describe the current point of our knowledge concerning the molecular, cellular, and tissular mechanisms involved; indirect data resulting from epidemiologic and clinical studies describing the impact of androgen suppression or supplementation on the prostatic gland. At the experimental level, it is generally allowed that the growth of prostate is controlled by androgens (testosterone and its metabolites). A suitable circulating testosterone level is necessary to maintain the growth, development, differentiation and function of the prostatic gland. Bilateral orchidectomy induces programmed cellular death (apoptosis) and the gland involution; exogenic testosterone administration is then able to induce the prostatic growth up to the normal level. The same applies when an impubescent animal is treated. The response of prostate to exogenic testosterone thus does not produce a growth beyond the normal volume, which is maintained by balance between proliferation and cellular death in the presence of physiological levels of androgens. The study of the mechanisms of regulation of the prostatic growth provides a fundamental justification to the chemical and hormonal treatments used by the urologists in the treatment of prostate benign hypertophy and cancer. Within the framework of the androgenic deficit related to age, a doubt persists about a potentially harmful action of the substitute androgenic treatment on prostate.

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Rapid paperMechanism of antiandrogen action: Conformational changes of the receptor

Abstract

J. Biol. Chem.

J. Steroid Biochem.

J. Steroid Biochem. Mol. Biol.

Cell

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Rapid paper
Mechanism of antiandrogen action: Conformational changes of the receptor