Antagonism, Androgen receptor

The androgen receptor (AR) and its function

Development of the male reproductive system and secondary male characteristics is dependent on androgens (foremost testosterone (T) and dihydrotestosterone (DHT). T and the more biologically active DHT act by binding to the AR (MacLean et al, 1993; MacLeod et al, 2010; Schwartz et al, 2019), with human AR mutations and mouse knock-out models having established its pivotal role in masculinization and spermatogenesis (Walters et al, 2010). The AR is a ligand-activated transcription factor belonging to the steroid hormone nuclear receptor family (Davey & Grossmann, 2016). The AR has three domains; the N-terminal domain, the DNA-binding domain and the ligand-binding domain, with the latter being most evolutionary conserved. Apart from the essential role AR plays for male reproductive development and function (Walters et al, 2010), the AR is also expressed in many other tissues and organs such as bone, muscles, ovaries and the immune system (Rana et al, 2014). 

AR antagonism as Key Event

The main function of the AR is to activate gene transcription in cells. Canonical signaling occurs by ligands (androgens) binding to AR in the cytoplasm which results in translocation to the cell nucleus, receptor dimerization and binding to specific regulatory DNA sequences (Heemers & Tindall, 2007). The gene targets regulated by AR activation depends on cell/tissue type and what stage of development activation occur, and is, for instance, dependent on available co-factors. Apart from the canonical signaling pathway, AR can also function through non-genomic modalities, for instance rapid change in cell function by ion transport changes (Heinlein & Chang, 2002). However, with regard to this specific KE the canonical signaling pathway is what is referred to.

AR antagonism can be measured in vitro by transient or stable transactivation assays to evaluate nuclear receptor activation. There is already a validated assay for AR (ant)agonism adopted by the OECD, Test No. 458: Stably Transfected Human Androgen Receptor Transcriptional Activation Assay for Detection of Androgenic Agonist and Antagonist Activity of Chemicals (OECD, 2016). The stably transfected AR-EcoScreen^TM cells (Satoh et al, 2004) should be used for the assay and is freely available for the Japanese Collection of Research Bioresources (JCRB) Cell Bank under reference number JCRB1328.

Other assays include the AR-CALUX reporter gene assay that is derived from human U2-OS cells stably transfected with the human AR and an AR responsive reporter gene (van der Burg et al, 2010), various transiently transfected reporter cell lines (Körner et al, 2004), and more.

Recently developed AR dimerization assay may soon be included in TGs for its improved ability to measure potential stressor-mediated dimerization/activation (Lee et al, 2021).

Alapi EM, Fischer J (2006) Table of Selected Analogue Classes. In Analogue-based Drug Discovery, Fischer J, Ganellin CR (eds), p 515. Weinheim: Wiley-VCH Verlag GmbH & Co

Davey RA, Grossmann M (2016) Androgen Receptor Structure, Function and Biology: From Bench to Bedside. Clin Biochem Rev 37: 3-15

Draskau MK, Boberg J, Taxvig C, Pedersen M, Frandsen HL, Christiansen S, Svingen T (2019) In vitro and in vivo endocrine disrupting effects of the azole fungicides triticonazole and flusilazole. Environ Pollut 255: 113309

Foster PM, Harris MW (2005) Changes in androgen-mediated reproductive development in male rat offspring following exposure to a single oral dose of flutamide at different gestational ages. Toxicol Sci 85: 1024-1032

Hass U, Scholze M, Christiansen S, Dalgaard M, Vinggaard AM, Axelstad M, Metzdorff SB, Kortenkamp A (2007) Combined exposure to anti-androgens exacerbates disruption of sexual differentiation in the rat. Environ Health Perspect 115 Suppl. 1: 122-128

Heemers HV, Tindall DJ (2007) Androgen receptor (AR) coregulators: a diversity of functions converging on and regulating the AR transcriptional complex. Endocr Rev 28: 778-808

Heinlein CA, Chang C (2002) The roles of androgen receptors and androgen-binding proteins in nongenomic androgen actions. Mol Endocrinol 16: 2181-2187

Kita DH, Meyer KB, Venturelli AC, Adams R, Machado DL, Morais RN, Swan SH, Gennings C, Martino-Andrade AJ (2016) Manipulation of pre and postnatal androgen environments and anogenital distance in rats. Toxicology 368-369: 152-161

Kjærstad MB, Taxvig C, Nellemann C, Vinggaard AM, Andersen HR (2010) Endocrine disrupting effects in vitro of conazole antifungals used as pesticides and pharmaceuticals. Reprod Toxicol 30: 573-582

Körner W, Vinggaard AM, Térouanne B, Ma R, Wieloch C, Schlumpf M, Sultan C, Soto AM (2004) Interlaboratory comparison of four in vitro assays for assessing androgenic and antiandrogenic activity of environmental chemicals. Environ Health Perspect 112: 695-702

Lee SH, Hong KY, Seo H, Lee HS, Park Y (2021) Mechanistic insight into human androgen receptor-mediated endocrine-disrupting potentials by a stable bioluminescence resonance energy transfer-based dimerization assay. Chem Biol Interact 349: 109655

MacLean HE, Chu S, Warne GL, Zajac JD (1993) Related individuals with different androgen receptor gene deletions. J Clin Invest 91: 1123-1128

MacLeod DJ, Sharpe RM, Welsh M, Fisken M, Scott HM, Hutchison GR, Drake AJ, van den Driesche S (2010) Androgen action in the masculinization programming window and development of male reproductive organs. Int J Androl 33: 279-287

OECD. (2016) Test No. 458: Stably Transfected Human Androgen Receptor Transcriptional Activation Assay for Detection of Androgenic Agonist and Antagonist Activity of Chemicals. OECD Guidelines for the Testing of Chemicals, Section 4, Paris.

Rana K, davey RA, Zajac JD (2014) Human androgen deficiency: insights gained from androgen receptor knockout mouse models. Asian J Androl 16: 169-177

Satoh K, Ohyama K, Aoki N, Iida M, Nagai F (2004) Study on anti-androgenic effects of bisphenol a diglycidyl ether (BADGE), bisphenol F diglycidyl ether (BFDGE) and their derivatives using cells stably transfected with human androgen receptor, AR-EcoScreen. Food Chem Toxicol 42: 983-993

Schwartz CL, Christiansen S, Vinggaard AM, Axelstad M, Hass U, Svingen T (2019) Anogenital distance as a toxicological or clinical marker for fetal androgen action and risk for reproductive disorders. Arch Toxicol 93: 253-272

Sonneveld E, Jansen HJ, Riteco JA, Brouwer A, van der Burg B (2005) Development of androgen- and estrogen-responsive bioassays, members of a panel of human cell line-based highly selective steroid-responsive bioassays. Toxicol Sci 83: 136-148

van der Burg B, Winter R, Man HY, Vangenechten C, Berckmans P, Weimer M, Witters H, van der Linden S (2010) Optimization and prevalidation of the in vitro AR CALUX method to test androgenic and antiandrogenic activity of compounds. Reprod Toxicol 30: 18-24

Vinggaard AM, Niemelä J, Wedebye EB, Jensen GE (2008) Screening of 397 chemicals and development of a quantitative structure--activity relationship model for androgen receptor antagonism. Chem Res Toxicol 21: 813-823

Walters KA, Simanainen U, Handelsman DJ (2010) Molecular insights into androgen actions in male and female reproductive function from androgen receptor knockout models. Hum Reprod Update 16: 543-558