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Event: 26
Key Event Title
Antagonism, Androgen receptor
Short name
Biological Context
Level of Biological Organization |
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Molecular |
Cell term
Cell term |
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eukaryotic cell |
Organ term
Key Event Components
Process | Object | Action |
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Key Event Overview
AOPs Including This Key Event
AOP Name | Role of event in AOP | Point of Contact | Author Status | OECD Status |
---|---|---|---|---|
AR antagonism leading to short AGD | MolecularInitiatingEvent | Terje Svingen (send email) | Under development: Not open for comment. Do not cite | Under Development |
AR antagonism leading to NR | MolecularInitiatingEvent | Terje Svingen (send email) | Under development: Not open for comment. Do not cite | |
AR antagonism leading to decreased fertility | MolecularInitiatingEvent | Terje Svingen (send email) | Under development: Not open for comment. Do not cite |
Stressors
Taxonomic Applicability
Life Stages
Life stage | Evidence |
---|---|
Foetal | High |
Embryo | Moderate |
During development and at adulthood | High |
Sex Applicability
Term | Evidence |
---|---|
Mixed | High |
Key Event Description
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.
How It Is Measured or Detected
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-EcoScreenTM 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.
Domain of Applicability
Both the DNA-binding and ligand-binding domains of the AR are highly evolutionary conserved, whereas the transactivation domain show more divergence which may affect AR-mediated gene regulation across species (Davey & Grossmann, 2016). Despite certain inter-species differences, AR function mediated through gene expression is highly conserved, with mutations studies from both humans and rodents showing strong correlation for AR-dependent development and function (Walters et al, 2010).
This KE is applicable for both sexes, across developmental stages into adulthood, in numerous cells and tissues and across taxa
Evidence for Perturbation by Stressor
Overview for Molecular Initiating Event
A large number of drugs and chemicals have been shown to antagonise the AR using various AR reporter gene assays. The AR is specifically targeted in AR-sensitive cancers, for example the use of the anti-androgenic drug flutamide in treating prostate cancer (Alapi & Fischer, 2006). Flutamide has also been used in several rodent in vivo studies showing anti-androgenic effects (feminization of male offspring) evident by e.g. short anogenital distance (AGD) in males (Foster & Harris, 2005; Hass et al, 2007; Kita et al, 2016). QSAR models can predict AR antagonism for a wide range of chemicals, many of which have shown in vitro antagonistic potential (Vinggaard et al, 2008).
Triticonazole
Using hAR-EcoScreen Assay, triticonazole showed a LOEC for antagonisms of 0.2 uM and an IC50 of 0.3 (±0.01) uM (Draskau et al, 2019)
Flusilazole
Using hAR-EcoScreen Assay, flusilazole showed a LOEC for antagonisms of 0.8 uM and an IC50 of 2.8 (±0.1) uM (Draskau et al, 2019).►
Epoxiconazole
Using transiently AR-transfected CHO cells, epoxiconazole showed a LOEC of 1.6 uM and an IC50 of 10 uM (Kjærstad et al, 2010)
Prochloraz
Using transiently AR-transfected CHO cells, prochloraz showed a LOEC of 6.3 uM and an IC50 of 13 uM (Kjærstad et al, 2010)
Propiconazole
Using transiently AR-transfected CHO cells, propiconazole showed a LOEC of 12.5 uM and an IC50 of 18 uM (Kjærstad et al, 2010)
Tebuconazole
Using transiently AR-transfected CHO cells, tebuconazole showed a LOEC of 3.1 uM and an IC50 of 8.1 uM (Kjærstad et al, 2010)
Flutamide
Using the AR-CALUX reporter assay in antagonism mode, flutamide showed an IC50 of 1.3 uM (Sonneveld et al, 2005).
Cyproterone acetate
Using the AR-CALUX reporter assay in antagonism mode, cyproterone acetate showed an IC50 of 7.1 nM (Sonneveld et al, 2005).
Vinclozolin
Using the AR-CALUX reporter assay in antagonism mode, vinclozolin showed an IC50of 1.0 uM (Sonneveld et al, 2005).