Cell-based assays for screening androgen receptor ligands

Review on activity-based detection of doping substances and growth promotors in biological matrices: do bioassays deserve a place in control programs?

BACKGROUND

Control programs such as anti-doping control and growth promotor residue surveillance programs are challenged by the emergence of designer drugs and the use of low-level drug cocktails. In order to cope with these challenges, the use of bioassays, measuring biological activity in a matrix, has been explored over the past two decades as a universal means to detect (combinations of) unknown drugs, regardless of their chemical structure.

RESULTS

This review compiles the experience on the use of activity-based assays to detect doping substances and growth promotors in biological matrices of humans (athletes) or live animals (race and/or food-producing animals). The aim is to learn from the scientific progress, going from initial research to the recent revival of this topic. Bioassay improvements and remaining limitations are discussed, along with a rational evaluation of possible applications of bioassays in control programs at their current functionality. Limitations include the possible interference by endogenous compounds and the challenge to detect metabolically activated (pro-)drugs. Nevertheless, successful validation of bioassays has been achieved, ensuring robust, reliable and valid results.

SIGNIFICANCE

We conclude by proposing three applications of bioassays that provide added-value to the current testing procedures: (i) characterization of compounds to provide indisputable proof of biological effects and to prioritize legislative (cf. expansion of bans) and research endeavors (cf. method development), (ii) bioassay-based screening of biological samples to direct intelligent sample storage, sample retesting and targeted athlete testing, (iii) bioassay-guided identification of drugs to overcome the challenges of suspicious peak selection, related to high-resolution techniques.

AOP Report: An Upstream Network for Reduced Androgen Signaling Leading to Altered Gene Expression of Androgen Receptor-Responsive Genes in Target Tissues

Adverse outcome pathways (AOPs) can aid with chemical risk assessment by providing plausible links between chemical activity at the molecular level and effect outcomes in intact organisms. Because AOPs can be used to infer causality between upstream and downstream events in toxicological pathways, the AOP framework can also facilitate increased uptake of alternative methods and new approach methodologies to help inform hazard identification. However, a prevailing challenge is the limited number of fully developed and endorsed AOPs, primarily due to the substantial amount of work required by AOP developers and reviewers. Consequently, a more pragmatic approach to AOP development has been proposed where smaller units of knowledge are developed and reviewed independent of full AOPs. In this context, we have developed an upstream network comprising key events (KEs) and KE relationships related to decreased androgen signaling, converging at a nodal KE that can branch out to numerous adverse outcomes (AOs) relevant to androgen-sensitive toxicological pathways. Androgen signaling represents an extensively studied pathway for endocrine disruption. It is linked to numerous disease outcomes and can be affected by many different endocrine-disrupting chemicals. Still, pathways related to disrupted androgen signaling remain underrepresented in the AOP-wiki, and endorsed AOPs are lacking. Given the pivotal role of androgen signaling in development and function across vertebrate taxa and life stages of both sexes, this upstream AOP network serves as a foundational element for developing numerous AOPs. By connecting the upstream network with various downstream AOs, encompassing different species, it can also facilitate cross-species extrapolations for hazard and risk assessment of chemicals. Environ Toxicol Chem 2024;43:2329-2337. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

5α-reduction of epitestosterone is catalysed by human SRD5A1 and SRD5A2 and increases androgen receptor transactivation

Epitestosterone is a stereoisomer of the active androgen testosterone and its circulating concentrations are similar to those of testosterone in women and children. However, its biological function and pathways of metabolism remain unknown. The structural similarity to testosterone suggests a potential function in the modulation of androgen receptor signalling. It is well established that the conversion of testosterone to 5α-dihydrotestosterone enhances local androgen receptor signalling. In this study, we show that epitestosterone is metabolized to 5α-dihydroepitestosterone by both human steroid 5α-reductase isoforms, SRD5A1 and SRD5A2. Using two different variations of a reporter assay for transactivation of the human androgen receptor, we show that epitestosterone is a partial AR agonist and that the 5α-reduction of epitestosterone increases its androgenic activity. In line with this, we show that 5α-reduction of epitestosterone reduces its ability to antagonize 5α-dihydrotestosterone-induced androgen receptor transactivation. In conclusion, we provide evidence that steroid 5α-reductases regulate the modulatory effect of epitestosterone on androgen receptor signalling.

A combined in vitro-in silico method for assessing the androgenic activities of bisphenol A and its analogues

Interactions between endocrine-disruptor chemicals (EDCs) and androgen receptor (AR) have adverse effects on the endocrine system, leading to human reproductive dysfunction. Bisphenol A (BPA) is an EDC that can damage both the environment and human health. Although numerous BPA analogues have been produced as substitutes for BPA, few studies have evaluated their endocrine-disrupting abilities. We assessed the (anti)-androgenic activities of BPA and its analogues using a yeast-based reporter assay. The BPA analogues tested were bisphenol S (BPS), 4-phenylphenol (4PP), 4,4'-(9-fluorenyliden)-diphenol (BPFL), tetramethyl bisphenol F (TMBPF), and tetramethyl bisphenol A (TMBPA). We also conducted molecular docking and dynamics simulations to assess the interactions of BPA and its analogues with the ligand-binding domain of human AR (AR-LBD). Neither BPA nor its analogues had androgenic activity; however, all except BPFL exerted robust anti-androgenic effects. Consistent with the in vitro results, anti-androgenic analogues of BPA formed hydrogen bonding patterns with key residues that differed from the patterns of endogenous hormones, indicating that the analogues display in inappropriate orientations when interacting with the binding pocket of AR-LBD. Our findings indicate that BPA and its analogues disrupt androgen signaling by interacting with the AR-LBD. Overall, BPA and its analogues display endocrine-disrupting activity, which is mediated by AR.

A Comprehensive Exploration of Bioluminescence Systems, Mechanisms, and Advanced Assays for Versatile Applications

Bioluminescence has been a fascinating natural phenomenon of light emission from living creatures. It happens when the enzyme luciferase facilitates the oxidation of luciferin, resulting in the creation of an excited-state species that emits light. Although there are many bioluminescent systems, few have been identified. D-luciferin-dependent systems, coelenterazine-dependent systems, Cypridina luciferin-based systems, tetrapyrrole-based luciferins, bacterial bioluminescent systems, and fungal bioluminescent systems are natural bioluminescent systems. Since different bioluminescence systems, such as various combinations of luciferin-luciferase pair reactions, have different light emission wavelengths, they benefit industrial applications such as drug discovery, protein-protein interactions, in vivo imaging in small animals, and controlling neurons. Due to the expression of luciferase and easy permeation of luciferin into most cells and tissues, bioluminescence assays are applied nowadays with modern technologies in most cell and tissue types. It is a versatile technique in a variety of biomedical research. Furthermore, there are some investigated blue-sky research projects, such as bioluminescent plants and lamps. This review article is mainly based on the theory of diverse bioluminescence systems and their past, present, and future applications.

Untargeted Detection of HIF Stabilizers in Doping Samples: Activity-Based Screening with a Stable In Vitro Bioassay

Hypoxia-inducible factor (HIF) stabilizers are listed in the World Anti-Doping Agency's prohibited list as they can increase aerobic exercise capacity. The rapid pace of emergence of highly structurally diverse HIF stabilizers could pose a risk to conventional structure-based methods in doping control to detect new investigational drugs. Therefore, we developed a strategy that is capable of detecting the presence of any HIF stabilizer, irrespective of its structure, by detecting biological activity. Previously developed cell-based HIF1/2 assays were optimized to a stable format and evaluated for their screening potential toward HIF stabilizers. Improved pharmacological characterization was established by the stable cell-based formats, and broad specificity was demonstrated by pharmacologically characterizing a diverse set of HIF stabilizers (including enarodustat, IOX2, IOX4, MK-8617, JNJ-42041935). The methodological (in solvent) limit of detection of the optimal HIF1 stable bioassay toward detecting the reference compound roxadustat was 100 nM, increasing to 50-100 ng/mL (corresponding to 617-1233 nM in-well) in matching urine samples, owing to strong matrix effects. In a practical context, a urinary limit of detection of 1.15 μg/mL (95% detection rate) was determined, confirming the matrix-dependent detectability of roxadustat in urine. Pending optimization of a universal sample preparation strategy and/or a methodology to correct for the matrix effects, this untargeted approach may serve as a complementing method in antidoping control, as theoretically, it would be capable of detecting any unknown substance with HIF stabilizing activity.

Evaluation of (Anti)androgenic Activities of Environmental Xenobiotics in Milk Using a Human Liver Cell Line and Androgen Receptor-Based Promoter-Reporter Assay

The recent reports on milk consumption and its associated risk with hormone related disorders necessitates the evaluation of dairy products for the presence of endocrine disrupting chemicals (EDCs) and ensure the safety of consumers. In view of this, we investigated the possible presence of (anti)androgenic contaminants in raw and commercialized milk samples. For this purpose, a novel HepARE-Luc cell line that stably expresses human androgen receptor (AR) and the androgen responsive luciferase reporter gene was generated and used in the present study. Treatment of this cell line with androgens and corresponding antiandrogen (flutamide) stimulated or inhibited expression of reporter luciferase, respectively. Real time polymerase chain reaction and immunostaining results exhibited transcription response and translocation of AR from the cytoplasm to the nucleus in response to androgen. Observations implied that a cell-based xenobiotic screening assay via AR response can be conducted for assessing the (anti)androgenic ligands present in food chain including milk. Therefore, the cell line was further used to screen the (anti)androgenic activity of a total of 40 milk fat samples procured as raw or commercial milk. Some of the raw and commercial milk fat samples distinctly showed antiandrogenic activities. Subsequently, some commonly used environmental chemicals were also evaluated for their (anti)androgenic activities. Initial observations with molecular docking studies of experimental compounds were performed to assess their interaction with AR ligand binding domain. Furthermore, (anti)androgenic activities of these compounds were confirmed by performing luciferase assay using the HepARE-Luc cell line. None of the test compounds showed androgenic activities rather some of them like Bisphenol A (BPA) and rifamycin showed antiandrogenic activities. In conclusion, our results provide a valuable information about the assessment of (anti)androgenic activities present in milk samples. Overall, it is proposed that a robust cell-based CALUX assay can be used to assess the (anti)androgenic activities present in milk which can be attributed to different environmental chemicals present therein.

Rapid and reagent-free bioassay using autobioluminescent yeasts to detect agonistic and antagonistic activities of bisphenols against rat androgen receptor and progesterone receptor

Bisphenol A (BPA) and its analogues have been classified as endocrine disruptors via binding to nuclear receptors. Two novel bioassays, BLYrARS and BLYrPRS, were developed for rapid detection of agonistic and antagonistic activities of BPA and five of its analogues binding rat androgen receptor (rAR) and rat progesterone receptor (rPR). The reporter bioassay was based on two autonomously bioluminescent strains of the yeast Saccharomyces cerevisiae, recombined with a bacterial luciferase reporter gene cassette (lux) that can produce autofluorescence, regulated by the corresponding hormone response element acting as the responsive promoter. The bioluminescent signal is autonomous and continuous without cell lysis or addition of exogenous reagents. The AR agonist R1881 could be detected at 4 h with a half-maximal effective concentration (EC₅₀) of ~9.4 nM. The PR agonist progesterone could be determined at 4 h with an EC₅₀ of ~2.74 nM. None of the sixteen bisphenols presented agonistic activities against rAR and rPR. However, thirteen BPs were rAR antagonists and eleven BPs acted as rPR antagonists with different potency. The BLYrARS and BLYrPRS bioassay characterized by automated signal acquisition without additional manipulations or cost can be applied for simple and rapid detection of agonistic and antagonistic activities of BPs and other compounds acting as agonists or antagonists of rAR and rPR. Based on data derived by use of this bioassay endocrine-disrupting activities of some BPA analogues are more potent than BPA.

Screening for androgen agonists using autonomously bioluminescent HEK293 reporter cells

Due to the public health concerns of endocrine-disrupting chemicals, there is an increasing demand to develop improved high-throughput detection assays for enhanced exposure control and risk assessment. A substrate-free, autobioluminescent HEK293_ARE/Gal4-Lux assay was developed to screen compounds for their ability to induce androgen receptor (AR)-mediated transcriptional activation. The assay was validated against a group of 40 recommended chemicals and achieved an overall 87.5% accuracy in qualitatively classifying positive and negative AR agonists. The HEK293_ARE/Gal4-Lux assay was demonstrated as a suitable tool for Tier 1 AR agonist screening. By eliminating exogenous substrate, this assay provided a significant advantage over traditional reporter assays by enabling higher-throughput screening with reduced testing costs while maintaining detection accuracy.

A human optimized version of the bacterial luciferase gene cassette was developed such that bioluminescence is controlled by exposure to androgen-disruptor chemicals. This cassette, along with the androgen receptor gene, was co-transfected into an HEK293 human cell host that naturally lacks hormone receptors. The resulting reporter cell line was used to screen compounds for androgenic activity in a low cost, high throughput format.

Nontargeted detection of designer androgens: Underestimated role of in vitro bioassays

Androgens, both steroidal and nonsteroidal in nature, are among the most commonly misused substances in competitive sports. Their recognized anabolic and performance enhancing effects through short- and long-term physiological adaptations make them popular. Androgens exist as natural steroids, or are chemically synthesized as anabolic androgenic steroids (AAS) or selective androgen receptor modulators (SARMs). In order to effectively detect misuse of androgens, targeted strategies are used. These targeted strategies rely heavily on mass spectrometry, and detection requires prior knowledge of the targeted structure and its metabolites. Although exquisitely sensitive, such approaches may fail to detect novel structures that are developed and marketed. A nontargeted approach to androgen detection involves the use of cell-based in vitro bioassays. Both yeast and mammalian cell androgen bioassays demonstrate a clear ability to detect AAS and SARMS, and if paired with high resolution mass spectrometry can putatively identify novel structures. In vitro cell bioassays are successfully used to characterize designer molecules and to detect exogenous androgens in biological samples. It is important to continue to develop new and effective detection approaches to prevent misuse of designer androgens, and in vitro bioassays represent a potential solution to nontargeted detection strategies.

Cell-Based Bioassay to Screen Environmental Chemicals and Human Serum for Total Glucocorticogenic Activity

Glucocorticoids are steroid hormones that have systemic effects that are mediated by the glucocorticoid receptor. Environmental chemicals that disrupt glucocorticoid receptor signaling and/or glucocorticoid homeostasis could adversely affect the health of human and nonhuman vertebrates. A major challenge in identifying environmental chemicals that alter glucocorticoid receptor signaling and/or glucocorticoid homeostasis is a lack of adequate screening methods. We developed a cell-based bioassay to measure total glucocorticogenic activity (TGA) of environmental chemicals and human serum. Human MDA-MB-231 breast cancer cells were stably transfected with a luciferase reporter gene driven by 3 tandem glucocorticoid-response elements. Dose-response curves for 6 glucocorticoids and 4 non-glucocorticoid steroid hormones were generated to evaluate the specificity of the bioassay. Cells were also optimized to measure TGA of 176 structurally diverse environmental chemicals and human serum samples in a high-throughput format. Reporter activity was glucocorticoid-specific and induced 400-fold by 1 μM dexamethasone. Furthermore, 3 of the screened chemicals (3,4,4'-trichlorocarbanilide, isopropyl-N-phenylcarbamate, and benzothiazole derivative 2-[4-chlorophenyl]-benzothiazole) potentiated cortisol-induced glucocorticoid receptor activity. Serum TGA estimates from the bioassay were highly correlated with a cortisol enzyme-linked immunosorbent assay. The present study establishes an in vitro method to rapidly screen environmental chemicals and human serum for altered glucocorticogenic activity. Future studies can utilize this tool to quantify the joint effect of endogenous glucocorticoids and environmental chemicals. Environ Toxicol Chem 2021;40:177-186. © 2020 SETAC.

Yeast-Based Fluorescent Sensors for the Simultaneous Detection of Estrogenic and Androgenic Compounds, Coupled with High-Performance Thin Layer Chromatography

The persistence of endocrine disrupting compounds (EDCs) throughout wastewater treatment processes poses a significant health threat to humans and to the environment. The analysis of EDCs in wastewater remains a challenge for several reasons, including (a) the multitude of bioactive but partially unknown compounds, (b) the complexity of the wastewater matrix, and (c) the required analytical sensitivity. By coupling biological assays with high-performance thin-layer chromatography (HPTLC), different samples can be screened simultaneously, highlighting their active components; these may then be identified by chemical analysis. To allow the multiparallel detection of diverse endocrine disruption activities, we have constructed Saccharomyces cerevisiae-based bioreporter strains, responding to compounds with either estrogenic or androgenic activity, by the expression of green (EGFP), red (mRuby), or blue (mTagBFP2) fluorescent proteins. We demonstrate the analytical potential inherent in combining chromatographic compound separation with a direct fluorescent signal detection of EDC activities. The applicability of the system is further demonstrated by separating influent samples of wastewater treatment plants, and simultaneously quantifying estrogenic and androgenic activities of their components. The combination of a chemical separation technique with an optical yeast-based bioassay presents a potentially valuable addition to our arsenal of environmental pollution monitoring tools.

Single-Cell Distribution Analysis of AR Levels by High-Throughput Microscopy in Cell Models: Application for Testing Endocrine-Disrupting Chemicals

Cell-to-cell variation of protein expression in genetically homogeneous populations is a common biological trait often neglected during analysis of high-throughput (HT) screens and is rarely used as a metric to characterize chemicals. We have captured single-cell distributions of androgen receptor (AR) nuclear levels after perturbations as a means to evaluate assay reproducibility and characterize a small subset of chemicals. AR, a member of the nuclear receptor family of transcription factors, is the central regulator of male reproduction and is involved in many pathophysiological processes. AR protein levels and nuclear localization often increase following ligand binding, with dihydrotestosterone (DHT) being the natural agonist. HT AR immunofluorescence imaging was used in multiple cell lines to define single-cell nuclear values extracted from thousands of cells per condition treated with DHT or DMSO (control). Analysis of numerous biological replicates led to a quality control metric that takes into account the distribution of single-cell data, and how it changes upon treatments. Dose-response experiments across several cell lines showed a large range of sensitivity to DHT, prompting us to treat selected cell lines with 45 Environmental Protection Agency (EPA)-provided chemicals that include many endocrine-disrupting chemicals (EDCs); data from six of the compounds were then integrated with orthogonal assays. Our comprehensive results indicate that quantitative single-cell distribution analysis of AR protein levels is a valid method to detect the potential androgenic and antiandrogenic actions of environmentally relevant chemicals in a sensitive and reproducible manner.

Pilot study of global endocrine disrupting activity in Iowa public drinking water utilities using cell-based assays

Some anthropogenic substances in drinking water are known or suspected endocrine disrupting compounds (EDCs), but EDCs are not routinely measured. We conducted a pilot study of 10 public drinking water utilities in Iowa, where common contaminants (e.g., pesticides) are suspected EDCs. Raw (untreated) and finished (treated) drinking water samples were collected in spring and fall and concentrated using solid phase extraction. We assessed multiple endocrine disrupting activities using novel mammalian cell-based assays that express nuclear steroid receptors (aryl hydrocarbon [AhR], androgenic [AR], thyroid [TR], estrogenic [ER] and glucocorticoid [GR]). We quantified each receptor's activation relative to negative controls and compared activity by season and utility/sample characteristics. Among 62 samples, 69% had AhR, 52% AR, 3% TR, 2% ER, and 0% GR activity. AhR and AR activities were detected more frequently in spring (p =0 .002 and < 0.001, respectively). AR activity was more common in samples of raw water (p =0 .02) and from surface water utilities (p =0 .05), especially in fall (p =0 .03). Multivariable analyses suggested spring season, surface water, and nitrate and disinfection byproduct concentrations as determinants of bioactivity. Our results demonstrate that AR and AhR activities are commonly found in Iowa drinking water, and that their detection varies by season and utility/sample characteristics. Screening EDCs with cell-based bioassays holds promise for characterizing population exposure to diverse EDCs mixtures.

Detection of SARMs in doping control analysis

The class of selective androgen receptor modulators (SARMs) has been the subject of intense and dedicated clinical research over the past two decades. Potential therapeutic applications of SARMs are manifold and focus particularly on the treatment of conditions manifesting in muscle loss such as general sarcopenia, cancer-associated cachexia, muscular dystrophy, etc. Consequently, based on the substantial muscle- and bone-anabolic properties of SARMs, these agents constitute substances with significant potential for misuse in sport and have therefore been added to the Word Anti-Doping Agency's (WADA's) Prohibited List in 2008. Since then, numerous adverse analytical findings have been reported for various different SARMs, which has underlined the importance of proactive and preventive anti-doping measures concerning emerging drugs such as these anabolic agents, which have evidently been misused in sport despite the fact that none of these SARMs has yet received full clinical approval. In this review, analytical data on SARMs generated in the context of research conducted for sports drug testing purposes are summarized and state-of-the-art test methods aiming at intact drugs as well as diagnostic urinary metabolites are discussed. Doping control analytical approaches predominantly rely on chromatography hyphenated to mass spectrometry, which have allowed for appropriately covering the considerable variety of pharmacophores present in SARMs such as the non-steroidal representatives ACP-105, BMS-564929, GLPG0492 (DT-200), LG-121071, LGD-2226, LGD-4033/VK 5211, ostarine/enobosarm, RAD-140, S-40503, etc. as well as steroidal compounds such as MK-0773 and YK-11.

In vitro assessment of sex steroids and related compounds in water and sediments - a critical review

Detection of endocrine disrupting compounds in water and sediment samples has gained much importance since the evidence of their effects was reported in aquatic ecosystems in the 1990s. The aim of this review is to highlight the advances made in the field of in vitro analysis for the detection of hormonally active compounds with estrogenic, androgenic and progestogenic effects in water and sediment samples. In vitro assays have been developed from yeast, mammalian and in a few cases from fish cells. These assays are based either on the hormone-mediated proliferation of sensitive cell lines or on the hormone-mediated expression of reporter genes. In vitro assays in combination with various sample enrichment methods have been used with limits of detection as low as 0.0027 ng L^-1 in water, and 0.0026 ng g^-1 in sediments for estrogenicity, 0.1 ng L^-1 in water, and 0.5 ng g^-1 in sediments for androgenicity, and 5 ng L^-1 in water for progestogenicity expressed as equivalent concentrations of standard reference compounds of 17β-estradiol, dihydrotestosterone and progesterone, respectively. The experimental results and limits of quantification, however, are influenced by the methods of sample collection, preparation, and individual laboratory practices.

Identification of New Activators of Mitochondrial Fusion Reveals a Link between Mitochondrial Morphology and Pyrimidine Metabolism

Mitochondria are dynamic organelles that produce most of the cellular ATP, and are involved in many other cellular functions such as Ca²⁺ signaling, differentiation, apoptosis, cell cycle, and cell growth. One key process of mitochondrial dynamics is mitochondrial fusion, which is catalyzed by mitofusins (MFN1 and MFN2) and OPA1. The outer mitochondrial membrane protein MFN2 plays a relevant role in the maintenance of mitochondrial metabolism, insulin signaling, and mutations that cause neurodegenerative disorders. Therefore, modulation of proteins involved in mitochondrial dynamics has emerged as a potential pharmacological strategy. Here, we report the identification of small molecules by high-throughput screen that promote mitochondrial elongation in an MFN1/MFN2-dependent manner. Detailed analysis of their mode of action reveals a previously unknown connection between pyrimidine metabolism and mitochondrial dynamics. Our data indicate a link between pyrimidine biosynthesis and mitochondrial dynamics, which maintains cell survival under stress conditions characterized by loss of pyrimidine synthesis.

Effects of sex hormone-binding globulin (SHBG) on androgen bioactivity in vitro

Biochemical assessments of androgen status (hyper- or hypoandrogenism) are usually based on serum testosterone concentrations. According to the free hormone hypothesis, sex hormone-binding globulin (SHBG) determines free and bioavailable testosterone concentrations. Previous studies have suggested that in vitro androgen bioassay results may also be influenced by SHBG and correlate with free or bioavailable testosterone concentrations. To test this hypothesis, we established a stable HEK293 cell line with high expression of the human androgen receptor (AR) and a luciferase reporter downstream of a classical androgen response element. Importantly, we demonstrate that bioassay results are sensitive to dilution effects which increase apparent bioactivity in an SHBG-dependent manner. We therefore adopted a method using undiluted serum, which reduced cell proliferation but did not significantly affect the luciferase signal, cell viability or cytotoxicity. To correct for serum matrix effects, we applied signal correction based on internal controls with AR agonists or antagonists. Using this method, we provide direct evidence that in vitro androgen bioactivity reflects the inhibitory effects of SHBG, and correlates with free or bioavailable testosterone concentrations in adult hypogonadal men receiving androgen replacement therapy. In men receiving anti-androgens, serum bioactivity decreased tenfold while serum testosterone concentrations decreased only four-fold. Further pilot results in prostate cancer patients showed that androgen synthesis inhibitors result in more complete inhibition of androgen bioactivity than gonadorelin-based androgen deprivation therapy, even in patients whose testosterone concentrations were undetectable by mass spectrometry. We conclude that in vitro androgen reporter bioassays are useful tools to study how androgen bioactivity in serum is determined by androgens, anti-androgens as well as SHBG, provided that dilution and matrix effects are accounted for.

Downscaling procedures reduce chemical use in androgen receptor reporter gene assay

Bioactivity screening studies often face sample amount limitation with respect to the need for reliable, reproducible and quantitative results. Therefore approaches that minimize sample use are needed. Low-volume exposure and chemical dilution procedures were applied in an androgen receptor reporter gene human cell line assay to evaluate environmental contaminants and androgen receptor modulators, which were the agonist 5α-dihydrotestosterone (DHT); and the antagonists flutamide, bisphenol A, 1-hydroxypyrene and triclosan. Cells were exposed in around 1/3 of the medium volume recommended by the protocol (70μL/well). Further, chemical losses during pipetting steps were minimized by applying a low-volume method for compound dilution in medium (250μL for triplicate wells) inside microvolume glass inserts. Simultaneously, compounds were evaluated following conventional procedures (200μL/well, dilution in 24-well plates) for comparison of results. Low-volume exposure tests produced DHT EC50 (3.4-3.7×10(-10)M) and flutamide IC50 (2.2-3.3×10(-7)M) values very similar to those from regular assays (3.1-4.2×10(-10) and 2.1-3.3×10(-7)M respectively) and previous studies. Also, results were within assay acceptance criteria, supporting the relevance of the downscaling setup for agonistic and antagonistic tests. The low-volume exposure was also successful in determining IC50 values for 1-hydroxypyrene (2.1-2.8×10(-6)M), bisphenol A (2.6-3.3×10(-6)M), and triclosan (1.2-1.9×10(-6)M) in agreement with values obtained through high-volume exposure (2.3-2.8, 2.5-3.4 and 1.0-1.3×10(-6)M respectively). Finally, experiments following both low-volume dosing and exposure produced flutamide and triclosan IC50 values similar to those from regular tests. The low-volume experimental procedures provide a simple and effective solution for studies that need to minimize bioassay sample use while maintaining method reliability. The downscaling methods can be applied for the evaluation of samples, fractions or chemicals which require minimal losses during the steps of pipetting, transference to medium and exposure in bioassays.

Development of a novel cell based androgen screening model

The androgen receptor (AR) mediates the majority of androgen effects on target cells. The DNA cis-regulatory elements that respond to AR share sequence similarity with cis-regulatory elements for glucocorticoid, mineralocorticoid and progesterone receptors (GR, MR and PR, respectively). As a result, many of the current AR screening models are complicated by inaccurate activation of reporters by one of these receptor pathways. Identification of more selective androgen testing systems would be beneficial for clinical, pharmacological and toxicologic screening of AR activators. The present study describes the development of a selective androgen-responsive reporter cell line that expresses AR but does not express GR, MR and PR. CV1 cells were stably transduced to express human AR and an androgen-responsive gaussia luciferase gene. Clonal populations of AR expressing cells were isolated. Quantitative RT-PCR (qPCR) and western analysis confirmed stable integration of AR in the most responsive clonal line which was named 'CV1-ARluc'. Stimulation of CV1AR-luc with androgenic ligands (testosterone and 5α-dihydrotestosterone) for 18h caused an increase in luciferase activity in a dose-dependent manner. Other steroid hormones including aldosterone, cortisol, and progesterone did not stimulate luciferase response. The CV1-ARluc also increased luciferase activity when treated with human serum extracts. In conclusion, the CV1-ARluc cells provide a novel model system for screening of new AR agonists and antagonists and can determine the androgenic activity of human serum samples.