A new highly androgen specific yeast biosensor, enabling optimisation of (Q)SAR model approaches

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• The human androgen receptor (hAR) plays a critical role in various physiological processes.
• Developing sensitive and specific bioassays is crucial for evaluating androgenic compounds.
• Understanding structure-activity relationships is key for drug design and risk assessment.

Purpose of the Study:

• To construct and validate a recombinant yeast bioassay for detecting androgenic activity.
• To determine the relative androgenic potencies (RAP) of various steroids.
• To assess the bioassay's suitability for verifying (Quantitative) Structure-Activity Relationship ((Q)SAR) models.

Main Methods:

• Engineered Saccharomyces cerevisiae to co-express human androgen receptor (hAR) and yeast enhanced green fluorescent protein (yEGFP).
• Quantified yEGFP expression as a readout for androgenic activity upon exposure to different steroids.
• Calculated EC50 values and Relative Androgenic Potencies (RAP) for tested compounds.

Main Results:

• The bioassay demonstrated high specificity, responding only to known androgenic compounds.
• 17beta-testosterone showed a half-maximal activation concentration (EC50) of 50 nM.
• RAP values for 19-nortestosterone (1.7) and tetrahydrogestrinone (1.2) were consistent with QSAR predictions, while 17beta-estradiol showed minimal activity (0.008).
• No agonistic response was observed for steroids targeting estrogen or glucocorticoid receptors, indicating no cross-reactivity.
• Studies with steroid isomers and designer steroids confirmed the importance of the 17beta-hydroxyl group, 3-keto group, and 5alpha-steroidal framework for activity.

Conclusions:

• The developed recombinant yeast bioassay is a robust tool for assessing androgenic activity.
• The system exhibits no detectable metabolism or crosstalk from endogenous hormone receptors.
• The bioassay effectively verifies (Q)SAR model predictions and aids in understanding steroid structure-activity relationships.