Janneke Simon1, Jonathan Thommis2, Karolien de Bosscher2, Onno Meijer3, Jan Kroon3
(1) Department of Medicine, Division of Endocrinology, Leiden University Medical Centre, Leiden, The Netherlands.
(2) Department of Biomolecular Medicine, VIB Center for Medical Biotechnology (CMB), Ghent, Belgium.
(3) Department of Medicine, Division of Endocrinology, Leiden University Medical Centre, Leiden, Netherlands.
Synthetic glucocorticoids (GCs) like dexamethasone (DEX) are widely used for their anti-inflammatory actions. Although highly effective, prolonged exposure to GCs is associated with metabolic, musculoskeletal and neurocognitive side effects. Transrepression, the tethering of ligand-activated glucocorticoid receptor (GR) to other transcription factors, largely drives its anti-inflammatory effects. Transactivation, entailing the binding of GR homodimers to the chromatin, is believed largely responsible for GC-induced side effects. To dissociate these mechanisms, we performed a high-throughput in vitro drug screening assay (2919 drugs, 1uM) using complementary A549 cell lines expressing firefly-luciferase reporter constructs. We aimed to identify drugs that affect GR signaling in a dissociative manner by decreasing DEX-induced GR transactivation (A549-GRE_Luc) while maintaining or enhancing GR transrepression (A549-NFkB_Luc). From the screening, we identified 85 non-toxic drugs attenuating DEX-induced GR transactivation by 25% or more. Of these, 53 maintained or enhanced DEX-driven GR transrepression. We excluded 7 drugs due to off-target effects or known toxicity (chemotherapeutics). Upon titration of the remaining 46 drugs, we identified six drugs exhibiting dissociating properties at low doses (10-30nM), including two drugs independently involved in the subcellular localization of the GR and intracellular levels of DEX. The other four drugs target a nuclear receptor, indicating crosstalk with the GR that skews GR-driven transcriptional outcomes. Concluding, we identified different targetable mechanisms by which GR signaling can be biased to favor transrepression over transactivation. Using in vivo and in vitro models, we will investigate how and to what extent these drugs can alleviate GC-induced side effects while maintaining GCs anti-inflammatory properties.