OR11-04 Activatable Glucocorticoid Receptor Agonists As Treatments For The Consequences Of Preterm Birth

Disclosure: R.S. Dhavan: None. K.L. Short: None. J. Ng: None. M.J. Wallace: None. P. Monaghan-Nichols: None. D. DeFranco: None. T.J. Cole: None. Glucocorticoid (GC) signaling is essential for normal fetal organ development. During late gestation a surge of endogenous GCs contributes to organ maturation, particularly important for the lung where thinning the mesenchymal tissue cause an increased alveolar-gas exchange surface area and decreased gas-exchange diffusion distance that is critical for lung function after birth. Currently potent synthetic GCs such as betamethasone (Bet) or dexamethasone (Dex) are administered antenatally to accelerate fetal lung maturation and reduce the risk of respiratory distress with preterm birth. There are however growing concerns that systemic exposure to powerful synthetic GCs such as Dex is associated with detrimental side effects, particularly in the developing fetal brain. We are currently assessing novel activatable and potentially partially selective agonists of the glucocorticoid receptor (GR) as new antenatal steroid treatments of preterm birth. One such GR agonist is a steroid prodrug called ciclesonide (Cic) that is activated in vivo to the GR agonist Des-Cic by a family of intracellular serine esterase enzymes, called carboxylesterases (Ces). We have previously demonstrated that postnatal administration of Cic and Dex drive similar stimulation of important preterm lung-specific biomarkers but in contrast to Dex, Cic produced no postnatal growth retardation, no reduction in brain weight, and no alteration in levels of neural myelination. In this current study we show by western blot analysis and immunofluorescence that the CES enzymes are expressed strongly in epithelial cells and the mesenchyme of peripheral organs such as the lung and kidney but are expressed at very low levels in the fetal and adult mouse brain, providing a basis for the preferential activation of Cic to Des-Cic only in peripheral organs. To examine the transcriptome changes induced by Cic vs Dex in the fetal mouse lung we have assessed cultured primary mouse fetal fibroblasts (the primary cell target for GCs during lung development) stimulated by 1μM Dex and Cic, for 6 hours. Changes in the fibroblast transcriptome was assessed by microarray analysis and relevant targets validated by real-time-qPCR. Analysis of the top 30 induced and repressed gene targets, including Fkbp5, Crispld2, Tgm2 and Zbtb16, demonstrated that Dex and Cic have almost identical activity profiles. Induction of transcriptional changes was completely lost in GR-null- derived fetal lung fibroblasts demonstrating specificity via the GR. The data suggests that Cic is able to regulate a respiratory genomic signature similar to Dex. Further studies will examine the effects of Cic vs Beta and Dex in mouse models of preterm birth, particularly in the context of unwanted side-effects in neural development. Presentation: Friday, June 16, 2023