Glucocorticoids (GCs) are used extensively in the treatment of inflammatory disease. Unfortunately, as GC act on virtually every organ system they also carry a broad range of serious side-effects which limits their clinical use.
The structure of the bound GC strongly impacts the final conformation of the glucocorticoid receptor (GR) and thereby dictates downstream events. Designing drugs with different GR binding properties therefore offers a plausible route to achieve dissociative effects on GR action.
This work describes two novel, high-affinity, high specificity, non-steroidal GCs (NSGs). Both NSGs were more potent than the synthetic GC dexamethasone for gene transactivation and transrepression and were equipotent for inhibition of cell proliferation.
Compared with dexamethasone, short treatment with the NSGs induced significantly less phosphorylation of PKB, which was accompanied by delayed, submaximal phosphorylation of GR at Ser211. Ser211GR is required for engagement of GR at some (eg IGFBP1) but not all gene targets, suggesting that the NSGs may mediate only a proportion of GR effects. Indeed, compared with dexamethasone, the NSGs showed impaired transactivation of IGFBP1.
Perhaps most surprisingly, the NSGs failed to promote downregulation of steady state GR expression, a well characterised response to dexamethasone. Previous reports have demonstrated that GSK3β, a downstream target of PKB, is important for targeting the GR for degradation by the proteasome. As the NSGs also fail to induce rapid activation of PKB, this provides a link between initiation of rapid kinase signalling events and GR turnover.
These novel NSGs therefore do not activate the full spectrum of rapid GC effects, impacting kinase signalling, GR activity and turnover. As a consequence the NSGs show an unexpected specificity of action. In particular, this highlights the requirement of rapid signalling events to mediate the full range of GC effects, representing an important and tractable model for drug design.