Design and x-ray crystal structures of high-potency nonsteroidal glucocorticoid agonists exploiting a novel binding site on the receptor

Abstract

Crystallography and computer modeling have been used to exploit a previously unexplored channel in the glucocorticoid receptor (GR). Highly potent, nonsteroidal indazole amides showing excellent complementarity to the channel were designed with the assistance of the computational technique AlleGrow. The accuracy of the design process was demonstrated through crystallographic structural determination of the GR ligand-binding domain-agonist complex of the D-prolinamide derivative 11. The utility of the channel was further exemplified through the design of a potent phenylindazole in which structural motifs, seen to interact with the traditional GR ligand pocket, were abandoned and replaced by interactions within the new channel. Occupation of the channel was confirmed with a second GR crystal structure of this truncated D-alaninamide derivative 13. Compound 11 displays properties compatible with development as an intranasal solution formulation, whereas oral bioavailability has been demonstrated with a related truncated exemplar 14. Data with the pyrrolidinone amide 12 demonstrate the potential for further elaboration within the ''meta'' channel to deliver compounds with selectivity for the desired transrepressive activity of glucocorticoids. The discovery of these interactions with this important receptor offers significant opportunities for the design of novel GR modulators. drug design ͉ AlleGrow ͉ glucocorticoid modulation ͉ intranasal glucocorticoid

Selective Glucocorticoid Receptor modulators

“…Therapeutic opportunities, away from the classic ligand-binding pocket, are being explored. Indeed, X-ray crystal structure determination of an indazole amide variant functioning as a non-steroidal GR modulator, confirmed the existence and occupation of a predicted "meta" channel in the GR LBD [82]. This offers additional possibilities for novel GR ligand design.…”

Selective glucocorticoid receptor modulation: New directions with non-steroidal scaffolds

“…Selective GR modulators (SEGRMs) differ from GCs in the way that upon binding to GR they trigger transrepression, but do not initiate transactivation. and modelling revealed a second binding site within the ligand-binding pocket of GR (Biggadike et al, 2009). Also the crystal structure of GR-LBD bound with compound 10, which retains full transrepression with a partial transactivation ability, shows a new binding mode, clearly different from the classic GC binding model (Carson et al, 2014).…”

Drug Design Approaches to Manipulate the Agonist-Antagonist Equilibrium in Steroid Receptors

“…An important lesson in this regard has been our change in understanding the dynamic nature of the steroid-receptor binding pocket. We have seen examples of extensive induced fits for amongst others the glucocorticoid receptor which is able to bind ligands beyond the conventional confines of its binding pocket whilst remaining in an agonistic conformation (Biggadike et al, 2009;Madauss et al, 2008;Suino-Powell et al, 2008). The pocket, behind the crucial helix-3 and helix-5 binding residues, Gln570 and Arg611, is normally water filled.…”

“…It has already been demonstrated to be a viable ligand-binding region with the potential to improve ligand potency. An interesting note regarding the exploration of the pocket is that GSK report difficulty in combining the use of this pocket with the maintenance of partial agonism (Biggadike et al, 2009). PR has been shown to adapt to steroids baring bulky 17 groups (Madauss et al, 2004) and Trp741 in AR adapts to different ligands, adopting a new position to open an additional channel in the receptor .…”