From virtual screening to selective angiotensin II type 2 receptor ligands: discovery of a novel scaffold

The angiotensin II type 2 receptor (AT 2 R) is part of the renin-angiotensin aldosterone system and modulates central nervous and cardiovascular functions. During various pathological conditions the receptor is upregulated to exert vasodilating, anti-inflammatory, and neuroprotective functions, and therefore represents a promising drug-target. As part of our continuous exploration of agonist and antagonist ligands binding the AT 2 R, a virtual screening campaign of an in-house library of ~82,000 compounds were performed. Several pharmacophores from known AT 2 R ligands were constructed, and in combination with the structural information from an AT 2 R homology model, we employed a ligand-based approach to identify new ligands with potential for high affinity to the receptor. Fifty hits were identified and tested in vitro , of which ten compounds, representing five scaffold clusters, were found to bind the AT 2 R. These clusters were validated via a hit expansion, where one of these hits, the first novel class of small molecule AT 2 R ligand identified in many years, was then selected for further exploration. Through structure-activity relationships studies, one ligand (compound 15a -( S,S )) with sub-micromolar AT 2 R affinity ( K i = 140 nM) was identified. The ligand also displayed a favorable in vitro profile; low metabolic clearance, good permeability, and fair solubility. Preliminary in vivo pharmacokinetic studies in mice revealed a good systemic exposure of the compound, with an estimated half-life of approximately six hours. The structure of compound 15a -( S,S ) differs significantly from all other previously reported AT 2 R ligands and can serve as a prototype and starting point for further AT 2 R ligand optimization, and investigation into its agonistic, antagonistic or other functions.