A class of highly selective inhibitors bind to an active state of PI3Kγ.

We have discovered a class of PI3Kγ inhibitors exhibiting over 1,000-fold selectivity over PI3Kα and PI3Kß. On the basis of X-ray crystallography, hydrogen-deuterium exchange-mass spectrometry and surface plasmon resonance experiments we propose that the cyclopropylethyl moiety displaces the DFG motif of the enzyme away from the adenosine tri-phosphate binding site, inducing a large conformational change in both the kinase- and helical domains of PI3Kγ. Site directed mutagenesis explained how the conformational changes occur. Our results suggest that these cyclopropylethyl substituted compounds selectively inhibit the active state of PI3Kγ, which is unique to these compounds and to the PI3Kγ isoform, explaining their excellent potency and unmatched isoform selectivity that were confirmed in cellular systems. This is the first example of a Class I PI3K inhibitor achieving its selectivity by affecting the DFG motif in a manner that bears similarity to DFG in/out for type II protein kinase inhibitors.

Backbone 1H, 13C, and 15N resonance assignments of the ligand binding domain of the human wildtype glucocorticoid receptor and the F602S mutant variant.

The glucocorticoid receptor (GR) is a nuclear hormone receptor that regulates key genes controlling development, metabolism, and the immune response. GR agonists are efficacious for treatment of inflammatory, allergic, and immunological disorders. Steroid hormone binding to the ligand-binding domain (LBD) of GR is known to change the structural and dynamical properties of the receptor, which in turn control its interactions with DNA and various co-regulators and drive the pharmacological response. Previous biophysical studies of the GR LBD have required the use of mutant forms to overcome issues with limited protein stability and high aggregation propensity. However, these mutant variants are known to also influence the functional response of the receptor. Here we report a successful protocol for protein expression, purification, and NMR characterization of the wildtype human GR LBD. We achieved chemical shift assignments for 90% of the LBD backbone resonances, with 216 out of 240 non-proline residues assigned in the 1H-15N TROSY spectrum. These advancements form the basis for future investigations of allosteric effects in GR signaling.