Exploring a non-ATP pocket for potential allosteric modulation of PI3Kα.

Allosteric modulators offer a novel approach for kinase inhibition because they target less conserved binding sites compared to the active site; thus, higher selectivity may be obtained. PIK-108, a known pan phosphoinositide 3-kinase (PI3K) inhibitor, was recently detected to occupy a non-ATP binding site in the PI3Kα C-lobe. This newly identified pocket is located close to residue 1047, which is frequently mutated in human cancers (H1047R). In order to assess the interactions, stability, and any possible allosteric effects of this inhibitor on PI3Kα, extensive molecular dynamics (MD) simulations in aqueous solution were performed for the wild type (WT) human, WT murine, and H1047R human mutant PI3Kα proteins with PIK-108 placed in both catalytic and non-ATP sites. We verify the existence of the second binding site in the vicinity of the hotspot H1047R PI3Kα mutation through binding site identification and MD simulations. PIK-108 remains stable in both sites in all three variants throughout the course of the simulations. We demonstrate that the pose and interactions of PIK-108 in the catalytic site are similar in the murine WT and human mutant forms, while they are significantly different in the case of human WT PI3Kα protein. PIK-108 binding in the non-ATP pocket also differs significantly among the three variants. Finally, we examine whether the non-ATP binding site is implicated in PI3Kα allostery in terms of its communication with the active site using principal component analysis and perform in vitro experiments to verify our hypotheses.