PI3Kδ is selectively inhibited by roginolisib through stabilizing of the C-terminal helix kα12

Phosphoinositide 3-kinases (PI3Ks) are major regulators of cell growth, proliferation and signalling, constituting key therapeutic targets in cancer, inflammation, and other diseases. Individual class I PI3K isoforms control key cellular functions, imposing the need to generate isoform-specific inhibition for therapeutic intervention. Roginolisib is a selective PI3Kδ inhibitor that shows promise for the treatment of cancer. Using a combination of X-ray crystallography, molecular dynamics simulations, and hydrogen-deuterium exchange mass spectrometry, we have uncovered the mechanism driving roginolisib’s potent and isoform-selective inhibition of PI3Kδ. Roginolisib uniquely stabilises the catalytic C-terminal helix kα12, locking the enzyme in an inactive conformation. This binding mode also results in more sustained inhibition of phosphatidylinositol 3,4,5-trisphosphate formation in tumour samples of CLL patients. Inhibition of PI3Ks by stabilization into an inactive conformation has not been described before and may provide the basis for novel, more selective and effective pharmacological strategies.