Targeting a Pleckstrin Homology Domain with a Lysine-Reactive Cova-lent Binder

Bruton's Tyrosine Kinase (BTK) is a validated target for haematological malignancies, with numerous FDA approved inhibitors on the market. Current therapies target the highly conserved ATP binding site and hence limit the therapeutic index given the site′s highly conserved nature across the kinome. We explore a novel approach for BTK inhibition, by targeting the PH domain-mediated membrane recruitment and activation of BTK. We have identified a fragment which covalently labels a lysine in the inositol phosphate (PIP3) binding site. Fragment growth and an extensive structure-binding relationship study uncovered 27 crystal structures and a best-in-class analog, 24 . Evaluation of pKa values of the targeted lysine in BTK and other PH domains suggests this as a more general approach to PH domain inhibition.