posted on 2021-09-17, 07:17authored byJulie
C. L. Fournier, John P. Evans, Francesca Zappacosta, Daniel A. Thomas, Vipulkumar K. Patel, Gemma V. White, Sebastien Campos, Nicholas C. O. Tomkinson
Covalent inhibition is a powerful
strategy to develop potent and
selective small molecule kinase inhibitors. Targeting the conserved
catalytic lysine is an attractive method for selective kinase inactivation.
We have developed novel, selective inhibitors of phosphoinositide
3-kinase δ (PI3Kδ) which acylate the catalytic lysine,
Lys779, using activated esters as the reactive electrophiles. The
acylating agents were prepared by adding the activated ester motif
to a known selective dihydroisobenzofuran PI3Kδ inhibitor. Three
esters were designed, including an acetate ester which was the smallest
lysine modification evaluated in this work. Covalent binding to the
enzyme was characterized by intact protein mass spectrometry of the
PI3Kδ-ester adducts. An enzymatic digest coupled with tandem
mass spectrometry identified Lys779 as the covalent binding site,
and a biochemical activity assay confirmed that PI3Kδ inhibition
was a direct result of covalent lysine acylation. These results indicate
that a simple chemical modification such as lysine acetylation is
sufficient to inhibit kinase activity. The selectivity of the compounds
was evaluated against lipid kinases in cell lysates using a chemoproteomic
binding assay. Due to the conserved nature of the catalytic lysine
across the kinome, we believe the covalent inhibition strategy presented
here could be applicable to a broad range of clinically relevant targets.