Targeting a Glutamic Acid in PDEδ with Fluoromethyl-Aryl Electrophiles Impairs K-Ras Signaling

For targeted covalent modification at low-reactivity carboxylates with biocompatible electrophiles, new approaches are in high demand. Engineering of the HaloTag protein facilitates such a covalent reaction between chloroalkanes and an aspartate residue. We demonstrate that conversely, engineering stable ligands can also enable covalent targeting of an acid residue in a protein binding site. Using the chaperone PDEδ, which shuttles lipidated oncoproteins and thereby mediates their signaling activity, we show that equipping noncovalent inhibitors with a benzyl fluoride-based electrophile leads to covalent modification of a specific glutamate p.E88 in the ligand binding site. The best inhibitor, Deltafluorine, embodies a 3-fluoromethyl-pyridyl group and is stable to nucleophiles like glutathione, phosphate, acetate, and citrate. In cells, Deltafluorine combines noncovalent and covalent reactivity to demonstrate distinct cellular profiles and inhibits signaling through the MAP-kinase and Akt-mTOR pathways. In an autochthonous mouse model of highly aggressive Kras^G12D-driven lung adenocarcinoma, Deltafluorine treatment significantly reduces tumor volume.