Neolymphostin A is a Covalent Phosphoinositide-3-kinase (PI3-K)/Mammalian Target of Rapamycin (mTOR) Dual Inhibitor that Employs an Unusual Electrophilic Vinylogous Ester

Gabriel Castro-Falcón, Grant Seiler, Ozlem Demir, Manoj Rathinaswamy, David Hamelin, Reece M. Hoffmann, Stefanie Makowski, Anne-Catrin Letzel, Seth Field, John Burke, Rommie E. Amaro, and Chambers C. Hughes

Journal of Medicinal Chemistry 2018
DOI: 10.1021/acs.jmedchem.8b00975

Using a novel chemistry-based assay for identifying electrophilic natural products from unprocessed extracts, we identified the PI3-kinase/mTOR dual inhibitor neolymphostin A from Salinispora arenicola CNY-486. The method further showed that the vinylogous ester substituent on the neolymphostin core was the exact site for enzyme conjugation. Tandem MS/MS experiments on PI3Kα treated with the inhibitor revealed that neolymphostin covalently modified Lys802 with a shift in mass of +306 amu, corresponding to addition of the inhibitor and elimination of methanol. The binding pose of the inhibitor bound to PI3Kα was modelled, and hydrogen-deuterium exchange mass spectrometry experiments supported this model. Against a panel of kinases, neolymphostin showed good selectivity for PI3-kinase and mTOR. In addition, the natural product blocked AKT phosphorylation in live cells with an IC50 of ~3 nM. Taken together, neolymphostin is the first reported example of a covalent kinase inhibitor from the bacterial domain of life.