Discovery of a Potent and Isoform-Selective Targeted Covalent Inhibitor of the Lipid Kinase PI3Kα

PI3Kα has been identified as an oncogene in human tumors. By use of rational drug design, a targeted covalent inhibitor <b>3</b> (CNX-1351) was created that potently and specifically inhibits PI3Kα. We demonstrate, using mass spectrometry and X-ray crystallography, that the selective inhibitor covalently modifies PI3Kα on cysteine 862 (C862), an amino acid unique to the α isoform, and that PI3Kβ, -γ, and -δ are not covalently modified. <b>3</b> is able to potently (EC₅₀ < 100 nM) and specifically inhibit signaling in PI3Kα-dependent cancer cell lines, and this leads to a potent antiproliferative effect (GI₅₀ < 100 nM). A covalent probe, <b>8</b> (CNX-1220), which selectively bonds to PI3Kα, was used to investigate the duration of occupancy of <b>3</b> with PI3Kα in vivo. This is the first report of a PI3Kα-selective inhibitor, and these data demonstrate the biological impact of selectively targeting PI3Kα

Orally Active Fumagillin Analogues: Transformations of a Reactive Warhead in the Gastric Environment

Semisynthetic analogues of fumagillin, <b>1</b>, inhibit methionine aminopeptidase-2 (MetAP2) and have entered the clinic for the treatment of cancer. An optimized fumagillin analogue, <b>3</b> (PPI-2458), was found to be orally active, despite containing a spiroepoxide function that formed a covalent linkage to the target protein. In aqueous acid, <b>3</b> underwent ring-opening addition of water and HCl, leading to four products, <b>4–7</b>, which were characterized in detail. The chlorohydrin, but not the diol, products inhibited MetAP2 under weakly basic conditions, suggesting reversion to epoxide as a step in the mechanism. In agreement, chlorohydrin <b>6</b> was shown to revert rapidly to <b>3</b> in rat plasma. In an ex vivo assay, rats treated with purified acid degradants demonstrated inhibition of MetAP2 that correlated with the biochemical activity of the compounds. Taken together, the results indicate that degradation of the parent compound was compensated by the formation of active equivalents leading to a pharmacologically useful level of MetAP2 inhibition