Development of Hsp90 paralog specific inhibitors with mitochondrial drug delivery system

The mitochondrial pool of Hsp90 and its mitochondrial paralog, TRAP1, suppresses cell death and reprograms energy metabolism in cancer cells; therefore, Hsp90 and TRAP1 have been suggested as target proteins for anticancer drug development. Here, we report that TRAP1, not Hsp90, plays predominant roles in the cancer mitochondria and current Hsp90 inhibitors cannot effectively inactivate TRAP1 due to insufficient accumulation in the mitochondria. To develop mitochondrial TRAP1 inhibitors, we determined the crystal structures of human TRAP1 complexed with Hsp90 inhibitors and identified the most solvent-exposed atom for each Hsp90 inhibitor through molecular docking analyses. A mitochondria-targeting moiety triphenylphosphonium was conjugated with the solvent exposed atom of Hsp90 inhibitors. The isopropyl amine of an Hsp90 inhibitor PU-H71 was replaced with the mitochondria-targeting moiety triphenylphosphonium to produce SMTIN-P01. SMTIN-P01 showed comparable inhibition of TRAP1 ATPase activity in vitro, a different mode of mechanism of drug action, and much improved cytotoxicity to cancer cells compared with the non-targeted PU-H7