The heat shock proteins (Hsps) act as molecular chaperones. Hsp90 is an abundant protein with roles in protein folding, cell signaling, and cancer. VER-50589 is an isoxazole compound that inhibits Hsp90 with an IC50 value of 21 nM. It produces a mean cellular antiproliferative GI50 value of 78 nM when tested against a human cancer cell line panel. Consistent with inhibition of Hsp90, VER-50589 induces the expression of Hsp27 and Hsp72 while reducing the client proteins C-RAF, B-RAF, survivin, and PRMT5, causing cell cycle arrest and apoptosis. VER-50589 shows favorable pharmacokinetics and impairs tumor growth in animals. Importantly, glioblastoma cells do not acquire resistance to VER-50589 and resistance to other Hsp90 inhibitors does not produce cross-resistance to VER-50589.
