Gamitrinib TPP (Gamitrinib, G-TPP), a small molecule that combines the Hsp90 ATPase inhibitory module of 17-allylamino geldanamycin (17-AAG) with the mitochondrial-targeting moiety of triphenylphosphonium. Gamitrinib TPP is selectively delivered to mitochondria and does not affect Hsp90 homeostasis outside the organelle. Within a 16-hour exposure, concentrations of Gamitrinib TPP of 15-20 μM indistinguishably kill patient-derived and cultured glioblastoma cell lines. This cell death response has the hallmarks of mitochondrial apoptosis, with loss of organelle inner membrane potential, release of cytochrome c in the cytosol, activation of initiator caspase-9 and effector caspase-3 and caspase-7, and cellular reactivity for annexin V.