Mortalin and PINK1/Parkin-Mediated Mitophagy Represent Ovarian Cancer-Selective Targets for Drug Development.

Mortalin is an essential chaperone for the import of nuclear-encoded proteins into mitochondria and is elevated in ovarian cancer in association with poor patient prognosis. The investigational new drug, SHetA2, interacts with mortalin releasing its client proteins. In this study, interactions of SHetA2 moieties and mortalin substrate binding domain (SBD) amino acids are demonstrated by surface plasmon resonance (SPR) and nuclear magnetic resonance (NMR) to occur at low micromolar SHetA2 concentrations that selectively kill cancer cells over noncancerous cells. In both ovarian cancer and noncancerous cells SHetA2 reduces: mitochondria import of mortalin, degradation of mortalin's mitochondrial localization sequence (MLS), mortalin/inositol 1,4,5-trisphosphate receptors complexes and oxidative phosphorylation. In cancer cells only, SHetA2 reduces calcium levels, mitochondrial length and fusion proteins, while inducing autophagy and PTEN-induced kinase 1 (PINK1)/PARKIN-mediated mitophagy. Noncancerous cells exhibit increased mitochondrial branch length in response to SHetA2 and a low level of inducible autophagy that is resistant to SHetA2. Inhibition of autophagosome-lysosome fusion reduces, or increases, SHetA2 cytotoxicity in ovarian cancer or noncancerous cells, respectively. SHetA2 inhibits mortalin and growth, and induces mitophagy in ovarian cancer xenografts and increases survival post-surgical tumor removal. In conclusion, SHetA2 binds directly to mortalin's SBD and causes distinct responses in ovarian cancer and noncancerous cells.