Pifithrin-µ induces necroptosis through oxidative mitochondrial damage but accompanies epithelial-mesenchymal transition-like phenomenon in malignant mesothelioma cells under lactic acidosis.

ABSTRACT

Heat shock protein 70 (HSP70), a chaperone protein associated with tumorigenesis and chemoresistance, has attracted significant attention as a potential therapeutic target for the development of anticancer drugs. Here, the effects of pifithrin-µ, an effective dual inhibitor of HSP70 and p53, on anticancer activities and epithelial-mesenchymal transition (EMT) were investigated in malignant mesothelioma (MM) cells. MSTO-211HAcT cells, pre-incubated in a medium containing lactic acid, showed more potent resistance to cisplatin and gemcitabine, compared with their acid-sensitive parental MSTO-211H cells. Pifithrin-µ treatment induced both apoptosis and necroptosis, which were accompanied by an EMT-like phenomenon, as evidenced by an elongated cell morphology, decreased levels of epithelial cell markers including E-cadherin, claudin-1, and ß-catenin, increased levels of mesenchymal markers including Snail, Slug, and vimentin, and increased cell migratory property. Moreover, pifithrin-µ increased intracellular ROS levels, which is associated with mitochondrial dysfunction and decreased cellular ATP content. A series of changes caused by pifithrin-µ treatment were effectively restored by lowering the ROS level through pretreatment with N-acetylcysteine. Collectively, our results suggest that pifithrin-µ may promote the metastatic behavior of surviving cells by triggering the EMT, despite its effective cell-killing action against MM cells, possibly linked to oxidative mitochondrial dysfunction and ATP depletion.