Mithramycin-A Induced Toxicity in HepG2 Cells is mediated by Disruption of Calcium Homeostasis

Abstract

Mithramycin A is a potent inhibitor of EWS-FLI1, a transcription factor implicated in Ewings sarcoma. However, a clinical trial initiated to evaluate its efficacy revealed hepatotoxicity at doses well below those required for inhibition of EWS-FLI1 activity. In the present study, we used a chemogenomic screen against gene deletion mutants of the yeast Saccharomyces cerevisiae to generate hypothesis on its cellular mechanism of hepatotoxicity. Our findings show that it disrupts calcium homeostasis in S. cerevisiae . Studies in HepG2 cells grown in monolayer and as spheroids confirmed that it not only induced sustained elevated cytosolic Ca 2+ levels but also induced endoplasmic reticulum stress. Cells exposed to the compound were ultimately found to undergo calpain mediated apoptosis. These data suggest that mithramycin A is a direct toxin to liver cells and its toxicity is mediated, at least in part, by disruption of Ca 2+ homeostasis.