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Eltrombopag: a powerful chelator of cellular or extracellular iron(III) alone or combined with a second chelator

Evangelia Vlachodimitropoulou, Yu-Lin Chen, Maciej Garbowski, Pimpisid Koonyosying, Bethan Psaila, Martha Sola-Visner, Nichola Cooper, Robert Hider and John Porter

Key Points

  • ELT is a powerful iron chelator, mobilizing iron and ferritin, reducing ROS, and restoring insulin production at clinically achievable levels.

  • ELT enhances cellular iron chelation when combined with clinically available iron chelators through the shuttling of iron(III).

Abstract

Eltrombopag (ELT) is a thrombopoietin receptor agonist reported to decrease labile iron in leukemia cells. Here we examine the previously undescribed iron(III)-coordinating and cellular iron-mobilizing properties of ELT. We find a high binding constant for iron(III) (log β2=35). Clinically achievable concentrations (1 µM) progressively mobilized cellular iron from hepatocyte, cardiomyocyte, and pancreatic cell lines, rapidly decreasing intracellular reactive oxygen species (ROS) and also restoring insulin secretion in pancreatic cells. Decrements in cellular ferritin paralleled total cellular iron removal, particularly in hepatocytes. Iron mobilization from cardiomyocytes exceeded that obtained with deferiprone, desferrioxamine, or deferasirox at similar iron-binding equivalents. When combined with these chelators, ELT enhanced cellular iron mobilization more than additive (synergistic) with deferasirox. Iron-binding speciation plots are consistent with ELT donating iron to deferasirox at clinically relevant concentrations. ELT scavenges iron citrate species faster than deferasirox, but rapidly donates the chelated iron to deferasirox, consistent with a shuttling mechanism. Shuttling is also suggested by enhanced cellular iron mobilization by ELT when combined with the otherwise ineffective extracellular hydroxypyridinone chelator, CP40. We conclude that ELT is a powerful iron chelator that decreases cellular iron and further enhances iron mobilization when combined with clinically available chelators.

  • Submitted October 13, 2016.
  • Accepted July 22, 2017.
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