Elucidating the high affinity copper(II) complexation by the iron chelator deferasirox provides therapeutic and toxicity insight.

Deferasirox (Def), an orally administered iron-chelating drug, has drawn significant interest in repurposing for anticancer application due to the elevated Fe demand by cancer cells. But there are also concerns about its severe off target health effects. Herein Cu(II) binding is studied as a potential off target interaction. The aqueous solution stability and speciation of the ternary complex Cu(Def)(pyridine) was studied by UV-Vis and EPR spectroscopy, ESI-mass spectrometry, and cyclic voltammetry under physiologically relevant conditions. The complex is observed to be a redox active, mononuclear Cu(II) complex in square planar geometry. UV-Vis spectroscopy demonstrates that at pH 7.4 the complex is quite stable (ε337nm = 10,820 M-1cm-1) with a log K = 16.65±0.1. Cu scavenging from the Cu transporters ceruloplasmin and albumin was also studied. Def does not inhibit ceruloplasmin activity but forms a ternary Cu(II) complex at the bovine serum albumin ATCUN site. Cu(Def)(py) displays potent but nonselective cytotoxicity against A549 cancer and MRC-5 noncancer lung cells but the potency of the ternary protein complex was more moderate. This work elucidates potential Def toxicity from Cu complexation in the body but also cytotoxic synergy between the metal and chelator that informs on new drug design directions.