Use of high-performance liquid chromatography-tandem electrospray ionization mass spectrometry to assess the speciation of a ruthenium(III) anticancer drug in the cytosol of cancer cells.

The discovery of intracellular active forms is a crucial issue for the approval of further anticancer metal-based drugs. This challenge calls for an apt analytical methodology to scrutinize the speciation changes of a metallodrug in cancer cytosol. In the current study, we have developed an approach for portraying low-molecular-mass cytosolic species of a Ru(III) drug, indazolium trans-[tetrachloridobis(1H-indazole)ruthenate(III)], based on using capillary high-performance liquid chromatography combined with tandem electrospray ionization mass spectrometry. The approach, which featured the use of the transferrin adduct as an eventual drug entity entering the cell, facilitated identification of components of the cytosol of cancer cells and their ruthenated forms in which the metal proved to be in +3 or +2 charge states. The Ru species released from the protein-bound form were also characterized with respect to the ligand environment.