X-ray fluorescence imaging of single human cancer cells reveals that the N-heterocyclic ligands of iodinated analogues of ruthenium anticancer drugs remain coordinated after cellular uptake.

Analogues of KP1019 containing iodinated indazole ligands were prepared to investigate the biological fate of the Ru-N-heterocycle bond in this class of anticancer agents. The new complexes, 5-iodoindazolium trans-tetrachloridobis(5-iodoindazole)ruthen(III)ate (1) and 5-iodoindazolium trans-tetrachlorido(dimethyl sulfoxide)(5-iodoindazole)ruthen(III)ate (3), were characterized by elemental analysis, mass spectrometry and UV-vis spectrophotometry. Tetramethylammonium salts of these complexes (2 and 4) were synthesized and characterized in a similar manner.

Distinct cellular fates for KP1019 and NAMI-A determined by X-ray fluorescence imaging of single cells.

Small molecule ruthenium complexes show great promise as anticancer pharmaceuticals, but further rational development of these as drugs is stymied by an incomplete understanding of the mechanisms that give rise to markedly different biological behaviour for structurally similar species. X-ray fluorescence imaging at two incident energies was used to reveal the intracellular distribution of Ru in single human cells treated with KP1019, showing Ru localised in both cytosol and in the nuclear region. In addition the imaging showed that treatment with KP1019 modulated Fe distribution to resemble the Ru distribution, without affecting cellular Fe content.