SEC-ICP-MS and ESI-MS as tools to study the interaction between cisplatin and cytosolic biomolecules

Most of cisplatin's citotoxic properties are due to the interaction of the drug with DNA. However, other biological molecules present in the cell cytosol, such as MT (metallothionein) and GSH (glutathione), are potential targets for cisplatin and have been related to its side-effects or with the cellular resistance mechanisms to the drug. Experiments simulating physiological conditions have been performed to study the specific cisplatin metabolites which interact with GSH and MT and to characterize the different drug -biomolecule adducts over time. A combination of size exclusion chromatography-inductively coupled plasma mass spectrometry (SEC-ICP-MS) and electrospray ionization-mass spectrometry (ESI-MS) techniques has been used to provide sensible multi-elemental detection and structural information of the species of interest. Time dependent transformation of 10 mu M cisplatin at neutral pH (7.4) produces different concentrations of the mono-aquo and oligomeric derivatives, as could be confirmed by ESI-MS. No di-aquo derivative was seen to be produced under these conditions at any of the incubation times used. Cisplatin and the oligomeric derivative were incubated with GSH and MT at different drug:biomolecule ratios. Adducts from cisplatin -GSH (1:500) and from cisplatin -MT (1:10) incubations were characterized by SEC-ICP-MS. While both GSH and MT reacted with cisplatin producing different compounds, only GSH reacted with the oligomeric derivative of cisplatin. SEC-ICP-MS experiments showed that, under neutral pH conditions, Cd atoms remained bound to the cisplatin:MT adducts, but Zn atoms were lost. Results were compared with those obtained by in vitro and in vivo experiments with rat kidney, liver and inner ear cytosols.