Study by HPLC-MS of the interaction of platinum antitumor complexes with potato carboxypeptidase inhibitor (PCI) Original Research Article

The interaction of the well-known antitumor drug cisplatin cis-[PtCl2(NH3)2] and the compound trans-[PtCl2NH3(4-hydroxymethylpyridine)] with the small protein potato carboxypeptidase inhibitor (PCI) and a PCI mutant in which glycine-39 was substituted by methionine has been followed by HPLC/mass spectrometry. Our results showed that both Pt drugs were able to bind PCI through Met-39 and histidines in mutated PCI, whereas only the trans complex interacted significantly with wild PCI. In the cytotoxic studies, the monofunctional adduct PCI-Met–cisplatin was neither more active nor more selective than cisplatin itself when tested against three tumor cell lines with different number of EGF receptors. Those results suggested that the poor activity of the adduct could be just due to the small fraction of cisplatin which was decoordinated from the adduct and able to penetrate the tumor cells, as well as to the changes in the structure of the platinum drug after the loss of NH3 groups upon binding PCI-Met.