Characterization of the cell growth inhibitory effects of a novel DNA-intercalating bipyridyl-thiourea-Pt(II) complex in cisplatin-sensitive and-resistant human ovarian cancer cells

The cellular effects of a novel DNA-intercalatingagent, the bipyridyl complex of platinum(II) with diphenylthiourea, [Pt(bipy)(Ph2-tu)2]Cl2, has been analyzed in thecisplatin (cDDP)—sensitive human ovarian carcinoma cellline, 2008, and its—resistant variant, C13* cells, in which thehighest accumulation and cytotoxicity was found among sixrelated bipyridyl thiourea complexes. We also show here thatthis complex causes reactive oxygen species to form andinhibits topoisomerase II activity to a greater extent in thesensitive than in the resistant line. The impairment of thisenzyme led to DNA damage, as shown by the comet assay.As a consequence, cell cycle distribution has also beengreatly perturbed in both lines. Morphological analysisrevealed deep cellular derangement with the presence of cellular masses, together with increased membrane permeability and depolarization of the mitochondrial membrane. Some of these effects, sometimes differentially evident between the two cell lines, might also be related to the decrease of total cell magnesium content caused by this thiourea complex both in sensitive and resistant cells, though the basal content of this ion was higher in the cDDP-resistant line. Altogether these results suggest that this compound exerts its cytotoxicity by mechanisms partly mediated by the resistance phenotype. In particular, cDDP-sensitive cells were affected mostly by impairing topoisomerase II activity and by increasing membrane permeability and the formation of reactive oxygen species; conversely, mitochondrial impairment appeared to play the most important role in the action of complex F in resistant cells.