New platinum(II) complexes containing both an O,O'-chelated acetylacetonate ligand and a sulfur ligand in the platinum coordination sphere induce apoptosis in HeLa cervical carcinoma cells

We report the cytotoxic effects obtained in HeLa cells of three newly synthesized platinum complexes containing both an O,O'-chelated acetylacetonate ligand and a sulfur ligand in the platinum coordination sphere, which show, by (1)H NMR, negligible reactivity with purine bases. These compounds induce cell death with [Pt(O,O'-acac)(gamma-acac)(DMS)] being the most effective (IC(50)=0.98+/-0.056 and 1.82+/-0.023 microM for [Pt(O,O'-acac)(gamma-acac)(DMS)] and cisplatin, respectively). About 50% of cells died after 5h treatment with 100 microM [Pt(O,O'-acac)(gamma-acac)(DMS)] whilst a 16 h incubation was required to get the same results using 100 microM cisplatin. Cellular accumulation measurements, after treatment with equimolar drug concentrations, indicated the major lipophilicity and cellular uptake of the new compounds. While the cytotoxicity of cisplatin was due to both intracellular accumulation and DNA binding, that of [Pt(O,O'-acac)(gamma-acac)(DMS)] was associated with intracellular Pt accumulation only, since it has low reactivity to DNA in intact cells and in vitro. The reaction of the new complexes with guanosine and 5'-GMP was negligible, whereas the L-methionine instantly reacted with the initial Pt complexes. Both cisplatin and [Pt(O,O'-acac)(gamma-acac)(DMS)] induced apoptosis in HeLa cells. [Pt(O,O'-acac)(gamma-acac)(DMS)] provoked the early signs of apoptosis induction (cleavage of PARP and activation of caspases-9, -3 and -7) only 1h after addition of the drug. However, in cisplatin-treated cells, cleavage of PARP was seen after 9h with activation of caspases also proceeding more slowly. In conclusion, these results indicate that the newly synthesized platinum(II) complexes have high and rapid cytotoxic activity in vitro, and suggest that DNA may not be their primary target.