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Presently, there is large interest in analysing the interactions in vitro with plasma proteins of some novel antitumor ruthenium(III) complexes that are in preclinical or clinical phase. The joint application of separation and spectroscopic techniques provides valuable information on the nature and the properties of the resulting ruthenium/protein adducts. Recent work carried out in our laboratory points out that, under physiological conditions, some selected ruthenium(III) complexes bind plasma proteins tightly with a marked preference for surface imidazole groups. Representative examples of interactions of antitumor ruthenium(III) complexes with plasma proteins such as albumin and transferrin are given. Notably the antitumor ruthenium(III) complexes considered here bind proteins much tighter than DNA; it is proposed that protein binding of ruthenium(III) complexes will have a large impact on the biodistribution, the pharmacokinetics and the mechanism of action of these experimental drugs.

The formation and isolation of the antitumor drug cisplatin analogue cis- The reactivity of the complex to model nucleobases 9-ethylguanine (9-EtGH) and 1-methylcytosine (1-MeC) has been investigated by 1 H NMR spectroscopy at 45°C in aqueous media. The results show that 1 reacts slowly with 9-EtGH (t 1/2 ≈ 5 days) by displacement of Cl -, producing cis- ) 2 (9-EtGH-N 7 ) 2 ], which is similar to the major cross-link adduct of cisplatin with DNA. However, 1 gives no reaction with 1-MeC. This appears to be due to the lesser reactivity of 1-MeC and to competition between the cross-link reaction and dimerization of 1 to [Pt 2 (µ-mtpo-N 3 ,N 4 ) 4 ]. Circular dichroism studies of DNA in the presence of 1 show that the platinum complex reacts efficiently after 48 h at a optimum ratio of 0.25 Pt atom/mol of DNA nucleotide. These results and those obtained from reaction of 1 with 9-EtGH suggest that the platinum compound binds the N7 atoms of two guanines of the same strand, forming intrastrand cross-linked adducts. Chelation of DNA bases by 1 causes important conformational changes, bringing the guanines close together. The anticancer activity of complex 1 has been tested against the human cancer cell lines MCF-7 breast carcinoma and A121 ovarian carcinoma. Results indicate a moderate antitumor activity against breast carcinoma and a marked and selective cytotoxic effect against ovarian carcinoma.