A novel approach to preparing water soluble prodrug forms of cisplatin analogues bearing chelating diamines

Effect of the aniline fragment in Pt(II) and Pt(IV) complexes as anti-proliferative agents. Standard reduction potential as a more reliable parameter for Pt(IV) compounds than peak reduction potential

The problems of resistance and side effects associated with cisplatin and other chemotherapeutic drugs have boosted research aimed at finding new compounds with improved properties. The use of platinum(IV) prodrugs is one alternative, although there is some controversy regarding the predictive ability of the peak reduction potentials. In the work described here a series of fourteen chloride Pt(II) and Pt(IV) compounds was synthesised and fully characterised. The compounds contain different bidentate arylazole heterocyclic ligands. Their cytotoxic properties against human lung carcinoma (A549), human breast carcinoma (MCF7) and human colon carcinoma (HCT116 and HT29) cell lines were studied. A clear relationship between the type of ligand and the anti-proliferative properties was found, with the best results obtained for the Pt(II) compound that contains an aniline fragment, (13), thus evidencing a positive effect of the NH₂ group. Stability and aquation studies in DMSO, DMF and DMSO/water mixtures were carried out on the active complexes and an in-depth analysis of the two aquation processes, including DFT analysis, of 13 was undertaken. It was verified that DNA was the target and that cell death occurred by apoptosis in the case of 13. Furthermore, the cytotoxic derivatives did not exhibit haemolytic activity. The reduction of the Pt(IV) compounds whose Pt(II) congeners were active was studied by several techniques. It was concluded that the peak reduction potential was not useful to predict the ability for reduction. However, a correlation between the cytotoxic activity and the standard reduction potential was found.

Unusual reactivity of cisplatin analogs that bear o-phenylenediamine ligands: insights for the design of more effective cytotoxic agents

The stabilities of dichloro(o-phenylenediamine)platinum(II) (1) and several 4,5-disubstituted analogs [i.e., with: Cl (2), Br (3), Me (4), or MeO (5)] were investigated under various aqueous conditions. The Pt complexes 1-5- decomposed by reactions which were independent of the amount of chloride in the medium. The poor aqueous stabilities of 1-5 were attributed to two factors: 1) The compounds underwent facile oxidation reactions in aqueous solution at pH 7.4 and 37 degrees C, resulting in the formation of intensely colored Pt-species as well as H2O2. Compounds 2 and 3 oxidized considerably faster than 1, 4, and 5. Based on the redox behavior and UV-Vis spectra of the decomposition products, it is proposed that they are o-benzoquinonediimine Pt complexes. 2) Compound 4 underwent an unusually rapid substitution reaction with L-methionine, a component of the culture medium, whereby both of the chloro ligands of platinum were replaced by an N,S-chelated methionine. At an L-methionine concentration of 0.5 mM, the reaction ran to completion within 1 min. Thus, the weak growth inhibitory activities of 1-5 on human cancer cells in vitro was likely a result of their poor chemical stability in the culture medium. Based on a knowledge of the decomposition pathways, analogs were designed to be resistant to these types of reactions. Dichloro(o-aminomethylaniline)platinum(II) (6) and [bis-1,2(aminomethyl)benzene]-di-chloroplatinum(II) (7) were synthesized and their aqueous stabilities investigated. Both 6 and 7 were considerably more stable than 1-5 under aqueous conditions, as well as being more effective in inhibiting the growth of human cancer cells in vitro.