We report studies of a novel series of Pt(IV) complexes exhibiting an asymmetric combination of acetylamido and carboxylato ligands in the axial positions. We demonstrate efficient synthesis of a series of analogues, differing in the alkyl chain length and hence lipophilicity, from a stable acetylamido/hydroxido complex formed by reaction of cisplatin with peroxyacetimidic acid (PAIA). NMR spectroscopy and X-ray crystallography confirm the identity of the resulting complexes, and highlight subtle differences in the structure and stability of acetylamido complexes compared to the equivalent acetato complexes. Reduction of acetylamido complexes, whether achieved chemically or electro-chemically, is significantly more difficult than that of acetate complexes, resulting in lower antiproliferative activity for shorter-chain complexes. For those with longer chains and hence greater cell uptake, this difference is negated and acetylamido complexes are as active as acetato analogues, both exhibiting antiproliferative potency (1/IC₅₀) against A2780 ovarian cancer cells similar to that of cisplatin.

The design, synthesis, characterization and biological properties of a Pt(IV) complex containing the very active inhibitor of histone deacetylase (2-propynyl)octanoic acid, POA, as an axial ligand are reported here. The title complex, namely (OC-6-44)-acetatodiamminedichlorido(2-(2-propynyl)octanoato)platinum(IV), 1, containing POA in racemic or in enantiomeric forms, was one/two orders of magnitude more active than cisplatin, depending on the chemo-sensitivity of the cancer cell lines. Moreover, 1 exhibited similar or even better antiproliferative activity than (OC-6-33)-diamminedichloridobis(2-propylpentanoato)platinum(IV), 2, containing two molecules of the well-known histone deacetylase inhibitor 2-propylpentanoic (valproic) acid. The high potency of 1 is likely due to its high cellular accumulation and to the synergism between the DNA-damaging cisplatin and the histone deacetylase inhibitor POA, both released upon the intracellular reduction of 1. Prodrug 1, after oral administration, caused an impressive reduction of the tumor mass (94%) in a model of solid tumor (murine Lewis lung carcinoma), compared to that of the control, whereas (intraperitoneal) cisplatin induced a tumor regression of 75% only. A good accumulation of 1 was observed in the tumor mass. The time course of the body weight attested that cisplatin induced elevated anorexia, whereas treatment with 1 did not induce significant body weight loss throughout the therapeutic experiment.