Cytotoxicity-boosting of kiteplatin by Pt(IV) prodrugs with axial benzoate ligands

Kiteplatin, the neglected drug analogous of cisplatin but containing cis-1,4-DACH in place of the two ammines, has been recently reevaluated for its activity against cisplatin- and oxaliplatin-resistant tumors, in particular colo-rectal cancer. With the aim of further improving the pharmacological activity of this drug, Pt(IV) prodrugs were derived by addition of two, differently substituted, benzoate groups in axial positions (X-ray structure). The cytotoxic activity of both compounds resulted markedly potentiated reaching nanomolar concentration against a wide panel of human cancer cells. The ability of benzoate ligands to enhance the activity of kiteplatin most likely originates from their lipophilicity promoting a higher drug accumulation in cancer cells; however, it is to be noted that the increase in pharmacological effect is far greater than the increase in cellular uptake. Overcoming cisplatin- and oxaliplatin-resistance by kiteplatin derivatives appears to relate to the inability of membrane extrusion pumps to remove active Pt species from tumor cells.