The effect of charge on the uptake and resistance to reduction of platinum(IV) complexes in human serum and whole blood models

cis- and trans-Platinum(IV) complexes with diaminetetracarboxylate coordination spheres possess the highly desirable property of exhibiting unusual resistance to reduction by blood serum components and endogenous reductants such as ascorbate. At the same time they are rapidly reduced in the intracellular environment of cancer cells. Consequently, they can potentially be tuned to remain intact in vivo until arrival at the tumour target where they are rapidly reduced to yield the active platinum(II) species. However, in order to achieve this, uptake must be largely restricted to tumour cells and therefore uptake by healthy cells including red blood cells must be prevented. In this proof of concept study, we report on the effect of net charge as a means of controlling the uptake by red blood cells. Using 1H NMR spectroscopy we found that modifying the net charge of the complex does not influence the rate of reduction of the complexes by an excess of ascorbate. Using XANES spectroscopy we found that modifying the net charge of the platinum(IV) complexes decreased the extent of reduction in whole blood, although probably not to the degree needed for the optimal delivery to tumours. Therefore, it is likely to be necessary to adopt higher charges and/or additional strategies to keep platinum(IV) prodrugs out of blood cells