Studies of the binding of a series of platinum(IV) complexes to plasma proteins

The platinum(IV) complexes: PtCl(4)(en)], cis,trans-PtCl(2)(OAc)(2)(en)], cis,trans-PtCl(2)(OH)(2)(en)] and trans-Pt(OH)(2)(ethmal)(en)], encompassing a range of reduction potentials and their platinum(II) analogue PtCl(2)(en)], have been assayed for their protein binding ability in the presence of albumin, albumin and L-cysteine and RPMI 1640 tissue culture medium supplemented with foetal calf serum (RPMI/FCS). cis,trans-PtCl(4)(en)] exhibited significant protein binding in all three experiments, in a similar fashion to the platinum(II) complex, presumably as a consequence of its rapid reduction. The remaining three platinum(IV) complexes displayed little if any protein binding, with the greatest amount of binding observed in the RPMI/FCS experiment. The extent of binding in the RPMI/FCS correlated with the reduction potentials of the complexes, with the most readily reduced species binding to the greatest extent.