Studies on the human metabolism of iproplatin

We have previously shown that a significant portion of the total platinum in the plasma of patients receiving iproplatin is protein-bound. We have also identified cis-dichloro-bis-isopropylamine platinum(II) (CIP) as a major metabolite of iproplatin. To understand the nature of the bound platinum, we carried out in vitro comparative protein-binding studies for iproplatin and CIP. These studies indicate that when CIP is incubated in plasma, protein binding occurs, with a 2.7-h half-life for the disappearance of CIP; the parent complex does not bind and is stable in plasma for at least 48 h. The time dependence of protein binding with CIP suggests the formation of other chemical species from CIP that may be responsible for the observed protein binding. The results indicate that in patients receiving the drug, the reduction of iproplatin to CIP must take place intracellularly and that CIP or its protein-binding derivatives must efflux from the cells into the plasma. Efflux studies carried out to explore this possibility with cells in the whole blood showed that iproplatin was taken up into cells, but the efflux of protein-binding iproplatin metabolites did not occur. To understand further the nature of the metabolites of iproplatin, we carried out 195Pt-NMR (nuclear magnetic resonance) studies with urine from two patients who received a high dose of iproplatin (500 mg/m2). The predominant signals from the 195Pt-NMR corresponded to the divalent platinum complexes and not to quadrivalent complexes, indicating that the iproplatin metabolites in urine are divalent in nature.