Ultratrace voltammetric determination of DNA-bound platinum in patients after administration of oxaliplatin

Oxaliplatin, a novel diaminocyclohexane-platinum complex, is used for the treatment of metastatic colorectal cancer. The amount of DNA-adduct formation of this drug in white blood cells of patients is determined after isolation of the DNA by density gradient centrifugation and a four-step solid phase extraction procedure. DNA is quantified by UV spectrometry, and platinum is determined after mineralization of the DNA sample by adsorptive stripping voltammetry (formazone method). It is possible to determine Pt-nucleotide ratios in clinical samples down to five Pt atoms in 10(8) nucleotides, and the dynamic range of the method covers three orders of magnitude. An absolute amount of 25 mug of DNA is sufficient for such measurements. With the method described, the time-dependent formation of oxaliplatin DNA adducts can be monitored in clinical studies, which may help us to understand inter-individual differences in the responses of patients to oxaliplatin-based therapy.