Simultaneous quantification of 2',2'-difluorodeoxycytidine and 2',2'-difluorodeoxyuridine nucleosides and nucleotides in white blood cells using porous graphitic carbon chromatography coupled with tandem mass spectrometry

A novel assay for the simultaneous quantification of the widely used anticancer agent 2',2'-difluorodeoxycytidine (gemcitabine; dFdC), its deaminated metabolite 2',2'-difluorodeoxyuridine (dFdU) and their mono-, di- and triphosphates (dFdCMP, dFdCDP, dFdCTP, dFdUMP, dFdUDP and dFdUTP) in peripheral blood mononuclear cells (PBMCs) is described. Separation of all eight compounds was achieved within 15 min using a porous graphitic carbon column (Hypercarb) with a gradient from 0 to 25 mM ammonium bicarbonate in acetonitrile/water (15:85, v/v). Calibration ranges in PBMC lysate from 4.29 to 429, 29.0 to 2900, 31.4 to 3140 and 36.9 to 3690 nM for dFdC, dFdCMP, dFdCDP and dFdCTP and from 42.1 to 4210, 25.4 to 2540, 43.2 to 4320 and 52.7 to 5270 nM for dFdU, dFdUMP, dFdUDP and dFdUTP, respectively, were validated. Accuracies were within 82.3-119% at the lower limit of quantification (LLOQ) and the precisions were less than 20.0%. At the other tested levels accuracies were within 91.4-114% and precisions less than 14.9%. Mixtures of (13)C,(15)N(2)-labeled dFdC and dFdU nucleotides were synthesized and used as internal standards. Whole blood samples showed extensive ongoing dFdC metabolism when stored at room temperature, but not on ice-water, which made the addition of enzyme inhibitors unnecessary. Stock solutions and samples were stable under all analytically relevant conditions. The method was successfully applied to clinical samples.