A sensitive LC–MS/MS method for quantifying clofarabine triphosphate concentrations in human peripheral blood mononuclear cells

Clofarabine triphosphate is an intracellular active metabolite of clofarabine. In the present study, we developed and validated a rapid, sensitive, and selective liquid chromatography–tandem mass spectrometry method (LC–MS/MS) for quantifying clofarabine triphosphate concentrations in human peripheral blood mononuclear cells (PBMCs). PBMCs were isolated from blood using the Ficoll gradient centrifugation method. Chromatographic separation was performed on a CN column using an isocratic mobile phase comprising acetonitrile/5 mM ammonium acetate with 0.001% ammonium hydroxide (20/80, v/v) at a flow rate of 0.60 mL/min. Detection was carried out by MS/MS in the multiple reaction monitoring mode using a negative electrospray ionization interface. The method was validated in concentration ranges of 1.25–100 ng/107 cells with acceptable accuracy and precision using 50 μL of cell extract. Clofarabine triphosphate was stable in a series of stability studies with bench-top, auto-sampler, and repeated freeze–thaw cycles. The validated method was successfully used to measure the concentrations of clofarabine triphosphate in PBMCs from cancer patients treated with clofarabine