Liquid chromatography tandem mass spectrometry quantitation of intracellular concentrations of ganciclovir and its phosphorylated forms.

Ganciclovir (GCV) is prescribed for cytomegalovirus infection which is a major issue in immunodepressed patients. It is however characterized by hematological toxicity. A better understanding of GCV concentration-effects relationships implies the measurement of intracellular forms. The objective of this study was to develop a method to measure GCV and its derivatives in cells. A four-stage procedure was developed with the following strategy: (1) to separate into different fractions the different intracellular forms of GCV (GCV itself and its phosphorylated forms) by solid-phase extraction (SPE) from blood cells, (2) to dephosphorylate the different phosphorylated forms into GCV, (3) to perform a second SPE to desalt samples and concentrate GCV, and (4) to measure GCV concentrations in the different extracts using a triple-quadrupole, linear ion trap mass spectrometer. Finally, the procedure was tested in 17 patients receiving GCV. From lysed cells, the different forms of GCV were fractionated, the phosphorylated forms were eluted with different KCl solutions, and the obtained fractions were treated with acid phosphatase to transform the phosphorylated metabolites back into GCV. The method was validated from 5 to 500 µg L(-1) with a limit of detection of 1 µg L(-1). The whole procedure was validated according to the US Food and Drug Administration guidelines and successfully applied in 17 patients receiving GCV. The method liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) allowing the measurement of GCV and its phosphorylated forms in blood cells was developed and can be used in developing clinical studies to explore the role of these biomarkers in the event of toxicity.