Abstract
DNA hypermethylation is an epigenetic event that is commonly found in malignant cells and is used as a therapeutic target for β-decitabine (β-DEC) containing hypomethylating agents (eg Dacogen® and guadecitabine). β-DEC requires cellular uptake and intracellular metabolic activation to β-DEC triphosphate before it can get incorporated into the DNA. Once incorporated in the DNA, β-DEC can exert its hypomethylating effect by trapping DNA methyltransferases (DNMTs), resulting in reduced 5-methyl-2'-deoxycytidine (5mdC) DNA content. β-DEC DNA incorporation and its effect on DNA methylation, however, have not yet been investigated in patients treated with β-DEC containing therapies. For this reason, we developed and validated a sensitive and selective LC-MS/MS method to determine total intracellular β-DEC nucleotide (β-DEC-XP) concentrations, as well as to quantify β-DEC and 5mdC DNA incorporation relative to 2'-deoxycytidine (2dC) DNA content. The assay was successfully validated according to FDA and EMA guidelines in a linear range from 0.5 to 100 ng/mL (β-DEC), 50 to 10,000 ng/mL (2dC), and 5 to 1,000 ng/mL (5mdC) in peripheral blood mononuclear cell (PBMC) lysate. An additional calibrator at a concentration of 0.1 ng/mL was added for β-DEC to serve as a limit of detection (LOD). Clinical applicability of the method was demonstrated in patients treated with guadecitabine. Our data support the use of the validated LC-MS/MS method to further explore the intracellular pharmacokinetics in patients treated with β-DEC containing hypomethylating agents.