Determination of ddATP levels in human immunodeficiency virus-infected patients treated with dideoxyinosine

The determination of human peripheral blood mononuclear cell counts using a genomic DNA standard and application in tenofovir diphosphate quantitation

A fluorescent quantitation method to determine PBMC-derived DNA amounts using purified human genomic DNA (gDNA) as the reference standard was developed and validated. gDNA was measured in a fluorescence-based assay using a DNA intercalant, SYBR green. The fluorescence signal was proportional to the amount (mass) of DNA in the sample. The results confirmed a linear fit from 0.0665 to 1.17 μg/μL for gDNA, corresponding to 2.0 × 10⁶ to 35.0 × 10⁶ cells/PBMC sample. Intra-batch and inter-batch accuracy (%RE) was within ±15%, and precision (%CV) was <15%. Benchtop stability, freeze/thaw stability and long term storage stability of gDNA in QC sample matrix, PBMC pellets samples, and pellet debris samples, respectively, as well as dilution linearity had been established. Consistency between hemocytometry cell counting method and gDNA-based counting method was established. 6 out of 6 evaluated PBMC lots had hemocytometry cell counts that were within ±20% of the cell counts determined by the gDNA method. This method was used in conjunction with a validated LC-MS/MS method to determine the level of tenofovir diphosphate (TFV-DP), the active intracellular metabolite of the prodrugs tenofovir alafenamide (TAF) and tenofovir disoproxil fumarate (TDF), measured in PBMCs in clinical trials of TAF or TDF-containing fixed dose combinations.

Mass spectrometry in the quantitative analysis of therapeutic intracellular nucleotide analogs

Nucleoside analogs are widely used in anti-cancer, anti-(retro)viral, and immunosuppressive therapy. Nucleosides are prodrugs that require intracellular activation to mono-, di-, and finally triphosphates. Monitoring of these intracellular nucleotides is important to understand their pharmacology. The relatively involatile salts and ion-pairing agents traditionally used for the separation of these ionic analytes limit the applicability of mass spectrometry (MS) for detection. Both indirect and direct methods have been developed to circumvent this apparent incompatibility. Indirect methods consist of de-phosphorylation of the nucleotides into nucleosides before the actual analysis. Various direct approaches have been developed, ranging from the use of relatively volatile or very low levels of regular ion-pairing agents, hydrophilic interaction chromatography (HILIC), weak anion-exchange, or porous graphitic carbon columns to capillary electrophoresis and matrix-assisted light desorption--time of flight (MALDI-TOF) MS. In this review we present an overview of the publications describing the quantitative analysis of therapeutic intracellular nucleotide analogs using MS. The focus is on the different approaches for their direct analysis. We conclude that despite the technical hurdles, several useful MS-compatible chromatographic approaches have been developed, enabling the use of the excellent selectivity and sensitivity of MS for the quantitative analysis of intracellular nucleotides.

Analysis of dideoxyadenosine triphosphate by CE with fluorescence detection. I. Derivatization through the phosphate group

A CZE method was developed, which separates 2',3'-dideoxyadenosine-5'-triphosphate (ddATP) from other metabolites and endogenous nucleotides at high concentrations (20-200 microg/mL) to allow UV detection. To enhance sensitivity, fluorescence detection which requires prior derivatization of compounds was examined. Precapillary derivatization of ddATP in the presence of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC) with dansyl ethylenediamine (dansyl EDA) was faster and stable compared to that of 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl ethylenediamine (BODIPY FL EDA). Reaction conditions, reagent concentrations and detection parameters were optimized and highest derivatization efficiency was achieved in 0.1 M 1-methylimidazole buffer (pH 8.0) with 140 mM EDAC in 1-methylimidazole buffer and 30 mM dansyl EDA in DMF for 90 min at 60 degrees C. Dansyl EDA derivatives of ddATP, 2'-deoxyadenosine-5'-triphosphate (dATP) and ATP were comigrating with the CZE method; therefore, a MEKC method was developed and optimized for repeatable separations. Upon dansylation, sensitivity of ddATP with fluorescence detection (LOQ = 12 ng/mL) was 160 times higher than UV detection (LOQ = 1.9 microg/mL).