Mass spectrometry in the quantitative analysis of therapeutic intracellular nucleotide analogs

REverSe TRanscrIptase chain termination (RESTRICT) for selective measurement of nucleotide analogs used in HIV care and prevention

Sufficient drug concentrations are required for efficacy of antiretroviral drugs used in HIV care and prevention. Measurement of nucleotide analogs, included in most HIV medication regimens, enables monitoring of short- and long-term adherence and the risk of treatment failure. The REverSe TRanscrIptase Chain Termination (RESTRICT) assay rapidly infers the concentration of intracellular nucleotide analogs based on the inhibition of DNA synthesis by HIV reverse transcriptase enzyme. Here, we introduce a probabilistic model for RESTRICT and demonstrate selective measurement of multiple nucleotide analogs using DNA templates designed according to the chemical structure of each drug. We measure clinically relevant concentrations of tenofovir diphosphate, emtricitabine triphosphate, lamivudine triphosphate, and azidothymidine triphosphate with agreement between experiment and theory. RESTRICT represents a new class of activity-based assays for therapeutic drug monitoring in HIV care and could be extended to other diseases treated with nucleotide analogs.

A Nanopore Based Molnupiravir Sensor

Nucleoside analogues are reagents that resemble the structure of natural nucleosides and are widely applied in antiviral and anticancer therapy. Molnupiravir, a recently reported nucleoside analogue drug, has shown its inhibitory effect against SARS-CoV-2. Rapid tracing of molnupiravir and its metabolites is important in the evaluation of its pharmacology effect, but direct sensing of molnupiravir as a single molecule has not been reported to date. Here, we demonstrate a nanopore-based sensor with which direct sensing of molnupiravir and its two major metabolites β-d-N4-hydroxycytidine and its triphosphate can be achieved simultaneously. In conjunction with a custom machine learning algorithm, an accuracy of 92% was achieved. This sensing strategy may be useful in the current pandemic and is in principle suitable for other nucleoside analogue drugs.

Challenges and stepwise fit-for-purpose optimization for bioanalyses of remdesivir metabolites nucleotide monophosphate and triphosphate in mouse tissues using LC-MS/MS

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A robust and reliable LC–MS/MS method for the quantification of RMP and RTP was optimized and validated.

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The novel method solved the major challenges of direct determination of RMP and RTP in biological matrix through improvement of LC retention, stability and recovery.

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The method was validated and successfully applied to mouse tissue distribution study.

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This method provides useful information for further study of remdesivir as well as extends the approach for phosphate determination.

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The method solved the major challenges for determining RMP and RTP in biological matrix such as LC retention, stability and recovery.

Remdesivir is a prodrug of the nucleotide analogue and used for COVID-19 treatment. However, the bioanalysis of the active metabolites remdesivir nucleotide triphosphate (RTP) and its precursor remdesivir nucleotide monophosphate (RMP) is very challenging. Herein, we established a novel method to separate RTP and RMP on a BioBasic AX column and quantified them by high-performance liquid chromatography-tandem mass spectrometry in positive electrospray ionization mode. Stepwise, we optimized chromatographic retention on an anion exchange column, improved stability in matrix through the addition of 5,5′-dithiobis-(2nitrobenzoic acid) and PhosSTOP EASYpack, and increased recovery by dissociation of tight protein binding with 2 % formic acid aqueous solution. The method allowed lower limit of quantification of 20 nM for RMP and 10 nM for RTP. Method validation demonstrated acceptable accuracy (93.6%–103% for RMP, 94.5%–107% for RTP) and precision (RSD < 11.9 % for RMP, RSD < 11.4 % for RTP), suggesting that it was sensitive and robust for simultaneous quantification of RMP and RTP. The method was successfully applied to analyze RMP and RTP in mouse tissues. In general, the developed method is suitable to monitor RMP and RTP, and provides a useful approach for exploring more detailed effects of remdesivir in treating diseases.

New Strategy to Preserve Phosphate by Ionic Liquid Matrices in Matrix-Assisted Laser Desorption/Ionization: A Case of Adenosine Nucleotides

Adenosine -5′-triphosphate (ATP) plays a valuable role in metabolic activity to produce adequate energy in a biosystem. A high ATP/AMP ratio has a correlation with diabetes that induces suppression of AMP-activated protein kinase (AMPK). Matrix-assisted laser desorption/ionization (MALDI)–mass spectrometry (MS) has outstanding potential in determining the ratio of several types of adenosine phosphates in a sample to rapidly understand the primary energy transfer in metabolism. Although MALDI is viewed as a soft ionization technique for MS analysis, excess photon energy might crack the phosphate bonds leading to misinterpretation of the ATP level. In this work, ionic liquid matrices (ILMs) were employed to reduce fragmentation and increase the detection efficiency during the MALDI process. This study demonstrated for the first time that 2,5-dihydroxybenzoic acid pyridine (DHBP) is one of the most effective matrices for further quantitative analysis of adenosine nucleotides. This systematic screening of ILMs also enhances the fundamental understanding of MALDI.

Pilot Study to Predict Pharmacokinetics of a Therapeutic Gemcitabine Dose From a Microdose

Microdose studies are exploratory trials to determine early drug pharmacokinetics in humans. In this trial we examined whether the pharmacokinetics of gemcitabine at a therapeutic dose could be predicted from the pharmacokinetics of a microdose. In this prospective, open-label microdosing study, a gemcitabine microdose (100 µg) was given intravenously to participants on day 1, followed by a therapeutic dose (1250 mg/m² ) on day 2. Gemcitabine and its metabolite 2',2'-difluorodeoxyuracil (dFdU) were quantified in plasma and intracellularly by using liquid chromatography-mass spectrometry). Noncompartmental pharmacokinetic analysis was performed. Ten patients participated in this study. The mean area under the plasma concentration-time curve (AUC_0-8 ) of gemcitabine after microdosing was 0.00074 h·mg/L and after therapeutic dosing was 16 h·mg/L. The mean AUC_0-8 of dFdU following the microdose and therapeutic dose were 0.022 h·mg/L and 169 h·mg/L, respectively. Exposure to gemcitabine after the therapeutic dose was within 2-fold of the exposure following a microdose, when linearly extrapolated to 1250 mg/m² . However, the shape of the concentration-time curve was different, as reflected by poor scalability in volume of distribution (939 L versus 222 L). Furthermore, intracellularly phosphorylated gemcitabine and phosphorylated dFdU levels could not be predicted from the microdose. The AUC_0-8 of gemcitabine at therapeutic dose was accurately predicted by the pharmacokinetics of a microdose, when linearly extrapolated to 1250 mg/m² . Volume of distribution, elimination rate constant, and intracellular pharmacokinetics of the therapeutic dose could not be predicted from the microdose, which demonstrates limitations of the microdose approach in this case.

Direct quantitation of tenofovir diphosphate in human blood with mass spectrometry for adherence monitoring

Inadequate adherence to chronic medications is a far-reaching problem with financial and human health consequences. By a wide margin, non-adherence is the leading cause of therapeutic failures of HIV pre-exposure chemoprophylaxis (PrEP) and antiretroviral therapy (ART). It has been proven that HIV infection can be prevented by daily dosing of emtricitabine and tenofovir disoproxil fumarate. Measurement of intracellular tenofovir diphosphate in red blood cells has been established as an effective way to assess cumulative adherence, however, the LC-MS-based analytical method developed for the purpose is both complicated and expensive. Here, we report a simple method for adherence monitoring based on direct MS quantification of intracellular tenofovir diphosphate in human whole blood. The method requires only microliters of whole blood, employs special membranes to perform plasma separation and concomitant desalting during blood collection, and uses nanoelectrospray on a triple quadrupole instrument. Quantitative performance in this proof-of-concept study includes RSDs of < 15% and successful analysis of a small number of patient samples with medium to high adherence levels. The results correlate with those of a validated LC-MS/MS method, and an R² value of 0.9962 is achieved. This methodology has promise for extension to point-of-care testing using miniature mass spectrometers. Graphical abstract.

Direct and indirect quantification of phosphate metabolites of nucleoside analogs in biological samples

Nucleoside reverse transcriptase inhibitors (NRTIs) are prodrugs that require intracellular phosphorylation to active triphosphate nucleotide metabolites (NMs) for their pharmacological activity. However, monitoring these pharmacologically active NMs is challenging due to their instability, high hydrophilicity, and their low concentrations in blood and tissues. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard technique for the quantification of NRTIs and their phosphorylated NMs. In this review, an overview of the publications describing the quantitative analysis of intracellular and total tissue concentration of NMs is presented. The focus of this review is the comparison of the different approaches and challenges associated with sample collection, tissue homogenization, cell lysis, cell counting, analyte extraction, sample storage conditions, and LC-MS analysis. Quantification methods of NMs via LC-MS can be categorized into direct and indirect methods. In the direct LC-MS methods, chromatographic retention of the NMs is accomplished by ion-exchange (IEX), ion-pairing (IP), hydrophilic interaction (HILIC), porous graphitic carbon (PGC) chromatography, or capillary electrophoresis (CE). In indirect methods, parent nucleosides are 1st generated from the dephosphorylation of NMs during sample preparation and are then quantified by reverse phase LC-MS as surrogates for their corresponding NMs. Both approaches have advantages and disadvantages associated with them, which are discussed in this review.

Toward highly sensitive and reproducible LC-MS/MS analysis of MK-8591 phosphorylated anabolites in human peripheral blood mononuclear cells

Aim: MK-8591 (EFdA), a novel anti-HIV nucleoside analog, is converted to mono-, di- and tri-phosphates (MK-8591-MP, MK-8591-DP and MK-8591-TP) intracellularly, among which MK-8591-TP is the active pharmacological form. An ultrasensitive LC-MS/MS assay was required to measure MK-8591-DP and MK-8591-TP levels in human peripheral blood mononuclear cells (PBMCs). Sensitivity and reproducibility were major bottlenecks in these analyses. Materials and methods: Human PBMCs were isolated from blood and lysed with 70/30 methanol/RPMI-1640. An LC-MS/MS method was developed to simultaneously quantify MK-8591-DP and MK-8581-TP in PBMC lysates. Results: Low flow LC and dimethyl sulfoxide mediated signal enhancement enabled an extreme sensitivity with limit of quantitation at 0.1 ng/ml. Assay accuracy was 92.5-106% and precision was 0.7-12.1% for a linear curve range of 0.1-40 ng/ml. Matrix variability and interference liability were comprehensively evaluated. Conclusion: Our study findings and steps taken in addressing clinical sample issues help understand and overcome the challenges facing intracellular nucleotide analog analysis.

Development, validation, and clinical application of a high-performance liquid chromatography-tandem mass spectrometry assay for the quantification of total intracellular β-decitabine nucleotides and genomic DNA incorporated β-decitabine and 5-methyl-2'-deoxycytidine

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.

Review of Chromatographic Bioanalytical Assays for the Quantitative Determination of Marine-Derived Drugs for Cancer Treatment

The discovery of marine-derived compounds for the treatment of cancer has seen a vast increase over the last few decades. Bioanalytical assays are pivotal for the quantification of drug levels in various matrices to construct pharmacokinetic profiles and to link drug concentrations to clinical outcomes. This review outlines the different analytical methods that have been described for marine-derived drugs in cancer treatment hitherto. It focuses on the major parts of the bioanalytical technology, including sample type, sample pre-treatment, separation, detection, and quantification.

Simultaneous quantification of intracellular lamivudine and abacavir triphosphate metabolites by LC-MS/MS

Nucleoside reverse transcriptase inhibitors (NRTIs) require intracellular phosphorylation to active triphosphate (TP) nucleotide metabolites before they can inhibit the HIV reverse transcriptase. However, monitoring these pharmacologically active TP metabolites is challenging due to their instability and their low concentrations at the pg/ml levels in blood and tissues. The combination of lamivudine (3TC) and abacavir (ABC) is one of the first lines for HIV therapy. Therefore, a sensitive, selective, accurate, and precise LC-MS/MS method was developed and validated for the simultaneous quantification of 3TC- and ABC-TP metabolites in mouse blood and tissues. Calibration curves were linear over the range of 10-100,000 pg/ml for 3TC-TP and 4-40,000 pg/ml for carbovir-TP (CBV-TP; phosphorylated metabolite of ABC). This corresponds to 2.1-21,322 fmol/10⁶ cells for 3TC-TP and 0.8-8000 fmol/10⁶ cells for CBV-TP. Accuracy and precision were less than 15% for all quality control sample (QCs), and absolute extraction recovery of were >65% for 3TC-TP and >90% for CBV-TP. The method was optimized to ensure stability of TP samples and standards during sample collection, preparation, analysis, and storage conditions. This method has enhanced sensitivity and requires smaller amounts of blood and tissue samples compared to previous LC-MS/MS methods for 3TC- and CBV-TP quantification. The developed method was successfully applied to characterize the pharmacokinetic profile of TP metabolites in mouse peripheral blood mononuclear cells (PBMCs), spleen, lymph nodes, and liver cells. In addition, another direct, simple, and high-throughput method for the quantification of TP standards was developed and used for the analysis of stability samples.

Validation of an LC-MS/MS assay to simultaneously monitor the intracellular active metabolites of tenofovir, emtricitabine, and lamivudine in dried blood spots

The ability to monitor adherence to antiretroviral therapy is critical for the interpretation of outcomes from clinical studies of HIV, and for optimizing patient care. The antiretrovirals tenofovir (TFV), emtricitabine (FTC), and lamivudine (3TC) are commonly included in drug regimens for HIV prevention and treatment. The active form of the drugs tenofovir diphosphate (TFVdp), emtricitabine triphosphate (FTCtp), and lamivudine triphosphate (3TCtp) are found intracellularly in erythrocytes and peripheral blood mononuclear cells (PBMCs). The ability to collect and analyze dried blood spot (DBS) samples is an attractive alternative to PBMC sampling in many resource limited settings. We developed and validated an assay to quantify all three intracellular metabolites over the range of 100-25000 fmol/sample. This assay utilizes a simple protein precipitation/liquid-liquid extraction of a single 3-mm DBS punch (from a Whatman 903 Protein Saver card) with isotopically labeled ¹³C₅-TFVdp included as the internal standard. Following extraction, samples are analyzed by anion exchange chromatography on a Thermo Biobasic AX 5μm column with detection by electrospray ionization in the positive mode on a AB Sciex API-5000 triple quadrupole mass spectrometer with a total run time of 8min. The assay was linear over the entire range (R²>0.996). The assay was accurate (inter-assay%bias within ±3.0%) and precise (inter-assay % CV≤9.8%). The assay was also reproducible from multiple punches within a spot as well as punches from separate blood spots. Stability was established at room temperature for 3days, and at -80°C for up to 63days. Clinical samples were analyzed from subjects on Truvada^®, Stribild^®, Descovy^®, and Triumeq^® regimens and intracellular metabolites were detected in all samples as expected, indicating the assay performs well for all current formulations of TFV, FTC, and 3TC.

Understanding the Complexity of Porous Graphitic Carbon (PGC) Chromatography: Modulation of Mobile-Stationary Phase Interactions Overcomes Loss of Retention and Reduces Variability

Porous graphitic carbon (PGC) is an important tool in a chromatographer's armory that retains polar compounds with mass spectrometry (MS)-compatible solvents. However, its applicability is severely limited by an unpredictable loss of retention, which can be attributed to contamination. The solutions offered fail to restore the original retention and our observations of retention time shifts of gemcitabine/metabolites on PGC are not consistent with contamination. The mobile phase affects the ionization state of analytes and the polarizable PGC surface that influences the strength of dispersive forces governing retention on the stationary phase. We hypothesized that failure to maintain the same PGC surface before and after running a gradient is a cause of the observed retention loss/variability on PGC. Herein, we optimize the choice of mobile phase solvent in a gradient program with three parts: a preparatory phase, which allows binding of analytes to column; an elution phase, which gives the required separation/peak shape; and a maintenance phase, to preserve the required retention capacity. Via liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis of gemcitabine and its metabolites extracted from tumor tissue, we demonstrate reproducible chromatography on three PGC columns of different ages. This approach simplifies use of the PGC to the same level as that of a C-18 column, removes the need for column regeneration, and minimizes run times, thus allowing PGC columns to be used to their full potential.

Liquid chromatography/tandem mass spectrometry method for simultaneous quantification of eight endogenous nucleotides and the intracellular gemcitabine metabolite dFdCTP in human peripheral blood mononuclear cells

Quantification of endogenous nucleotides is of interest for investigation of numerous cellular biochemical processes, such as energy metabolism and signal transduction, and may also be applied in cancer and antiretroviral therapies in which nucleoside analogues are used. For these purposes we developed and validated a sensitive and high accuracy ion-pair liquid chromatography tandem mass spectrometry (IP LC-MS/MS) method for simultaneous quantification of eight endogenous nucleotides (ATP, CTP, GTP, UTP, dATP, dCTP, dGTP, dTTP) and 2',2'-difluoro-2'-deoxycytidine triphosphate (dFdCTP), an intracellular metabolite of the nucleoside analogue gemcitabine. The assay was validated using 200μL aliquots of peripheral blood mononuclear cell (20×10(6)cells/ml, 4×10(6)cells) extracts, pretreated with activated charcoal and spiked with unlabeled nucleotides, deoxynucleotides and dFdCTP. Analytes were extracted by simple precipitation with cold 60% methanol containing isotope labeled internal standards and separated on a porous graphitic carbon column. For method validation, the concentration ranges were: 0.125-20.8pmol injected for deoxynucleotides, 0.25-312.5pmol injected for dFdCTP and 5-3200pmol injected for nucleotides. The highest coefficients of variation (CV) were 12.1% for within run assay and 11.4% for between run assay, both representing the precision at the lowest analyte concentrations. The method was applied to monitor dFdCTP and changes in endogenous nucleotides in patients who were receiving gemcitabine infusions.

Development of an LC-MS/MS assay for the quantitative determination of the intracellular 5-fluorouracil nucleotides responsible for the anticancer effect of 5-fluorouracil

5-Fluorouracil (5-FU) and its oral prodrug capecitabine are among the most widely used chemotherapeutics. For cytotoxic activity, 5-FU requires cellular uptake and intracellular metabolic activation. Three intracellular formed metabolites are responsible for the antineoplastic effect of 5-FU: 5-fluorouridine 5'-triphosphate (FUTP), 5-fluoro-2'-deoxyuridine 5'-triphosphate (FdUTP) and 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP). In this paper, we describe the development of an LC-MS/MS assay for quantification of these active 5-FU nucleotides in peripheral blood mononuclear cells (PBMCs). Because the intracellular 5-FU nucleotide concentrations were very low, maximization of the release from the cell matrix and minimization of interference were critical factors. Therefore, a series of experiments was performed to select the best method for cell lysis and nucleotide extraction. Chromatography was optimized to obtain separation from endogenous nucleotides, and the effect of different cell numbers was examined. The assay was validated for the following concentration ranges in PBMC lysate: 0.488-19.9 nM for FUTP, 1.66-67.7 nM for FdUTP and 0.748-30.7 nM for FdUMP. Accuracies were between -2.2 and 7.0% deviation for all analytes, and the coefficient of variation values were ≤ 4.9%. The assay was successfully applied to quantify 5-FU nucleotides in PBMC samples from patients treated with capecitabine and patients receiving 5-FU intravenously. FUTP amounts up to 3054 fmol/10(6) PBMCs and FdUMP levels up to 169 fmol/10(6) PBMCs were measured. The FdUTP concentrations were below the lower limit of quantification. To our knowledge, this is the first time that 5-FU nucleotides were quantified in cells from patients treated with 5-FU or capecitabine without using a radiolabel.

Fully validated assay for the quantification of endogenous nucleoside mono- and triphosphates using online extraction coupled with liquid chromatography-tandem mass spectrometry

An analytical method coupling online solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed to quantify 16 endogenous nucleoside mono- and triphosphates in cellular samples. Separation was achieved on a porous graphitic carbon (PGC) column without ion-pairing agent in the mobile phase. Low levels of the ion-pairing agent diethylamine (DEA) added to the reconstitution solution were necessary to prevent peak tailing of nucleoside triphosphates. The mass spectrometer, a triple quadrupole with an electrospray ionisation source, was operated in positive mode. Two multiple reaction monitoring (MRM) segments were programmed, each an internal standard. Extraction and separation of nucleoside mono- and triphosphates were obtained within 20 min. The total duration of a single run was 37 min. Calibration curves, performed with labelled nucleotides added to the sample matrix, ranged from 0.29 to 18.8 pmol injected for deoxyribonucleotides and from 3.9 to 3,156 pmol for ribonucleotides. Accuracy did not deviate more than -14.6 and 10.2 % from nominal values for all compounds at all levels. CV results were all lower than 17.0 % for the LLOQ level and 14.6 % for the other levels. Quality control (QC) samples were also in agreement with acceptance criteria, except for the lower QC of GMP. Ion suppression, matrix effect, extraction recoveries and stability were assessed. After validation, the method was applied to the evaluation of the effects of gemcitabine and hydroxyurea on nucleotide pools in Messa cells.

Strategies for quantitation of endogenous adenine nucleotides in human plasma using novel ion-pair hydrophilic interaction chromatography coupled with tandem mass spectrometry

We present here a novel and highly sensitive ion-pair hydrophilic interaction chromatography-tandem mass spectrometry (IP-HILIC-MS/MS) method for quantitation of highly polar acid metabolites like adenine nucleotides. A mobile phase based on diethylamine (DEA) and hexafluoro-2-isopropanol (HFIP) and an aminopropyl (NH2) column were applied for a novel chromatographic separation for the determination of AMP, ADP and ATP in biological matrices. This novel IP-HILIC mechanism could be hypothesized by the ion-pairing reagent (DEA) in the mobile phase forming neutral and hydrophilic complexes with the analytes of polar organic acids. The IP-HILIC-MS/MS assay for adenine nucleotides was successfully validated with satisfactory linearity, sensitivity, accuracy, reproducibility and matrix effects. The lower limit of quantitation (LLOQ) at 2.00ng/mL obtained for ATP showed a least 10-fold higher sensitivity than previous LC-MS/MS assays except nano-LC-MS/MS assay. In summary, this novel IP-HILIC-MS/MS assay provides a sensitive method for nucleotides bioanalysis and shows great potential to determine a number of organic acids in biological matrices.

Improved method for therapeutic drug monitoring of 6-thioguanine nucleotides and 6-methylmercaptopurine in whole-blood by LC/MSMS using isotope-labeled internal standards

OBJECTIVES

Thiopurine drugs (azathioprine, 6-mercaptopurine) show wide interindividual variability and a narrow therapeutic range thus making therapeutic monitoring of their active metabolite 6-thioguanine nucleotides (6-TGN) desirable. We improved the currently available laborious and complex methodology of therapeutic drug monitoring of 6-TGN and the metabolite 6-methylmercaptopurine (6-MMP) in washed erythrocytes (ery) based on a whole-blood method.

METHODS

The analytes were hydrolyzed and extracted from 25-µL ethylenediaminetetraacetic acid-anticoagulated whole-blood spiked with isotope labeled 6-TG-C2N and 6-MMP-d3 internal standards. Chromatography was performed in 5.1 minutes on a C18 reverse phase column followed by detection via electrospray interface-coupled API 4000 mass spectrometer set up in the positive multiple reaction monitoring mode. The hemoglobin concentration was measured in 20 µL of the original sample (AHD575 method), and the results were standardized to 120 g/L of hemoglobin.

RESULTS

Calibration curves were linear with r > 0.999 (6-TGN and 6-MMP up to 10,000 pmol/0.2 mL). The limit of quantification was 30 pmol/0.2 mL for 6-TGN and 6-MMP. Intraassay and interassay imprecision was <7.5% at 3 tested levels for 6-TGN and 6-MMP, respectively. Method comparisons were as follows: Ery 6-TGN: y = 1.3x - 11 and ery 6-MMP y = 1.1x - 124.

CONCLUSIONS

The new method compares favorably with established ones, allowing for rapid single run determination of 6-TGN and 6-MMP from <50 µL of fresh or frozen whole blood. Linearity and limits of quantification cover the clinically relevant range. Variability during sample preparation and matrix effects are compensated by the use of isotope-labeled internal standards. The whole-blood method is hemoglobin standardized to avoid falsely low results in the case of anemia. The method correlates well with 6-TGN measured in washed erythrocytes, but it requires significantly less hands-on time. Preliminary therapeutic ranges for the most common indications of azathioprine and 6-MP are provided.

Applicability of 2D gel electrophoresis and liquid chromatography in proteomic analysis of urine using mass spectrometry MALDI-TOF

Proteomics including the studies of the structure, function and dependences between proteins is more and more extensively applied in human medicine and veterinary medicine. The analysis of protein profiles of tissues and body fluid from healthy and ill individuals allows to identify diagnostic, prognostic and predictive markers in various pathological states in people and animals. This paper presents preparation of urine samples for analysis in the mass spectrometer MALDI-TOF (Ultraflextreme, Bruker, Bremen, Germany) by means of two methods: liquid chromatography based on the system Nano-LC (PROTEINER FC II, Bruker Daltonics, Bremen Germany). and two-direction electrophoresis 2DE (GE Healthcare, United Kingdom). Both methods enable separation of the mixture under consideration into individual fractions of high purity indispensable for obtaining readable mass spectra. The purpose of this paper is to determine applicability of these methods in analysis of protein composition of urine samples.

Improved ruggedness of an ion-pairing liquid chromatography/tandem mass spectrometry assay for the quantitative analysis of the triphosphate metabolite of a nucleoside reverse transcriptase inhibitor in peripheral blood mononuclear cells

RATIONALE

Nucleotide analogs are highly polar and ionic, which impose great challenges on bioanalysis. Ion-pairing liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the predominant reported approach for such compounds. Assay ruggedness of ion-pairing LC/MS/MS methods was often a challenge due to the potential contamination of the ion source of the mass spectrometer and LC column performance deterioration caused by ion-pairing reagents.

METHODS

An ion-pairing reagent was only added to the reconstitution solution to minimize its exposure to the MS ion source. To achieve optimum sensitivity, high pH mobile phases and negative ion ESI were needed for the LC/MS/MS method. However, high pH mobile phases led to the accumulation of ion-pairing reagent on the analytical column, which was washed off with an acidic solution to restore the column performance. In addition, isopropanol was used as a mobile phase modifier to improve peak shape and sensitivity.

RESULTS

The limit of detection was established at 1.0 ng/mL in the cell lysate. The calibration curve showed good linearity over the range of 1.0 to 100 ng/mL. The overall accuracy was no less than 87.7% based on four levels of quality control samples. Inter-run precision and intra-run precision across four analytical runs for low, geometric, medium and high QCs were less than 12.9.

CONCLUSIONS

By identifying and addressing the root cause of the assay ruggedness problem, we have developed a rugged ion-pairing LC/MS/MS method for a triphosphate (TP) metabolite of BMS-986001 in peripheral blood mononuclear cells. The new method overcame challenges such as a rapid deterioration of the peak shape, increased carryover and extremely poor column life. The peak shape was well maintained throughout multiple analytical runs. This method has been successfully applied to a toxicology study in cynomolgus monkey.

Decitabine triphosphate levels in peripheral blood mononuclear cells from patients receiving prolonged low-dose decitabine administration: a pilot study

PURPOSE

Decitabine is a nucleoside analog used in the treatment for myelodysplastic syndrome. The compound requires intracellular conversion to its triphosphate to become active. Decitabine triphosphate has, however, never been quantified in peripheral blood mononuclear cells (PBMCs) from patients.

METHOD

This article describes a method for the quantitative determination of decitabine triphosphate in PBMCs using liquid chromatography coupled to tandem mass spectrometry. The method was applied to ex vivo incubated whole blood samples and samples from three patients receiving prolonged low-dose decitabine treatment.

RESULTS

We successfully quantitated decitabine triphosphate in PBMCs. Considerable levels were detected in PBMCs from two patients that responded well to therapy, whereas only low levels were present in a non-responding patient. Moreover, the data show that, in contrast to plasma decitabine, intracellular decitabine triphosphate accumulates during a treatment cycle of nine infusions at a dose of 15 mg/m(2).

CONCLUSIONS

The results suggest a relationship between decitabine triphosphate levels and response to therapy. Based on the observed accumulation of decitabine triphosphate during a treatment cycle, a less intensive dose scheme could be feasible.

Comprehensive analysis of the intracellular metabolism of antiretroviral nucleosides and nucleotides using liquid chromatography-tandem mass spectrometry and method improvement by using ultra performance liquid chromatography

Nucleoside reverse transcriptase inhibitors (NRTIs) are a key class of drugs for the treatment of HIV infection. NRTIs are intracellularly phosphorylated to their active triphosphate metabolites and compete with endogenous deoxynucleotides (dNTP) for substrate binding. It is therefore important to analyze the intracellular concentrations of these compounds to understand drug efficacy and toxicity. To that purpose an analytical platform was developed that is capable of analyzing 8 NRTIs, 12 phosphorylated NRTIs and 4 dNTPs in small numbers of peripheral blood mononuclear cells, i.e. 1 × 10(6) cells. The platform consists of two liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods: a reversed-phase method for NRTIs using positive electrospray ionization (ESI) and an ion-pair LC-MS/MS method for the phosphorylated compounds using negative ESI. The methods use the same LC-MS system and column and changing from one method to the other only includes changing the mobile phase. The methods were partially validated, focussing on sensitivity, accuracy and precision. Successful transfer of the methods to ultra performance liquid chromatography (UPLC) led to a significant improvement of speed for the analysis of NRTIs and sensitivity for both NRTIs and phosphorylated NRTIs. The latter was demonstrated by the improved separation by UHPLC of dGTP vs. AZT-TP and ATP which made direct analysis of dGTP possible using the optimal MS/MS transition thereby significantly improving the detection limit of dGTP. Typically LLOQs observed for both the NRTIs and phosphorylated NRTIs were 1 nM, while the mean accuracy varied between 82 and 120% and inter- and intra-assay precision was generally <20%.