Determination of beta4-galactosyltransferase-7 activity using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

Synthesis and Screening of α-Xylosides in Human Glioblastoma Cells

Glycosaminoglycans (GAGs) such as heparan sulfate and chondroitin sulfate decorate all mammalian cell surfaces. These mucopolysaccharides act as coreceptors for extracellular ligands, regulating cell signaling, growth, proliferation, and adhesion. In glioblastoma, the most common type of primary malignant brain tumor, dysregulated GAG biosynthesis results in altered chain length, sulfation patterns, and the ratio of contributing monosaccharides. These events contribute to the loss of normal cellular function, initiating and sustaining malignant growth. Disruption of the aberrant cell surface GAGs with small molecule inhibitors of GAG biosynthetic enzymes is a potential therapeutic approach to blocking the rogue signaling and proliferation in glioma, including glioblastoma. Previously, 4-azido-xylose-α-UDP sugar inhibited both xylosyltransferase (XYLT-1) and β-1,4-galactosyltransferase-7 (β-GALT-7)-the first and second enzymes of GAG biosynthesis-when microinjected into a cell. In another study, 4-deoxy-4-fluoro-β-xylosides inhibited β-GALT-7 at 1 mM concentration in vitro. In this work, we seek to solve the enduring problem of drug delivery to human glioma cells at low concentrations. We developed a library of hydrophobic, presumed prodrugs 4-deoxy-4-fluoro-2,3-dibenzoyl-(α- or β-) xylosides and their corresponding hydrophilic inhibitors of XYLT-1 and β-GALT-7 enzymes. The prodrugs were designed to be activatable by carboxylesterase enzymes overexpressed in glioblastoma. Using a colorimetric MTT assay in human glioblastoma cell lines, we identified a prodrug-drug pair (4-nitrophenyl-α-xylosides) as lead drug candidates. The candidates arrest U251 cell growth at an IC50 = 380 nM (prodrug), 122 μM (drug), and U87 cells at IC50 = 10.57 μM (prodrug). Molecular docking studies were consistent with preferred binding of the α- versus β-nitro xyloside conformer to XYLT-1 and β-GALT-7 enzymes.

UPLC-MRM Mass Spectrometry Method for Measurement of the Coagulation Inhibitors Dabigatran and Rivaroxaban in Human Plasma and Its Comparison with Functional Assays

Introduction

The fast, precise, and accurate measurement of the new generation of oral anticoagulants such as dabigatran and rivaroxaban in patients’ plasma my provide important information in different clinical circumstances such as in the case of suspicion of overdose, when patients switch from existing oral anticoagulant, in patients with hepatic or renal impairment, by concomitant use of interaction drugs, or to assess anticoagulant concentration in patients’ blood before major surgery.

Methods

Here, we describe a quick and precise method to measure the coagulation inhibitors dabigatran and rivaroxaban using ultra-performance liquid chromatography electrospray ionization-tandem mass spectrometry in multiple reactions monitoring (MRM) mode (UPLC-MRM MS). Internal standards (ISs) were added to the sample and after protein precipitation; the sample was separated on a reverse phase column. After ionization of the analytes the ions were detected using electrospray ionization-tandem mass spectrometry. Run time was 2.5 minutes per injection. Ion suppression was characterized by means of post-column infusion.

Results

The calibration curves of dabigatran and rivaroxaban were linear over the working range between 0.8 and 800 μg/L (r >0.99). Limits of detection (LOD) in the plasma matrix were 0.21 μg/L for dabigatran and 0.34 μg/L for rivaroxaban, and lower limits of quantification (LLOQ) in the plasma matrix were 0.46 μg/L for dabigatran and 0.54 μg/L for rivaroxaban. The intraassay coefficients of variation (CVs) for dabigatran and rivaroxaban were < 4% and 6%; respectively, the interassay CVs were < 6% for dabigatran and < 9% for rivaroxaban. Inaccuracy was < 5% for both substances. The mean recovery was 104.5% (range 83.8–113.0%) for dabigatran and 87.0% (range 73.6–105.4%) for rivaroxaban. No significant ion suppressions were detected at the elution times of dabigatran or rivaroxaban. Both coagulation inhibitors were stable in citrate plasma at -20°C, 4°C and even at RT for at least one week. A method comparison between our UPLC-MRM MS method, the commercially available automated Direct Thrombin Inhibitor assay (DTI assay) for dabigatran measurement from CoaChrom Diagnostica, as well as the automated anti-Xa assay for rivaroxaban measurement from Chromogenix both performed by ACL-TOP showed a high degree of correlation. However, UPLC-MRM MS measurement of dabigatran and rivaroxaban has a much better selectivity than classical functional assays measuring activities of various coagulation factors which are susceptible to interference by other coagulant drugs.

Conclusions

Overall, we developed and validated a sensitive and specific UPLC-MRM MS assay for the quick and specific measurement of dabigatran and rivaroxaban in human plasma.

Bioanalytical strategies for developing highly sensitive liquid chromatography/tandem mass spectrometry based methods for the peptide GLP-1 agonists in support of discovery PK/PD studies

Highly sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS)-based methods have been developed and implemented for the quantitative determination of a number of peptides under evaluation in our Glucagon-Like Peptide-1 (GLP-1) discovery program for the treatment of diabetes. These peptides are GLP-1 receptor agonists. Due to the high potency, low dose, and low exposure of these peptides, LC/MS/MS-based methods with Lower Limits of Quantitation (LLOQs) (low picomolar range) were required to support discovery pharmacokinetic/ pharmacodynamic (PK/PD) studies. Compared with small molecules, many of these peptides posed significant bioanalytical challenges in the development of highly sensitive methods because of their parent signal splitting as a result of the formation of multiply charged states, the unfavorable fragmentation patterns for Selected Reaction Monitoring (SRM) transitions due to the generation of a large number of small mass product ions with relative low intensities, and adsorption issues observed during sample preparation. This paper details the strategies developed to maximize the sensitivity and improve LLOQs from aspects of mass spectrometry, chromatography, and sample preparation. A LLOQ of 10 picomolar was achieved for all of the investigated peptides using 100 μL of mouse plasma. This is a 100-fold improvement on LLOQs over generic LC/MS/MS-based methods when the same sample volume and the same mass spectrometer platform were used. The methods have been implemented in the support of discovery PK/PD studies.