Which electrospray-based ionization method best reflects protein-ligand interactions found in solution? A comparison of ESI, nanoESI, and ESSI for the determination of dissociation constants with mass spectrometry

We present a comparison of three different electrospray-based ionization techniques for the investigation of noncovalent complexes with mass spectrometry. The features and characteristics of standard electrospray ionization (ESI), chip-based nanoESI, and electrosonic spray ionization (ESSI) mounted onto a hybrid quadrupole time-of-flight mass spectrometer were compared in their performance to determine the dissociation constant (K D) of the model system hen egg white lysozyme (HEWL) binding to N,N′,N″-triacetylchitotriose (NAG3). The best K D value compared with solution data were found for ESSI, 19.4 ± 3.6 µM. Then, we determined the K Ds of the two nucleotide binding sites of adenylate kinase (AK), where we obtained K Ds of 2.2 ± 0.8 µM for the first and 19.5 ± 8.0 µM for the second binding site using ESSI. We found a weak charge state dependence of the K D for both protein-ligand systems, where for all ionization techniques the K D value decreases with increasing charge state. We demonstrate that ESSI is very gentle and insensitive to instrumental parameters, and the K D obtained is in good agreement with solution phase results from the literature. In addition, we tried to determine the K D for the lymphocyte-specific kinase LCK binding to a kinase inhibitor using nanoESI due to the very low amount of sample available. In this case, we found K D values with a strong charge state dependence, which were in no case close to literature values for solution phas

A prospective study to analyse the concentration of octenidine in hand wounds after disinfection by LC-MS/MS.

Toxic reactions can appear after pressurised flushing of soft tissue with octenidine (OCT) containing disinfectants. Their use for surgical disinfection could complicate the diagnosis of possible contamination. In patients with open lacerations of their hand's subcutaneous tissue samples were taken before and after surgical disinfection with Octenisept® and analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). In 16 out of 20 tissue samples, OCT was detected after disinfection (lower limit of quantification (LLOQ)=10 pg/mL/mg). The concentration of OCT was below the LLOQ, estimation of mean of 0.6 pg/mL/mg (0.22-0.98 pg/mL/mg, 95%-CI) before disinfection and mean of 179.4 pg/mL/mg (13.35-432.0 pg/mL/mg, 95%-CI) after disinfection. This study shows that the disinfection of open wounds with Octenisept® leads to a quantifiable concentration of OCT in open wounds. In cases of suspected OCT-mediated toxic reaction, the use of antiseptics containing OCT should be avoided

Identification of Endocrine-Disrupting Compounds Using Nanoelectrospray Ionization Mass Spectrometry

A method using chip-based nanoelectrospray mass spectrometry (nanoESI-MS) is described to detect noncovalent ligand binding to the human estrogen receptor alpha ligand-binding domain (hER? LBD). This system represents an important environmental interest, because a wide variety of molecules, known as endocrine-disrupting compounds (EDCs), can bind to the estrogen receptor (ER) and induce adverse health effects in wildlife and humans. An efficient analytical method is therefore required to identify EDCs and characterize their solution-phase binding affinity and character (i.e. agonist or antagonist). Using proper experimental conditions, the nanoESI-MS approach allowed the detection of specific ligand interactions with hER? LBD. The best approach to evaluate solution-binding affinity by nanoESI-MS was to perform competitive binding experiments with 17?-estradiol (E2) as a reference ligand. Among the ligands tested, the relative binding affinity for hER? LBD measured by nanoESI-MS was 4-hydroxytamoxifen ? diethylstilbestrol > E2 ? genistein ? bisphenol A, consistent with the order of the binding affinities in solution. To discern agonist from antagonist, we used the specificity of a coactivator peptide for agonist-bound receptor. A specific coactivator-hER? LBD complex was detected only in the presence of an agonist ligand. Therefore, the specificity of nanoESI-MS combined with its speed (1 min/ligand), low sample consumption (90 pmol protein/ligand), and its sensitivity for ligand (30 ng/ml) demonstrates that this method is promising for the identification and characterization of suspected ER ligands in a high-throughput manner

Detection of nucleic acid-nuclear hormone receptor complexes with mass spectrometry

Nuclear receptors, such as the retinoic acid receptor (RAR) or the 9-cis retinoic acid receptor (RXR), interact not only with their ligands but also with other types of receptors and with DNA. Here, two complementary mass spectrometry (MS) methods were used to study the interactions between retinoic receptors (RXR/RAR) and DNA: non-denaturing nano-electrospray (nanoESI MS), and high-mass matrix-assisted laser desorption ionization (MALDI MS) combined with chemical cross-linking. The RAR·RXR heterodimer was studied in the presence of a specific DNA sequence (DR5), and a specific RAR·RXR·DNA complex was detected with both MS techniques. RAR by itself showed no significant homodimerization. A complex between RAR and the double stranded DR5 was detected with nanoESI. After cross-linking, high-mass MALDI mass spectra showed that the RAR binds the single stranded DR5, and the RAR dimer binds both single and double stranded DR5. Moreover, the MALDI mass spectrum shows a larger RAR dimer signal in the presence of DNA. These results suggest that a gene-regulatory site on DNA can induce quaternary structural changes in a transcription factor such as RA

Prothrombinase-Induced Clotting Time to Measure Drug Concentrations of Rivaroxaban, Apixaban, and Edoxaban in Clinical Practice: A Cross-Sectional Study.

Prothrombinase-induced clotting time (PiCT) is proposed as a rapid and inexpensive laboratory test to measure direct oral anticoagulant (DOAC) drug levels. In a prospective, multicenter cross-sectional study, including 851 patients, we aimed to study the accuracy of PiCT in determining rivaroxaban, apixaban, and edoxaban drug concentrations and assessed whether clinically relevant drug levels could be predicted correctly. Citrated plasma samples were collected, and the Pefakit® PiCT was utilized. Ultra-high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to measure drug concentrations. Cut-off levels were established using receiver-operating characteristics curves. We calculated sensitivities and specificities with respect to clinically relevant drug concentrations. Spearman's correlation coefficient between PiCT and drug concentrations was 0.85 in the case of rivaroxaban (95% CI 0.82, 0.88), 0.66 for apixaban (95% CI 0.60, 0.71), and 0.78 for edoxaban (95% CI 0.65, 0.86). The sensitivity to detect clinically relevant drug concentrations was 85.1% in the case of 30 µg L-1 (95% CI 82.0, 87.7; specificity 77.9; 72.1, 82.7), 85.7% in the case of 50 µg L-1 (82.4, 88.4; specificity 77.3; 72.5, 81.5), and 85.1% in the case of 100 µg L-1 (80.9, 88.4; specificity 73.2%; 69.1, 76.9). In conclusion, the association of PiCT with DOAC concentrations was fair, and the majority of clinically relevant drug concentrations were correctly predicted

Determination of Anti-Xa Inhibitor Plasma Concentrations Using a Universal Edoxaban Calibrator

A universal calibrator for the determination of all anti-Xa inhibitors would support laboratory processes. We aimed to test the clinical performance of an anti-Xa assay utilizing a universal edoxaban calibrator to determine clinically relevant concentrations of all anti-Xa inhibitors. Following a pilot study, we enrolled 553 consecutive patients taking rivaroxaban, edoxaban, or apixaban from nine study centers in a prospective cross-sectional study. The Technochrom$^{®}$ anti-Xa assay was conducted using the Technoview$^{®}$ edoxaban calibrator. Using ultra-high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS), anti-Xa inhibitor drug concentrations were determined. Sensitivities and specificities to detect three clinically relevant drug concentrations (30 µgL$^{-1}$, 50 µgL$^{-1}$, 100 µgL$^{-1}$) were determined. Overall, 300 patients treated with rivaroxaban, 221 with apixaban, and 32 with edoxaban were included. The overall correlation coefficient (r$_{s}$) was 0.95 (95% CI 0.94, 0.96). An area under the receiver operating characteristic curve of 0.96 for 30 µgL$^{-1}$, 0.98 for 50 µgL$^{-1}$, and 0.99 for 100 µgL$^{-1}$ was found. The sensitivities were 92.3% (95% CI 89.2, 94.6), 92.7% (89.4, 95.1), and 94.8% (91.1, 97.0), respectively (specificities 82.2%, 93.7%, and 94.4%). In conclusion, the clinical performance of a universal, edoxaban-calibrated anti-Xa assay was solid and most drug concentrations were predicted correctly

Population pharmacokinetic analyses of regorafenib and capecitabine in patients with locally advanced rectal cancer (SAKK 41/16 RECAP)

Aims: Locally advanced rectal cancer (LARC) is an area of unmet medical need with one third of patients dying from their disease. With response to neoadjuvant chemo-radiotherapy being a major prognostic factor, trial SAKK 41/16 assessed potential benefits of adding regorafenib to capecitabine-amplified neoadjuvant radiotherapy in LARC patients. Methods: Patients received regorafenib at three dose levels (40/80/120 mg once daily) combined with capecitabine 825 mg/m2 bidaily and local radiotherapy. We developed population pharmacokinetic models from plasma concentrations of capecitabine and its metabolites 5'-deoxy-5-fluorocytidine and 5'-deoxy-5-fluorouridine as well as regorafenib and its metabolites M-2 and M-5 as implemented into SAKK 41/16 to assess potential drug-drug interactions (DDI). After establishing parent-metabolite base models, drug exposure parameters were tested as covariates within the respective models to investigate for potential DDI. Simulation analyses were conducted to quantify their impact. Results: Plasma concentrations of capecitabine, regorafenib and metabolites were characterized by one and two compartment models and absorption was described by parallel first- and zero-order processes and transit compartments, respectively. Apparent capecitabine clearance was 286 L/h (relative standard error [RSE] 14.9%, interindividual variability [IIV] 40.1%) and was reduced by regorafenib cumulative area under the plasma concentration curve (median reduction of 45.6%) as exponential covariate (estimate -4.10 × 10-4 , RSE 17.8%). Apparent regorafenib clearance was 1.94 L/h (RSE 12.1%, IIV 38.1%). Simulation analyses revealed significantly negative associations between capecitabine clearance and regorafenib exposure. Conclusions: This work informs the clinical development of regorafenib and capecitabine combination treatment and underlines the importance of studying potential DDI with new anticancer drug combinations. Keywords: capecitabine; drug-drug interaction; population pharmacokinetics; rectal cancer; regorafenib

Accuracy of a Single, Heparin-Calibrated Anti-Xa Assay for the Measurement of Rivaroxaban, Apixaban, and Edoxaban Drug Concentrations: A Prospective Cross-Sectional Study

Background: Applying a single anti-Xa assay, calibrated to unfractionated heparin to measure rivaroxaban, apixaban, and edoxaban would simplify laboratory procedures and save healthcare costs. Aim: We hypothesized that a heparin-calibrated anti-Xa assay would accurately measure rivaroxaban, apixaban, and edoxaban drug concentrations and correctly predict clinically relevant drug levels. Methods: This analysis is part of the Simple-Xa study, a prospective multicenter cross-sectional study conducted in clinical practice. Patients treated with rivaroxaban, apixaban, or edoxaban were included. Anti-Xa activity was measured using the Siemens INNOVANCE® Heparin assay. Drug concentrations were determined using ultra-high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cut-off levels were determined in a derivation dataset (50% of patients) and sensitivities and specificities were calculated in a verification dataset (50% of patients). Results: Overall, 845 patients were available for analysis. Correlation coefficients (r s ) between the heparin-calibrated anti-Xa assay and drug concentrations were 0.97 (95% CI 0.97, 0.98) for rivaroxaban, 0.96 (0.96, 0.97) for apixaban, and 0.96 (0.94, 0.99) for edoxaban. The area under the receiver operating characteristics curve (ROC) was 0.99 for all clinically relevant drug concentrations. In the verification dataset, the sensitivity was 94.2% (95% CI 90.8-96.6) for 30 μg L-1, 95.8% (92.4-98.0) for 50 μg L-1, and 98.7% (95.5-99.9) for 100 μg L-1. Specificities were 86.3% (79.2-91.7), 89.8% (84.5-93.7), and 88.7% (84.2-92.2), respectively. Conclusion: In a large prospective study in clinical practice, a strong correlation of heparin-calibrated anti-Xa measurements with LC-MS/MS results was observed and clinically relevant drug concentrations were predicted correctly. Keywords: anti-Xa assay; diagnostic accuracy; direct oral anticoagulants; laboratory monitoring; rivaroxaban

An English cover-up: masks, murders, and English cruelty in Goncourt, Lorrain, and Schwob

Fin-de-siècle writers from diverse disciplines were drawn to the seductive potential of masks and disguise; mask-wearing characters of indefinite identity, indeterminate gender, and insecure psychology proliferate in their texts. However, when characters are designated as English in such stories, they are also, and with remarkable frequency, associated with cruelty or murder: the mask-wielding murderers of Marcel Schwob’s ‘MM. Burke et Hare, Assassins’ carry out their crimes in Britain upon British victims; Edmond de Goncourt weaves his theatrical narrative around the mask-like demeanour of Lord Annandale in La Faustin; and Jean Lorrain’s malicious Lord Ethal exacerbates the Duc de Fréneuse’s perverse obsessions with masks in Monsieur de Phocas. This article explores this unexpected correlation, and examines the ways that English masks are used as narrative devices – at once to mould and play with national distinctions, and to reflect upon the psychological state of the French subject