Determination of carryover and contamination for mass spectrometry-based chromatographic assays

High-pH mobile phase in reversed-phase liquid chromatography-tandem mass spectrometry to improve the separation efficiency of aminoglycoside isomers

In chromatography, the use of extreme conditions can often lead to unique separation selectivity. In this study, a highly basic mobile phase (pH > 11), which is not typically employed for reversed-phase liquid chromatography (RPLC), was utilized in RPLC-tandem mass spectrometry (MS/MS) to achieve effective separation between electrically neutral bases of aminoglycosides (AGs). A mixture of AGs was simultaneously analyzed using 500 mmol L-1 ammonia aqueous solution (pH 11.8) as the mobile phase. A total of 11 AGs, including 2 stereoisomers of neomycin (B and C) and 5 structurally similar components of gentamicin (C1, C1a, C2, C2a, and C2b), were completely separated for the first time. The high separation performance for AGs was mainly due to two factors: First, slight differences in hydrophobicity among the AGs were significantly enhanced at a high pH by the complete acid dissociation of amines. Second, the high pH of the mobile phase minimized any electrostatic interactions between the AGs and residual silanol groups in the stationary phase, resulting in extremely sharp peaks for the AGs. The sensitivity of spectinomycin decreased by more than 20% when using the highly basic mobile phase (pH 11.8) due to its degradation, therefore, a mixture of 10 AGs was analyzed with 250 mmol L-1 ammonia aqueous solution (pH 11.5) with less degradation as the optimum condition. The developed analytical method could be used to determine the concentrations of trace AGs in milk with high accuracy and precision. Thus, RPLC-MS/MS using a high-pH mobile phase has great potential for the efficient separation of basic compounds containing amino sugars such as AGs.

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

A New Broad-Spectrum Drug Screen for 127 Analytes by LC-MS/MS

BACKGROUND

Broad-spectrum drug screening is offered by many clinical laboratories to support investigation of possible drug exposures. The traditional broad-spectrum drug screen employed at our laboratory utilizes several different analytical platforms, thus requiring relatively high volumes of sample and a cumbersome workflow. Here we describe the development and validation of a consolidated broad-spectrum drug screen assay designed to qualitatively detect 127 compounds in urine (Ur) and serum/plasma (S/P) samples.

METHODS

An LC-MS/MS method was developed using the Ultivo LC-MS/MS and designed to be qualitative with a 1-point calibration curve and 50% to 150% controls. Sample preparation included the addition of 122 internal standards (IS) followed by mixed-mode strong cation exchange solid-phase extraction and reverse-phase chromatographic separation on a biphenyl column.

RESULTS

For the method described herein, ≥ 95% of analytes in urine and serum control samples had a CV of ≤20% for total imprecision. Accuracy testing included 46 external controls and demonstrated 99.9% accuracy. Method comparison studies to quantitative testing are discussed. The high level of coverage of the analytes with a stable isotope-labeled IS (SIL-IS) helped normalize for matrix effects when significant ion suppression (>25%) was present. Analyte stability in the matrix, the impact of potentially interfering compounds, and method ruggedness were demonstrated. Method limitations include limited detection of glucuronidated drugs and potential cross-contamination with samples at very high concentrations (>>100 × cutoff).

CONCLUSIONS

The broad-spectrum drug screen method developed here qualitatively detected 127 drugs and select metabolites. This method could be used to support investigations of possible drug exposures in a clinical setting.

Identification of a frit-related sample carryover in newborn screening by tandem mass spectrometry

The need for high-throughput analysis of multiple analytes for inborn errors of metabolism in newborn screening (NBS) has led to the introduction of tandem mass spectrometry (MS/MS) into the NBS laboratory. In a flow-injection analysis (FIA), the predominant MS/MS method utilized for NBS, samples are introduced directly into the mass spectrometer without chromatographic separation. When a high-throughput FIA-based MS/MS method is implemented on newer generations of mass spectrometers with increased sensitivity, the risk of carryover and contamination increases. In the present study, we report the carryover of ornithine identified during the implementation of the NeoBase™ 2 (PerkinElmer) non-derivatized kits on the Xevo-TQD platform (Waters Corporation) and describe the source of the carryover, which was traced to the stainless-steel frit-type inline filter. Furthermore, a possible compound-dependent interaction with the stainless-steel frit is suggested based on the structure of ornithine and its effect on separation techniques. Investigation and mitigation of carryover can be a time and resource consuming process, and to this end, our report on identification of a stainless-steel frit as the source of delayed elution and carryover of ornithine should be recognized as a rare, albeit possible source of carryover in FIA-MS/MS methods adopted for NST.

Simultaneous quantitation of befotertinib (D-0316) and its metabolite D-0865 in human plasma by LC-MS/MS method

A sensitive and reliable method was developed to determine befotertinib (D-0316) and its metabolite D-0865 from human plasma by LC-MS/MS. The samples were prepared by simple protein precipitation and 2 µL of the supernatant were chromatographed on a C18 analytical column (ACE Excel 2 Super C₁₈, 50 × 2.1 mm). Elution was performed with mobile phase A (10 mM ammonium acetate in water containing 1 % formic acid) and mobile phase B (acetonitrile containing 1 % formic acid) under a gradient program in a total run time of 4 min. Triple Quadruple 5500 equipped with Turbo Ion Spray source and multiple reaction monitoring (MRM) were used for the analysis detection. The transitions were m/z 568.3 → 72.1 m/z (befotertinib), m/z 554.2 → 497.2 (D-0865), and m/z 455.2 → 164.9 (verapamil, internal standard). According to the Chinese Pharmacopeia Commission and ICH Harmonised Guideline for Bioanalytical Method Validation, this method was validated within the spectrum of its accuracy, precision, selectivity, linearity, recovery, matrix effect, and stability. This LC-MS/MS method was successfully applied for the quantitation of befotertinib and its metabolite D-0865 in human plasma during the pharmacokinetics study of befotertinib in non-small cell lung cancer (NSCLC) patients.

Development and validation of a simple and rapid HILIC-MS/MS method for the quantification of low-abundant lysoglycerophospholipids in human plasma

Lysoglycerophospholipids (Lyso-GPLs) are an essential class of signaling lipids with potential roles in human diseases, such as cancer, central nervous system diseases, and atherosclerosis. Current methods for the quantification of Lyso-GPLs involve complex sample pretreatment, long analysis times, and insufficient validation, which hinder the research of Lyso-GPLs in human studies, especially for Lyso-GPLs with low abundance in human plasma such as lysophosphatidic acid (LPA), lysophosphatidylinositol (LPI), lysophosphatidylglycerol (LPG), lysophosphatidylserine (LysoPS), lyso-platelet-activating factor (LysoPAF), and cyclic phosphatidic acid (cPA). Herein, we report the development and validation of a simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of Lyso-GPLs with low abundance in plasma. Protein precipitation using MeOH for Lyso-GPL extraction, quick separation (within 18 min) based on hydrophilic interaction liquid chromatography (HILIC), and sensitive MS detection under dynamic multiple reaction monitoring (dMRM) mode enabled efficient quantification of 22 Lyso-GPLs including 2 cPA, 4 LPG, 11 LPA, 2 LysoPS, and 3 LysoPAF in 50 μL of human plasma. The present method showed good linearity (goodness of fit, 0.99823-0.99995), sensitivity (lower limit of quantification, 0.03-14.06 ng/mL), accuracy (73-117%), precision (coefficient of variation ≤ 28%), carryover (≤ 17%), recovery (80-110%), and stability (83-123%). We applied the method in an epidemiological study and report concentrations of 18 Lyso-GPLs in 567 human plasma samples comparable to those of previous studies. Significant negative associations of LysoPAF C18, LysoPAF C18:1, and LysoPAF C16 with homeostatic model assessment for insulin resistance (HOMA-IR) level were observed; this indicates possible roles of LysoPAF in glucose homeostasis. The application of the present method will improve understanding of the roles of circulating low-abundant Lyso-GPLs in health and diseases.

Impact of valproic acid on busulfan pharmacokinetics: In vitro assessment of potential drug-drug interaction

Busulfan (Bu) is an alkylating agent commonly used at high doses in the preparative regimens of hematopoietic stem cell transplantation (HSCT). It has been shown that such high doses of Bu are associated with generalized seizures which are usually managed by prophylactic antiepileptic drugs (AEDs) such as valproic acid (VPA). Being a strong enzyme inhibitor, VPA may inhibit Bu metabolism and thus increase its potential toxicity. Despite its clinical relevance, the potential interaction between Bu and VPA has not yet been evaluated. The aim of the present study was to assess and evaluate the potential drug-drug interaction (DDI) between Bu and VPA. This study was carried out by incubating Bu in laboratory-prepared rat liver-subcellular fractions including S9, microsomes, and cytosol, alone or in combination with VPA. The liver fractions were prepared by differential centrifugation of the liver homogenate. Analysis of Bu was employed using a fully validated LC-MS/MS method. The validation parameters were within the proposed limits of the international standards guidelines. Bu metabolic stability was assessed by incubating Bu at a concentration of 8 μg/ml in liver fractions at 37°C. There were significant reductions in Bu levels in S9 and cytosolic fractions, whereas these levels were not significantly (P ˃ 0.05) changed in microsomes. However, in presence of VPA, Bu levels in S9 fraction remained unchanged. These results indicated, for the first time, the potential metabolic interaction of Bu and VPA being in S9 only. This could be explained by inhibiting Bu cytosolic metabolism by the interaction with VPA either by sharing the same metabolic enzyme or the required co-factor. In conclusion, the present findings suggest, for the first time, a potential DDI between Bu and VPA in vitro using rat liver fractions. Further investigations are warranted in human-derived liver fractions to confirm such an interaction.

Progress on the development of a metal salt-assisted ionization source for the mass spectrometric analysis of polymers

The mass spectrometric analysis of polymers has been addressed as a challenging research topic due to poor ionization and complicated analysis using conventional mass spectrometry. The ionization source has demonstrated a promising future in rapid mass spectrometric analysis. Soft ionization techniques, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) are the most ionization sources appeared to be a powerful tools for polymer characterization when combined with MS. However, they always need metal salts to be introduced during the ionization protocol for polymers due to the crucial role played by their ions (cations and anions). The current review focuses on the progress in the development of metal ion-assisted-ionization sources for the mass spectrometric analysis of polymers. Different ionization systems are comprehensively reviewed. The application of metal ion-assisted ESI, nanoESI, PSI, and MALDI-MS for polymer sample analyses is systematically discussed. The future research trends and challenges in this cutting-edge research field are summarized. It also aims to provide the current state-of-the-art of metal salts as a platform for ionization systems for the mass spectrometric characterization of polymers and offers the current challenges and perspectives on the promising future to improve analytical performance in this field. Finally, this mini-review provides a comprehensive handbook to researchers from different research backgrounds wishing to work in this area.

An UHPLC-MS/MS method for quantification of the CDK4/6 inhibitor abemaciclib in human serum

BACKGROUND

Abemaciclib is a new oral targeted treatment option for patients with advanced breast cancer. The emerging field of oral antitumor therapeutics presents challenges for both patients and healthcare teams; non-adherence and high inter-individual pharmacokinetic variability can influence response rates.

METHODS

For monitoring abemaciclib in human sera, a rapid novel ultra-high-performance liquid chromatography-tandem mass spectrometry method was developed and fully validated. Sample preparation was based on a protein precipitation step followed by on-line solid phase extraction. Chromatographic separation was achieved using a biphenyl column and the isotope labeled standard abemaciclib-d8 was used for quantification.

RESULTS

The method showed linearity over a wide calibration range from 20.0 to 2500 ng/mL. With accuracies and precisions of ≤13.9% and ≤4.42%, respectively, the validation results were within the criteria of acceptance. The fitness of the method was tested by monitoring abemaciclib levels under compassionate use for a single individual.

CONCLUSIONS

The novelty of the presented two dimensional isotope dilution UHPLC-MS/MS method is in the semi-automated sample preparation, which results in negligible matrix effects, thereby allowing the introduction of abemaciclib into robust routine therapeutic drug monitoring (TDM). This method provides an efficient tool to verify the usefulness of personalized anticancer therapy in clinical practice.

A simple and rapid method for extraction and measurement of circulating sphingolipids using LC-MS/MS: a targeted lipidomic analysis

Sphingolipids are a class of lipids with high structural diversity and biological pleiotropy. Mounting evidence supports a role for sphingolipids in regulating pathophysiology of cardiometabolic diseases, and they have been proposed as potential cardiometabolic biomarkers. Current methods for quantifying sphingolipids require laborious pretreatment and relatively large sample volumes, and cover limited species, hindering their application in epidemiological studies. Herein, we applied a time-, labor-, and sample-saving protocol simply using methanol for plasma sphingolipid extraction. It was compared with classical liquid-liquid extraction methods and showed significant advantages in terms of simplicity, sphingolipid coverage, and sample volume. By coupling the protocol with liquid chromatography using a wide-span mobile phase polarity parameter and tandem mass spectrometry operated in dynamic multiple reaction monitoring mode, 37 sphingolipids from 8 classes (sphingoid base, sphingoid base phosphate, ceramide-1-phosphate, lactosylceramide, hexosylceramide, sphingomyelin, ceramide, and dihydroceramide) were quantified within 16 min, using only 10 μL of human plasma. The current method showed good performance in terms of linearity (R² > 0.99), intra- and interbatch accuracy (70-123%) and precision (RSD < 12%), matrix effect (91-121%), recovery (96-101%), analyte chemical stability (deviation < 19%), and carryover (< 16%). We successfully applied this method to quantify 33 detectable sphingolipids from 579 plasma samples of an epidemiological study within 10 days. The quantified sphingolipid concentrations were comparable with previous studies. Positive associations of ceramide C22:0/C24:0 and their precursors with homeostasis model assessment of insulin resistance suggested that the synthesis of the ceramides might be involved in insulin resistance. This novel method constitutes a simple and rapid approach to quantify circulating sphingolipids for epidemiological studies using targeted lipidomic analysis, which will help elucidate the sphingolipid-regulated pathways underlying cardiometabolic diseases.

Isolation of N-nitrosodimethylamine from drug substances using solid-phase extraction-liquid chromatography-tandem mass spectrometry

N-Nitrosodimethylamine (NDMA) has been detected in some drug substances and pharmaceutical products containing sartans, ranitidine and metformin, and a potential risk of NDMA contamination exists in other drug substances and their pharmaceutical products. To quantitate NDMA in various drugs having diverse physicochemical properties, a specific, sensitive, and reliable analytical method is required, in addition to methods that can be applied to a class of nitrosamines. We aimed to develop an off-line isolation method for NDMA in drug substances using SPE for quantification with LC-APCI-MS/MS. Impediments to accurate quantitation of NDMA in drug substances using LC-MS/MS and insufficient durability of the system are attributed to the extremely large amounts of active pharmaceutical ingredients (APIs) in sample solutions in comparison to the trace amount of NDMA. A reduced retention of NDMA and/or decreased separation from other substances in LC, matrix effect in MS detection, and undesirable contamination of instruments with API and other substances may be occasionally encountered, all of which consequently result in deterioration of system performance and generation of unreliable data, even in the cases where a divert valve is configured between the column and ion source of the MS instrument. To address these problems, an off-line NDMA isolation methodology from APIs exhibiting diverse physicochemical properties, namely ranitidine hydrochloride (ranitidine), metformin hydrochloride (metformin), nizatidine, valsartan, and telmisartan, was developed. The applicability of the method was confirmed by batch analysis of metformin and ranitidine. Furthermore, contrary to previous reports, NDMA was found to be stable over a wide pH range. The proposed methodology and data from this study would contribute to the control of NDMA contamination in various drugs to realize the safe delivery of pharmaceuticals to patients.

Determination and structural characterization of ravidasvir metabolites by LC coupled to triple quadrupole linear ion trap MS: Application to pharmacokinetics and phase I metabolism in rats

Hepatitis C virus (HCV) is an infectious disease that has become a global clinical issue because of its significant morbidity and mortality. Novel anti-hepatitis C drugs are continuously developed to decrease the pervasiveness of the infection globally. A synthetic ravidasvir, benzimidazole-naphthylene-imidazole derivatives, has been used as an anti-HCV drug. This study determined the metabolites of ravidasvir and its pharmacokinetics in rats using information-dependent acquisition and multiple reaction monitoring scanning modes in linear ion trap LC-MS/MS instrument, respectively. Two time-programming linear-gradient chromatographic methods were employed using a Kinetex C₁₈ column (50 × 3 mm, 2.6 μm) and a Luna HILIC column (100 × 4.6 mm, 3 μm) for the qualitative and quantitative determination of ravidasvir and its metabolites, respectively. In silico prediction where sites in a molecule are susceptible to metabolism by cytochrome P₄₅₀ was implemented, which helped in proposing the metabolic pathway of ravidasvir. The most dominant metabolite in rat liver microsomal samples was oxidative ravidasvir, where one O-demethylated metabolite and eight isomers of the oxidative ravidasvir metabolites were identified. The study provides essential data for proposing the metabolic pathway and successfully applied it to determine the pharmacokinetics of ravidasvir in rat plasma.

Application of an ultra-performance liquid chromatography-tandem mass spectrometric method for the detection and quantification of cannabis in cerumen samples

In this study, cerumen, a non-conventional biological secretion, was examined as an alternative matrix for forensic analyzis. A fully validated analytical UPLC-MS/MS method was developed for the detection and quantification of the most prevalent psychoactive illicit drug globe wide, Δ⁹-tethrahydrocannabinol, commonly known as THC, and four major cannabinoids found in cannabis Sativa. The method was validated, and standard external calibration curves were established with correlation coefficients > 0.99. A validated experimental procedure, along with a direct extraction of cannabinoids with acidified acetonitrile resulted in a short total analyzis time and a good extraction efficiency for all the analytes under study. LOD and LOQ values were determined to be 0.01-0.08 pg/mg and 0.04-0.23 pg/mg, respectively. To prove applicability of the proposed assay, volunteers were selected, and cerumen samples were examined for cannabis. The analyzis by use of UPLC-MS/MS indicated that all samples were positive, reporting recent cannabis abuse. Surprisingly, both THC and Cannabinol (CBN) were detected, and quantification was possible in 75% of the cases.

Rapid determination of thyroid hormones in blood plasma from Glaucous gulls and Baikal seals by HybridSPE®-LC-MS/MS

A rapid hybrid solid phase extraction (HybridSPE®) protocol tailored to liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis, was developed for the determination of four thyroid hormones, L-Thyroxine (T₄), 3,3',5-triiodo-L-thyronine (T₃), 3,3',5'-triiodo-L-thyronine (rT₃) and 3,3'-diiodo-L-thyronine (T₂) in blood plasma from Glaucous gulls (Larus hyperboreus) and Baikal seals (Phoca sibirica). The use of target analyte specific ¹³C internal standards allowed quantification to be performed through the standard solvent calibration curves and alleviated the need to perform quantification with matrix match curves. The relative recoveries were 100.0-110.1 % for T₄, 99.1-102.2 % for T₃, 100.5-108.0 % for rT₃, and 100.5-104.6 % for T₂. The matrix effects ranged from -1.52 to -6.10 %, demonstrating minor signal suppression during analysis. The method intra-day precision (method repeatability, RSD %, N = 5, k = 1 day) and inter-day precision (method reproducibility, RSD %, N = 10, k = 2 days) at the 1 ng/mL concentration of fortification were 8.54-15.4 % and 15.4-24.8 %, respectively, indicating acceptable chromatographic peak stabilities for all target THs even at trace level concentrations. The method limit of detection (LOD) for T₄, T₃, rT₃ and T₂ was 0.17, 0.16, 0.30 and 0.17 ng/mL, respectively. The HybridSPE® protocol was simple and rapid (<1 min) upon application, while the HybridSPE® cartridge did not require (as in classical SPE cartridges) any additional equilibration nor conditioning step prior sample loading. A total of 46 blood plasma samples, 30 samples collected from Glaucous gulls and 16 samples collected from Baikal seals, were analyzed for thyroid hormones to demonstrate the applicability of the developed method in these wildlife species. The concentrations of T₄ and T₃ in blood plasma from the Glaucous gulls were 5.95-44.2 and 0.37-5.61 ng/mL, respectively, whereas those from Baikal seals were 3.57-46.5 and 0.45-2.07 ng/mL, respectively. In both species, rT₃ demonstrated low detection rate, while T₂ was not detected. Furthermore, cross-array comparison between the HybridSPE®-LC-MS/MS protocol and an established routine radioimmunoassay (RIA) kit-based method was performed for T₄ and T₃ concentrations from selected Baikal seal plasma samples.

Determination of Crizotinib in Mouse Tissues by LC-MS/MS and Its Application to a Tissue Distribution Study

Toxicity induced by crizotinib, a small-molecule tyrosine kinase inhibitor, is a significant clinical issue during treatment. A tissue distribution study is required to explore the organs affected by this molecule. In this study, a simple liquid chromatography tandem mass spectrometry method was developed and validated for the determination of crizotinib in various mouse tissues. Mouse tissue homogenates were processed by protein precipitation with methanol, and apatinib was chosen as the internal standard. The analytes were separated on a Phenomenex Kinetex C₁₈ (50 mm × 2.1 mm, 2.6 μm) column with gradient elution using methanol and 0.3% formic acid water solution. Tandem mass spectrometric detection was conducted using multiple reaction monitoring via an electrospray ionization source in the positive mode. The monitored ion transitions were m/z 450.1 ⟶ 260.2 for crizotinib and m/z 398.2 ⟶ 212.0 for apatinib. The problem of the severe carryover effect was successfully resolved. The method was validated and applied to a tissue distribution study of crizotinib in mice, which was reported for the first time. The results of the study showed that the main target organs of crizotinib were the lung, liver, and spleen, and a high concentration of crizotinib was found in the gastrointestinal tract. This study offers a reliable method for quantifying crizotinib and provides a basis for further research on crizotinib toxicity.

Drugs in bone: Detectability of substances of toxicological interest in different states of preservation

In forensic contexts of advanced decomposition, when conventional matrices are no longer available for toxicological analyses, finding alternative matrices is necessary. The skeleton, which is fundamental for anthropologists and geneticists, could be useful also for toxicological purposes. The present study aims to examine what kind of information toxicological analysis performed on bones (the cranium and the ribs) in different states of preservation could provide to the forensic practitioner. Thirty cadavers with known pharmacological history, subjected to forensic autopsy at the Institute of Legal Medicine of Milan, were selected. Rib and cranium samples were collected from each body and separated into two parts in order to create two different states of preservation: One was cleaned from soft tissues and analyzed as a well-preserved bone sample; the other was submitted to a long maceration process, simulating complete skeletonization. All specimens were then processed with accelerated solvent extraction and the eluates analyzed using Q-Exactive™ Orbitrap™ Mass Spectrometer. The analysis of blood and skeletal matrices showed positive results for the tested substances in 63% of cases, mainly benzodiazepines, antidepressants, and drug abuse. Significant Pearson correlations were observed between non-macerated vs. macerated bone samples: r = 0.79 for rib samples, r = 0.61 for cranium samples, and r = 0.69 for all bone samples. As a consequence, the positive results confirm the potential of the bone tissue as an alternative matrix in forensic toxicology, even in cases of extremely decomposed bodies. This study also highlighted important elements for reconstructing the biological profile in cases of forensic anthropological concern.

Development and validation of a simple LC-MS/MS method for simultaneous determination of moxifloxacin, levofloxacin, prothionamide, pyrazinamide and ethambutol in human plasma

Treatment of multidrug-resistant tuberculosis (MDR-TB) is challenging due to high treatment failure rate and adverse drug events. This study aimed to develop and validate a simple LC-MS/MS method for simultaneous measurement of five TB drugs in human plasma and to facilitate therapeutic drug monitoring (TDM) in MDR-TB treatment to increase efficacy and reduce toxicity. Moxifloxacin, levofloxacin, prothionamide, pyrazinamide and ethambutol were prepared in blank plasma from healthy volunteers and extracted using protein precipitation reagent containing trichloroacetic acid. Separation was achieved on an Atlantis T3 column with gradient of 0.1% formic acid in water and acetonitrile. Drug concentrations were determined by dynamic multiple reaction monitoring in positive ion mode on a LC-MS/MS system. The method was validated according to the United States' Food and Drug Administration (FDA) guideline for bioanalytical method validation. The calibration curves for moxifloxacin, levofloxacin, prothionamide, pyrazinamide and ethambutol were linear, with the correlation coefficient values above 0.993, over a range of 0.1-5, 0.4-40, 0.2-10, 2-100 and 0.2-10 mg/L, respectively. Validation showed the method to be accurate and precise with bias from 6.5% to 18.3% for lower limit of quantification and -5.8% to 14.6% for LOW, medium (MED) and HIGH drug levels, and with coefficient of variations within 11.4% for all levels. Regarding dilution integrity, the bias was within 7.2% and the coefficient of variation was within 14.9%. Matrix effect (95.7%-112.5%) and recovery (91.4%-109.7%) for all drugs could be well compensated by their isotope-labelled internal standards. A benchtop stability test showed that the degradation of prothionamide was over 15% after placement at room temperature for 72 h. Clinical samples (n = 224) from a cohort study were analyzed and all concentrations were within the analytical range. The signal of prothionamide was suppressed in samples with hemolysis which was solved by sample dilution. As the method is robust and sample preparation is simple, it can easily be implemented to facilitate TDM in programmatic MDR-TB treatment.

Intact mAb LC–MS for drug concentration from pre-clinical studies: bioanalytical method performance and in-life samples

Background: Antibody biotherapeutic measurement from pharmacokinetic studies has not been traditionally based on intact molecular mass as is the case for small molecules. However, recent advancements in protein capture and mass spectrometer technology have enabled intact mass detection and quantitation for dosed biotherapeutics. A bioanalytical method validation is part of the regulatory requirement for sample analysis to determine drug concentration from in-life study samples. Results/methodology: Here, an intact protein LC–MS assay is subjected to mock bioanalytical method validation, and unknown samples are compared between intact protein LC–MS and established bioanalytical assay formats: Ligand-binding assay and peptide LC–MS/MS. Discussion/conclusion: Results are presented from the intact and traditional bioanalytical method evaluations, where the in-life sample concentrations were comparable across method types with associated data analyses presented. Furthermore, for intact protein LC–MS, modification monitoring and evaluation of data processing parameters is demonstrated.

Strategies for effective development of ultra-sensitive LC–MS/MS assays: application to a novel STING agonist

Background: The continual need for the development and validation of ultra-sensitive (low pg/ml) LC–MS/MS assays in the pharmaceutical industry is largely driven by the ultra-low analyte exposure or very low sample volume. Methodology: Strategies and systematic approaches for sensitivity enhancement are provided which cover all aspects of a LC–MS/MS bioanalysis. A case study where such strategies were applied for the validation of a 5.0 pg/ml assay for a STING agonist is discussed. Conclusion: Analytical protocols were developed to extract analytes from large volume of plasma samples (600 and 400 μl) with high throughput. The guidance provided in this publication can serve as a resource to influence LC–MS/MS method development activities.

Spatially Controlled Molecular Analysis of Biological Samples Using Nanodroplet Arrays and Direct Droplet Aspiration

Mass spectrometry (MS) has emerged as a valuable technology for molecular and spatial evaluation of biological samples. Ambient ionization MS techniques, in particular, allow direct analysis of tissue samples with minimal pretreatment. Here, we describe the design and optimization of an alternative ambient liquid extraction MS approach for metabolite and lipid profiling and imaging from biological samples. The system combines a piezoelectric picoliter dispenser to form solvent nanodroplets onto the sample surface with controlled and tunable spatial resolution and a conductive capillary to directly aspirate/ionize the nanodroplets for efficient analyte transmission and detection. Using this approach, we performed spatial profiling of mouse brain tissue sections with different droplet sizes (390, 420, and 500 μm). MS analysis of normal and cancerous human brain and ovarian tissues yielded rich metabolic profiles that were characteristic of disease state and enabled visualization of tissue regions with different histologic composition. This method was also used to analyze the lipid profiles of human ovarian cell lines. Overall, our results demonstrate the capabilities of this system for spatially controlled MS analysis of biological samples.

Metal salt assisted electrospray ionization mass spectrometry for the soft ionization of GAP polymers in negative ion mode

Glycidyl azide polymers (GAP) are one of the most important energetic polymers, but it is still a challenge to elucidate their structures using mass spectrometry due to their fragility upon ionization. Herein we developed a soft metal salt assisted electrospray ionization (MSAESI) to characterize directly GAP polymers using mass spectrometry. This technique combines paper spray ionization and the complexing effect of anions from metal salts with GAP in the negative ion mode to softly ionize GAP polymers prior to mass spectrometry analysis. The effects of experimental parameters (e.g., ion mode, applied voltage, and type and concentration of metal salts) have been investigated in detail. In contrast to the positive ion mode, a softer ionization was observed for GAP polymers when the negative ion mode was applied. The radius and average charge of cations and anions in metal salts were found to play crucial roles in determining the performance of the MSAESI analysis of GAP. For a given charge number, a smaller radius of cations favored the soft ionization of GAP polymers (e.g., Na+ > K+ > Rb+), whereas a larger radius of anions led to a preferred performance (e.g., F- < Cl- < Br- < I-) due to variation in dissolution ability. For anions with multiple charges, the ones with fewer charges gave a more favorable ionization to the GAP sample because of their better complexing to GAP molecules than those with more charges in the structure of anions (e.g., NO3- > SO42- > PO43-). According to the experimental observation and evidence from mass spectrometry, we proposed the plausible electrospray mechanisms of MSAESI for GAP analysis with the involvement of metal salts. Moreover, the developed protocol has been applied successfully to the analysis of various GAP samples, and works for other types of sources such as nanoelectrospray ionization.

Automation of mass spectrometric detection of analytes and related workflows: A review

The developments in mass spectrometry (MS) in the past few decades reveal the power and versatility of this technology. MS methods are utilized in routine analyses as well as research activities involving a broad range of analytes (elements and molecules) and countless matrices. However, manual MS analysis is gradually becoming a thing of the past. In this article, the available MS automation strategies are critically evaluated. Automation of analytical workflows culminating with MS detection encompasses involvement of automated operations in any of the steps related to sample handling/treatment before MS detection, sample introduction, MS data acquisition, and MS data processing. Automated MS workflows help to overcome the intrinsic limitations of MS methodology regarding reproducibility, throughput, and the expertise required to operate MS instruments. Such workflows often comprise automated off-line and on-line steps such as sampling, extraction, derivatization, and separation. The most common instrumental tools include autosamplers, multi-axis robots, flow injection systems, and lab-on-a-chip. Prototyping customized automated MS systems is a way to introduce non-standard automated features to MS workflows. The review highlights the enabling role of automated MS procedures in various sectors of academic research and industry. Examples include applications of automated MS workflows in bioscience, environmental studies, and exploration of the outer space.

Monitoring of system conditioning after blank injections in untargeted UPLC-MS metabolomic analysis

Ultra-performance liquid chromatography – mass spectrometry (UPLC-MS) is widely used for untargeted metabolomics in biomedical research. To optimize the quality and precision of UPLC-MS metabolomic analysis, evaluation of blank samples for the elimination of background features is required. Although blanks are usually run either at the beginning or at the end of a sequence of samples, a systematic analysis of their effect of the instrument performance has not been properly documented. Using the analysis of two common bio-fluids (plasma and urine), we describe how the injection of blank samples within a sequence of samples may affect both the chromatographic and MS detection performance depending on several factors, including the sample matrix and the physicochemical properties of the metabolites of interest. The analysis of blanks and post-blank conditioning samples using t-tests, PCA and guided-PCA provides useful information for the elimination of background UPLC-MS features, the identification of column carry over and the selection of the number of samples required to achieve a stable performance.

Bioanalytical LC-MS/MS validation of therapeutic drug monitoring assays in oncology

Therapeutic drug monitoring (TDM) has shown to benefit patients treated with drugs of many drug classes, among which is oncology. With an increasing demand for drug monitoring, new assays have to be developed and validated. Guidelines for bioanalytical validation issued by the European Medicines Agency and US Food and Drug Administration are applicable for clinical trials and toxicokinetic studies and demand fully validated bioanalytical methods to yield reliable results. However, for TDM assays a limited validation approach is suggested based on the intended use of these methods. This review presents an overview of publications that describe method validation of assays specifically designed for TDM. In addition to evaluating current practice, we provide recommendations that could serve as a guide for future validations of TDM assays.

Inferring Protein-Protein Interaction Networks From Mass Spectrometry-Based Proteomic Approaches: A Mini-Review

Studying protein-protein interaction networks provide key evidence for the underlying molecular mechanisms. Mass spectrometry-based proteomic approaches have been playing a pivotal role in deciphering these interaction networks, along with precise quantification for individual interactions. In this mini-review we discuss the available techniques and methods for qualitative and quantitative elucidation of protein-protein interaction networks. We then summarize the down-stream computational strategies for identification and quantification of interactions from those techniques. Finally, we highlight the challenges and limitations of current computational pipelines in eliminating false positive interactors, followed by a summary of the innovative algorithms to address these issues, along with the scope for future improvements.

Quantification below the LLOQ in regulated LC–MS/MS assays: a review of bioanalytical considerations and cautions

In response to an earlier workshop covering the pros and cons of quantification below the LLOQ (BLQ) the author reviews the topics discussed from the bioanalytical standpoint. Important considerations for estimating concentrations below the LLOQ include: method signal-to-noise, baseline shape and condition, close lying interference peaks (especially for protein methods), matrix effect, adsorption and stability of the analyte at low concentrations and carryover. These methodological issues are discussed as possible contributors to inaccuracy in BLQ estimations, and appropriate cautions are provided via examples. A proposed method for the evaluation of BLQ estimations utilizes extended incurred sample reanalysis analysis where BLQ samples or spiked simulated samples are analyzed with quality controls and standards in addition to those in the original study. Generally, BLQ estimations are discouraged, with the recommendation that any extrapolations should be done in close collaboration between the pharmacokinetic (PK) and bioanalytical scientists in consultation with the regulatory agency.

High sensitivity methods to quantify chloroquine and its metabolite in human blood samples using LC-MS/MS

Aim:

Chloroquine is an antimalarial drug used in the treatment of Plasmodium vivax malaria. Three methods to quantify chloroquine and its metabolite in blood matrices were developed and validated.

Methodology & results:

Different high-throughput extraction techniques were used to recover the drugs from whole blood (50 μl), plasma (100 μl) and dried blood spots (15 μl as punched discs) followed by quantification with LC–MS/MS. The intra- and inter-batch precisions were below 15%, and thus meet regulatory acceptance criteria.

Conclusion:

The developed methods demonstrated satisfactory validation performance with high sensitivity and selectivity. The assays used simple and easy to automate extraction techniques. All methods were reliable with robust performance and demonstrated to be suitable to implement into high-throughput routine analysis of clinical pharmacokinetic samples.

Simultaneous analysis of 310 pesticide multiresidues using UHPLC-MS/MS in brown rice, orange, and spinach

In this study, we developed a multiresidue method for the analysis of 310 pesticides in representative agricultural produce (brown rice, orange, and spinach) using ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) combined with a modified QuEChERS procedure. The optimal mobile phase composition (Methanol containing 5 mM ammonium formate and 0.1% formic acid) produced high sensitivity and reliable results. Also, the relationship between injection volume and repeatability of peak area was investigated. Most of the target pesticides had a limit of quantitation under 10 ng g^-1, and correlation coefficients (r²) > 0.99 in matrix-matched standards within the range of 1-100 ng g^-1. To validate the optimized method, recovery tests were performed with each of the crops at 10 and 50 ng g^-1 spiking levels (n = 5). Satisfactory recoveries were achieved showing that 86.8-88.7% (at 10 ng g^-1) and 91.9-96.1% (at 50 ng g^-1) of the pesticides met the validation criteria (recoveries in the range of 70-120% and relative standard deviation ≤ 20%). Fifteen compounds were found to show a loss of recovery due to adsorption by primary and secondary amine or graphite carbon black. In the case of brown rice, 86.1% of pesticides showed an insignificant matrix effect (<±20%), while 35.2% and 41.6% of pesticides in orange and spinach were in that range, respectively. Sixteen apple samples from local markets were analyzed to evaluate the applicability of the optimized method. Nineteen pesticides were detected, of which the concentrations were lower than the maximum residue limit.

Quality control in mass spectrometry-based proteomics

Mass spectrometry is a highly complex analytical technique and mass spectrometry-based proteomics experiments can be subject to a large variability, which forms an obstacle to obtaining accurate and reproducible results. Therefore, a comprehensive and systematic approach to quality control is an essential requirement to inspire confidence in the generated results. A typical mass spectrometry experiment consists of multiple different phases including the sample preparation, liquid chromatography, mass spectrometry, and bioinformatics stages. We review potential sources of variability that can impact the results of a mass spectrometry experiment occurring in all of these steps, and we discuss how to monitor and remedy the negative influences on the experimental results. Furthermore, we describe how specialized quality control samples of varying sample complexity can be incorporated into the experimental workflow and how they can be used to rigorously assess detailed aspects of the instrument performance.

A LC-MS/MS method to monitor the concentration of HYD-PEP06, a RGD-modified Endostar mimetic peptide in rat blood

HYD-PEP06 is a novel RGD-modified Endostar mimetic peptide with 30 amino acids that is intended to suppress the formation of neoplasm vessels. This assay was developed and validated to monitor the level of the peptide HYD-PEP06 in rat blood, using liquid chromatography tandem mass spectrometry (LC-MS/MS). HYD-PEP10, another peptide similar to the analyte, was used as an internal standard (IS). A triple quadrupole mass spectrometry in Multiple Reaction Monitoring (MRM) mode and an electrospray interface (ESI) in the positive mode were used for MS analysis. The analysis was optimized with addition of 0.3% formic acid (FA) into the mobile phase as well as with a needle washing solution to overcome the carryover effect. In addition, the carryover was reduced by optimizing the mobile phase gradient. Methanol was used as a diluent of working solutions to avoid any adsorption. Methanol:acetonitrile (1:1, v:v) containing 0.3% FA was employed to precipitate the blood samples. Unknown blood samples must be placed in ice bath immediately, and precipitating agents should be added within 30 min to ensure the stability of blood samples. The assay was established and validated. This method showed a good linear relationship for the HYD-PEP06 in the range of 10 ng·mL^-1 to 2000 ng·mL^-1, with R > 0.99. HYD-PEP06 was determined with accuracy values (RE%) of -5.06%-8.54%, intra- and inter-day precisions (RSD%) of 3.13%-4.87% and 4.81%-9.42%. The method was successfully in monitoring the concentration of HYD-PEP06 in rat blood.

Simultaneous quantification of cefepime, meropenem, ciprofloxacin, moxifloxacin, linezolid and piperacillin in human serum using an isotope-dilution HPLC-MS/MS method

The aim of the current study was to develop and validate a robust multi-analyte high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method for simultaneous quantification of cefepime, meropenem, ciprofloxacin, moxifloxacin, linezolid and piperacillin, which are the most commonly used antibiotics in intensive care units. Sample clean-up included a protein precipitation protocol, followed by chromatographic separation on a C₈ reverse phase HPLC column within 4 min, using a formic acid-ammonium formiate methanol step-elution gradient. All compounds were detected with electrospray ionization (ESI+) mass spectrometry in multiple reaction time monitoring. The method was validated according to the protocol from the European Medicines Agency and was thoroughly evaluated for interferences and quantification linearity. Linear relationships between peak area responses and drug concentrations were obtained in the range of 0.25-200 mg/l for cefepime, 0.25-120 mg/l for meropenem, 0.05-10 mg/l for ciprofloxacin, 0.125-10 mg/l for moxifloxacin, 0.125-50 mg/l for linezolid and 0.5-400 mg/l for piperacillin with an R² > 0.997. Imprecision and inaccuracy values (both intra- and inter-assay) were ≤ 6.8% and ≤10.9% for all analytes in quality control samples, respectively. The assay proved to be selective for the study antibiotics, and the internal standards consistently compensated for matrix effects. The described simple and reliable HPLC-MS/MS assay is a powerful tool for routine TDM of cefepime, meropenem, ciprofloxacin, moxifloxacin, linezolid and piperacillin in human serum in clinical laboratories. With a total process time of approximately 30 min, it allows for accurate and selective quantification up to the expected pharmacokinetic peak concentrations.

Development and validation of analytical method for the determination of radotinib in human plasma using liquid chromatography-tandem mass spectrometry

This study describes the development of an analytical method to determine radotinib levels in human plasma using high performance liquid chromatography (HPLC) coupled with triple quadrupole tandem mass spectrometry (MS/MS) for pharmacokinetic application. Plasma samples were sequentially processed by liquid-liquid extraction using methyl tert-butyl ether, evaporation, and reconstitution. Analytes were separated and analyzed using HPLC-MS/MS in selected reaction monitoring mode, monitoring the specific transitions of m/z 531 to 290 for radotinib and m/z 409 to 238 for amlodipine (internal standard). The HPLC-MS/MS analytical method was validated with respect to selectivity, linearity, sensitivity, accuracy, precision, recovery, and stability. Calibration curves were linear over a concentration range 5–3,000 ng/mL with correlation coefficients (r) > 0.998. The lower limit of quantification for radotinib in plasma was 5 ng/mL. The accuracy and precision of the analytical method were acceptable within 15% at all quality control levels. This method was suitable to determine radotinib levels in human plasma because of its simplicity, selectivity, precision, and accuracy.

A sensitive liquid chromatography/electrospray tandem mass spectroscopy method for simultaneous quantification of a disulfide bond doxorubicin conjugation prodrug and activated doxorubicin: Application to cellular pharmacokinetic and catabolism studies

In recent years, drug conjugates as a prodrug strategy have been widely studied, especially combined with nanotechnology. Disulfide-linked doxorubicin drug-drug conjugate (DOX-S-S-DOX) nanoparticles, have recently been developed as a doxorubicin prodrug nanoparticles with greater anticancer activity and less toxicity than doxorubicin in vivo, while its intracellular kinetics and metabolism is unclear which may provide us with a deeper understanding of its pharmacological mechanism and antitumor effect. Hence, in this study, a rapid and sensitive ultra high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to detect doxorubicin (DOX) activated from DOX-S-S-DOX, as well as the prodrug itself in human breast cancer tumor cells (MCF-7). Sample preparation involved acetonitrile precipitation to extract the analytes simultaneously and bath sonication to remove intercalated DOX from DNA. The calibration range was 3-60ng/mL for DOX and 20-400ng/mL for DOX-S-S-DOX with the correlation coefficients (r²)≥0.99, using daunorubicin as internal standard (IS). The inter- and intra-assay precision (relative standard deviation, RSD%) of quality control samples was in the acceptable range (<15%) and relative error (RE%) for accuracy was between -5.35 and 9.18% for all analytes. Recovery (59.28-69.53% for DOX-S-S-DOX and 99.13-100.10% for DOX) and matrix effect (99.69-111.19%) was consistent, precise, and reproducible at different quality control levels in accordance with FDA guidance. Stability studies showed that DOX-S-S-DOX was unstable both during the bench-top and long-term storage, while the stability during sample preparation and LC-MS runtime was suitable for all the analytes. Hence, the samples should be prepared as soon as possible at the time point to prevent the catabolism of DOX-S-S-DOX. The assay was successfully used in the cellular metabolism and pharmacokinetics study of DOX-S-S-DOX and it may give a clue to explore analytical methods of other prodrug forms of DOX.

Quality assurance procedures for mass spectrometry untargeted metabolomics. a review

Untargeted metabolomics, as a global approach, has already proven its great potential and capabilities for the investigation of health and disease, as well as the wide applicability for other research areas. Although great progress has been made on the feasibility of metabolomics experiments, there are still some challenges that should be faced and that includes all sources of fluctuations and bias affecting every step involved in multiplatform untargeted metabolomics studies. The identification and reduction of the main sources of unwanted variation regarding the pre-analytical, analytical and post-analytical phase of metabolomics experiments is essential to ensure high data quality. Nowadays, there is still a lack of information regarding harmonized guidelines for quality assurance as those available for targeted analysis. In this review, sources of variations to be considered and minimized along with methodologies and strategies for monitoring and improvement the quality of the results are discussed. The given information is based on evidences from different groups among our own experiences and recommendations for each stage of the metabolomics workflow. The comprehensive overview with tools presented here might serve other researchers interested in monitoring, controlling and improving the reliability of their findings by implementation of good experimental quality practices in the untargeted metabolomics study.

Determination of rivaroxaban in patient's plasma samples by anti-Xa chromogenic test associated to High Performance Liquid Chromatography tandem Mass Spectrometry (HPLC-MS/MS)

Rivaroxaban is an oral direct factor Xa inhibitor, therapeutically indicated in the treatment of thromboembolic diseases. As other new oral anticoagulants, routine monitoring of rivaroxaban is not necessary, but important in some clinical circumstances. In our study a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was validated to measure rivaroxaban plasmatic concentration. Our method used a simple sample preparation, protein precipitation, and a fast chromatographic run. It was developed a precise and accurate method, with a linear range from 2 to 500 ng/mL, and a lower limit of quantification of 4 pg on column. The new method was compared to a reference method (anti-factor Xa activity) and both presented a good correlation (r = 0.98, p < 0.001). In addition, we validated hemolytic, icteric or lipemic plasma samples for rivaroxaban measurement by HPLC-MS/MS without interferences. The chromogenic and HPLC-MS/MS methods were highly correlated and should be used as clinical tools for drug monitoring. The method was applied successfully in a group of 49 real-life patients, which allowed an accurate determination of rivaroxaban in peak and trough levels.

Mass Spectrometry-Based Escherichia coli H Antigen/Flagella Typing: Validation and Comparison with Traditional Serotyping

BACKGROUND

Escherichia coli H antigen typing with antisera, a useful method for flagella clinical identification and classification, is a time-consuming process because of the need to induce flagella growth and the occurrence of undetermined strains. We developed an alternative rapid and analytically sensitive mass spectrometry (MS) method, termed MS-based H antigen typing (MS-H), and applied it at the protein sequence level for H antigen typing. We also performed a comparison with traditional serotyping on reference strains and clinical isolates.

METHODS

On the basis of international guidelines, the analytical selectivity and sensitivity, imprecision, correlation, repeatability, and reproducibility of the MS-H platform was evaluated using reference strains. Comparison of MS-H typing and serotyping was performed using 302 clinical isolates from 5 Canadian provinces, and discrepant results between the 2 platforms were resolved through whole genome sequencing.

RESULTS

Repeated tests on reference strain EDL933 demonstrated a lower limit of the measuring interval at the subsingle colony (16.97 μg or 1.465 × 10(7) cells) level and close correlation (r(2) > 0.99) between cell culture biomass and sequence coverage. The CV was <10.0% among multiple repeats with 4 reference strains. Intra- and interlaboratory tests demonstrated that the MS-H method was robust and reproducible under various sample preparation and instrumentation conditions. Using discrepancy analysis via whole genome sequencing, performed on isolates with discrepant results, MS-H accurately identified 12.3% more isolates than conventional serotyping.

CONCLUSIONS

MS-H typing of E. coli is useful for fast and accurate flagella typing and could be very useful during E. coli outbreaks.

Effect of Ethanol on the Metabolic Characteristics of HIV-1 Integrase Inhibitor Elvitegravir and Elvitegravir/Cobicistat with CYP3A: An Analysis Using a Newly Developed LC-MS/MS Method

Elvitegravir (EVG), an integrase inhibitor for the treatment HIV infection, is increasingly becoming the part of first-line antiretroviral therapy (ART) regimen. EVG is mainly metabolized through cytochrome P450 (CYP) 3A4. Previously, we have shown that ethanol alters ART-CYP3A4 interactions with protease inhibitors thereby altering their metabolisms. However, as EVG is a fairly new class of drug, its kinetic characteristics and the effect of ethanol on EVG-CYPP3A4 interaction is poorly understood. In this study, we characterized EVG and cobicistat (COBI)-boosted EVG metabolism in human microsomes followed by ethanol-EVG, ethanol-COBI-EVG interaction with CYP3A. First, we developed and validated a simple, sensitive, and robust liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of EVG in the human liver microsomes. The lower limit of quantification for the drug was at 0.003 μM (1.34ng/ml). Extraction yield, matrix effects, drug stability, and calibration curves for the proposed method were validated according to the FDA guidelines. Time dependent kinetics data showed that 20mM ethanol decreases the apparent half-life of EVG degradation by ~50% compared to EVG alone. Our substrate kinetic results revealed that ethanol mildly decreases the catalytic efficiency for EVG metabolism. Inhibition studies demonstrated that EVG inhibits CYP3A4, and 20 mM ethanol causes a decrease in the IC₅₀ of EVG. However, in the presence of COBI we were unable to determine these parameters effectively because COBI, being a strong inhibitor of CYP3A4, blocked the EVG/ethanol-CYP3A4 interactions. Docking studies predicted a shift of EVG or COBI binding to the active site of CYP3A4 in the presence of ethanol. Taken together, these results suggest that ethanol interacts with microsomal CYP3A and alters EVG-CYP3A4 interaction thereby altering EVG metabolism and inhibition of CYP3A4 by EVG. This finding has clinical significance because alcohol use is highly prevalent in HIV population, and there are no separate guidelines for these patients while they are on ART medication.

Simultaneous determination of gefitinib and its major metabolites in mouse plasma by HPLC-MS/MS and its application to a pharmacokinetics study

Gefitinib (Iressa) is the first oral EGFR tyrosine kinase inhibitor and it brings benefits to non-small cell lung cancer patients with EGFR mutation. In this study, a simple, rapid and credible high performance liquid chromatography-tandem mass spectrometry method was established and validated for the simultaneous quantification of gefitinib and its main metabolites M523595, M537194, M387783 and M608236 in NSCLC tumor-bearing mouse plasma. Sample extraction was done by protein precipitation using acetonitrile containing dasatinib as the internal standard. The chromatography run time was 6min using an Agilent RRHD SB-C18 column with a gradient of acetonitrile and water (0.1% formic acid, v/v). The mass analysis was performed by a triple quadrupole mass spectrometry in positive multiple reaction monitoring mode. The calibration range was 0.5-100ng/mL for M608236 and 1-200ng/mL for other analytes with the correlation coefficients (r(2))≥0.99. For quality control samples, inter- and intra-assay precision was less than 15% and accuracies ranged from 92.6% to 107.58% for all analytes. The extraction recoveries were in the range of 86-105% and no significant matrix effect was observed. This simple and reproducible high-throughput method was successfully applied to the pharmacokinetic study of gefitinib and its major metabolites in mouse.