Principles and applications of LC-MS in new drug discovery

Data processing for high-throughput mass spectrometry in drug discovery

INTRODUCTION

High-throughput mass spectrometry that could deliver > 10 times faster sample readout speed than traditional LC-based platforms has emerged as a powerful analytical technique, enabling the rapid analysis of complex biological samples. This increased speed of MS data acquisition has brought a critical demand for automatic data processing capabilities that should match or surpass the speed of data acquisition. Those data processing capabilities should serve the different requirements of drug discovery workflows.

AREAS COVERED

This paper introduced the key steps of the automatic data processing workflows for high-throughput MS technologies. Specific examples and requirements are detailed for different drug discovery applications.

EXPERT OPINION

The demand for automatic data processing in high-throughput mass spectrometry is driven by the need to keep pace with the accelerated speed of data acquisition. The seamless integration of processing capabilities with LIMS, efficient data review mechanisms, and the exploration of future features such as real-time feedback, automatic method optimization, and AI model training is crucial for advancing the drug discovery field. As technology continues to evolve, the synergy between high-throughput mass spectrometry and intelligent data processing will undoubtedly play a pivotal role in shaping the future of high-throughput drug discovery applications.

Pharmacokinetic-Pharmacodynamic (PK-PD) Analysis of Second-Line Anti-Tubercular Drugs in Indian Children with Multi-Drug Resistance

OBJECTIVES

To conduct a thorough pharmacokinetic (PK) - pharmacodynamic (PD) analysis of second-line anti-tubercular therapy (ATT) in children diagnosed with multi-drug resistant tuberculosis (MDR-TB).

METHODS

Twenty-seven children undergoing second-line ATT, including kanamycin (KM, n = 13), fluoroquinolones (FQs, n = 26), ethionamide (ETH, n = 20), para amino salicylic acid (PASA, n = 4), and cycloserine (CS, n = 15), were sampled at 0 (pre-dose), 1, 2, 3, and 4 h post-drug administration. Plasma drug levels were determined using a mass spectrometer and the collected dataset underwent non-compartmental PK analysis using PK solver ver2.0. PK/PD assessments involved individual drug simulation studies on 1000 subjects using Modviz Pop ver 1.0 in R-software.

RESULTS

A total of 22 and 5 children were considered as responders and non-responders, respectively. Non-compartmental PK analysis revealed mean plasma drug levels of this study cohort attained the targeted maximum drug plasma concentration (Cmax). The ratio of Cmax /minimum inhibitory concentration (MIC) or the area under the curve (AUC)/MIC of the studied drugs had not shown a significant difference between responders and non-responders. Non-responders of ETH and ofloxacin had shown deviation from the derived dose-response profile for the simulated population.

CONCLUSIONS

The management of MDR-TB with second-line ATT following national guidelines had cured the majority of the children (> 80%) who participated in the study. Inter-individual variability in few children from the targeted Cmax range suggests the need for future investigations on pharmacogenomic aspects of drug metabolism.

Immunopurification Reagents and Their Application in Biologics and Biomarker Quantitation Using LC-MS/MS in Drug Discovery

The LC-MS/MS technology is one of the most utilized bio-analytical tools owing to its advantage of selectivity, sensitivity and multitasking. The advent of novel biological therapies and increasing demand for protein biomarker identification and quantitation have put the LC-MS/MS technology at the forefront. The questions which are been posed to the LC-MS/MS scientist are complex. The complexity of the question increases further with the matrices in which these questions need to be answered. To bring down the complexity of the analysis, LC-MS/MS technology is utilizing the immunopurification (IP) technique as the new sample preparation technique. The IP reagents are the most common reagents which are used to decrease the matrices' complexity and allow the LC-MS/MS system to reach greater sensitivity. The utilization of these reagents is increasing every day, but the proper utilization of these reagents is still unknown to the common analyst in drug discovery. The present review throws light on the utilization aspect of these reagents, as we have classified these reagents on basis of their utilization, which will allow the readers to gain an understanding of these reagents. This review will also talk about the merits and the demerits of each approach and the current understanding of utilizing these reagents.

Metabolomics and NMR

The purpose of this manuscript will be to convince the reader to dive deeper into NMR spectroscopy and prevent the technique from being just another "black-box" in the lab. We will try to concisely highlight interesting topics and supply additional references for further exploration at each stage. The advantages of delving into the technique will be shown. The secondary objective, i.e., avoiding common problems before starting, will hopefully then become clear. Lastly, we will emphasize the spectrometer information needed for manuscript reporting to allow reproduction of results and confirm findings.

Quality Control of Chemogenomic Library Using LC-MS

In chemical biology, using compounds with incorrect identity or insufficient purity can lead to misleading biological activity data. Chemical quality control for confirmation of purity and compound identity is thus central to chemogenomics. We have established a medium-throughput LC-MS-based semi-automated quality control (QC) workflow with a minimal requirement for materials suitable for chemogenomics and other small molecule libraries. This rapid method can cover a broad chemical space of small organic compounds with diverse physicochemical properties such as polarity or lipophilicity.

Mycotoxins of Concern in Children and Infant Cereal Food at European Level: Incidence and Bioaccessibility

Cereals are of utmost importance for the nutrition of infants and children, as they provide important nutrients for their growth and development and, in addition, they are easily digestible, being the best choice for the transition from breast milk/infant formula to solid foods. It is well known that children are more susceptible than adults to toxic food contaminants, such as mycotoxins, common contaminants in cereals. Many mycotoxins are already regulated and controlled according to strict quality control standards in Europe and around the world. There are, however, some mycotoxins about which the level of knowledge is lower: the so-called emerging mycotoxins, which are not yet regulated. The current review summarizes the recent information (since 2014) published in the scientific literature on the amounts of mycotoxins in infants’ and children’s cereal-based food in Europe, as well as their behaviour during digestion (bioaccessibility). Additionally, analytical methods used for mycotoxin determination and in vitro methods used to evaluate bioaccessibility are also reported. Some studies demonstrated the co-occurrence of regulated and emerging mycotoxins in cereal products used in children’s food, which highlights the need to adopt guidelines on the simultaneous presence of more than one mycotoxin. Although very little research has been done on the bioaccessibility of mycotoxins in these food products, very interesting results correlating the fiber and lipid contents of such products with a higher or lower bioaccessibility of mycotoxins were reported. LC-MS/MS is the method of choice for the detection and quantification of mycotoxins due to its high sensibility and accuracy. In vitro static digestion models are the preferred ones for bioaccessibility evaluation due to their simplicity and accuracy.

A tandem liquid chromatography and tandem mass spectrometry (LC/LC-MS/MS) technique to separate and quantify steroid isomers 11β-methyl-19-nortestosterone and testosterone

Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) has become a mainstay analytical technique in pharmaceutical research and development and clinical diagnosis due to several advantages including excellent selectivity, specificity, and high sensitivity. LC-MS/MS has become the method of choice for steroids analysis due to its fast analytical time and improved specificity yet has a challenge in the separation and measurement of isomers with the same product ions. Here we describe a high-sensitivity LC/LC-MS/MS method that combines chiral chromatography and reverse-phase chromatography (LC/LC) along with MS/MS to rapidly separate and quantify steroid isomers of 11ß-methyl-19-nortestosterone (11ß-MNT) and endogenous testosterone in serum.

Hydrothermally Grown ZnO Nanostructures for Water Purification via Photocatalysis

Semiconductor-based photocatalysis is a well-known and efficient process for achieving water depollution with very limited rejects in the environment. Zinc oxide (ZnO), as a wide-bandgap metallic oxide, is an excellent photocatalyst, able to mineralize a large scale of organic pollutants in water, under UV irradiation, that can be enlarged to visible range by doping nontoxic elements such as Ag and Fe. With high surface/volume ratio, the ZnO nanostructures have been shown to be prominent photocatalyst candidates with enhanced photocatalytic efficiency, owing to their being low-cost, non-toxic, and able to be produced with easy and controllable synthesis. Thus, ZnO nanostructures-based photocatalysis can be considered as an eco-friendly and sustainable process. This paper presents the photocatalytic activity of ZnO nanostructures (NSs) grown on different substrates. The photocatalysis has been carried out both under classic mode and microfluidic mode. All tests show the notable photocatalytic efficiency of ZnO NSs with remarkable results obtained from a ZnO-NSs-integrated microfluidic reactor, which exhibited an important enhancement of photocatalytic activity by drastically reducing the photodegradation time. UV-visible spectrometry and high-performance liquid chromatography, coupled with mass spectrometry (HPLC-MS), are simultaneously used to follow real-time information, revealing both the photodegradation efficiency and the degradation mechanism of the organic dye methylene blue.

Use of Spectroscopic Methods and Their Clinical Applications in Drug Abuse: A Review

Assurance of substance abuse in plasma and different parts of the body is vital in clinical and legal toxicology. Detection techniques are evaluated for their appropriateness in scientific and clinical sciences, where extraordinary prerequisites must be met. Recognition and affirmation are for the most part done by gas chromatography-Mass spectrometry (GC-MS) or liquid chromatography (LC-MS), Surface-enhanced Raman spectroscopy (SERS), Magnetic resonance imaging, Positron Emission Tomography, Infrared Spectroscopy, and UV Spectroscopy. Progressed spectroscopic techniques provided helpful quantitative or qualitative data about the natural chemistry and science of exploited substances. These spectroscopic techniques are assumed as quick, precise, and some of them are non-damaging investigation apparatus that may be assumed as a substitution for previously used compound investigation. Spectroscopy with its advances in technology is centralized to novel applications in the detection of abused drug substances and clinical toxicology. These techniques have attracted growing interest as forensic tools for the early detection and monitoring of exploited drugs. This review describes the principle, role, and clinical application of various spectroscopic techniques which are utilized for the identification of drug abuse like morphine, cocaine, codeine, alcohol, amphetamines, and their metabolites in whole blood, plasma, hair, and nails.

Combined Paper Centrifugal Chromatographic Separation and SERS Detection for Multicomponent Substances

The separation and chemical analysis of mixtures in an emergency situation represent major challenges, especially in remote or poverty-stricken areas. A novel method was developed for the rapid separation and detection of multiple components via paper centrifugal chromatography, which costs as little as $2.26 US. The method was realized based on the combination of portable paper centrifugal chromatography and surface-enhanced Raman scattering (SERS) detection. This coupled technique was successfully implemented for the separation and qualitative analysis of a rhodamine 6G-crystal violet mixture and a colorless aniline-pyrocatechol-benzidine mixture. A chromatographic mobile phase was collected using absorbent cotton, which was demonstrated to have no effect on the SERS results. The optimized device achieved rapid and effective separation of the colorless aniline-pyrocatechol-benzidine mixture with a high centrifugal force (0.3303π² N). The newly developed method involving multicomponent paper centrifugal chromatography-SERS detection will be of great value for emergency-related substance separation and analysis in remote and poor areas.

A highly sensitive and selective UPLC-MS/MS assay for the determination of enarodustat (JTZ-951) in human plasma

Enarodustat, a potent, orally bioavailable, selective inhibitor of hypoxia inducible factor-Prolyl hydroxylase (HIF-PH), has been approved recently in Japan for the treatment of anemia in patients with chronic kidney disease (CKD). To evaluate the pharmacokinetics of enarodustat, a bioanalytical assay in human plasma was needed for the quantitation of enarodustat for both healthy subjects and patients with CKD. The UPLC-MS/MS method for the quantitation of enarodustat was initially validated in a bioanalytical laboratory in Japan to support clinical studies conducted in Japan, and then was transferred and validated in a bioanalytical laboratory in United States to support clinical studies conducted here. A cross-validation was successfully performed between the two bioanalytical laboratories using both quality control (QC) samples and incurred study samples. Enarodustat was fortified with its isotopically labeled internal standard in a 25 µL plasma aliquot and extracted with protein precipitation. The chromatographic separation was achieved on an Acquity UPLC BEH C18 (1.7 µm, 2.1 × 50 mm) column with gradient elution. The calibration curve range for the assay was 1.00-500 ng/mL. Assay precision, accuracy, linearity, selectivity, sensitivity and analyte stability covering sample storage and analysis were established. No interferences were observed from medications that may be co-administered along with enarodustat. The validated UPLC-MS-MS method at the US bioanalytical laboratory has been successfully applied to eight clinical studies for the determination of enarodustat concentrations in human plasma for both healthy subjects and patients with CKD.

Advancements in practical and scientific bioanalytical approaches to metabolism studies in drug development

Advancement in metabolism profiling approaches and bioanalytical techniques has been revolutionized over the last two decades. Different in vitro and in vivo approaches along with advanced bioanalytical techniques are enabling the accurate qualitative and quantitative analysis of metabolites. This review summarizes various modern in vitro and in vivo approaches for executing metabolism studies with special emphasis on the recent advancement in the field. Advanced bioanalytical techniques, which can be employed in metabolism studies, have been discussed suggesting their particular application based on specific study objectives. This article can efficiently guide the researchers to scientifically plan metabolism studies and their bioanalysis during drug development programs taking advantage of a detailed understanding of instances of failure in the past.

A Review of Analytical Methods for Codeine Determination

Codeine is derived from morphine, an opioid analgesic, and has weaker analgesic and sedative effects than the parent molecule. This weak opioid is commonly used in combination with other drugs for over-the-counter cough relief medication. Due to the psychoactive properties of opioid drugs, the easily obtained codeine often becomes subject to misuse. Codeine misuse has emerged as a concerning public health issue due to its associated adverse effects such as headache, nausea, vomiting, and hemorrhage. Thus, it is very important to develop reliable analytical techniques to detect codeine for both quality control of pharmaceutical formulations and identifying drug misuse in the community. This review aims to provide critical outlooks on analytical methods applicable to the determination of codeine.

Localisation of clozapine during experimental autoimmune encephalomyelitis and its impact on dopamine and its receptors

Multiple sclerosis is a disease characterised by axonal demyelination in the central nervous system (CNS). The atypical antipsychotic drug clozapine attenuates experimental autoimmune encephalomyelitis (EAE), a mouse model used to study multiple sclerosis, but the precise mechanism is unknown and could include both peripheral and CNS-mediated effects. To better understand where clozapine exerts its protective effects, we investigated the tissue distribution and localisation of clozapine using matrix-assisted laser desorption ionization imaging mass spectrometry and liquid chromatography-mass spectrometry. We found that clozapine was detectable in the brain and enriched in specific brain regions (cortex, thalamus and olfactory bulb), but the distribution was not altered by EAE. Furthermore, although not altered in other organs, clozapine levels were significantly elevated in serum during EAE. Because clozapine antagonises dopamine receptors, we analysed dopamine levels in serum and brain as well as dopamine receptor expression on brain-resident and infiltrating immune cells. While neither clozapine nor EAE significantly affected dopamine levels, we observed a significant downregulation of dopamine receptors 1 and 5 and up-regulation of dopamine receptor 2 on microglia and CD4+-infiltrating T cells during EAE. Together these findings provide insight into how neuroinflammation, as modelled by EAE, alters the distribution and downstream effects of clozapine.

A procedure for method development and protein binding ratio as the indicator of sensitivity with anticancer agents on MALDI mass spectrometry imaging

The concentration and distribution of a drug and its metabolites in tissues are key factors for elucidating both drug efficacy and toxicity in drug development. In this study we developed a pharamaco-imaging procedure for 12 agents and investigated the relationship between the properties of target compounds and the sensitivities of detection in matrix-assisted laser desorption/ionization-mass spectrometer imaging (MALDI-MSI). We prepared mock samples with mouse liver homogenates diluted with gelatin solution, limit of detection concentrations of each compound was confirmed. The correlation was evaluated between the intensities of mass signals obtained in MALDI-MSI with each test compound (the intensities of the test compounds) at a consistent concentration and the properties of each test compound. The liver homogenate diluted with gelatin solution showed easier handling and lower coefficients of variation than did liver homogenate only, and can be used as a good surrogate matrix. Based on the analysis of 12 agents, the protein binding ratios showed significant correlation to the detection sensitivities. We presented a procedure for standardization of pharmaco-imaging method development with an in-tissue method using MALDI-MS. Our results indicated the correlation between test compound's sensitivity and their protein binding ratios in plasma or serum.

Electroanalysis from the past to the twenty-first century: challenges and perspectives

A personal mini-review is presented on the history of electroanalysis and on their present achievements and future challenges. The manuscript is written from the subjective view of two generations of electroanalytical chemists that have witnessed for many years the evolution of this discipline.

Current status and contemporary approaches to the discovery of antitumor agents from higher plants

Higher plant constituents have afforded clinically available anticancer drugs. These include both chemically unmodified small molecules and their synthetic derivatives currently used or those in clinical trials as antineoplastic agents, and an updated summary is provided. In addition, botanical dietary supplements, exemplified by mangosteen and noni constituents, are also covered as potential cancer chemotherapeutic agents. Approaches to metabolite purification, rapid dereplication, and biological evaluation including analytical hyphenated techniques, molecular networking, and advanced cellular and animal models are discussed. Further, enhanced and targeted drug delivery systems for phytochemicals, including micelles, nanoparticles and antibody drug conjugates (ADCs) are described herein.

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.

A classification of liquid chromatography mass spectrometry techniques for evaluation of chemical composition and quality control of traditional medicines

Natural products (NPs) and traditional medicines (TMs) are used for treatment of various diseases and also to develop new drugs. However, identification of drug leads within the immense biodiversity of living organisms is a challenging task that requires considerable time, labor, and computational resources as well as the application of modern analytical instruments. LC-MS platforms are widely used for both drug discovery and quality control of TMs and food supplements. Moreover, a large dataset generated during LC-MS analysis contains valuable information that could be extracted and handled by means of various data mining and statistical tools. Novel sophisticated LC-MS based approaches are being introduced every year. Therefore, this review is prepared for the scientists specialized in pharmacognosy and analytical chemistry of NPs as well as working in related areas, in order to navigate them in the world of diverse LC-MS based techniques and strategies currently employed for NP discovery and dereplication, quality control, pattern recognition and sample comparison, and also in targeted and untargeted metabolomic studies. The suggested classification system includes the following LC-MS based procedures: elemental composition determination, isotopic fine structure analysis, mass defect filtering, de novo identification, clustering of the compounds in Molecular Networking (MN), diagnostic fragment ion (or neutral loss) filtering, manual dereplication using MS/MS data, database-assisted peak annotation, annotation of spectral trees, MS fingerprinting, feature extraction, bucketing of LC-MS data, peak profiling, predicted metabolite screening, targeted quantification of biomarkers, quantitative analysis of multi-component system, construction of chemical fingerprints, multi-targeted and untargeted metabolite profiling.

Rilpivirine as a potential candidate for the treatment of HIV-associated neurocognitive disorders (HAND)

As the HIV epidemic continues to contribute to global morbidity and mortality, the prevalence of HIV-associated neurological disorders (HAND) also continues to be a major concern in infected individuals, despite the widespread use of combination antiretroviral therapy. Therefore, current antiretroviral drugs should be able to reach therapeutic levels in the brain for the treatment of HAND. The brain distribution of the next-generation non-nucleoside reverse transcriptase inhibitor, rilpivirine (RPV) was investigated in healthy female Sprague-Dawley (SD) rats. The presented study involves the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) to estimate the concentrations of RPV in plasma and brain homogenate samples. The use of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) provided regional spatial distribution of RPV in brain tissue sections. The localization of RPV was found to be relatively high in the hypothalamus, thalamus and corpus callosum, brain regions known to be associated with neurodegeneration during HAND (including the cerebral cortex). This study has shown that RPV has an excellent blood-brain barrier penetrability. Thus, in combination with other antiretroviral drugs, better central nervous system (CNS) protection against HAND can possibly be achieved.

Various Dereplication Strategies Using LC-MS for Rapid Natural Product Lead Identification and Drug Discovery

Natural products are the most consistently successful source of drug leads. The rapid identification of known compounds from natural product extracts, or ‘dereplication’, is an important step in an efficiently run drug discovery program. Modern spectroscopic methods have largely revolutionized compound identification and tremendously accelerated the pace at which isolated compounds can be identified. Dereplication strategies use analytical techniques and database searching to determine the identity of an active compound at the earliest possible stage in the discovery process. This prevents wasted effort on samples with no potential for development and allows resources to be focused on the most promising lead. In the past few years, advances in technology have allowed the development of tandem analytical techniques, such as HPLC-PDA, LC-MS, LC-MS-MS, LC-NMR, and LC-NMR-MS. This review describes the principles and performance of a number of hyphenated techniques involving LC-MS that can be used for dereplication of natural products for rapid lead identification.

A UHPLC-MS/MS method coupled with simple and efficient alkaline hydrolysis for free and total determination of conjugate nanomedicine: Pharmacokinetic and biodistribution study of poly (l-glutamic acid)-graft-methoxy poly (ethylene glycol)/combretastatin A4

Poly (l-glutamic acid)-Combretastatin A4 conjugate (PLG-CA4) is a novel nano-anticancer drug. For macromolecule conjugate nanomedicine, its pharmacology mechanism is closely related to the pharmacokinetic profiles in vivo. It is a great significance that evaluates this polymer drug combined by covalently bound via studying the pharmacokinetics and distribution characteristics. Therefore, it is urgent to develop a simple, accurate and practical analytical method for such conjugated polymers combined by covalently bound. In this study, a simple and complete alkali hydrolysis was designed and optimized for the total CA4 concentrations obtained from PLG-CA4. Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method with multiple-reaction monitoring (MRM) mode and the internal standard (IS) were adopted to develop a sensitive and accurate method satisfied both free and total determination of PLG-CA4 in biosamples. The method was validated which showed good linearity over a wide concentration range (R² > 0.99), and the intra- and inter-day assay variability was less than 15% for CA4. The mean extraction recoveries of CA4 from plasma were all more than 80.0%. Furthermore, the method was applied to the study of pharmacokinetics (PK) and tissue distribution of PLG-CA4 in tumor-bearing nude mice. PLG-CA4 significantly prolonged retention time and enhanced distribution of CA4 in tumor.

Simultaneous extraction and analysis of multiple cystine-dense peptides by μSPE and microflow-MS/MS from plasma

Aim: Develop a universal extraction and liquid chromatography-mass spectrometer method to simultaneously analyze cystine-dense peptide (CDP) miniproteins from rat and human plasma. The results of the analysis will be used to assist selection of therapeutic drug candidates from the vast CDP library. Methods & results: A micro-elution solid-phase extraction method was developed for the sample preparation of the CDP peptides in rat and human plasma followed by analysis by microflow liquid chromatography MS/MS. The methods developed for drug discovery were found to be accurate (±≤15.2% from nominal concentrations) and precise (≤13.4% CV), with a dynamic range of 1.00–500 ng/ml and extraction recoveries of 47.2–99.0%. Conclusion: This bioanalytical method can be utilized to screen CDP proteins and other miniproteins for drug discovery, candidate selection and further drug development.

Determination of donepezil in human plasma using ultra performance liquid chromatography-tandem mass spectrometry

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the quantification of donepezil in human plasma. Donepezil and donepezil-D4 were extracted from human plasma by liquid-liquid extraction using a mixture of hexane and ethyl acetate (70:30 v/v). The extracted samples were analyzed using a Thermo Hypersil Gold C18 column with 5% acetic acid in 20 mM ammonium acetate buffer (pH 3.3) and 100% acetonitrile as a mobile phase with the 60:40 (v:v) isocratic method, at a flow rate of 0.3 mL/min. The injection volume was 3 µL, and the total run time was 3 min. Inter- and intra-batch accuracies ranged from 98.0% to 110.0%, and the precision was below 8%. The developed method was successfully applied to the quantification of donepezil in human plasma. The mean (standard deviation) maximum concentration and the median (range) time to maximum concentration were 8.6 (2.0) ng/mL and 2.0 h (1.0~5.0 h), respectively, in healthy Koreans after oral administration of 5 mg donepezil.

LC–MS/MS assay for N1-methylnicotinamide in humans, an endogenous probe for renal transporters

Background: N1-methylnicotinamide (1-NMN) has been proposed as a potential clinical biomarker to assess drug–drug interactions involving organic cation transporters (OCT2) and multidrug and toxin extrusion protein transporters. Results: A hydrophilic interaction liquid chromatography–MS/MS assay, to quantify 1-NMN, in human plasma and urine is reported. Materials & methods: A hydrophilic interaction chromatography (HILIC)-tandem mass spectrometry (MS/MS) assay to quantify 1-NMN in human plasma and urine is reported. The basal 1-NMN levels in plasma and urine were 4–120 and 2000–15,000 ng/ml, respectively. Conclusion: 1-NMN plasma AUCs increased two- to fourfold versus placebo following the administration of a clinical candidate that in vitro experiments indicated was an OCT2 inhibitor. The described hydrophilic interaction liquid chromatography–MS/MS assay can be used to assess a clinical compound candidate for the inhibition of OCT2 and multidrug and toxin extrusion protein transporter in first-in-human studies.

Recent (2000-2015) developments in the analysis of minor unknown natural products based on characteristic fragment information using LC-MS

Liquid chromatography-Mass Spectrometry (LC-MS) has been widely used in natural product analysis. Global detection and identification of nontargeted components are desirable in natural product research, for example, in quality control of Chinese herbal medicine. Nontargeted components analysis continues to expand to exciting life science application domains such as metabonomics. With this background, the present review summarizes recent developments in the analysis of minor unknown natural products using LC-MS and mainly focuses on the determination of the molecular formulae, selection of precursor ions, and characteristic fragmentation patterns of the known compounds. This review consists of three parts. Firstly, the methods used to determine unique molecular formula of unknown compounds such as accurate mass measurements, MSⁿ spectra, or relative isotopic abundance information, are introduced. Secondly, the methods improving signal-to-noise ratio of MS/MS spectra by manual-MS/MS or workflow targeting-only signals were elucidated; pure precursor ions can be selected by changing the precursor ion isolated window. Lastly, characteristic fragmentation patterns such as Retro-Diels-Alder (RDA), McLafferty rearrangements, "internal residue loss," and so on, occurring in the molecular ions of natural products are summarized. Classical application of characteristic fragmentation patterns in identifying unknown compounds in extracts and relevant fragmentation mechanisms are presented (RDA reactions occurring readily in the molecular ions of flavanones or isoflavanones, McLafferty-type fragmentation reactions of some natural products such as epipolythiodioxopiperazines; fragmentation by "internal residue loss" possibly involving ion-neutral complex intermediates). © 2016 Wiley Periodicals, Inc. Mass Spec Rev 37:202-216, 2018.

Alkaline degradation of lyophilized DMSA prior to labeling with 99mTc: Identification and development of the degradation pathway by HPLC and MS

INTRODUCTION

Complexes of technetium-99m (99mTc) with meso-dimercaptosuccinic acid (DMSA) have been widely used as diagnostic agents in nuclear medicine. The degradation products (DP) of DMSA formed under different forced conditions have been identified through HPLC-DAD and LC-MSⁿ studies. In this study, the DMSA kit was subjected to forced degradation under hydrolysis conditions as prescribed by the International Conference on Harmonization (ICH) guideline Q1A.

METHODS

Chromatographic separation was accomplished on a reverse phase Shim-Pack VP-ODS (150 mm × 4.6 mm; 5 μm) analytical column using the gradient elution method. LC-MSⁿ analysis was performed using an Esquire 3000 Plus ion trap mass spectrometer, operating under electrospray ionization (ESI).

RESULTS

No products were found under acidic or neutral stress conditions. All the products found were identified through LC-MSⁿ analyses and their fragmentation pathways were proposed. The DMSA standard degraded into an adduct DMSA dimer (2DMSA[-2H+Na]⁺) and adduct DMSA bound to fumaric acid and dithioglucolic acid (DTGA). In the DMSA kit, the degradation products were dimers and trimers of DMSA with tin. A possible degradation pathway is presented.

CONCLUSIONS

This method proved to be convenient and effective since it provided fast and efficient separation of DMSA from its degradation products. The degradation studies carried out were able to delineate the stability of the DMSA standard and the DMSA kit.

Bioanalytical methods for the detection of antidiabetic drugs: a review

Type 2 diabetes mellitus, a disease which prevalence has been progressively increasing worldwide, is characterized by chronic hyperglycemia resulting from the combination of inappropriate insulin secretion and/or resistance to insulin action. If left uncontrolled, diabetes is associated with complications such as dysfunction and failure of various organs, and even premature death. Along with lifestyle-modification strategies, several classes of oral antidiabetic agents can be employed for glycemic control. Thus, therapeutic drug monitoring of these drugs is essential to maintain appropriate treatment. This review discusses the most frequently employed analytical techniques and sample preparation systems to obtain a reliable and trustworthy method to quantify antidiabetic drugs in biological matrices. An adequate choice of internal standard, ideal chromatography conditions and most suitable analytical detector are reported.

Using miniature MS system with automatic blood sampler for preclinical pharmacokinetics study

AIM

Preclinical pharmacokinetic studies are an essential part of modern drug development. In this work, we explored a new solution with onsite analysis using a miniature MS system, which can significantly improve the efficiency of the preclinical study. Materials & methods: A miniature mass spectrometer was used with an automatic blood sampler for onsite quantitation of drug compounds in whole blood samples. Slug-flow microextraction was used to replace the in-lab sample preparation.

RESULTS & CONCLUSION

Animal studies were carried out using two drug compounds, using the auto sampler to take blood samples at preprogrammed time points. The miniature MS system was used to obtain drug concentrations, which were subsequently used to calculate the pharmacokinetic parameters.

A highly selective and sensitive LC–MS/HRMS assay for quantifying coproporphyrins as organic anion-transporting peptide biomarkers

Aim: Coproporphyrin-I (CP-I) and coproporphyrin-III (CP-III) in plasma and urine have been proposed as biomarkers for assessing drug–drug interactions involving hepatic drug transporters such as organic anion-transporting peptides (OATP), 1B1 and 1B3. Materials & methods: Plasma and urine extracts were analyzed for CP-I/CP-III using a TripleTOF API6600 mass spectrometer. Results: Previously unreported, CP-I/CP-III doubly charged ions (m/z 328.14) were used as precursor ions to improve the assay sensitivity and selectivity over the singly charged precursor ions (m/z 655.28). Levels of CP-I and CP-III measured ranged 0.45–1.1 and 0.050–0.50 ng/ml in plasma and 5–35 and 1–35 ng/ml in urine, respectively. Conclusion: The described highly selective and sensitive CP-I/CP-III LC–HRMS assay offers options for earlier characterization and clinical safety projections for OATP1B1/3-mediated drug–drug interactions along with pharmacokinetic analyses of a new chemical entity as part of first-in-human clinical studies.

Development and validation of HPLC-MS/MS procedure for determination of 3,4,4',5-tetra-methoxystilbene (DMU-212) and its metabolites in ovarian cancer cells and culture medium

The synthetic resveratrol analogue DMU-212 (3,4,4',5-tetramethoxystilbene) has been shown to possess stronger anticancer activity than resveratrol in a variety of tumour cells. To date, there has been no appropriate procedure that would ensure a reliable data about levels of metabolic products of DMU-212 in cancer cell lines. The purpose of this study was to develop a new procedure for determination of DMU-212 and its three metabolites (DMU-214, DMU-281, DMU-291) in cell lines. Analyses were performed using an HPLC system coupled with a triple quadrupole mass spectrometer operating in multiple reaction monitoring mode. Separation was conducted using a C18 column at a flow rate 800μL/min with a mobile phase consisting of 5mM ammonium acetate with 0.1% formic acid (solvent A) and acetonitrile (solvent B). The new methodology is fast, simple and has excellent specificity. Moreover, it showed good linearity in two matrices - cell lysates and culture media. Accuracy values for analytes evaluated at different concentration levels ranged from 0.43 to 18% (%bias). The intra-day and inter-day precision, expressed as CV, was in a range 0.49-5.5% and 0.83-13%, respectively. The validated procedure was successfully applied to quantify the resveratrol analogues in the human ovarian cancer cell line SKOV3.

Development and validation of HPLC-MS/MS method for the determination of lixivaptan in mouse plasma and its application in a pharmacokinetic study

The aim of the present study was to develop a simple, sensitive and accurate liquid chromatography-electrospray ionization tandem mass spectrometry (ESI-MS/MS) method for the determination of lixivaptan (LIX) in mouse plasma using vildagliptin as the internal standard (IS). A precipitation procedure was used for the extraction of LIX and vildagliptin from mouse plasma. Chromatographic separation of LIX was achieved using a C₁₈ analytical column (50 × 2.1 mm, 1.8 μm) at 25°C. The mobile phase comprised acetonitrile and ammonium formate (10 mm, pH 3.1; 40:60, v/v) pumped at a flow rate of 0.3 mL min^-1 . A tandem mass spectrometer with an electrospray ionization source was used to perform the assay. Quantification of LIX at m/z 290 → 137 and IS at 154 → 97 was attained through multiple reaction monitoring. The investigated method was authenticated following the bio-analytical method of validation guidelines of the US Food and Drug Administration. The developed method showed a good linearity over the concentration range from 5 to 500 ng mL^-1 , and the calibration curve was linear (r = 0.9998). The mean recovery of LIX from mouse plasma was 99.2 ± 0.68%. All validation parameters for LIX were within the levels required for acceptance. The proposed method was effectively used for a pharmacokinetic study of LIX in mouse plasma.

The Applications and Features of Liquid Chromatography-Mass Spectrometry in the Analysis of Traditional Chinese Medicine

With increasingly improved separation of complex samples and detection of unknown material capabilities, liquid chromatography coupled with mass spectrometry (LC-MS) has been widely used in traditional Chinese medicine (TCM) research. This article describes the principles of liquid chromatography (LC) and mass spectrometry (MS) and their advantages and disadvantages in qualitative and quantitative analysis of TCM. We retrieved research literatures about the application of LC-MS in TCM published during the past five years at home and abroad. To better guide the analysis of TCM, this review mainly focuses on the applications category of LC-MS, how often different kinds of LC-MS are used, and the qualitative and quantitative ability of various LC-MS in the study of TCM.

Detection of Carbofuran-Protein Adducts in Serum of Occupationally Exposed Pesticide Factory Workers in Pakistan

This study was conducted to investigate the protein adducts with pesticides in a cohort of 172 factory workers that were exposed to a mixture of pesticides. The 35 samples showing considerable variation in biochemical parameters, i.e., butyrylcholinestrase (BChE), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetic transaminase (SGOT), gamma-glutamyl transferase (GGT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase (ALP/ALKP), lactate dehydrogenase (LDH), creatine phosphokinase (CPK) enzymes, and controls were analyzed by reversed-phase nanoscale liquid chromatography tandem mass spectrometry (nLC-MS/MS) on an Orbitrap mass spectrometer employing a shotgun proteomics approach. Only protein adducts with carbofuran were found on serum proteins of these workers. These adducts were of carbofuran labeled lysine (Lys-142, Lys-183, Lys-287, and Lys-467), arginine (Arg-210, Arg-242, and Arg-256) from serum albumin, and serine (Ser-07, Ser-54, and Ser-150) from immunoglobulin proteins. The arginine residues (Arg-210, Arg-242, Arg-246, and Arg-434) from albumin were also found to be glycated in serum of workers showing a high level of glucose who also had glycated arginine (Arg-1120) modified with carbofuran in their tankyrase-1-binding protein. The number of tandem mass spectra of modified peptides increased with increasing time of exposure. This is the first report to demonstrate the presence of carbofuran-labeled albumin, immunoglobulin, and glycated arginine, which shows that lysine and arginine of human albumin and serine of immunoglobulin are covalently modified in the serum of workers that were occupationally exposed to carbofuran, and the modification is detectable by tandem mass spectrometry. These peptides modified with carbofuran can potentially be used as a biomarker of carbofuran exposure.

HRMS using a Q-Exactive series mass spectrometer for regulated quantitative bioanalysis: how, when, and why to implement

High-resolution MS (HRMS) has seen an uptake in use for discovery qual/quan workflows, however, its utilization in late discovery/development has been slow. Past reports comparing HRMS to triple quadrupole (QQQ) instrumentation to date have indicated that HRMS instruments are capable of producing data acceptable for regulated bioanalysis, however lack the sensitivity required for sub ng/ml LLOQ assays. Recent advances in HRMS instrumentation have closed the sensitivity gap with QQQ and have even provided improved selectivity and sensitivity over QQQ SRM assays. Herein, the authors will describe how, when, and why HRMS (specifically Q-Exactive series mass spectrometers) should be considered for implementation in regulated quantitative bioanalysis assays.

Discovery bioanalysis and in vivo pharmacology as an integrated process: a case study in oncology drug discovery

Background: A bioanalytical team dedicated to in vivo pharmacology was set up to accelerate the selection and characterization of compounds to be evaluated in animal models in oncology. Results: A DBS-based serial microsampling procedure was optimized from sample collection to extraction to obtain a generic procedure. UHPLC–high-resolution mass spectrometer configuration allowed for fast quantitative and qualitative analysis. Using an optimized lead compound, we show how bioanalysis supported in vivo pharmacology by generating blood and tumor exposure, drug monitoring and PK/PD data. Conclusion: This process provided unique opportunities for the characterization of drug properties, selection and assessment of compounds in animal models and to support and expedite proof-of-concept studies in oncology.

Mercapturic acids: recent advances in their determination by liquid chromatography/mass spectrometry and their use in toxicant metabolism studies and in occupational and environmental exposure studies

This review describes recent selected HPLC/MS methods for the determination of urinary mercapturates that are useful as noninvasive biomarkers in characterizing human exposure to electrophilic industrial chemicals in occupational and environmental studies. High-performance liquid chromatography/mass spectrometry is a sensitive and specific method for analysis of small molecules found in biological fluids. In this review, recent selected mercapturate quantification methods are summarized and specific cases are presented. The biological formation of mercapturates is introduced and their use as indicators of metabolic processing of reactive toxicants is discussed, as well as future trends and limitations in this area of research.

A batch correction method for liquid chromatography-mass spectrometry data that does not depend on quality control samples

The need for reproducible and comparable results is of increasing importance in non-targeted metabolomic studies, especially when differences between experimental groups are small. Liquid chromatography-mass spectrometry spectra are often acquired batch-wise so that necessary calibrations and cleaning of the instrument can take place. However this may introduce further sources of variation, such as differences in the conditions under which the acquisition of individual batches is performed. Quality control (QC) samples are frequently employed as a means of both judging and correcting this variation. Here we show that the use of QC samples can lead to problems. The non-linearity of the response can result in substantial differences between the recorded intensities of the QCs and experimental samples, making the required adjustment difficult to predict. Furthermore, changes in the response profile between one QC interspersion and the next cannot be accounted for and QC based correction can actually exacerbate the problems by introducing artificial differences. "Background correction" methods utilise all experimental samples to estimate the variation over time rather than relying on the QC samples alone. We compare non-QC correction methods with standard QC correction and demonstrate their success in reducing differences between replicate samples and their potential to highlight differences between experimental groups previously hidden by instrumental variation.

Development of a functional assay to detect inhibitors of Plasmodium falciparum glutathione reductase utilizing liquid chromatography-mass spectrometry

Plasmodium falciparum (Pf) like most other organisms, has a sophisticated antioxidant system, part of which includes glutathione reductase (GR). GR works by recycling toxic glutathione disulfide to glutathione, thereby reducing reactive oxygen species and making a form of glutathione (GSH) the parasite can use. Inhibition of this enzyme in Pf impedes parasite growth. In addition, it has been confirmed that PfGR is not identical to human GR. Thus, PfGR is an excellent target for antimalarial drug development. A functional assay utilizing liquid chromatography-mass spectrometry was developed to specifically identify and evaluate inhibitors of PfGR. Using recombinant PfGR enzyme and 1,4-naphthoquinone (1) as a reference compound and 4-nitrobenzothiadiazole (2) and methylene blue (3) as additional compounds, we quantified the concentration of GSH produced compared with a control to determine the inhibitory effect of these compounds. Our results coincide with that presented in literature: compounds 1-3 inhibit PfGR with IC50 values of 2.71, 8.38, and 19.23 µm, respectively. Good precision for this assay was exhibited by low values of intraday and interday coefficient of variation (3.1 and 2.4%, respectively). Thus, this assay can be used to screen for other potential inhibitors of PfGR quickly and accurately.

Evaluation of two blood microsampling approaches for drug discovery PK studies in rats

Background: Serial sampling in discovery rat PK studies could be performed via capillary microsampling (CMS) of blood or by using the Mitra™ device to collect dried blood samples. Results: Blood CMS results were compared with Mitra sampling results for four test compounds dosed in rat PK studies. The PK profiles obtained from CMS sampling were found to be very similar to those obtained from the Mitra sampling. For 15-µl blood CMS samples, freezing before the dilution step was found to be acceptable. Conclusion: Blood CMS using 15-µl glass capillary microsamples works well for serial blood sampling in rat PK studies. The Mitra microsampling device provides an alternative method for collecting 10 µl of blood as a dried blood sample.