Discovery and Validation of Pyridoxic Acid and Homovanillic Acid as Novel Endogenous Plasma Biomarkers of Organic Anion Transporter (OAT) 1 and OAT3 in Cynomolgus Monkeys.

Perturbation of organic anion transporter (OAT) 1- and OAT3-mediated transport can alter the exposure, efficacy, and safety of drugs. Although there have been reports of the endogenous biomarkers for OAT1/3, none of these have all of the characteristics required for a clinical useful biomarker. Cynomolgus monkeys were treated with intravenous probenecid (PROB) at a dose of 40 mg/kg in this study. As expected, PROB increased the area under the plasma concentration-time curve (AUC) of coadministered furosemide, a known substrate of OAT1 and OAT3, by 4.1-fold, consistent with the values reported in humans (3.1- to 3.7-fold). Of the 233 plasma metabolites analyzed using a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics method, 29 metabolites, including pyridoxic acid (PDA) and homovanillic acid (HVA), were significantly increased after either 1 or 3 hours in plasma from the monkeys pretreated with PROB compared with the treated animals. The plasma of animals was then subjected to targeted LC-MS/MS analysis, which confirmed that the PDA and HVA AUCs increased by approximately 2- to 3-fold by PROB pretreatments. PROB also increased the plasma concentrations of hexadecanedioic acid (HDA) and tetradecanedioic acid (TDA), although the increases were not statistically significant. Moreover, transporter profiling assessed using stable cell lines constitutively expressing transporters demonstrated that PDA and HVA are substrates for human OAT1, OAT3, OAT2 (HVA), and OAT4 (PDA), but not OCT2, MATE1, MATE2K, OATP1B1, OATP1B3, and sodium taurocholate cotransporting polypeptide. Collectively, these findings suggest that PDA and HVA might serve as blood-based endogenous probes of cynomolgus monkey OAT1 and OAT3, and investigation of PDA and HVA as circulating endogenous biomarkers of human OAT1 and OAT3 function is warranted.

Bioanalysis of acetylcarnitine in cerebrospinal fluid by HILIC-mass spectrometry.

Acetyl-L-carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high-throughput scale, a new and simple HILIC-MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via 'dilute and shoot' directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC-MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high-throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies.

Analysis of L-serine-O-phosphate in cerebrospinal spinal fluid by derivatization-liquid chromatography/mass spectrometry.

L-serine-O-phosphate (L-SOP), the precursor of L-serine, is a potent agonist against the group III metabotropic glutamate receptors (mGluRs) and, thus, is of interest as a potential biomarker for monitoring modulation of neurotransmitter release. So far, no reports are available on the analysis of L-SOP in cerebrospinal fluid (CSF). Here a novel method is presented to determine L-SOP levels in CSF employing precolumn derivatization with (5-N-succinimidoxy-5-oxopentyl)triphenylphosphonium bromide (SPTPP) coupled to liquid chromatography/mass spectrometry (derivatization-LC/MS, d-LC/MS).

Addressing the need for biomarker liquid chromatography/mass spectrometry assays: a protocol for effective method development for the bioanalysis of endogenous compounds in cerebrospinal fluid.

RATIONALE: Research on disorders of the central nervous system (CNS) has shown that an imbalance in the levels of specific endogenous neurotransmitters may underlie certain CNS diseases. These alterations in neurotransmitter levels may provide insight into pathophysiology, but can also serve as disease and pharmacodynamic biomarkers. To measure these potential biomarkers in vivo, the relevant sample matrix is cerebrospinal fluid (CSF), which is in equilibrium with the brain's interstitial fluid and circulates through the ventricular system of the brain and spinal cord. Accurate analysis of these potential biomarkers can be challenging due to low CSF sample volume, low analyte levels, and potential interferences from other endogenous compounds. METHODS: A protocol has been established for effective method development of bioanalytical assays for endogenous compounds in CSF. Database searches and standard-addition experiments are employed to qualify sample preparation and specificity of the detection thus evaluating accuracy and precision. RESULTS: This protocol was applied to the study of the histaminergic neurotransmitter system and the analysis of histamine and its metabolite 1-methylhistamine in rat CSF. CONCLUSIONS: The protocol resulted in a specific and sensitive novel method utilizing pre-column derivatization ultra high performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS), which is also capable of separating an endogenous interfering compound, identified as taurine, from the analytes of interest.

Metabolomic and transcriptomic changes induced by overnight (16 h) fasting in male and female Sprague-Dawley rats.

The overnight (16-h) fast is one of the most common experimental manipulations performed in rodent studies. Despite its ubiquitous employment, a comprehensive evaluation of metabolomic and transcriptomic sequelae of fasting in conjunction with routine clinical pathology evaluation has not been undertaken. This study assessed the impact of a 16-h fast on urine and serum metabolic profiles, transcript profiles of liver, psoas muscle, and jejunum as well as on routine laboratory clinical pathology parameters. Fasting rats had an approximate 12% relative weight decrease compared to ad libitum fed animals, and urine volume was significantly increased. Fasting had no effect on hematology parameters, though several changes were evident in serum and urine clinical chemistry data. In general, metabolic changes in biofluids were modest in magnitude but broad in extent, with a majority of measured urinary metabolites and from 1/3 to 1/2 of monitored serum metabolites significantly affected. Increases in fatty acids and bile acids dominated the upregulated metabolites. Downregulated serum metabolites were dominated by diet-derived and/or gut-microflora derived metabolites. Major transcriptional changes included genes with roles in fatty acid, carbohydrate, cholesterol, and bile acid metabolism indicating decreased activity in glycolytic pathways and a shift toward increased utilization of fatty acids. Typically, several genes within these metabolic pathways, including key rate limiting genes, changed simultaneously, and those changes were frequently correlative to changes in clinical pathology parameters or metabolomic data. Importantly, up- or down-regulation of a variety of cytochrome P450s, transporters, and transferases was evident. Taken together, these data indicate profound consequences of fasting on systemic biochemistry and raise the potential for unanticipated interactions, particularly when metabolomic or transcriptomic data are primary end points.

Critical role of kinase activity of hematopoietic progenitor kinase 1 in anti-tumor immune surveillance.

Immunotherapy has fundamentally changed the landscape of cancer treatment. Despite the encouraging results with the checkpoint modulators, response rates vary widely across tumor types, with a majority of patients exhibiting either primary resistance without a significant initial response to treatment or acquired resistance with subsequent disease progression. Hematopoietic progenitor kinase 1 (HPK1) is predominantly expressed in hematopoietic cell linages and serves as a negative regulator in T cells and dendritic cells (DC). While HPK1 gene knockout (KO) studies suggest its role in anti-tumor immune responses, the involvement of kinase activity and thereof its therapeutic potential remain unknown. To investigate the potential of pharmacological intervention using inhibitors of HPK1, we generated HPK1 kinase dead (KD) mice which carry a single loss-of-function point mutation in the kinase domain and interrogated the role of kinase activity in immune cells in the context of suppressive factors or the tumor microenvironment (TME). Our data provide novel findings that HKP1 kinase activity is critical in conferring suppressive functions of HPK1 in a wide range of immune cells including CD4+, CD8+, DC, NK to Tregs, and inactivation of kinase domain was sufficient to elicit robust anti-tumor immune responses. These data support the concept that an HPK1 small molecule kinase inhibitor could serve as a novel agent to provide additional benefit in combination with existing immunotherapies, particularly to overcome resistance to current treatment regimens.

An automated liquid chromatography-mass spectrometry process to determine metabolic stability half-life and intrinsic clearance of drug candidates by substrate depletion.

An automated process is described for the detailed assessment of the in vitro metabolic stability properties of drug candidates in support of pharmaceutical property profiling. Compounds are incubated with liver microsomes using a robotic liquid handler. Aliquots are taken at various time points, and the resulting samples are quantitatively analyzed by liquid chromatography-mass spectrometry utilizing ion trap mass spectrometers to determine the amount of compound remaining. From these data metabolism rates can be calculated. A high degree of automation is achieved through custom software, which is employed for instrument setup, data processing, and results reporting. The assay setup is highly configurable, allowing for any combination of up to six user-selected time points, variable substrate concentration, and microsomes or other biologically active media. The data, based on relative substrate depletion, affords an estimate of metabolic stability through the calculation of half-life (t(1/2)) and intrinsic clearance, which are used to differentiate and rank order drug leads. In general, t(1/2) is the time necessary for the metabolism, following first-order kinetics, of 50% of the initial compound. Intrinsic clearance is the proportionality constant between rate of metabolism of a compound and its concentration at the enzyme site. Described here is the setup of the assay, and data from assay test compounds are presented.

An automated high throughput liquid chromatography-mass spectrometry process to assess the metabolic stability of drug candidates.

An automated high throughput process, termed the MetFast assay, is described to assess in vitro the general microsomal cytochrome P450 beta-nicotinamide adenine dinucleotide phosphate-mediated first-pass metabolic stability of potential drug candidates as a utility for pharmaceutical profiling. Utilizing robotic protocols with a multiprobe liquid handler, compounds are incubated with liver microsomes from different species. Samples are then analyzed by in-line liquid chromatography (LC)-mass spectrometry (MS) to determine the amount of compound remaining after a certain time, which allows calculation of metabolism rates. To quantitatively assess large numbers of structurally diverse compounds by LC-MS, a strategy based on an iterative two-step process was devised. Initially compounds are qualitatively analyzed by LC-ultraviolet (UV)/MS (step 1) to determine purity (UV detection) and structural integrity (MS detection). This step ensures that only correct and verified compounds with sufficient purity are being assayed to obtain reproducible high data quality. In addition, all necessary information is gathered to automatically generate specific quantitative methods for the subsequent bioanalytical analysis of metabolic stability samples by LC-UV/MS (step 2). In-house-developed, highly flexible and sophisticated data management software, termed SmartReport, is utilized for automated qualitative and quantitative LC-MS analysis set-up, data processing, and results reporting. The integration of key aspects, inherent "universal" collision-induced dissociation settings of ion trap mass spectrometers for tandem mass spectrometric scan functions utilized for compound-specific and sensitive quantitative MS methods, generic fast-LC conditions, generic MS instrument settings, and the functionality of SmartReport software resulted in an analytical process that routinely provides reproducible high-quality metabolic stability data on structurally diverse compounds. Described here is the setup of the MetFast assay, and metabolic stability data from assay validation compounds are given.

Beyond classical derivatization: analyte 'derivatives' in the bioanalysis of endogenous and exogenous compounds.

The analysis of endogenous and exogenous analytes in biological matrices presents several challenges to the bioanalyst. These analytes are often present at low concentrations, typically in complex matrices, and may have physicochemical properties that are not amenable to LC-MS analysis. The bioanalyst thus relies heavily on the formation of analyte derivatives for the efficient quantification of these compounds. These derivatives are also critically employed to derive information on the biology of living systems, potential drug or disease targets, and biomarkers of drug efficacy, safety, or disease progression. In this perspective, we demonstrate how analyte derivatives are applied in modern bioanalytical workflows and we discuss the potential use of these derivatives in the future.

Labware additives identified to be selective monoamine oxidase-B inhibitors.

Plastic labware is used in all processes of modern pharmaceutical research, including compound storage and biological assays. The use of these plastics has created vast increases in productivity and cost savings as experiments moved from glass test tubes and capillary pipettes to plastic microplates and multichannel liquid handlers. One consequence of the use of plastic labware, however, is the potential release of contaminants and their resultant effects on biological assays. We report herein the identification of biologically active substances released from a commonly used plastic microplate. The active contaminants were identified by gas chromatography-mass spectroscopy as dodecan-1-ol, dodecyl 3-(3-dodecoxy-3-oxopropyl)sulfanylpropanoate, and dodecanoic acid, and they were found to be selective monoamine oxidase-B inhibitors.

Bioanalysis of (1R,4R,5S,6R)-4-amino-2-oxabicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY379268) in rat plasma using derivatization liquid chromatography/mass spectrometry.

BACKGROUND: (1R,4R,5S,6R)-4-amino-2-oxabicyclo[3.1.0]hexane-4,6-dicarboxylic acid, also known as LY379268, a group II metabotropic glutamate receptor agonist, has been widely used in neuroscience as a model compound in studies evaluating antipsychotic drugs for the treatment of schizophrenia. MATERIALS & METHODS: So far, no reports describing methods of the bioanalysis of LY379268 have been published. Here, a novel method is presented for determining LY379268 in rat plasma employing precolumn derivatization with pentafluorobenzoyl chloride reagent coupled to liquid chromatography/mass spectrometry. CONCLUSION: Chemical derivatization of a low-molecular-weight and highly polar molecule yields a derivative that is retained on a reversed-phase liquid chromatography column with improved tandem mass spectrometric response.