Agonists at the nicotinic acetylcholine alpha 7 receptor (nAChR α7) subtype have the potential to treat cognitive deficits in patients with Alzheimer's disease (AD) or schizophrenia. Visuo-spatial paired associates learning (vsPAL) is a task that has been shown to reliably predict conversion from mild cognitive impairment to AD in humans and can also be performed by nonhuman primates. Reversal of scopolamine-induced impairment of vsPAL performance may represent a translational approach for the development of nAChR α7 agonists. The present study investigated the effect of treatment with the acetylcholinesterase inhibitor, donepezil, or three nAChR α7 agonists, BMS-933043, EVP-6124 and RG3487, on vsPAL performance in scopolamine-treated cynomolgus monkeys. Scopolamine administration impaired vsPAL performance accuracy in a dose- and difficulty- dependent manner. The impairment of eventual accuracy, a measure of visuo-spatial learning during the task, was significantly ameliorated by treatment with donepezil (0.3 mg/kg, i.m.), EVP-6124 (0.01 mg/kg, i.m.) or BMS-933043 (0.03, 0.1 and 0.3 mg/kg, i.m.). Both nAChR α7 agonists showed inverted-U shaped dose-effect relationships with EVP-6124 effective at a single dose only whereas BMS-933043 was effective across at least a 10 fold dose/exposure range. RG3487 was not efficacious in this paradigm at the dose range examined (0.03-1 mg/kg, i.m.). These results are the first demonstration that the nAChR α7 agonists, EVP-6124 and BMS-933043, can ameliorate scopolamine-induced cognitive deficits in nonhuman primates performing the vsPAL task.

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).

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.

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.

High throughput screening led to the identification of a novel series of quinolone α7 nicotinic acetylcholine receptor (nAChR) agonists. Optimization of an HTS hit (1) led to 4-phenyl-1-(quinuclidin-3-ylmethyl)quinolin-2(1H)-one, which was found to be potent and selective. Poor brain penetrance in this series was attributed to transporter-mediated efflux, which was in turn due to high pKa. A novel 4-fluoroquinuclidine significantly lowered the pKa of the quinuclidine moiety, reducing efflux as measured by a Caco-2 assay.

Phenacetin is widely used as an in vitro probe to measure CYP1A2 activity across species. To investigate whether phenacetin can be used as an in vivo probe substrate to phenotype CYP1A2 activity in dogs, beagle dogs previously genotyped for a single nucleotide polymorphism that yields an inactive CYP1A2 protein were selected and placed into one of three groups: CC (wild-type), CT (heterozygous), or TT (homozygous mutants). The dogs were dosed with phenacetin orally at 5 and 15 mg/kg and intravenously at 15 mg/kg. Plasma samples were analyzed by liquid chromatography-tandem mass spectrometry, and phenacetin and its primary metabolite, acetaminophen, were monitored. After intravenous dosing, all groups showed similar exposure of phenacetin irrespective of genotype. After oral dosing at 15 mg/kg, the exposure of phenacetin in CC and CT dogs was similar, but phenacetin exposure was 2-fold greater in TT dogs. Exposure of the metabolite, acetaminophen, was similar in all groups; however, the mean acetaminophen/phenacetin ratio in TT dogs was 1.7 times less than that observed in CC dogs. Similar trends between the groups of dogs with respect to phenacetin exposure were also observed after a lower 5 mg/kg p.o. dose of phenacetin; however, a proportionally greater amount of acetaminophen was generated. Although oral exposure of phenacetin was 2-fold higher and acetaminophen exposure was 2-fold lower in CYP1A2-deficient (TT) dogs, these results were considered modest and suggest that phenacetin is not a selective or robust in vivo probe to measure CYP1A2 enzyme activity in the dog.

The purpose of this study was to develop a mechanistic pharmacokinetic-pharmacodynamic (PK-PD) model to describe the effects of rifampicin on hepatic Cyp3a11 RNA, enzymatic activity, and triazolam pharmacokinetics. Rifampicin was administered to steroid and xenobiotic X receptor (SXR) humanized mice at 10 mg/kg p.o. (every day for 3 days) followed by triazolam (4 mg/kg p.o.) 24 h after the last dose of rifampicin. Rifampicin and triazolam concentrations and Cyp3a11 RNA expression and activity in the liver were measured over the 4-day period. Elevations in Cyp3a11 RNA expression were observed 24 h after the first dose of rifampicin, reaching a maximum (∼10 times baseline) after the third dose and were sustained until day 4 and began declining 48 h after the last rifampicin dose. Similar changes in enzymatic activity were also observed. The triazolam serum area under the curve (AUC) was 5-fold lower in mice pretreated with rifampicin, consistent with enzyme induction. The final PK-PD model incorporated rifampicin liver concentration as the driving force for the time-delayed Cyp3a11 induction governed by in vitro potency estimates, which in turn regulated the turnover of enzyme activity. The PK-PD model was able to recapitulate the delayed induction of Cyp3a11 mRNA and enzymatic activity by rifampicin. Furthermore, the model was able to accurately anticipate the reduction in the triazolam plasma AUC by integrating a ratio of the predicted induced enzyme activity and basal activity into the equations describing triazolam pharmacokinetics. In conjunction with the SXR humanized mouse model, this mathematical approach may serve as a tool for predicting clinically relevant drug-drug interactions via pregnane X receptor-mediated enzyme induction and possibly extended to other induction pathways (e.g., constitutive androstane receptor).

BACKGROUNDBioanalytical support of drug-discovery efforts increasingly requires more complex multiple component analysis, including the bioanalysis of drugs, prodrugs and metabolites. Just as the physiochemical properties of these components may differ widely from each other, optimal LC and MS conditions, including polarity, can also vary greatly among the analytes of interest, thus presenting significant challenges during quantitative LC-MS-based bioanalysis. A single compromised method for the determination of all analytes may sacrifice sensitivity or chromatographic conditions for one analyte in order to achieve adequate results for another. Manually switching between assay conditions to analyze samples under separately optimized conditions for individual compounds can be time consuming.RESULTSThe method presented here addresses the problem of differential analyte optimization using a multiplexed approach for simultaneous quantitative bioanalysis of multiple analytes in the same sample, employing a mixed mode of both turbulent- and laminar-flow chromatography.CONCLUSIONThe approach is illustrated with the quantitation of a lipophilic drug and its hydrophilic phosphate ester prodrug in a biological matrix under individually optimized LC-MS conditions.

3-Methylindole (3MI), a respiratory tract toxicant, can be metabolized by a number of cytochromes P450 (P450), primarily through either dehydrogenation or epoxidation of the indole. In the present study, we assessed the bioactivation of 3MI by recombinant CYP2A13, a human P450 predominantly expressed in the respiratory tract. Four metabolites were detected, and the two principal ones were identified as indole-3-carbinol (I-3-C) and 3-methyloxindole (MOI). Bioactivation of 3MI by CYP2A13 was verified by the observation of three glutathione (GSH) adducts designated as GS-A1 (glutathione adduct 1), GS-A2 (glutathione adduct 2), and GS-A3 (glutathione adduct 3) in a NADPH- and GSH-fortified reaction system. GS-A1 and GS-A2 gave the same molecular ion at m/z 437, an increase of 305 Da over 3MI. Their structures are assigned to be 3-glutathionyl-S-methylindole and 3-methyl-2-glutathionyl-S-indole, respectively, on the basis of the mass fragmentation data obtained by high-resolution mass spectrometry. Kinetic parameters were determined for the formation of I-3-C (Vmax = 1.5 nmol/min/nmol of P450; Km = 14 μM), MOI (Vmax = 1.9 nmol/min/nmol of P450; Km = 15 μM) and 3-glutathionyl-S-methylindole (Vmax = 0.7 nmol/min/nmol of P450; Km = 13 μM). The structure of GS-A3, a minor adduct with a protonated molecular ion at m/z 453, is proposed to be 3-glutathionyl-S-3-methyloxindole. We also discovered that 3MI is a mechanism-based inactivator of CYP2A13, given that it produced a time-, cofactor-, and 3MI concentration-dependent loss of activity toward 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, with a relatively low KI value of ∼10 μM and a kinact of 0.046 min−1. Thus, CYP2A13 metabolizes 3MI through multiple bioactivation pathways, and the process can lead to a suicide inactivation of CYP2A13.

Ion suppression is a common concern when utilizing liquid chromatography-tandem mass spectrometry for quantitation of analytes in biological samples. Ion suppression can cause the analytical signal for the analyte and/or the internal standard to be reduced compared with prepared analytical standards, leading to erroneous quantitation values for the desired analyte of interest. While it has become commonplace to note ion suppression due to the dosing vehicle in in vivo experiments, we have observed a similar phenomenon of ion suppression due to the components of the locking solution used to keep the cannula patent in certain rodent experiments. During one such typical bioanalysis of a drug candidate dosed to a cannulated rodent, significant ion suppression (∼60%) was observed for the structural analogue internal standard, which led to this investigation that revealed the cannula locking solution as the source of the ion suppression.

The SXR humanized mouse model was used to quantitatively assess an in vivo induction response of the human PXR agonist, rifampicin. Three days of rifampicin treatment increased RNA expression and microsomal enzyme activity of CYP3A11, as well as significantly reduced triazolam plasma exposure. These results indicate that the humanized SXR mouse can be used as a model to predict human CYP3A4 induction and the resulting pharmacokinetic changes of CYP3A4 substrates in humans.

A preclinical canine model capable of predicting a compound's potential for a human food effect was developed. The beagle dog was chosen as the in vivo model. A validation set of compounds with known propensities for human food effect was studied. Several diets were considered including high-fat dog food and various quantities of the human FDA meal. The effect of pentagastrin pretreatment was also investigated. The high-fat dog food did not predict human food effect and was discontinued from further evaluation. The amount of FDA meal in the dog was important in the overall prediction of the magnitude of human food effect. Fed/fasted Cmax and AUC ratios using a 50-g aliquot of the FDA meal in the dog were in the closest qualitative agreement to human data. Pentagastrin pretreatment did not affect the AUC in the fed state, but increased the fasted AUC for weakly basic compounds. Pentagastrin pretreatment and a 50-g aliquot of the FDA meal in the dog predicted the human food effect for a validation set of compounds. This model, which is intended for compound screening, will be helpful for determining food effect as a liability when compounds progress from discovery to clinical development.