Prediction of the Renal Organic Anion Transporter 1 (OAT1)- Mediated Drug Interactions for LY404039, the Active Metabolite of Pomaglumetad Methionil.

PURPOSE: The objective of this work was to demonstrate that clinical OAT1-mediated DDIs can be predicted using physiologically based pharmacokinetic (PBPK) modeling. METHODS: LY404039 is a metabotropic glutamate receptor 2/3 agonist and the active moiety of the prodrug pomaglumetad methionil (LY2140023). After oral administration, pomaglumetad methionil is rapidly taken up by enterocytes via PEPT1 and once absorbed, converted to LY404039 via membrane dehydropeptidase 1 (DPEP1). LY404039 is renally excreted by both glomerular filtration and active secretion and in vitro studies showed that the active secretion of LY404039 was mediated by the organic anion transporter 1 (OAT1). Both clinical and in vitro data were used to build a PBPK model to predict OAT1-mediated DDIs. RESULTS: In vitro inhibitory potencies (IC50) of the known OAT inhibitors, probenecid and ibuprofen, were determined to be 4.00 and 2.63 µM, respectively. Subsequently, clinical drug-drug interaction (DDI) study showed probenecid reduced the renal clearance of LY404039 by 30 to 40%. The PBPK bottom-up model, predicted a renal clearance that was approximately 20% lower than the observed one. The middle-out model, using an OAT1 relative activity factor (RAF) of 3, accurately reproduced the renal clearance of LY404039 and pharmacokinetic (PK) changes of LY404039 in the presence of probenecid. CONCLUSIONS: OAT1- mediated DDIs can be predicted using in vitro measured IC50 and PBPK modeling. The effect of ibuprofen was predicted to be minimal (AUC ratio of 1.15) and not clinically relevant.

Quantification and pharmacokinetic property of verubecestat an BACE1 inhibitor in rat plasma.

In the present study, an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) approach was designed to measure the rat plasma levels of verubecestat with diazepam as the internal standard. Acetonitrile-based protein precipitation was applied for sample preparation, then the analyte verubecestat was subjected to gradient elution chromatography with a mobile phase composed of acetonitrile (A) and 0.1% formic acid in water (B). Verubecestat was monitored by m/z 410.1 → 124.0 transition for quantification by multiple reaction monitoring (MRM) in positive ion electrospray ionization (ESI) source. When the concentration of verubecestat ranged from 1 to 2500 ng/mL, the method exhibited good linearity. For verubecestat, the intra- and inter-day precision were determined with the values of 2.9-9.0% and 0.4-6.5%, respectively; and the accuracy ranged from -2.2% to 10.4%. Matrix effect, extraction recovery, and stability data were in line with the standard FDA guidelines for validating a bioanalytical method. The validity of the developed method was confirmed through the pharmacokinetic study.

Brain PET Imaging of α7-nAChR with [18F]ASEM: Reproducibility, Occupancy, Receptor Density, and Changes in Schizophrenia.

Background: The α7 nicotinic acetylcholine receptor increasingly has been implicated in normal brain physiology, as well as in neuropsychiatric disorders. The highly cortical distribution of α7 nicotinic acetylcholine receptor suggests a role in cognition. Methods: We expanded the first-in-human PET imaging of α7 nicotinic acetylcholine receptor with [18F]ASEM from 5 to 21 healthy nonsmoking volunteers and added a feasibility study in 6 male patients with schizophrenia. Study aims included: (1) confirmation of test-retest reproducibility of [18F]ASEM binding, (2) demonstration of specificity by competition with DMXB-A, an α7 nicotinic acetylcholine receptor partial agonist, (3) estimation of [18F]ASEM binding potentials and α7 nicotinic acetylcholine receptor density in vivo in humans, and (4) demonstrating the feasibility of studying α7 nicotinic acetylcholine receptor as a target for schizophrenia. Results: Test-retest PET confirmed reproducibility (>90%) (variability ≤7%) of [18F]ASEM volume of distribution (VT) estimates in healthy volunteers. Repeated sessions of PET in 5 healthy subjects included baseline and effect of inhibition after oral administration of 150 mg DMXB-A. From reduction of binding potentials, we estimated the dose-dependent occupancy of α7 nicotinic acetylcholine receptor by DMXB-A at 17% to 49% for plasma concentrations at 60 to 200 nM DMXB-A. In agreement with evidence postmortem, α7 nicotinic acetylcholine receptor density averaged 0.67 to 0.82 nM and inhibitor affinity constant averaged 170 to 385 nM. Median VT in a feasibility study of 6 patients with schizophrenia was lower than in healthy volunteers in cingulate cortex, frontal cortex, and hippocampus (P = 0.02, corrected for multiple comparions, Mann-Whitney test). Conclusions: The current results confirm the reproducibility of [18F]ASEM VT estimates and the specificity of the tracer for α7 nicotinic acetylcholine receptor. Preliminary findings from our feasibility study of [18F]ASEM binding in patients with schizophrenia are suggestive and provide guidance for future studies with more subjects.

PET imaging evaluation of [(18)F]DBT-10, a novel radioligand specific to α7 nicotinic acetylcholine receptors, in nonhuman primates.

PURPOSE: Positron emission tomography (PET) radioligands specific to α7 nicotinic acetylcholine receptors (nAChRs) afford in vivo imaging of this receptor for neuropathologies such as Alzheimer's disease, schizophrenia, and substance abuse. This work aims to characterize the kinetic properties of an α7-nAChR-specific radioligand, 7-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-2-[(18)F]-fluorodibenzo[b,d]thiophene 5,5-dioxide ([(18)F]DBT-10), in nonhuman primates. METHODS: [(18)F]DBT-10 was produced via nucleophilic substitution of the nitro-precursor. Four Macaca mulatta subjects were imaged with [(18)F]DBT-10 PET, with measurement of [(18)F]DBT-10 parent concentrations and metabolism in arterial plasma. Baseline PET scans were acquired for all subjects. Following one scan, ex vivo analysis of brain tissue was performed to inspect for radiolabeled metabolites in brain. Three blocking scans with 0.69 and 1.24 mg/kg of the α7-nAChR-specific ligand ASEM were also acquired to assess dose-dependent blockade of [(18)F]DBT-10 binding. Kinetic analysis of PET data was performed using the metabolite-corrected input function to calculate the parent fraction corrected total distribution volume (V T/f P). RESULTS: [(18)F]DBT-10 was produced within 90 min at high specific activities of 428 ± 436 GBq/µmol at end of synthesis. Metabolism of [(18)F]DBT-10 varied across subjects, stabilizing by 120 min post-injection at parent fractions of 15-55%. Uptake of [(18)F]DBT-10 in brain occurred rapidly, reaching peak standardized uptake values (SUVs) of 2.9-3.7 within 30 min. The plasma-free fraction was 18.8 ± 3.4%. No evidence for radiolabeled [(18)F]DBT-10 metabolites was found in ex vivo brain tissue samples. Kinetic analysis of PET data was best described by the two-tissue compartment model. Estimated V T/f P values were 193-376 ml/cm(3) across regions, with regional rank order of thalamus > frontal cortex > striatum > hippocampus > occipital cortex > cerebellum > pons. Dose-dependent blockade of [(18)F]DBT-10 binding by structural analog ASEM was observed throughout the brain, and occupancy plots yielded a V ND/f P estimate of 20 ± 16 ml/cm(3). CONCLUSION: These results demonstrate suitable kinetic properties of [(18)F]DBT-10 for in vivo quantification of α7-nAChR binding in nonhuman primates.

Preclinical and clinical evidence for the collaborative transport and renal secretion of an oxazolidinone antibiotic by organic anion transporter 3 (OAT3/SLC22A8) and multidrug and toxin extrusion protein 1 (MATE1/SLC47A1).

N-({(5S)-3-[4-(1,1-dioxidothiomorpholin-4-yl)-3,5-difluorophenyl]-2-oxo-1,3-oxazolidin-5-yl}methyl)acetamide (PNU-288034), an oxazolidinone antibiotic, was terminated in phase I clinical development because of insufficient exposure. Analysis of the drug pharmacokinetic and elimination profiles suggested that PNU-288034 undergoes extensive renal secretion in humans. The compound was well absorbed and exhibited approximately linear pharmacokinetics in the oral dose range of 100 to 1000 mg in human. PNU-288034 was metabolically stable in liver microsomes across species, and unchanged drug was cleared in the urine by an apparent active renal secretion process in rat and monkey (two to four times glomerular filtration rate) but not dog. In vitro studies conducted to characterize the transporters involved demonstrated PNU-288034 uptake by human organic anion transporter 3 (OAT3; K(m) = 44 +/- 5 microM) and human multidrug and toxin extrusion protein 1 (hMATE1; K(m) = 340 +/- 55 microM). The compound was also transported by multidrug resistance P-glycoprotein and breast cancer resistance protein. In contrast, human organic cation transporter 2, human OAT1, and hMATE2-K did not transport PNU-288034. Coadministration of PNU-288034 and the OAT3 inhibitor probenecid significantly increased PNU-288034 plasma area under the curve (170%) and reduced both plasma and renal clearance in monkey. Coadministration of PNU-288034 and cimetidine, a MATE1 inhibitor, also reduced plasma clearance in rat to a rate comparable with probenecid coadministration. Collectively, our results demonstrated a strong in vitro-in vivo correlation for active renal secretion coordinated through the vectorial transport process of OAT3 and MATE1, which ultimately resulted in limiting the systemic exposure of PNU-288034.

Imidazo-pyrazine derivatives as potent CXCR3 antagonists.

A general way of improving the potency of CXCR3 antagonists with fused hetero-bicyclic cores was identified. Optimization efforts led to the discovery of a series of imidazo-pyrazine derivatives with improved pharmacokinetic properties in addition to increased potency. The efficacy of the lead compound 21 is evaluated in a mouse lung inflammation model.

Safety, Tolerability, and Pharmacokinetics of the ß-Site Amyloid Precursor Protein-Cleaving Enzyme 1 Inhibitor Verubecestat (MK-8931) in Healthy Elderly Male and Female Subjects.

ß-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is required for the production of ß-amyloid peptides, which are implicated in the etiology of Alzheimer's disease. The safety and pharmacokinetics of the BACE1 inhibitor verubecestat have previously been studied in young adults aged 19-45 years. In this randomized, placebo-controlled, phase I study (protocol MK-8931-006), we investigated the safety, tolerability, and pharmacokinetics of a single dose (100 mg) or multiple doses (30, 80, and 120 mg) once daily for 28 days of verubecestat in healthy elderly subjects. Safety end points were assessed at baseline and during the duration of the study period and indicated that verubecestat was generally well tolerated. Verubecestat pharmacokinetics were similar between healthy elderly male and female subjects and similar to those reported in healthy young males in previous studies. These data supported subsequent studies to assess the potential efficacy of verubecestat in subjects with Alzheimer's disease.

Pharmacokinetics and Pharmacodynamics of the BACE1 Inhibitor Verubecestat (MK-8931) in Healthy Japanese Adults: A Randomized, Placebo-Controlled Study.

ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) is required for the production of ß-amyloid (Aß) peptides and is considered a potential treatment target for Alzheimer's disease (AD). To support Japan's participation in the global clinical development program, we characterized the safety, pharmacokinetics (PKs), and pharmacodynamics of the BACE1 inhibitor verubecestat (MK-8931) in 24 healthy Japanese adults in a two-part, single-center, randomized, placebo-controlled phase I trial (protocol MK-8931-007) and compared the results with historical data from non-Japanese subjects. Both single (20, 100, and 450 mg) and multiple (80 and 150 mg once daily for 14 days) doses of verubecestat were well tolerated. Verubecestat's PK profile was similar in Japanese and non-Japanese subjects. Verubecestat also reduced mean cerebrospinal fluid concentrations of the Aß proteins Aß40, Aß42, and soluble ß fragment of amyloid precursor protein; the level of reduction was comparable between Japanese and non-Japanese subjects. These results support the continued global development of verubecestat as a potential disease-modifying agent for Japanese and non-Japanese subjects who are at risk for developing AD.

Second generation of hydroxyethylamine BACE-1 inhibitors: optimizing potency and oral bioavailability.

BACE-1 inhibition has the potential to provide a disease-modifying therapy for the treatment of Alzheimer's disease. Optimization of a first generation of BACE-1 inhibitors led to the discovery of novel hydroxyethylamines (HEAs) bearing a tricyclic nonprime side. These derivatives have nanomolar cell potency and are orally bioavailable.

5-tert-Butyl-2-(4'-[18F]fluoropropynylphenyl)-1,3-dithiane oxides: potential new GABA A receptor radioligands.

As potential new ligands targeting the binding site of gamma-aminobutyric acid (GABA) receptor ionophore, trans-5-tert-butyl-2-(4'-fluoropropynylphenyl)-2-methyl-1,1-dioxo-1,3-dithiane (1) and cis/trans-5-tert-butyl-2-(4'-fluoropropynylphenyl)-2-methyl-1,1,3,3-tetroxo-1,3-dithiane (2) were selected for radiolabeling and initial evaluation as in vivo imaging agents for positron emission tomography (PET). Both compounds exhibited identical high in vitro binding affinities (K(i)=6.5 nM). Appropriate tosylate-substituted ethynyl precursors were prepared by multistep syntheses involving stepwise sulfur oxidation and chromatographic isolation of desired trans isomers. Radiolabeling was accomplished in one step using nucleophilic [(18)F]fluorination. In vivo biodistribution studies with trans-[(18)F]1 and trans-[(18)F]2 showed significant initial uptake into mouse brain and gradual washout, with heterogeneous regional brain distributions and higher retention in the cerebral cortex and cerebellum and lower retention in the striatum and pons-medulla. These regional distributions of the new radioligands correlated with in vitro and ex vivo measures of standard radioligands binding to the ionophore- and benzodiazepine-binding sites of GABA(A) receptor in rodent brain. A comparison of these results with previously prepared radiotracers for other neurochemical targets, including successes and failures as in vivo radioligands, suggests that higher-affinity compounds with increased retention in target brain tissues will likely be needed before a successful radiopharmaceutical for human PET imaging can be identified.

Applicability of DPI formulations for novel neurokinin receptor antagonist.

A novel triple neurokinin receptor antagonist (TNRA) could have pharmaceutical efficacy for asthma and/or chronic obstructive pulmonary disease. TNRA is potentially developed as inhalation medicine. The aim of this investigation was to evaluate the applicability of dry powder inhaler (DPI) formulation for TNRA. DPI formulation containing lactose was used for this feasibility study. Mechanofusion process for surface modification was applied on lactose particles to prepare four different DPI formulations. The mixture of TNRA and lactose was administered to rats intratracheally using an insufflator. The deposition pattern and blood concentration profile of TNRA were evaluated. Although there was no significant difference in deposition on deep lungs between the four formulations, DPI formulations containing mechanofusion-processed lactose showed longer T(max) and t(1/2) and higher AUC(0-infinity) and MRT compared to that containing intact lactose. On the other hand, the contact angle measurement showed that the mechanofusion process decreased the polar part of the surface energy of the lactose. Therefore, the prolongation of the wetting of the formulated powder mixture seemed to delay the dissolution of TNRA deposited in respiratory tract. It was concluded that DPI formulation containing mechanofusion-processed lactose could be suitable for inhalation of TNRA.

Pharmacokinetics of taurolidine following repeated intravenous infusions measured by HPLC-ESI-MS/MS of the derivatives taurultame and taurinamide in glioblastoma patients.

BACKGROUND AND OBJECTIVE: Taurolidine is known to have antimicrobial activity. Furthermore, at lower concentrations, it has been found to exert a selective antineoplastic effect in vitro and in vivo. The aim of this study was to investigate the pharmacokinetics of taurolidine in vivo following repeated intravenous infusion in a schedule used for the treatment of glioblastoma. As a prerequisite, the pharmacokinetics of taurolidine in human blood plasma and whole blood in vitro was investigated. PATIENTS AND METHODS: The pharmacokinetics of taurolidine and its derivatives taurultame and taurinamide were investigated in human blood plasma and in whole blood in vitro using blood from a healthy male volunteer. During repeated intravenous infusion therapy with taurolidine, plasma samples were taken every hour for a period of 13 hours per day in seven patients (three male, four female; mean age 48.4 +/- 12.8 years, range 27-66 years) with a glioblastoma. Following dansyl derivatisation, the concentrations of taurultame and taurinamide were determined using a new method based on high-performance liquid chromatography (HPLC) online coupled to electrospray ionisation tandem mass spectrometry (ESI-MS/MS) in the multiple reaction monitoring mode. Under the experimental conditions used, taurolidine could not be determined directly and was back-calculated from the taurultame and taurinamide values. RESULTS: The new HPLC-ESI-MS/MS method demonstrated high accuracy and reproducibility. In vitro plasma concentrations of taurultame and taurinamide remained constant over the incubation period. In whole blood in vitro, a time-dependent formation of taurinamide was observed. At the start of the incubation, the taurultame-taurinamide ratio (TTR) was 0.95 at an initial taurolidine concentration of 50 microg/mL, and 1.69 at 100 microg/mL. The concentration of taurultame decreased at the same rate as the taurinamide concentration increased, showing logarithmic kinetics. The calculated taurolidine concentration remained largely constant over the 6-hour incubation period. During repeated infusions in patients, calculated plasma concentrations of taurolidine showed a strong increase after the start of each infusion and continued to increase until the end of infusion, followed by a rapid decline. The TTR was found to fluctuate between 0.1 and 0.3, depending on the relation to the previous or next infusion period. The volume of distribution was markedly higher for taurolidine, taurultame and taurinamide than the plasma volume. CONCLUSIONS: Taurolidine displayed a stable pattern of derivatives in plasma in vitro, whereas in whole blood, a time- and concentration-dependent conversion was apparent. In patients, the calculated average taurolidine plasma concentration, achieved with the repeated infusion regimen, was in the antineoplastic-effective concentration range. The tissue concentrations of taurolidine and taurultame are expected to be higher than the plasma concentrations, taking into account the calculated volumes of distribution. Repeated infusion of taurolidine is the therapeutically adequate mode of administration for the indication of glioblastoma.

Approaches to intravenous clinical pharmacokinetics: Recent developments with isotopic microtracers.

Obtaining pharmacokinetic data from the intravenous route for drugs intended for oral administration has traditionally been expensive and time consuming because of the toxicology requirements and challenges in intravenous formulations. Such studies are necessary, however, particularly when regulator agencies request absolute bioavailability data. A method has emerged whereby the drug administered intravenously is isotopically labeled and dosed at a maximum of 100 µg concomitantly with an oral administration given at a therapeutically relevant level. The intravenous administration has been termed a microtracer and obviates intravenous toxicology requirements as well as simplifying formulations. The study design also essentially removes issues of nonlinear pharmacokinetics that may occur when oral and intravenous doses are administered separately. This review examines the methodology and the literature to date, including those studies intended for regulatory submission. The method has been extended to the study of prodrug-to-active drug kinetics and to obtaining clearance, volume of distribution, and absolute bioavailability at steady-state conditions.

Chronic exposure to KATP channel openers results in attenuated glucose sensing in hypothalamic GT1-7 neurons.

Individuals with Type 1 diabetes (T1D) are often exposed to recurrent episodes of hypoglycaemia. This reduces hormonal and behavioural responses that normally counteract low glucose in order to maintain glucose homeostasis, with altered responsiveness of glucose sensing hypothalamic neurons implicated. Although the molecular mechanisms are unknown, pharmacological studies implicate hypothalamic ATP-sensitive potassium channel (KATP) activity, with KATP openers (KCOs) amplifying, through cell hyperpolarization, the response to hypoglycaemia. Although initial findings, using acute hypothalamic KCO delivery, in rats were promising, chronic exposure to the KCO NN414 worsened the responses to subsequent hypoglycaemic challenge. To investigate this further we used GT1-7 cells to explore how NN414 affected glucose-sensing behaviour, the metabolic response of cells to hypoglycaemia and KATP activity. GT1-7 cells exposed to 3 or 24 h NN414 exhibited an attenuated hyperpolarization to subsequent hypoglycaemic challenge or NN414, which correlated with diminished KATP activity. The reduced sensitivity to hypoglycaemia was apparent 24 h after NN414 removal, even though intrinsic KATP activity recovered. The NN414-modified glucose responsiveness was not associated with adaptations in glucose uptake, metabolism or oxidation. KATP inactivation by NN414 was prevented by the concurrent presence of tolbutamide, which maintains KATP closure. Single channel recordings indicate that NN414 alters KATP intrinsic gating inducing a stable closed or inactivated state. These data indicate that exposure of hypothalamic glucose sensing cells to chronic NN414 drives a sustained conformational change to KATP, probably by binding to SUR1, that results in loss of channel sensitivity to intrinsic metabolic factors such as MgADP and small molecule agonists.

Pharmacokinetic characterization of 2-(3-benzoyl)-4-hydroxy-1,1-dioxo-2H-1,2-benzothiazine-2-yl-1-phenylethanone, a novel 11ß-hydroxysteroid dehydrogenase type 1 inhibitor in rats.

11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) is associated with metabolic syndromes such as type 2 diabetes mellitus and obesity. A new 11ß-HSD1 inhibitor known as 2-(3-benzoyl)-4-hydroxy-1, 1-dioxo-2H-1, 2-benzothiazine-2-yl-1-phenylethanone (KR-66344) is being developed as a therapeutic agent for these metabolic diseases. The purpose of this study was to characterize the pharmacokinetics of KR-66344 to support further preclinical development. KR-66344 showed high liver microsomal stability with T1/2 values >3 h and high permeability with apparent permeability coefficients of 15.2-24.2 × 10(-6) cm/s in Caco-2 cell monolayers. KR-66344 was also strongly bound to plasma proteins (>98%). After intravenous dosing, KR-66344 exhibited low systemic clearance (0.27-0.37 L/h/kg) and a low to moderate volume of distribution at steady state (0.79-0.8 L/kg). The bioavailability and terminal half-lives of KR-66344 following oral administration were 25% and 1.7-3.3 h, respectively. In addition, KR-66344 showed dose-independent pharmacokinetics at 0.5-10 mg/kg in intravenous and oral pharmacokinetic studies.

The effects of NN414, a SUR1/Kir6.2 selective potassium channel opener, in healthy male subjects.

The aim of the present study was to investigate the effect of a single dose of NN414 (a selective SUR1/Kir6.2 potassium channel opener). Sixty-four healthy male subjects were enrolled at 8 dose levels (0.625-12.5 mg/kg or placebo). The study consisted of a baseline day and a dosing day. NN414 or placebo was administered in the evening about 10 pm. On both study days, an oral glucose tolerance test (OGTT) was performed following an overnight fast (corresponding to 9 hours postdose), and glucose, insulin, glucagon, and growth hormone concentrations were determined. NN414 was well tolerated, with no clinically relevant changes in safety parameters, although there was an increase in gastrointestinal side effects. NN414 treatment lowered glucose during the OGTT and 24-hour insulin and glucose levels. In conclusion, a single dose of NN414 is associated with improvements in glucose-related parameters in healthy male subjects.

Identification of key factors affecting the oral absorption of salts of lipophilic weak acids: a case example.

OBJECTIVES: Evaluate the ability of biorelevant media to adequately predict solubility in human gastrointestinal aspirates collected in the fasted state for the sodium salt of a highly dosed, Biopharmaceutics Classification System II (BCS II) compound with weakly acidic properties (L-870,810, pKa 7.3, HA (5-(1,1-dioxothiazinan-2-yl)-N-((4-fluorophenyl)methyl)-8-hydroxy-1,6-naphthyridine-7-carboxamide)). Identify key luminal processes that dictate the behaviour of sodium salt of HA (NaA), after single-dose administrations of high (relatively to solubility limit) doses corresponding to 400 and 800 mg of HA in the fasted state. METHODS: Aspirates from stomach and upper small intestine were collected from eight healthy fasted adults, after administration of 240 ml of water. Solubilities of NaA and HA were measured in aspirated samples and biorelevant media. Dissolution experiments of NaA granules were performed in biorelevant media. Prediction of oral pharmacokinetics was evaluated in silico using Stella software. KEY FINDINGS: Equilibrium solubility of NaA in fluids aspirated from the upper gastrointestinal tract is more transient than of HA. Solubility in upper gastrointestinal lumen was adequately estimated by data in biorelevant media. Supersaturation, followed by precipitation, which did not fully revert to the equilibrium solubility of HA, was observed during the dissolution of NaA granules in biorelevant media. Physiologically based pharmacokinetic modelling indicated that while intragastric processes had no significant impact on absorption kinetics, dissolution kinetics, kinetic solubility, radial transport rates and, for the 800-mg dose, precipitation kinetics in the small intestine had the greatest impact on absorption profiles. CONCLUSIONS: Adequate prediction of the average plasma profile, after administration of NaA, required consideration of region-dependent dissolution rates and/or solubilisation.

Relative contributions of presystemic and systemic peptidases to oral exposure of a novel metabotropic glutamate 2/3 receptor agonist (LY404039) after oral administration of prodrug pomaglumetad methionil (LY2140023).

Pomaglumetad methionil (LY2140023) is the prodrug of a novel metabotropic glutamate 2/3 receptor agonist (LY404039) being investigated for the treatment of schizophrenia. Using accelerator mass spectrometry (AMS) and an intravenous (i.v.) radiolabeled tracer approach, the absolute bioavailability of the prodrug and the extent of its conversion to active moiety (LY404039) were estimated at presystemic (intestinal/first pass) and systemic sites after simultaneous oral and i.v. dosing in healthy subjects. The mean absolute bioavailability of prodrug (80 mg oral) was 0.68. On the basis of these data and a previous radiolabeled mass balance study in which no prodrug was recovered in feces, we concluded that 0.32 of the dose is converted to active drug in the intestinal tract. The fraction of prodrug converted to active moiety was approximately 1, indicating complete conversion of the prodrug that reaches the systemic circulation to the active moiety. Prodrug (80 mg oral and 100 µg i.v.) and active moiety (100 µg i.v.) were well tolerated in healthy subjects. Thus, the absolute bioavailability of prodrug LY2140023 and the fraction converted presystemically and systemically to active moiety LY404039 were estimated simultaneously using radiolabeled tracer microdosing and AMS.

Synthesis and antifungal activity of 1,3,2-benzodithiazole S-oxides.

The preparation of 1,3,2-benzodithiazole S-oxide analogs exhibiting in vitro antifungal activity against several strains of Candida is described. For the preparation of derivatives bearing aromatic substituents, a novel electrophilic aromatic thiolation reaction was utilized which produced substituted aromatic 1,2-dithiol intermediates. The reactions of nucleophiles with the parent heterocyclic system have led to an efficient transamidation process which allows for the direct production of these analogs. The S-oxide bond exhibits poor stereochemical stability and has been found to epimerize under ambient conditions. The structure-activity data report that a side chain of greater than 10 carbons effects a loss in activity as does the placement of polar groups in this chain.

Autoradiographic studies of RP 62203, a potent 5-HT2 receptor antagonist. Pharmacological characterization of [3H]RP 62203 binding in the rat brain.

The binding properties and localization of [3H]RP 62203, a novel ligand for 5-HT2 receptors, were investigated on rat brain sections. The specific binding of this 5-HT2 receptor antagonist was reversible and could be displaced by ritanserin (1 microM). Saturation experiments revealed a single class of binding sites with a KD of 0.128 +/- 0.018 nM and a Bmax of 1.67 +/- 0.06 pmol/mg protein. Pharmacological specificity was demonstrated by the potency order of displacing agents: RP 62203 > ritanserin > spiperone > methysergide > mianserin > pipamperone > cinanserin > 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Quantitative autoradiography showed a heterogeneous distribution of [3H]RP 62203 binding sites, with the highest densities in the frontal, parietal and auditory cortices (layer IV), claustrum and olfactory bulb. Binding densities in the occipital cortex, caudate putamen and thalamic nuclei were moderate, whereas the hippocampus and substantia nigra displayed a very low density of binding sites. The cerebellar cortex appeared almost devoid of [3H]RP 62203 binding sites. The anatomical distribution of binding sites demonstrated that [3H]RP 62203 essentially bound only to rat brain regions known to contain 5-HT2 receptors. This ligand could thus be a useful tool to visualize 5-HT2 receptors.