N-GLUCURONIDATION OF THE PLATELET-DERIVED GROWTH FACTOR RECEPTOR TYROSINE KINASE INHIBITOR 6,7-(DIMETHOXY-2,4-DIHYDROINDENO[1,2-C]PYRAZOL-3-YL)-(3-FLUORO-PHENYL)-AMINE BY HUMAN UDP-GLUCURONOSYLTRANSFERASES

The potential cancer therapeutic agent, 6,7-(dimethoxy-2, 4-dihydroindeno[1,2-c]pyrazol-3-yl)-(3-fluoro-phenyl)-amine (JNJ-10198409), formed three N-glucuronides that were positively identified by liquid chromatography-tandem mass spectrometry and NMR as N-amine-glucuronide (Glu-A), 1-N-pyrazole-glucuronide (Glu-B), and 2-N-pyrazole-glucuronide (Glu-C). All three N-glucuronides were detected in rat liver microsomes, whereas only Glu-A and -B were found in monkey and human liver microsomes. In contrast to common glucuronides, Glu-B was completely resistant to beta-glucuronidase. Kinetic analyses revealed that glucuronidation of JNJ-10198409 in human liver microsomes exhibited atypical kinetics that may be described by a two-site binding model. For the high affinity binding, K(m) values were 1.2 and 5.0 microM, and V(max) values were 2002 and 2,403 nmol min(-1) mg(-1) for Glu-A and Glu-B, respectively. Kinetic constants of low affinity binding were not determined due to low solubility of the drug. Among the human UDP-glucuronosyltransferases (UGTs) tested, UGT1A9, 1A8, 1A7, and 1A4 were the most active isozymes to produce Glu-A; for the formation of Glu-B, UGT1A9 was the most active enzyme, followed by UGT1A3, 1A7, and 1A4. Glucuronidation of JNJ-10198409 by those UGT1A enzymes followed classic Michaelis-Menten kinetics. In contrast, no glucuronides were formed by all UGT2B isozymes tested, including UGT2B4, 2B7, 2B15, and 2B17. Collectively, these results suggested that glucuronidation of JNJ-10198409 in human liver microsomes is catalyzed by multiple UGT1A enzymes. Since UGT1A enzymes are widely expressed in various tissues, it is anticipated that both hepatic and extrahepatic glucuronidation will likely contribute to the elimination of the drug in humans. Additionally, conjugation at the nitrogens of the pyrazole ring represents a new structural moiety for UGT1A-mediated reactions.

Metabolism and excretion of the antiepileptic/antimigraine drug, topiramate in animals and humans

The metabolism and excretion of 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (TOPAMAX, topiramate, TPM) have been investigated in animals and humans. Radiolabeled [14C] TPM was orally administered to mice, rats, rabbits, dogs and humans. Plasma, urine and fecal samples were collected and analyzed. TPM and a total of 12 metabolites were isolated and identified in these samples. Metabolites were formed by hydroxylation at the 7- or 8-methyl of an isopropylidene of TPM followed by rearrangement, hydroxylation at the 10-methyl of the other isopropylidene, hydrolysis at the 2,3-O-isopropylidene, hydrolysis at the 4,5-O-isopropylidene, cleavage at the sulfamate group, glucuronide conjugation and sulfate conjugation. A large percentage of unchanged TPM was recovered in animal and human urine. The most dominant metabolite of TPM in mice, male rats, rabbits and dogs appeared to be formed by the hydrolysis of the 2,3-O-isopropylidene group.

In vitro identification of metabolic pathways and cytochrome P450 enzymes involved in the metabolism of etoperidone

1. In vitro studies have been carried out to investigate the metabolic pathways and identify the hepatic cytochrome P450 (CYP) enzymes involved in etoperidone (Et) metabolism. 2. Ten in vitro metabolites were profiled, quantified and tentatively identified after incubation with human hepatic S9 fractions. Et was metabolized via three metabolic pathways: (A) alkyl hydroxylation to form OH-ethyl-Et (M1); (B) phenyl hydroxylation to form OH-phenyl-Et (M2); and (C) N-dealkylation to form 1-m-chlorophenylpiperazine (mCPP, M8) and triazole propyl aldehyde (M6). Six additional metabolites were formed by further metabolism of M1, M2, M6 and M8. 3. Kinetic studies revealed that all metabolic pathways were monophasic, and the pathway leading to the formation of OH-ethyl-Et was the most efficient at eliminating the drug. On incubation with microsomes expressing individual recombinant CYPs, formation rates of M1-3 and M8 were 10-100-fold greater for CYP3A4 than that for other CYP forms. The formation of these metabolites was markedly inhibited by the CYP3A4-specific inhibitor ketoconazole, whereas other CYP-specific inhibitors did not show significant effects. In addition, the production of M1-3 and M8 was strongly correlated with CYP3A4-mediated testosterone 6beta-hydroxylase activities in 13 different human liver microsome samples. 4. Dealkylation of the major metabolite M1 to form mCPP (M8) was also investigated using microsomes containing recombinant CYP enzymes. The rate of conversion of M1 to mCPP by CYP3A4 was 503.0 +/- 3.1 pmole nmole(-1) min(-1). Metabolism of M1 to M8 by other CYP enzymes was insignificant. In addition, this metabolism in human liver microsomes was extensively inhibited by the CYP3A4 inhibitor ketoconazole, but not by other CYP-specific inhibitors. In addition, conversion of M1 to M8 was highly correlated with CYP3A4-mediated testosterone 6beta-hydroxylase activity. 5. The results strongly suggest that CYP3A4 is the predominant enzyme-metabolizing Et in humans.

Rapidly distinguishing reversible and irreversible CYP450 inhibitors by using fluorometric kinetic analyses

In this study we have evaluated the reliability of a fluorescence-based method used for rapid identification of irreversible CYP inhibitors (mechanism-based inhibitors). This was accomplished by comparing the time-dependence pattern of IC50 values from fluorometric kinetic measurements. For irreversible CYP inhibitors, IC50 values decreased as incubation proceeded. This was due to progressive inactivation of corresponding enzymes by reactive metabolites generated during the incubation. This change pattern was confirmed using a number of known irreversible CYP inhibitors, including furafylline, midazolam, erythromycin, clarithromycin, oleandomycin, 17alpha-ethynylestradiol and verapamil. The pattern was different in reversible inhibition, depending upon the compounds tested in the fluorometric kinetic assay. For some compounds, such as clotrimazole, IC50 values remained relatively stable, whereas other compounds, such as miconazole, terfenadine and ketoconazole showed a significant increase with incubation time. Monitoring tested compounds by LC-MS/MS during the incubation confirmed that increases of IC50 were probably caused by the loss of inhibitors, resulting from either metabolic degradation, or non-specific binding to microsomal proteins.

Evaluation of the excretion and metabolism of the new analgesic agent RWJ-22757 in male and female CR Wistar rats

The excretion and metabolism of (+/-)-trans-3-(2-bromophenyl)octahydroindolizine hydrochloride (RWJ-22757) have been investigated in male and female CR Wistar rats. Radiolabeled [14C] RWJ-22757 was administered orally to each of the rats as a single 60 mg/kg suspension dose. Plasma (0-48 h), urine (0-168 h) and fecal (0-168 h) samples were collected and analyzed. There were no significant gender differences observed in the data. The estimated elimination half-life of the total radioactivity from plasma was 19 h while the estimated elimination half-life of RWJ-22757 was 15 h. Recoveries of total radioactivity in urine and feces were 58.4+/-5.8 and 42.4+/-6.3%, respectively. RWJ-22757 and a total of 11 metabolites were isolated in rat plasma, urine, and fecal extracts. The structures of four of these metabolites were tentatively identified. Unchanged RWJ-22757 accounted for < 4% of the dose in plasma and urine and 28% in feces; thus, indicating the drug was extensively metabolized and either not absorbed well or biliary excreted. Identified metabolites accounted for > 80% of the total radioactivity contained in the samples. The following pathways were used to describe the formation of the metabolites identified in rats: octahydroindolizine ring oxidation, phenyl hydroxylation, octahydroindolizine ring oxidation followed by ring opening to a carboxylic acid function and octahydroindolizine ring oxidation followed by ring opening and N-methylation.

Evaluation of the absorption, excretion and metabolism of [14C] etoperidone in man

1. The absorption, excretion and metabolism of 2-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-4,5-diethyl-2,4-dihydro-3H-1,2,4- triazole-3-one hydrochloride (etoperidone HCl) was investigated in six healthy men. Subjects were tasted overnight before receiving a single oral dose of a 100 mg solution [14C] etoperidone HCl. 2. Plasma (0-48 h), urine (0-120 h) and faecal (0-120 h) samples were collected. The terminal half-life of the total radioactivity from plasma was 21.7 +/- 2.8h with an apparent clearance of 1.01 +/- 0.08 ml min(-1). Recoveries of total radioactivity in urine and faeces were 78.8 +/- 3.6% and 9.6 +/- 4.1% of the dose, respectively. 3. Etoperidone and 21 metabolites were isolated and identified in the plasma, urine and faecal extracts. Unchanged etoperidone accounted for <0.01% of the dose in all excreta samples. Nine metabolites were identified in the plasma extracts and 21 urinary metabolites were identified. Seven faecal metabolites were identified. 4. Five proposed pathways were used to describe the formation of the metabolites: alkyl oxidation, piperazinyl oxidation, N-dealkylation, phenyl hydroxylation and conjugation. Alkyl oxidation of etoperidone resulted in the formation of 2-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-4-ethyl-2,4-dihydro-5- (1-hydroxyethyl)-3H-1,2,4-triazole-3-one. Piperazinyl oxidation of this metabolite leads to the formation of its N-oxide. N-dealkylation of the piperazinyl group led to the formation of 1-(3-chlorophenyl) piperazine and triazole propionic acid. Phenyl hydroxylation led to three important metabolites in the urine and faeces.

The new pre-preclinical paradigm: compound optimization in early and late phase drug discovery

The attrition rates of new chemical entities (NCEs) in preclinical and clinical development are staggeringly high. NCEs are abandoned due to insufficient efficacy, safety issues, and economic reasons. Uncovering drug defects that produce these failures as early as possible in drug discovery would be highly effective in lowing the cost and time of developing therapeutically useful drugs. Unfortunately, there is no single factor that can account for these NCE failures in preclinical and clinical development since factors, such as solubility, pKa, absorption, metabolism, formulation, pharmacokinetics, toxicity and efficacy, to name a few, are all interrelated. In addition, there are many problems in scaling-up drug candidates from the laboratory bench scale to the pilot plant scale. To address the problem of attrition rates of NCEs in preclinical and clinical development and drug scale-up issues, pharmaceutical companies need to reorganize their preclinical departments from a traditional linear approach to a parallel approach. In this review, a strategy is put forth to integrate certain aspects of drug metabolism/pharmacokinetics, toxicology functions and process chemistry into drug discovery. Compound optimization in early and late phase drug discovery occurs by relating factors such as physicochemical properties, in vitro absorption, in vitro metabolism, in vivo pharmacokinetics and drug scale-up issues to efficacy optimization. This pre-preclinical paradigm will improve the success rate of drug candidates entering development.

Evaluation of the excretion, and metabolism of the cardiotonic agent bemoradan in male rats and female beagle dogs

The excretion and metabolism of (+/-) [6-(3,4-dihydro-3-oxo-1,4[2H]-benzoxazine-yl)-2,3,4,5-tetrahydro-5-methylpyridazin-3-one] (bemoradan; RWJ-22867) have been investigated in male Long-Evans rats and female beagle dogs. Radiolabeled [14C] bemoradan was administered to rats as a singkle 1 mg/kg suspension dose while the dogs received 0.1 mg/kg suspension dose. Plasma (0-24 h; rat and dog), urine (0-72 h; rat and dog) and fecal (0-72 h; rat and dog) samples were collected and analyzed. The terminal half-life of the total radioactivity for rats from plasma was estimate to be 4.3 +/- 0.1 h while for dogs it was 7.5 +/- 1.3 h. Recoveries of total radioactivity in urine and feces for rats were 49.1 +/- 2.4% and 51.1 +/- 4.9% of th dose, respectively. Recoveries of total radioactivity in urine and feces for dogs were 56.2 +/- 12.0% and 42.7 V 9.9% of the dose, respectively. Bemoradan and a total of nine metabolites were isolated and tentatively identified in rat and dog plasma, urine, and fecal extracts. Unchanged bemoradan accounted for approimately < 2% of the dose in rat urine and 20% in rat feces. Unchanged bemoradan accounted for approximately 5% of the dose in urine and 16% in feces in dog. Six proposed pathways were used to describe the metabolites found in rats and dogs: pyridazinyl oxidations, methyl hydroxylation, hydration, N-oxidation, dehydration and phase II conjugations.

Evaluation of the absorption, excretion, and metabolism of the antihypertensive agent RWJ-26899 in male and female CR Wistar rats and Beagle dogs

The absorption, excretion and metabolism of N-(2, 6-dichlorophenyl)-beta-[[(1-methylcyclohexyl)methoxylmethyl]-N-(phenylmethyl)-1-pyrrolidineethanamine (RWJ-26899; McN-6497) has been investigated in male and female CR Wistar rats and beagle dogs. Radiolabeled [14C] RWJ-26899 was administered to rats as a single 24 mg/kg suspension dose while the dogs received 15 mg/kg capsules. Plasma (0-36 h; rat and 0-48 h; dog), urine (0-192 h; rat and dog) and fecal (0-192 h; rat and dog) samples were collected and analyzed. There were no significant gender differences observed in the data. The terminal half-life of the total radioactivity for rats from plasma was estimated to be 7.7 +/- 0.6 h while for dogs it was 22.9 +/- 4.4 h. Recoveries of total radioactivity in urine and feces for rats were 8.7 +/- 2.9% and 88.3 +/- 10.4% of the dose, respectively. Recoveries of total radioactivity in urine and feces for dogs were 4.1 +/- 1.4% and 90.0 +/- 4.7% of the dose, respectively. RWJ-26899 and a total of nine metabolites were isolated and tentatively identified in rat urine, and fecal extracts. Unchanged RWJ-26899 accounted for approximately 1% of the dose in rat urine and 8% in rat feces. RWJ-26899 and a total of four metabolites were isolated and identified in dog urine, and fecal extracts. Unchanged RWJ-26899 accounted for approximately 1% of the dose in urine and 63% in feces in dog. Five proposed pathways were used to describe the metabolites found in rats: N-oxidation, oxidative N-debenzylation, pyrrolidinyl ring hydroxylation, phenyl hydroxylation and methyl or cyclohexyl hydroxylation. Two biotransformation pathways in dogs are proposed: N-oxidation and methyl or cyclohexyl ring hydroxylation.

Using affinity capillary electrophoresis to study the interaction of the extracellular binding domain of erythropoietin receptor with peptides

We have shown that affinity capillary electrophoresis (ACE) can be utilized to screen peptides that bind to the extracellular binding domain of the erythropoietin receptor (EBP). The comparison of the cyclic peptides GGTYSCHFGPLTWVCKPQGG (EMP1) GGTYSCHFGPLTAVCKPQGG (EMP13), and LGRKYSCHFGPLTWVCQPAKKD (EMP37) with the linear peptides HFGPLTWV (EMP26) and FMRF as ACE buffer additives were investigated. When EMP1 and EMP37 were the buffer additives, an abrupt change in the electrophoretic mobility of EBP was observed in the electropherogram. When EMP13, EMP26, and FMRF were examined under identical ACE conditions as EMP1 and EMP37, no significant change in the electrophoretic mobility of EBP was observed. These results correlate well with previously reported IC50 competitive binding data; that is, EMP1 and EMP37 bind to EBP while EMP13 and EMP26 bind very weakly. These observations strongly infer that peptide.EBP dimerization were induced by EMP1, and EMP37 but not by EMP13, EMP26 or FMRF. This ACE method provides a rapid tool for the detection of small peptides or drugs that bind to EBP.

Mass spectrometric determination of a novel modification of the N-terminus of histidine-tagged proteins expressed in bacteria

Two proteins, FKBP, and Spo0F, were expressed in bacteria as histidine-tagged fusion proteins and isolated under native conditions. MALDI-TOF-MS analysis revealed that each protein preparation contained two components, neither of which corresponded to the molecular weights predicted from DNA sequences. The difference in molecular weight between the two FKBP components and two Spo0F components was approximately 178 +/- 14 Da. Site-specific proteolytic cleavage resulted in the release of histidine-tagged peptide from the recombinant proteins. MALDI mass spectra of the cleaved proteins showed a single molecular ion peak for each species with the predicted molecular weights. The histidine-tagged peptide released from both fusion proteins displayed two distinct peaks by MALDI-FT-MS corresponding to monoisotopic molecular weights of 2269. 027 Da and 2447.087 Da, respectively, which were both inconsistent with the predicted peptide sequence M-G-H-H-H-H-H-H-H-H-H-H-S-S-G-H-I-E-G-R of 2400.055 Da. The peptide at 2269.027 Da was sequenced by ESI-MS-MS and found to be a truncated histidine tag resulting from an initiator methionine deletion. ESI-MS-MS analysis of the peptide at 2447.087 Da indicated a moiety of 178.0 Da attached to the second residue glycine of the histidine tag. This alteration of the N-terminus does not fit any known modifications. A synthetic peptide with the identical sequence of the isolated his-tag M-G-H-H-H-H-H-H-H-H-H-H remained unmodified during the protein purification process, suggesting that modification of the initiator methionine was carried out in vivo, rather than the result of a chemical reaction from the isolation procedure.

High throughput liquid chromatography-mass spectrometry assessment of the metabolic activity of commercially available hepatocytes from 96-well plates

We have assessed the metabolic activity of freshly isolated and commercially preserved rat, monkey, and human primary hepatocytes in a 96 well plate format utilizing eight beta-adrenolytic drugs as model compounds. Sample introduction from 96 well plates, HPLC solvent delivery, mass spectrometric (MS) detection, and/or UV detection were fully integrated and operated unattended. After drugs were incubated with hepatocytes for three or six hr, LC-MS analyses were carried out to determine the amount of drug which was not metabolized. Two LC-MS methods were used which had a sample throughput of 4 samples/hr and 12 samples/hr. Under optimal conditions, this hepatic assay could screen 300 samples/week or 1200 samples/month. Although freshly isolated hepatocytes were more active, commercially available rat, monkey, and human primary isolated hepatocytes metabolized drug substrates in similar relative rank orders. This drug-hepatocyte assay provides useful information for prioritizing pharmaceutical leads in relative rank orders or in a high/low manner according to their resistance toward liver metabolism.

Biotransformation of an antihypertensive arylalkylamine analogue in the rat

1. The excretion and metabolism of N-[2-(3,4-dimethoxyphenyl)ethyl]-5-methoxy-N,alpha-dimethyl-2-(phenyl ethynyl) benzenepropanamine (RWJ-26240) in the Wistar rat has been investigated after a single oral dose of 14C-RWJ-26240 (50 mg/kg free base). 2. Plasma samples were obtained for 24 h after dosing and urine and faecal samples were collected over 8 days, and they accounted for 0.9 and 96% of the dose, respectively. 3. Representative samples of plasma, urine and faecal samples were purified for metabolite isolation and identification using HPLC, tlc, mass spectra (CI and EI), 1H-NMR and derivatization. 4. Unchanged RWJ-26240 plus 11 metabolites were identified and accounted for > 80% of the sample radioactivity. 5. Four metabolic pathways for RWJ-26240 are proposed; namely (1) N-demethylation, (2) O-demethylation, (3) phenyl hydroxylation and (4) N-dealkylation. Pathways 1-3 appeared to be quantitatively more important.

In vitro permeability of eight beta-blockers through Caco-2 monolayers utilizing liquid chromatography/electrospray ionization mass spectrometry

It is demonstrated that the apparent permeability (P(app)) coefficients of beta-adrenoceptor antagonist drugs can easily be determined for Caco-2 cell culture intestinal models utilizing liquid chromatography/mass spectrometry (LC/MS). The LC/MS method with electrospray ionization in the single ion monitoring mode showed an increased sensitivity of 1000-fold compared with LC/UV detection and enhanced selectivity with respect to both LC/UV and radioactivity assays. The P(app) coefficients of beta-adrenoceptor antagonists determined by LC/MS have the same ranking order as those determined by LC/UV and radioactivity assays. However, the P(app) coefficients determined in this study showed significant discrepancies from those determined in other laboratories. There are several experimental factors that directly affect the absolute value of the P(app) coefficients, including pH gradients, additional diffusion barriers (i.e. unstirred water layer and type of filter support), analyte concentration, detection method and possibly cell culture variations. These parameters should be controlled when generating Caco-2 P(app) coefficients for different compounds.

Comparison of the retention behavior of beta-blockers using immobilized artificial membrane chromatography and lysophospholipid micellar electrokinetic chromatography

We have demonstrated that significant differences exist between the retention of eight beta-blockers analyzed with immobilized artificial membrane (IAM) and lysophospholipid micellar electrokinetic capillary (LMEKC) chromatographic methods. The general retention trends are maintained with highly hydrophilic compounds such as atenolol eluting first and more hydrophobic compounds such as propranolol eluting last. The retention order, however, is different and would result in major ranking differences. LMEKC demonstrates a better correlation with liposomal partitioning (R2 = 0.95) than does IAM chromatography (R2 = 0.60). LMEKC, with its higher efficiency, can allow a more specific evaluation of lipophilicity than IAM chromatography and is useful in the analysis of pharmaceutical candidates, particularly for ranking purposes.

Evaluation of the immobilized artificial membrane phosphatidylcholine. Drug discovery column for high-performance liquid chromatographic screening of drug-membrane interactions

Chromatographic retention factors (k') of a series of eight beta-adrenoceptor antagonist compounds (beta-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k' values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The beta-adrenolytic drug's log k'IAM values obtained with an IAM.PC.DD column were compared to an esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k'IAM and the logarithm of the n-octanol-water partition coefficients (rIAM.PC.DD = 0.8710 vs. rIAM.PC.MG = 0.9538), the C18 HPLC retention factors (rIAM.PC.DD = 0.8408 vs. rIAM.PC.MG = 0.9380), the liposome partition coefficients (rIAM.PC.DD = 0.8887 vs. rIAM.PC.MG = 0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the esterIAM.PC.MG column than the IAM.PC.DD column.

Using capillary electrophoresis/frontal analysis to screen drugs interacting with human serum proteins

We have used capillary electrophoresis in the frontal analysis mode (CE/FA) to determine the binding capacity of beta-adrenoceptor blocking drugs to individual serum proteins, serum protein mixtures and human serum. The free drug concentration was directly measured from the height of the frontal peak and used to calculate the bound drug concentration. From the bound drug concentration, the percentage of drug bound to the serum proteins alpha1-acid glycoprotein (AGP) and human serum albumin (HSA) was then determined. In addition to determining the percent of a drug bound to a protein, the drug-protein association constant (Ka) was determined for AGP binding to beta-blockers. The data-estimated association constants were consistent with literature values. The CE/FA studies on the beta-adrenoceptor blocking drugs and the serum proteins indicated that HSA, AGP, high density lipoprotein (HDL), and low density lipoprotein (LDL) were the main contributors to serum binding for this series of compounds. The serum-drug binding data sorted the beta-adrenoceptor blocking drugs into high and low binding categories. The protein mixture (AGP + HSA + HDL + LDL) resulted in dividing the beta-blockers into the same high/low rankings. The protein mixture (AGP + HSA + HDL + LDL) was amenable to automation, did not autoaggregate, and had constant concentrations for the proteins.

Excretion and metabolism of the antihypertensive agent, RWJ-26240 (McN-5691) in dogs

The excretion and metabolism of a 2-ethynylbenzenealkanamine analog, antihypertensive RWJ-26240 (McN-5691), in beagle dogs was investigated. Recoveries of total radioactivity in urine and feces in the 7 days after oral administration of 14C-RWJ-26240 (6 mg/kg dose) were 2.8% and 96.8% of the radioactive dose, respectively. Representative plasma, urine, and fecal samples were pooled and purified for metabolite profiling, isolation, and identification. Unchanged RWJ-26240 (<19% of the dose) plus 12 metabolites were isolated and identified from these samples using chromatography (TLC, HPLC), spectroscopy (NMR, MS), and derivatization techniques. Unchanged RWJ-26240 plus identified metabolites accounted for >75% of the sample radioactivity in plasma and feces. The formation of RWJ-26240 metabolites can be depicted by the following proposed pathways: 1) N-demethylation, 2) O-demethylation, 3) phenyl hydroxylation, and 4) N-dealkylation. The first three pathways appeared to be quantitatively important steps which led to the production of four major metabolites (each >5% of the sample radioactivity). RWJ-26240 was extensively metabolized in the dog, and fecal excretion was the major route of elimination of RWJ-26240 and its metabolites.

In vivo microdialysis and liquid chromatography/thermospray mass spectrometry of the novel anticonvulsant 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate) in rat brain fluid

The concentration of a novel anticonvulsant, 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate), was determined in the extracellular fluid of rat brain by in vivo microdialysis combined off-line with liquid chromatography/thermospray mass spectrometry. A microdialysis probe was stereotaxically implanted in the nucleus accumbens region of the rat brain. The maximum concentration of topiramate in the brain dialysate for a dose of 50 mg kg-1 i.v. was approximately 10 microM and occurred 45 min post-injection. The detection limit of topiramate in the extracellular fluid of rat brain was in the 0.1 microM range using selected ion monitoring techniques. The base peak, which was the ammonium adduct ion [M + NH4]+, was used for detection. An internal standard of d12-labeled topiramate was utilized for quantitation by isotope dilution analysis.