Mapping the ρ1 GABAC Receptor Agonist Binding Pocket

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. The GABA receptor type C (GABA(C)) is a ligand-gated ion channel with pharmacological properties distinct from the GABA(A) receptor. To date, only three binding domains in the recombinant rho1 GABA(C) receptor have been recognized among six potential regions. In this report, using the substituted cysteine accessibility method, we scanned three potential regions previously unexplored in the rho1 GABA(C) receptor, corresponding to the binding loops A, E, and F in the structural model for ligand-gated ion channels. The cysteine accessibility scanning and agonist/antagonist protection tests have resulted in the identification of residues in loops A and E, but not F, involved in forming the GABA(C) receptor agonist binding pocket. Three of these newly identified residues are in a novel region corresponding to the extended stretch of loop E. In addition, the cysteine accessibility pattern suggests that part of loop A and part of loop E have a beta-strand structure, whereas loop F is a random coil. Finally, when all of the identified ligand binding residues are mapped onto a three-dimensional homology model of the amino-terminal domain of the rho1 GABA(C) receptor, they are facing toward the putative binding pocket. Combined with previous findings, a complete model of the GABA(C) receptor binding pocket was proposed and discussed in comparison with the GABA(A) receptor binding pocket.

A new heterobifunctional reagent for immobilization of biomolecules on glass surface

Synthesis of a new heterobifunctional reagent, [N-(2-trifluoroethanesulfonatoethyl)-N-(methyl)-triethoxysilylpropyl-3-amine] (NTMTA) is described for the immobilization of a variety of biomolecules on glass surface. Its triethoxysilyl group reacts with glass surface and trifluoroethanesulfonate ester structure reacts selectively with aminoalkyl/mercaptoalkyl function in biomolecules. The immobilization can be achieved by two ways involving two steps. The first route involves the reaction of NTMTA with glass beads followed by attachment of aminoalkyl- or mercaptoalkylated biomolecules. The second one involves the reaction of biomolecules, viz., oligonucleotides, proteins, etc., with NTMTA via their aminoalkyl or mercaptoalkyl functions to form a biomolecule conjugate, which is then reacted with glass beads (unmodified) to complete immobilization process. This has been demonstrated by successful immobilization of 5'-mercaptoalkyl- or aminoalkylated oligonucleotides and some commonly used enzymes on glass beads using NTMTA reagent.

The Mechanism of Nitrogenase. Computed Details of the Site and Geometry of Binding of Alkyne and Alkene Substrates and Intermediates

The chemical mechanism by which the enzyme nitrogenase effects the remarkable reduction of N(2) to NH(3) under ambient conditions continues to be enigmatic, because no intermediate has been observed directly. Recent experimental investigation of the enzymatic consequences of the valine --> alanine modification of residue alpha-70 of the component MoFe protein on the reduction of alkynes, together with EPR and ENDOR spectroscopic characterization of a trappable intermediate in the reduction of propargyl alcohol or propargyl amine (HCC[triple bond]C-CH(2)OH/NH(2)), has localized the site of binding and reduction of these substrates on the FeMo-cofactor and led to proposed eta(2)-Fe coordination geometry. Here these experimental data are modeled using density functional calculations of the allyl alcohol/amine intermediates and the propargyl alcohol/amine reactants coordinated to the FeMo-cofactor, together with force-field calculations of the interactions of these models with the surrounding MoFe protein. The results support and elaborate the earlier proposals, with the most probable binding site and geometry being eta(2)-coordination at Fe6 of the FeMo-cofactor (crystal structure in the Protein Database), in a position that is intermediate between the exo and endo coordination extremes at Fe6. The models described account for (1) the steric influence of the alpha-70 residue, (2) the crucial hydrogen bonding with Nepsilon of alpha-195(His), (3) the spectroscopic symmetry of the allyl-alcohol intermediate, and (4) the preferential stabilization of the allyl alcohol/amine relative to propargyl alcohol/amine. Alternative binding sites and geometries for ethyne and ethene, relevant to the wild-type protein, are described. This model defines the location and scene for detailed investigation of the mechanism of nitrogenase.

Atomoxetine Hydrochloride: Clinical Drug-Drug Interaction Prediction and Outcome

In the studies reported here, the ability of atomoxetine hydrochloride (Strattera) to inhibit or induce the metabolic capabilities of selected human isoforms of cytochrome P450 was evaluated. Initially, the potential of atomoxetine and its two metabolites, N-desmethylatomoxetine and 4-hydroxyatomoxetine, to inhibit the metabolism of probe substrates for CYP1A2, CYP2C9, CYP2D6, and CYP3A was evaluated in human hepatic microsomes. Although little inhibition of CYP1A2 and CYP2C9 activity was observed, inhibition was predicted for CYP3A (56% predicted inhibition) and CYP2D6 (60% predicted inhibition) at concentrations representative of high therapeutic doses of atomoxetine. The ability of atomoxetine to induce the catalytic activities of CYP1A2 and CYP3A in human hepatocytes was also evaluated; however, atomoxetine did not induce either isoenzyme. Based on the potential of interaction from the in vitro experiments, drug interaction studies in healthy subjects were conducted using probe substrates for CYP2D6 (desipramine) in CYP2D6 extensive metabolizer subjects and CYP3A (midazolam) in CYP2D6 poor metabolizer subjects. Single-dose pharmacokinetic parameters of desipramine (single dose of 50 mg) were not altered when coadministered with atomoxetine (40 or 60 mg b.i.d. for 13 days). Only modest changes (approximately 16%) were observed in the plasma pharmacokinetics of midazolam (single dose of 5 mg) when coadministered with atomoxetine (60 mg b.i.d. for 12 days). Although at high therapeutic doses of atomoxetine inhibition of CYP2D6 and CYP3A was predicted, definitive in vivo studies clearly indicate that atomoxetine administration with substrates of CYP2D6 and CYP3A does not result in clinically significant drug interactions.

The putrescine analogue 1-aminooxy-3-aminopropane perturbs polyamine metabolism in the phytopathogenic fungus Sclerotinia sclerotiorum

The effects of the putrescine analogue 1-aminooxy-3-aminopropane on fungal polyamine metabolism were evaluated using Sclerotinia sclerotiorum as an experimental model. The compound inhibited ornithine decarboxylase, spermidine synthase, and S -adenosyl-methionine decarboxylase in mycelial extracts. Addition of 1-aminooxy-3-aminopropane at 1 mM to the culture medium did not reduce mycelial growth and caused a 29% decrease in free spermidine and a two-fold increase in free spermine. When added 4.5 h before the determination of ornithine decarboxylase, 1-aminooxy-3-aminopropane reduced in vivo activity of this enzyme by 40-50%. When added 48 h before the determination, 1-aminooxy-3-aminopropane at 0.01 and 0.1 mM caused a slight increase of in vivo ornithine decarboxylase activity, while it had no effect at 1 mM. Comparison of the action of 1-aminooxy-3-aminopropane with that of other inhibitors of polyamine biosynthesis suggested that its effects on in vivo ornithine decarboxylase activity resulted from a balance between direct inhibition of enzyme activity and indirect stimulation of enzyme synthesis and/or activity mediated by the decrease in spermidine levels, which in turn was due to inhibition of spermidine synthase and S -adenosyl-methionine decarboxylase. The potential of 1-aminooxy-3-aminopropane as a tool for studies on fungal polyamine metabolism and for the control of plant diseases of fungal origin is discussed.

Oligoamine-acridine conjugates for promotion of gap-selective DNA hydrolysis by Ce(IV)/EDTA complex

Oligoamines (spermidine, dipropylenetriamine and propylenediamine) were covalently attached to acridine via a hexamethylene linker. These oligoamine-acridine conjugates were efficiently bound to gap sites in substrate DNA, and promoted the DNA hydrolysis by a homogeneous Ce(IV)/ethylenediamine-N,N,N',N'-tetraacetate (EDTA) complex at these sites. In contrast, the hydrolysis of the double-stranded portion in the DNA was little affected by these conjugates, although they were strongly bound thereto by the intercalation of their acridine moieties. As a result, the gap site was selectively and efficiently hydrolyzed by combining the Ce(IV)/EDTA complex with the oligoamine--acridine conjugate. Either the oligoamine or the acridine was only poorly active for the purpose, substantiating the essential role of cooperation between them. The promotion of gap-selective DNA hydrolysis by the conjugates has been ascribed to electrostatic stabilization of a negatively charged transition state by their positive charges.

Atomoxetine: a selective noradrenaline reuptake inhibitor for the treatment of attention-deficit/hyperactivity disorder

Atomoxetine (Strattera, Eli Lilly & Co.) is a selective noradrenaline reuptake inhibitor that has been studied for use in the treatment of attention-deficit/hyperactivity disorder (ADHD). So far, two open-label and seven randomised, double-blind, placebo-controlled, clinical trials have been published, six in youths and three in adults. Each of these trials has shown a positive response as measured by the primary efficacy measures, the ADHD-IV Rating Scale (ADHD RS) or the Conners Adult ADHD Rating Scale (CAARS). Atomoxetine has generally been well tolerated. In November of 2002 the FDA approved atomoxetine for use in the US for the treatment of ADHD in children, adolescents and adults. Atomoxetine is the first nonstimulant approved by the FDA for the treatment of ADHD and the first medication approved for the treatment of adult ADHD.

3-Aminopropanal is a lysosomotropic aldehyde that causes oxidative stress and apoptosis by rupturing lysosomes

During cerebral ischemia and following trauma, potent cytotoxic polyamine-derived aminoaldehydes form, diffuse, and damage adjacent tissues not directly subjected to the initial insult. One such aldehyde is 3-aminopropanal (3-AP). The mechanisms by which such a small aldehydic compound is excessively cytotoxic have been unclear until recently when we showed that 3-AP, having the structure of a weak lysosomotropic base, concentrates within the acidic vacuolar compartment and causes lysosomal rupture that, in turn, induces caspase activation and apoptotic cell death. Here, using cultured J774 cells and 3-AP as a way to selectively burst lysosomes, we show that moderate lysosomal rupture induces a transient wave of oxidative stress. The start of this oxidative stress period is concomitant with a short period of enhanced mitochondrial membrane potential that later fades and is replaced by a decreased potential before the oxidative stress diminishes. The result of the study suggests that oxidative stress, which has often been described during apoptosis induced by agonists other than oxidative stress per se, may be a consequence of lysosomal rupture with direct and/or indirect effects on mitochondrial respiration and electron transport causing a period of passing enhanced formation of reactive oxygen species.

Highly potent propargylamine and allylamine inhibitors of bovine plasma amine oxidase

Propargylamine was reported many years ago to be a mechanism-based inhibitor of bovine plasma amine oxidase (BPAO), though the potency was modest and allylamine was a substrate. Herein, selected 3-substituted propargylamines and allylamines were found to be potent time-dependent inactivators of BPAO, exhibiting IC(50) values of 2-13 microM at 30 degrees C, making them the most potent BPAO inhibitors reported to date. The most potent compound, trans-3-chloroallylamine, was previously found not to inhibit the flavin-dependent monoamine oxidase (the cis isomer did), and thus appears to be a highly selective inhibitor.

3-Aminopropanal, formed during cerebral ischaemia, is a potent lysosomotropic neurotoxin

Cytotoxic polyamine-derived amino aldehydes, formed during cerebral ischaemia, damage adjacent tissue (the so-called 'penumbra') not subject to the initial ischaemic insult. One such product is 3-aminopropanal (3-AP), a potent cytotoxin that accumulates in ischaemic brain, although the precise mechanisms responsible for its formation are still unclear. More relevant to the present investigations, the mechanisms by which such a small aldehydic compound might be cytotoxic are also not known, but we hypothesized that 3-AP, having the structure of a weak lysosomotropic base, might concentrate within lysosomes, making these organelles a probable focus of initial toxicity. Indeed, 3-AP leads to lysosomal rupture of D384 glioma cells, a process which clearly precedes caspase activation and apoptotic cell death. Immunohistochemistry reveals that 3-AP concentrates in the lysosomal compartment and prevention of this accumulation by the lysosomotropic base ammonia, NH(3), protects against 3-AP cytotoxicity by increasing lysosomal pH. A thiol compound, N-(2-mercaptopropionyl)glycine, reacts with and neutralizes 3-AP and significantly inhibits cytoxocity. Both amino and aldehyde functions of 3-AP are necessary for toxicity: the amino group confers lysosomotropism and the aldehyde is important for additional, presently unknown, reactions. We conclude that 3-AP exerts its toxic effects by accumulating intralysosomally, causing rupture of these organelles and releasing lysosomal enzymes which initiate caspase activation and apoptosis (or necrosis if the lysosomal rupture is extensive). These results may have implications for the development of new therapeutics designed to lessen secondary damage arising from focal cerebral ischaemia.

New propylamine oligopyrrole carboxamides linked to a heterocyclic or anthraquinone system: synthesis, DNA binding, topoisomerase I inhibition and cytotoxicity

Continuing our studies on combilexines, compounds consisting of a DNA intercalator linked to a minor groove ligand, new results are presented. The synthesis of a series of new propylamine oligopyrrole carboxamides closely related to netropsin and distamycin A, linked to a heterocyclic or anthraquinone system is reported. The cytotoxic activity in vitro, the DNA binding characteristics and the inhibition of the topoisomerase I of the compounds were studied in order to explain the biological mechanism of action of these new potential combilexines. Some of the synthesised compounds showed cytotoxic activity against human tumour cell lines, as well as DNA binding and topoisomerase I inhibiting properties.

Differences in cytochrome P450 forms involved in the metabolism of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100), a novel sigma ligand, in human liver and intestine

N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100) has been developed to treat subjects with schizophrenia. This drug is mainly excreted in the form of oxidative metabolites. In the present study, identification of p450 forms involved in the metabolism was carried out using human livers and intestinal microsomes (HLM and HIM). Eadie-Hofstee plots for NE-100 disappearance in HLM were biphasic, thus indicating the involvement of at least two p450 forms. The metabolism of NE-100 was mediated with recombinant CYP1A1, CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. A significant correlation was observed between activities of NE-100 metabolism and dextromethorphan O-demethylation (a specific activity for CYP2D6) or testosterone 6beta-hydroxylation (a specific activity for CYP3A4) in HLM. The activity of NE-100 metabolism was inhibited by approximately 80% by an anti-CYP2D6 antibody and only by quinidine among the p450-selective inhibitors at a low substrate concentration (0.1 microM). In contrast, with a high substrate concentration (10 microM), the activity was inhibited by an anti-CYP3A4 antibody and by ketoconazole. On the other hand, in HIM, the Eadie-Hofstee plots for NE-100 disappearance were monophasic, and the metabolism was strongly inhibited by an anti-CYP3A4 antibody and by ketoconazole but not by other inhibitors used. These results strongly suggest that NE-100 has different profiles regarding metabolism between liver and intestine. During absorption, NE-100 is mainly metabolized by CYP3A4 in the intestine and thereafter by CYP2D6 in the liver in the presence of therapeutic doses.

Disposition and metabolic fate of atomoxetine hydrochloride: pharmacokinetics, metabolism, and excretion in the Fischer 344 rat and beagle dog

These studies were designed to characterize the disposition and metabolism of atomoxetine hydrochloride [(-)-N-methyl-gamma-(2-methylphenoxy)benzenepropanamine hydrochloride; formerly know as tomoxetine hydrochloride] in Fischer 344 rats and beagle dogs. Atomoxetine was well absorbed from the gastrointestinal tract and cleared primarily by metabolism with the majority of its metabolites being excreted into the urine, 66% of the total dose in the rat and 48% in the dog. Fecal excretion, 32% of the total dose in the rat and 42% in the dog, appears to be due to biliary elimination and not due to unabsorbed dose. Nearly the entire dose was excreted within 24 h in both species. In the rat, low oral bioavailability was observed (F = 4%) compared with the high oral bioavailability in dog (F = 74%). These differences appear to be almost purely mediated by the efficient first-pass hepatic clearance of atomoxetine in rat. The biotransformation of atomoxetine was similar in the rat and dog, undergoing aromatic ring hydroxylation, benzylic oxidation (rat only), and N-demethylation. The primary oxidative metabolite of atomoxetine was 4-hydroxyatomoxetine, which was subsequently conjugated forming O-glucuronide and O-sulfate (dog only) metabolites. Although subtle differences were observed in the excretion and biotransformation of atomoxetine in rats and dogs, the primary difference observed between these species was the extent of first-pass metabolism and the degree of systemic exposure to atomoxetine and its metabolites.

Disposition and metabolic fate of atomoxetine hydrochloride: the role of CYP2D6 in human disposition and metabolism

The role of the polymorphic cytochrome p450 2D6 (CYP2D6) in the pharmacokinetics of atomoxetine hydrochloride [(-)-N-methyl-gamma-(2-methylphenoxy)benzenepropanamine hydrochloride; LY139603] has been documented following both single and multiple doses of the drug. In this study, the influence of the CYP2D6 polymorphism on the overall disposition and metabolism of a 20-mg dose of (14)C-atomoxetine was evaluated in CYP2D6 extensive metabolizer (EM; n = 4) and poor metabolizer (PM; n = 3) subjects under steady-state conditions. Atomoxetine was well absorbed from the gastrointestinal tract and cleared primarily by metabolism with the preponderance of radioactivity being excreted into the urine. In EM subjects, the majority of the radioactive dose was excreted within 24 h, whereas in PM subjects the majority of the dose was excreted by 72 h. The biotransformation of atomoxetine was similar in all subjects undergoing aromatic ring hydroxylation, benzylic oxidation, and N-demethylation with no CYP2D6 phenotype-specific metabolites. The primary oxidative metabolite of atomoxetine was 4-hydroxyatomoxetine, which was subsequently conjugated forming 4-hydroxyatomoxetine-O-glucuronide. Due to the absence of CYP2D6 activity, the systemic exposure to radioactivity was prolonged in PM subjects (t(1/2) = 62 h) compared with EM subjects (t(1/2) = 18 h). In EM subjects, atomoxetine (t(1/2) = 5 h) and 4-hydroxyatomoxetine-O-glucuronide (t(1/2) = 7 h) were the principle circulating species, whereas atomoxetine (t(1/2) = 20 h) and N-desmethylatomoxetine (t(1/2) = 33 h) were the principle circulating species in PM subjects. Although differences were observed in the excretion and relative amounts of metabolites formed, the primary difference observed between EM and PM subjects was the rate at which atomoxetine was biotransformed to 4-hydroxyatomoxetine.

Specialization of function among aldehyde dehydrogenases: the ALD2 and ALD3 genes are required for beta-alanine biosynthesis in Saccharomyces cerevisiae

The amino acid beta-alanine is an intermediate in pantothenic acid (vitamin B(5)) and coenzyme A (CoA) biosynthesis. In contrast to bacteria, yeast derive the beta-alanine required for pantothenic acid production via polyamine metabolism, mediated by the four SPE genes and by the FAD-dependent amine oxidase encoded by FMS1. Because amine oxidases generally produce aldehyde derivatives of amine compounds, we propose that an additional aldehyde-dehydrogenase-mediated step is required to make beta-alanine from the precursor aldehyde, 3-aminopropanal. This study presents evidence that the closely related aldehyde dehydrogenase genes ALD2 and ALD3 are required for pantothenic acid biosynthesis via conversion of 3-aminopropanal to beta-alanine in vivo. While deletion of the nuclear gene encoding the unrelated mitochondrial Ald5p resulted in an enhanced requirement for pantothenic acid pathway metabolites, we found no evidence to indicate that the Ald5p functions directly in the conversion of 3-aminopropanal to beta-alanine. Thus, in Saccharomyces cerevisiae, ALD2 and ALD3 are specialized for beta-alanine biosynthesis and are consequently involved in the cellular biosynthesis of coenzyme A.

Stable DNA triple helix formation using oligonucleotides containing 2'-aminoethoxy,5-propargylamino-U

We have prepared oligonucleotides containing the novel base analogue 2'-aminoethoxy,5-propargylamino-U in place of thymidine and examined their ability to form intermolecular and intramolecular triple helices by DNase I footprinting and thermal melting studies. The results were compared with those for oligonucleotides containing 5-propargylamino-dU and 2'-aminoethoxy-T. We find that the bis-substituted derivative produces a large increase in triplex stability, much greater than that produced by either of the monosubstituted analogues, which are roughly equipotent with each other. Intermolecular triplexes with 9-mer oligonucleotides containing three or four base modifications generate footprints at submicromolar concentrations even at pH 7.5, in contrast to the unmodified oligonucleotide, which failed to produce a footprint at pH 5.0, even at 30 microM. UV- and fluorescence melting studies with intramolecular triplexes confirmed that the bis-modified base produces a much greater increase in T(m) than either modification alone.

Transformation of isopropylamine to L-alaninol by Pseudomonas sp. strain KIE171 involves N-glutamylated intermediates

Pseudomonas sp. strain KIE171 was able to grow with isopropylamine or L-alaninol [S-(+)-2-amino-1-propanol] as the sole carbon source, but not with D-alaninol. To investigate the hypothesis that L-alaninol is an intermediate in the degradation of isopropylamine, two mini-Tn5 mutants unable to utilize both isopropylamine and L-alaninol were isolated. Whereas mutant KIE171-BI transformed isopropylamine to L-alaninol, mutant KIE171-BII failed to do so. The two genes containing a transposon insertion were cloned, and the DNA regions flanking the insertions were sequenced. Two clusters, one comprising eight ipu (isopropylamine utilization) genes (ipuABCDEFGH) and the other encompassing two genes (ipuI and orf259), were identified. Comparisons of sequences of the deduced Ipu proteins and those in the database suggested that isopropylamine is transported into the cytoplasm by a putative permease, IpuG. The next step, the formation of gamma-glutamyl-isopropylamide from isopropylamine, ATP, and L-glutamate, was shown to be catalyzed by IpuC, a gamma-glutamylamide synthetase. gamma-Glutamyl-isopropylamide is then subjected to stereospecific monooxygenation by the hypothetical four-component system IpuABDE, thereby yielding gamma-glutamyl-L-alaninol [gamma(L-glutamyl)-L-hydroxy-isopropylamide]. Enzymatic hydrolysis by a hydrolase, IpuF, was shown to finally liberate L-alaninol and to regenerate L-glutamate. No gene(s) encoding an enzyme for the next step in the degradation of isopropylamine was found in the ipu clusters. Presumably, L-alaninol is oxidized by an alcohol dehydrogenase to yield L-2-aminopropionaldehyde or it is deaminated by an ammonia lyase to propionaldehyde. Genetic evidence indicated that the aldehyde formed is then further oxidized by the hypothetical aldehyde dehydrogenases IpuI and IpuH to either L-alanine or propionic acid, compounds which can be processed by reactions of the intermediary metabolism.

Neuroprotection in cerebral ischemia by neutralization of 3-aminopropanal

Cerebral ischemia stimulates increased activity of polyamine oxidase, a ubiquitous enzyme that catabolizes polyamines to produce 3-aminopropanal. 3-Aminopropanal is a reactive aldehyde that mediates progressive neuronal necrosis and glial apoptosis. Here we report that increased levels of 3-aminopropanal-modified protein levels in humans after aneurysmal subarachnoid hemorrhage correlate with the degree of cerebral injury as measured by admission Hunt/Hess grade. In vitro screening of clinically approved drugs reveals that N-2-mercaptopropionyl glycine (N-2-MPG), an agent clinically approved for prevention of renal stones in patients with cysteinuria, significantly inhibits the cytotoxicity of 3-aminopropanal. N-2-MPG reacts with 3-aminopropanal to yield a nontoxic thioacetal adduct, as confirmed by electrospray ionization mass spectroscopy. Administration of N-2-MPG in clinically relevant doses to rats significantly reduces cerebral 3-aminopropanal-modified protein immunoreactivity and infarct volume in a standardized model of middle cerebral artery occlusion, even when the agent is administered after the onset of ischemia. These results implicate 3-aminopropanal as a therapeutic target for cerebral ischemia.

Identification of the human cytochromes P450 responsible for atomoxetine metabolism

Studies were performed to determine the human enzymes responsible for the biotransformation of atomoxetine to its major metabolite, 4-hydroxyatomoxetine, and to a minor metabolite, N-desmethylatomoxetine. Utilizing human liver microsomes containing a full complement of cytochrome P450 (P450) enzymes, average K(m) and CL(int) values of 2.3 microM and 103 microl/min/mg, respectively, were obtained for 4-hydroxyatomoxetine formation. Microsomal samples deficient in CYP2D6 exhibited average apparent K(m) and CL(int) values of 149 microM and 0.2 microl/min/mg, respectively. In a human liver bank characterized for P450 content, formation of 4-hydroxyatomoxetine correlated only to CYP2D6 activity. Of nine expressed P450s examined, 4-hydroxyatomoxetine was formed at a rate 475-fold greater by CYP2D6 compared with the other P450s. These results demonstrate that CYP2D6 is the enzyme primarily responsible for the formation of 4-hydroxyatomoxetine. Multiple P450s were found to be capable of forming 4-hydroxyatomoxetine when CYP2D6 was not expressed. However, the efficiency at which these enzymes perform this biotransformation is reduced compared with CYP2D6. The formation of the minor metabolite N-desmethylatomoxetine exhibited average K(m) and CL(int) values of 83 microM and 0.8 microl/min/mg, respectively. Utilizing studies similar to those outlined above, CYP2C19 was identified as the primary enzyme responsible for the biotransformation of atomoxetine to N-desmethylatomoxetine. In summary, CYP2D6 was found to be the primary P450 responsible for the formation of the major oxidative metabolite of atomoxetine, 4-hydroxyatomoxetine. Furthermore, these studies indicate that in patients with compromised CYP2D6 activity, multiple low-affinity enzymes will participate in the formation of 4-hydroxyatomoxetine. Therefore, coadministration of P450 inhibitors to poor metabolizers of CYP2D6 substrates would not be predicted to decrease the clearance of atomoxetine in these individuals.

1-[2-methoxy-5-(3-phenylpropyl)]-2-aminopropane unexpectedly shows 5-HT(2A) serotonin receptor affinity and antagonist character

Certain phenylethylamines, such as 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB; 1a), are high-affinity 5-HT(2) agonists. Previous structure-affinity studies have concluded that both the 2,5-dimethoxy substitution pattern and the nature of substituents at the 4-position are important determinants of high affinity. We recently demonstrated that replacement of the bromo group of DOB with a 3-(phenyl)propyl substituent results in retention of affinity and that, counter to established structure-affinity relationships, the 2,5-dimethoxy substitution pattern is no longer a requirement for the binding. The present investigation extends these findings by examining a series of analogues, 3, lacking a 5-methoxy group. It was additionally found that shifting the phenylalkyl substituent from the 4- to the 5-position (e.g., 4i) also results in retention of affinity. For example, 1-(2-methoxy-5-(3-phenylpropyl)-2-aminopropane (6; the alpha-methyl derivative of 4i) binds at 5-HT(2A) receptors with high affinity (K(i) = 13 nM) and possesses 5-HT(2A) antagonist character. Thus, not only is the 2,5-dimethoxy substitution pattern not a requirement for the binding of certain phenylethylamines at 5-HT(2A) receptors, the presence of a 4-position substituent (previously thought to serve as a modulator of affinity of DOB-like agents) is also not required. Striking differences in the 5-HT(2A) binding requirements of the present compounds as compared to DOB-like agents suggest multiple substituent-dependent modes of binding.

Interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate: a distinctive B(12)-dependent carbon-skeleton rearrangement

The interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate catalyzed by B(12)-dependent glutamate mutase is discussed using results from high-level ab initio molecular orbital calculations. Evidence is presented regarding the possible role of coenzyme-B(12) in substrate activation and product formation via radical generation. Calculated electron paramagnetic resonance parameters support experimental evidence for the involvement of substrate-derived radicals and will hopefully aid the future detection of other important radical intermediates. The height of the rearrangement barrier for a fragmentation-recombination pathway, calculated with a model that includes neutral amino and carboxylic acid substituents in the migrating glycyl group, supports recent experimental evidence for the interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate through such a pathway. Our calculations suggest that the enzyme may facilitate the rearrangement of (S)-glutamate through (partial) proton-transfer processes that control the protonation state of substituents in the migrating group.

DNA probes on chip surfaces studied by scanning force microscopy using specific binding of colloidal gold

Single-stranded DNA was covalently bound on chip surfaces using two different silanization procedures. The resulting surfaces were characterized by fluorescence and scanning force microscopy using sequence-complementary DNA molecules with labels. Colloidal gold (30 nm) was used as the topographic label. Scanning force microscopy revealed the individual labels on the surface and their distribution. Steps of silane layers or DNA-modified surfaces prepared using an elastomeric mask provided internal controls for comparison of modified with unmodified surfaces.

Evaluation of electrochemiluminescent technology for inhibitors of granulocyte colony-stimulating factor receptor binding

An electrochemiluminescent (ECL) assay was developed to identify compounds that inhibit the interaction of granulocyte colony-stimulating factor (GCSF) with its recombinant human receptor. The ECL technology uses a tris-(bipyridine) chelate of ruthenium, which, in the presence of excess tripropylamine, undergoes a redox reaction cycle to produce light. Paramagnetic beads with primary antibody were coated with secondary anti-GCSF receptor antibody, which were then bound with GCSF receptor. These samples were incubated with ruthenylated GCSF in the presence and absence of test compounds. The bead density, receptor and ligand concentrations, and incubation time were optimized in the assay. A set of mixed compound plates was screened to examine the feasibility of using this technology in high throughput screening. The results from this format were found to be comparable to the assay performed using a time-resolved fluorescence format.

1-[4-(3-Phenylalkyl)phenyl]-2-aminopropanes as 5-HT(2A) partial agonists

Phenylalkylamines such as 1-(4-bromo-2, 5-dimethoxyphenyl)-2-aminopropane (DOB; 1a) and its corresponding iodo derivative DOI (2) are commonly used 5-HT(2) serotonin agonists. Previous studies have established that the 2,5-dimethoxy substitution pattern found in these compounds is optimal for high affinity at 5-HT(2A) receptors and that substituents at the 4-position can modulate affinity over a wide range. We have previously shown, however, that when the 4-position is substituted with a 3-phenylpropyl substituent (i.e., 3), the compound binds with an affinity comparable to that of 1a but that it possesses 5-HT(2A) antagonist character. The present study examined the structure-affinity relationships of 3, and the results were very much unexpected. That is, the 2,5-dimethoxy substitution pattern of 3 is not required for high affinity. Either of the two methoxy groups can be removed without untoward effect on affinity, and relocation of the methoxy substituents actually enhances affinity by as much as an order of magnitude. None of the compounds displayed more than 20-fold selectivity for 5-HT(2A) over 5-HT(2C) receptors. In addition, several were demonstrated to act as 5-HT(2A) partial agonists. As such, the results of this study suggest that the structure-affinity relationships of phenylalkylamines as 5-HT(2A) ligands now be reinvestigated in greater detail.