RESUMO
Lomibuvir (1) is a non-nucleoside, allosteric inhibitor of the hepatitis C virus NS5B polymerase with demonstrated clinical efficacy. Further development efforts within this class of inhibitor focused on improving the antiviral activity and physicochemical and pharmacokinetic properties. Recently, we reported the development of this series, leading to compound 2, a molecule with comparable potency and an improved physicochemical profile relative to 1. Further exploration of the amino amide-derived side chain led to a series of lactam derivatives, inspired by the X-ray crystal structure of related thiophene carboxylate inhibitors. This series, exemplified by 12f, provided 3-5-fold improvement in potency against HCV replication, as measured by replicon assays. The synthesis, structure-activity relationships, in vitro ADME characterization, and in vivo evaluation of this novel series are discussed.
RESUMO
Under the guidance of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ), scientists from 20 pharmaceutical companies formed a Victim Drug-Drug Interactions Working Group. This working group has conducted a review of the literature and the practices of each company on the approaches to clearance pathway identification (fCL), estimation of fractional contribution of metabolizing enzyme toward metabolism (fm), along with modeling and simulation-aided strategy in predicting the victim drug-drug interaction (DDI) liability due to modulation of drug metabolizing enzymes. Presented in this perspective are the recommendations from this working group on: 1) strategic and experimental approaches to identify fCL and fm, 2) whether those assessments may be quantitative for certain enzymes (e.g., cytochrome P450, P450, and limited uridine diphosphoglucuronosyltransferase, UGT enzymes) or qualitative (for most of other drug metabolism enzymes), and the impact due to the lack of quantitative information on the latter. Multiple decision trees are presented with stepwise approaches to identify specific enzymes that are involved in the metabolism of a given drug and to aid the prediction and risk assessment of drug as a victim in DDI. Modeling and simulation approaches are also discussed to better predict DDI risk in humans. Variability and parameter sensitivity analysis were emphasized when applying modeling and simulation to capture the differences within the population used and to characterize the parameters that have the most influence on the prediction outcome.
Assuntos
Descoberta de Drogas/normas , Indústria Farmacêutica/normas , Enzimas/metabolismo , Modelos Teóricos , Preparações Farmacêuticas/metabolismo , Animais , Biotransformação , Simulação por Computador , Árvores de Decisões , Descoberta de Drogas/métodos , Interações Medicamentosas , Humanos , Cinética , Preparações Farmacêuticas/química , Medição de Risco , Especificidade da Espécie , Especificidade por SubstratoRESUMO
We report the discovery of piperazine urea based compound 1, a potent, selective, orally bioavailable melanocortin subtype-4 receptor partial agonist. Compound 1 shows anti-obesity efficacy without potentiating erectile activity in the rodent models.
Assuntos
Piperazinas/química , Receptor Tipo 4 de Melanocortina/agonistas , Ureia/análogos & derivados , Administração Oral , Animais , Disponibilidade Biológica , Modelos Animais de Doenças , Cães , Avaliação Pré-Clínica de Medicamentos , Ingestão de Alimentos/efeitos dos fármacos , Haplorrinos , Camundongos , Obesidade/tratamento farmacológico , Piperazinas/farmacocinética , Piperazinas/uso terapêutico , Ratos , Ratos Sprague-Dawley , Receptor Tipo 4 de Melanocortina/genética , Receptor Tipo 4 de Melanocortina/metabolismo , Relação Estrutura-Atividade , Ureia/química , Ureia/farmacocinética , Ureia/uso terapêuticoRESUMO
We report an SAR study of MC4R analogs containing spiroindane heterocyclic privileged structures. Compound 26 with N-Me-1,2,4-triazole moiety possesses exceptional potency at MC4R and potent anti-obesity efficacy in a mouse model. However, the efficacy is not completely mediated through MC4R. Additional SAR studies led to the discovery of compound 32, which is more potent at MC4R. Compound 32 demonstrates MC4R mediated anti-obesity efficacy in rodent models.
Assuntos
Obesidade/tratamento farmacológico , Receptor Tipo 4 de Melanocortina/agonistas , Triazóis/farmacologia , Animais , Cromatografia Líquida de Alta Pressão , Modelos Animais de Doenças , Camundongos , Camundongos Knockout , Estrutura Molecular , Ratos , Receptor Tipo 4 de Melanocortina/genética , Relação Estrutura-Atividade , Triazóis/química , Triazóis/uso terapêuticoRESUMO
Design, syntheses and structure-activity relationships of N-acetylated piperazine privileged structures containing MC4R agonist compounds were described. The most potent derivatives were low nM MC4R selective full agonists. Several compounds from the series had modest pharmacokinetic properties.
Assuntos
Ligantes , Receptor Tipo 4 de Melanocortina/agonistas , Animais , Humanos , Piperazina , Piperazinas/síntese química , Piperazinas/química , Piperazinas/farmacocinética , Ratos , Ratos Sprague-Dawley , Receptor Tipo 4 de Melanocortina/metabolismo , Relação Estrutura-AtividadeRESUMO
We report a series of potent and selective MC4R agonists based on spiroindane amide privileged structures for potential treatments of obesity. Among the synthetic methods used, Method C allows rapid synthesis of the analogs. The series of compounds can afford high potency on MC4R as well as good rodent pharmacokinetic profiles. Compound 1r (MK-0489) demonstrates MC4R mediated reduction of food intake and body weight in mouse models. Compound 1r is efficacious in 14-day diet-induced obese (DIO) rat models.
Assuntos
Amidas/química , Fármacos Antiobesidade/química , Obesidade/tratamento farmacológico , Pirrolidinas/química , Receptor Tipo 4 de Melanocortina/agonistas , Compostos de Espiro/química , Amidas/farmacocinética , Amidas/uso terapêutico , Animais , Fármacos Antiobesidade/farmacocinética , Fármacos Antiobesidade/uso terapêutico , Peso Corporal/efeitos dos fármacos , Humanos , Camundongos , Camundongos Knockout , Pirrolidinas/farmacocinética , Pirrolidinas/uso terapêutico , Ratos , Ratos Sprague-Dawley , Receptor Tipo 4 de Melanocortina/metabolismo , Compostos de Espiro/farmacocinética , Compostos de Espiro/uso terapêutico , Relação Estrutura-AtividadeRESUMO
We report the design, synthesis and properties of spiroindane based compound 1, a potent, selective, orally bioavailable, non-peptide melanocortin subtype-4 receptor agonist. Compound 1 shows excellent erectogenic activity in the rodent models.
Assuntos
Disfunção Erétil/tratamento farmacológico , Indanos/química , Indanos/uso terapêutico , Receptor Tipo 4 de Melanocortina/agonistas , Receptor Tipo 4 de Melanocortina/metabolismo , Compostos de Espiro/química , Compostos de Espiro/uso terapêutico , Animais , Células CHO , Cricetinae , Cricetulus , Cães , Haplorrinos , Humanos , Indanos/farmacocinética , Indanos/farmacologia , Masculino , Camundongos , Estrutura Molecular , Ligação Proteica , Ratos , Compostos de Espiro/farmacocinética , Compostos de Espiro/farmacologia , Relação Estrutura-AtividadeRESUMO
Bombesin receptor subtype 3 (BRS-3) is a G protein coupled receptor whose natural ligand is unknown. We developed potent, selective agonist (Bag-1, Bag-2) and antagonist (Bantag-1) ligands to explore BRS-3 function. BRS-3-binding sites were identified in the hypothalamus, caudal brainstem, and several midbrain nuclei that harbor monoaminergic cell bodies. Antagonist administration increased food intake and body weight, whereas agonists increased metabolic rate and reduced food intake and body weight. Prolonged high levels of receptor occupancy increased weight loss, suggesting a lack of tachyphylaxis. BRS-3 agonist effectiveness was absent in Brs3(-/Y) (BRS-3 null) mice but was maintained in Npy(-/-)Agrp(-/-), Mc4r(-/-), Cnr1(-/-), and Lepr(db/db) mice. In addition, Brs3(-/Y) mice lost weight upon treatment with either a MC4R agonist or a CB1R inverse agonist. These results demonstrate that BRS-3 has a role in energy homeostasis that complements several well-known pathways and that BRS-3 agonists represent a potential approach to the treatment of obesity.
Assuntos
Fármacos Antiobesidade/uso terapêutico , Obesidade/tratamento farmacológico , Peptídeos/uso terapêutico , Receptores da Bombesina/agonistas , Receptores da Bombesina/metabolismo , Animais , Fármacos Antiobesidade/farmacocinética , Peso Corporal/efeitos dos fármacos , Encéfalo/metabolismo , Ingestão de Alimentos/efeitos dos fármacos , Metabolismo Energético/efeitos dos fármacos , Humanos , Ligantes , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Obesidade/metabolismo , Peptídeos/farmacocinética , Ratos , Ratos Sprague-Dawley , Receptores da Bombesina/antagonistas & inibidoresRESUMO
Recent clinical reports have suggested that the cyclooxygenase-2 inhibitor, lumiracoxib (Prexige), may cause a rare but serious hepatotoxicity in patients. In view of the close structural resemblance between lumiracoxib and diclofenac, a widely used nonsteroidal anti-inflammatory drug whose use also has been associated with rare cases of liver injury, it is possible that the toxicity of the two agents may share a common mechanism. Because it is believed that chemically reactive metabolites may play a role as mediators of diclofenac-mediated hepatotoxicity, the present in vitro study was carried out to test the hypothesis that lumiracoxib also undergoes metabolic activation when incubated with liver microsomal preparations and hepatocytes from rats and humans. By means of liquid chromatography tandem mass spectrometry and nuclear magnetic resonance spectrometry techniques, two previously unknown N-acetylcysteine (NAC) conjugates were identified, namely, 3'-NAC-4'-hydroxy lumiracoxib (M1) and 4'-hydroxy-6'-NAC-desfluoro lumiracoxib (M2), the structures of which reveal the intermediacy of an electrophilic quinone imine species. Based on the results of studies with immunoinhibitory antibodies, it was demonstrated that the formation of M1 and M2 in human liver microsomes was catalyzed by cytochrome P450 (P450) 2C9. These findings demonstrate that lumiracoxib is subject to P450-mediated bioactivation in both rat and human liver preparations, leading to the formation of a reactive intermediate analogous to species generated during the metabolism of diclofenac.
Assuntos
Inibidores de Ciclo-Oxigenase 2/metabolismo , Diclofenaco/análogos & derivados , Hepatócitos/metabolismo , Microssomos Hepáticos/metabolismo , Acetilcisteína/farmacologia , Animais , Células Cultivadas , Cromatografia Líquida , Diclofenaco/metabolismo , Humanos , Ratos , Espectrometria de Massas em TandemRESUMO
Two novel metabolites of the dipeptidyl peptidase inhibitor sitagliptin (MK-0431, (2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)-butan-2-amine), were identified after purification from dog urine. The metabolites (referred to as M2 and M5) were characterized by hydrogen/deuterium exchange tandem mass spectrometry and NMR spectroscopy nuclear Overhauser effect experiments as the cis and trans stereoisomers formed by cyclization of the primary amino group with the alpha carbon of the piperazine ring, following oxidative desaturation.
Assuntos
Inibidores Enzimáticos/metabolismo , Hipoglicemiantes/metabolismo , Pirazinas/metabolismo , Triazóis/metabolismo , Animais , Biotransformação , Ciclização , Dipeptidil Peptidase 4/metabolismo , Inibidores da Dipeptidil Peptidase IV , Cães , Inibidores Enzimáticos/farmacologia , Inibidores Enzimáticos/urina , Hipoglicemiantes/farmacologia , Hipoglicemiantes/urina , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Oxirredução , Pirazinas/farmacologia , Pirazinas/urina , Fosfato de Sitagliptina , Espectrometria de Massas por Ionização por Electrospray , Estereoisomerismo , Espectrometria de Massas em Tandem , Triazóis/farmacologia , Triazóis/urinaRESUMO
The pharmacokinetics, metabolism, and excretion of sitagliptin [MK-0431; (2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine], a potent dipeptidyl peptidase 4 inhibitor, were evaluated in male Sprague-Dawley rats and beagle dogs. The plasma clearance and volume of distribution of sitagliptin were higher in rats (40-48 ml/min/kg, 7-9 l/kg) than in dogs ( approximately 9 ml/min/kg, approximately 3 l/kg), and its half-life was shorter in rats, approximately 2 h compared with approximately 4 h in dogs. Sitagliptin was absorbed rapidly after oral administration of a solution of the phosphate salt. The absolute oral bioavailability was high, and the pharmacokinetics were fairly dose-proportional. After administration of [(14)C]sitagliptin, parent drug was the major radioactive component in rat and dog plasma, urine, bile, and feces. Sitagliptin was eliminated primarily by renal excretion of parent drug; biliary excretion was an important pathway in rats, whereas metabolism was minimal in both species in vitro and in vivo. Approximately 10 to 16% of the radiolabeled dose was recovered in the rat and dog excreta as phase I and II metabolites, which were formed by N-sulfation, N-carbamoyl glucuronidation, hydroxylation of the triazolopiperazine ring, and oxidative desaturation of the piperazine ring followed by cyclization via the primary amine. The renal clearance of unbound drug in rats, 32 to 39 ml/min/kg, far exceeded the glomerular filtration rate, indicative of active renal elimination of parent drug.
Assuntos
Inibidores da Dipeptidil Peptidase IV , Inibidores Enzimáticos/farmacocinética , Hipoglicemiantes/farmacocinética , Pirazinas/farmacocinética , Triazóis/farmacocinética , Adenosina Desaminase/metabolismo , Inibidores de Adenosina Desaminase , Administração Oral , Animais , Bile/metabolismo , Disponibilidade Biológica , Biotransformação , Ciclização , Dipeptidil Peptidase 4/metabolismo , Cães , Inibidores Enzimáticos/administração & dosagem , Inibidores Enzimáticos/sangue , Inibidores Enzimáticos/urina , Fezes/química , Glucuronídeos/metabolismo , Glicoproteínas/antagonistas & inibidores , Glicoproteínas/metabolismo , Haplorrinos , Humanos , Hidroxilação , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/sangue , Hipoglicemiantes/urina , Técnicas In Vitro , Rim/metabolismo , Masculino , Microssomos Hepáticos/metabolismo , Estrutura Molecular , Oxirredução , Ligação Proteica , Pirazinas/administração & dosagem , Pirazinas/sangue , Pirazinas/urina , Ratos , Ratos Sprague-Dawley , Fosfato de Sitagliptina , Especificidade da Espécie , Ésteres do Ácido Sulfúrico/metabolismo , Triazóis/administração & dosagem , Triazóis/sangue , Triazóis/urinaRESUMO
Although zomepirac (ZP) and tolmetin (TM) induce anaphylactic reactions and form reactive acyl glucuronides, a direct link between the two events remains obscure. We report herein that, in addition to acyl glucuronidation, both drugs are subject to oxidative bioactivation. Following incubations of ZP with human liver microsomes fortified with NADPH and glutathione (GSH), a metabolite with an MH+ ion at m/z 597 was detected by LC/MS/MS. On the basis of collision-induced dissociation and NMR evidence, the structure of this metabolite was determined to be 5-[4'-chlorobenzoyl]-1,4-dimethyl-3-glutathionylpyrrole-2-acetic acid (ZP-SG), suggesting that the pyrrole moiety of ZP had undergone oxidation to an epoxide intermediate, followed by addition of GSH and loss of the elements of H2O to yield the observed conjugate. The oxidative bioactivation of ZP most likely is catalyzed by cytochrome P450 (P450) 3A4, since the formation of ZP-SG was reduced to approximately 10% of control values following pretreatment of human liver microsomes with ketoconazole or with an inhibitory anti-P450 3A4 IgG. A similar GSH adduct, namely 5-[4'-methylbenzoyl]-1-methyl-3-glutathionylpyrrole-2-acetic acid (TM-SG), was identified when TM was incubated with human liver microsomal preparations. The relevance of these in vitro findings to the in vivo situation was established through the detection of the same thiol adducts in rats treated with ZP and TM, respectively. Taken together, these data suggest that, in addition to the formation of acyl glucuronides, oxidative metabolism of ZP and TM affords reactive species that may haptenize proteins and thereby contribute to the drug-mediated anaphylactic reactions.
Assuntos
Glutationa/metabolismo , Microssomos Hepáticos/metabolismo , Tolmetino/análogos & derivados , Tolmetino/metabolismo , Animais , Cromatografia Líquida/métodos , Feminino , Glutationa/química , Glutationa/farmacologia , Hepatócitos/química , Hepatócitos/efeitos dos fármacos , Hepatócitos/metabolismo , Humanos , Masculino , Microssomos Hepáticos/química , Microssomos Hepáticos/efeitos dos fármacos , NADP/metabolismo , NADP/farmacologia , Oxirredução/efeitos dos fármacos , Ratos , Espectrometria de Massas por Ionização por Electrospray/métodos , Trítio , Troleandomicina/metabolismo , Troleandomicina/farmacologiaRESUMO
The discovery of 1-amino-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid analogs as potent human melanocortin-4 selective agonists is described.
Assuntos
Ácidos Carboxílicos/farmacologia , Receptor Tipo 4 de Melanocortina/agonistas , Tetra-Hidroisoquinolinas/química , Tetra-Hidronaftalenos/farmacologia , Humanos , Conformação Molecular , Mimetismo Molecular , Ligação Proteica/efeitos dos fármacos , Receptor Tipo 4 de Melanocortina/metabolismo , Relação Estrutura-AtividadeRESUMO
A novel isoquinuclidine containing selective melanocortin subtype-4 receptor small molecule agonist, 3 (RY764), is reported. Its in vivo characterization revealed mechanism-based food intake reduction and erectile activity augmentation in rodents.
Assuntos
Compostos Aza/farmacologia , Ingestão de Alimentos/efeitos dos fármacos , Ereção Peniana/efeitos dos fármacos , Piperazinas/farmacologia , Piperidinas/farmacologia , Receptor Tipo 4 de Melanocortina/agonistas , Animais , Compostos Aza/síntese química , Humanos , Masculino , Microssomos Hepáticos/metabolismo , Piperazinas/química , Piperidinas/síntese química , Ligação Proteica , Quinuclidinas/química , Ratos , Ratos Sprague-Dawley , Roedores , Relação Estrutura-Atividade , Fatores de TempoRESUMO
Estrogens and selective estrogen receptor modulators (SERMs) are prescribed widely in the clinic to alleviate symptoms in postmenopausal women, and they are metabolized to reactive intermediates, which may elicit adverse effects. As part of our efforts to develop safer SERMs, in vitro covalent protein binding of (2S,3R)-(+)-3-(4-hydroxyphenyl)-2-[4-(2-piperidin-1-ylethoxy)phenyl]-2,3-dihydro-1,4-benzoxathiin-6-ol (I) was evaluated. Radioactivity from [3H]I became covalently bound to proteins in a fashion that was both time- and NADPH-dependent in human liver microsomes and reached a value of 1106 pmol equiv/mg protein following a 45 min incubation. At least three pathways are involved in the bioactivation of I, namely, oxidative cleavage of the dihydrobenzoxathiin moiety to give a hydroquinone/para-benzoquinone redox couple, hydroxylation at position 5 or 7 of the benzoxathiin moiety leading to an o-quinone intermediate, and metabolism of the piperidine ring to give an iminium ion. The latter reactive intermediate was identified as its bis-cyano adduct when human liver microsomal incubations were performed in the presence of sodium cyanide. Structural modification of I, including a replacement of the piperidine with a pyrrolidine group, led to (2S,3R)-(+)-3-(3-hydroxyphenyl)-2-[4-(2-pyrrolidin-1-ylethoxy)phenyl]-2,3-dihydro-1,4-benzoxathiin-6-ol (II), which did not form a reactive iminium ion. Following the incubation of II with human liver microsomes, covalent binding to proteins was reduced (461 pmol equiv/mg protein), the residual level of binding apparently due to the formation of a rearranged biphenyl quinone type metabolite. Studies with inhibitory antibodies and chemical inhibitors showed that P450 3A4 was the primary enzyme responsible for oxidative bioactivation of I and II in human liver microsomes. These studies thus demonstrated that gaining an understanding of bioactivation mechanisms may be exploited in terms of guiding structural modifications of drug candidates to minimize covalent protein binding and, hopefully, to lower the potential for drug-mediated adverse effects.
Assuntos
Sistema Enzimático do Citocromo P-450/fisiologia , Microssomos Hepáticos/metabolismo , Oxati-Inas/farmacocinética , Moduladores Seletivos de Receptor Estrogênico/farmacocinética , Benzoquinonas/metabolismo , Biotransformação , Citocromo P-450 CYP3A , Hepatócitos/metabolismo , Humanos , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Ligação ProteicaRESUMO
We report the discovery and optimization of substituted 2-piperazinecarboxamides as potent and selective agonists of the melanocortin subtype-4 receptor. The 5- and 6-alkylated piperazine compounds exhibit low bioactivation potential as measured by covalent binding in microsome preparations.
Assuntos
Piperazinas/química , Piperazinas/farmacologia , Receptor Tipo 4 de Melanocortina/agonistas , Humanos , Piperazinas/metabolismo , Receptor Tipo 4 de Melanocortina/metabolismo , Relação Estrutura-AtividadeRESUMO
MB243 (a 1,3-disubstituted piperazine) is a new, potent, and selective melanocortin receptor subtype-4 agonist with potential application in the treatment of obesity and/or erectile dysfunction. MB243 was observed to covalently bind extensively to liver microsomal proteins from rats and humans. In the presence of glutathione, two thioether adducts were detected in liver microsomal incubations by radiochromatography and LC/MS/MS analysis. These adducts were also formed when bile duct-cannulated rats were dosed with MB243. The two adducts were isolated, and their structures were determined by accurate mass MS/MS and NMR analyses. The proposed structures resulted from a novel contraction of the piperazine ring to yield a substituted imidazoline. A mechanism is proposed, which involves an initial six electron oxidation of the piperazine ring to form a reactive intermediate, which is trapped by glutathione. Hydrolysis of the glutamic acid residue followed by internal aminolysis by the cysteine amino group resulted in opening of the piperazine ring, which is followed by ring closure to an imidazoline. The resulting cysteinyl-glycine conjugate underwent subsequent hydrolysis of the glycine residue. Understanding of the mechanism of bioactivation led to the design of MB243 analogues that exhibited reduced covalent protein binding.
Assuntos
Imidazolinas/síntese química , Imidazolinas/metabolismo , Piperazinas/farmacocinética , Animais , Bile/efeitos dos fármacos , Biotransformação , Ciclização , Glutationa/efeitos dos fármacos , Humanos , Masculino , Microssomos Hepáticos/efeitos dos fármacos , Microssomos Hepáticos/metabolismo , Estrutura Molecular , NADP/efeitos dos fármacos , Piperazinas/administração & dosagem , Piperazinas/síntese química , Ligação Proteica , Ratos , Ratos Sprague-DawleyRESUMO
We report the discovery and optimization of substituted 2-piperazinecarboxamides as potent and selective agonists of the melanocortin subtype-4 receptor. Further in vivo development of lead agonist, MB243, is disclosed.
Assuntos
Piperazinas/farmacologia , Piperidinas/farmacologia , Receptor Tipo 4 de Melanocortina/agonistas , Animais , Cães , Disfunção Erétil/tratamento farmacológico , Haplorrinos , Masculino , Camundongos , Obesidade/tratamento farmacológico , Piperazinas/química , Piperazinas/farmacocinética , Piperazinas/uso terapêutico , Piperidinas/química , Piperidinas/farmacocinética , Piperidinas/uso terapêutico , RatosRESUMO
The current study evaluated the potential for two dipeptidyl peptidase-IV (DPP-IV) inhibitor analogs (1S)-1-(trans-4-([(4-trifluoromethoxyphenyl)sulfonyl]amino)cyclohexyl)-2-[(3S)-3-fluoropyrrolidin-1-yl]-2-oxoethanaminium chloride and (1S)-1-(trans-4-([(2,4-difluorophenyl)sulfonyl]amino)cyclohexyl)-2-[(3S)-3-fluoropyrrolidin-1-yl]-2-oxoethanaminium chloride (MRL-A and MRL-B), containing a fluoropyrrolidine moiety in the structure, to undergo metabolic activation. The irreversible binding of these tritium-labeled compounds to rat liver microsomal protein was time- and NADPH-dependent and was attenuated by the addition of reduced glutathione (GSH) or N-acetylcysteine (NAC) to the incubation, indicating that chemically reactive intermediates were formed and trapped by these nucleophiles. Mass spectrometric analyses and further trapping experiments with semicarbazide indicated that the fluoropyrrolidine ring had undergone sequential oxidation and defluorination events resulting in the formation of GSH or NAC conjugates of the pyrrolidine moiety. The bioactivation of MRL-A was catalyzed primarily by rat recombinant CYP3A1 and CYP3A2. Pretreatment of rats with prototypic CYP3A1 and 3A2 inducers (pregnenolone-16alpha-carbonitrile and dexamethasone) enhanced the extent of bioactivation which, in turn, led to a higher degree of in vitro irreversible binding to microsomal proteins (5- and 9-fold increase, respectively). Herein, we describe studies that demonstrate that the fluoropyrrolidine ring is prone to metabolic activation and that GSH or NAC can trap the reactive intermediates to form adducts that provide insight into the mechanisms of bioactivation.
Assuntos
Dipeptidil Peptidase 4/metabolismo , Microssomos Hepáticos/enzimologia , Inibidores de Proteases/metabolismo , Inibidores de Proteases/farmacologia , Pirrolidinas/metabolismo , Animais , Biotransformação , Flúor/química , Flúor/metabolismo , Flúor/farmacologia , Masculino , Inibidores de Proteases/química , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/fisiologia , Pirrolidinas/química , Pirrolidinas/farmacologia , Ratos , Ratos Sprague-DawleyRESUMO
Stimulation by quinidine of warfarin metabolism in vitro was first demonstrated with liver microsomal preparations. We report herein that this drug interaction is reproducible in an animal model but that it exhibits profound species differences. Thus, using rabbit liver microsomes and a kinetic model incorporating two binding sites, the hepatic intrinsic clearance of R-warfarin via the 10-hydroxylation pathway (CL(int)(W)) was projected to be 6 +/- 1 and 128 +/- 51 microl/min/g liver, respectively, in the absence and presence of 21 microM unbound quinidine. These estimates were consistent with the results from studies in which rabbit livers (n = 5) were perfused in situ with R-warfarin or R-warfarin plus quinidine. The CL(int)(W) increased from 7 +/- 3 to 156 +/- 106 microl/min/g liver after increasing the hepatic exposure of unbound quinidine from 0 to 21 microM. In contrast, when liver microsomes or intact livers from rats were examined, R-warfarin metabolism was inhibited by quinidine, the CL(int)(W) decreasing to 26% of the control value after exposure of perfused rat livers (n = 5) to 22 microM unbound quinidine. The third example involved monkey liver microsomes, in which the rate of 10-hydroxylation of R-warfarin was little affected in the presence of quinidine (<2-fold increase). In all three species, the 10-hydroxylation of R-warfarin was catalyzed primarily by members of CYP3A, based on immuno- and chemical inhibition analyses. These findings not only highlight the variability of drug interactions among different species but also suggest that changes in hepatic clearance resulting from stimulation of cytochrome P450 activity may be projected based on estimates generated from corresponding liver microsomal preparations.