RESUMO
The discovery of an orally bioavailable selective estrogen receptor downregulator (SERD) with equivalent potency and preclinical pharmacology to the intramuscular SERD fulvestrant is described. A directed screen identified the 1-aryl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole motif as a novel, druglike ER ligand. Aided by crystal structures of novel ligands bound to an ER construct, medicinal chemistry iterations led to (E)-3-(3,5-difluoro-4-((1R,3R)-2-(2-fluoro-2-methylpropyl)-3-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-1-yl)phenyl)acrylic acid (30b, AZD9496), a clinical candidate with high oral bioavailability across preclinical species that is currently being evaluated in phase I clinical trials for the treatment of advanced estrogen receptor (ER) positive breast cancer.
Assuntos
Antineoplásicos/metabolismo , Cinamatos/química , Cinamatos/metabolismo , Antagonistas de Estrogênios/síntese química , Antagonistas de Estrogênios/farmacologia , Moduladores de Receptor Estrogênico/síntese química , Moduladores de Receptor Estrogênico/farmacologia , Indóis/química , Indóis/metabolismo , Antineoplásicos/química , Neoplasias da Mama/tratamento farmacológico , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Ensaios Clínicos Fase I como Assunto , Regulação para Baixo/efeitos dos fármacos , Desenho de Fármacos , Feminino , Humanos , Injeções Intramusculares , Difração de Raios XRESUMO
The discovery of the activating mutation V617F in the JH2 domain of Jak2 and the modulation of oncogenic Stat3 by Jak2 inhibitors have spurred a great interest in the inhibition of the Jak2/Stat pathway in oncology. In this Letter, we communicate the discovery of novel inhibitors of the Jak2/Stat5 axis, the N-(1H-pyrazol-3-yl)pyrimidin-2-amino derivatives. The rationale, synthesis and biological evaluation of these derivatives are reported. Two lead analogs from this series, 6 and 9, displayed prolonged residence time on Jak2, at enzymatic level. Although 6 and 9 exhibited moderate selectivity in a selected kinase panel, we chose to test these inhibitors in vivo as a consequence to their long residence time. However, extended inhibition of Jak2 due to the long residence time, in the form of inhibiting phosphorylation of downstream Stat5, was not recapitulated in an in vivo setting.
Assuntos
Descoberta de Drogas , Janus Quinase 2/antagonistas & inibidores , Inibidores de Proteínas Quinases/farmacologia , Fator de Transcrição STAT5/antagonistas & inibidores , Animais , Linhagem Celular Transformada , Proliferação de Células/efeitos dos fármacos , Cães , Relação Dose-Resposta a Droga , Feminino , Humanos , Janus Quinase 2/genética , Janus Quinase 2/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos , Modelos Moleculares , Conformação Molecular , Fosforilação/efeitos dos fármacos , Inibidores de Proteínas Quinases/síntese química , Inibidores de Proteínas Quinases/química , Ratos , Ratos Wistar , Fator de Transcrição STAT5/metabolismo , Relação Estrutura-Atividade , Especificidade por Substrato , Fatores de TempoRESUMO
Understanding the roles of noncovalent interactions within the enzyme molecule and between enzyme and substrate or inhibitor is an essential goal of the investigation of active center chemistry and catalytic mechanism. Studies on members of the papain family of cysteine proteinases, particularly papain (EC 3.4.22.2) itself, continue to contribute to this goal. The historic role of the catalytic site Cys/His ion pair now needs to be understood within the context of multiple dynamic phenomena. Movement of Trp177 may be necessary to expose His159 to solvent with consequent decrease in its degree of electrostatic solvation of (Cys25)-S(-). Here we report an investigation of this possibility using computer modeling of quasi-transition states and pH-dependent kinetics using 3,3'-dipyridazinyl disulfide, its n-propyl and phenyl derivatives, and 4,4'-dipyrimidyl disulfide as reactivity probes that differ in the location of potential hydrogen-bonding acceptor atoms. Those interactions that influence ion pair geometry and thereby catalytic competence, including by transmission of the modulatory effect of a remote ionization with pK(a) 4, were identified. A key result is the correlation between the kinetic influence of the modulatory trigger of pK(a) 4 and disruption of the hydrogen bond donated by the indole N-H of Trp177, the hydrophobic shield of the initial "intimate" ion pair. This hydrogen bond is accepted by the amide O of Gln19-a component of the oxyanion hole that binds the tetrahedral species formed from the substrate during the catalytic act. The disruption would be expected to contribute to the mobility of Trp177 and possibly to the effectiveness of the binding of the developing oxyanion.
Assuntos
Papaína/química , Papaína/metabolismo , Domínio Catalítico , Dissulfetos/química , Histidina/química , Ligação de Hidrogênio , Concentração de Íons de Hidrogênio , Cinética , Modelos Moleculares , Pirimidinas/química , TriptofanoRESUMO
Pectate lyases harness anti beta-elimination chemistry to cleave the alpha-1,4 linkage in the homogalacturonan region of plant cell wall pectin. We have studied the binding of five pectic oligosaccharides to Bacillus subtilis pectate lyase in crystals of the inactive enzyme in which the catalytic base is substituted with alanine (R279A). We discover that the three central subsites (-1, +1, and +2) have a profound preference for galacturonate but that the distal subsites can accommodate methylated galacturonate. It is reasonable to assume therefore that pectate lyase can cleave pectin with three consecutive galacturonate residues. The enzyme in the absence of substrate binds a single calcium ion, and we show that two additional calcium ions bind between enzyme and substrate carboxylates occupying the +1 subsite in the Michaelis complex. The substrate binds less intimately to the enzyme in a complex made with a catalytic base in place but in the absence of the calcium ions and an adjacent lysine. In this complex, the catalytic base is correctly positioned to abstract the C5 proton, but there are no calcium ions binding the carboxylate at the +1 subsite. It is clear, therefore, that the catalytic calcium ions and adjacent lysine promote catalysis by acidifying the alpha-proton, facilitating its abstraction by the base. There is also clear evidence that binding distorts the relaxed 2(1) or 3(1) helical conformation of the oligosaccharides in the region of the scissile bond.
Assuntos
Polissacarídeo-Liases/química , Polissacarídeo-Liases/metabolismo , Bacillus subtilis/enzimologia , Bacillus subtilis/metabolismo , Sítios de Ligação , Catálise , Cristalografia por Raios X , Modelos Moleculares , Oligossacarídeos/química , Oligossacarídeos/metabolismo , Pectinas/metabolismo , Conformação Proteica , Especificidade por SubstratoRESUMO
Current drug therapies against Trypanosoma cruzi, the causative agent of Chagas disease, have limited effectiveness and are highly toxic. T. cruzi-specific metabolic pathways that utilize trypanothione for the reduction of peroxides are being explored as potential novel therapeutic targets. In the present study we solved the X-ray crystal structure of one of the T. cruzi enzymes involved in peroxide reduction, the glutathione peroxidase-like enzyme TcGPXI (T. cruzi glutathione peroxidase-like enzyme I). We also characterized the wild-type, C48G and C96G variants of TcGPXI by NMR spectroscopy and biochemical assays. Our results show that residues Cys48 and Cys96 are required for catalytic activity. In solution, the TcGPXI molecule readily forms a Cys48-Cys96 disulfide bridge and the polypeptide segment containing Cys96 lacks regular secondary structure. NMR spectra of the reduced TcGPXI are indicative of a protein that undergoes widespread conformational exchange on an intermediate time scale. Despite the absence of the disulfide bond, the active site mutant proteins acquired an oxidized-like conformation as judged from their NMR spectra. The protein that was used for crystallization was pre-oxidized by t-butyl hydroperoxide; however, the electron density maps clearly showed that the active site cysteine residues are in the reduced thiol form, indicative of X-ray-induced reduction. Our crystallographic and solution studies suggest a level of structural plasticity in TcGPXI consistent with the requirement of the atypical two-cysteine (2-Cys) peroxiredoxin-like mechanism implied by the behaviour of the Cys48 and Cys96 mutant proteins.
Assuntos
Glutationa Peroxidase/química , Trypanosoma cruzi/metabolismo , Animais , Catálise , Domínio Catalítico , Cisteína/química , Dissulfetos/química , Cinética , Espectroscopia de Ressonância Magnética , Mutação , Peróxidos/química , Reação em Cadeia da Polimerase , Conformação Proteica , Dobramento de Proteína , Interferência de RNARESUMO
Studies on papain (EC 3.4.22.2), the most thoroughly investigated member of the cysteine proteinase superfamily, have contributed substantially to our understanding of the roles of noncovalent interactions in enzyme active center chemistry. Previously, we reported evidence that the long-held view that catalytic competence develops synchronously with formation of the catalytic site (Cys25)-S-/(His159)-Im+H ion pair is incorrect and that conformational rearrangement is necessary for each of the partners to play its role in catalysis. A decrease in the level of mutual solvation of the partners of the noncatalytic "intimate" ion pair should release the nucleophilic character of (Cys25)-S- and allow association of (His159)-Im+H with the leaving group of a substrate to provide its general acid-catalyzed elimination. Hypotheses by which this could be achieved involve electrostatic modulation of the ion pair and perturbation of its hydrophobic shielding from solvent by Trp177. The potential electrostatic modulator closest to the catalytic site is Asp158, the mutation of which to Ala substantially decreases catalytic activity. Here we report an investigation of these hypotheses by a combination of computer modeling and stopped-flow pH-dependent kinetic studies using a new series of cationic aminoalkyl 2-pyridyl disulfide time-dependent inhibitors as reactivity probes. These probes 2-4 (n = 2-4), which exist as equilibrium mixtures of H3N+-[CH2]n-S-S-2-pyridyl+H and H3N+-[CH2]n-S-S-2-pyridyl which predominate in acidic and weakly alkaline media, respectively, were shown by modeling and kinetic analysis to bind with various degrees of effectiveness near Asp158 and in some cases also near Trp177. Kinetic analysis of the reactions of 2-4 and of the reaction of CH3-[CH2]2-S-S-2-pyridyl+H <==>CH3-[CH2]2-S-S-2-pyridyl 1 and normal mode calculations lead to the conclusion that Asp158 is not involved in the generation of nucleophilic character in the ion pair and demonstrates a key role for Trp177.
Assuntos
Ácido Aspártico/química , Cisteína/química , Histidina/química , Papaína/química , Triptofano/química , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Espectrometria de Massas por Ionização por Electrospray , Eletricidade EstáticaRESUMO
The crystal structure of internalin C (InlC) from Listeria monocytogenes has been determined at 2.0 A resolution. Several observations implicate InlC in infection: inlC has the same transcriptional activator as other virulence genes, it is only present in pathogenic Listeria strains and an inlC deletion mutant is significantly less virulent. While the extended concave receptor-binding surfaces of the leucine-rich repeat (LRR) domains of internalins A and B have aromatic clusters involved in receptor binding, the corresponding surface of InlC is smaller, flatter and more hydrophilic, suggesting that InlC may be involved in weak or transient associations with receptors; this may help explain why no receptor has yet been discovered for InlC. In contrast, the Ig-like domain, to which the LRR domain is fused, has surface aromatics that may be of functional importance, possibly being involved in binding to the surface of the bacteria or in receptor binding.
Assuntos
Proteínas de Bactérias/química , Listeria monocytogenes/química , Proteínas de Bactérias/genética , Sequência de Bases , Cristalografia por Raios X/métodos , Listeria monocytogenes/genética , Listeria monocytogenes/patogenicidade , Proteínas de Membrana/química , Proteínas de Membrana/genética , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Deleção de Sequência , Relação Estrutura-Atividade , Virulência/genéticaRESUMO
The substrate selectivities of an anti-phosphonate and an anti-phosphate kinetically homogeneous polyclonal catalytic antibody preparation and two hydrolytic enzymes were compared by using hapten-analogous and truncated carbonate and ester substrates each containing a 4-nitrophenolate leaving group. Syntheses of the truncated substrates devoid of recognition features in the non-leaving group parts of the substrates are reported. The relatively high kinetic selectivity of the more active anti-phosphonate antibody preparation is considered to depend on a relatively rigid catalytic site with substantial reaction centre specificity together with other important recognition interactions with the extended non-leaving group part of the substrate. In contrast, the less catalytically active, more flexible anti-phosphate antibody exhibits much lower kinetic selectivity for the substrate reaction centre comparable with that of the hydrolytic enzymes with activity much less dependent on recognition interactions with the non-leaving group part of the substrate. The ways in which haptenic flexibility and IgG architecture might contribute to the differential kinetic selectivities are indicated.
Assuntos
Anticorpos Catalíticos/química , Anticorpos Catalíticos/metabolismo , Domínio Catalítico , Organofosfonatos/imunologia , Fosfatos/imunologia , Animais , Afinidade de Anticorpos , Reações Antígeno-Anticorpo , Sítios de Ligação de Anticorpos , Bovinos , Quimotripsina/metabolismo , Esterases/metabolismo , Hidrolases/metabolismo , Hidrólise , Fígado/enzimologia , Modelos Moleculares , Organofosfonatos/síntese química , Pâncreas/enzimologia , Fosfatos/síntese química , Especificidade por Substrato , Suínos , Vacinas Sintéticas/química , Vacinas Sintéticas/imunologia , Vacinas Sintéticas/metabolismoRESUMO
The effects of increasing the content of the aprotic dipolar organic co-solvent acetonitrile on the observed first-order rate constant (k(obs)) of the pre-steady state acylation phases of the hydrolysis of N-acetyl-Phe-Gly methyl thionester catalysed by the cysteine proteinase variants actinidin and papain in sodium acetate buffer, pH 5.3, were investigated by stopped-flow spectral analysis. With low acetonitrile content, plots of k(obs) against [S]0 for the actinidin reaction are linear with an ordinate intercept of magnitude consistent with a five-step mechanism involving a post-acylation conformational change. Increasing the acetonitrile content results in marked deviations of the plots from linearity with a rate minimum around [S]0=150 microM. The unusual negative dependence of k(obs) on [S]0 in the range 25-150 microM is characteristic of a rate-determining isomerization of the free enzyme before substrate binding, additional to the five-step mechanism. There was no evidence for this phenomenon nor for the post-acylation conformational change in the analogous reaction with papain. For this enzyme, however, acetonitrile acts as an inhibitor with approximately uncompetitive characteristics. Possible mechanistic consequences of the differential solvent-perturbed kinetics are indicated. The free enzyme isomerization of actinidin may provide an explanation for the marked difference in sensitivity between this enzyme and papain of binding site-catalytic site signalling in reactions of substrate-derived 2-pyridyl disulphide reactivity probes.
Assuntos
Acetonitrilas/química , Cisteína Endopeptidases/química , Cisteína Endopeptidases/metabolismo , Solventes/química , Acilação , Catálise , Isomerismo , Cinética , Oligopeptídeos/química , Oligopeptídeos/metabolismo , Papaína/metabolismoRESUMO
To investigate the hypothesis that decreased hapten flexibility may lead to increased catalytic antibody activity, we used two closely related immunogens differing only in the flexibility of the atomic framework around the structural motif of the haptens, analogous to the reaction centre of the corresponding substrates. Identical leaving-group determinants in the haptens and identical leaving groups in the substrates removed the ambiguity inherent in some data reported in the literature. Anti-phosphate and anti-phosphonate kinetically homogeneous polyclonal catalytic antibody preparations were compared by using carbonate and ester substrates respectively, each containing a 4-nitrophenolate leaving group. Synthetic routes to a new phosphonate hapten and new ester substrate were developed. The kinetic advantage of the more rigid anti-phosphonate/ester system was demonstrated at pH 8.0 by a 13-fold advantage in k(cat)/k(non-cat) and a 100-fold advantage in the proficiency constant, k(cat)/k (non-cat) x K(m). Despite these differences, the pH-dependences of the kinetic and binding characteristics and the results of chemical modification studies suggest closely similar catalytic mechanisms. The possible origin of the kinetic advantage of the more rigid hapten/substrate system is discussed.
Assuntos
Anticorpos Catalíticos/metabolismo , Haptenos/química , Haptenos/metabolismo , Anticorpos Catalíticos/química , Concentração de Íons de Hidrogênio , Hidrólise , Cinética , Modelos Químicos , Movimento (Física) , Organofosfonatos/química , Fosfatos/químicaRESUMO
The acylation and deacylation stages of the hydrolysis of N -acetyl-Phe-Gly methyl thionoester catalysed by papain and actinidin were investigated by stopped-flow spectral analysis. Differences in the forms of pH-dependence of the steady-state and pre-steady-state kinetic parameters support the hypothesis that, whereas for papain, in accord with the traditional view, the rate-determining step is the base-catalysed reaction of the acyl-enzyme intermediate with water, for actinidin it is a post-acylation conformational change required to permit release of the alcohol product and its replacement in the catalytic site by the key water molecule. Possible assignments of the kinetically influential p K (a) values, guided by the results of modelling, including electrostatic-potential calculations, and of the mechanistic roles of the ionizing groups, are discussed. It is concluded that Asp(161) is the source of a key electrostatic modulator (p K (a) 5.0+/-0.1) in actinidin, analogous to Asp(158) in papain, whose influence is not detected kinetically; it is always in the 'on' state because of its low p K (a) value (2.8+/-0.06).