RESUMO
Peptides based upon the non-prime side residues of the NS4A-4B cleavage site of hepatitis C virus (HCV) NS3-4A proteinase containing an alpha-ketoamide moiety in place of the scissile amide bond are potent inhibitors of this enzyme.
Assuntos
Peptídeos/farmacologia , Inibidores de Serina Proteinase/síntese química , Proteínas não Estruturais Virais/antagonistas & inibidores , Amidas/farmacologia , Antivirais/síntese química , Antivirais/farmacologia , Técnicas de Química Combinatória , Humanos , Concentração Inibidora 50 , Mimetismo Molecular , Peptídeos/síntese química , Inibidores de Serina Proteinase/farmacologia , Relação Estrutura-AtividadeRESUMO
Use of a resin bound diol as a boronic acid protecting group has been developed to allow the parallel synthesis of potent inhibitors of the hepatitis C virus NS3 serine proteinase.
Assuntos
Antivirais/síntese química , Ácidos Borônicos/síntese química , Hepacivirus/enzimologia , Inibidores de Serina Proteinase/síntese química , Proteínas não Estruturais Virais/antagonistas & inibidores , Antivirais/química , Antivirais/farmacologia , Ácidos Borônicos/química , Ácidos Borônicos/farmacologia , Desenho de Fármacos , Hepacivirus/efeitos dos fármacos , Indicadores e Reagentes , Estrutura Molecular , RNA Helicases , Serina Endopeptidases , Inibidores de Serina Proteinase/química , Inibidores de Serina Proteinase/farmacologia , Relação Estrutura-AtividadeRESUMO
Hepatitis C virus (HCV) is the cause of the majority of transfusion-associated hepatitis and a significant proportion of community-acquired hepatitis worldwide. Infection by HCV frequently leads to persistent infections that result in a range of clinical conditions including an asymptomatic carrier state, severe chronic active hepatitis, cirrhosis and, in some cases, hepatocellular carcinoma. The HCV genome consists of a single-stranded, positive sense RNA containing an open reading frame of approximately 9060 nucleotides. This is translated into a single polyprotein of approximately 3020 amino acids (C-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS5B), which in turn is processed by a series of host and viral proteinases into at least 10 cleavage products. The N-terminal portion of the NS3 protein encodes a serine proteinase that is responsible for the cleavage at the NS3-4A, NS4A-4B, NS4B-5A and NS5A-5B junctions. The 54 amino acid NS4A protein is a cofactor that binds to the NS3 protein and enhances its proteolytic activity. This report describes the expression of a recombinant NS3-4A proteinase fusion protein in Escherichia coli and the in vitro characterization of the enzyme activity using synthetic peptide substrates. It then demonstrates how these results were employed to guide the design of potent inhibitors of this enzyme.
Assuntos
Antivirais/síntese química , Antivirais/farmacologia , Desenho de Fármacos , Endopeptidases/metabolismo , Hepacivirus/enzimologia , Serina Endopeptidases , Inibidores de Serina Proteinase/síntese química , Inibidores de Serina Proteinase/farmacologia , Proteínas não Estruturais Virais/antagonistas & inibidores , Sequência de Aminoácidos , Antivirais/química , Sítios de Ligação , Endopeptidases/química , Endopeptidases/genética , Escherichia coli/enzimologia , Escherichia coli/genética , Hepacivirus/genética , Dados de Sequência Molecular , Peptídeos/síntese química , Peptídeos/metabolismo , RNA Helicases , Proteínas Recombinantes de Fusão/biossíntese , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Inibidores de Serina Proteinase/química , Especificidade por Substrato , Proteínas não Estruturais Virais/química , Proteínas não Estruturais Virais/genéticaRESUMO
A water calorimeter has been used for the direct measurement of absorbed dose to water in a d(15) + Be neutron beam. The absorbed dose measured with the calorimeter was compared with that measured with an Exradin ionisation chamber, constructed of A-150 plastic. The doses measured by the ionisation chamber were calculated according to the European (ECNEU) protocol. Absorbed dose to tissue measured with the calorimeter was 4.3% lower than that measured with the ionisation chamber. Relative to ionisation chamber dosimetry, dose measurements with the calorimeter in the neutron beam were 9% lower than similar measurements in 4 and 9 MV photon beams. The significance of the results is discussed in terms of the heat defect in water.
Assuntos
Nêutrons , Dosagem Radioterapêutica , Radioterapia/instrumentação , Calorimetria , Humanos , Radioterapia/métodos , ÁguaRESUMO
The poor agreement in the photon calibrations of tissue-equivalent ionisation chambers between different participants in two major neutron dosimetry intercomparisons is noted. The methods of converting measurements made with a calibrated secondary standard exposure meter to the absorbed dose in the wall of a tissue-equivalent chamber are discussed. Calibrations of a TE ionisation chamber were made in five photon beams (250 kV, 300 kV, 137Cs, 60Co and 4 MV) and the different calibration factors were compared both for in-air and in-phantom measurements. Good agreement was found in these factors provided that allowance was made for the attenuation and scattering in the wall and build-up cap of the TE chamber for the in-air measurements, and that revised values of C lambda were used for the in-phantom measurements at the two higher energies.
Assuntos
Nêutrons , Radiometria/instrumentação , Dosagem Radioterapêutica/normas , Radioterapia de Alta Energia/normasRESUMO
The theoretical basis of Clambda and Ce is re-examined and consistent expressions derived involving the quantity Fwa which is a combination of a stopping-power ratio and an energy-absorption coefficient ratio, thereby taking into account the extent to which the ionisation chamber acts as an 'electron detector' and as a 'photon detector' for a particular radiation quality. An extension of the Spencer-Attix cavity ionisation theory to include energy dissipation due to photon interactions with the cavity wall and gas given in a recent paper by Nahum has been used to calculate values for Fwa appropriate to the Baldwin-Farmer ionisation chamber assuming an air-equivalent inner wall, and new values of Clambda and Ce are presented for this and similarly constructed instruments. Clambda also depends on whether the radiation is produced by a linac or a betatron of a given maximum photon energy. The new set of Clambda and Ce has been used to recalculate the experimental ferrous sulphate G-values of Law and Naylor with the result that the difference between G for high energy photons and electrons disappears.
