Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Process development for biopharmaceuticals is dictated by product quality, drug safety and economy of the manufacturing process. Not surprisingly, these factors also play a key role in the evaluation of mammalian cell expression systems to be used in the production of pharmacologically active glycoproteins. To date, the most prominent candidates for efficient expression of glycoproteins are mammalian cell lines such as mouse fibroblast cells (C 127-BPV), Chinese hamster ovary cells (CHO-DHFR, CHO-NEOSPLA, CHO-GS), mouse myeloma cells (NSO-GS) as well as transgenic animals carrying c-DNA or genomic DNA which codes for the protein of interest. The expression titer in the case of glycoproteins is mainly determined by the promoter construct, the site of integration into the chromosome, the copy number and the type of protein in question. Based on expression titer, CHO-NEOSPLA and NSO-GS expression systems are most effective in the production of monoclonal antibodies and, to a lesser extent, of recombinant DNA derived proteins. However, based on overall product yield, expression of recombinant DNA derived proteins in transgenic animals is by far the most promising system. Therefore, for proteins required in large quantities, transgenic expression systems offer an attractive choice. However, cost of goods for products for which the dosage or the overall annual quantities are low, is dominated by downstream processing, filling, lyophilization and packaging and not by the fermentation process. Such proteins are preferentially produced by classical mammalian cell culture systems. Concerns which have to be addressed with respect to drug safety in the transgenic animal approach are the size of the herd, genetic stability from animal to animal, variation in productivity and in impurity profiles during lactation periods, microbial, viral, mycoplasma and prion contaminants, the dependence on health status and the life span of the animal. In a number of cases glycosylation of the protein is relevant for the prevention of immunogenicity of the protein, the pharmacological activity, the pharmacokinetic profile, solubility and stability against proteolysis. The glycosylation pattern, depending on protein structure, is influenced by the enzymatic system of the host cell as well as by fermentation conditions. Therefore, selection of host cells and culture conditions must take into account the requirement for a specific and stable glycosylation pattern. For the assessment of glycovariants, a number of protein analytical methods such as peptide mapping, isoelectric focusing, oligosaccharide mapping, MALDI-TOF (matrix assisted laser desorption mass spectrometry-time of flight), capillary electrophoresis and specific potency assays are available. In our experiments, glycosylation of proteins expressed in CHO cells was demonstrated to be very stable. Only extreme process times, cultivation methods and ammonium ion concentrations had an influence on the glycosylation profile. Among the three products investigated--tissue plasminogen activator (t-PA), interferon omega and soluble intercellular adhesion molecule (s-ICAM)--t-PA expressed the most stable glycosylation pattern. Only at extreme ammonium concentrations an increase of mannose-5 structures was observed, whereas biantennary complex structures were reduced. On the other hand, interferon omega and s-ICAM showed greater susceptibility to increased ammonium concentrations and to adherent cultivation. Such conditions induced quantitative changes to the glycosylation pattern favoring the appearance of higher branched structures. Short cultivation times resulted in more heterogenous oligosaccharide structures. Since the glycosylation of the three proteins is different in the same host cell, the amino acid sequence of the protein apparently influences the glycosylation pattern and its sensitivity to culture conditions. In NSO-mouse myeloma cells, production of s-ICAM is two times as high as in CHO cells
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PMID:Appropriate mammalian expression systems for biopharmaceuticals. 974 18

Poly(ethylene glycol)s (PEGs) are potential drug carriers for improving the therapeutic index of anticancer agents. In this work, the anticancer drug methotrexate (MTX) was activated with N,N'-dicyclohexylcarbodiimide (DCC) and coupled to amino group bearing PEGs of MW 750, 2000, 5000, 10 000, 20,000, and 40,000. First, the activation process of MTX with DCC in the presence and absence of N-hydroxysuccinimide was analyzed through HPLC. Preincubation of methotrexate with DCC alone at 0 degrees C proved to be favorable with respect to the amount of activated species and the formation of byproducts. MTX-PEG conjugates were synthesized according to this procedure, isolated through size-exclusion chromatography, and characterized through analytical HPLC, MALDI-TOF spectrometry, and gel permeation chromatography. In a cell-free assay, all of the drug polymer conjugates inhibited the target enzyme of MTX, dihydrofolate reductase (DHFR), to a similar extent, but were not as active as free MTX. Additionally, incubation of the MTX-PEG40000 conjugate for 6 days at 37 degrees C in phosphate buffered saline (pH 7.4), in cell-conditioned medium, or in human serum revealed no significant release of methotrexate. These results, taken together, indicate that release of MTX from polymer conjugates is not necessary for an effective interaction with the active site of dihydrofolate reductase. Evaluation of the in vitro cytotoxicity of the MTX-PEG conjugates in two adherent and three suspension human tumor cell lines revealed that the IC(50) values of the tested compounds increased with the size of the drug-polymer conjugates. The most effective compound tested in these assays was the free drug MTX itself (IC(50) value ranging from approximately 0.01 to 0.05 microM), while the IC(50) values of the polymer conjugates were higher (IC(50) value for MTX-PEG750, 2000 and 5000: approximately 0.6-3 microM; for MTX-PEG10000 and 20000: approximately 2-7 microM; and for MTX-PEG40000: > 6 microM). Subsequently, MTX-PEG5000, MTX-PEG20000, and MTX-PEG40000 were evaluated in a human mesothelioma MSTO-211H xenograft model, and their antitumor effects were compared with free methotrexate and the albumin conjugate MTX-HSA, a conjugate that is currently in phase II clinical trials. In contrast to the in vitro results, the high molecular weight MTX-PEG conjugates exhibited the highest in vivo antitumor activity: At a dose of 40 and 80 mg/kg MTX-PEG5000 was less active than MTX at its optimal dose of 100 mg/kg; MTX-PEG20000 at a dose of 40 mg/kg showed antitumor efficacy comparable to MTX, but MTX-PEG40000 at a dose of 20 mg/kg was superior to MTX and demonstrated antitumor activity of the same order as MTX-HSA (20 mg/kg).
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PMID:Polyethylene glycol conjugates of methotrexate varying in their molecular weight from MW 750 to MW 40000: synthesis, characterization, and structure-activity relationships in vitro and in vivo. 1212 Nov 33

Increasing resistance, recrudescences, and treatment failure have led to the replacement of chloroquine with the combination of pyrimethamine (PYR) and sulfadoxine (SDX) as the first-line antimalarial drugs for treatment of uncomplicated Plasmodium falciparum malaria in several areas where this disease is endemic. The development of resistance to PYR-SDX is favored by incomplete treatment courses or by subtherapeutic levels in plasma. PYR-SDX resistance has been associated with several single-nucleotide polymorphisms (SNPs) in the P. falciparum dihydrofolate reductase (pfdhfr) and the P. falciparum dihydropteroate synthetase (pfdhps) genes. We have established assays based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) that conveniently allow the identification of SNPs associated with PYR resistance. Variants occurring at codon positions 16, 51, 59, and 108 of the pfdhfr gene were analyzed by MALDI-TOF MS in synthetic oligonucleotides to determine the detection threshold. In addition, 63 blood samples from subjects with P. falciparum parasitemia of various degrees were analyzed. The results were compared to those obtained by DNA sequencing of the respective gene fragment. The results of MALDI-TOF MS and DNA sequencing were consistent in 40 samples. In 23 samples two or three pfdhfr variants were detected by MALDI-TOF assays, whereas DNA-sequencing revealed one variant only. Simultaneous detection of two different mutations by biplex assays was, in principle, feasible. As demonstrated by the example of PYR resistance, MALDI-TOF MS allows for rapid and automated high-throughput assessment of drug sensitivity in P. falciparum malaria.
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PMID:Genotyping of Plasmodium falciparum pyrimethamine resistance by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry. 1474 96

Hydrogen atoms play a central role in many biochemical processes yet are difficult to visualize by x-ray crystallography. Spallation neutron sources provide a new arena for protein crystallography with TOF measurements enhancing data collection efficiency and allowing hydrogen atoms to be located in smaller crystals of larger biological macromolecules. Here we report a 2.2-A resolution neutron structure of Escherichia coli dihydrofolate reductase (DHFR) in complex with methotrexate (MTX). Neutron data were collected on a 0.3-mm(3) D(2)O-soaked crystal at the Los Alamos Neutron Scattering Center. This study provides an example of using spallation neutrons to study protein dynamics, to identify protonation states directly from nuclear density maps, and to analyze solvent structure. Our structure reveals that the occluded loop conformation [monomer (mon.) A] of the DHFR.MTX complex undergoes greater H/D exchange compared with the closed-loop conformer (mon. B), partly because the Met-20 and beta(F-G) loops readily exchange in mon. A. The eight-stranded beta sheet of both DHFR molecules resists H/D exchange more than the helices and loops. However, the C-terminal strand, betaH, in mon. A is almost fully exchanged. Several D(2)Os form hydrogen bonds with exchanged amides. At the active site, the N1 atom of MTX is protonated and thus charged when bound to DHFR. Several D(2)Os are observed at hydrophobic surfaces, including two pockets near the MTX-binding site. A previously unidentified D(2)O hydrogen bonds with the catalytic D27 in mon. B, stabilizing its negative charge.
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PMID:Neutron diffraction studies of Escherichia coli dihydrofolate reductase complexed with methotrexate. 1713 Apr 56

Chinese hamster ovary (CHO) cells are the major mammalian host for producing various therapeutic proteins. Among CHO cells, the dihydrofolate reductase-deficient CHO DG44 cell line has been used as a popular mammalian host because of the availability of a well-characterized genetic selection and amplification system. However, this cell line has not been studied at the proteome level. Here, the first detailed proteome analysis of the CHO DG44 cell line is described. A protein reference map of the CHO DG44 cell line was established by analyzing whole cellular proteins using 2-DE with various immobilized pH gradients (pHs 3-10, 5-8, and 3-6) in the first dimension and a 12% acrylamide gel in the second dimension. The map is composed of over 1400 silver-stained protein spots. Among them, 179 protein spots, which represent proteins associated with various biological processes and cellular compartments, were identified based on MALDI-TOF-MS and MS/MS. This proteome database should be valuable for better understanding of CHO cell physiology and protein expression patterns which may lead to efficient therapeutic protein production.
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PMID:Protein reference mapping of dihydrofolate reductase-deficient CHO DG44 cell lines using 2-dimensional electrophoresis. 2039 28

We studied on the proteomic characteristics of Toxoplasma gondii KI-1 tachyzoites which were originally isolated from a Korean patient, and compared with those of the well-known virulent RH strain using 2-dimensional electrophoresis (2-DE), mass spectrometry, and quantitative real-time PCR. Two-dimensional separation of the total proteins isolated from KI-1 tachyzoites revealed up to 150 spots, of which 121 were consistent with those of RH tachyzoites. Of the remaining 29 spots, 14 showed greater than 5-fold difference in density between the KI-1 and RH tachyzoites at a pH of 5.0-8.0. Among the 14 spots, 5 from the KI-1 isolate and 7 from the RH strain were identified using MALDI-TOF mass spectrometry and database searches. The spots from the KI-1 tachyzoites were dense granule proteins (GRA 2, 3, 6, and 7), hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGRPTase), and uracil phosphoribosyltransferase (UPRTase). The spots from the RH strain were surface antigen 1 (SAG 1), L-lactate dehydrogenase (LDH), actin, chorismate synthase, peroximal catalase, hexokinase, bifunctional dihydrofolate reductase-thymidylate synthase (DHTR-TS), and nucleoside-triphosphatases (NTPases). Quantitative real-time PCR supported our mass spectrometric results by showing the elevated expression of the genes encoding GRA 2, 3, and 6 and UPRTase in the KI-1 tachyzoites and those encoding GRA 7, SAG 1, NTPase, and chorismate synthase in the RH tachyzoites. These observations demonstrate that the protein compositions of KI-1 and RH tachyzoites are similar but differential protein expression is involved in virulence.
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PMID:Proteomic analysis of Toxoplasma gondii KI-1 tachyzoites. 2087 97

Therapeutic glycoprotein drugs require a high degree of sialylation of their N-glycans for a better circulatory half-life that results in greater efficacy. It has been demonstrated that Chinese hamster ovary (CHO) glycosylation mutants lacking N-acetylglucosaminyltransferase I (GnT I), when restored by introduction of a functional GnT I, produced highly sialylated erythropoietin (EPO). We have now further engineered one of such mutants, JW152, by inactivating the dihydrofolate reductase (DHFR) gene to allow for the amplification of the EPO gene with methotrexate (MTX). Several MTX-amplified clones maintained the ability to produce highly sialylated EPO and one was selected for culture in a perfusion bioreactor that is used in an existing industrial EPO-production bioprocess. Extensive characterization of the EPO produced was performed using total sialic quantification, HPAEC-PAD and MALDI-TOF MS analyses. Our results demonstrated that the EPO produced by the mutant line exhibits superior sialylation compared to the commercially used EPO-producing CHO clone cultured under the same conditions. Therefore, this mutant has the industrial potential for producing highly sialylated recombinant EPO and potentially other recombinant glycoprotein therapeutics.
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PMID:Highly sialylated recombinant human erythropoietin production in large-scale perfusion bioreactor utilizing CHO-gmt4 (JW152) with restored GnT I function. 2491 84