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Antimicrobial Agents and Chemotherapy Nov 2000Dihydrofolate reductase (DHFR) is the target of trimethoprim (TMP), which has been widely used in combination with sulfa drugs for treatment and prophylaxis of...
Dihydrofolate reductase (DHFR) is the target of trimethoprim (TMP), which has been widely used in combination with sulfa drugs for treatment and prophylaxis of Pneumocystis carinii pneumonia. While the rat-derived P. carinii DHFR has been well characterized, kinetic studies of human-derived P. carinii DHFR, which differs from rat-derived P. carinii DHFR by 38% in amino acid sequence, have not been reported to date. Here we report on the expression and kinetic characterization of the recombinant human-derived P. carinii DHFR. The 618-bp coding sequence of the human-derived P. carinii DHFR gene was expressed in Escherichia coli. As determined by sodium dodecyl sulfate-polyacrylamide gel eletrophoresis, the purified enzyme had a molecular mass of 25 kDa, consistent with that predicted from the DNA sequence. Kinetic analysis showed that the K(m) values for dihydrofolate and NADPH were 2.7 +/- 0.3 and 14.0 +/- 4.3 microM, respectively, which are similar to those reported for rat-derived P. carinii DHFR. Inhibition studies revealed that both TMP and pyrimethamine were poor inhibitors of human-derived P. carinii DHFR, with K(i) values of 0.28 +/- 0.08 and 0.065 +/- 0.005 microM, respectively, while trimetrexate and methotrexate were potent inhibitors, with K(i) values of 0.23 +/- 0.03 and 0.016 +/- 0.004 nM, respectively. The availability of purified recombinant enzyme in large quantities should facilitate the identification of antifolate inhibitors with greater potency and higher selectivity for human-derived P. carinii DHFR.
Topics: Binding, Competitive; Catalysis; Escherichia coli; Folic Acid Antagonists; Humans; Inhibitory Concentration 50; Kinetics; Pneumocystis; Polymerase Chain Reaction; Recombinant Proteins; Tetrahydrofolate Dehydrogenase; Transfection
PubMed: 11036028
DOI: 10.1128/AAC.44.11.3092-3096.2000 -
The Journal of Biological Chemistry Feb 1993We describe the characterization of an antitumor drug resistance following multiple step selection of hamster cells to the 2,4-diaminopyrimidines (DAP) metoprine,...
We describe the characterization of an antitumor drug resistance following multiple step selection of hamster cells to the 2,4-diaminopyrimidines (DAP) metoprine, pyrimethamine (Pyr), and trimethoprim (Tmp). Pyr and Tmp are DAP lipophilic antifolates currently used as antiparasitic and antibacterial antibiotics, respectively. Dihydrofolate reductase (DHFR) from hamster cells bore a low or poor affinity to these DAP as compared to the hydrophilic folate antagonist methotrexate (MTX). Metoprine-resistant cells over-expressed DHFR enzyme and consequently displayed a high level of resistance to both hydrophilic and lipophilic antifolates including DAP but maintained wild type sensitivity to pleiotropic drugs involved in multi-drug resistance (MDR). In contrast, although Pyr- and Tmp-resistant cells expressed parental levels of wild type DHFR, they displayed a high degree of resistance to DAP and, surprisingly, to the lipophilic MTX analogs piritrexim (PTX) and trimetrexate (TMTX), while maintaining sensitivity to MTX. These drug-resistant cells maintained wild type mRNA levels of the MDR gene product P-glycoprotein and showed collateral hypersensitivity to pleiotropic drugs. To study the underlying mechanism of this apparently new resistance phenotype, we have employed fluorescein-methotrexate (F-MTX) labeling of cells and its displacement by different antifolates. Parental AA8 and Pyr-resistant cells showed a similar level of F-MTX labeling, however, while DAP, TMTX, and PTX showed an efficient competitive displacement of F-MTX from AA8 cells, Pyr-resistant cells displayed a persistent retention of F-MTX labeling in the presence of high concentrations of these lipophilic antifolates. Pyr-resistant cells showed a wild type displacement of F-MTX with MTX. This DAP resistance phenotype was unstable as it was rapidly lost upon growth under nonselective conditions. Furthermore, when the antifolate resistance levels of Pyr-resistant cells were plotted versus the ratios of the 50% F-MTX displacement values obtained with resistant and parental AA8 cells, a good correlation (r2 > 0.98) was obtained. We conclude that Pyr-resistant cells possess a novel phenotype that derives its resistance to lipophilic antifolates solely from a predominant decrease in the accumulation of DAP and lipid-soluble analogs of MTX.
Topics: Animals; CHO Cells; Cell Survival; Cricetinae; Drug Resistance; Flow Cytometry; Folic Acid Antagonists; Leucovorin; Pyrimethamine; RNA, Messenger; Tetrahydrofolate Dehydrogenase; Trimethoprim
PubMed: 8440739
DOI: No ID Found -
Biochemistry Feb 2016Mycobacterium tuberculosis (Mtb) Rv2671 is annotated as a 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5'-phosphate (AROPP) reductase (RibD) in the riboflavin...
Mycobacterium tuberculosis (Mtb) Rv2671 is annotated as a 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5'-phosphate (AROPP) reductase (RibD) in the riboflavin biosynthetic pathway. Recently, a strain of Mtb with a mutation in the 5' untranslated region of Rv2671, which resulted in its overexpression, was found to be resistant to dihydrofolate reductase (DHFR) inhibitors including the anti-Mtb drug para-aminosalicylic acid (PAS). In this study, a biochemical analysis of Rv2671 showed that it was able to catalyze the reduction of dihydrofolate (DHF) to tetrahydrofolate (THF), which explained why the overexpression of Rv2671 was sufficient to confer PAS resistance. We solved the structure of Rv2671 in complex with the NADP(+) and tetrahydrofolate (THF), which revealed the structural basis for the DHFR activity. The structures of Rv2671 complexed with two DHFR inhibitors, trimethoprim and trimetrexate, provided additional details of the substrate binding pocket and elucidated the differences between their inhibitory activities. Finally, Rv2671 was unable to catalyze the reduction of AROPP, which indicated that Rv2671 and its closely related orthologues are not involved in riboflavin biosynthesis.
Topics: Aminosalicylic Acid; Antitubercular Agents; Bacterial Proteins; Catalytic Domain; Drug Resistance, Bacterial; Enzyme Inhibitors; Folic Acid Antagonists; Kinetics; Ligands; Models, Molecular; Molecular Conformation; Mycobacterium tuberculosis; NADP; Nucleotide Deaminases; Phylogeny; Recombinant Proteins; Tetrahydrofolate Dehydrogenase; Tetrahydrofolates; Trimethoprim; Trimetrexate
PubMed: 26848874
DOI: 10.1021/acs.biochem.5b00993 -
The Journal of Clinical Investigation Feb 1987Trimetrexate, a highly lipid-soluble quinazoline antifolate now undergoing trials as an anticancer agent, was found to be a potent inhibitor of the dihydrofolate...
Trimetrexate, a highly lipid-soluble quinazoline antifolate now undergoing trials as an anticancer agent, was found to be a potent inhibitor of the dihydrofolate reductase (DHFR) isolated from Toxoplasma gondii. The concentration required for 50% inhibition of protozoal DHFR was 1.4 nM. As an inhibitor of this enzyme, trimetrexate was almost 600-fold (amount of antifolate required to inhibit catalytic reaction by 50%) and 750-fold (inhibition constant) more potent than pyrimethamine, the DHFR inhibitor currently used to treat toxoplasma infection. When the protozoan was incubated with 1 microM trimetrexate, the drug rapidly reached high intracellular concentrations. Since toxoplasma organisms lack a transmembrane transport system for physiologic folates, host toxicity can be prevented by co-administration of the reduced folate, leucovorin, without reversing the antiprotozoal effect. The effectiveness of trimetrexate against toxoplasma was demonstrated both in vitro and vivo. Proliferation of toxoplasma in murine macrophages in vitro was completely inhibited by exposure of these cells to 10(-7) M trimetrexate for 18 h. When used alone, trimetrexate was able to extend the survival of T. gondii-infected mice.
Topics: Animals; Folic Acid Antagonists; Kinetics; Lacticaseibacillus casei; Mice; Mice, Inbred BALB C; Quinazolines; Solubility; Toxoplasma; Toxoplasmosis; Trimetrexate
PubMed: 2948969
DOI: 10.1172/JCI112837 -
Parasitology Research May 2008The folate derivatives folic acid (FA) and folinic acid (FNA) decrease the in vivo and in vitro activities of antifolate drugs in Plasmodium falciparum. However, the...
The folate derivatives folic acid (FA) and folinic acid (FNA) decrease the in vivo and in vitro activities of antifolate drugs in Plasmodium falciparum. However, the effects of 5-methyl-tetrahydrofolate (5-Me-THF) and tetrahydrofolate (THF), the two dominant circulating folate forms in humans, have not been explored yet. We have investigated the effects of FA, FNA, 5-Me-THF, and THF on the in vitro activity of the antimalarial antifolates pyrimethamine and chlorcycloguanil and the anticancer antifolates methotrexate (MTX), aminopterin, and trimetrexate (TMX), against P. falciparum. The results indicate that these anticancers are potent against P. falciparum, with IC50 < 50 nM. 5-Me-THF does not significantly decrease the activity of all tested drugs, and none of the tested folate derivatives significantly decrease the activity of these anticancers. Thus, malaria folate metabolism has features different from those in human, and the exploitation of this difference could lead to the discovery of new drugs to treat malaria. For instance, the combination of 5-Me-THF with a low dose of TMX could be used to treat malaria. In addition, the safety of a low dose of MTX in the treatment of arthritis indicates that this drug could be used alone to treat malaria.
Topics: Aminopterin; Animals; Antimalarials; Antineoplastic Agents; Folic Acid; Folic Acid Antagonists; Inhibitory Concentration 50; Leucovorin; Methotrexate; Molecular Structure; Plasmodium falciparum; Proguanil; Pyrimethamine; Tetrahydrofolates; Triazines; Trimetrexate
PubMed: 18259776
DOI: 10.1007/s00436-008-0897-4 -
International Journal of Cancer Jul 1999Various gene alterations are involved in the drug resistance of leukemia cells. To understand the mechanism that underlies the emergence of cells with such gene...
Various gene alterations are involved in the drug resistance of leukemia cells. To understand the mechanism that underlies the emergence of cells with such gene alterations in human leukemia, we performed clonal analysis of the gene expression of mutant dihydrofolate reductase (DHFR) and mdr1 in trimetrexate-resistant human leukemia MOLT-3 cells. Trimetrexate-resistant (70- and 60-fold) sublines were developed in the presence or absence of an exogenous supply of thymidine (MOLT-3/TMQ70/Th+, MOLT-3/TMQ60/Th-, respectively). Ten clonal lines were isolated by methyl cellulose cloning from each of the 2 trimetrexate-resistant MOLT-3 sublines. All the clonal lines from the 2 sublines expressed mutated DHFR mRNA, with a base change (T --> C) at the second position of codon 31, as well as the wild-type mRNA, in accordance with cross-resistance to methotrexate. On the other hand, mdr1 mRNA expression was demonstrated by reverse-transcription polymerase chain reaction only in clonal lines from MOLT-3/TMQ70/Th+ cells. mdr1 mRNA expression in clonal lines from MOLT-3/TMQ70/Th+ cells and subclonal lines subsequently obtained from the 3 clonal lines with different mdr1 mRNA expression levels was heterogeneous, and its high expression levels were correlated with acquisition of the multidrug resistance (MDR) phenotype. Polymerase chain reaction-based assay for separate microsatellites, mfd27 and mfd41, demonstrated genomic instability among clonal and subclonal lines of MOLT-3. The clonal analysis of polymorphic microsatellites also suggested that emergence of MDR in trimetrexate-resistant MOLT-3 cells in thymidine was not only heterogeneous but also progressively expanding among clones. Genomic instability may play a role in the establishment and clonal evolution of drug resistance in leukemia cells.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Antimetabolites, Antineoplastic; Drug Resistance, Neoplasm; Humans; Leukemia; Microsatellite Repeats; RNA, Messenger; Tetrahydrofolate Dehydrogenase; Thymidine; Trimetrexate; Tumor Cells, Cultured
PubMed: 10360822
DOI: 10.1002/(sici)1097-0215(19990702)82:1<63::aid-ijc12>3.0.co;2-2 -
The Journal of Biological Chemistry Jan 1987This report describes studies designed to evaluate possible inhibitory effects of diaminoantifolates on folate-dependent biosynthetic enzymes in intact L1210 leukemia...
This report describes studies designed to evaluate possible inhibitory effects of diaminoantifolates on folate-dependent biosynthetic enzymes in intact L1210 leukemia cells. A novel approach is described which involves an assessment of the metabolism of and biosynthetic flux of the one-carbon moiety from (6S)5-formyltetrahydrofolate in folate-depleted cells. Pretreatment with methotrexate (10 microM), resulting in the formation of methotrexate polyglutamates, or continuous incubation with trimetrexate (1 microM) inhibited growth of folate-depleted L1210 cells in the presence of folic acid or 5-formyltetrahydrolate. In both control and drug-treated cells, double-labeled (6S)-5-[14C]formyl[3H]tetrahydrofolate was rapidly metabolized with the loss of the [14C]formyl group. Under all conditions, the predominant metabolite was 10-formyl[3H]tetrahydrofolate, detectable both intracellularly and extracellularly. In drug-treated cells, there was a remarkably small decrease in the level of 10-formyl[3H]tetrahydrofolate (approximately 30%) and a 10-fold rise in the level of [3H]dihydrofolate to less than 20% of the total folate pool. The incorporation of [14C]formyl group from 5-[14C]formyltetrahydrofolate into thymidylate, serine, and methionine was unaffected by the presence of 1 microM trimetrexate, consistent with the generation of sufficient 5,10-[14C]methylenetetrahydrofolate to drive these reactions. Similarly, the presence of methotrexate polyglutamates had no effect at the level of amino acid synthesis; however, carbon transfer into thymidylate was markedly inhibited. Even though 10-formyltetrahydrofolate was readily formed from 5-formyltetrahydrofolate in this model, the net incorporation of 14C from 5-[14C]formyltetrahydrofolate into purine nucleotides was inhibited by both methotrexate and trimetrexate treatments. Similar findings were obtained when [14C]glycine incorporation into purine nucleotides was monitored in cells incubated with unlabeled 5-formyltetrahydrofolate. Finally, in antifolate-treated cells incubated with unlabeled 5-formyl-tetrahydrofolate, transfer of 14C from [14C]formate or [14C]serine into biosynthetic products or incorporation of [3H]deoxyuridine into nucleic acids was potently inhibited. These results suggest that insufficient levels of tetrahydrofolate and 5, 10-methylenetetrahydrofolate were formed to drive these reactions despite the presence of high levels of 10-formyltetrahydrofolate.(ABSTRACT TRUNCATED AT 400 WORDS)
Topics: Adenosine; Animals; Cell Division; Floxuridine; Folic Acid; Kinetics; Leucovorin; Leukemia L1210; Mice; Thymidine
PubMed: 2948949
DOI: No ID Found -
Antimicrobial Agents and Chemotherapy Apr 1990In summary, recent advances in our ability to diagnose, treat, and prevent recurrences of pneumocystis pneumonia have significantly improved the clinical management of... (Review)
Review
In summary, recent advances in our ability to diagnose, treat, and prevent recurrences of pneumocystis pneumonia have significantly improved the clinical management of this infection, especially in HIV-1-infected individuals. As current investigations allow our therapeutic armamentarium in this disease to be strengthened even further, it is likely that pneumocystis pneumonia will pose a diminishing threat to those patients currently most susceptible to this infection.
Topics: Acquired Immunodeficiency Syndrome; Antineoplastic Agents; Humans; Opportunistic Infections; Pneumonia, Pneumocystis; Quinazolines; Trimethoprim, Sulfamethoxazole Drug Combination; Trimetrexate
PubMed: 2140495
DOI: 10.1128/AAC.34.4.499 -
The Journal of Biological Chemistry Mar 1992We have studied the discrepancy in the degree of methotrexate (MTX) resistance that exists between two clonal cell lines, mouse 3T6 R50 cells and Chinese hamster ovary...
We have studied the discrepancy in the degree of methotrexate (MTX) resistance that exists between two clonal cell lines, mouse 3T6 R50 cells and Chinese hamster ovary B11 0.5 cells that overexpress comparable levels of dihydrofolate reductase, yet exhibit a 100-fold difference in MTX resistance while maintaining similar sensitivity to the lipophilic antifolates trimetrexate and piritrexim. These data suggested that R50 cells may possess additional mechanism(s) of antifolate resistance, such as MTX transport alteration. Flow cytometric analysis using fluorescein methotrexate revealed comparable levels of fluorescein MTX displacement with lipophilic antifolates in viable R50 and B11 0.5 cells, but marked insensitivity of R50 cells to MTX competition, thus suggesting a poor uptake of MTX into R50 cells. Analysis of the kinetic parameters of dihydrofolate reductase from R50 cells neither showed alterations in enzyme affinities for various antifolates nor in the Michaelis constant for folic acid and NADPH nor a change in the pH activity optimum. R50 cell-free extracts contained wild-type levels of folylpoly-gamma-glutamyl synthetase activity. However, following metabolic labeling with [3H]MTX, no MTX polyglutamates could be detected in R50 cells. We conclude that the high level of MTX resistance in R50 cells is multifactorial, including overexpression of dihydrofolate reductase, reduced MTX transport, and possibly altered formation of MTX polyglutamates. The potential interactions between the different modalities of MTX resistance in R50 cells are being discussed.
Topics: Animals; Blotting, Northern; Blotting, Southern; CHO Cells; Cell Line; Cell Survival; Clone Cells; Cricetinae; DNA; Dose-Response Relationship, Drug; Drug Resistance; Electrophoresis, Gel, Two-Dimensional; Fibroblasts; Flow Cytometry; Folic Acid Antagonists; Hydrogen-Ion Concentration; Methotrexate; Mice; Protein Biosynthesis; Proteins; Pyrimidines; RNA; Tetrahydrofolate Dehydrogenase; Thymidylate Synthase; Trimetrexate
PubMed: 1372892
DOI: No ID Found -
The Journal of Biological Chemistry Dec 2019The endoplasmic reticulum-associated degradation (ERAD) pathway mediates the endoplasmic reticulum-to-cytosol retrotranslocation of defective proteins through protein...
The endoplasmic reticulum-associated degradation (ERAD) pathway mediates the endoplasmic reticulum-to-cytosol retrotranslocation of defective proteins through protein complexes called retrotranslocons. Defective proteins usually have complex conformations and topologies, and it is unclear how ERAD can thread these conformationally diverse protein substrates through the retrotranslocons. Here, we investigated the substrate conformation flexibility necessary for transport via retrotranslocons on the ERAD-L, ERAD-M, and HIV-encoded protein Vpu-hijacked ERAD branches. To this end, we appended various ERAD substrates with specific domains whose conformations were tunable in flexibility or tightness by binding to appropriate ligands. With this technique, we could define the capacity of specific retrotranslocons in disentangling very tight, less tight but well-folded, and unstructured conformations. The Hrd1 complex, the retrotranslocon on the ERAD-L branch, permitted the passage of substrates with a proteinase K-resistant tight conformation, whereas the E3 ligase gp78-mediated ERAD-M allowed passage only of nearly completely disordered but not well-folded substrates and thus may have the least unfoldase activity. Vpu-mediated ERAD, containing a potential retrotranslocon, could unfold well-folded substrates for successful retrotranslocation. However, substrate retrotranslocation in Vpu-mediated ERAD was blocked by enhanced conformational tightness of the substrate. On the basis of these findings, we propose a mechanism underlying polypeptide movement through the endoplasmic reticulum membrane. We anticipate that our biochemical system paves the way for identifying the factors necessary for the retrotranslocation of membrane proteins.
Topics: Endoplasmic Reticulum; Endoplasmic Reticulum-Associated Degradation; HEK293 Cells; Human Immunodeficiency Virus Proteins; Humans; Leupeptins; Proteasome Endopeptidase Complex; Protein Unfolding; Receptors, Autocrine Motility Factor; Substrate Specificity; Trimetrexate; Ubiquitin-Protein Ligases; Viral Regulatory and Accessory Proteins
PubMed: 31748412
DOI: 10.1074/jbc.RA119.010019