Dihydrofolate reductase antagonists

Phospholipids, 19 (1982) 111 Photodecomposition of drugs, 27 (1990) 51 Plasmodium, 43 (2005) 190 Plasmodium flaciparum dihydrofolate reductase (PfDHFR), 43 (2005) 226 Platelet-aggregating factor, antagonists, 27 (1990) 325... 

Folic acid antagonist inhibits dihydrofolate reductase (DHFR) blocks reduction of folate to tetrahydrofolate inhibits de novo purine synthesis results in arrest of DNA, RNA, and protein synthesis... 

Drug efficacy is directly related to its intracellular concentration level, so it is necessary to evaluate the MTX concentration in cells. In particular, MTX is a folate antagonist, thus it binds to dihydrofolate reductase in competition with folate [71-77]. A low intracellular level of MTX caused by high efflux and low uptake in resistant cells is also the main disadvantage of MTX medication [78,79]. This leads to a high dosage of MTX for cancer treatment, which is also directly associated with adverse effects. 

E. A. An affinity selection-mass spectrometry method for the identification of small molecule ligands from self-encoded combinatorial libraries, discovery of a novel antagonist of E. coli dihydrofolate reductase. Int. J. Mass. Spectrom. 2004, 238, 77-83. 

These are pyrimidine derivatives and are effective because of differences in susceptibility between the enzymes in humans and in the infective organism. Anticancer agents based on folic acid, e.g. methotrexate, inhibit dihydrofolate reductase, but they are less selective than the antimicrobial agents and rely on a stronger binding to the enzyme than the natural substrate has. They also block pyrimidine biosynthesis. Methotrexate treatment is potentially lethal to the patient, and is usually followed by rescue with folinic acid (A -formyl-tetrahydrofolic acid) to counteract the folate-antagonist action. The rationale is that folinic acid rescues normal cells more effectively than it does tumour cells. 

Pharmacology Leucovorin is one of several active, chemically reduced derivatives of folic acid. It is useful as an antidote to drugs that act as folic acid antagonists. Administration of leucovorin can counteract the therapeutic and toxic effects of folic acid antagonists such as methotrexate, which act by inhibiting dihydrofolate reductase. 

Pharmacology Trimetrexate, a 2.4-diaminoquinazoline, nonclassical folate antagonist, is a synthetic inhibitor of the enzyme dihydrofolate reductase. The end result is disruption of DNA, RNA, and protein synthesis, with consequent cell death. Pharmacokinetics Clearance was 38 15 ml /min/m and volume of distribution at steady state (Vdgs) was 20 8 L/m. The plasma concentration time profile declined... 

Trimethoprim (TMP)-Sulfamethmazole (SMX) [Co-Trimoxazole] (Bactrim, Septra) [Antibiotic/Folate Antagonist] Uses un Rx prophylaxis, otitis media, sinusitis, bronchitis Action SMX T synth of dihydro-folic acid TMP T dihydrofolate reductase to impair protein synth Dose Adul. 1 DS tab PO bid or 5-20 mg/kg/24 h (based on TMP) IV in 3-4 doses P. jiroveci ... 

Mechanism of Action A folate antagonist that inhibits the enzyme dihydrofolate reductase (DHFR). Therapeutic Effect Disrupts purine, DNA, RNA, protein synthesis,... 

Folic Acid Antagonists. Folic acid antagonists block the biosynthesis of purine nucleotides. Methotrexate (7.76) is the prototypic fohc acid antagonist and functions by binding to the active catalytic site of dihydrofolate reductase, thereby interfering with the synthesis of the reduced form that accepts one-carbon units lack of this cofactor blocks the synthesis of purine nucleotides. As well as being used in the treatment of cancer, methotrexate has been used in the management of rheumatoid arthritis, psoriasis, and even asthma. 

The other major class of antimalarials are the folate synthesis antagonists. There is a considerable difference in the drug sensitivity and affinity of dihydrofolate reductase enzyme (DHFR) between humans and the Plasmodium parasite. The parasite can therefore be eliminated successfully without excessive toxic effects to the human host. DHFR inhibitors block the reaction that transforms deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) at the end of the pyrimidine-synthetic pathway. This reaction, a methylation, requires N °-methylene-tetrahydrofolate as a carbon carrier, which is oxidized to dihydrofolate. If the dihydrofolate cannot then be reduced back to tetrahydrofolate (THF), this essential step in DNA synthesis will come to a standstill. 

It is used as leucovorin calcium (calcium folinate). It is 5-formyl derivative of tetrahydrofolic acid and it acts as an antidote to folic acid antagonists like methotrexate or pyrimethamine which inhibit the enzyme dihydrofolate reductase. 

The main folate antagonist is methotrexate, an analogue of folic acid. Methotrexate competitively inhibits dihydrofolate reductase, the enzyme responsible for the synthesis of purine and pyramidine from folic acid. Trimetrexate, a methotrexate analogue, is useful in treating methotrexate-resistant tumours. It is also used to treat Pneumocystis carinii infections. Methotrexate is usually given orally, but may also be given intravenously or intrathecally. In addition to its use in cancer therapy, it is used in the treatment of psoriasis. Methotrexate can cause an obstructive nephropathy due to its precipitation in the renal calyx. 

In many areas, resistance to folate antagonists and sulfonamides is common for P falciparum and less common for P vlvax. Resistance is due primarily to mutations in dihydrofolate reductase and dihydropteroate synthase, with increasing numbers of mutations leading to increasing levels of resistance. At present, resistance seriously limits the efficacy of sulfadoxine-pyrimethamine (Fansidar) for the treatment of malaria in most areas, but in Africa most parasites exhibit only moderate resistance, such that antifolates appear to continue to offer preventive efficacy against malaria. Because different mutations may mediate resistance to different agents, cross-resistance is not uniformly seen. 

Methotrexate (Amethopterin) is a folic acid antagonist that binds to dihydrofolate reductase, thus interfering with the synthesis of the active cofactor tetrahydrofolic acid, which is necessary for the synthesis of thymidylate, purine nucleotides, and the amino acids serine and methionine. 

Annis D.A., Athanasopoulos J., Curran P.J., Felsch J.S., Kalghatgi K., Lee W.H., Nash H.M., Orminati J.P.A., Rosner K.E., Shipps GW., Thaddupathy G.R.A., Tyler A.N., Vilenchik L., Wagner C.R., Wintner E.A., An affinity selection-mass spectrometry method for the identification of small molecule ligands from self-encoded combinatorial libraries. Discovery of a novel antagonist of E. coli dihydrofolate reductase Int. J. Mass Spectrom. 2004, 238, 77-83. 

Methotrexate is a folic acid antagonist, binding reversibly to dihydrofolate reductase. This prevents purine/pyrimidine biosynthesis and DNA synthesis.3... 

Another way to reduce the supply of deoxynucleotides for cell replication is to target the reduction of dihydrofolate to tetrahydrofo-late. Folate antagonists are used in antimicrobial and anticancer chemotherapy. These compounds are competitive inhibitors of dihydrofolate reductase because they resemble the natural substrate. For example, methotrexate is used in antitumor therapy. 

Folate antagonists can be overcome by increasing the amount of dihydrofolate reductase in the tumor cells. These resistant cells increase the amount of the enzyme by amplifying the DNA sequence encoding the enzyme. More copies of the gene make more molecules of enzyme. You can understand this by remembering that the Michaelis-Menten equation gives the velocity of an enzyme. 

Methotrexate, for example, a folic acid antagonist, competitively inhibits dihydrofolate reductase, preventing the synthesis of tetrahydrofolic acid (the coenzyme that is important in synthesis of amino and nucleic acids). This drug also provides a cogent illustration of the need to exploit every possible... 

Methotrexate is an antagonist of folic acid and is used for treating neoplastic diseases and non-neoplastic diseases such as rheumatoid arthritis and psoriasis. As methotrexate reduces the activity of dihydrofolate reductase, supplementation with folic acid and especially with folinic acid could reduce the beneficial effects of methotrexate. This assumption has been supported by the results of an intervention study (40). Patients with rheumatoid arthritis treated with methotrexate (15 g/week) had an increase in symptoms. An open intervention trial of folinic acid 45 mg/week also showed an increase in arthritis symptoms (41). However, other trials showed no effects of this sort, and administration of folic acid or folinic acid is important in preventing methotrexate-induced blood dyscrasias. 

Methotrexate is a foUc acid antagonist that acts by inhibiting dihydrofolate reductase. Owing to its immunosuppressive and anti-inflammatory properties, low-dosage methotrexate (7.5-15 mg/week) has been extensively investigated for other therapeutic purposes characterized by inflammation or cellular proliferation. Since the mid-... 

Methotrexate, a folic acid antagonist, is used in the treatment of several disorders. Its major action is inhibition of dihydrofolate reductase, a critical enzyme in intracellular folate metabolism. Co-trimoxazole competes with methotrexate in inhibiting dihydrofolate reductase and further impairs DNA synthesis. 

Methotrexate is a folic acid antagonist that inhibits the enzyme dihydrofolate reductase. This agent is mainly used in the treatment of both cancer [trophoblastic neoplasms, leukemias, breast carcinoma, carcinoma of gastric, esophagus, testes, lymphomas] and non-cancer diseases [psoriasis rheumatoid arthritis]. Recent successful results using high-dose [>lg/ m ] methotrexate followed by leucoverin in the treatment of head and neck carcinomas and osteosarcoma has led to a more widespread use of this therapy in patients with these and other tumors. 

DIHYDROFOLATE REDUCTASE INHIBITORS have as a target the enzyme dihydrofolate reductase, and are known as folate antagonists. These include anttcancer agents ( antimetabolites ) such as methotrexate, antibacterial AGENTS such as trimethoprim, and the antiprotozoals pyrimethamine and proguanil (which are used to treat malaria). Folate is required for synthesis of purine nucleotides, which in turn are essential for DNA synthesis and cell division. In mammals it is necessary to convert body folates, through two separate enzyme-catalysed reduction... 

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