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)

2,4-Diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)-methyl]quinazoline (I) is a promising new "nonclassical" antifolate. Inhibition of dihydrofolate reductase from bacterial (Lactobacillus casei)and mammalian (beef liver) sources was employed to develop useful enzymatic assays for this compound. A linear relationship was obtained by plotting the I concentration versus 1/V. The resultant standard curves maintained linearity particularly well between the 30 and 70% control range, with a correlation coefficient of 0.99 for both enzyme systems. The two enzyme systems are characterized by differences in sensitivity, stability, and day-to-day variation. The ID50 for the beef liver reductase system was 1.6 X 10(-9) M (+/-0.03); for the L. casei system, it was 1.35 X 10(-8) M (+/- 0.2). The apparent advantage for the beef liver enzyme was offset somewhat by its relative instability and its higher day-to-day variability. Studies in mice demonstrated that these assays are suitable for pharmacokinetic studies in vivo. Such studies indicated that I has a serum t1/2 of 45 min in mice; a similar serum t1/2 (50 min) was estimated in studies with 14C-labeled I in position 6.
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PMID:Enzymatic assays for 2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline, a promising new "nonclassical" antifolate. 645 13

The pharmacology of trimetrexate (JB-11, NSC 249008, 2,4-diamino-5-methyl-5-[(3,4,5-trimethoxyanilino)methyl]quinazoline), an antitumor agent effective against several mouse tumors, was studied in normal dogs. A high-performance liquid chromatographic technique with electrochemical detection, dihydrofolate reductase inhibition assay, and 14C-labeled drug were used to measure plasma disappearance, tissue distribution, excretion, and metabolism of the drug at doses from 0.5 to 6 mg/kg. Doses of 2 mg/kg were well tolerated without toxicity. Higher doses (3 to 6 mg/kg) produced mainly intestinal toxicity without significant hematological or liver abnormalities. The 6-mg/kg dose caused severe bloody diarrhea. After administration of 3 mg/kg, plasma concentrations of trimetrexate were 1 microM and were equal to or greater than 0.1 microM at 1 and 24 hr, respectively. The predominant pharmacokinetics of trimetrexate plasma disappearance was an elimination phase with a t1/2 of 3.5 hr. Concentrations in the cerebrospinal fluid were 2 to 5% of that in plasma and were maximum within 1 to 2 hr after i.v. administration. Highest tissue concentrations of drug were measured in liver and kidney; lowest were found in brain and lung. A dose equivalent to 3 mg/kg in humans (on a sq m basis) should produce adequate plasma concentrations (greater than 0.1 microM) for therapeutic effects.
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PMID:Pharmacology and toxicity of a potent "nonclassical" 2,4-diamino quinazoline folate antagonist, trimetrexate, in normal dogs. 646 9

Inhibition by a variety of substituted triazines and quinazolines of a methotrexate-insensitive form of dihydrofolate reductase from highly MTX-resistant L5178Y mouse leukemia cells was examined. Some of these compounds were significantly more potent than MTX (up to 100-fold). Two triazenes, terminally substituted with benzenesulfonylfluoride residues, were approximately 30-fold more potent than MTX. Quinazoline analogs of folic acid with alterations in different parts of the molecule varied in their potencies as inhibitors. Although none of the compounds tested was as potent as MTX against MTX-sensitive dihydrofolate reductases, these studies show that some types of folate antagonists have increased specificity against this MTX-insensitive dihydrofolate reductase. This finding increases the likelihood that it may be possible to produce compounds with marked specificity for the insensitive reductase. Such compounds might have utility in antifolate combinations designed to overcome methotrexate resistance.
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PMID:Inhibition of a methotrexate-insensitive dihydrofolate reductase from L5178Y cells by substituted triazines and quinazolines. 683 39

Extensions are presented for the distance geometry approach to rationalizing ligand binding data. These are algorithms to (i) detect when homologues are not binding with the same orientation in the binding site although they are chemically similar; (ii) deduce what the binding site's size and shape must be; and (iii) calculate the optimal set of interaction energies between parts of the site and parts of the ligand molecules. This improved methodology is tested on a set of 68 quinazoline inhibitors of S. faecium dihydrofolate reductase. Results are discussed and compared with the Hansch method of QSAR, and an improved inhibitor is predicted.
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PMID:Quantitative structure-activity relationships by distance geometry: systematic analysis of dihydrofolate reductase inhibitors. 739 27

The transport properties and growth-inhibitory potential of 37 classic and novel antifolate compounds have been tested in vitro against human and murine cell lines expressing different levels of the reduced folate carrier (RFC), the membrane-associated folate binding protein (mFBP), or both. The intracellular targets of these drugs were dihydrofolate reductase (DHFR), glycinamide ribonucleotide transformylase (GARTF), folylpolyglutamate synthetase (FPGS), and thymidylate synthase (TS). Parameters that were investigated included the affinity of both folate-transport systems for the antifolate drugs, their growth-inhibitory potential as a function of cellular RFC/mFBP expression, and the protective effect of either FA or leucovorin against growth inhibition. Methotrexate, aminopterin, N10-propargyl-5,8-dideazafolic acid (CB3717), ZD1694, 5,8-dideazaisofolic acid (IAHQ), 5,10-dideazatetrahydrofolic acid (DDATHF), and 5-deazafolic acid (efficient substrate for FPGS) were used as the basic structures in the present study, from which modifications were introduced in the pteridine/quinazoline ring, the C9-N10 bridge, the benzoyl ring, and the glutamate side chain. It was observed that RFC exhibited an efficient substrate affinity for all analogues except CB3717, 2-NH2-ZD1694, and glutamate side-chain-modified FPGS inhibitors. Substitutions at the 2-position (e.g., 2-CH3) improved the RFC substrate affinity for methotrexate and aminopterin. Other good substrates included PT523 (N alpha-(4-amino-4-deoxypteroyl)-N delta-hemiphthaloyl-L-ornithine), 10-ethyl-10-deazaaminopterin, and DDATHF. With respect to mFBP, modifications at the N-3 and 4-oxo positions resulted in a substantial loss of binding affinity. Modifications at other sites of the molecule were well tolerated. Growth-inhibition studies identified a series of drugs that were preferentially transported via RFC (2,4-diamino structures) or mFBP (CB3717, 2-NH-ZD1694, or 5,8-dideazaisofolic acid), whereas other drugs were efficiently transported via both transport pathways (e.g., DDATHF, ZD1694, BW1843U89, or LY231514). Given the fact that for an increasing number of normal and neoplastic cells and tissue, different expression levels of RFC and mFBP are being recognized, this folate antagonist structure-activity relationship can be of value for predicting drug sensitivity and resistance of tumor cells or drug-related toxicity to normal cells and for the rational design and development of novel antifolates.
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PMID:Carrier- and receptor-mediated transport of folate antagonists targeting folate-dependent enzymes: correlates of molecular-structure and biological activity. 756 26

Ten heretofore undescribed 2,4-diamino-5-chloroquinazoline analogues of trimetrexate (TMQ) and piritrexim (PTX) were synthesized and tested as inhibitors of dihydrofolate reductase (DHFR) from rat liver, Pneumocystis carinii, and Toxoplasma gondii. The most active quinazolines against both the P. carinii and the T. gondii enzyme were those with an ArCH2-NH or ArNHCH2 side chain. Among ArNH(CH2)n compounds with n = 1-3 and either 2',5'-dimethoxyphenyl or 3',4',5'-trimethoxyphenyl as the Ar moiety, activity decreased in the order n = 1 > n = 2 > n = 3. The best inhibitor of P. carinii DHFR, 2,4-diamino-5-chloro-6-[(N-methyl-3',4',5'-trimethoxyanilino)methy l] quinazoline (10) had an IC50 of 0.012 microM and was slightly more potent than TMQ and PTX. Compound 10 was also the best inhibitor of T. gondii DHFR, with an IC50 of 0.0064 microM corresponding again to a minor increase in activity over TMQ and PTX. However, as with these standard agents, 10 showed no appreciable selectivity for either the P. carinii or T. gondii enzyme relative to the rat liver enzyme. The highest selectivity achieved in this limited series was with 2,4-diamino-5-chloro-6-[N-(3',4',5'-trimethoxybenzyl)-N-methylamino] quinazoline (17) against T. gondii DHFR. While 17 (IC50 = 0.016 microM) was somewhat less potent than 10, its selectivity, as defined by the ratio IC50(rat liver)/IC50(T. gondii) was ca. 30-fold higher than that of TMQ or PTX. Two compounds, 2,4-diamino-5-chloro-6-[(3',4',5'-trimethoxyanilino)methyl] quinazoline (9) and 2,4-diamino-5-chloro-6-[N-(3',4',5'-trimethoxybenzyl) amino]quinazoline (15), were also tested against human DHFR and were found to have an IC50/[E] of 0.5, indicating that their binding was near-stoichiometric.
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PMID:2,4-Diamino-5-chloroquinazoline analogues of trimetrexate and piritrexim: synthesis and antifolate activity. 779 2

1954U89, 1,3-diamino-7-(1-ethylpropyl)-8-methyl-7H-pyrrolo-(3, 2-f)quinazoline, is a potent, lipid-soluble inhibitor of dihydrofolate reductase. The pharmacokinetics and bioavailability of 1954U89 were examined in male beagle dogs and male CD rats. Dogs received single intravenous (2.5 mg kg-1) and oral (5.0 mg kg-1) doses of 1954U89 with and without successive administration of calcium leucovorin. Single intravenous (5.0 mg kg-1) and oral (10 mg kg-1) doses of [1,3-14C2]1954U89 were administered to rats. Plasma concentrations of total radiocarbon were determined by scintillation counting, and intact 1954U89 was measured by HPLC. The mean plasma half-life was 3.2 +/- 0.62 and 4.2 +/- 0.68 h after intravenous and oral administration, respectively, to dogs. The pooled plasma half-life after intravenous administration to rats averaged 1.2 h; a reliable plasma half-life value after oral administration could not be determined. Mean total-body clearance was 2.4 +/- 0.39 and 4.5 +/- 1.1 L h-1 kg-1 after intravenous and oral administration, respectively, to dogs, and averaged 12 and 77 L h-1 kg-1 after intravenous and oral administration, respectively, to rats. Neither clearance nor bioavailability of 1954U89 in dogs was affected significantly by administration of calcium leucovorin. Absolute bioavailability was 54 +/- 12% in dogs and 16% in rats.
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PMID:The pharmacokinetics of 1954U89, 1,3-diamino-7-(1-ethylpropyl)-8-methyl-7H-pyrrolo-(3,2-f)quinazoline, in dogs and rats after intravenous and oral administration. 921 Sep 81

The synergistic effect of trimetrexate (TMTX) and sulphonamide derivatives of quinazoline on the cultured 5178Y murine leukemia cells was examined. On exposure to the slightly inhibitory concentrations of TMTX (0.1 nM) in combination with 2-desamino-2-methyl-10-propargyl-5,8-dideaza-pteroyl-sulphoglyc ine (DMPDDSF) (0.02 microM) a synergistic inhibitory effect of the antifolates on cell growth was observed. These two drugs in the same combination caused also synergistic inhibition of de novo synthesis of thymidylate in intact cells as measured by tritium release from [5-(3)H]deoxyuridylate. This was accompanied by a marked reduction in intracellular concentration of 5,10-methylenetetrahydro-pteroyl-polyglutamate (5,10CH2H4PteGlu(n)) (0.2 microM) and dihydropteroyl-polyglutamate (0.12 microM). In these conditions de novo biosynthesis of purine was decreased by 50%. These observations show that growth inhibition by combined antifolates is mediated by intracellular depletion of the substrate of thymidylate synthase -- 5,10CH2H4PteGlu(n). The results obtained strongly suggest that under certain conditions inhibition of thymidylate synthesis by DMPDDSF is intensified by prior application of TMTX -- an inhibitor of dihydrofolate reductase.
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PMID:The effects of combined antifolates on inhibition of growth of murine leukemia cells cultured in vitro. 958 54

Extensive biochemical and pharmacological evidence indicates that LY231514 is a novel antifolate antimetabolite. LY231514 is transported into cells mainly through the reduced folate carrier system and extensively metabolized to polyglutamated forms. The polyglutamates of LY231514 inhibit at least three key folate enzymes: TS, DHFR, and GARFT, and to a lesser extent AICARFT and C1-tetrahydrofolate synthase. The combined effects of the inhibition exerted by LY231514 at each target give rise to an unusual end-product reversal pattern at the cellular level that is distinct from those of other inhibitors such as methotrexate and the quinazoline antifolates. The metabolic effects exerted by LY231514 on the folate and nucleotide pools are also quite distinct from those of MTX and LY309887. The efficient polyglutamation, longer cellular retention and the multiple folate enzyme inhibition mechanism may all have contributed directly to the exciting antitumor responses now observed in Phase I and II studies. The multitargeted inhibition mechanism of LY231514 is particularly intriguing. This new level of mechanistic insight, which has evolved from the study of LY231514, challenges the traditional concept and paradigm of antifolate drug discovery and development which focused on developing very potent and selective inhibitors of single folate enzyme targets, such as DHFR, TS or one of the enzymes along the de novo purine biosynthetic pathway. Given the complex nature of folate metabolism and the critical role of folates in maintaining the physiological functions of living systems, it is completely reasonable to suspect that agents which can interfere at multiple sites in the folate pathway may trigger and cause more biochemical imbalance in the cellular DNA and RNA synthesis of malignant cells than agents that act on a single point (Fig. 5). In conclusion, LY231514 (MTA) is a new generation antifolate antimetabolite demonstrating inhibitory activity against multiple folate enzymes including TS, DHFR and GARFT. In current phase II studies, MTA is broadly active as a single agent and is showing very encouraging antitumor activity in multiple solid tumors including colorectal, breast and non-small cell lung cancers (38-43). The every three week dosing schedule has proven to be convenient and easy to administer and the clinical toxicities of LY231514 seem to be well tolerated. More advanced and extensive clinical trials of LY231514 are currently in progress.
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PMID:Multiple folate enzyme inhibition: mechanism of a novel pyrrolopyrimidine-based antifolate LY231514 (MTA). 976 51

X-ray crystallographic analysis of 5-(4'-substituted phenyl)sulfanyl-2,4-diaminoquinazoline inhibitors in ternary complex with Candida albicans dihydrofolate reductase (DHFR) and NADPH revealed two distinct modes of binding. The two compounds with small 4'-substituents (H and CH3) were found to bind with the phenyl group oriented in the plane of the quinazoline ring system and positioned adjacent to the C-helix. In contrast, the more selective inhibitors with larger 4'-substituents (tert-butyl and N-morpholino) were bound to the enzyme with the phenyl group perpendicular to the quinazoline ring and positioned in the region of the active site that typically binds the dihydronicotinamide moiety of NADPH. The cofactor appeared bound to DHFR but with the disordered dihydronicotinamide swung away from the protein surface and into solution. This unusual inhibitor binding mode may play an important role in the high DHFR selectivity of these compounds and also may provide new ideas for inhibitor design.
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PMID:X-Ray crystal structures of Candida albicans dihydrofolate reductase: high resolution ternary complexes in which the dihydronicotinamide moiety of NADPH is displaced by an inhibitor. 1152 Feb 1


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