Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The poor solubility of the thymidylate synthase (TS) inhibiting antifolate 10-propargyl-5,8-dideazafolic acid has posed problems for its clinical use and is probably responsible for its renal toxicity. The insolubility is caused by the 2-amino-3,4-dihydro-4-oxopyrimidine moiety of the drug which stabilizes the solid state by intermolecular hydrogen bonding. In examining this moiety we have removed the 2-amino group and now report on 2-desamino-10-propargyl-5,8-dideazafolic acid (8e) and four analogues with H, Me, Et, and allyl at N10. 3,4-Dihydro-4-oxo-6-methylquinazoline was solubilized by alkylating the lactam nitrogen with chloromethyl pivalate. Reaction with N-bromosuccinimide gave the corresponding 6-bromomethyl compound, which was coupled with diethyl N-(4-aminobenzoyl)-L-glutamate or the appropriate N-substituted derivative thereof. The quinazoline N3 nitrogen and carboxyl groups in the product were simultaneously deprotected by cold alkali in the final step to give the desired five antifolates. These were tested against L1210 TS and it was found that removal of the 2-amino group caused a slight (3-9-fold) loss of TS inhibition. 8e was only 8-fold a lesser TS inhibitor than the parent drug. Inhibition of rat liver dihydrofolate reductase was reduced by over 1 order of magnitude for three compounds tested. All five analogues were more cytotoxic to L1210 cells in culture than their 2-amino counterparts; 8e was 8.5-fold more active with an ID50 of 0.4 microM. This remarkable result probably owes to increased cellular penetration. 8e was 5-fold more soluble than 1 at pH 5.0 and greater than 340-fold more soluble at pH 7.4.
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PMID:Quinazoline antifolates inhibiting thymidylate synthase: 2-desamino derivatives with enhanced solubility and potency. 270 30

A selected number of 1,3-diaminobenzo[f]quinazolines and 1,3-diamino-5,6-dihydrobenzo[f]quinazolines, which may be viewed as tricyclic analogues of the lipid-soluble antifolates pyrimethamine (PM), metoprine (DDMP), and etoprine (DDEP), were tested as inhibitors of purified dihydrofolate reductase (DHFR) from WI-L2 lymphoblasts, and as inhibitors of the growth of Streptococcus faecium ATCC 8043 and L1210 murine leukemia cells in culture. In addition, these tricyclic compounds were tested for antimalarial activity against Plasmodium berghei in mice, and for the ability to inhibit the growth of Pneumocystis carinii trophozoites in WI-38 human lung fibroblast cultures in the presence of leucovorin (LV). The most potent analogues were those with chlorine substitution in the ring distal to the 2,4-diaminopyrimidine moiety. Fully aromatic compounds tended to be more active than those in which the 5,6-bond was reduced, suggesting that planarity favors binding to the DHFR active site and may be favorable for cellular uptake. Several of the 2,4-diaminopyrimidine analogues showed greater potency than PM, DDMP or DDEP, and were more nearly comparable to the bicyclic 2,4-diaminopyrimidine antifolates trimetrexate (TMQ) or piritrexim (BW301U), which are known to be selectively toxic to P. carinii in the presence of LV. Two of the tricyclic compounds, 1,3-diamino-8-chlorobenzo[f]quinazoline and 1,3-diamino-9-chlorobenzo[f]quinazoline, proved to have activity similar to TMQ and BW301U in this system.
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PMID:Tricyclic 2,4-diaminopyrimidines with broad antifolate activity and the ability to inhibit Pneumocystis carinii growth in cultured human lung fibroblasts in the presence of leucovorin. 278 20

Twenty-two patients with advanced solid tumors were treated with a quinazoline folate antagonist, trimetrexate, to determine the toxicity spectrum, the maximal tolerated dose, and the pharmacokinetics of the drug. Negligible toxicity was seen with single doses of 10-70 mg/m2 given as a 1-h infusion. Single doses of 120 mg/m2 infused over 1 h caused moderate to grade 4 toxicity in five of nine patients treated. Two patients who had no toxicity at this level were escalated to a dose of 213 mg/m2 with mild to moderate toxicity. The primary dose-limiting toxicity was myelosuppression. Moderate transaminase elevations, rash, anorexia, nausea and vomiting, and mucositis were occasionally seen. Although there was variation in dose tolerance to this drug, with selected patients able to tolerate higher doses, we consider 120 mg/m2 every 2 weeks to be the maximal tolerated dose, and the recommended Phase II starting dose. Trimetrexate plasma concentration-time curves were best described as biphasic (N = 9) or triphasic (N = 5) in form. The half-life of the terminal elimination-phase was 16.4 h. The mean residence time was 17.8 h. The volume of distribution of the plasma compartment and the volume of distribution at steady-state were 0.17 and 0.62 liter/kg, respectively. Plasma clearance was 53 ml/min. Plasma concentrations as determined by dihydrofolate reductase enzyme inhibition assay and high-performance liquid chromatography were initially identical, but diverged at later times. Divergences were seen also in urinary recovery as determined by the two methods. Both results suggest the appearance of metabolite(s) of trimetrexate which can inhibit dihydrofolate reductase. Measurable objective solid tumor responses were not seen in this Phase I study, although three patients with colon cancer had stable disease lasting 18, 26, and 26 weeks, respectively.
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PMID:Phase I studies with trimetrexate: clinical pharmacology, analytical methodology, and pharmacokinetics. 294 79

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.
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PMID:Potent in vitro and in vivo antitoxoplasma activity of the lipid-soluble antifolate trimetrexate. 294 69

The crystal structures of trimetrexate (TMQ) (2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoli ne) and 4-[N-[(2,4-diamino-6-pteridinyl)methyl]amino]benzoic acid (PMAB) were determined to examine their conformational features with respect to the enzyme-bound form of methotrexate (MTX). TMQ and MTX are antineoplastic drugs that act by inhibiting the enzyme dihydrofolate reductase. The molecular conformation of TMQ is extended with the trimethoxyanilino ring twisted 89 degrees from the quinazoline plane, and the molecular conformation of PMAB is completely planar. The geometry of the 2,4-diaminopteridine and 2,4-diaminoquinazoline rings are sensitive to protonation, and both TMQ and PMAB have geometries characteristic to a free base. TMQ crystallizes as a dimethyl sulfoxide hydrate. The quinazoline ring forms an antiparallel stacking arrangement in the lattice and forms a network of N...O hydrogen bonds with the solvent molecules. In PMAB there are both pteridine-benzoic acid (N...O) hydrogen bonds and pteridine-pteridine (N...N) hydrogen bonds. Although the molecular conformation of TMQ and PMAB differ from enzyme-bound MTX, rotational energy barriers calculated using CAMSEQ indicate that they can adopt a similar conformation to that seen for MTX complexed with dihydrofolate reductase. These energy calculations show that PMAB is quite flexible and further suggest that the 5-methyl in TMQ reduces its conformational flexibility in a different manner than the N(10)-methyl in MTX. These structural data also show that full geometry optimization and proper parameterization of electronic effects at N(10) are required to accurately represent antifolate conformational preferences for enzyme binding.
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PMID:Conformational analysis of antineoplastic antifolates: the crystal structure of trimetrexate and the aminopterine derivative 4-[N-[(2,4-diamino-6-pteridinyl)methyl]amino]benzoic acid. 295 29

A series of folate analogs containing ornithine instead of glutamate was synthesized and tested for inhibition of folylpolyglutamate synthetase (FPGS) and other folate-dependent enzymes of human leukemia cell lines. Reduced derivatives of 2-amino-4-oxo-10-methyl-pteroyl-ornithine had dramatically increased inhibitory potency against FPGS compared to the oxidized parent. The amino-pterin analog (2,4-diamino-pteroylornithine) was a potent inhibitor of both dihydrofolate reductase and FPGS. It was a much more potent linear competitive inhibitor of human FPGS than the corresponding methotrexate derivative previously described (Ki = 0.15-0.26 and 3 microM respectively). A quinazoline folate analog, 2-amino-4-oxo-5,8-dideazapteroyl-ornithine, was a relatively poor inhibitor of isolated dihydrofolate reductase and thymidylate synthase; however, it is the most potent human FPGS inhibitor identified to date (Ki = 100-150 nM). Because of the lack of appreciable interaction with other folate-dependent enzymes, structures incorporating the 2-amino-4-oxo-5,8-dideazapteroate nucleus may thus lead to selective inhibition of FPGS. Substitution of ornithine for glutamate caused a profound decrease in cytotoxic potency for these analogs; this was apparently the result of poor transport. Together with earlier studies, these data indicate that the potency of FPGS inhibition by an analog containing ornithine closely parallels the relative substrate activity of its glutamate-containing counterpart. The substitution of ornithine apparently does not perturb the pterin specificity of FPGS. The close parallel between substrate and inhibitor specificity may thus allow the use of currently available structure-activity studies on FPGS to design more potent and more selective inhibitors of FPGS.
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PMID:Structural specificity of inhibition of human folylpolyglutamate synthetase by ornithine-containing folate analogs. 319 Jul 39

C8H7N7.HCl has a formula weight Mr237.7, and crystallizes in space group P21/n with a = 6.498(1), b = 10.333(8), c = 15.406(5) A, beta = 91.72(2) degrees. The final R factor was 0.049 for 1010 unique observed reflections. The azido substituent is almost linear, coplanar with the heterocycle, and parallel to the C(7)-C(6) ring bond. The heterocycle is protonated at N(1) and extensively hydrogen bonded. The 6-azido compound is at least a 100-fold better inhibitor of Escherichia coli dihydrofolate reductase than the analogue lacking the azido group, according to I50 values. Superimposing the quinazoline moiety upon the pteridine ring of the methotrexate-dihydrofolate reductase (E. coli) complex reveals two orientations of the N3 group in which it can fit the enzyme, making van der Waals contacts. Ab initio molecular orbital calculations suggest that one of these conformations, with torsion angle phi = C(5)-C(6)-N(61)-N(62) = -163.8 degrees, is low in energy.
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PMID:Structural studies on bio-active compounds. Part 9. 2,4-Diamino-6-azidoquinazoline hydrochloride. 344 92

A human T-lymphoblast cell line, CCRF-CEM/R1, resistant to methotrexate by virtue of increased dihydrofolate reductase activity, was grown in stepwise increasing concentrations of methotrexate. This additional selection pressure resulted in a cell line, CCRF-CEM/R2, resistant to methotrexate by virtue of both an elevation of dihydrofolate reductase activity and a marked decrease in methotrexate transport. The R1 and R2 cells were approximately 70- and 350-fold more resistant to methotrexate than were the parent cells. The effects of three folate antagonists were studied on these cell lines and also on CCRF-CEM/R3 cells, characterized by impaired methotrexate transport but normal levels of dihydrofolate reductase. The elevated reductase subline CCRF-CEM/R1 was cross-resistant to triazinate [Baker's antifol, NSC 139105; ethanesulfonic acid compounded with alpha-(2-chloro-4-[4,6-diamino-2,2-dimethyl-S-triazine-1-(2H)-yl] phenoxyl)-N,N-dimethyl-m-toluamide (1:1)] and trimetrexate (NSC 249008, JB-11, TMQ; 2,4-diamino-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline), two nonclassical folate antagonists. In contrast, the transport defective subline, CCRF-CEM/R3 was not cross-resistant to these two compounds. In cells resistant to MTX by virtue of both mechanisms, CCRF-CEM/R2, triazinate, and trimetrexate were partially cross-resistant. All three methotrexate-resistant sublines showed minor cross-resistance to isoaminohydroxyquinazoline (IAHQ, NSC 289517; 5,8-dideazaisopteroylglutamate), a folate antagonist inhibitor of thymidylate synthase. These data demonstrate that methotrexate-resistant tumor cells may be effectively inhibited by antifolates with different route of entry into cells or with different enzyme targets.
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PMID:Cytotoxic effects of folate antagonists against methotrexate-resistant human leukemic lymphoblast CCRF-CEM cell lines. 385 84

The molecular structure of quinespar, a quinazoline analogue of methotrexate and aminopterin, has been determined by X-ray crystallography. The molecule displays an extended conformation with the p-aminobenzoyl plane rotated 66 degrees from the plane of the quinazoline. The orientation of the quinazoline ring relative to the rest of the molecule is intermediate between the orientations of the comparable pteridine rings in folic acid and in DHFR-bound methotrexate. Evidence is presented to suggest that 2,4-diaminoquinazolines bind to DHFR in the same manner as do 2,4-diaminopteridines.
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PMID:Crystal structure of quinespar, a quinazoline analogue of methotrexate. 394 9

Data are presented on the systematic analysis of thirty-five quinazoline and substituted triazine compounds as inhibitors of a methotrexate-insensitive form of dihydrofolate reductase purified from methotrexate-resistant L5178Y murine leukemia cells. Several of the compounds were found to be more potent inhibitors of this enzyme activity than was methotrexate. Two of the triazine compounds had IC50 values approaching 10nM, which is close to that of methotrexate for the normal drug-sensitive dihydrofolate reductase. In addition, some of these compounds, especially the triazines, exhibit a specificity of inhibition for the methotrexate-insensitive enzyme as compared to the normal methotrexate-sensitive dihydrofolate reductase derived from the same cell line. These compounds may, therefore, be potentially useful in the treatment of those methotrexate-resistant tumours which express an altered, methotrexate-insensitive dihydrofolate reductase.
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PMID:Further studies on substituted quinazolines and triazines as inhibitors of a methotrexate-insensitive murine dihydrofolate reductase. 396 94


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