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

The substituted ethyl-2-phenacyl-3-phenylpyrrole-4-carboxylates were synthesized by a condensation of a beta-chloroenal and an alpha-aminoketone under neutral conditions. They proved to be potent cytotoxic agents against the growth of murine L1210 and P388 leukemias and human HL-60 promyelocytic leukemia, HuT-78 lymphoma, and HeLa-S(3) uterine carcinoma. Selective compounds were active against the growth of Tmolt(3) and Tmolt(4) leukemias and THP-1 acute monocytic leukemia, liver Hepe-2, ovary 1-A9, ileum HCT-8 adenocarcinoma, and osteosarcoma HSO. A mode of action study in HL-60 cells demonstrated that DNA and protein syntheses were inhibited after 60 min at 100 microM. DNA and RNA polymerases, PRPP-amido transferase, dihydrofolate reductase, thymidylate synthase, and TMP kinase activities were interfered with by the agent with reduction of d[NTP] pools. Nonspecific interaction with the bases of DNA and cross-linking of the DNA may play a role in the mode of action of these carboxylates.
 ...
PMID:Synthesis and cytotoxicity of substituted ethyl 2-phenacyl-3-phenylpyrrole-4-carboxylates. 1282 84

Antifolates are the oldest of the antimetabolite class of anticancer agents and were one of the first modern anticancer drugs. The first clinically useful antifolate, described in 1947, was 2,4-diamino-pteroylglutamate (4-amino-folic acid; aminopterin; AMT) which yielded the first-ever remissions in childhood leukemia. AMT was soon superseded by its 10-methyl congener, methotrexate (MTX), based on toxicity considerations; MTX remains, with one limited exception, the only antifolate anticancer agent in clinical use to this date. Because of the safety and utility of MTX, considerable effort has been invested in attempting to design more therapeutically selective antifolates or antifolates with a wider tumor spectrum. Initially, the design was based on the burgeoning knowledge of folate-dependent pathways and the determinants of the mechanism of action of MTX. These determinants include transport, the tight-binding inhibition of its target (the folate-dependent enzyme dihydrofolate reductase (DHFR)), and metabolism of MTX to poly-gamma-glutamate (Glu(n)) metabolites. These early studies led to the development of other antifolate DHFR inhibitors of two types: (1). "classical" analogs that use the same cellular transport systems as MTX and are also metabolized to Glu(n); and (2). "nonclassical" (i.e., lipophilic) analogs that do not require transport systems and that are not metabolized to Glu(n). Although several of these analogs have undergone clinical trial, none is proved superior to MTX. Detailed examination of the mechanisms of cytotoxicity and selectivity of MTX showed that inhibition of both dTMP synthesis and de novo purine synthesis, secondary to DHFR inhibition, led to DNA synthesis inhibition and subsequent cell death; inhibition of other folate-dependent pathways did not appear necessary for cell death. Further studies showed that the contribution of inhibition of dTMP or purine synthesis to cell death varied in different cell types. These data suggested that inhibition of one of these pathways individually might (at least in some cases) be therapeutically superior to the dual inhibition induced by MTX. Thus in rational design and in structure-based design studies, two new classes of antifolate enzyme inhibitors were elaborated-direct inhibitors of thymidylate synthase (TMPS) and direct inhibitors of one or both of the two folate-dependent enzymes of de novo purine synthesis. Members of each class included both classical and nonclassical types. After preclinical evaluation, several of these have moved into clinical trials. To date only one new TMPS inhibitor has successfully completed clinical trials and been approved for routine use; this drug, Tomudex (D1694, raltitrexed) is currently approved only in Europe and only for the treatment of colon cancer. This still represents a step forward for antifolates, however, since MTX is well-known to be ineffective in colon cancer; thus Tomudex extends the tumor range of antifolates. Antifolate development continues. Based on the immense body of knowledge now extant on antifolates, specific aspects of the mechanism of action have been the focus. Newer antifolates have been described that inhibit more than one pathway in folate metabolism, that have improved delivery, or that inhibit other targets in folate metabolism. These new analogs are in various stages of preclinical and clinical development.
 ...
PMID:Anticancer antifolates: current status and future directions. 1452 44

In a continuing effort to design small-molecule inhibitors of dihydrofolate reductase (DHFR) that combine the enzyme-binding selectivity of 2,4-diamino-5-(3',4',5'-trimethoxybenzyl)pyrimidine (trimethoprim, TMP) with the potency of 2,4-diamino-5-methyl-6-(2',5'-dimethoxybenzyl)pyrido[2,3-d]pyrimidine (piritrexim, PTX), seven previously undescribed 2,4-diamino-5-[2'-methoxy-5'-(substituted benzyl)]pyrimidines were synthesized in which the substituent at the 5'-position was a carboxyphenyl group linked to the benzyl moiety by a bridge of two or four atoms in length. The new analogues were all obtained from 2,4-diamino-5-(5'-iodo-2'-methoxybenzyl)pyrimidine via a Sonogashira reaction, followed, where appropriate, by catalytic hydrogenation. The new analogues were tested as inhibitors of DHFR from Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), and Mycobacterium avium (Ma), three life-threatening pathogens often found in AIDS patients and individuals whose immune system is impaired as a result of treatment with immunosuppressive chemotherapy or radiation. The selectivity index (SI) of each compound was obtained by dividing its 50% inhibitory concentration (IC(50)) against Pc, Tg, or Ma DHFR by its IC(50) against rat DHFR. 2,4-Diamino-[2'-methoxy-5'-(3-carboxyphenyl)ethynylbenzyl]pyrimidine (28), with an IC(50) of 23 nM and an SI of 28 in the Pc DHFR assay, had about the same potency as PTX and was 520 times more potent than TMP. As an inhibitor of Tg DHFR, 28 had an IC(50) of 5.5 nM (510-fold lower than that of TMP and similar to that of PTX) and an SI value of 120 (2-fold better than TMP and vastly superior to PTX). Against Ma DHFR, 28 had IC(50) and SI values of 1.5 nM and 430, respectively, compared with 300 nM and 610 for TMP. Although it had 2.5-fold lower potency than 28 against Ma DHFR (IC(50) = 3.7 nM) and was substantially weaker against Pc and Tg DHFR, 2,4-diamino-[2'-methoxy-5'-(4-carboxyphenyl)ethynylbenzyl]pyrimidine (29), with the carboxy group at the para rather than the meta position, displayed 2200-fold selectivity against the Ma enzyme and was the most selective 2,4-diamino-5-(5'-substituted benzyl)pyrimidine inhibitor of this enzyme we have encountered to date. Additional bioassay data for these compounds are also reported.
 ...
PMID:New 2,4-diamino-5-(2',5'-substituted benzyl)pyrimidines as potential drugs against opportunistic infections of AIDS and other immune disorders. Synthesis and species-dependent antifolate activity. 1499 35

2,4-Diamino-5-[3',4'-dimethoxy-5'-(5-carboxy-1-pentynyl)]benzylpyrimidine (6) and 2,4-diamino-5-[3',4'-dimethoxy-5'-(4-carboxyphenylethynyl)benzylpyrimidine (7) were synthesized from 2,4-diamino-5-(5'-iodo-3',4'-dimethoxybenzyl)pyrimidine (9) via a Sonogashira reaction with appropriate acetylenic esters followed by saponification, and were tested as inhibitors of dihydrofolate reductase (DHFR) from Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), Mycobacterium avium (Ma), and rat in comparison with the widely used antibacterial agent 2,4-diamino-5-(3',4',5'-trimethoxybenzyl)pyrimidine (trimethoprim, TMP). The selectivity index (SI) for each compound was calculated by dividing its 50% inhibitory concentration (IC(50)) against rat DHFR by its IC(50) against Pc, Tg, or Ma DHFR. The IC(50) of 6 against Pc DHFR was 1.0 nM, with an SI of 5000. Compound 7 had an IC(50) of 8.2 nM against Ma DHFR, with an SI of 11000. By comparison, the IC(50) of TMP was 12000 nM against Pc, 300 nM against Ma, and 180000 against rat DHFR. The potency and selectivity values of 6 and 7 were not as high against Tg as they were against Pc or Ma DHFR, but nonetheless exceeded those of TMP. Because of the outstanding selectivity of 6 against Pc and of 7 against Ma DHFR, these novel analogues may be viewed as promising leads for further structure-activity optimization.
 ...
PMID:Preliminary in vitro studies on two potent, water-soluble trimethoprim analogues with exceptional species selectivity against dihydrofolate reductase from Pneumocystis carinii and Mycobacterium avium. 1502 78

Here we report on a Chlamydia trachomatis gene that complements the growth defect of a thymidylate synthase-deficient strain of Escherichia coli. The complementing gene encodes a 60.9-kDa protein that shows low level primary sequence homology to a new class of thymidylate-synthesizing enzymes, termed flavin-dependent thymidylate synthases (FDTS). Purified recombinant chlamydial FDTS (CTThyX) contains bound flavin. Results with site-directed mutants indicate that highly conserved arginine residues are required for flavin binding. Kinetic characterization indicates that CTThyX is active as a tetramer with NADPH, methylenetetrahydrofolate, and dUMP required as substrates, serving as source of reducing equivalents, methyl donor, and methyl acceptor, respectively. dTMP and H(4)folate are products of the reaction. Production of H(4)folate rather than H(2)folate, as in the classical thymidylate synthase reaction, eliminates the need for dihydrofolate reductase, explaining the trimethoprim-resistant phenotype displayed by thyA(-) E. coli-expressing CTThyX. In contrast to the extensively characterized thyA-encoded thymidylate synthases, which form a ternary complex with substrates dUMP and CH(2)H(4)folate and follow an ordered sequential mechanism, CTThyX follows a ping-pong kinetic mechanism involving a methyl enzyme intermediate. Mass spectrometry was used to localize the methyl group to a highly conserved arginine, and site-directed mutagenesis showed this arginine to be critical for thymidylate synthesizing activity. These differentiating characteristics clearly distinguish FDTS from ThyA, making this class of enzymes attractive targets for rational drug design.
 ...
PMID:Catalytic mechanism of Chlamydia trachomatis flavin-dependent thymidylate synthase. 1559 Oct 67

Antifolates are used in the treatment of various human malignancies and exert their cytotoxic activity by inhibiting folate-dependent enzymes resulting in disruption of DNA synthesis and cell death. Here we devised a computerized hybrid functional petri nets (HFPN) modelling of folate metabolism under physiological and antifolate inhibitory conditions. This HFPN modelling proved valid as a good agreement was found between the simulated steady-state concentrations of various reduced folates and those published for cell extracts; consistently, the simulation derived total folate pool size (11.3 microM) was identical to that published for cell extracts. In silico experiments were conducted to characterize the inhibitory profile of four distinct antifolates including methotrexate (MTX), tomudex, and LY309887, which inhibit dihydrofolate reductase (DHFR), thymidylate synthase (TS) and glycineamide ribonucleotide transformylase (GARTFase), respectively, as well as pemetrexed which has the capacity to inhibit all three enzymes. In order to assess the inhibitory activity of antifolates on purines and pyrimidines, the biosynthesis rates of IMP (20.53 microM/min) and dTMP (23.8 microM/min) were first simulated. Whereas the biochemical inhibitory profile of MTX was characterized by increased dihydrofolate and decreased tetrahydrofolate (THF) concentrations, the remaining antifolates did not decrease THF levels. Furthermore, MTX was 766- and 10-fold more potent in decreasing the production rates of IMP and dTMP, respectively, than pemetrexed. LY309887 indirectly decreased the rate of dTMP production by reducing the levels of 5-CH2-THF, a folate cofactor for TS. Surprisingly, pemetrexed failed to inhibit DHFR even at high concentrations. This HFPN-based simulation offers an inexpensive, user-friendly, rapid and reliable means of pre-clinical evaluation of the inhibitory profiles of antifolates.
 ...
PMID:Computer modelling of antifolate inhibition of folate metabolism using hybrid functional petri nets. 1635 13

Cryptosporidiosis, an opportunistic infection affecting immunocompromised patients, the elderly, and children, is still an untreatable disease since the causative agent, Cryptosporidium hominis, is essentially resistant to all clinically used antimicrobial agents. In order to accelerate the design of new potent and selective inhibitors targeting dihydrofolate reductase of C. hominis (ChDHFR), we determined the structural basis for the potency of existing DHFR inhibitors using superpositions of the structure of ChDHFR with other species and analysis of active site complexes of ChDHFR bound to ligands exhibiting a wide range of IC(50) values. This information was used to develop an accurate docking model capable of identifying potent inhibitors in silico. A series of C7-trimethoprim derivatives, designed to exploit a unique pocket in ChDHFR, was synthesized and evaluated; 7-ethyl TMP has four times higher activity than TMP against ChDHFR.
 ...
PMID:Analysis of complexes of inhibitors with Cryptosporidium hominis DHFR leads to a new trimethoprim derivative. 1675 Mar 61

Opportunistic infections are known to cause morbidity and mortality in immunocompromised individuals. In addition, serious infections due to several parasites are also known to affect the quality and duration of life in normal individuals. The importance of dihydrofolate reductase (DHFR) in parasitic chemotherapy arises from its function in DNA biosynthesis and cell replication. DHFR catalyzes the reduction of dihydrofolate (DHF) to tetrahydrofolate (THF), an essential cofactor in the biosynthesis of thymidylate monophosphate (dTMP). Inhibition of DHFR leads to a deficiency of dTMP since DHF cannot be recycled, and thus causes inhibition of cell growth. Methotrexate (MTX) and aminopterin (AMT) were among the first known classical inhibitors of DHFR. Trimethoprim (TMP) and pyrimethamine (PYR) are among the first known non classical inhibitors of DHFR. TMP and PYR are selective but weak inhibitors of DHFR from several parasitic organisms and coadministration of sulfonamides is required to provide synergistic effects for clinical utility. Unfortunately, the side effects associated with sulfa drugs in this combination often result in cessation of therapy. Trimetrexate (TMQ) and piritrexim (PTX) are two potent non classical inhibitors, neither of which exhibit selectivity for pathogen DHFR and must be used with host rescue. However, the current combination therapy suffers from high cost, in addition, several mutations have been reported in the active site of parasitic DHFR rendering the infections refractive to known DHFR inhibitors. The selectivity of TMP is a hallmark in the development of DHFR inhibitors and several efforts have been made to combine the potency of PTX and TMQ with the selectivity of TMP. Thus the structural requirements for DHFR inhibition are of critical importance in the design of antifolates for parasitic chemotherapy. Structural requirements for inhibition have been studied extensively and novel agents that exploit the differences in the active site of human and parasitic DHFR have been proposed. This review discusses the synthesis and structural requirements for selective DHFR inhibition and their relevance to parasitic chemotherapy, since 1995.
 ...
PMID:Dihydrofolate reductase as a target for chemotherapy in parasites. 1734 78

Spores of Bacillus anthracis are the infectious agent of anthrax. Current antibiotic treatments are limited due to resistance and patient age restrictions; thus, additional targets for therapeutic intervention are needed. One possible candidate is dihydrofolate reductase (DHFR), a biosynthetic enzyme necessary for anthrax pathogenicity. We determined the crystal structure of DHFR from B. anthracis (baDHFR) in complex with methotrexate (MTX; 1) at 2.4 Angstrom resolution. The structure reveals the crucial interactions required for MTX binding and a putative molecular basis for how baDHFR has natural resistance to trimethoprim (TMP; 2). The structure also allows insights for designing selective baDHFR inhibitors that will have weak affinities for the human enzyme. Additionally, we have found that 5-nitro-6-methylamino-isocytosine (MANIC; 3), which inhibits another B. anthracis folate synthesis enzyme, dihydropteroate synthase (DHPS), can also inhibit baDHFR. This provides a starting point for designing multi-target inhibitors that are less likely to induce drug resistance.
 ...
PMID:Crystal structure of the anthrax drug target, Bacillus anthracis dihydrofolate reductase. 1769 33

Nickel(II) complexes of thiosemicarbazons were observed to be potent cytotoxic agents in human and rodent tissue cultured tumor cells. Each compound demonstrated a slightly different profile in the various histological types of tumors. The nickel complex of Appip demonstrated the most potent in vivo activity in the Ehrlich ascites carcinoma. This agent selectively inhibited L1210 DNA and purine syntheses, and DNA polymerase alpha, PRPP-amido transferase, IMP-dehydrogenase, dihydrofolate reductase, TMP-kinase and thymidylate synthetase activities. L1210 DNA strand scission was evident and DNA viscosity was reduced after 24 hr incubation. The nickel complexes were not L1210 DNA topoisomerase II inhibitors.
 ...
PMID:Antineoplastic and Cytotoxic Activities of Nickel(II) Complexes of Thiosemicarbazones. 1847 74


<< Previous 1 2 3 4 5 6 7 8 Next >>