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)

Trimetrexate and BW301U (piritrexim isethionate), lipid-soluble inhibitors of dihydrofolate reductase, are potent inhibitors of the growth of Pneumocystis carinii in culture with WI-38 cells. Inhibition was observed with 0.1 microgram of trimetrexate or BW301U per ml. Trimethoprim is ineffective at 100 micrograms/ml in this culture system. Both trimetrexate and BW301U were effective as prophylactic agents against P. carinii pneumonia in rats; trimetrexate at 7.5 mg/kg protected 9 of 10 rats, and BW301U at 5 mg/kg protected 4 of 10.
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PMID:Activity of lipid-soluble inhibitors of dihydrofolate reductase against Pneumocystis carinii in culture and in a rat model of infection. 244 81

Trimetrexate (TMTX) is a potent inhibitor of dihydrofolate reductase that circumvents the transport resistance seen with methotrexate and has a wide spectrum of preclinical activity. A total of 18 patients with advanced cancer were treated in a clinical and pharmacological phase I trial with TMTX given as a continuous 5-day intravenous infusion. Neutropenia, thrombocytopenia and stomatitis were the dose-limiting toxicities at the maximum tolerated dose of 50 mg/m2 per 120 h (10 mg/m2 per day for 5 days). There was one septic death associated with neutropenia. Other toxicities were mild rash, mild nausea and transiently raised serum transminase levels. Significant relationships between the dose given and the AUC of plasma TMTX and the steady-state plasma level were established. Significant, although weak, relationships between the percentage of change in neutrophils and platelets and both the AUC and steady-state plasma level of TMTX were also observed. No objective tumour responses were seen, although six patients had stable disease. The recommended phase II dose for a continuous infusion of trimetrexate is 40 mg/m2 per 120 h.
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PMID:A phase I study of trimetrexate (NSC 352122) administered by 5-day continuous intravenous infusion. 252 92

The new folate antagonist trimetrexate is an inhibitor of dihydrofolate reductase, but unlike methotrexate (MTX) it is not polyglutamylated. We have compared the cell killing effects of MTX and trimetrexate/5-fluorouracil (FUra) and 5-fluoro-2'-deoxyuridine (FdUrd) combinations on HCT-8 cells in vitro, in an attempt to explore indirectly the role of polyglutamylation of the antifol in determining the known sequence-dependent synergism between MTX and FUra. The comparisons were made in a number of equitoxic concentrations and times of exposure. Trimetrexate given for 4, 24 or 48 h followed by FUra, for 4, 24 or 196 h, produced synergistic HTC-8 cell kill, whereas antagonism was observed when FUra preceded or was given simultaneously with trimetrexate. The degree of interaction was essentially identical to those obtained when MTX was combined with FUra. The interactions between MTX/FdUrd and trimetrexate/FdUrd were also similar: synergistic cell kill resulted from the sequences trimetrexate or MTX followed by FdUrd, while additive effects were produced by trimetrexate or MTX + FdUrd combinations or FdUrd followed by MTX or trimetrexate. Because the same interactions observed with MTX/FUra or FdUrd combinations were also obtained when trimetrexate was combined with the fluoropyrimidines, it is unlikely that polyglutamylation of the antifols plays a significant role in determining the different sequence-dependent effects of these antimetabolites. However, these studies do not rule out the possibility that increased levels of dihydrofolate polyglutamates increase fluoropyrimidine cytotoxicity.
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PMID:Sequence-dependent enhancement of HCT-8 cell kill by trimetrexate and fluoropyrimidines: implications for the mechanism of this interaction. 252 36

Trimetrexate (TMQ) is a lipophilic antifolate shown to have antitumor activity in humans. TMQ-resistant sublines of the MOLT-3 human acute lymphoblastic leukemia cell line were developed and were designated as MOLT-3/TMQ200, MOLT-3/TMQ800, and MOLT-3/TMQ2500 based on degrees of resistance to TMQ. The TMQ resistance was accompanied by 5- to 7-fold increases in dihydrofolate reductase activity and markedly reduced cellular TMQ accumulation. Methotrexate accumulation was not impaired in TMQ-resistant cells. TMQ retention (efflux) was unchanged in these TMQ-resistant cells. Verapamil enhanced the TMQ accumulation in the resistant cells to the level seen in the parent cells but had no effects on the TMQ retention. These sublines were cross-resistant not only to methotrexate but also to vincristine, doxorubicin, daunorubicin, and mitoxantrone. There was no cross-resistance to bleomycin or cisplatin. Resistance to vincristine, doxorubicin, daunorubicin, and mitoxantrone was reversed by verapamil. TMQ resistance was only minimally reversed by verapamil and methotrexate resistance not affected at all. Both cellular accumulation and retention of vincristine and daunorubicin in the TMQ-resistant cells were markedly decreased. Verapamil enhanced both accumulation and retention of the drug. Plasma membrane fractions of the TMQ-resistant cells analyzed by urea-sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by staining with Coomassie Blue revealed the presence of a distinct band with a molecular weight of 170,000. Immunoblot analysis with 125I-labeled monoclonal antibody raised against P-glycoprotein of multidrug-resistant Chinese hamster ovary cells (C219) cross-reacted with the Mr 170,000 protein of the TMQ-resistant cells. These results show that the TMQ-resistant cells displayed not only decreased TMQ uptake and increased dihydrofolate reductase but also characteristics associated with a classical multidrug-resistant phenotype. Multidrug resistance includes lipophilic antifolate.
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PMID:Multidrug resistance in a human leukemic cell line selected for resistance to trimetrexate. 257 16

The classic inhibitor of dihydrofolate reductase (DHFR), methotrexate (MTX), has been shown to be an effective inducer of the differentiation of HL-60 promyelocytic leukemia cells (Bodner A.J. et al.; J. Natl. Cancer Inst. 67:1025-1030; 1981). We have obtained evidence that induction of the differentiation of these cells by MTX, as well as by other folic acid antagonists, is the result of the effects of these agents on purine and thymine nucleotide biosynthesis. Thymidine (10 microM) completely blocked both the cytotoxicity and induction of differentiation produced by the specific inhibitor of thymidylate synthase (TS), N10-propargyl-5,8-dideazafolic acid (CB-3717). Thymidine also blocked the acute cytotoxicity caused by MTX and trimetrexate (TMQ); the induction of differentiation and the loss of proliferative capacity, however, were only partially prevented by thymidine. Hypoxanthine (100 microM), which completely restored antifolate-depleted purine nucleotide levels, had no effect on either the cytotoxicity or the induction of maturation produced by these agents. The growth inhibitory effects and the induction of differentiation caused by dideazatetrahydrofolic acid (DDATHF), which acts on de novo purine nucleotide biosynthesis rather than on DHFR or TS, was completely prevented by hypoxanthine. Hypoxanthine also completely prevented the inhibition of cellular replication and induction of differentiation by MTX and TMQ when combined with thymidine. The findings suggest that the depletion of intracellular thymine nucleotide levels by the antifolates, MTX, TMQ, and CB-3717 is the primary event involved in the maturation of HL-60 leukemia cells produced by these agents and that maturation occurs concomitantly with a high level of cytotoxicity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanism of the induction of the differentiation of HL-60 leukemia cells by antifolates. 270 Sep 13

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

The pharmacokinetics of trimetrexate was studied in Rhesus monkeys following i.v. bolus, continuous i.v. infusion, oral, and subcutaneous administration. Two methods were used to measure drug concentration in plasma, cerebrospinal fluid (CSF), and urine: the dihydrofolate reductase inhibition assay, and a reverse phase high-pressure liquid chromatography assay. The pharmacokinetic behavior of trimetrexate was characterized by triexponential plasma disappearance, elimination primarily by biotransformation, substantial plasma protein binding, poor CSF penetration, and limited oral bioavailability. Methotrexate, administered in an equimolar dose for comparison, was cleared more rapidly from plasma than was trimetrexate. Trimetrexate concentration remained above 0.1 microM 3-fold longer. In contrast to methotrexate, which is cleared almost exclusively by renal excretion, renal clearance of trimetrexate accounted for less than 5% of total clearance. A significant discrepancy was observed in plasma and urine trimetrexate concentrations measured by the two assay methods. The dihydrofolate reductase inhibition assay gave results approximately 2- to 4-fold higher in plasma. Two metabolites of trimetrexate which inhibit dihydrofolate reductase were identified in urine (one was also found in plasma) and appear to account for the different results obtained by the two assays. These metabolites would probably also interfere with the competitive protein binding assay currently being used to measure trimetrexate in ongoing phase I trials.
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PMID:Pharmacokinetics of trimetrexate (NSC 352122) in monkeys. 293 45

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

Trimetrexate is a potent inhibitor of dihydrofolate reductase and has demonstrated significant antitumor activity against murine and human cell lines both in vitro and against several murine transplanted tumors. The importance of antifolate concentration and exposure time in determining toxic and therapeutic effects necessitates an assay of suitable sensitivity, accuracy and specificity for investigation of trimetrexate pharmacokinetics. This paper describes a gas chromatographic-mass spectrometric (GC-MS) procedure using selected-ion monitoring (SIM) for the determination of plasma trimetrexate levels. Using the C18 Bond-Elut extraction columns, the drug and internal standard are removed from plasma, derivatized to their bis(trimethylsilyl) derivatives and analysed by GC-SIM-MS. The reproducibility of the daily standard curves had coefficients of variation ranging from 4.9 to 11.4%. The precision of the assay yielded a coefficient of variation ranging from 5.6 to 10.1%, and the concentration means for the seeded control samples were found to be within -3.7 to +0.7% of the theoretical values for trimetrexate. No interfering peaks have been observed in application of the procedure on patient samples. The minimum detectable level under the conditions described was 0.005-0.014 microM trimetrexate.
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PMID:Determination of plasma trimetrexate levels using gas chromatography-mass spectrometry with selected-ion monitoring. 295 Jan 25


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