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Proceedings of the National Academy of... Feb 1996P-glycoprotein (Pgp), a transmembrane efflux pump encoded by the MDR1 gene, transports various lipophilic drugs that enter the cell by passive diffusion through the...
P-glycoprotein (Pgp), a transmembrane efflux pump encoded by the MDR1 gene, transports various lipophilic drugs that enter the cell by passive diffusion through the lipid bilayer. Pgp-expressing multidrug-resistant cell lines are not usually cross-resistant to a hydrophilic antifolate methotrexate (MTX). MTX enters cells primarily through a folate carrier, but passive diffusion becomes the primary mode of MTX uptake in carrier-deficient cells. To test if a deficiency in MTX carrier would allow Pgp to confer resistance to MTX, a MTX carrier-deficient cell line (3T6-C26) was infected with a recombinant retrovirus expressing the human MDR1 gene. The infected 3T6-C26 cells showed increased survival in MTX relative to uninfected cells. Multistep selection of the infected cells with vinblastine led to increased Pgp expression and a concomitant increase in resistance to MTX. MTX resistance of Pgp-expressing 3T6-C26 cells was reduced by Pgp inhibitors, including a Pgp-specific monoclonal antibody UTC2. In contrast, the expression and the inhibition of Pgp had no effect on MTX resistance in 3T6 cells with normal carrier-mediated MTX uptake. Thus, a deficiency in the MTX carrier enables Pgp to confer resistance to MTX, suggesting that hydrophilic compounds may become Pgp substrates when such compounds enter cells by passive diffusion.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Animals; Antibodies, Monoclonal; Biological Transport; Carrier Proteins; Cell Line; Clone Cells; Colony-Forming Units Assay; Drug Resistance, Multiple; Fibroblasts; Flow Cytometry; Folic Acid Antagonists; Humans; Intracellular Signaling Peptides and Proteins; Kinetics; Methotrexate; Mice; Neoplasm Proteins; Phleomycins; Pyrimidines; Recombinant Proteins; Retroviridae; Transfection; Vinblastine
PubMed: 8577747
DOI: 10.1073/pnas.93.3.1238 -
The Oncologist 1996Many new antifolate compounds with unique clinical properties are currently in clinical development. Some of these agents have been rationally designed to circumvent...
Many new antifolate compounds with unique clinical properties are currently in clinical development. Some of these agents have been rationally designed to circumvent known mechanisms of resistance to methotrexate, the most useful and extensively studied antifolate in clinical practice. Resistance to methotrexate can result from decreased active transport into cells, decreased polyglutamation resulting in enhanced drug efflux from cells, mutations in dihydrofolate reductase which reduce drug binding affinity, and increased expression of dihydrofolate reductase due to gene amplification or increased translational efficiency. As a consequence, the newer antifolates may differ from methotrexate because of increased lipid solubility, improved cellular uptake or increased ability to undergo polyglutamation. Several of these newer agents also uniquely target specific folate-dependent enzymes such as thymidylate synthase or glycinamide ribonucleotide transformylase. Antifolates currently in clinical development include trimetrexate, edatrexate, piritrexim, ZD1694, lometrexol, AG337, LY231514 and 1843U89. This report summarizes the basic pharmacology and potential clinical applications of these promising new agents.
PubMed: 10387971
DOI: No ID Found -
American Journal of Clinical Oncology Dec 1995A Phase II trial was conducted in patients with metastatic malignant melanoma with DTIC 250 mg/m2 intravenously for 5 days alternating monthly with Piritrexim (PTX)... (Clinical Trial)
Clinical Trial
A Phase II trial was conducted in patients with metastatic malignant melanoma with DTIC 250 mg/m2 intravenously for 5 days alternating monthly with Piritrexim (PTX) using an intermittent, low-dose oral administration schedule. PTX was administered at a starting dose of 25 mg orally three times per day for 5 days weekly for 3 weeks followed by 1 week of rest. Twenty-one patients were entered into the study. Among the 17 patients assessable for response, 1 patient had a minor response, and 3 patients had stable disease. No partial or complete response were observed. Toxicity was tolerable and consistent mainly of myelosuppression. Using this alternating dose schedule, PTX and DTIC produced little response in metastatic melanoma.
Topics: Administration, Oral; Adult; Aged; Antineoplastic Combined Chemotherapy Protocols; Dacarbazine; Drug Administration Schedule; Female; Humans; Infusions, Intravenous; Liver Neoplasms; Lung Neoplasms; Male; Melanoma; Middle Aged; Pyrimidines; Remission Induction
PubMed: 8526190
DOI: 10.1097/00000421-199512000-00006 -
British Journal of Cancer Sep 1995Piritrexim is a lipid-soluble drug which is as effective an inhibitor of dihydrofolate reductase as methotrexate. Phase I and II studies have indicated activity in some... (Clinical Trial)
Clinical Trial
Piritrexim is a lipid-soluble drug which is as effective an inhibitor of dihydrofolate reductase as methotrexate. Phase I and II studies have indicated activity in some tumour types. Because of its lipophilicity we have conducted a phase II study in recurrent high-grade malignant glioma (grades III and IV). Twenty-seven patients were treated with 25 mg p.o. three times daily for five consecutive days, repeated weekly, with provision for dose escalation or reduction according to toxicity. Five patients received less than 4 weeks' treatment because of disease progression or death. Twenty-two patients were evaluable for response. One complete and one partial response was seen (duration 262+ and 241+ weeks) and 13 patients had static disease for a median duration of 13 weeks (range 7-35). The major toxicity was myelosuppression. This response rate of 9% of evaluable patients is much lower than that seen for some conventionally used drugs and we conclude that piritrexim is unlikely to be of value in the management of high-grade gliomas.
Topics: Administration, Oral; Adult; Aged; Antineoplastic Agents; Brain Neoplasms; Drug Administration Schedule; Female; Folic Acid Antagonists; Glioma; Humans; Male; Middle Aged; Neoplasm Recurrence, Local; Pyrimidines
PubMed: 7669591
DOI: 10.1038/bjc.1995.407 -
Journal of Medicinal Chemistry Sep 1995The recent increase in fungal infections, especially among AIDS patients, has resulted in the need for more effective antifungal agents. In our search for such agents,...
The recent increase in fungal infections, especially among AIDS patients, has resulted in the need for more effective antifungal agents. In our search for such agents, we focused on developing compounds which inhibit fungal dihydrofolate reductase (DHFR). A series of 25 5-(arylthio)-2,4-diaminoquinazolines were synthesized as potentially selective inhibitors of Candida albicans DHFR. The majority of the compounds were potent inhibitors of C. albicans DHFR and much less active against human DHFR. High selectivity, as defined by the ratio of the I50 values for human and C. albicans DHFR, was achieved by compounds with bulky and rigid 4-substituents in the phenylthio moiety. For example, 5-[(4-morpholinophenyl)thio]-2,4-diaminoquinazoline displayed a selectivity ratio of 540 and was the most selective inhibitor synthesized to date. Substitution in the 2- or 3-position of the 5-phenylthio group provided only marginal selectivity. 6-Substituted-5-[(4-tert-butylphenyl)thio]-2,4-diaminoquinazolines showed potent activity against the C. albicans enzyme but were equally active against human DHFR. Most of the selective compounds were also good inhibitors of C. albicans cell growth, with minimum inhibitory concentration values as low as 0.05 microgram/ mL.
Topics: Animals; Antifungal Agents; Candida albicans; Drug Design; Folic Acid Antagonists; Humans; Mice; Pyrimethamine; Pyrimidines; Quinazolines; Recombinant Proteins; Structure-Activity Relationship; Trimethoprim; Trimetrexate
PubMed: 7658448
DOI: 10.1021/jm00018a021 -
Journal of Medicinal Chemistry Jul 1995Six previously unknown 2,4-diamino-6-(anilinomethyl)- and 2,4-diamino-6-[(N-methylanilino)-methyl]pyrido[3,2-d]pyrimidines (5-10) were synthesized from...
Six previously unknown 2,4-diamino-6-(anilinomethyl)- and 2,4-diamino-6-[(N-methylanilino)-methyl]pyrido[3,2-d]pyrimidines (5-10) were synthesized from 2,4-diamino-6-(bromomethyl)-pyrido[3,2-d]pyrimidine hydrobromide (11.HBr) by treatment with the appropriate aniline or N-methylaniline in dimethylformamide at room temperature, with or without NaHCO3 present. Compounds 5-10 were tested as inhibitors of dihydrofolate reductase from Pneumocystis carinii, Toxoplasma gondii, and rat liver as a part of a larger effort directed toward the discovery of lipophilic nonclassical antifolates combining high enzyme selectivity and high potency. Of the six analogues tested, the most potent and selective against T. gondii DHFR was 2,4-diamino-6-[(3',4',5'-trimethoxy-N-methylanilono)methyl]pyrido[ 3,2-d d pyrimidine (7), which had an IC50 of 0.0047 microM against this enzyme as compared with 0.026 microM against the rat liver enzyme. The potency of 7 against T. gondii DHFR was similar to that of trimetrexate (TMQ, 1) and piritrexim (PTX, 2) but was > 500-fold greater than that of trimethoprim (TMP, 3). However, while 7 was more selective than either TMQ (19x) or PTX (63x) against this enzyme, its selectivity in comparison with TMP was 8-fold lower. 2,4-Diamino-6-[3',4',5'-trimethoxyanilino)methyl]pyrido[3,2-d]pyri midin e (6) was 17-fold less active than 7 and was also less selective. 2,4-Diamino-6-[(3',4'-dichloro-N-methylanilino)methyl]pyrido[3, 2-d]pyrimidine (10) had an IC50 of 0.022 microM against P. carinii DHFR and was comparable in potency to TMQ and PTX. The species selectivity of 10 for P. carinii versus rat liver DHFR was greater than that of either TMQ (21-fold) or PTX (31-fold). On the other hand, even though 10 was slightly more active than TMQ against the P. carinii enzyme, its selectivity was 7-fold lower than that of TMP. Thus, the goal of combining high enzyme binding activity, which is characteristic of the fused-ring compounds TMQ and PTX, with high selectivity for T. gondii and P. carinii DHFR versus rat liver DHFR, which is characteristic of the monocyclic compound TMP, remained unmet in this limited series.
Topics: Animals; Chromatography, Thin Layer; Folic Acid Antagonists; Liver; Magnetic Resonance Spectroscopy; Pneumocystis; Pyrimidines; Rats; Spectrophotometry, Infrared; Toxoplasma
PubMed: 7629801
DOI: 10.1021/jm00014a014 -
Oncology (Williston Park, N.Y.) Jul 1995Numerous new antifolate drugs have been developed in an attempt to overcome the potential mechanisms of tumor cell resistance to methotrexate, which can include... (Review)
Review
Numerous new antifolate drugs have been developed in an attempt to overcome the potential mechanisms of tumor cell resistance to methotrexate, which can include decreased drug transport into cells; decreased polyglutamation, leading to increased drug efflux from cells; decreased drug affinity for folate-dependent enzymes; mutations of dihydrofolate reductase (DHFR), a key enzyme required for the maintenance of adequate intracellular reduced folate levels that is inhibited by methotrexate; and increased expression of the DHFR protein. Promising antifolate compounds undergoing clinical testing as anticancer agents include trimetrexate (which was recently approved by the FDA for the treatment of Pneumocystis carinii pneumonia), edatrexate, piritrexim, Tomudex, and lometrexol. The mechanisms of action, dosage, pharmacokinetics, clinical toxicity, and antitumor activity of these drugs are profiled.
Topics: Aminopterin; Antimetabolites, Antineoplastic; Antineoplastic Agents; Drugs, Investigational; Folic Acid Antagonists; Humans; Neoplasms; Pyrimidines; Quinazolines; Thiophenes; Trimetrexate
PubMed: 8924375
DOI: No ID Found -
Archiv Der Pharmazie Jun 1995Two strategies towards the synthesis of Iso-Piritrexim (12) are described. A) The Mannich-reaction of ketone 2 yields the bases 4-HCl and 5-HCl. By means of LC base 4 is...
Two strategies towards the synthesis of Iso-Piritrexim (12) are described. A) The Mannich-reaction of ketone 2 yields the bases 4-HCl and 5-HCl. By means of LC base 4 is separated and treated with in situ generated 3,3-diaminoacrylonitrile (9) to yield the 2-aminonicotinonitrile 11. The cyclocondensation of 11 with guanidine provides Iso-PTX (12). B) Reduction and oxidation of the beta-ketoester 15 leads to the beta-ketoaldehyde 17, which is cyclocondensed with 2,4,6-triaminopyrimidine (18) to yield Iso-PTX (12). In the NCl-tumor-test Iso-PTX (12) shows a moderate activity against some leukemia and lung cancer cell lines.
Topics: Animals; Antineoplastic Agents; Drug Screening Assays, Antitumor; Folic Acid Antagonists; Humans; Mannich Bases; Pyrimidines; Tumor Cells, Cultured
PubMed: 7677569
DOI: 10.1002/ardp.19953280612 -
The Journal of Biological Chemistry Mar 1995Although substitution of tyrosine, phenylalanine, tryptophan, or arginine for leucine 22 in human dihydrofolate reductase greatly slows hydride transfer, there is little... (Comparative Study)
Comparative Study
Although substitution of tyrosine, phenylalanine, tryptophan, or arginine for leucine 22 in human dihydrofolate reductase greatly slows hydride transfer, there is little loss in overall activity (kcat) at pH 7.65 (except for the arginine 22 variant), but Km for dihydrofolate and NADPH are increased significantly. The greatest effect, decreased binding of methotrexate to the enzyme-NADPH complex by 740- to 28,000-fold due to a large increase in the rate of methotrexate dissociation, makes these variants suitable to act as selectable markers. Affinities for four other inhibitors are also greatly decreased. Binding of methotrexate to apoenzyme is decreased much less (decreases as much as 120-fold), binding of tetrahydrofolate is decreased as much as 23-fold, and binding of dihydrofolate is decreased little or increased. Crystal structures of ternary complexes of three of the variants show that the mutations cause little perturbation of the protein backbone, of side chains of other active site residues, or of bound inhibitor. The largest structural deviations occur in the ternary complex of the arginine variant at residues 21-27 and in the orientation of the methotrexate. Tyrosine 22 and arginine 22 relieve short contacts to methotrexate and NADPH by occupying low probability conformations, but this is unnecessary for phenylalanine 22 in the piritrexim complex.
Topics: Amino Acid Sequence; Binding Sites; Crystallography, X-Ray; Drug Resistance; Enzyme Stability; Genetic Variation; Humans; Hydrogen-Ion Concentration; Kinetics; Leucine; Methotrexate; Models, Molecular; Mutagenesis, Site-Directed; NADP; Point Mutation; Protein Conformation; Recombinant Proteins; Tetrahydrofolate Dehydrogenase
PubMed: 7890613
DOI: 10.1074/jbc.270.10.5057 -
Journal of Medicinal Chemistry Mar 19952,4-Diaminoquinazoline antifolates with a lipophilic side chain at the 5-position, and in one case with a classical (p-aminobenzoyl)-L-glutamate side chain, were...
2,4-Diamino-5-substituted-quinazolines as inhibitors of a human dihydrofolate reductase with a site-directed mutation at position 22 and of the dihydrofolate reductases from Pneumocystis carinii and Toxoplasma gondii.
2,4-Diaminoquinazoline antifolates with a lipophilic side chain at the 5-position, and in one case with a classical (p-aminobenzoyl)-L-glutamate side chain, were synthesized as potentially selective inhibitors of a site-directed mutant of human dihydrofolate reductase (DHFR) containing phenylalanine instead of leucine at position 22. This mutant enzyme is approximately 100-fold more resistant than native enzyme to the classical antifolate methotrexate (MTX), yet shows minimal cross resistance to the nonclassical antifolates piritrexim (PTX) and trimetrexate (TMQ). Although they were much less potent than trimetrexate and piritrexim, the lipophilic 5-substituted analogues were all found to bind approximately 10 times better to the mutant DHFR than to the wild-type enzyme. The potency of the analogue with a classical (p-aminobenzoyl)-L-glutamate side chain was similarly diminished in comparison with MTX, but the difference in its binding affinity to the two DHFR species was only 5-fold. Thus, by making subtle structural changes in the antifolate molecule, it may be possible to attack resistance due to mutational alterations in the active site of the target enzyme. Also, to test the hypothesis that DHFR from Pneumocystis carinii and Toxoplasma gondii may have a less sterically restrictive active site than the enzyme from mammalian cells, inhibition assays using several of the lipophilic analogues in the series were carried out against the P. carinii and T. gondii reductases in comparison with the enzyme from rat liver. In contrast to their preferential binding to mutant versus wild-type human DHFR, binding of these analogues to the P. carinii and T. gondii enzymes was weaker than binding to rat enzyme. It thus appears that, if the active site of the DHFR from these parasites is less sterically restrictive than the active site of the mammalian enzyme, this difference cannot be successfully exploited by moving the side chain from the 6-position to the 5-position.
Topics: Animals; Folic Acid Antagonists; Humans; In Vitro Techniques; Liver; Mutagenesis, Site-Directed; Pneumocystis; Quinazolines; Rats; Structure-Activity Relationship; Toxoplasma
PubMed: 7877140
DOI: 10.1021/jm00005a002