-
Advances in Experimental Medicine and... 1993
Comparative Study
Topics: Amino Acid Sequence; Aminopterin; Codon; Folic Acid Antagonists; Humans; Hydrogen-Ion Concentration; Kinetics; Leucine; Methotrexate; Mutagenesis, Site-Directed; Polymerase Chain Reaction; Pyrimidines; Recombinant Proteins; Tetrahydrofolate Dehydrogenase
PubMed: 8304170
DOI: 10.1007/978-1-4615-2960-6_104 -
Seminars in Oncology Dec 1992A number of promising new antifolates have been entered in clinical trials in recent years. These agents have been rationally designed based on the current understanding... (Review)
Review
A number of promising new antifolates have been entered in clinical trials in recent years. These agents have been rationally designed based on the current understanding of folate transport and metabolism and of the mechanisms by which cells become resistant to methotrexate. Methotrexate-resistant cell lines are generally sensitive to one or more of the newer antifolates, which differ from methotrexate by being either more lipid soluble, more extensively polyglutamated, or by inhibiting folate-requiring enzymes other than dihydrofolate reductase. Five of the agents furthest along in clinical testing, trimetrexate, piritrexim, edatrexate, lometrexol, and D1694, are discussed. These drugs offer exciting opportunities to expand the role of antifolates in cancer chemotherapy, as well as in antimicrobial and antirheumatic therapy.
Topics: Aminopterin; Animals; Antineoplastic Agents; Chemistry, Pharmaceutical; Clinical Trials as Topic; Drug Evaluation; Folic Acid Antagonists; Forecasting; Humans; Neoplasms; Pyrimidines; Quinazolines; Tetrahydrofolates; Thiophenes; Trimetrexate
PubMed: 1462168
DOI: No ID Found -
Investigational New Drugs Jul 1992
Clinical Trial
Topics: Administration, Oral; Adult; Aged; Drug Administration Schedule; Drug Evaluation; Female; Folic Acid Antagonists; Humans; Male; Middle Aged; Pyrimidines; Sarcoma; Soft Tissue Neoplasms; Treatment Outcome
PubMed: 1500271
DOI: 10.1007/BF00873124 -
The Journal of Biological Chemistry Jun 1992The pathway for de novo biosynthesis of purine nucleotides contains two one-carbon transfer reactions catalyzed by glycinamide ribotide (GAR) and...
The pathway for de novo biosynthesis of purine nucleotides contains two one-carbon transfer reactions catalyzed by glycinamide ribotide (GAR) and 5-aminoimidazole-4-carboxamide ribotide (AICAR) transformylases in which N10-formyltetrahydrofolate is the one-carbon donor. We have found that the antifolates methotrexate (MTX) and piritrexim (PTX) completely block the de novo purine pathway in mouse L1210 leukemia cells growing in culture but with only minor accumulations of GAR and AICAR to less than 5% of the polyphosphate derivatives of N-formylglycinamide ribotide (FGAR) which accumulate when the pathway is blocked completely by azaserine. This azaserine-induced accumulation of FGAR polyphosphates is completely abolished by MTX, indicating that inhibition of the pathway is at or before GAR transformylase (reaction 3; Lyons, S. D., and Christopherson, R. I. (1991) Biochem. Int. 24, 187-197). Three h after the addition of MTX (0.1 microM), cellular 5-phosphoribosyl-1-pyrophosphate has accumulated 3.4-fold while 6-methyl-mercaptopurine riboside (25 microM) induces a 6.3-fold accumulation. These data suggest that amido phosphoribosyltransferase catalyzing reaction 1 of the pathway is the primary site of inhibition. In support of this conclusion, we have found that dihydrofolate-Glu5, which accumulates in MTX-treated cells, is a noncompetitive inhibitor of amido phosphoribosyltransferase with a dissociation constant of 3.41 +/- 0.08 microM for interaction with the enzyme-glutamine complex in vitro. Folate-Glu5, MTX-Glu5, PTX, dihydrotriazine benzenesulfonyl fluoride, and AICAR also inhibit amido phosphoribosyltransferase.
Topics: Amidophosphoribosyltransferase; Aminoimidazole Carboxamide; Animals; Azaserine; Folic Acid Antagonists; Leukemia, Experimental; Methotrexate; Methylthioinosine; Mice; Purines; Pyrimidines; Ribonucleotides; Tumor Cells, Cultured
PubMed: 1597445
DOI: No ID Found -
Archives of Dermatology Apr 1992
Topics: Adult; Aged; Antineoplastic Agents; Female; Humans; Male; Middle Aged; Mycosis Fungoides; Pilot Projects; Pyrimidines; Skin Neoplasms
PubMed: 1580670
DOI: No ID Found -
British Journal of Cancer Apr 1992Exogenous purines (greater than or equal to 10(-5)M) can modulate the cytotoxicity of methotrexate (MTX) in cultured cells, protecting cells at low MTX concentrations...
Exogenous purines (greater than or equal to 10(-5)M) can modulate the cytotoxicity of methotrexate (MTX) in cultured cells, protecting cells at low MTX concentrations (less than or equal to 8 x 10(-8) M) and markedly potentiating its effect at higher concentrations. The ability of hypoxanthine (HX) to modulate the effects of two antifolates-ICI 198583 (an inhibitor of thymidylate synthetase) and piritrexim (PTX, a lipophilic inhibitor of DHFR)-was investigated using cultured mouse leukaemic cells, L1210. HX (10(-4) M) was found to potentiate only the cytotoxicity of DHFR inhibitors (MTS and PTX), increasing cell kill by 20-70 fold to the level achieved by an equivalent concentration (10(-5) M) of ICI 198583 alone. Agarose gel electrophoresis of DNA extracted from cells exposed to antifolates for 24 h demonstrated that the chromatin was cleaved into multimers of 200 base pairs. This pattern of DNA cleavage indicates cell death via apoptosis. The degree of DNA fragmentation was found to be closely linked to cytotoxicity. DNA fragmentation increased from 50% in cells treated with 10(-5) M MTX or PTX to 70% when HX was added with the drugs, a level achieved by 10(-5)M ICI 198583 alone. HX potentiation of cytotoxicity was correlated with a substantial increase in dATP in conjunction with low dTTP pools. The specific potentiation of DHFR inhibitors by HX may be due to their inhibition of purine synthesis with a concurrent rise in PRPP levels. Addition of HX with MTX substantially raised intracellular purine levels via the salvage pathway as indicated by ribonucleotide pool measurements. ICI 198583, on the other hand, stimulated de novo purine synthesis with or without added HX. Treatment with MTX plus HX or ICI 198583 (with or without HX) caused a reduction of dTTP pools to 8% of untreated control and excess dATP accumulation. The subsequent elevation (to 300% of control) of the dATP pool may provide a signal for endonucleolytic fragmentation of DNA and subsequent cell death.
Topics: Animals; DNA Damage; Deoxyadenine Nucleotides; Drug Synergism; Folic Acid; Hypoxanthine; Hypoxanthines; In Vitro Techniques; Leukemia L1210; Methotrexate; Mice; Tumor Cells, Cultured
PubMed: 1562458
DOI: 10.1038/bjc.1992.104 -
The Journal of Biological Chemistry Mar 1992We have studied the discrepancy in the degree of methotrexate (MTX) resistance that exists between two clonal cell lines, mouse 3T6 R50 cells and Chinese hamster ovary...
We have studied the discrepancy in the degree of methotrexate (MTX) resistance that exists between two clonal cell lines, mouse 3T6 R50 cells and Chinese hamster ovary B11 0.5 cells that overexpress comparable levels of dihydrofolate reductase, yet exhibit a 100-fold difference in MTX resistance while maintaining similar sensitivity to the lipophilic antifolates trimetrexate and piritrexim. These data suggested that R50 cells may possess additional mechanism(s) of antifolate resistance, such as MTX transport alteration. Flow cytometric analysis using fluorescein methotrexate revealed comparable levels of fluorescein MTX displacement with lipophilic antifolates in viable R50 and B11 0.5 cells, but marked insensitivity of R50 cells to MTX competition, thus suggesting a poor uptake of MTX into R50 cells. Analysis of the kinetic parameters of dihydrofolate reductase from R50 cells neither showed alterations in enzyme affinities for various antifolates nor in the Michaelis constant for folic acid and NADPH nor a change in the pH activity optimum. R50 cell-free extracts contained wild-type levels of folylpoly-gamma-glutamyl synthetase activity. However, following metabolic labeling with [3H]MTX, no MTX polyglutamates could be detected in R50 cells. We conclude that the high level of MTX resistance in R50 cells is multifactorial, including overexpression of dihydrofolate reductase, reduced MTX transport, and possibly altered formation of MTX polyglutamates. The potential interactions between the different modalities of MTX resistance in R50 cells are being discussed.
Topics: Animals; Blotting, Northern; Blotting, Southern; CHO Cells; Cell Line; Cell Survival; Clone Cells; Cricetinae; DNA; Dose-Response Relationship, Drug; Drug Resistance; Electrophoresis, Gel, Two-Dimensional; Fibroblasts; Flow Cytometry; Folic Acid Antagonists; Hydrogen-Ion Concentration; Methotrexate; Mice; Protein Biosynthesis; Proteins; Pyrimidines; RNA; Tetrahydrofolate Dehydrogenase; Thymidylate Synthase; Trimetrexate
PubMed: 1372892
DOI: No ID Found -
Cancer Feb 1992Piritrexim (PTX) is a newly developed lipid-soluble folate antagonist that crosses the cell membrane by a simple, rapid, carrier-independent diffusion process. A Phase... (Clinical Trial)
Clinical Trial
Piritrexim (PTX) is a newly developed lipid-soluble folate antagonist that crosses the cell membrane by a simple, rapid, carrier-independent diffusion process. A Phase II study was conducted to evaluate the activity of PTX in 34 patients with previously chemotherapy-naive squamous cell cancer of the head and neck area (SCCHN). Among them, 30 patients had received previous radiation therapy and/or surgery. Of 33 patients who could be examined, 3 had a complete response (CR), 6 had a partial response (PR), 11 had no change, and 13 had disease progression. The overall response rate (CR + PR) was 27% (9 of 33; 95% confidence interval, 13% to 46%). The response duration ranged from 36 to 360 + days (median, 162) and was similar to the best studies reported with methotrexate. The three most severe side effects (Grades 3 and 4 by World Health Organization criteria) were leukopenia, thrombocytopenia, and mucositis. These occurred in 41%, 26%, and 15% of the 34 patients, respectively. This study established PTX as an agent with some activity in SCCHN. The use of PTX in combination chemotherapeutic regimens needs to be explored.
Topics: Adult; Aged; Antineoplastic Agents; Carcinoma, Squamous Cell; Drug Evaluation; Female; Head and Neck Neoplasms; Humans; Male; Methotrexate; Middle Aged; Pyrimidines
PubMed: 1735068
DOI: 10.1002/1097-0142(19920215)69:4<1008::aid-cncr2820690430>3.0.co;2-h -
Cancer Research Feb 1992Piritrexim, an orally administered, lipid-soluble antifolate, was evaluated in a multi-institutional phase I trial in children. The starting dose was 10 mg/m2/dose... (Clinical Trial)
Clinical Trial
Piritrexim, an orally administered, lipid-soluble antifolate, was evaluated in a multi-institutional phase I trial in children. The starting dose was 10 mg/m2/dose administered every 8 h daily for 5 days for 3 consecutive weeks, with dose escalations in increments of 5 mg/m2/dose. Eighteen patients (16 with metastatic sarcoma, 1 with acute lymphoblastic leukemia, and 1 with a brainstem glioma), 3.5-20 years of age, with malignancy refractory to therapy, were entered into the study. The dose-limiting toxicities (DLTs), which were myelosuppression and mucositis, occurred in 4 of 4 patients treated at the 25-mg/m2/dose level but in none of the patients treated at the 15- and 20-mg/m2/dose levels. The recommended dose for phase II trials is 20 mg/m2/dose. Pharmacokinetic monitoring was performed in 15 of the 18 children. The area under the concentration-time curve (AUC) was linearly related to the dose administered. Piritrexim was rapidly absorbed, with the median time to peak level occurring 1.5 h after an oral dose. The terminal half-life of piritrexim ranged from 1.5 to 4.5 h. A limited sampling strategy developed earlier, capable of predicting the AUC based on the plasma concentrations at 3 and 6 h after an oral dose, was prospectively tested in this trial and proved to be highly predictive of the AUC (r = 0.98, P = 0.0001). Pharmacodynamic-pharmacokinetic correlations were obtained after combining data from this and the prior phase I pediatric trial. Trough plasma piritrexim concentration strongly correlated with DLT (P = 0.0016). A trough plasma piritrexim concentration greater than 0.5 microM appeared to be predictive of toxicity. Eleven of 15 patients with trough concentrations exceeding this threshold experienced DLTs. Therapeutic drug monitoring may thus play an important role in adjusting the dose and schedule of piritrexim in future trials.
Topics: Adolescent; Adult; Antineoplastic Agents; Brain Neoplasms; Child; Child, Preschool; Drug Administration Schedule; Drug Evaluation; Female; Glioma; Humans; Leukocyte Count; Male; Neoplasms; Platelet Count; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Pyrimidines; Sarcoma
PubMed: 1732038
DOI: No ID Found -
Chest Feb 1992Pneumocystis carinii pneumonia and therapies to treat this infection are associated with frequent and severe morbidity in patients with acquired immunodeficiency...
Pneumocystis carinii pneumonia and therapies to treat this infection are associated with frequent and severe morbidity in patients with acquired immunodeficiency syndrome (AIDS). Mortality rates remain in the 20 to 40 percent range for severe episodes. Thus, less toxic and more effective therapies are needed. For mild-to-moderately severe episodes (PaO2 greater than 70 mm Hg or [A-a]DO2 less than 35 mm Hg), studies suggest that trimethoprim-dapsone, clindamycin-primaquine, and BW 566C80 may cause less toxicity than conventional therapy with trimethoprim-sulfamethoxazole or parenteral pentamidine. However, prospective, controlled trials are needed to establish whether the newer therapies are as effective as the existing licensed treatments. Aerosolized pentamidine is another new therapy that is better tolerated than trimethoprim-sulfamethoxazole but may not be as effective as parenteral treatment when there is extensive airspace consolidation. For severe episodes (PaO2 less than 70 mm Hg or [A-a]DO2 greater than 35 mm Hg), recent studies have established that adjunctive therapy with corticosteroids reduces mortality approximately twofold. For patients who have failed conventional treatments and are unable to ingest oral medications, trimetrexate may be tried. Other compounds being tested may further expand the therapeutic armamentarium with safer and more effective drugs.
Topics: Adrenal Cortex Hormones; Aerosols; Dapsone; Drug Therapy, Combination; Eflornithine; Folic Acid Antagonists; Humans; Pentamidine; Pneumonia, Pneumocystis; Pyrimidines; Trimethoprim; Trimethoprim, Sulfamethoxazole Drug Combination; Trimetrexate
PubMed: 1531191
DOI: 10.1378/chest.101.2.451