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Biomedical subjects

B A Chabner

Publications and source records attributed to B A Chabner.

At least 127 records · Page 7Linked to original sources
PubMed1985

Determinants of the sensitivity of human small-cell lung cancer cell lines to methotrexate.

We have characterized the determinants of methotrexate (MTX) responsiveness in eight patient-derived cell lines of small-cell lung cancer (SCLC). Clonogenic survival was correlated with factors known to affect sensitivity to drug. NCI-H209 and NCI-H128 were most drug sensitive, with drug concentrations required to inhibit clonogenic survival by 50% with less than 0.1 microM MTX. Six cell lines (NCI-H187, NCI-H345, NCI-H60, NCI-H524, NCI-H146, and NCI-N417D) were relatively drug resistant. In all cell lines studied, higher molecular weight MTX-polyglutamates (MTX-PGs) with 3-5 glutamyl moieties (MTX-Glu3 through MTX-Glu5) were selectively retained. Relative resistance to low (1.0 microM) drug concentrations appeared to be largely due to decreased intracellular metabolism of MTX. Five of the six resistant lines were able to synthesize polyglutamates at higher (10 microM) drug concentrations, although one resistant cell line (NCI-N417D) did not synthesize higher molecular weight MTX-PGs, even after exposure to 10 microM drug. Two cell lines with resistance to 10 microM MTX (NCI-H146 and NCI-H524) synthesized and retained higher molecular weight MTX-PGs in excess of binding capacity after exposure to 10 microM drug. However, the specific activity of thymidylate synthase in these cell lines was low. MTX sensitivity in patient-derived cell lines of SCLC requires the ability of cells to accumulate and retain intracellular drug in the form of polyglutamate metabolites in excess of dihydrofolate reductase, as well as a high basal level of consumption of reduced folates in the synthesis of thymidylate.

Biological Transport, Active↗
PubMed1985

Cellular pharmacokinetics of mercaptopurine in human neoplastic cells and cell lines.

The accumulation, metabolism, and retention of mercaptopurine (MP) was studied in four human neoplastic cell lines (three acute leukemia lines Molt-4, CCRF-CEM, and HL-60; and one Burkitt's lymphoma line, Wilson), each of which was sensitive to MP. Two cell lines resistant to MP (WilsonR and CCRF-CEMR) were also studied. The cell lines were incubated for 3 h in 10 microM [14C]MP and then placed in drug-free media for an additional 3 h. Cell samples were obtained at regular intervals, and the intracellular MP metabolites were measured in the acid-soluble fractions by anion-exchange high-pressure liquid chromatography. MP accumulated progressively within cells during the 3-h drug exposure period and declined rapidly when the cells were placed in drug-free media. Over 80% of the intracellular MP was present in the form of three nucleotide metabolites, MP ribose monophosphate, thioxanthosine monophosphate, and thioguanosine monophosphate. MP ribose monophosphate was found in greatest amount, accounting for 59-85% of the intracellular metabolite pool. Thioxanthosine monophosphate thioguanosine monophosphate were detected in lesser amounts. Study of leukemic cells obtained from patients demonstrated a similar pattern of MP accumulation, metabolism, and retention, although the overall amounts of the various metabolites formed were less. In contrast, there was essentially no MP nucleotide metabolite formation in the two MP-resistant cell lines. A more complete understanding of the cellular pharmacokinetics of MP in human neoplastic cells is likely to lead to a more rational use of the drug in the clinical setting.

Adenosine Triphosphate↗
PubMed1985

Competitive protein-binding assay for trimetrexate.

A competitive protein-binding assay has been developed for trimetrexate (TMTX) based on the tight binding of this drug to human dihydrofolate reductase (tetrahydrofolate dehydrogenase). In this assay, TMTX competes with 3H-methotrexate for binding to the enzyme. Free drug is separated from that bound to reductase by adsorption with dextran-albumin-coated charcoal. TMTX is measurable over a range from 2 X 10(-9) to 5 X 10(-8) M in plasma, with a coefficient of variation of less than 10%. Measurements of TMTX in plasma, cerebrospinal fluid, and urine agreed closely with parallel determinations in aqueous solutions.

Animals↗
PubMed1985

Enrichment of myeloid progenitor cells from normal human bone marrow using an immune-rosette technique.

In this study we have developed methods for purification of myeloid progenitor cells (CFU-Cs) from normal human bone marrow cells. Bone marrow aspirates were obtained from volunteers, and mononuclear cells (MNCs) were separated by Ficoll-Hypaque gradient centrifugation. T- and B-lymphocytes, monocytes, mature granulocytes, and erythroid precursors were eliminated by an immune-rosette technique using a panel of murine monoclonal antibodies and immunoglobulin (Ig)-coated sheep red blood cells (SRBCs). MNCs were treated with OKT3, B1, M3, Mo5, and EP1 monoclonal antibodies, which are reactive with T cells, B cells, monocytes, granulocytes, and erythroid precursors, respectively. Antibody-treated MNCs were incubated with SRBCs that had been coated with goat antirabbit IgG F(ab')2 and rabbit antimouse Ig for immune rosetting. Rosetted cells were then separated from nonrosetted cells in Ficoll-Hypaque. Nonrosetted cells were, in the second step, treated with an OKIa1 monoclonal antibody and again separated into an Ia+ and Ia- cell fraction by the same manner; 39% +/- 19.2% (mean +/- 1 SD, range 16.3%-75.4%) of CFU-Cs (colonies plus clusters) were recovered in the OKT3-, B1-, M3-, Mo5-, EP1- cell fraction, and the number of CFU-Cs grown in semisolid agar was 149.6 +/- 73.0 (64.0-309.0)/10(4) plated cells in this purified fraction, representing an enrichment of 14.2 +/- 6.4 (6.0-27.3)-fold when compared with unseparated marrow cell fractions. CFU-Cs were enriched 17.7 +/- 8.6 (6.1-28.3)-fold in the Ia+ cell fraction. These purified myeloid precursors would be of value for in-depth studies of the interactions between hematopoietic progenitor cells and regulatory factors that influence their proliferation and differentiation and also of drug metabolism and determinants of cytotoxicity.

Adolescent↗
PubMed1984

Cancer chemotherapy. Progress and expectations, 1984.

Progress in the treatment of cancer with drugs has radically altered the clinical approach to patients with malignancy. Not only have new drugs produced promising results in hitherto untreatable tumors, but they have extended and enhanced the effectiveness of other modalities, including surgery and radiotherapy. In this article, the authors consider avenues of research that likely to aid in the discovery of new anticancer drugs and improve the effectiveness of established agents. Promising new efforts in drug development include the use of new screening systems, particularly those employing human tumor material; the development of improved analogs of existing active agents particularly those of the anthracycline and platinum complex types; and the search for agents that which promote differentiation or prevent metastasis. In an effort to improve the effectiveness of established agents, the authors consider the application of pharmacokinetic principles in developing regional perfusion routes, intraperitoneal chemotherapy, and central nervous system penetration. Finally, the contribution of biochemical pharmacology to the current understanding of drug action, mechanisms of resistance, and drug interactions are considered, and the impact of this knowledge on clinical protocol design is assessed.

Antineoplastic Agents↗
PubMed1983

Synthesis, binding and intracellular retention of methotrexate polyglutamates by cultured human breast cancer cells.

Synthesis, binding, and intracellular retention of methotrexate polyglutamates by cultured human breast cancer cells were investigated by gel filtration and high-pressure liquid chromatography to separate methotrexate from its metabolites. MCF-7, ZR-75-1, and MDA-231 human breast cancer cells were found to readily convert methotrexate to higher polyglutamates during a 24-hr incubation period, although at differing rates. Examination of that portion of intracellular methotrexate specifically bound to dihydrofolate reductase revealed that, with prolonged incubation, methotrexate polyglutamates become the predominant drug form bound to the enzyme. Similarly, methotrexate polyglutamates accumulated free in the cytosol and when cells were suspended in drug-free medium, were retained intracellularly both bound to dihydrofolate reductase and in the unbound fraction, indicating their slow passage through the cell membrane. Studies of methotrexate polyglutamate binding to purified bacterial dihydrofolate reductase revealed high affinity binding for compounds with up to 6 additional glutamyl residues. These studies demonstrate that methotrexate polyglutamates are readily formed in human breast cancer cells, bind intracellularly to dihydrofolate reductase, and are selectively retained both bound to the enzyme and free in the cell cytosol.

Binding Sites↗
PubMed1983

Kinetic behaviour and allosteric regulation of human deoxycytidylate deaminase derived from leukemic cells.

Deoxycytidylate deaminase has been highly purified (1232-fold) from human leukemia CCRF-CEM cells. The native molecular weight of the enzyme is 108 000 and subunit molecular weight 50 500, suggesting that the native enzyme exists as a dimer. The enzyme exhibits a sigmoidal initial velocity vs substrate concentration curve and is regulated by allosteric effectors, dCTP and TTP. The curve relating substrate concentration to initial velocity was changed from a sigmoidal shape to a hyperbolic one by the activator dCTP, while the inhibitor TTP increased the sigmoidicity of the curve. The molecular weight of deoxycytidylate deaminase was unchanged in the presence of allosteric effectors, indicating that aggregation-disaggregation is not the basis of regulation. Deoxycytidylate deaminase exhibited the greatest affinity for the substrate dCMP, with lesser affinity for ara-CMP, and least affinity for CMP. Ara-CMP was an effective substrate in the presence of dCTP concentrations exceeding 4 microM. These data indicate that human neoplastic cell deoxycytidylate deaminase is a highly regulated allosteric enzyme, which is likely to have a significant influence on cellular dUMP, dCTP and TTP pools. These findings further suggest, that the enzyme through its influence on dUMP levels is likely to modulate the biochemical effects of pyrimidine antimetabolites active against the thymidylate synthetase reaction and in the presence of elevated dCTP pools will promote deamination of ara-CMP to the inactive ara-UMP.

Cell Line↗
PubMed1983

Inhibition of first-pass metabolism in cancer chemotherapy: interaction of 6-mercaptopurine and allopurinol.

Earlier studies suggested that the dose of 6-mercaptopurine (6-MP) can be reduced substantially when the drug is given with allopurinol. We studied the effect of allopurinol on the kinetics of oral and intravenous 6-MP. Studies conducted initially in rhesus monkeys and subsequently in man with 6-MP doses of 100 mg/m2 and 75 mg/m2, demonstrated that allopurinol pretreatment resulted in a nearly 400% increase in peak plasma concentration of oral 6-MP in monkeys (from a mean of 0.54 microM to a mean of 2.1 microM) and a 500% increase in man (0.74 microM to 3.7 microM). Allopurinol pretreatment also led to a 300% increase in plasma AUC in monkeys after oral 6-MP (from a mean of 121 microM/min to a mean of 391 microM/min) and a 500% increase in AUC in man (from a mean of 142 microM/min to a mean of 716 microM/min). In contrast, allopurinol pretreatment had no effect on the kinetics of intravenous 6-MP. This difference was found to be due to inhibition of first-pass metabolism of oral 6-MP as the result of the action of allopurinol on liver or intestinal xanthine oxidase. Our results indicate that, although dose reduction of oral 6-MP given in conjunction with allopurinol is appropriate, it is not necessary when 6-MP is injected intravenously.

Administration, Oral↗
PubMed1983

Test dose for predicting high-dose methotrexate infusions.

Eighteen evaluable patients were studied to determine whether individual methotrexate (MTX) kinetics, determined by test-dose bolus injection, could be used to predict plasma drug concentrations during and after high-dose infusion. Small nontoxic doses of MTX (10 mg/m2) was given to patients who were followed for 12 to 24 hr and the kinetic data were used to predict subsequent kinetic behavior of moderate- and high-dose methotrexate infusions (150 to 1500 mg/m2 over 12 to 18 hr). After test-dose injection, MTX clearance varied from 36 to 138 ml/min/m2 and decreased with advancing age (r = -0.49, P less than 0.05). MTX clearance varied from 24 to 100 ml/min/m2 after high-doses. Although there was a trend to decreasing clearance with advancing age, this was not as clear as with the test dose (r = -0.42, P greater than 0.05). There was no correlation between MTX clearance and creatinine clearance in this group of patients in whom creatinine clearance varied from 32 to 63 ml/min/m2. When the kinetic parameters derived from the test-dose data were used, accurate predictions could be made of the infusion plateau (r = 0.89, P less than 0.001) and 24-hr (r = 0.92, P less than 0.001) MTX concentrations after high-dose infusions. Our results indicate that test-dose MTX kinetics may serve as a guide to dose modification of MTX infusions in some high-risk patients.

Adult↗
PubMed1983

Intracellular pharmacokinetics of methotrexate polyglutamates in human breast cancer cells. Selective retention and less dissociable binding of 4-NH2-10-CH3-pteroylglutamate4 and 4-NH2-10-CH3-pteroylglutamate5 to dihydrofolate reductase.

Methotrexate (MTX-Glu1) exerts its antitumor effects through its potent inhibition of dihydrofolate reductase (DHFR), the enzyme responsible for maintaining the cellular pool of reduced folates. Since the drug-enzyme complex (bound drug) is slowly dissociable, an excess of drug (unbound or free drug) above that required to bind all enzyme sites is required in order to compete with substrate for sites made available by enzyme-drug dissociation. We have examined the role of the polyglutamyl metabolites of MTX-Glu1 containing two to five glutamyl (MTX-Glu2-5) groups in gamma peptide linkage in maintaining an intracellular pool of free drug and in forming slowly dissociable complexes with DHFR. During 24-h incubations of ZR-75-B human breast cancer cells with 2 microM MTX-Glu1, we observed the progressive formation of derivatives with two to five glutamyl groups, which rapidly replaced the parent compound on enzyme binding sites and represented 85% of both unbound and bound intracellular drug at the end of incubation. When cells were then placed in drug-free medium, the rates of disappearance of drug and metabolites from the intracellular bound and free fractions decreased with increasing glutamyl chain length. Over 90% of both bound and free MTX-Glu1 left the cells within 1 h, greater than 90% of MTX-glu2 left within 6 h, and greater than 90% of MTX-Glu3 left the bound and free fractions within 24 h. In contrast, free MTX-Glu4 fell by only 63% and bound by only 23% after 24 h, while free MTX-Glu5 increased by 52% after 6 h in drug-free medium and bound MTX-Glu5 increased threefold after 24 h, as it replaced the other forms of drug bound to DHFR. These results suggested a rapid dissociation of MTX-GLu1 and -Glu2 from the enzyme, and a slower dissociation of the longer chain length derivatives. This conclusion was confirmed by examining the rates at which [3H]MTX-Glu1 through -Glu5 could be replaced on enzyme binding sites by a fivefold or greater excess of unlabeled MTX-Glu1. Bound [3H]MTX-Glu1 and -Glu2 had dissociation t 1/2 of 12 and 30 min, respectively, while -Glu3, -Glu4, and -Glu5 had t 1/2 of 102, 108, and 120 min. These experiments demonstrated that the longer chain polyglutamates have prolonged intracellular retention and can be dissociated less readily than MTX-Glu2 from DHFR, properties likely to make them more efficient DHFR inhibitors than the parent drug and of potential importance in extending the duration of drug action in tumor cells.

Binding Sites↗
PubMed1983

Diffuse aggressive lymphomas: increased survival after alternating flexible sequences of proMACE and MOPP chemotherapy.

A new treatment program was developed in an attempt to increase the complete remission rate and survival of previously untreated patients with advanced stages of diffuse aggressive lymphomas. A flexible number of cycles of ProMACE chemotherapy (prednisone, methotrexate, doxorubicin, cyclophosphamide, and epipodophyllotoxin VP-16) was alternated with a flexible number of cycles of MOPP chemotherapy (mechlorethamine, vincristine sulfate, procarbazine, and prednisone), and finally late intensification with ProMACE therapy was given. The duration of each phase of treatment was determined by the patient's rate of tumor response. Complete remissions were achieved in 55 of 74 patients (74%) with a median duration of follow-up exceeding 2 1/2 years. Only ten of the complete responders (18%) have had relapse. The dose-limiting toxicity is myelosuppression, and eight patients (10%) died from sepsis. Median survival for all patients has not been reached but is predicted to exceed 4 years with 65% of patients alive at 4 years. Previously we achieved a 46% complete remission rate with 38% of all patients alive at 4 years; relapse-free survival beyond 2 years was tantamount to cure. Therefore, ProMACE-MOPP chemotherapy represents a substantial improvement in treating patients with diffuse aggressive lymphomas.

Adolescent↗