UMLS:C0023418 - FACTA Search

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Query: UMLS:C0023418 (leukemia)
93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanisms of acquired resistance to MTX were studied in P388 murine leukemia cell lines that were sensitive or resistant to ADR. The rate of MTX accumulation in ADR-sensitive cells that have acquired resistance to MTX was found to be lower than that measured in cells that were sensitive to both drugs. Furthermore, in contrast to drug-sensitive cells, in the ADR-sensitive MTX-resistant cells, most of the intracellular MTX (86.2%) was bound and MTX polyglutamation was not detected. The initial rate of MTX accumulation in cells that were resistant to both drugs was comparable to that measured in cells that were sensitive to both drugs or that were resistant only to ADR. However, in the cells that were resistant to both drugs, the rate of MTX accumulation was maintained at its initial level for a period that was considerably longer than that found in the other cell lines. After 3 h of exposure to MTX, the accumulation of MTX in cells that were resistant to both drugs was fourfold higher than that measured in cells that were sensitive to both drugs. Furthermore, while 65 to 70% of the intracellular MTX was free, in cells sensitive to both drugs, or resistant only to ADR, the corresponding value in cells that were resistant to both drugs was less than 1.5%, and a much lower proportion of the MTX was polyglutamated. The sensitivity to TMQ of ADR-sensitive, MTX-resistant cells was similar to that found in cells that were sensitive to ADR and MTX. However, ADR-resistant cells, sensitive or resistant to MTX, were markedly resistant to TMQ. The sensitivity of ADR-resistant MTX-sensitive cells to TMQ was restored by the presence of 10 microM verapamil. Such an effect was not observed in cells resistant to both drugs. It is suggested that P388 cells that have previously acquired resistance to ADR, when now selected by MTX, retain the MTX-transport system (in contrast to ADR-sensitive, MTX-resistant cells) and become resistant to MTX by increasing the activity of DHFR. The results obtained in ADR-resistant cells also suggested that resistance to TMQ was part of the multidrug resistance phenomenon.
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PMID:Mechanism of acquired resistance to methotrexate in P388 murine leukemia cells and in their doxorubicin-resistant subline. 297 48

The goals of new antifolate development are: 1) improved selectivity, 2) improved penetration into pharmacologic sanctuaries, and 3) effectiveness vs. tumors either with intrinsic or acquired resistance to methotrexate (MTX). The major target for antifolate development has been dihydrofolate reductase (DHFR), but other critical folate-dependent enzymes, i.e., thymidylate synthase, methionine synthetase, and folylpolyglutamate synthetase are also important targets for new antifolate development. The possibility that DHFR from tumor tissue differs significantly from normal tissue DHFR now seems improbable, and the ideas of the late Bill Baker to design specific inhibitors of the tumor enzyme vs. the normal tissue DHFR are unlikely to succeed. However, the experience with triazinate (Baker's antifol; TZT) indicates that transport of antifols could be exploited to provide selective toxicity, as well as to provide agents effective vs. MTX-resistant cells. This work led to a second generation of "nonclassical" folate antagonists, of which trimetrexate (JB-11; TMQ) is now in clinical trial. Uptake of TMQ is via an MTX-independent membrane system, and extremely high intracellular levels of this drug are achieved in human leukemia cells.
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PMID:Design and rationale for novel antifolates. 343 93

Trimetrexate is a novel lipophilic folate antagonist that causes growth inhibition, inhibition of nucleic acid biosynthesis, and cytotoxicity at nanomolar concentrations in tissue cultures. The potency of trimetrexate cytotoxicity against most cell lines is greater than that of methotrexate. Trimetrexate has antitumor activity in vivo in several murine leukemia and solid tumor systems, including tumors in which methotrexate is inactive. Antitumor activity was seen following oral, intravenous, or intraperitoneal administration. Trimetrexate causes a pronounced and early depression in incorporation of deoxyuridine into DNA. In tumor cell lines resistant to methotrexate because of a drug transport defect, trimetrexate retains activity. In many such cases the methotrexate-resistant tumors show collateral sensitivity to trimetrexate. In methotrexate-resistant cells with impaired drug transport, trimetrexate sensitivity was even more pronounced when cells were grown in folate-free medium supplemented with physiological levels of tetrahydrofolate cofactor. In the human tumor stem cell colony assay, trimetrexate, at concentrations achievable in vivo, gave activity against many human tumors, including samples that were unresponsive to methotrexate. Trimetrexate crosses the blood-brain barrier, and at very high doses may cause neurotoxicity. At conventional doses the primary toxic effects in mice are gastrointestinal. This toxicity is reversible at therapeutic doses. Unlike earlier lipophilic antifolates, trimetrexate has rapid plasma clearance (t1/2 in mice of 45 minutes). Trimetrexate is a tight-binding competitive inhibitor of dihydrofolate reductase. The Ki,slope for inhibition of the human enzyme was 4 X 10(-11) M. A dose-dependent decrease in cellular purine ribonucleotide pools is given by trimetrexate. Pyrimidine ribonucleotide pools tend to increase in treated cells. Trimetrexate caused a marked depression of cellular pools of dTTP and dGTP, and a lesser depression in dATP. Cytotoxicity of trimetrexate in vitro was prevented by leucovorin. Leucovorin also protected mice from trimetrexate toxicity. Thymidine protected cells from lethal effects of low concentrations of trimetrexate, but not from high concentrations. The combination of thymidine and hypoxanthine completely protected cells from low and high concentrations of trimetrexate. A new, stable and highly water-soluble formulation of trimetrexate has been developed. Because of the interesting biochemical and pharmacological properties of trimetrexate, and its experimental antitumor activity, clinical trials are planned.
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PMID:Biochemical pharmacology of the lipophilic antifolate, trimetrexate. 623 75

Various alterations of the dihydrofolate reductase (DHFR) gene are involved in resistance. In order to understand the mechanism that induce such gene alterations in human leukemia cells, we studied the expression products of DHFR gene in trimetrexate (TMQ)- and/or methotrexate (MTX)-resistant sublines derived from a MOLT-3 human leukemia cell line. A 200-fold TMQ-resistant subline (MOLT-3/TMQ200) expressed the mutated DHFR mRNA, with a base change (T-->C) at the second position of codon 31, as well as the wild type gene. A MTX-resistant subline derived from MOLT-3/TMQ200 (MOLT-3/TMQ200-MTX500) showed a further increase in the expression of the mutated DHFR mRNA, compared to MOLT-3/TMQ200, with a marked decrease of expression of the wild type DHFR mRNA, which is confirmation of amplification of the mutated DHFR gene. By contrast, a 10,000-fold MTX-resistant subline (MOLT-3/MTX10,000) over-expressed the wild type DHFR mRNA, which is confirmation of amplification of the wild type gene. Increased levels of the DHFR enzyme in these sublines were proportional to expression levels of the DHFR mRNA. The DHFR enzyme expressed in MOLT-3/TMQ200-MTX500 cells showed a 40-fold increase in the Ki values for both MTX and TMQ, compared with values for the wild type DHFR expressed in both MOLT-3/MTX10,000 and its parent cell line. These findings suggest that the altered DHFR gene, which was introduced in MOLT-3 cells by exposure to TMQ, gave rise to a variant enzyme with reduced affinity to antifolates, and that complex DHFR alterations confer drug-resistant phenotypes in antifolate-resistance. Structural difference between the antifolates could be important in the introduction of the differential DHFR gene alterations in the antifolate resistance.
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PMID:Expression of variant dihydrofolate reductase with decreased binding affinity to antifolates in MOLT-3 human leukemia cell lines resistant to trimetrexate. 785 Jul 79

Three methods for analyzing the products of polymerase chain reaction were applied to detect complex alterations of dihydrofolate reductase (DHFR) gene, in order to assess their value in detection of folate-resistance in leukemia cells. A single point mutation in the second position of codon 31, a T-to-C transition, in trimetrexate (TMQ) resistant MOLT-3/TMQ200 cells was detected by either allele-specific oligonucleotide hybridization or restriction pattern of the PCR product. These two analyses allowed us to detect not only the presence of the mutation, but also the amplification of the mutated gene in TMQ-methotrexate (MTX) doubly-resistant MOLT-3/TMQ200-MTX500 cells. The base change was confirmed by direct sequencing method of the PCR product. Using these analyses of the PCR product, the complex alterations of DHFR gene are to be examined in leukemic patient cells.
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PMID:[Detection of alterations of dihydrofolate reductase gene in folate-resistant leukemia cells by in vitro enzymatic amplification]. 836 Oct 48

In order to clarify a molecular mechanism of folate resistance in leukemia cells, we studied alterations of the dihydrofolate reductase (DHFR) gene in a human leukemia cell line, MOLT-3, and its sublines made resistant to methotrexate (MTX), trimetrexate (TMQ) and N10-propargyl-5,8-dideazafolic acid (CB3717), alone or in combination. Major alterations of the DHFR gene were examined by Southern analysis of high-molecular-weight DNA. The presence of a base change (T-->C) at nucleotide position 91 of the DHFR gene, which is reported to be responsible for the reduced affinity of the enzyme for MTX in an MTX-resistant human colon carcinoma cell, was examined by allele-specific oligonucleotide hybridization. In a 10,000-fold MTX-resistant subline (MOLT-3/MTX10,000), the normal allele of DHFR gene had been amplified. In contrast, a 200-fold TMQ-resistant subline (MOLT-3/TMQ200) and a 30-fold CB3717-resistant subline selected from MOLT-3/TMQ200 (MOLT-3/TMQ200-CB-3717(30)) were shown to have the mutant allele. Furthermore, the mutant allele had been amplified in a 500-fold MTX-resistant subline, which was established by the continuous exposure of the MOLT-3/TMQ200 cells to stepwise increases of drug concentration and designated as MOLT-3/TMQ200-MTX500. On the other hand, a 40-fold-resistant subline to CB3717 alone (MOLT-3/CB3717(40)) showed the normal allele without amplification. These data suggest that complex alterations of the DHFR gene are involved in the molecular mechanisms of folate resistance that can be differentially introduced into leukemia cells by exposure to various folate analogues, alone or in combination.
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PMID:Differential alterations of dihydrofolate reductase gene in human leukemia cell lines made resistant to various folate analogues. 844 31

The biological activity and cellular metabolism of ZD1694, a novel folate-based thymidylate synthase (TS) inhibitor, were analyzed in a human leukemia cell line, MOLT-3, and its antifolate-resistant sublines with different mechanisms of resistance to methotrexate (MTX), trimetrexate (TMQ) and N10-propargyl-5,8-dideazafolic acid (CB3717). MOLT-3/CB3717(40), which was selected for CB3717 resistance, demonstrated impaired membrane drug transport via reduced folate carrier (RFC) and lower accumulation of [3H]ZD1694-polyglutamates in the cells with a shift in the polyglutamate distribution profile to shorter chain length polyglutamates, indicating an alteration in polyglutamation capacity in this subline. Impaired RFC and reduced rate of polyglutamation could explain the cross-resistance (12-fold) of this subline to ZD1694. On the other hand, there was little or no cross-resistance to this drug in a subline (MOLT-3/TMQ800) reportedly resistant to TMQ through impaired membrane transport for TMQ and an increase in dihydrofolate reductase (DHFR) activity. Total amount of ZD1694 polyglutamated to a level higher than diglutamate was approximately 1.7-fold higher in the TMQ-resistant cells than that in the parent cells, but a low degree of increase in TS activity in the cells counteracted the supposed increase in sensitivity to ZD1694. MOLT-3/TMQ800-MTX10000 cells, which were established by sequential exposure of the TMQ-resistant cells to MTX and were previously shown to amplify mutated DHFR with low affinity for MTX, showed a decreased accumulation of polyglutamated ZD1694 as compared with the parent line and this was consistent with cross-resistance to ZD1694 in this subline. Overproduction of variant DHFR scarcely influenced the sensitivity to this drug. These results indicate that ZD1694 could overcome antifolate resistance through a mechanism such as amplified DHFR activity, and the biological activity of this drug against the cells paralleled the amount of polyglutamated drug inside the cells. Determination of polyglutamation capacity in tumor cells may allow prediction of sensitivity to this drug.
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PMID:Biological activity and intracellular metabolism of ZD1694 in human leukemia cell lines with different resistance mechanisms to antifolate drugs. 869 29

Cytotoxicity of trimetrexate (TMQ), a lipophilic dihydrofolate reductase inhibitor, was examined in antifolate-resistant human T-cell leukemia cell lines developed in oxidized or reduced folate. An approximately 60-fold methotrexate (MTX)-resistant subline was developed in oxidized folate (pteroylglutamic acid: PGA) (CCRF-CEM/MTX60-PGA) from human T-cell leukemia cell line CCRF-CEM; this line exhibited impaired membrane transport of the drug. Further enhancement of MTX resistance resulted in selection of an approximately 5000-fold MTX-resistant subline (CCRF-CEM/ MTX5000-PGA), which showed increased dihydrofolate reductase activity due to gene amplification in addition to further impairment of MTX transport. An approximately 140-fold MTX-resistant subline, and then a 1500-fold MTX-resistant subline were developed in reduced folate (10 nM leucovorin) (CCRF-CEM/MTX140-LV and CCRF-CEM/MTX1500-LV); they exhibited increased dihydrofolate reductase due to gene amplification accompanied by increased intracellular drug accumulation of MTX. While CCRF-CEM/MTX140-LV and CCRF-CEM/MTX1500-LV cells showed cross-resistance to TMQ, CCRF-CEM/MTX60-PGA and CCRF-CEM/MTX5000-PGA cells were at least as sensitive to TMQ as the parent cells. TMQ was more potent against approximately 200-fold N10-propargyl-5,8-dideazafolic-acid (CB3717)-resistant human T-cell leukemia MOLT-3 sublines developed in PGA (MOLT-3/CB3717(200)-PGA) or leucovorin (MOLT-3/CB3717(200)-LV), as compared to the parent cells; MOLT-3/CB3717(200)-PGA and MOLT-3/CB3717(200)-LV cells were resistant to CB3717 by virtue of impaired transport, only the former possessing gene amplification of thymidylate synthase. The cytotoxicity of TMQ in both MOLT-3/CB3717(200)-PGA and MOLT-3/CB3717(200)-LV cells was reduced by addition of leucovorin in a dose-dependent manner, suggesting intracellular folate deficiency as a cause of TMQ sensitivity. These results demonstrate that TMQ overcomes transport-impaired antifolate resistance, irrespective of gene amplification of dihydrofolate reductase or thymidylate synthase. Types of folate used during the development of antifolate resistance seem to be important in relation to the mechanism of TMQ responsiveness as well as that of antifolate resistance.
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PMID:Cytotoxicity of trimetrexate against antifolate-resistant human T-cell leukemia cell lines developed in oxidized or reduced folate. 936 39

The resistance to folate-based antifolates is associated with impaired function of the reduced folate carrier (RFC), one of the major routes of folate transport into cancer cells. To clarify the importance of RFC functions in the antifolate resistance, we have examined the expression of RFC1 and its phenotype as a folate transporter in human leukemia cell lines resistant to various antifolates. MOLT-3 cells resistant to ZD9331 (a thymidylate synthase (TS) inhibitor that utilizes the RFC for cell entry) (MOLT-3/ZD9331) showed decreased expression of RFC1 concomitant with diminished cellular uptake of [3H]methotrexate (MTX). K562 cells resistant to raltitrexed (ZD1694, another TS inhibitor that utilizes the RFC for cell entry) (K562/ ZD1694 x C) scarcely expressed RFC1, which is in accordance with the impaired uptake of folate analogs and the high degree of resistance to ZD1694 and MTX. On the other hand, no apparent decrease of RFCI1 expression was found in transport-deficient MTX-resistant MOLT-3 cells (MOLT-3/MTX10000) though its phenotype showed defective transport of MTX or ZD1694. In these cell lines with impaired RFC function, [3H]leucovorin (LV) uptake was only moderately decreased as compared to [3H]MTX or [3H]ZD1694 uptake. These cells grew with a minimal retardation in folate-free medium supplemented with 10 nM LV, suggesting that these cell lines with impaired RFC function had enough folate transporters to transport LV. In contrast to downregulation of RFC, the much greater uptake of [3H]MTX was observed in the MOLT-3/trimetrexate (TMQ)800-MTX10000 in parallel with increased RFC1 expression. These cell lines with the altered expression of RFC1 may serve as models useful for investigating the regulation of RFC1 expression and for understanding the molecular mechanism(s) behind the transport-mediated antifolate resistance.
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PMID:Variable expression of RFC1 in human leukemia cell lines resistant to antifolates. 950 Feb 2

Various gene alterations are involved in the drug resistance of leukemia cells. To understand the mechanism that underlies the emergence of cells with such gene alterations in human leukemia, we performed clonal analysis of the gene expression of mutant dihydrofolate reductase (DHFR) and mdr1 in trimetrexate-resistant human leukemia MOLT-3 cells. Trimetrexate-resistant (70- and 60-fold) sublines were developed in the presence or absence of an exogenous supply of thymidine (MOLT-3/TMQ70/Th+, MOLT-3/TMQ60/Th-, respectively). Ten clonal lines were isolated by methyl cellulose cloning from each of the 2 trimetrexate-resistant MOLT-3 sublines. All the clonal lines from the 2 sublines expressed mutated DHFR mRNA, with a base change (T --> C) at the second position of codon 31, as well as the wild-type mRNA, in accordance with cross-resistance to methotrexate. On the other hand, mdr1 mRNA expression was demonstrated by reverse-transcription polymerase chain reaction only in clonal lines from MOLT-3/TMQ70/Th+ cells. mdr1 mRNA expression in clonal lines from MOLT-3/TMQ70/Th+ cells and subclonal lines subsequently obtained from the 3 clonal lines with different mdr1 mRNA expression levels was heterogeneous, and its high expression levels were correlated with acquisition of the multidrug resistance (MDR) phenotype. Polymerase chain reaction-based assay for separate microsatellites, mfd27 and mfd41, demonstrated genomic instability among clonal and subclonal lines of MOLT-3. The clonal analysis of polymorphic microsatellites also suggested that emergence of MDR in trimetrexate-resistant MOLT-3 cells in thymidine was not only heterogeneous but also progressively expanding among clones. Genomic instability may play a role in the establishment and clonal evolution of drug resistance in leukemia cells.
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PMID:Microsatellite instability and clonal heterogeneity of MDR1 messenger RNA expression in trimetrexate-resistant human leukemia MOLT-3 cells developed in thymidine. 1036 Aug 22

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