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)

We have investigated the effects of N-(phosphonacetyl)-L-aspartate (PALA) administered i.v. as a single dose (100 mg/kg) on the antitumor activity of 5-fluoro-2'-deoxyuridine (FdUrd) and 5-fluorouracil (FUra), on the pharmacokinetic parameters of FdUrd and FUra, and on the tumor pyrimidine ribonucleotide triphosphate pools in mice bearing advanced colon carcinoma 26 and leukemia 1210. The antitumor activity was evaluated with PALA administered i.v. 24 h prior to the maximum tolerated dose of FUra and FdUrd administered by: (a) 4 days of continuous infusion (schedule 1, c.i. days 1-4); (b) daily for 4 days by i.v. push (schedule 2, i.v. days 1-4); and (c) weekly for 3 weeks (schedule 3, i.v. weekly for 3 weeks). The maximum tolerated doses of FdUrd were 20, 150, and 400 mg/kg/day and for FUra were 25, 50, and 80 mg/kg/day for schedule 1, 2, and 3, respectively. At the maximum tolerated doses, the antitumor activity in mice bearing advanced colon carcinoma can be summarized as follows: (a) FdUrd is significantly more active than FUra; (b) for both drugs the weekly for 3 weeks i.v. push schedule is superior to the c.i. or i.v. push daily for 4 days schedules; (c) pretreatment with PALA enhances the antitumor activity of FdUrd and FUra and resulted in 95 and 13% complete responses, respectively; (d) long-term survivors with FUra could only be achieved in the presence of PALA; in mice bearing leukemia 1210 cells, FdUrd or FUra with or without PALA exhibited no significant antitumor activity when PALA was administered in a single dose 24 h prior to fluoropyrimidine treatment; and (e) in C-26 and L1210, PALA reduced the pools of CTP and UTP equally, to about 10% of controls with significant difference in their rates of recovery.
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PMID:Antitumor activity of the weekly intravenous push schedule of 5-fluoro-2'-deoxyuridine +/- N-phosphonacetyl-L-aspartate in mice bearing advanced colon carcinoma 26. 845 23

Cyclopentenyl cytosine (CPE-C), a carbocyclic analogue of cytidine, has preclinical antineoplastic activity against ara-C resistant murine leukemias and a broad spectrum of human tumor xenografts. CPE-C is a prodrug and requires intracellular phosphorylation to cyclopentenyl cytosine triphosphate (CPE-CTP) which depletes endogenous CTP pools. The initial step in this activation process is catalyzed by uridine/cytidine kinase. We studied the mechanism of resistance to CPE-C in a Molt-4 T-cell leukemia line made resistant to CPE-C (Molt-4R) by culturing it in the continuous presence of increasing concentrations of CPE-C. Using a tetrazolium based colorimetric assay to assess cytotoxicity, the IC90 for the parent Molt-4 cells (Molt-4WT) was 0.5 microM after a 24 hr drug exposure. In contrast, cytotoxicity was not observed at concentrations as high as 1 mM in the Molt-4R cells. Following a brief exposure to 1 microM CPE-C, parent drug could be detected intracellularly in the resistant and sensitive cell lines. However, CPE-CTP formation was reduced markedly in the resistant cell line. Measurement of the activity of anabolic and catabolic enzymes in the Molt-4WT and Molt-4R cells revealed equivalent activities of alkaline and acid phosphatases as well as cytidine and dCMP deaminase but there was a significant reduction in uridine/cytidine kinase activity in Molt-4R cells. Endogenous ribonucleotide pools and CPE-CTP pools were measured in the absence and presence of CPE-C. CTP pools were reduced markedly in Molt-4WT cells following exposure to CPE-C. However, CTP pools in Molt-4R cells exposed to 100 microM CPE-C were two times greater than in the untreated Molt-4WT cells. At high concentrations of CPE-C (10 and 100 microM), Molt-4R cells were able to generate amounts of CPE-CTP equivalent to that seen in Molt-4WT cells exposed to 1 microM CPE-C (a cytotoxic concentration of drug in Molt-4WT cells), but no cytotoxic effect was seen in Molt-4R cells. Therefore, in addition to decreased uridine/cytidine kinase activity, a second mechanism of resistance that is the result of alterations in CTP synthetase activity also appears to be operative. Elucidation of the mechanism of resistance in vitro may provide insight into the mechanism of action of the drug and potential mechanisms of resistance in vivo.
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PMID:Mechanism of resistance to cyclopentenyl cytosine (CPE-C) in Molt-4 lymphoblasts. 847 Oct 71

Analysis of different ribonucleotide reductase inhibitors to modulate arabinosylcytosine (ara-C) metabolism suggested that pretreatment with arabinosyl-2-fluoroadenine (F-ara-A) significantly potentiated the rate of ara-CTP (5'-triphosphate of ara-C) accumulation in both quiescent lymphocytes (p = 0.046) and in cycling blasts (p = 0.017). In vitro incubations of freshly isolated leukemia cells from patients with chronic (n = 7) or acute (n = 5) leukemias with F-ara-A, increased the rate of ara-CTP accumulation by a median of 1.5 or 1.7-fold, respectively, when subsequently incubated with ara-C. The objective of the present investigation was to test the hypothesis that ara-C can be biochemically modulated during therapy of leukemias. To test the biochemical modulation of ara-C in the clinical setting, we designed two protocols to administer fludarabine (clinical formulation of F-ara-A) and ara-C in a pharmacologically directed sequence for patients with chronic lymphocytic leukemia (CLL) refractory to conventional fludarabine therapy or for patients with acute myelogenous leukemia (AML) in relapse. Comparison of ara-CTP pharmacokinetics demonstrated a significant increase in the area under concentration curve (AUC) of ara-CTP both in CLL (median 1.5-fold) and AML cells (median 1.8-fold) after fludarabine infusion. Analyses of different processes involved in the metabolism of ara-CTP indicated that the increase in AUC was due to potentiation of the rate of ara-CTP accumulation. These studies demonstrate that protocols designed on biochemical and pharmacological rationales modulate ara-C metabolism during therapies.
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PMID:Biochemical modulation of arabinosylcytosine for therapy of leukemias. 848 60

Cytosine arabinoside (Ara-C) is one of the most effective drugs in inducing remission in acute nonlymphocytic leukemia (ANLL) patients. However, the high recurrence rate indicates that a subpopulation of leukemic cells escapes drug effect. This cellular heterogeneity in drug response may play a major role in chemotherapeutic outcome. We have recently developed the individual colony-formation assay (ICFA) to study drug effects on the kinetics of proliferation of individual cells and their progeny. Thus parameters of proliferation are calculated for individual colonies. Three categories of drug responses were defined, including immediate growth cessation, delayed growth cessation (growth stops several days after drug exposure) and growth slowdown (logarithmic growth at a reduced rate compared to control). In the experiments included in this report, murine leukemia (L1210) cells were exposed to various concentrations of Ara-C for 1, 6 or 24 hours, and their responses quantified. Regardless of the Ara-C concentration or exposure time, subpopulations of cells were observed in each of the three response categories: immediate or delayed arrest or growth slowdown. As expected, the fraction of cells exhibiting immediate growth cessation generally increased with increasing drug dose and was markedly increased with longer exposure time. Delayed arrest was most prevalent at intermediate drug concentrations at all exposure times. If exposure was limited to 1 hour, at least 30% of cells continued to grow, although at a reduced rate (71% control rate after exposure to 1 mM Ara-C). This limited effect was paralleled by saturation of Ara-C triphosphate (Ara-CTP) formation. Six-hour exposure left at least 6.4% of cells growing, with an average rate of 45% of control. Under these conditions, no saturation in Ara-CTP formation was observed. Even 24-hour exposure to 5 microM Ara-C left 4.8% of colonies growing, at 42% of control rate. Thus a subpopulation of cells continued to grow even after 24-hour exposure to a relatively high concentration of Ara-C. Surviving, but slowly growing, cells may represent a previously unrecognized population that may contribute to therapeutic failure.
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PMID:Characterization of tumor cell heterogeneity of a murine leukemia cell line (L1210) in response to arabinosylcytosine: quantitation using a computerized image analysis system. 851 59

The effectiveness of arabinosylcytosine (ara-C) for the treatment of acute myelogenous leukemia (AML) depends on the formation of its active metabolite, the triphosphate of ara-C (ara-CTP). Using biochemical modulation strategies to increase the accumulation of ara-CTP in leukemia blasts, a clinical protocol was designed combining 2-chlorodeoxyadenosine (CdA), an inhibitor of ribonucleotide reductase, and ara-C for adults with AML. The protocol stipulated an infusion of 1 g/m2 of ara-C over 2 hours on day 1. A continuous infusion of CdA (12 mg/m2/d) begun 24 hours later and continued for 5 days. Identical doses of ara-C were administered on days 3, 4, 5, and 6. Pharmacokinetic and pharmacodynamic interactions between CdA and ara-C during therapy were investigated. To complement these studies, molecular actions of the triphosphate of ara-C and CdA on DNA extension by human DNA polymerase alpha in an in vitro model system was conducted. In the circulating leukemia blasts of 7 of the 9 patients studied, ara-CTP pharmacokinetics showed a median 40% increase in the rate of ara-CTP accumulation after 24 hours of CdA infusion. The ex vivo effect of CdA on accumulation of ara-CTP in AML blasts was similar to that during therapy except that the enhancement was less. The DNA synthetic capacity of the circulating blasts was inhibited to a greater extent by administration of CdA and ara-C in combination than by either one alone. Additionally the lowered level of DNA synthesis was maintained until the next infusion of ara-C. Endogenous levels of deoxynucleotides increased 24 hours after ara-C infusion. Administration of CdA in general lowered the concentrations of all dNTPs. DNA pol alpha incorporated CdATP and ara-CTP with high affinity in a DNA primer extending over an oligonucleotide template of defined sequence. Human DNA polymerase alpha extended DNA primers terminated by CdA monophosphate (CdAMP) at its 3'-end by incorporating ara-C monophosphate (ara-CMP). The tandem incorporation of CdAMP and ara-CMP resulted in nearly complete inhibition of DNA primer extension. The insertion of two analogs in sequence, inhibition of ribonucleotide reductase, and the metabolic potentiation of ara-CTP by CdA infusion may be responsible for sustained inhibition of DNA synthesis in the circulating leukemia blasts during therapy with this combination regimen.
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PMID:Chlorodeoxyadenosine and arabinosylcytosine in patients with acute myelogenous leukemia: pharmacokinetic, pharmacodynamic, and molecular interactions. 854 50

Camptothecin (CPT), a specific topoisomerase I inhibitor, in the presence of hematopoietic growth factors exerted an antiproliferative effect against normal bone marrow cells (NBMC) as well as chronic myelogenous leukemia-chronic phase (CML-CP) and blast crisis (CML-BC) cells. In the absence of growth factors, however, only the colony formation by CML-BC cells was inhibited by CPT, leaving NBMC and CML-CP cells intact or much less affected. Analysis of the cellular DNA content revealed that CPT induced specific changes in cell cycle distribution: decrease in S and G2/M fraction with simultaneous accumulation of the cells in G1 phase and the appearance of "sub-diploid" (apoptotic) peak. To determine if CPT is able to exert selective antileukemic effect, 1:1 mixture of NBMC and CML-BC cells was exposed to CPT in the absence of growth factors and assayed for growth ability in clonogenic assay and for expression of BCR/ABL transcript in single colonies. BCR/ABL transcript was not detected in colonies incubated with CTP, in contrast, most of colonies arising from untreated cells possessed leukemic origin (BCR/ABL expression). Our results indicate that CPT is selectively effective in vitro against the leukemia cells. This offers the prospect of a novel and more selective treatment of CML.
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PMID:The diverse effect of topoisomerase I specific inhibitor (camptothecin) on normal and BCR/ABL-dependent hematopoietic cells proliferation: therapeutic implications. 861 72

Cytosine arabinoside (Ara-C) activation to cytosine arabinoside triphosphate (Ara-CTP) and subsequent incorporation into DNA is regulated by the pyrimidine nucleotides UTP, CTP and dCTP. Inhibition of the de novo synthesis of these pyrimidine nucleotides by N-(phosphon)-acetyl-L-aspartate (PALA) may enhance the cytotoxicity of Ara-C. We therefore studied the effect of PALA on Ara-C cytotoxicity and on Ara-CTP accumulation and incorporation into DNA on cell lines and patient samples. Fifty micromolar PALA increased the growth inhibitory effect of Ara-C in U937 cells several fold both with pre- and coincubation. Ara-C cytotoxicity was not potentiated by PALA in Hl60 cells. However, coincubation with PALA did not enhance Ara-CTP accumulation both in HL60 and U937 cells, nor affect Ara-C incorporation into DNA. Ara-C cytotoxicity to leukemic blast cells from 11 untreated patients with different types of leukemia was only modulated to a small extent by high PALA concentrations in only two cases. Ara-CTP accumulation in leukemic blast cells varied from non-detectable levels to 200 pmol/10(6) cells. Fifty micromolar PALA enhanced the accumulation of Ara-CTP significantly in only one patient with no apparent effect on UTP and CTP levels. Raising PALA to 500 microM decreased UTP and CTP levels to 50% but had no effect on Ara-CTP levels. In conclusion, modulation by PALA of Ara-C cytotoxicity and metabolism is limited in leukemic cells, both in culture and from patients. This suggests the possibility for selective modulation of other agents by PALA on non-hematological cells.
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PMID:Modulation of metabolism and cytotoxicity of cytosine arabinoside with N-(phosphon)-acetyl-L-aspartate in human leukemic blast cells and cell lines. 862 11

Under resting conditions, steady-state [Ca] in agonist-sensitive Ca stores reflects a balance between active uptake (usually mediated by a thapsigargin-sensitive Ca-ATPase of the SERCA family) and passive efflux of Ca. Even though this pump-leak cycle appears to be a common property of Ca-storing organelles, little is known about the nature of the leak pathway. Ca homeostasis in thapsigargin-sensitive internal Ca stores of single permeabilized BHK-21 fibroblasts was examined using digital image processing of compartmentalized mag-fura-2 (a low-affinity Ca indicator). It is shown here that the leak of Ca from internal stores is regulated specifically by the cytosolic ATP concentration. The rate of leak was 3.6 times slower in 0.375 mM[ATP] than in 4 mM [ATP] (Na or Mg salt). These effects were observed in the presence of 0 Ca/EGTA, thapsigargin, heparin, and ruthenium red, and therefore appear to be independent of the Ca-ATPase, the InsP(3) receptor and the ryanodine receptor. The ATP-stimulated leak was seen in a variety of cell types, including rat basophilic leukemia cells and mouse pancreatic acinar cells. Other nucleotides (ADP, GTP, CTP, and UTP) and nonhydrolyzable ATP analogs (AMP-PNP and ATPgammaS) did not reproduce the action of ATP. Changes in cellular metabolism and ensuing alterations in [ATP] will be expected to influence the filling state of internal Ca stores through effects on the passive leak pathway, potentially leading to modulation of Ca signaling and organellar function.
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PMID:ATP regulates calcium leak from agonist-sensitive internal calcium stores. 864 63

It is uncertain if acute lymphoblastic leukemia (ALL) cells expressing myeloid makers can respond to granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF). We investigated the effects of G-CSF (0.01 microgram/ml) and GM-CSF (0.01 microgram/ml) on [3H]thymidine (TdR) uptake, and the cytotoxicity of 1-beta-D-arabinofuranosylcytosine (ara-C) in leukemia cells from 17 pediatric patients. ALL cells without myeloid markers did not respond to G-CSF or GM-CSF. On the other hand, these cytokines enhanced the [3H]TdR uptake and cell growth, not only of AML cells but also of ALL cells expressing myeloid antigens. However, G-CSF and GM-CSF did not always enhance the growth inhibitory effect of the cell cycle specific drug ara-C when the cells were co-cultured with the drug. There was no relationship between cell growth and the amount of [3H]TdR incorporation or the intracellular ara-CTP level. These results indicate the heterogeneous effects of G-CSF and GM-CSF on cell growth and ara-C sensitivity in childhood leukemia cells.
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PMID:Heterogeneous effects of G-CSF and GM-CSF on cell growth and ara-C cytotoxicity in childhood leukemias which express myeloid markers. 881 77

Previous studies in pediatric patients with acute myelogenous leukemia (AML) have suggested that 2-chlorodeoxyadenosine (2CdA) is an effective therapeutic agent. Santana et al (J Clin Oncol 1992; 10: 364-370) reported a CR rate of 8/17 (95% Cl 23-72%) in children with relapsed AML and a median first CR of 21 months. The activity of 2CdA in adults with relapsed or refractory leukemia was therefore investigated in a phase I study. In the phase II study, based on biochemical modulation rationale, 2CdA was combined with Ara-C for adults with relapsed AML to test the effectiveness of this combination therapy. In the phase I study 27 patients (25 AML and two MDS) with a median first CR duration of 21 weeks, received 2CdA at doses ranging from 5 to 13 mg/m2/day by continuous infusion (CI) for 7 days. In vitro and ex vivo pharmacologic studies performed to determine the effect of pretreatment with 2CdA on Ara-CTP accumulation in leukemic blasts demonstrated a 50-65% increase in the rate of Ara-CTP accumulation. Based on this biochemical modulation, 2CdA (12 mg/m2/day x 5 days by CI) was combined with Ara-C (1 g/m2/day over 2 h) in a phase II study. Seventeen patients (15 AML, two MDS) with relapsed AML (median 1st CR of 19 weeks) were treated. In the phase I study two patients died before the day 14 marrow (ED). Marrow hypoplasia developed in 16 of the remaining 25. Leukemic regrowth occurred in nine after a median hypoplastic period of 2 weeks (range 1-3 weeks). The other seven patients died with aplastic marrows, median duration of hypoplasia was 2 weeks, range 1-4 weeks. None achieved CR and the median survival was 10.5 weeks. Toxicity generally was mild except for three late occurring cases of grade III or IV renal dysfunction and two cases of tumor lysis syndrome. The MTD was 10.8 mg/m2/day x 7 days. In the phase II study two patients, both with AML, achieved CR (95% CI 1-33%). In both cases leukemia relapsed after 10 weeks and 17 weeks. There was one ED. Most (11/16) cleared their marrow although leukemic infiltrate regrew in six cases. Toxicity was generally mild, with two episodes of grade 2 GI bleeding, one episode of severe renal dysfunction and one case of grade 2 CNS toxicity. We conclude that as a single agent 2CdA at the MTD is a cytoreductive agent but is not sufficient to achieve CR in adults with relapsed AML. While combination of Ara-C with 2CdA increases the Ara-CTP uptake in these heavily treated patients this regimen does not appear to be an improvement over existing modalities.
Leukemia 1996 Oct
PMID:Clinical and laboratory studies of 2-chlorodeoxyadenosine +/- cytosine arabinoside for relapsed or refractory acute myelogenous leukemia in adults. 884 90

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