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PubMed1994

Cytosylglucuronic acid synthase (cytosine: UDP-glucuronosyltransferase) from Streptomyces griseochromogenes, the first prokaryotic UDP-glucuronosyltransferase.

Cytosylglucuronic acid synthase (cytosine: UDP-glucuronosyltransferase), the first prokaryotic UDP-GT and a key enzyme in the biosynthesis of the antibiotic blasticidin S, was purified 870-fold. It has optimum activity at a pH of 8.4 to 8.6, Kms of 6.0 (UDP-glucuronic acid) and 243 (cytosine) microM, and a maximum rate of metabolism of 14.6 mumol/min/mg. The apparent M(r) is 43,000. Activity was slightly enhanced by Mg2+ or Ca2+ but was not inhibited by EDTA. Activity was strongly inhibited by UDP. Cytosylglucuronic acid differs from eukaryotic UDP-glucuronosyltransferases in being a soluble protein with no apparent phospholipid requirement.

Chromatography, Affinity↗
PubMed2001

New plasmid system to select for Saccharomyces cerevisiae purine-cytosine permease affinity mutants.

The FCY2 gene of Saccharomyces cerevisiae encodes a purine-cytosine permease (PCP) that mediates the active transport of purines and cytosine. A structure-function model for this PCP has been recently proposed. In this study, we developed a plasmid-based system that generated a number of affinity-mutated alleles, enabling us to define new amino acids critical for permease function.

Alleles↗
PubMed1971

Synergistic effect of herpes simplex virus and cytosine arabinoside on human chromosomes.

The combined treatment of cultures of human embryonic lung cells with herpes simplex virus type 2 and cytosine arabinoside produced a significantly increased number of cells containing multiple chromatid and chromosome breaks. The incidence of such cells was found to be approximately two and one half times greater than the additive effects of virus and cytosine arabinoside induced separately and is therefore synergistic.

Autoradiography↗
PubMed1996

Evaluation of cytosine arabinoside, carboplatin and etoposide chemotherapy in the treatment of relapsing and refractory non-Hodgkin's lymphoma.

Twenty-eight patients (14 with relapsing and 14 with refractory non-Hodgkin's lymphoma; NHL) were treated with a combination of CACE chemotherapy (cytosine arabinoside, carboplatin, and etoposide) and recombinant granulocyte colony-stimulating factor (G-CSF) to investigate the efficacy and adverse effects of this regimen. Twenty-eight NHL patients (16 men and 12 women, median age 52 years) received intravenous infusions of cytosine arabinoside (100 mg/m2) on days 1-7, carboplatin (250 mg/m2) on day 1, and etoposide (70 mg/m2) on days 1-3, as well as the subcutaneous administration of G-CSF (2 micrograms/kg) beginning on day 9. Eleven of 28 (39.3%) patients achieved complete remission (CR) and 10 patients (35.7%) partial remission (PR). Therefore, a total response rate of 75% was achieved. Nine patients with relapsing disease and 2 with refractory NHL achieved CR. Of the 28 patients 51.5% were alive at 3 years, while the 3-year survival rate for those who achieved CR was 87.5%. The 50% disease-free survival duration was 20.8 months. Adverse effects included leukopenia (2 x 10(9)/l) in 4 patients (14.2%) and thrombocytopenia (50 x 10(9)/l) in 18 patients (64.3%). Although the efficacy of the CACE regimen was demonstrated for treatment of relapsing NHL, the efficacy of CACE was not satisfactory for the treatment of refractory NHL. Further study is required to determine the value of the CACE regimen as therapy for the refractory NHL.

Adult↗
PubMed1979

Drug-induced kinetic perturbations of the marrow blasts in acute leukemia. Effects of the daunorubicin, cytosine arabinoside and 6-thioguanine combination.

Cell kinetic changes induced in the marrow blasts by treatment with a triple cytotoxic regimen including daunorubicin, cytosine arabinoside and 6-thioguanine (DAT) were investigated in 6 previously untreated acute nonlymphocytic leukemia patients. A decrease in the labeling and mitotic indices was consistently observed 24 h after administration of daunorubicin, suggesting a G2 block and a preferential lytic effect on the S-phase cells operated by the drug. Conversely, cytosine arabinoside and 6-thioguanine in combination induced a series of kinetic perturbations variable from case to case; however, three principal patterns of kinetic response were recogized and discussed in detail. Useful information for the planning of a more rational antileukemic therapy can be drawn from a systematic study of the kinetic effects induced by drug combinations.

Adolescent↗
PubMed1977

Alteration of rat bone marrow megakaryocytes following administration of cytosine arabinoside, daunomycin and hydroxyurea.

The in vivo effects of three cytotoxic agents--cytosine arabinoside, daunomycin and hydroxyurea on rat bone marrow megakaryocytes were studied, specifically the relative count, the type percentage and the morphology. All three agents caused thrombo-cytopenia, a decrease in the number of megakaryocytes relative to the nucleated bone marrow cells, and a decrease in the percentage of megakaryoblasts, associated with an increase in the percentage of granular megakaryocytes. A decreased lobulation of the megakaryocytes was observed following the administration of cytosine arabinoside and of daunomycin. Thrombosthenin, examined immunologically, remained detectable in the bone marrow smears throughout the various stages of megakaryocyte alteration.

Animals↗
PubMed2006

Fludarabine and cytosine are less effective than standard ADE chemotherapy in high-risk acute myeloid leukemia, and addition of G-CSF and ATRA are not beneficial: results of the MRC AML-HR randomized trial.

The optimum chemotherapy schedule for reinduction of patients with high-risk acute myeloid leukemia (relapsed, resistant/refractory, or adverse genetic disease) is uncertain. The MRC AML (Medical Research Council Acute Myeloid Leukemia) Working Group designed a trial comparing fludarabine and high-dose cytosine (FLA) with standard chemotherapy comprising cytosine arabinoside, daunorubicin, and etoposide (ADE). Patients were also randomly assigned to receive filgrastim (G-CSF) from day 0 until neutrophil count was greater than 0.5 x 10(9)/L (or for a maximum of 28 days) and all-trans retinoic acid (ATRA) for 90 days. Between 1998 and 2003, 405 patients were entered: 250 were randomly assigned between FLA and ADE; 356 to G-CSF versus no G-CSF; 362 to ATRA versus no ATRA. The complete remission rate was 61% with 4-year disease-free survival of 29%. There were no significant differences in the CR rate, deaths in CR, relapse rate, or DFS between ADE and FLA, although survival at 4 years was worse with FLA (16% versus 27%, P = .05). Neither the addition of ATRA nor G-CSF demonstrated any differences in the CR rate, relapse rate, DFS, or overall survival between the groups. In conclusion these findings indicate that FLA may be inferior to standard chemotherapy in high-risk AML and that the outcome is not improved with the addition of either G-CSF or ATRA.

Adolescent↗
PubMed1985

Cytosine-arabinoside-induced colitis and peritonitis: nonoperative management.

Cytosine arabinoside is known to cause severe gastrointestinal side effects in an already very ill patient population. Three cases are reviewed in which apparent surgical peritonitis was managed conservatively, with very careful clinical monitoring. Two of the patients recovered completely, and one died of systemic fungal infection. No patient had a surgically remediable condition, and all were extremely poor surgical risks. A review of our experience and the literature leads us to recommend careful conservative management in patients receiving cytosine arabinoside who appear to have a "surgical abdomen," but in whom a definitive surgical diagnosis cannot be made.

Abdomen↗
PubMed1986

Neurotoxicity associated with systemic high-dose cytosine arabinoside.

High doses of cytosine arabinoside (ara-C) have been used in the treatment of refractory forms of acute nonlymphoblastic leukemia (ANLL) and ANLL occurring after previous antineoplastic therapy. In addition to the usual toxicities associated with antimetabolites, neurotoxicity, mainly in the form of cerebellar dysfunction, develops in a significant proportion of patients receiving high-dose cytosine arabinoside HDara-C. This study was performed to determine the incidence of cerebellar dysfunction in our patients and to determine any factors that predict its development. In this series of 30 consecutive patients receiving HDara-C, confusion with cerebellar signs and symptoms developed in seven (23%). Factors that appear to predispose patients to the development of neurotoxicity are (1) past history of neurologic dysfunction and (2) preexisting and progressive hepatic dysfunction. No peripheral neuropathy was seen. In contrast to previous reports, we did not find neurotoxicity to be dose related. Prophylactic use of pyridoxine does not prevent neurotoxicity.

Acute Disease↗
PubMed1989

Cytosine arabinoside plus hemin treatment of a human erythroid cell line, KMOE, strongly induces embryonic, fetal, and adult beta-like globin genes.

A variety of regimens were utilized on KMOE cells to maximally raise globin mRNA levels for the purpose of improving the usefullness of this line for globin gene studies. Steady-state mRNA levels of embryonic (epsilon), fetal (gamma) and adult (beta) globin genes were assayed by the S1-nuclease protection method before and after exposure to inducing compounds. Exposure of KMOE cells to cytosine arabinoside and hemin leads to over 20-fold increases in beta- and gamma-globin mRNA steady-state levels, and an over 60-fold increase in epsilon-globin mRNA level. Exposure to cytosine arabinoside alone induced beta- and epsilon-globin but not gamma-globin gene expression. The alpha-like globin genes (zeta and alpha) were also monitored but found to be poorly expressed and not significantly inducible. The presence of epsilon-globin mRNA and the lack of alpha-globin mRNA distinguishes this line, KMOE-EL, from the KMOE sublines previously described.

Aminolevulinic Acid↗
PubMed1986

Cytosine arabinoside induced changes in natural killer and antibody dependent cellular cytotoxicity functions in multiple sclerosis patients.

Five multiple sclerosis patients were treated weekly with cytosine arabinoside (araC) on an escalating dose schedule. The dose was initiated at 50 mg/M2 and then increased once each week by 50 mg/M2 (unless toxicity caused delay). Dosage decisions were based on whether or not the antibody-dependent cellular-cytotoxicity (ADCC) or natural killer (NK) cytotoxicity levels had been reduced to a level more than 2 standard deviations below the control range. Cytosine arabinoside treatment was discontinued in 2 of 5 subjects at doses of 500 mg/M2 due to toxicity. The 3 remaining patients demonstrated sustained reductions in the percentage of FcR+ cells in their peripheral blood. The maximum percentage reductions from the baseline values ranged from 50% to 76%. Concomitant reductions in the NK activity at the same doses ranged from 65% to 83%. ADCC activity in all 3 patients, however, was relatively resistant to suppression. The nadirs for the ADCC activity were only 16% to 44% below the baseline minimum. AraC was shown to reduce the proportion of FcR+ cells and NK cytotoxic activity in preference to ADCC activity.

Antibody-Dependent Cell Cytotoxicity↗
PubMed2003

Immunization with Th-CTL fusion peptide and cytosine-phosphate-guanine DNA in transgenic HLA-A2 mice induces recognition of HIV-infected T cells and clears vaccinia virus challenge.

We evaluated immunogenicity of a novel Th-CTL fusion peptide composed of the pan DR Th epitope and a CTL epitope derived from HIV-pol in two transgenic HLA-A*0201/K(b) mouse models. The immunogenicity of peptides of this structure is highly dependent on coadministered cytosine-phosphate-guanine DNA. Initial evaluations of peptide-specific immunity are based on results of chromium release assay, intracellular cytokine, and tetramer staining. Significant cytotoxic T cell responses are found upon a single immunization with as low as 0.1 nmol both peptide and cytosine-phosphate-guanine DNA. Splenocytes from immunized mice recognize naturally processed HIV-pol expressed from vaccinia virus (pol-VV). Translation of immunologic criteria into more relevant assays was pursued using systemic challenge of immunized mice with pol-VV. Only mice receiving both peptide and DNA together successfully cleared upward of 6 logs of virus from ovaries, compared with controls. Challenge with pol-VV by intranasal route of intranasal immunized mice showed a significant reduction in the levels of VV in lung compared with naive mice. A convincing demonstration of the relevance of these vaccines is the robust lysis of HIV-infected Jurkat T cells (JA2/R7/Hyg) by immune splenocytes from peptide- and DNA-immunized mice. This surprisingly effective immunization merits consideration for clinical evaluation, because it succeeded in causing immune recognition and lysis of cells infected with its target virus and reduction in titer of highly pathogenic VV.

AIDS Vaccines↗
PubMed2006

Immunological characterization and antibacterial function of persisting granulocytes in leukemic patients receiving pulse cytosine arabinoside-consolidation chemotherapy on days 1, 3, and 5.

High-dose cytosine arabinoside (HiDAC) and intermediate-dose cytosine arabinoside (IDAC) have been introduced as effective and safe consolidation chemotherapy in acute myeloid leukemia, with relatively low rates of life-threatening infections despite the high total dose of the cytostatic drug. To explore the biological background of low toxicity, we examined the numbers, immunophenotype, and functional properties of granulocytes in patients with acute myeloid leukemia receiving HiDAC or IDAC. Interestingly, the absolute numbers of neutrophils remained >500/microl until day 10 in 92 of 125 (74%) HiDAC cycles and in 106 of 113 (94%) IDAC cycles. As assessed by electron microscopy, these day-10 granulocytes surviving chemotherapy were found to be mature cells containing secondary granules and phagolysosomes. They also expressed opsonization- and phagocytosis-linked surface Ags (C3biR, CR1, C1qR, C5aR, FcgammaRI, FcgammaRII, FcgammaRIII, and G-CSF and GM-CSF receptors) like neutrophils in healthy controls. Moreover, these day-10 neutrophils exhibited oxidative burst activity and took up and digested bacteria in the same way as neutrophils in healthy controls. There was a negative correlation between absolute neutrophil counts and severe infections in HiDAC- and IDAC-treated patients with a later onset of infections in IDAC patients (median: IDAC, day 18; HiDAC, day 16). Together, functionally mature neutrophils are detectable at least until day 10 in patients treated with HiDAC or IDAC, and may explain the relatively low hematologic toxicity of these consolidation protocols. IDAC is a superior protocol in this regard and may therefore be most suitable for elderly patients and those at high risk for severe infections.

Acute Disease↗
PubMed1999

Leukaemic blasts differ from normal bone marrow mononuclear cells and CD34+ haemopoietic stem cells in their metabolism of cytosine arabinoside.

Different metabolites of cytosine arabinoside (AraC) contribute to its cytotoxicity including incorporation of AraCTP into DNA, the incorporation of AraUMP into RNA, inhibition of polymerase alpha and beta (AraCMP/CTP), an impairment of repair mechanisms (AraCTP), alterations of phospholipid metabolism (AraCDP-choline), a direct membrane interaction (AraC), the alteration of signal transduction pathways (AraCDP-choline, AraCTP) and the induction of apoptosis. Since little is known about the potential differences in AraC metabolism between leukaemic blasts and normal haemopoietic progenitor cells, the formation of all known AraC metabolites was determined in bone marrow samples from patients with acute myeloid leukaemia (AML), healthy volunteers and specimens of cellsorted CD34+ haemopoietic stem cells. Highly significant differences were found for phosphorylated AraC metabolites (AraCMP, -CDP, -CTP, AraUMP) between AML and normal mononuclear bone marrow (ng/107 cells respectively 1.30 v 2.66; 2.65 v 7.50; 33.68 v 99.0; 1.18 v 5.70). The highest differences were found for formation of AraCDP-choline (3.75 v 12.86) which might be relevant for the high efficacy of high-dose AraC regimens. In contrast, no differences were found in the deamination product AraU (2.01 v 2.91). Only minute amounts of phosphorylated AraU derivatives were detected, providing an explanation for the lacking contribution of AraU to cytosine arabinoside cytotoxicity. Results in normal CD34+ haemopoietic stem cells did not differ significantly from normal bone marrow mononuclear cells and therefore justify their use as a surrogate in determining AraC-induced haematotoxicity. These data suggest a metabolic basis for the relative selectivity of AraC cytotoxicity for AML blasts and provide a means to determine the role of different metabolites and their related mechanism of action for overall AraC cytotoxicity.

Acute Disease↗
PubMed1999

Sequential standard dose mitoxantrone and cytosine arabinoside for newly diagnosed adult acute myeloblastic leukemia.

Twenty one adult patients with previously untreated acute myeloblastic leukemia (AML) were treated with sequential mitoxantrone and standard dose cytosine arabinoside remission induction therapy. The median age was 33 years (range 17-56 years). Complete remission (CR) was achieved in 80% (17/21 cases) and 76% (16/21 cases) achieved CR after one course of induction therapy. The median duration of disease free survival was 9 months with an actuarial disease free survival of 22% at 43 months. The non-hematological toxicity was acceptable. We conclude that sequential mitoxantrone and cytosine arabinoside combination therapy is an effective antileukemic regimen which produces high CR rates in previously untreated adult patients with AML.

Adolescent↗
PubMed1975

Topical treatment of recurrent herpes simplex with cytosine arabinoside.

A double-blind controlled clinical trial of the topical use of cytosine arabinoside in recurrent herpes simplex of the face and genital region showed no significant difference in the efficiency of a placebo as compared with cytosine arabinoside. The high rate of placebo response (70%) found in this trial makes the assessment of any drug treatment for herpes simplex particularly difficult.

Administration, Topical↗
PubMed1975

Alkylated cytosine nucleosides: substrate and inhibitor properties in enzymatic deamination.

Cytosine nucleoside deaminase (EC 3.5.4.5) from Salmonella typhimurium LT2 catalyses the deamination of ribo-, deoxyribo- and arabinosyl nucleosides of cytosine alkylated at the C-5, but not at the N3 or exocyclic N4, of the pyrimidine ring. The enzyme was inert towards analogues etherified at the 3'-OH and 5'-OH of the sugar ring; it was active against the 2'-O-methyl derivative of cytidine, but not arabinosycytosine. The N4-and 5'-O-alkyl non-substrate analogues competitively inhibited deamination of deoxycytidine and arabinosylcytosine, the most inhibitory being 5'-O-methylarabinosylcytosine. The alpha anomer of 5'-ethyldeoxycytidine, the 2,2'-anhydro derivative of cytidine, and the 3'-O-alkyl derivatives were neither substrates nor inhibitors. The presence of cytidine deaminase was demonstrated in both granulocytes and lymphocytes from human peripheral blood. The specificity of this enzyme differed significantly from that of the bacterial enzyme, a finding of some relevance in relation to the frequently encountered intracellular deamination of therapeutically active arabinosylcytosine to the inactive arabinosyluracil.

Alkylation↗
PubMed1999

[Poor response in patients with de novo acute myeloid leukemia and erythroblastic or megakaryocytic dysplasia to treatment with standard doses of cytosine arabinoside and daunorubicin].

Erythroid and/or megakaryocytic dysplasia (EMD) was evaluated in diagnostic bone marrow smears of 37 consecutively treated cases with de novo acute myeloid leukemia (AML) M0-M2 and M4-M5 types and three newly diagnosed cases of refractory anaemia with excess of blasts in transformation. This evaluation was possible in 38 of 40 (95%) patients and 17 cases were categorized without EMD and 21 cases with EMD. One or two cycles with 3-4 doses of daunorubicin 45 mg/m2/d and cytosine arabinoside 200 mg/m2/12 h x 14 lead to complete remission in 13 of 16 cases without EMD but only in 4 of 16 cases with EMD (p = 0.004). However, 10 of 13 patients with EMD reached complete remission with 2000 mg/m2/12 h x 10 of cytosine arabinoside plus daunorubicin. After intensive consolidations 20 patients under 65 years with EMD showed significantly worse overall survival (p = 0.017) with a median 11.5 months, while the median survival was estimated 66.8 months in 15 cases under 65 years without EMD. The proposed categorization of de novo AML patients according to the EMD seems to be useful for selection of optimal induction therapy, clinically relevant for survival and might reflect two biologic groups of AML arising in two different stages of differentiation.

Acute Disease↗