1,723,003 research outputs found
Fludarabine-Mediated Circumvention of Cytarabine Resistance Is Associated with Fludarabine Triphosphate Accumulation in Cytarabine-Resistant Leukemic Cells
Full text linkThe combination of cytarabine (ara-C) with fludarabine is a common approach to treating resistant acute myeloid leukemia. Success depends on a fludarabine triphosphate (F-ara-ATP)-mediated increase in the active intracellular metabolite of ara-C, ara-C 5'-triphosphate (ara-CTP). Therapy-resistant leukemia may exhibit ara-C resistance, the mechanisms of which might induce cross-resistance to fludarabine with reduced F-ara-ATP formation. The present study evaluated the effect of combining ara-C and fludarabine on ara-C-resistant leukemic cells in vitro. Two variant cell lines (R1 and R2) were 8-fold and 10-fold more ara-C resistant, respectively, than the parental HL-60 cells. Reduced deoxycytidine kinase activity was demonstrated in R1 and R2 cells, and R2 cells also showed an increase in cytosolic 5'-nucleotidase II activity. Compared with HL-60 cells, R1 and R2 cells produced smaller amounts of ara-CTP. Both variants accumulated less F-ara-ATP than HL-60 cells and showed cross-resistance to fludarabine nucleoside (F-ara-A). R2 cells, however, accumulated much smaller amounts of F-ara-ATP and were more F-ara-A resistant than R1 cells. In HL-60 and R1 cells, F-ara-A pretreatment followed by ara-C incubation produced F-ara-ATP concentrations sufficient for augmenting ara-CTP production, thereby enhancing ara-C cytotoxicity. No potentiation was observed in R2 cells. Nucleotidase might preferentially degrade F-ara-A monophosphate over ara-C monophosphate, leading to reduced F-ara-ATP production and thereby compromising the F-ara-A-mediated potentiation of ara-C cytotoxicity in R2 cells. Thus, F-ara-A-mediated enhancement of ara-C cytotoxicity depended on F-ara-ATP accumulation in ara-C-resistant leukemic cells but ultimately was associated with the mechanism of ara-C resistance.othe
Acylation of ara-C with vinyl laurate catalyzed by whole-cells (1: Ara-C; 2: VL; 3: Unstable enol; 4: Aldehyde; 5: 3′-O-lauryl ara-C; 6: 5′-O-lauryl ara-C).
No full text<p>Acylation of ara-C with vinyl laurate catalyzed by whole-cells (1: Ara-C; 2: VL; 3: Unstable enol; 4: Aldehyde; 5: 3′-O-lauryl ara-C; 6: 5′-O-lauryl ara-C).</p
miR-181a sensitizes resistant leukaemia HL-60/Ara-C cells to Ara-C by inducing apoptosis
No full textAra-C is one of the most commonly used drugs in the treatment of AML. However, the development of drug resistance always prevented its further use. It has been shown that miR-181a is associated with the clinical outcome of AML patients. Here, we investigated the possible role of miR-181a in AML Ara-C resistance. miR-181a expression was measured by real-time PCR. Cell viability was detected by MTT assay. Protein expressions were measured by western blotting. Caspase activity was examined by florescence assay. We found that miR-181a expression was downregulated in the Ara-C-resistant cell line HL-60/Ara-C compared with its parental cell line HL-60. Overexpression of miR-181a in HL-60/Ara-C cells sensitized the cells to Ara-C treatment. Furthermore, Bcl-2 was confirmed as a direct miR-181a target by immunoblot analysis and reporter gene assays. Knockdown of Bcl-2 mimicked the effect of enforced miR-181a expression by reducing cell viability. In addition, the apoptosis pathway was activated by cytochrome C release and caspase 9/caspase 3 activation after miR-181a overexpression. This study for the first time demonstrated that downregulation of miR-181a and upregulation of Bcl-2 in leukaemia cells confer resistance to Ara-C-based therapy. These results suggest that restoration of miR-181a expression might provide a promising therapeutic in drug resistance of leukaemia.Shanghai Jiaotong University Affiliated Shanghai First People's Hospital [061138
PEG-Ara-C conjugates for controlled release.
No full textThe antitumour agent 1-beta-D arabinofuranosilcytosyne (Ara-C) was covalently linked to poly(ethylene glycol) (PEG) in order to improve the in vivo stability and blood residence time. Eight PEG conjugates were synthesised, with linear or branched PEG of 5000, 10000 and 20000 Da molecular weight through an amino acid spacer. Starting from mPEG-OH or HO-PEG-OH, conjugation was carried out to the one or two available hydroxyl groups at the polymer's extreme. Furthermore, to increase the drug loading of the polymer, the hydroxyl functions of PEG were functionalised with a bicarboxylic amino acid yielding a tetrafunctional derivative and, by recursive conjugation with the same bicarboxylic amino acid, products with four or eight Ara-C molecules for each PEG chain were prepared. A computer graphic investigation demonstrated that aminoadipic acid was a suitable bicarboxylic amino acid to overcome the steric hindrance between the vicinal Ara-C molecules in the dendrimeric structure. In this paper we report the optimised conditions for synthesis and purification of PEG-Ara-C products with a low amount of remaining free drug, studies toward the hydrolysis of PEG-Ara-C and the Ara-C deamination by cytidine deaminase, pharmacokinetics in mice and cytotoxicity towards HeLa human cells were also investigated. Increased stability towards degradation of the conjugated Ara-C products, in particular for the highly loaded ones, improved blood residence time in mice and a reduced cytotoxicity with respect to the free Ara-C form was demonstrated
Differential mRNA expression of Ara-C-metabolizing enzymes explains Ara-C sensitivity in MLL gene-rearranged infant acute lymphoblastic leukemia
Full text linkInfant acute lymphoblastic leukemia (ALL) is characterized by a high
incidence of mixed lineage leukemia (MLL) gene rearrangements, a poor
outcome, and resistance to chemotherapeutic drugs. One exception is
cytosine arabinoside (Ara-C), to which infant ALL cells are highly
sensitive. To investigate the mechanism underlying Ara-C sensitivity in
infants with ALL, mRNA levels of Ara-C-metabolizing enzymes were measured
in infants (n = 18) and older children (noninfants) with ALL (n = 24). In
the present study, infant ALL cells were 3.3-fold more sensitive to Ara-C
(P =.007) and accumulated 2.3-fold more Ara-CTP (P =.011) upon exposure to
Ara-C, compared with older children with ALL. Real-time quantitative
reverse trancriptase-polymerase chain reaction (RT-PCR) (TaqMan) revealed
that infants express 2-fold less of the Ara-C phosphorylating enzyme
deoxycytidine kinase (dCK) mRNA (P =.026) but 2.5-fold more mRNA of the
equilibrative nucleoside transporter 1 (hENT1), responsible for Ara-C
membrane transport (P =.001). The mRNA expression of pyrimidine
nucleotidase I (PN-I), cytidine deaminase (CDA), and deoxycytidylate
deaminase (dCMPD) did not differ significantly between both groups. hENT1
mRNA expression inversely correlated with in vitro resistance to Ara-C
(r(s) = -0.58, P =.006). The same differences concerning dCK and hENT1
mRNA expression were observed between MLL gene-rearranged (n = 14) and
germ line MLL cases (n = 25). An oligonucleotide microarray screen
(Affymetrix) comparing patients with MLL gene-rearranged ALL with those
with nonrearranged ALL also showed a 1.9-fold lower dCK (P =.001) and a
2.7-fold higher hENT1 (P =.046) mRNA expression in patients with MLL
gene-rearranged ALL. We conclude that an elevated expression of hENT1,
which transports Ara-C across the cell membrane, contributes to Ara-C
sensitivity in MLL gene-rearranged infant ALL
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IL-1 synergizes with ARA-C in aborting the development of chloroleukemia while protecting from ARA-C-induced alopecia in the rat model
No full textRecently, interleukin 1 (IL-1) was shown to protect rats from ARA-C-induced alopecia. The present study was designed to investigate the effect of combination rHu-IL-1 and ARA-C on transplantable chloroleukemia (C51) and at the same time evaluate the protective effect of IL-1 on the ARA-C-induced alopecia in the rat model. In vitro, IL-1 had no direct effect on growth, viability or differentiation of C51 cells, neither did IL-1 protect the C51 cells from ARA-C cytotoxicity. In vivo, the combination treatment of ARA-C + IL-1 aborted the development of transplanted chloroleukemia in 100% of rats, vs 60%, 10% and 0% survival for rats treated with IL-1, ARA-C and buffer respectively. All rates treated with ARA-C alone developed complete body alopecia. In contrast, none of the rats treated with combination IL-1 and ARA-C combination developed alopecia. Thus, IL-1 demonstrated a double beneficial effect, synergism with ARA-C against the leukemic cells on the one hand, and protection from ARA-C-induced alopecia, on the other
Labelling of liposomes with intercalating perylene fluorescent dyes
Full text linkThe high fluorescent potential and the exceptional photostability of lipophilic derivatives of perylene-3,4:9,10-bis(dicarboximides) are utilized for the fluorescence-labelling of liposomes. The preparation of the liposomes is affected by supersonic starting from a lipid mixture consisting of the matrix lipids soy lecithin, cholesterol, -tocopherol and the perylene dyes. From a multitude of perylene derivatives investigated only those are optimally incorporated inot the bilayer membrane of unilamellar liposomes which are substituted at both nitrogen atoms by one or two linear hydrocarbon groups. In order to attain an optimal fluorescent quantum yield, about 200 to 300 dye molecules can be incorporated per liposome. The liposomes thus obtained have a diameter of about 70 to 80 nm, are homogeneous and may be stored for more than seven months. Neither the fluorescent properties nor the stability of these liposomes are influenced by the additional incorporation of various ara C-derivatives and lipophilic anchor groups which subsequently enable the coupling of antibodies to the liposomes. As the water-insoluble perylene dyes are incorporated into the bilayer membrane, the aqueous inner volume of the liposomes remains available for a fruther utilization
Induction of topoisomerase I cleavage complexes by 1-beta -D-arabinofuranosylcytosine (ara-C) in vitro and in ara-C-treated cells
No full textInternational audience1-beta-d-Arabinofuranosylcytosine (Ara-C) is a nucleoside analog commonly used in the treatment of leukemias. Ara-C inhibits DNA polymerases and can be incorporated into DNA. Its mechanism of cytotoxicity is not fully understood. Using oligonucleotides and purified human topoisomerase I (top1), we found a 4- to 6-fold enhancement of top1 cleavage complexes when ara-C was incorporated at the +1 position (immediately 3') relative to a unique top1 cleavage site. This enhancement was primarily due to a reversible inhibition of top1-mediated DNA religation. Because ara-C incorporation is known to alter base stacking and sugar puckering at the misincorporation site and at the neighboring base pairs, the observed inhibition of religation at the ara-C site suggests the importance of the alignment of the 5'-hydroxyl end for religation with the phosphate group of the top1 phosphotyrosine bond. This study also demonstrates that ara-C treatment and DNA incorporation trap top1 cleavage complexes in human leukemia cells. Finally, we report that camptothecin-resistant mouse P388/CPT45 cells with no detectable top1 are crossresistant to ara-C, which suggests that top1 poisoning is a potential mechanism for ara-C cytotoxicity
Protective Effect of Vitamin A on ARA-C Induced Intestinal Damage in Mice
No full textBackground Cytarabine (ARA-C) has been used for many years in the treatment of patients with leukemia and lymphoma. Gastrointestinal ulceration and mucositis are two of the well-known side effects of ARA-C. We set out to investigate whether vitamin A (VA) can help prevent ARA-C-induced mucosal lesions in mice. Materials and methods Mice were divided into 5 groups. Group I (control group) received only saline; group II received ARA-C plus saline; group III received ARA-C plus VA; group IV received ARA-C plus a lipid solution, and group V received VA alone. VA (5000 IU/kg) was administered orally to the mice once daily for 7 days. ARA-C (3.6 mg) was administered intraperitoneally for 5 days to groups II, III and IV, starting on the third day of VA treatment. Intestinal segments from the proximal end of the jejunum of treated mice were isolated. Results There was improved mucosal integrity, less necrosis and increased villus length with advanced mucosal proliferation in crypts in the VA plus ARA-C group when compared to the ARA-C groups without VA. Conclusion We conclude that VA has a protective effect against ARA-C-induced mucosal damage in mice. </jats:sec
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