Disease relevance of Arabinosylcytosine triphosphate

• Measurements of intracellular AraCTP levels were complemented by determinations of plasma AraC and AraU concentrations and were performed in 32 patients with acute myeloid leukemia undergoing combination therapy including either conventional (100 mg/m2 daily) or high-dose (1.0 or 3.0 g/m2 twice daily) AraC [1].
• Liposomally trapped AraCTP to overcome AraC resistance in a murine lymphoma in vitro [2].
• Typical HIDAC regimens deliver 6 g/m2/d in infusion rates of 500-3000 mg/m2/h. However, pharmacokinetic measurements indicate that intracellular Ara-CTP formation is saturated at lower infusion rates than used in HIDAC schedules, probably causing cytarabine accumulation in the plasma and increased toxicity [3].

High impact information on Arabinosylcytosine triphosphate

• The intracellular accumulation of Ara-CTP relative to dCTP, Ara-C DNA incorporation and Ara-C-induced early DNA damage in the form of strand breaks (detected by alkaline elution assay) were not significantly different between HL-60/Bcl-2 and HL-60/neo cells [4].
• While neither 3H-Ara-C uptake, nor intracellular Ara-CTP concentration, TK nor DCK activity were predictive for response, a high 3H-TdR incorporation and a high poly alpha activity were associated with adequate blast cell reduction [5].
• Proliferative activity was assessed by 3H-thymidine (3H-TdR) incorporation and thymidine kinase (TK) activity, parameters of Ara-C metabolism comprised the activities of deoxycytidine kinase (DCK) and DNA polymerase alpha (poly alpha) as well as Ara-CTP concentrations and 3H-Ara-C uptake into DNA [5].
• The current study aims at adding to this approach by detecting differences in the intracellular metabolism of AraC 5'-triphosphate (AraCTP) between leukemic and normal mononuclear blood cells [1].
• Similar findings emerged after in vitro exposure of normal bone marrow cells from six healthy volunteers to 20 mumol/l AraC for 3 h revealing a > 10% decrease of intracellular AraCTP within the first post-treatment hour in all cases with AraCTP retention times of 2.29 to 8.63 h (median 3.20 h) [1].

Biological context of Arabinosylcytosine triphosphate

• These differences in AraCTP pharmacokinetics between leukemic and normal blood cells may provide the basis for a modified timing of AraC administration with the aim of selectively maintaining cytotoxic AraCTP levels in leukemic blasts while allowing an intermittent drop of AraCTP levels in normal cells.(ABSTRACT TRUNCATED AT 400 WORDS)[1]
• Ara-CTP inhibited both the initiation and elongation stages, whereas CPT produced most of its effects by inhibiting the elongation phase of DNA replication [6].
• Ara-CTP levels were measured by high-performance liquid chromatography (HPLC), cytotoxicity by the tetrazolium (MTT) assay, and apoptosis by occurrence of DNA fragmentation (gel electrophoresis), cell shrinkage and DNA loss (flow cytometry) [7].
• Even in patients with low phosphorylation increasing Ara-C concentration increased Ara-CTP levels proportionally, but up to 10 times conventional doses may be necessary to exceed endogenous dCTP levels [8].
• However, exposure to either of the HGFs for 20 hours followed by a combined treatment for 4 hours with HIDAC plus either of the HGFs versus HIDAC alone significantly enhanced the intracellular Ara-CTP accumulation and the oligonucleosomal DNA fragmentation characteristic of PCD [9].

Anatomical context of Arabinosylcytosine triphosphate

• Exposure of HL-60 cells to 1 mM HU enhanced the accumulation of Ara-CTP up to 2.5-fold, whereas HU did not have significant effects on Ara-C metabolism in CEM cells [10].
• The studies indicate that different B- and T-lymphoblastic leukaemia cell lines accumulate Ara-CTP to a markedly different extent [11].
• In addition, formation and retention of intracellular levels of AraC triphosphate (AraCTP) and DNA incorporation of AraC were measured, as was the proliferative activity of leukaemic blasts by [3H]-TdR incorporation before and after stimulation with granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte CSF (G-CSF) for 48 h [12].
• Ara-CTP elimination appeared slower in lymphoblasts than in myeloblasts [13].

Associations of Arabinosylcytosine triphosphate with other chemical compounds

• Ara-CTP, CPT, and DOX have been found to affect different stages of the in vitro DNA replication process mediated by the complex [6].
• In HL-60 cells a linear correlation between the concentration of STI-571 (1-10 microg/ml) and the subsequent levels of Ara-CTP was observed [14].
• Preincubation of HL-60 cells with 75 and 100 microM amidox for 24 hours caused an increase in the intracellular Ara-CTP concentrations by 576% and 1143%, respectively [15].
• Although both AraCTP and dFdCTP impede DNA replication through pausing of DNA polymerases, both nucleoside analogs are ultimately incorporated into replicated DNA and interfere in DNA-mediated processes [16].

Gene context of Arabinosylcytosine triphosphate

• In contrast, pre-exposure to HGFs led to significant increases in AraCTP formation (G-CSF 556.0 ng/107 cells, 2.31-fold increase, P < 0.001; GM-CSF 447.9 ng/107 cells, 1.87-fold increase, P < 0.0001) [17].
• In the infected cells, Ara-CTP levels decreased to 20% of that found in uninfected H9 cells after 3 h incubation at Ara-C concentration of 1 microM, and 8.1-fold increase of cytidine deaminase activity was observed in the infected H9 cells [18].
• This was associated with intracellular Ara-CTP and dFdCtriphosphate levels in 2008/C13 significantly higher than those in 2008 cells [19].
• Treatment of the cells with rhG-CSF resulted in a 17-fold increase in DNA synthesis, 4.6-fold increase in percentage of S-phase, and a two-fold increase in Ara-CTP formation [20].
• Deoxycytidine kinase, thymidine kinase and cytidine deaminase and the formation of Ara-CTP in leukemic cells in different phases of the cell cycle [21].

Analytical, diagnostic and therapeutic context of Arabinosylcytosine triphosphate

• The Ara-CTP-concentrations were measured by high pressure liquid chromatography (HPLC) [11].
• Intracellular levels of Ara-CTP measured by HPLC were increased 1.5-3 fold in leukemia cells with most promiment effects in HL-60, Kasumi and Raji cells [14].
• The method enables intracellular drug monitoring of Ara-CTP with standard HPLC equipment [22].
• Therefore, it may be possible to determine patients most likely to benefit from High Dose chemotherapy by measuring pre-treatment in vitro intracellular Ara-CTP [23].
• On the other hand, both the intracellular deoxyribonucleoside triphosphate (dNTP) pools and Ara-CTP level increased gradually after oral administration of C18PCA [24].

References