Development and application of a rapid and sensitive liquid chromatography-mass spectrometry method for simultaneous analysis of cytarabine, cytarabine monophosphate, cytarabine diphosphate and cytarabine triphosphate in the cytosol and nucleus.

In this study, a sensitive and rapid ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed for the simultaneous analysis of cytarabine (ara-C), cytarabine monophosphate (ara-CMP), cytarabine diphosphate (ara-CDP) and cytarabine triphosphate (ara-CTP) in the cytosol and nucleus. The separation of analytes and endogenous interferents was achieved in 8 min on a hypercarb column (2.1 mm × 100 mm, 3 µm) by using a gradient elution with 95% acetonitrile and aqueous 5 mM hexylamine with 0.4% (v/v) diethylamine adjusted to pH 10. The analytes were detected with both negative and positive electrospray ionization in multiple reaction monitoring (MRM) mode. The calibration curve demonstrated good linearity ranging from 5 to 750 nM for ara-C, 50-7500 nM for ara-CMP, 20-3000 nM for ara-CDP and 1-150 nM for ara-CTP in the cytosol. In the nucleus, good linearity was achieved over a concentration range of 1-100 nM for ara-C, 5-500 nM for ara-CMP, 2.5-250 nM for ara-CDP and 0.5-50 nM for ara-CTP. Intra- and interbatch accuracies and precisions met the standards of validation. The matrix effect, recovery and stability were also within acceptable ranges. After incubation with 10 µM ara-C for 3 h, the levels of ara-C, ara-CMP, ara-CDP and ara-CTP in the cytosol and nucleus of HL-60 cells and HL-60/ara-C cells were determined. Most of the metabolites were found within the quantitation range. The results showed that the nuclear ara-CTP level was significantly different than the intracellular ara-CTP level between HL-60 and HL-60/ara-C cells.

Rapid in-vitro testing for chemotherapy sensitivity in leukaemia patients.

Bioluminescent bacterial biosensors can be used in a rapid in vitro assay to predict sensitivity to commonly used chemotherapy drugs in acute myeloid leukemia (AML). The nucleoside analog cytarabine (ara-C) is the key agent for treating AML; however, up to 30 % of patients fail to respond to treatment. Screening of patient blood samples to determine drug response before commencement of treatment is needed. To achieve this aim, a self-bioluminescent reporter strain of Escherichia coli has been constructed and evaluated for use as an ara-C biosensor and an in vitro assay has been designed to predict ara-C response in clinical samples. Transposition mutagenesis was used to create a cytidine deaminase (cdd)-deficient mutant of E. coli MG1655 that responded to ara-C. The strain was transformed with the luxCDABE operon and used as a whole-cell biosensor for development an 8-h assay to determine ara-C uptake and phosphorylation by leukemic cells. Intracellular concentrations of 0.025 µmol/L phosphorylated ara-C were detected by significantly increased light output (P < 0.05) from the bacterial biosensor. Results using AML cell lines with known response to ara-C showed close correlation between the 8-h assay and a 3-day cytotoxicity test for ara-C cell killing. In retrospective tests with 24 clinical samples of bone marrow or peripheral blood, the biosensor-based assay predicted leukemic cell response to ara-C within 8 h. The biosensor-based assay may offer a predictor for evaluating the sensitivity of leukemic cells to ara-C before patients undergo chemotherapy and allow customized treatment of drug-sensitive patients with reduced ara-C dose levels. The 8-h assay monitors intracellular ara-CTP (cytosine arabinoside triphosphate) levels and, if fully validated, may be suitable for use in clinical settings.

Simultaneous determination of 1-ß-d-Arabinofuranosylcytosine and two metabolites, 1-ß-d-Arabinofuranosyluracil and 1-ß-d-Arabinofuranosylcytosine triphosphate in leukemic cell by HPLC-MS/MS and the application to cell pharmacokinetics.

A specific and reliable HPLC-MS/MS method was developed and validated for the simultaneous determination of 1-ß-d-Arabinofuranosylcytosine (ara-C), 1-ß-d-Arabinofuranosyluracil (ara-U) and 1-ß-d-Arabinofuranosylcytosine triphosphate (ara-CTP) in the leukemic cells for the first time. The analytes were separated on a C18 column (100mm×2.1mm, 1.8µm) and a triple-quadrupole mass spectrometry equipped with an electrospray ionization (ESI) source was used for detection. The ion-pairing reagent, NFPA, was added to the mobile phase to retain the analytes in the column. The cell homogenates sample was prepared by the simple protein precipitation. The calibration curves were linear over a concentration range of 3.45-3450.0ng/mL for ara-C, 1.12-1120.0ng/mL for ara-U and 4.13-4130.0ng/mL for ara-CTP. The intra-day and inter-day precision was less than 15% and the relative error (RE) were all within ±15%. The validated method was successfully applied to assess the disposition characteristics of ara-C and support cell pharmacokinetics after the patients with leukemia were intravenously infused with SDAC and HiDAC. The result of the present study would provide the valuable information for the ara-C therapy.

A novel bioluminescent bacterial biosensor for measurement of Ara-CTP and cytarabine potentiation by fludarabine in seven leukaemic cell lines.

This study evaluates an in vitro biosensor assay capable of detecting the intracellular levels of the tri-phosphorylated form of cytarabine (Ara-CTP) within one working day. The biosensor predicted the response of seven leukaemic cell lines with varying known sensitivities to cytarabine alone and in combination with fludarabine. High-performance liquid chromatography (HPLC), 3-day assessment of cellular viable mass, and flow cytometric assessment of apoptosis were used to validate biosensor performance. A correlation between the biosensor results and Ara-CTP quantitation by HPLC was confirmed (R=0.972). The biosensor was also capable of detecting enhanced accumulation of Ara-CTP following sequential pre-treatment of leukaemic cells with cytarabine ± fludarabine.

A new, simple method for quantifying gemcitabine triphosphate in cancer cells using isocratic high-performance liquid chromatography.

A deoxycytidine analog, gemcitabine (dFdC), is effective for treating solid tumors and hematological malignancies. After being transported into cancer cells, dFdC is phosphorylated to dFdC triphosphate (dFdCTP), which is subsequently incorporated into the DNA strand, thereby inhibiting DNA synthesis. Intracellular dFdCTP is the critical determinant for dFdC cytotoxicity, so therapeutic drug monitoring or in vitro testing of the capability of cancer cells to accumulate dFdCTP may be informative for optimizing dFdC administration. We have developed a new isocratic-elution high-performance liquid chromatography method for quantifying dFdCTP in cancer cells. Samples (500 microL) were eluted isocratically using 0.06 M Na(2)HPO(4) (pH 6.9) containing 20% acetonitrile, at a constant flow rate of 0.7 mL/min and at ambient temperature. Separation was carried out using an anion-exchange column (TSK gel DEAE-2SW; 250 mm x 4.6 mm inside diameter, particle size 5 microL) and monitored at 254 nm. The standard curve was linear with low within-day and interday variability. The lower detection limit (20 pmol) was as sensitive as that of the previous gradient-elution method. dFdCTP was well separated from other nucleoside triphosphates. The method could measure dFdCTP in cultured or primary leukemic cells treated in vitro with dFdC. The method was also applicable to simultaneous determination of dFdCTP and cytarabine triphosphate, the results of which demonstrated ara-CTP production augmented by dFdC pretreatment. Thus, our isocratic high-performance liquid chromatography assay method will be of great use because of its sensitivity and simplicity as well as its applicability to biological materials.

Close correlation of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate, an intracellular active metabolite, to the therapeutic efficacy of N(4)-behenoyl-1-beta-D-arabinofuranosylcytosine therapy for acute myelogenous leukemia.

N(4)-Behenoyl-1-beta-D-arabinofuranosylcytosine (BHAC), a prodrug of 1-beta-D-arabinofuranosylcytosine, is used effectively for the treatment of leukemia in Japan. BHAC therapy may be more effective if it is delivered in conjunction with monitoring of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP), the intracellular active metabolite of ara-C derived from BHAC. However, previous monitoring methods for ara-CTP were insufficiently sensitive. Here, using our new sensitive method, we evaluated the ara-CTP pharmacokinetics in relation to the therapeutic response in 11 acute myelogenous leukemia patients who received a 2-h infusion of BHAC (70 mg / m(2)) in combination remission induction therapy. ara-CTP could be monitored at levels under 1 mM. BHAC maintained effective levels of plasma ara-C and intracellular ara-CTP for a longer time, even compared with historical values of high-dose ara-C. The area under the concentration-time curve of ara-CTP was significantly greater in the patients with complete remission than in the patients without response. This greater amount of ara-CTP was attributed to the higher ara-CTP concentrations achieved in the responding patients. There was no apparent difference of plasma ara-C pharmacokinetics between the two groups. Thus, for the first time, the ara-CTP pharmacokinetics was evaluated in relation to the therapeutic effect of BHAC, and the importance of ara-CTP was proven. Administration of optimal BHAC therapy may require monitoring of the ara-CTP pharmacokinetics in each individual patient.

Monitoring of intracellular 1-beta-D-arabinofuranosylcytosine 5'-triphosphate in 1-beta-D-arabinofuranosylcytosine therapy at low and conventional doses.

1-beta-D-Arabinofuranosylcytosine (ara-C) is used empirically at a low, conventional, or high dose. Ara-C therapy may be optimal if it is directed by the clinical pharmacokinetics of the intracellular active metabolite of ara-C, 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP). However, ara-CTP has seldom been monitored during low- and conventional-dose ara-C therapies because detection methods were insufficiently sensitive. Here, with the use of our newly established method (Cancer Res., 56, 1800 -- 1804 (1996)), ara-CTP was monitored in leukemic cells from acute myelogenous leukemia patients receiving low- or conventional-dose ara-C [subcutaneous ara-C administration (10 mg / m(2) ) (3 patients), continuous ara-C infusion (20 or 70 mg / m(2) / 24 h) (7 patients), 2-h ara-C infusion (70 mg / m(2) ) (4 patients), and 2-h infusion of N(4)-behenoyl-1-beta-D-arabinofuranosylcytosine, a deaminase-resistant ara-C derivative (70 mg / m(2) ) (6 patients)]. Ara-CTP could be determined at levels under 1 microM. There was a close correlation between the elimination half-life values of the plasma ara-C and the intracellular ara-CTP. The presence of ara-C in the plasma was important to maintain ara-CTP. The continuous ara-C and the 2-h N(4)-behenoyl-1-beta-D-arabinofuranosylcytosine infusions maintained ara-CTP and the plasma ara-C longer than the subcutaneous ara-C or the 2-h ara-C infusion. They also afforded relatively higher ara-CTP concentrations, and consequently produced ara-CTP more efficiently than the 2-h ara-C infusion. Different administration methods produced different quantities of ara-CTP even at the same dose.

Inhibition of ribonucleotide reductase by a new class of isoindole derivatives: drug synergism with cytarabine (Ara-C) and induction of cellular apoptosis.

The hydroxyisoindole dione derivatives ISID and MISID are new compounds with structures resembling purines and possessing a hydroxamic acid moiety which is the pharmacophore of hydroxyurea (HU), an inhibitor of ribonucleotide reductase (RR). ISID and MISID exhibited 100- to 500-fold higher cytotoxicity as compared to HU against cell lines sensitive (CEM/0) or resistant to ara-C (CEM/ara-C/7A; CEM/dCk[-]). Both MISID and ISID showed significant inhibitory activity of ribonucleotide reductase (RR). Treatment of CEM/0 cells with 10 microM ISID showed a linear decrease in all the dNTPs leading to a complete depletion by 4 hours with no recovery of enzymatic activity of RR up to 48 hours in the presence of the drug, suggesting an irreversible inhibition of this enzyme. However, 10 microM MISID caused a significant time dependent, but reversible inhibition of RR in a whole cell assay in CEM/0 cells. Pretreatment of CEM/0 cells with 10 microM MISID for 1 hour increased cellular ara-CTP concentrations approximately 2-fold as compared to untreated controls. However, a reduction in intracellular ara-CTP concentration was observed following a commensurate depletion of ATP in these cells after 4 hrs of ISID pretreatment. Similarly, the ara-CTP concentration was augmented by 1.6-fold following pretreatment of CEM/0 cells with 10 microM MISID for 4 hours. Significant apoptotic cell death was detected in CEM/0 cells treated with ara-C, ISID or MISID alone or in combination. Ara-C treatment induced HMW (high molecular weight) DNA fragmentation at earlier times which subsequently led to oligonucleosomal DNA fragmentation by 48 hrs. The sequential treatment of CEM/0 cells with MISID followed by ara-C resulted in increased DNA fragmentation in the 2.0 to 4.0 Kb range in comparison to those cells treated with either ara-C or MISID alone. The increased apoptotic cell death explained the synergistic cytotoxicity of the combination of ara-C and MISID against CEM/0 cells observed earlier. We conclude that the inhibition of RR by these agents induces leukemic cell apoptosis, a mechanism which is further potentiated when these RR inhibitors are combined with ara-C. Since new compounds do not require activation, as do other clinically useful RR inhibitors, further studies for their potential use against leukemias and solid tumors are warranted.

Modulation of resistance to ara-C by bryostatin in fresh blast cells from patients with AML.

Bryostatin has shown promise both as a cytotoxic agent and more recently as a modulator of 1-beta-D-arabinofuranosylcytosine (ara-C) resistance. This compound is currently in phase I and II trials as a single agent. We have used the 3-4,5-dimethylthiazol-2,5-diphenyltetrazolium bromide (MTT) assay as a means of investigating the direct effects of bryostatin and the effects of co-incubating this agent with ara-C on fresh blast cells from 53 patients with acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS). Additional studies evaluated the levels of accumulation and retention of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP) in cells exposed to ara-C with and without bryostatin. Cells were exposed to bryostatin at a range of concentrations (0.1-100 nM) for 48 h and at 1 nM for both modulation studies and assessment of ara-CTP production. We found bryostatin to be cytotoxic in 18/58 (31%) tests whilst potentiation of formazan production in the MTT assay was seen in 21/58 (36%) patients. On co-incubation with bryostatin, 16/58 (27%) tests showed increased cytotoxicity to ara-C. Furthermore, there was a significant increase in the accumulation of ara-CTP on co-incubation with bryostatin (p = 0.0401). We found patients with in vitro resistance were more likely to become sensitised following exposure to bryostatin (p < 0.01). This study has emphasised the need to optimise treatment regimens for individual patients using this approach.

Apoptosis-resistant phenotype selected by alternating exposure to camptothecin and etoposide.

We selected an apoptosis-resistant subline (VC-33) in a human promyelocytic leukemia cell line, HL-60, by alternating exposure to camptothecin (CPT) and etoposide (VP-16). When wild-type (WT) and VC-33 cells were incubated with various concentrations of either CPT or VP-16 for 4 h, VC-33 showed several-fold resistance to apoptosis induced by these agents in comparison with WT cells. VC-33 cells also exhibited cross-resistance to apoptosis induced by 1-beta-d-arabinofuranosylcytosine, hydroxyurea, a calcium ionophore (A23187), cycloheximide, or UV irradiation. The levels of protein-DNA cross-linking induced by CPT or VP-16, and the amounts of ara-CTP generation, tended to be smaller in VC-33 cells, but the difference was not sufficient to explain the difference in the sensitivity to apoptosis. The initial rise of intracellular calcium ions with A23187 and the expression of P-glycoprotein, Bcl-2, and Bcl-Xl were comparable between WT and VC-33 cells. This mutant may represent a new phenotype of resistance to apoptosis induced by a variety of agents, and may thus be useful in the study of the mechanisms of apoptosis.

Deoxycytidine kinase mRNA levels in leukemia cells with competitive polymerase chain reaction assay.

Deoxycytidine kinase (dCyd kinase) is important for the phosphorylation of several different nucleoside antimetabolites. To understand the significance of dCyd kinase levels in chemotherapy, dCyd kinase mRNA levels were evaluated in several cells with a quantitative competitive polymerase chain reaction (PCR) assay. dCyd kinase catalytic activity and intracellular ara-CTP production were also compared with the levels of dCyd kinase mRNA. The assay was able to show: (i) that dCyd kinase catalytic activity and dCyd kinase mRNA levels were correlated in cells; (ii) that dCyd kinase mRNA levels were more sensitive in lower levels of 10 amol/micrograms of total RNA; and (iii) in cytosine arabinoside (ara-C)-resistant cells, both dCyd kinase mRNA levels and intracellular ara-CTP levels were lower compared with levels in sensitive cells. The PCR assay for dCyd kinase mRNA could be useful in the selection and monitoring of patients treated with nucleosides that are activated by this enzyme.

A new sensitive method for determination of intracellular 1-beta-D-arabinofuranosylcytosine 5'-triphosphate content in human materials in vivo.

A new sensitive method for the measurement of 1-beta-D-arabinofuranosyl-CTP (ara-CTP), an intracellular active metabolite of 1-beta-D-arabinofuranosylcytosine (ara-C), in human materials in vivo has been established. An acid-soluble fraction containing ara-CTP was extracted from blastic cells by ara-C treatment with trichloroacetic acid (final concentration, 0.3 M) neutralized with an equal volume of cold freon containing 0.5 M tri-n-octylamine. The ara-CTP fraction was separated from the acid -soluble fraction by high-performance liquid chromatography (TSK gel diethylaminoethyl-2 SW column) eluted with 0.05 M phosphate buffer (pH 6.9) and 20% acetonitrile. ara-CTP was lyophilized, dephosphorylated to ara-C by incubation with 10 units alkaline phosphatase for 12 h at 55 degrees C, and measured by RIA using anti-ara-C serum. Recovery through the whole procedure was 92%. In the human chronic myelogenous leukemia cell line K562, the intracellular ara-CTP levels produced when the cells were incubated with ara-c were assayed as above, and they showed a linear increase depending on Ara-C concentrations from 0.01 to 10 microns, demonstrating a very close correlation with the labeled ara CTP levels yielded by cells on incubation with radiolabeled ara-C (r2 = 0.99). The detection limit was 0.1 pmol/5 x 10(6) cells, and a sample amount of only 5 x 10(6) cells was enough for each assay. In the clinical applications, our method proved capable of detecting a wide concentration range of ara-CTP produced when patients were treated with ara-C or its derivatives from very low to intermediate doses. No radiolabeled drug was necessary. The method was very useful for in vivo pharmacodynamic studies of ara-C therapy.

Differences in the intracellular pharmacokinetics of cytosine arabinoside (AraC) between circulating leukemic blasts and normal mononuclear blood cells.

The increasing insights into the pharmacokinetics and the metabolism of cytosine arabinoside (AraC) have improved the rationale for its application in leukemia therapy and have led to a pharmacologically directed design of antileukemic treatment. 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. 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. Plasma AraC concentration showed a linear relationship to the applied AraC dose but did not correlate with intracellular AraCTP levels. During conventional-dose AraC therapy little interpatient variation was observed in AraCTP retention times in leukemic blasts from 5 patients with t1/2 values ranging from 1.70 to 2.50 h (median 2.14 h). In all cases AraCTP levels declined rapidly after the end of the AraC infusion. Substantial differences in AraCTP retention times were revealed, however, during 3 h infusions of either 1.0 or 3.0 g/m2 AraC in leukemic blasts from 10 patients with t1/2 values between 1.60 to 7.63 h (median 2.42 h). In addition, AraCTP levels declined in only one patient by > 10% within the first hour after the end of therapy and remained constant or even increased up to 1.5-fold in a post-treatment period of 1 to 2.5 h in the other nine cases. In contrast, AraCTP retention times were relatively uniform in normal mononuclear blood cells from 11 patients with t1/2 values of 3.34 to 5.29 h (median 3.85 h). More importantly, AraCTP levels dropped by > 10% within the first hour after the end of the high-dose AraC infusion in eight of 11 cases. A post-therapeutic increase > 10% was not observed in any patient. 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). 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)

Determination of pyrimidine deoxynucleoside triphosphates in leukaemia cell extracts containing 1-beta-D-arabinofuranosylcytosine triphosphate.

Deoxynucleoside 5'-triphosphates (dNTPs) can be determined in cell extracts by high performance liquid chromatography after prior selective degradation of ribonucleoside 5'-triphosphates with sodium periodate and methylamine. When the method is used for the evaluation of deoxynucleoside triphosphates in 1-beta-D-arabinofuranosylcytosine triphosphate (ara-CTP)-containing cell extracts, an additional peak coeluting with thymidine triphosphate (dTTP) is observed. This peak is due to the formation of a carboxylic acid derivative of ara-CTP by periodate oxidation, and it can lead to considerable overestimation of dTTP. Formation of this peak can be avoided by using alkaline reaction conditions (pH 7.5) and by changing the sequence of addition of the reagents used in the periodation procedure. By employing this modified protocol, cellular dNTP and ara-CTP levels can be monitored in extracts of leukaemic blasts during cytosine arabinoside treatment in two separate HPLC runs.

Intracellular dCTP/ara-CTP ratio and the cytotoxic effect of ara-C.

In this study, the relationship between the dCTP/ara-CTP ratio and the cytotoxic effect of cytosine arabinoside (ara-C) was investigated. Intracellular levels of dNTPs and ara-CTP were analyzed by high-performance liquid chromatography. Although doubling time and intracellular dCTP levels were different in each of the cells, there was a consistent relation between the intracellular dCTP/ara-CTP ratio and the cytotoxic concentration of ara-C. These data suggest that the intracellular dCTP/ara-CTP ratio is one of the important factors for considering the cytotoxic action of ara-C.

A simple isocratic ion-pair high-performance liquid chromatographic determination of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate for intracellular drug-monitoring and in vitro incubation assays.

A sensitive isocratic ion-pair HPLC method using a reversed-phase C18 column and phosphate buffer at pH 6 for the determination of the cytotoxic intracellular anabolite 1-beta-D-arabinofuranosylcytosine-triphosphate (Ara-CTP) of the antineoplastic drug cytarabine in leukaemic cells in vivo is described. Simultaneous determination of the physiological nucleotide deoxycytidine-triphosphate is possible. The recovery from cells is greater than 90%, the limit of detection is 25 ng ml-1 (51 nM l-1) and about 10 pM mg-1 cell protein. Extraction procedure and pitfalls are discussed. The method enables intracellular drug monitoring of Ara-CTP with standard HPLC equipment.

Cellular pharmacology of 1-beta-D-arabinofuranosylcytosine in human myeloid, B-lymphoid and T-lymphoid leukemic cells.

The in vitro inhibitory action and metabolism of 1-beta-D-arabinofuranosylcytosine (ara-C) on human myeloid (HL-60), B-lymphoid (RPMI-8392), and T-lymphoid (Molt-3) leukemic cells was compared. Ara-C produced greater inhibitory effects in Molt-3 cells than in either HL-60 or RPMI-8392 cells. At a 48 h exposure, ara-C was 7 and 10 times more cytotoxic to Molt-3 cells than to HL-60 and RPMI-8392 cells, respectively. The total ara-C uptake to nucleotides and the formation of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (ara-CTP) was about 5 times greater in Molt-3 cells than in either HL-60 or RPMI-8392 cells. The incorporation of ara-C into DNA was also higher in Molt-3 cells than in either HL-60 or RPMI-8392 cells. The mean intracellular half-life of ara-CTP was 31.7, 59.4, and 155 min for RPMI-8392, HL-60, and Molt-3 leukemic cells, respectively. The Km and Vmax values of ara-C for deoxycytidine kinase and the feedback inhibition of this enzyme by ara-CTP in the different leukemic cell lines could not explain the differences in metabolism of this analogue in these cells. These data indicate the increased sensitivity of T-lymphoid leukemic cells to ara-C than as compared with B-lymphoid and myeloid leukemic cells was due to an increased rate of formation and a longer half-life of ara-CTP in the T-cells.

Detection and separation of intracellular 1-beta-D-arabinofuranosylcytosine-5-triphosphate by ion-pair high-performance liquid chromatography.

An ion-pair high-performance liquid chromatographic method, using a reversed-phase C18 column, was developed to provide an isocratic, sensitive, fast and reproducible separation of intracellular 1-beta-D-arabinofuranosylcytosine-5-triphosphate and its measurement at a low limit of 5 pmol by ultraviolet absorbance at 280 nm with a coefficient of variation lower than 10%. A rapid separation is achieved by using a backflush procedure at 16 min and the retention time is 14 min.

[Relation between plasma Ara-C and intracellular Ara-CTP levels by intermediate dose and high dose Ara-C administration in the treatment of AML].

Plasma level of cytosine arabinoside (Ara-C) and intracellular cytosine arabinoside triphosphate (Ara-CTP) in peripheral blood and bone marrow were measured in 8 patients with non treated acute myelogenous leukemia. Ara-C was administered by 1 hr infusion (3 g/m2 and 500 mg/m2) and was followed for 12 hrs. The AUC of Ara-C in plasma following 3 g/m2 infusion were greater than the 500 mg/m2 (p less than 0.05). Intracellular Ara-CTP in peripheral blood following 3 g/m2 and 500 mg/m2 infusions were on the same level, after 1 hr. But AUC of intracellular Ara-CTP following 3 g/m2 infusion was greater than 500 mg/m2. There was a correlation between AUC of Ara-C in the peripheral blood (p less than 0.01). Intracellular Ara-CTP in the bone marrow and peripheral blood showed a similar level. Intracellular Ara-CTP in bone marrow was lower than in peripheral blood, however, there was no correlation between intracellular Ara-CTP in bone marrow and in peripheral blood.