The pattern of deoxycytidine- and deoxyguanosine kinase activity in relation to messenger RNA expression in blood cells from untreated patients with B-cell chronic lymphocytic leukemia

Deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK) catalyze the first step in the intracellular cascade of fludarabine (2-fluoroadenine-beta-D-arabinofuranoside) and cladribine (2-chlorodeoxyadenosine) phosphorylation, which leads to activation of these prodrugs, commonly used for treatment of chronic lymphocytic leukemia (CLL). Thus, resistance to nucleoside analogues may primarily be due to low levels of deoxynucleoside kinase activity. The purpose of this study was to investigate the activity profiles of dCK and dGK and characterize the possible relationship between the levels of dCK enzymatic activities and mRNA levels in B-CLL cells from untreated patient samples in an attempt to determine the best approach for predicting sensitivity to nucleoside analogues and thereby optimizing treatment of CLL. For this purpose, dCK and dGK analyses were done in blood cells from 59 untreated symptomatic patients with CLL. The dGK activity towards 2-chlorodeoxyadenosine was significantly lower than of dCK (median 73 pmol/mg protein/min (85-121, 95% CI) versus 353 pmol/mg protein/min (331-421)). The median dCK mRNA level was 0.107 (0.096-0.120, 95% CI). There was a lack of correlation between the activities of dCK and dGK, which indicates that these proteins are regulated independently. We also found that the dCK and dGK activity measurement towards their endogenous substrates were comparable to the nucleoside analogues tested. Such variations in enzyme activities and mRNA levels may well explain differences in clinical responses to treatment. There was no correlation between the levels of dCK mRNAs and enzymatic activities using a quantitative real-time PCR procedure. Sequencing of dCK mRNA did not reveal alternate splicing or mutations in the coding region. The relation between activity and mRNA levels was studied by short interfering RNA (siRNA) method, which showed that in the siRNA treated cells the down-regulation of dCK expression, and activity followed each other. However, in control cells the mRNA levels remained stable but the protein activity markedly decreased. These data demonstrate that the dCK activity is not reflected by dCK mRNA expression that indicates a post-translational mechanism(s).

Deoxycytidine kinase and cN-II nucleotidase expression in blast cells predict survival in acute myeloid leukaemia patients treated with cytarabine

The cytotoxic activity of cytarabine (ara-C) in leukaemic blasts depends on activating enzymes such as deoxycytidine kinase (dCK) and inactivating enzymes such as the 5'-nucleotidases. We have analysed dCK and 'high-Km' 5'-nucleotidase (cN-II) mRNA expression by the quantitative real-time polymerase chain reaction at diagnosis in leukaemic blasts from 115 acute myeloid leukaemia (AML) patients treated with ara-C. The prognostic value of these parameters as well as that of the cN-II/dCK ratio was determined. In univariate analyses: (1) low levels of dCK, high levels of cN-II and a high cN-II/dCK ratio predicted shorter disease-free survival (DFS); (2) low levels of dCK and cN-II/dCK ratio also predicted shorter overall survival (OS). In a multivariate analysis taking into account other clinical and laboratory variables: (1) high cN-II expression, a high cN-II/dCK ratio, age >/= 60 years and an unfavourable karyotype were independent prognostic factors for DFS; and (2) a high cN-II/dCK ratio, age >/= 60 years and an unfavourable karyotype predicted shorter OS. Age, karyotype and cN-II/dCK ratio were used to define a prognostic score that permitted the identification of high- and low-risk groups. Our results suggest that dCK and cN-II mRNA expression in leukaemic blasts at diagnosis is correlated with clinical outcome and may play a functional role in the resistance to ara-C in patients with AML.

Purine metabolism in leukocytes and erythrocytes in Graves' or Hashimoto's disease

INTRODUCTION

Adenosine deaminase (ADA), purine nucleoside phosphorylase (PNPase), S-adenosylhomocysteine hydrolase (SAHH), 5'-nucleotidase (5N), and deoxycytidine kinase (dCK) are involved in purine salvage metabolism. Changes of the activities of the above enzymes have been observed in blood cells in patients with immunological disorders.

MATERIALS AND METHODS

The activities of ADA, PNPase, SAHH, 5'N, and dCK in lysates of leukocytes and erythrocytes, obtained from patients with Graves' or Hashimoto's disease, were measured, using chromatographic analysis. Serum concentrations of antithyroglobulin (Tg Ab) and antithyroperoxidase (TPO Ab) antibodies were measured by an immunoenzymatic method.

RESULTS

(1) ADA activity in leukocytes, obtained from patients with Hashimoto's disease, was significantly higher than in control leukocytes, as well as in leukocytes from patients with Graves' disease; (2) dCK activities in leukocytes from patients with both Graves' and Hashimoto's diseases were approximately four and five times higher, respectively, than in leukocytes of control subjects; (3) a positive correlation was observed between dCK activity in leukocytes and serum Tg Ab concentration in patients with Graves' disease. In conclusion, the increased ADA and dCK activities in leukocytes from patients with Graves' and Hashimoto's diseases may be regarded as indicators of autoimmunological thyroid diseases.

Differential phosphorylation of azidothymidine, dideoxycytidine, and dideoxyinosine in resting and activated peripheral blood mononuclear cells

The antiviral activity of azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyinosine (ddI) against HIV-1 was comparatively evaluated in PHA-stimulated PBM. The mean drug concentration which yielded 50% p24 Gag negative cultures were substantially different: 0.06, 0.2, and 6 microM for AZT, ddC, and ddI, respectively. We found that AZT was preferentially phosphorylated to its triphosphate (TP) form in PHA-PBM rather than unstimulated, resting PBM (R-PBM), producing 10- to 17-fold higher ratios of AZTTP/dTTP in PHA-PBM than in R-PBM. The phosphorylation of ddC and ddI to their TP forms was, however, much less efficient in PHA-PBM, resulting in approximately 5-fold and approximately 15-fold lower ratios of ddCTP/dCTP and ddATP/dATP, respectively, in PHA-PBM than in R-PBM. The comparative order of PHA-induced increase in cellular enzyme activities examined was: thymidine kinase > uridine kinase > deoxycytidine kinase > adenosine kinase > 5'-nucleotidase. We conclude that AZT, ddC, and ddI exert disproportionate antiviral effects depending on the activation state of the target cells, i.e., ddI and ddC exert antiviral activity more favorably in resting cells than in activated cells, while AZT preferentially protects activated cells against HIV infection. Considering that HIV-1 proviral DNA synthesis in resting lymphocytes is reportedly initiated at levels comparable with those of activated lymphocytes, the current data should have practical relevance in the design of anti-HIV chemotherapy, particularly combination chemotherapy.

Relationship of deoxycytidine kinase and cytoplasmic 5'-nucleotidase to the chemotherapeutic efficacy of 2-chlorodeoxyadenosine

The agent 2-chlorodeoxyadenosine (2-CdA) has chemotherapeutic activity in hairy cell leukemia (HCL) and in refractory chronic lymphocytic leukemia (CLL). The cytotoxic activity of 2-CdA requires the intracellular accumulation of 2-CdA nucleotides. Deoxycytidine kinase (dCK) and cytoplasmic 5'-nucleotidase (5'-NT) are the principal enzymes that phosphorylate 2-CdA and dephosphorylate 2-CdA 5'-monophosphate, respectively. The net accumulation of 2-CdA nucleotides may therefore depend on both dCK and 5'-NT. The purpose of the present experiments was to determine if there is a relationship between pretreatment levels of dCK and 5'-NT in HCL and in CLL cells, and the clinical outcome of 2-CdA treatment. As measured by a direct immunoassay for dCK in 25 CLL patients, and by a 5'-NT activity assay in 23 patients, mean dCK levels were significantly higher in 2-CdA responders than in nonresponders (P < .01), whereas mean 5'-NT levels were significantly lower in 2-CdA responders than in nonresponders (P < .05). Mean dCK levels were higher in six HCL 2-CdA responders than in one nonresponder, whereas mean 5'-NT levels were lower in the 2-CdA responders than in the nonresponder. These results suggest that both dCK and 5'-NT are determinants of 2-CdA responsiveness.

Affinity purification of human deoxycytidine kinase: avoidance of structural and kinetic artifacts arising from limited proteolysis

Homogeneous deoxycytidine kinase has been isolated from leukemic human T-lymphoblasts by affinity chromatography based on a multisubstrate analog, deoxycytidine 5'-adenosine 5"'-P1,P4-tetraphosphate (dCp4A). Chromatography of extract treated with protease inhibitors yielded a monomeric polypeptide, inasmuch as the Mr of the native protein, 59,300, is comparable to the value of 52,000 from sodium dodecyl sulfate polyacrylamide gel electrophoresis. The isoelectric pH was 6.1. But, enzyme isolated without protease inhibitors exhibited two fragments of Mr = 30,000 and 33,000, suggesting that proteolytic cleavage of the parental polypeptide had occurred during affinity chromatography. Both the parental and proteolyzed enzymes phosphorylated deoxyadenosine and deoxyguanosine, as well as deoxycytidine. However, the proteolyzed enzyme had an increased apparent Km for deoxycytidine. In consequence of this, a mixture of the two forms produced bimodal kinetic plots, whereas linear kinetics were displayed by each form alone.

Enzymatic studies on possible improvement of cytosine arabinoside treatment

Initial phosphorylation and deamination of cytosine arabinoside (Ara-C) and the natural metabolite deoxycytidine (CdR) were estimated in cell free extracts of leucocytes from patients with CML and controls. Phosphorylation of CdR had been increased while deamination of CdR in extracts of CML cells from peripheral blood had been decreased compared with normal leucocytes. Comparing the ratios between Ara-C and CdR phosphorylation it was revealed that these were twice as high in CML cells as in normal leucocytes, whereas no difference was found when comparing ratios between Ara-C and CdR deamination. From these discoveries it is proposed that Ara-C can be combined with CdR with advantage, because apparently CdR protects the normal cells more than the malignant ones.