Treatment of normal and malignant cells with nucleoside analogues and etoposide enhances deoxycytidine kinase activity

Deoxycytidine kinase (dCK), one of the rate-limiting enzymes in the intrace llular metabolism of many antileukaemic drugs, was shown to be stimulated a fter treatment of human tonsillar lymphocytes by 2-chloro-2'-deoxyadenosine (cladribine, CdA) (Sasvari-Szekely, et al., Biochem Pharmacol 1998, 56, 11 75-1179). Here we present a comparative study of different normal and malig nant cells in respect to the activation of dCK by CdA. G-phase lymphocytes showed a higher sensitivity for dCK stimulation than S-phase cells. Normal and leukaemic peripheral blood mononuclear cells, as well as the promyelocy tic cell line HL60 responded to CdA treatment by a 2-5-fold increase in act ivity of dCK. However, no significant stimulation was detected either in CC RF-CEM T-lymphoblastoid cells, or in K562 myeloid cells. Thymidine kinase ( TK) activity was not stimulated in any cases. Treatment of these cells with several other analogues beside CdA, such as 2-chloro-2'-arabino-fluoro-2'- deoxyadenosine (CAFdA), 2-fluoro-1-beta-D-arabinosyladenine (Fludarabine, F araA) and 1-beta-D-arabinosylcytosine (cytarabine, araC) gave similar resul ts to CdA treatment. Enhancement of dCK activity could also be achieved wit h the topoisomerase II inhibitor, etoposide. In contrast, 2-chloro-riboaden osine (CrA) had no effect on the dCK at concentrations of 10 mu M or less, while dCyd and 5-aza-dCyd caused slight inhibition. These results indicate that treatment of cells with several inhibitors of DNA synthesis potentiate s the dCK activity. The drugs widely differ in their stimulatory effect on dCK, and there are also 'responsive' and 'non-responsive' cells with respec t to dCK activation. Thus, enhancement of the dCK activity by specific drug s in 'responsive' cells might give a rationale for combination chemotherapy . (C) 1999 Elsevier Science Ltd. All rights reserved.