Deoxycytidine kinase and cN-II nucleotidase expression in blast cells predict survival in acute myeloid leukaemia patients treated with cytarabine Carlos Marı´a Galmarini, 1 Xavier Thomas, 2 Kathryn Graham, 3 Assia El Jafaari, 2 Emeline Cros, 1 Lars Jordheim, 1 John R. Mackey 3 and Charles Dumontet 1 1 Unite ´ INSERM 590, 2 Service d’He ´matologie et Centre de Transfusion, Ho ˆpital Edouard Herriot, Lyon, France, and 3 Department of Oncology, Cross Cancer Institute, Edmonton, Canada Received 9 January 2003; accepted for publication 28 February 2003 Summary. 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 diag- nosis 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 unfa- vourable 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. Keywords: drug resistance, leukaemia, cytarabine, deoxy- cytidine kinase, 5¢-nucleotidase. Cytarabine (ara-C; 1-b-d-arabinofuranosylcytosine) repre- sents one of the most active agents in the treatment of acute myeloid leukaemia (AML) (Galmarini et al, 2002a). Ara-C is intracellularly metabolized through the pathways normally utilized by natural nucleotide precursors. Deoxycytidine kinase (dCK; EC 2.7.1.74) is the key enzyme in the series of phosphorylating steps necessary to metabolize ara-C to its pharmacologically active form, ara-C triphosphate (ara- CTP) (Plagemann et al, 1978). It catalyses the transfer of the c-phosphate of adenosine triphosphate or uridine triphosphate to ara-C to give rise to ara-C 5¢-monophos- phate (ara-CMP) (Coleman et al, 1975; Shewach et al, 1992). Ara-CMP is further activated by other kinases to yield ara-CTP (Liliemark et al, 1985). Ara-C is catabolized by deamination by the cytidine deaminase enzyme (Momparler et al, 1996). Also, monophosphate forms of ara-C are substrates for 5¢-nucleotidases (Amici & Magni, 2002). These enzymes have an effect opposite to that of the nucleoside kinases, decreasing the amount of activated ara-C forms intracellularly. Ara-C cytotoxicity results from DNA synthesis arrest due to the direct inhibition of DNA polymerase a and incorpor- ation of ara-CTP into the DNA, causing chain termination (Kufe et al, 1980; Major et al, 1981). Inhibition of DNA polymerase a by ara-CTP is dependent on the ara-CTP concentration. Sustained high cellular concentrations of ara-CTP relative to that of dCTP also favour drug incorpor- ation into replicating DNA, initiating leukaemic cell death (Gunji et al, 1991). The efficient intracellular transformation of ara-C into ara-CTP is thus essential to obtain the cytotoxic response observed after ara-C treatment (Kufe et al, 1984; Rustum & Raymakers, 1992). In vitro, dCK deficiency has been repor- ted to be associated with reduced ara-CTP concentrations Correspondence: Carlos Galmarini, MD, INSERM 590, Faculte ´ de Me ´decine Rockefeller, 8 Avenue Rockefeller 69373, Lyon CEDEX 08, France. E-mail: cmgalma@yahoo.com.ar British Journal of Haematology, 2003, 122, 53–60 Ó 2003 Blackwell Publishing Ltd 53