Cytotoxicity of Ara-C and expression levels of dCK, ABCC5, hENT1 and RRM1 genes in K562 and HL60 cells. (A) Cytotoxicity of Ara-C in K562 and HL60 cells. (B) Expression levels of dCK, ABCC5, hENT1 and RRM1 in K562 and HL60 cells genes, as determined by real-time PCR. Ara-C, cytosine arabinoside; dCK, deoxycytidine kinase; ABCC5, multidrug resistance protein 5; hENT1, human equilibrative nucleoside transporter 1; RRM1, ribonucleoside reductase subunit M1; IC50, concentration for 50% cell survival; CI, confidence interval; RR, resistance rate.