Supplementary Material for: Deoxycytidine Kinase (<b><i>DCK</i></b>) Mutations in Human Acute Myeloid Leukemia Resistant to Cytarabine

Resistance to cytarabine is an important cause of therapy failure in persons with acute myeloid leukemia (AML). Deoxycytidine kinase, encoded by <i>DCK</i>, catalyzes phosphorylation of cytarabine to cytarabine monophosphate, a necessary step for eventual incorporation of cytarabine triphosphate into DNA and for clinical efficacy. Whether <i>DCK</i> mutations make AML cells resistant to cytarabine is controversial. We studied <i>DCK</i> mutations and messenger RNA (mRNA) concentrations in leukemia cells from 10 subjects with AML who received cytarabine-based therapy and relapsed and in 2 artificially induced cytarabine-resistant AML cell lines. <i>DCK</i> mutations were detected in 4 subjects with AML relapsing after achieving a complete remission and receiving high-dose cytarabine postremission therapy. Most mutations were in exons 4–6 and were not present before therapy. <i>DCK</i> was also mutated in cytarabine-resistant but not parental AML cell lines. <i>DCK</i> mRNA concentrations were significantly decreased in cytarabine-resistant K562 and SHI-1 cells compared with cytarabine-sensitive parental cells. Mutation frequency of <i>DCK</i> and mRNA concentration did not correlate with the extent of cytarabine resistance indicating other factors operate. Overexpression of wild-type <i>DCK</i> restored cytarabine sensitivity to previously resistant leukemia cell lines. Our data contribute to the understanding of cytarabine resistance in persons with AML.