title: Pharmacogenetics of deoxycytidine kinase: identification and characterization of novel genetic variants.
abstract: Deoxycytidine kinase (DCK) is a rate-limiting enzyme in the activation of nucleoside analogs such as cytarabine (ara-C), gemcitabine, clofarabine, and others. The present study was undertaken to identify and to determine the functional consequences of genetic variants in DCK. We sequenced 1.5 kilobases of the DCK proximal promoter and all seven coding exons in International HapMap Project panels (n = 90 each) with European (Centre d' Etude du Polymorphisme Humain; CEPH) or African (Yoruba people in Ibadan, Nigeria; YRI) ancestry. Sixty-four genetic polymorphisms, including three nonsynonymous coding changes (I24V, A119G, and P122S) were identified. Compared with DCK-wild-type (WT) protein, the activity of the recombinant DCK24Val, DCK119Gly, and DCK122Ser proteins was 85 +/- 5, 66 +/- 3, and 43 +/- 4%, respectively. DCK119Gly and DCK122Ser mutants had lower Km (p < 0.01) and Vmax (p < 0.001) compared with DCK-WT protein. Lymphoblast cell lines from subjects heterozygous for the coding changes had significantly lower DCK activity compared with homozygous WT subjects. Ethnic differences were observed, with African ancestry subjects demonstrating significantly higher DCK mRNA expression compared with subjects with European ancestry. In both CEPH and YRI subjects, the C allele of a 3'-untranslated region single-nucleotide polymorphism (SNP) (35708 C>T) was significantly associated with lower DCK mRNA expression. This SNP was strongly linked with other intronic SNPs, forming a major haplotype block in both ethnic groups. In an exploratory analysis, the 35708C allele was also associated with lower blast ara-C-5'-triphosphate (ara-CTP) levels in acute myeloid leukemia patients receiving ara-C as continuous infusion. These results suggest that genetic variation in DCK influences its activity and expression and may predict the variability observed in intracellular levels of the ara-C active metabolite ara-CTP.
authors.affiliation: Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, 332 North Lauderdale St., Memphis, TN 38105, USA. jatinder.lamba@stjude.org
authors.forename: Jatinder K
authors.initials: JK
authors.lastname: Lamba
authors.forename: Kristine
authors.initials: K
authors.lastname: Crews
authors.forename: Stanley
authors.initials: S
authors.lastname: Pounds
authors.forename: Erin G
authors.initials: EG
authors.lastname: Schuetz
authors.forename: Jessica
authors.initials: J
authors.lastname: Gresham
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
authors.forename: William
authors.initials: W
authors.lastname: Plunkett
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Rubnitz
authors.forename: Raul
authors.initials: R
authors.lastname: Ribeiro
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D001085:Arabinofuranosylcytosine Triphosphate / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002648:Child; D018076:DNA, Complementary / Q000235:genetics; D003842:Deoxycytidine Kinase / Q000235:genetics* / Q000378:metabolism; D004334:Drug Administration Schedule; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D015810:Linkage Disequilibrium; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000964:Antimetabolites, Antineoplastic; D018076:DNA, Complementary; D012333:RNA, Messenger; D001085:Arabinofuranosylcytosine Triphosphate; D003842:Deoxycytidine Kinase