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 ϭ 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 Ϯ 5, 66 Ϯ 3, and 43 Ϯ 4%, respectively. DCK119Gly and DCK122Ser mutants had lower K m (p Ͻ 0.01) and V max (p Ͻ 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 3Ј-untranslated region singlenucleotide polymorphism (SNP) (35708 CϾT) 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-5Ј-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.

Homozygous CDA*3 is a major cause of life-threatening toxicities in gemcitabine-treated Japanese cancer patients

“…No SNPs of DCK, including DCK364C4T (Pro122Ser), which were reported to have reduced enzymatic activity (Lamba et al, 2007), were identified in our three patients. Plasma CDA activities of patients A, B, and C were compared with those of 121 patients in our earlier study (Sugiyama et al, 2007) (Figure 1A).…”

Bystander killing of malignant cells via the delivery of engineered thymidine-active deoxycytidine kinase for suicide gene therapy of cancer

“…Wild-type dCK is a key kinase in the cell and is able to phosphorylate deoxyadenosine (dA), deoxyguanosine (dG), and deoxycytidine (dC) nucleosides, but not deoxythymidine (dT) or deoxyuridine (dU). Activation of a number of chemotherapeutic agents, such as cytarabine, gemcitabine and clofarabine, is mediated by dCK, 22 and it is also uniquely capable of activating nucleosides with the nonphysiological L-chirality. 23 The dCK variant utilized herein contains three amino-acid mutations from wild-type.…”

Noninvasive prediction of tumor responses to gemcitabine using positron emission tomography

“…Single-nucleotide polymorphisms in the regulatory region (rSNPs) of DCK correlate with responses to ara-C in acute myeloid leukemia (AML) (17). Other rSNPs correlate with low DCK expression and lower blast ara-C-5Ј-triphosphate levels in AML patients receiving ara-C as continuous infusion (18). Treatment-induced resistance to dFdC has been documented in cell lines and animal models (reviewed in ref.…”

“…Noninvasive methods that can detect DCK activity in tumor lesions throughout the body could circumvent these limitations. Here, we demonstrate an approach to detecting DCK activity in vivo by using positron emission tomography (PET) and 18 …”

“…Positron emission tomography (PET) using [ 18 (4,5), high-grade soft tissue sarcomas (3), metastatic breast cancer (6), lung cancer (7), and adenocarcinoma of the esophagogastric junction (8).…”