Skip to main content
 
Notice: Users may be experiencing issues with displaying some pages on stanfordhealthcare.org. We are working closely with our technical teams to resolve the issue as quickly as possible. Thank you for your patience.
 

See our updated masking policy »

Stanford Health Care

Arabinosylguanine is phosphorylated by both cytoplasmic deoxycytidine kinase and mitochondrial deoxyguanosine kinase CANCER RESEARCH Rodriguez, C. O., Mitchell, B. S., Ayres, M., Eriksson, S., Gandhi, V. 2002; 62 (11): 3100-3105

Abstract

The prodrug of 9-beta-D-arabinosylguanine (ara-G), nelarabine, demonstrated efficacy against T-cell acute lymphoblastic leukemia, and its effectiveness correlated with the accumulation of the triphosphate form (ara-GTP). Although in vitro investigations using purified deoxycytidine kinase (dCK) or deoxyguanosine kinase (dGK) suggested that ara-G is a substrate for both enzymes, controversy exists in regard to the role of these enzymes in whole cells. In this work, we used a CEM mutant cell line containing low endogenous levels of dGK and deficient in dCK (dCK-) to assess the role of these kinases in ara-G phosphorylation. Using a retroviral vector system, we infected the dCK- mutant cell line to obtain cell lines with overexpression of dCK (dCK+) or dGK (dGK+). Only the dCK+ cell line phosphorylated 1-beta-D-arabinofuranosylcytosine (used as a substrate for dCK) in a cell-free system; phosphorylation of this compound by dGK+ was below the limit of detection. Again in in vitro assays, the dCK-and dCK+ cell lines phosphorylated dGuo to similar levels (0.91 +/- 0.15 and 0.93 +/- 0.19 pmol/mg/min, respectively), whereas dGK+ phosphorylated dGuo more efficiently (150 pmol at 60 min). When ara-G was used as a substrate in a cell-free system, the maximum accumulation of phosphorylated product was observed in dGK+ extracts at low ara-G levels (10 microM) and in dCK+ extracts at high concentrations of ara-G (100 microM). Thus, both dCK and dGK can phosphorylate ara-G, but at low ara-G concentrations, dGK seems to predominate, whereas at higher ara-G concentrations, dCK seems to be the preferred enzyme. In whole-cell systems after a 3-h incubation with 10 microM ara-G, both dCK+ and dGK+ cells accumulated ara-GTP; however, the levels were significantly (P = 0.0008) higher in dGK+ cells. In contrast, at 100 microM ara-G, intracellular ara-GTP accumulated to similar levels (P = 0.5529) in these cell types; 25 +/- 3.7 microM in dCK+, and 27.8 +/- 2.7 microM in the dGK+ cells. These results from whole-cell experiments are consistent with those from the cell-free system and strongly suggest that ara-G is phosphorylated by both kinases, and at low substrate concentrations, dGK is preferred enzyme. Evaluation of the expression of each of these kinases in primary leukemia cells may reveal a biochemical basis for the pharmacological differences in the accumulation of ara-GTP.

View details for Web of Science ID 000176038500019

View details for PubMedID 12036920