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Dual Mechanisms of 9-β-d-Arabinofuranosylguanine Resistance in CEM T-Lymphoblast Leukemia Cells

https://doi.org/10.1006/bbrc.2001.5124Get rights and content

Abstract

The guanine nucleoside analog araG is selectively toxic to T-lymphoblasts and has recently shown promise in treatment of lymphoid malignancies of T-cell origin. The molecular mechanism of this tissue-selective cytotoxicity is, however, yet unclear. AraG is phosphorylated, and thereby pharmacologically activated, by the mitochondrial deoxguanosine kinase and the cytosolic/nuclear deoxycytidine kinase. We have recently shown that araG is predominantly incorporated into mitochondrial DNA of cancer cell lines, which suggests a role of mitochondria as its pharmacological target. In the present study, we have generated araG-resistant CEM T-lymphoblast cell lines and show that araG resistance may occur by two separate molecular mechanisms that can occur sequentially. The first mechanism is associated with a decrease of araG incorporation into mitochondrial DNA, and the second event is associated with loss of dCK activity.

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      Therefore we do not know if Ara-G can be phosphorylated in the mitochondria by dGK and then transported to the cytosol. Recent work demonstrates that Ara-G can induce resistance via more than one mechanism [16]. Primarily, a decrease in Ara-G incorporation into mitochondrial DNA was observed, followed by selection for dCK-deficient cells at high Ara-G concentration.

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    Abbreviations used: dGK, deoxyguanosine kinase; dCK, deoxycytidine kinase; TK1, thymidine kinase 1; TK2, thymidine kinase 2; araG, 9-β-d-arabinofuranosylguanine; araC, 1-β-d-arabinofuranosylcytosine; araT, 1-β-d-arabinofuranosylthymine; CdA, 2-chloro-2′-deoxyadenosine; dThd, deoxythymidine; dCyd, deoxycytidine; dFdC, 2′,2′-difluorodeoxycytidine.

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