Accumulation of arabinosyluracil 5'-triphosphate during arabinosylcytosine therapy in circulating blasts of patients with acute myelogenous leukemia.
Arabinosylcytosine (ara-C) is the most effective nucleoside analogue for treatment of acute myelogenous leukemia. The cytotoxicity of ara-C depends on its conversion to the triphosphate ara-CTP. In plasma, a major metabolite of ara-C is its deamination product, arabinosyluracil (ara-U). Both ara-U and ara-U monophosphate have been detected in primary leukemia cells during in vitro investigations. Because other ara-U metabolites, especially the triphosphate (ara-UTP), may serve as additional effectors of cytotoxicity, the present study investigated whether ara-UTP accumulates in circulating leukemia blasts during ara-C therapy. Patients with relapsed acute myelogenous leukemia received 2- or 4-h infusions of 0.5 g/m2/h ara-C. Intracellular accumulation of ara-CTP and ara-UTP in circulating leukemia blasts from six patients was quantitated by high-pressure liquid chromatography, revealing that ara-UTP accumulated during ara-C therapy. The intracellular concentration of ara-UTP ranged from 6-50 microM and was between 2 and 10% of the accumulated ara-CTP. In circulating blasts, ara-UTP was maintained for several hours after the end of ara-C infusion. Leukemia blasts from patients (n=27) were incubated for 1-2 h with 1, 10, or 25 microM [3H]ara-C, and radiolabeled metabolites of ara-C were separated and quantitated by high-pressure liquid chromatography. Consistent with data obtained during ara-C therapy, [3H]ara-UTP also accumulated in blasts from all these patients during in vitro incubations with [3H]ara-C. The concentration of ara-UTP after 1 h of incubation ranged from 0.2-40 microM. Incubation of cells with the cytidine deaminase inhibitor tetrahydrouridine did not perturb ara-UTP accumulation, whereas incubation with the deoxycytidylate deaminase inhibitor tetrahydrodeoxyuridine suppressed ara-UTP formation from ara-C. These observations suggested that ara-UTP is generated through deamination of ara-C monophosphate to ara-U monophosphate by deoxycytidylate deaminase, followed by its phosphorylation to ara-UTP. Consistent with these results, incubation of blasts with up to 100 microM [3H]ara-U did not result in ara-UTP accumulation, indicating that ara-U is not phosphorylated directly in these cells. The present study demonstrated that circulating leukemia blasts accumulate ara-UTP during in vitro incubations with ara-C and during ara-C therapy.
Gandhi
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Department of Clinical Investigation, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Xu
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Estey
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D000964:Antimetabolites, Antineoplastic / Q000378:metabolism* / Q000627:therapeutic use; D001085:Arabinofuranosylcytosine Triphosphate / Q000378:metabolism; D003561:Cytarabine / Q000378:metabolism / Q000627:therapeutic use*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism
D000964:Antimetabolites, Antineoplastic; D003561:Cytarabine; D001085:Arabinofuranosylcytosine Triphosphate; C025327:ara-UTP; D014544:Uridine Triphosphate