title: Saturation of 1-beta-D-arabinofuranosylcytosine 5'-triphosphate accumulation in leukemia cells during high-dose 1-beta-D-arabinofuranosylcytosine therapy.
abstract: Twenty-seven patients with refractory leukemia were treated with 1-beta-D-arabinofuranosylcytosine (ara-C), 0.3 to 3.0 g/m2 as i.v. infusions over 1, 2, 4, or 24 h. The pharmacokinetics of ara-C in plasma and its 5'-triphosphate (ara-CTP) in leukemic cells from peripheral blood were studied after a single infusion of 3 g/m2 over 2 h in 13 patients. Accumulation of ara-CTP in leukemic cells remained linear until 1 to 2 h after the infusion. At the time when the rate of ara-CTP accumulation deviated from linearity, the plasma concentration of ara-C was 5- to 20-fold lower [8.1 +/- 4.4 (SD) microM] than the steady-state level during the infusion. Plasma ara-C and cellular ara-CTP pharmacokinetics were studied after two serial infusions in 14 additional patients. Varying the duration of infusion of an ara-C dose between 1, 2, and 4 h (corresponding to infusion rates of 3000, 1500, and 750 mg/m2/h) did not substantially change the rate of ara-CTP accumulation by leukemic cells. The peak ara-CTP concentration and the area under the concentration times time curve (AUC) of ara-CTP in leukemic cells increased with prolongation of the infusion. Although steady-state concentration of ara-C and AUC of ara-C in plasma were proportionally reduced by 1.0 or 0.5 g/m2 infusion over 2 h, ara-CTP accumulation rate and AUC in leukemic cells did not change compared with administration of 3 g/m2 over 2 h. However, when the infusion rate was further reduced to 0.4 or 0.3 g/m2 over 2 h, resulting in steady-state plasma ara-C concentrations of less than 7 microM, the accumulation rate of ara-CTP was substantially reduced as was the ara-CTP intracellular AUC. The cellular elimination rate of ara-CTP remained constant under all infusion conditions. These findings support the conclusion that high-dose ara-C therapy, as currently administered, results in plasma ara-C concentrations that saturate the accumulation of ara-CTP by circulating leukemic cells. We recommend that intermediate dose rates, 200 to 250 mg/m2/h, be evaluated in future studies as an alternative to the substantially higher ara-C dose rates currently in use.
authors.forename: W
authors.initials: W
authors.lastname: Plunkett
authors.forename: J O
authors.initials: JO
authors.lastname: Liliemark
authors.forename: T M
authors.initials: TM
authors.lastname: Adams
authors.forename: B
authors.initials: B
authors.lastname: Nowak
authors.forename: E
authors.initials: E
authors.lastname: Estey
authors.forename: H
authors.initials: H
authors.lastname: Kantarjian
authors.forename: M J
authors.initials: MJ
authors.lastname: Keating
mesh_terms: D001085:Arabinofuranosylcytosine Triphosphate / Q000378:metabolism*; D001088:Arabinonucleotides / Q000378:metabolism*; D001752:Blast Crisis; D003561:Cytarabine / Q000008:administration & dosage* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006801:Humans; D007262:Infusions, Intravenous; D007938:Leukemia / Q000188:drug therapy / Q000378:metabolism*; D007951:Leukemia, Myeloid / Q000378:metabolism; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism; D008657:Metabolic Clearance Rate
chemical_list: D001088:Arabinonucleotides; D003561:Cytarabine; D001085:Arabinofuranosylcytosine Triphosphate