Es Nucleoside Transporter Content of Acute Leukemia Cells: Role in Cell Sensitivity to Cytarabine (araC)

Abstract

Nucleoside analogs are important components of treatment regimens for acute leukemia in adults. Plasma membrane permeation of the nucleoside analog molecules, the initial event in the cellular conversion of nucleosides to active agents, is mediated by nucleoside-specific membrane transporters. The widely-expressed es nucleoside transporter accepts as substrates diverse nucleoside analogs, including cytarabine (araC), 2-chlorodeoxyadenosine, and fludarabine. The cellular content of es transporter sites has been measured in blasts from patients with acute lymphoblastic leukemia and acute myelogenous leukemia, by a sensitive, quantitative flow cytometry assay that employs the tightly-bound es ligand, SAENTA fluorescein. Values for es transporter expression varied ten-fold among samples from patients with acute myelogenous leukemia. In this article, we review current findings that document, in confocal fluorescence microscopy images and in flow cytometry assays of SAENTA fluorescein-stained cells, the patient-to-patient variance of es transporter expression in leukemic blasts from patients. Our data show a correlation between the expression of es transporters and the in vitro sensitivity to nucleoside drugs of blasts from acute leukemia patients. These findings show that the flow cytometry assay of es expression provides a facile means of predicting resistance of leukemia cells to the cytotoxicity of araC and other nucleosides.

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

“…94 Several cell lines exhibit cross-resistance to a spectrum of NA because of reduced uptake. 11,54,95 In isolated leukemic blasts, sensitivity to ara-C, fludarabine and 2-CdA correlated with the cellular abundance of hENT1 96,97 determined by cellular binding of NBMPR. In these cells, the number of such binding sites ranged from 500 to 27 600 sites/cell.…”

Nucleoside anticancer drugs: the role of nucleoside transporters in resistance to cancer chemotherapy

“…Before entering cells, fludara is dephosphorylated by plasma phosphatases and ecto-5 0 -nucleotidase to fludarabine (F-araA), which is transported into cells by NTs present on plasma membranes. Fludarabine enters cells mainly by hENT1 and hCNT3 (Gati et al, 1998;Ritzel et al, 2001b). Like other nucleoside analogs, fludarabine is initially phosphorylated by dCK to its monophosphate (fludara, FaraAMP) form after which it is further phosphorylated to F-araATP (Sirotnak et al, 1983).…”

Nucleoside transporters in chronic lymphocytic leukaemia

“…This is also consistent with previous observations demonstrating that sensitivity of acute leukaemia cells to cytarabine is associated with hENT1 carrier protein amounts. 82 Pathways involved in resistance of CLL cells to purine nucleoside analogues differ from those implicated in the therapeutic action of anthracyclines, vinca alkaloids and alkylating agents. Bax expression correlates with sensitivity to doxorubicin, cyclophosphamide and chlorambucil, but not to fludarabine or cladribine.…”