title: Enhancement of retention and cytotoxicity of 2-chlorodeoxyadenosine in cultured human leukemic lymphoblasts by nitrobenzylthioinosine, an inhibitor of equilibrative nucleoside transport.
abstract: In leukemic cells exposed to 2-chlorodeoxyadenosine (2-CdA), levels of the nucleoside drug and its phosphate metabolites decay with time in the absence of external 2-CdA; an intrinsic part of this process is the efflux of 2-CdA. The effects of nitrobenzylthioinosine (NBMPR) and of dipyridamole (DPM), both potent inhibitors of es (e, equilibrative; s, sensitive to NBMPR) nucleoside transport processes, were studied in four lines of cultured leukemic lymphoblasts. Suspensions of 2-CdA-loaded cells were diluted 10-fold with 2-CdA-free medium to initiate the cellular 2-CdA decay processes, which followed a biexponential time course. When diluting media contained NBMPR or DPM, intracellular levels of 2-CdA and its metabolites were substantially increased (P < 0.001) compared with cells in media lacking the transport inhibitors, and 2-CdA loss followed a monoexponential time course. As a consequence, the AUCs (area under time-course plots of intracellular 2-CdA and its metabolites) were significantly (P < 0.001) lower in untreated control cells compared to inhibitor-treated cells. These results suggest that nucleoside transport processes contribute to the efflux of 2-CdA from the cultured lymphoblasts. The cytotoxicity of 1-h exposure to 2-CdA of Reh-A2 and CCRF-CEM cells was enhanced three-fold by subsequent exposure to 0.5 microM NBMPR relative to that of control cells subjected to the same manipulations without NBMPR exposure. However, before such a strategy may be considered to have a therapeutic application, careful examination of effects in normal lymphocytes and ex vivo leukemic lymphoblasts must first be undertaken. Leukemia (2000) 14, 52-60.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7.
authors.forename: A M
authors.initials: AM
authors.lastname: Wright
authors.forename: W P
authors.initials: WP
authors.lastname: Gati
authors.forename: A R
authors.initials: AR
authors.lastname: Paterson
mesh_terms: D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001692:Biological Transport; D002851:Chromatography, High Pressure Liquid; D017338:Cladribine / Q000493:pharmacokinetics / Q000494:pharmacology*; D004357:Drug Synergism; D006801:Humans; D009705:Nucleosides / Q000378:metabolism*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology*; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D009705:Nucleosides; D013868:Thioinosine; D017338:Cladribine; C001789:4-nitrobenzylthioinosine