Cytotoxicity of 2‐chlorodeoxyadenosine and arabinosylcytosine in leukaemic lymphoblasts from paediatric patients: significance of cellular nucleoside transporter content

Abstract

Summary. 2‐chlorodeoxyadenosine (2‐CdA) and arabinosylcytosine (araC) are nucleoside drugs that are used to treat various leukaemias, although 2‐CdA has not been tested extensively in children with acute lymphoblastic leukaemia (ALL). Nucleoside cytotoxicity depends on the conversion of these agents to 5′‐phosphate derivatives, following drug entry into cells via nucleoside transport (NT) processes. This study compared es nucleoside transporter content, determined using a flow cytometric assay with SAENTA [5′‐S‐(2‐aminoethyl)‐N6‐(4‐nitrobenzyl)‐5′‐thioadenosine] fluorescein, and cytotoxicities of 2‐CdA and araC in fresh lymphoblasts from previously untreated paediatric ALL patients and the human T‐lymphoblast cell line, CCRF‐CEM. Lymphoblast samples from individual patients ranged widely in sensitivity to both 2‐CdA (IC50, 6 nmol/l to > 5 μmol/l; mean = 418 nmol/l; n = 8) and araC (IC50, 59 nmol/l to > 5 μmol/l; mean = 1050 nmol/l; n = 7), although IC50 values for the two drugs were correlated (r = 0·78, P = 0·032, n = 7). Cellular es nucleoside transporter content varied more than 35‐fold among samples from 10 patients. The correlation between es nucleoside transporter content and drug sensitivity was statistically significant for araC (r = −0·93, P = 0·023, n = 5), but not for 2‐CdA (r = −0·57, P = 0·23, n = 6). Exposure of CCRF‐CEM cells to araC resulted in a substantial araC concentration‐dependent increase in the relative survival of es transporter‐deficient cells, whereas the increase was slight following exposure to 2‐CdA. We conclude that, in ALL lymphoblasts, es nucleoside transporter content is a determinant of araC sensitivity and that a deficiency in NT may impart resistance to araC.

Determinants of sensitivity and resistance to gemcitabine: The roles of human equilibrative nucleoside transporter 1 and deoxycytidine kinase in non‐small cell lung cancer

“…11) In vitro and in the clinical setting, sensitivity to nucleoside analogues such as cladribine (2-chloro-2′-deoxyadenosine, CdA), fludarabine (9-β-D-arabinofuranosyl-2-fluoroadenine, Fara-A), and cytosine arabinoside (1-β-Darabinofuranosylcytosine, cytarabine, Ara-C) has been shown to be correlated with the expression of hENT1. [12][13][14][15][16] Inside the cell, gemcitabine is phosphorylated by deoxycytidine kinase (dCK) to its monophosphate form. This first stage of phosphorylation is the rate-limiting step for further phosphorylation to active metabolites and thus is essential for activation of gemcitabine.…”

Identification of TIGAR in the equilibrative nucleoside transporter 2-mediated response to fludarabine in chronic lymphocytic leukemia cells

“…An increasing body of evidence suggests that the amount of particular types of nucleoside transporters might determine drug-induced cytotoxicity and, accordingly, statistical correlations between the pharmacological effects of nucleoside-derived drugs and expression of nucleoside transporters have been found in a variety of types of cancer so far. Thus, the number of high-affinity binding sites for NBTI (a specific inhibitor of hENT1) has been correlated with cytarabine cytotoxicity in acute myeloid leukemia and acute lymphocytic leukemia cells, 32,33 while similar positive correlations have been reported when quantifying hENT1-related mRNA levels. [34][35][36] In fact, hENT1 protein has been reported to be a suitable biomarker for predicting survival in patients suffering from pancreatic adenocarcinoma and treated with gemcitabine (a good hENT1 substrate) as a single therapy.…”

Development of multidrug resistance due to multiple factors including P‐glycoprotein overexpression under K‐selection after MYC and HRAS oncogene activation

“…39 SLC29A1 expression decreases in some hematological malignancies and breast cancer, and plays a significant role in clinical resistance to Ara-C in leukemia patients. 40 In summary, in the present study using a rodent cell culture system with MYC and EJ-RAS transfection, we demonstrated that Kselection, but not r-selection, facilitated MDR development, which could not be explained by a single molecular event, and appeared to be a multifactorial process. The events identified here as occurring under K-selection have actually been observed in clinical settings of certain cancers and hematological malignancies and are often associated with chemoresistance and/or poor clinical outcome.…”