thioinosine and Leukemia--Lymphocytic--Chronic--B-Cell

WSU-CLL cells, a fludarabine resistant B-cell chronic lymphocytic leukemia cell line, has been shown to exhibit enhanced sensitivity to 2-chlorodeoxyadenosine (2-CdA) following 48-72 h exposure to bryostatin 1. For 2-CdA to manifest its chemotherapeutic activity, it must first enter the cell through one of several specific nucleoside transporter systems. We present data to show that bryostatin 1-induced enhanced influx of 2-CdA is in part the result of bryostatin 1-induced modulation of nucleoside transporters in WSU-CLL cells. The bi-directional equilibrative NBMPR sensitive transporters in WSU-CLL cells were significantly down-regulated 90 min post-exposure to 1-200 nM bryostatin 1. This down-regulation was evident up to 144 h. In contrast, WSU-CLL cells exhibited a transient increase in Na+-dependent concentrative 2-CdA influx from 48 to 96 h after bryostatin 1 exposure which was evident for a longer duration than that accounted for by the increase in deocycytidine kinase activity. These data may, in part, explain the enhanced efficacy of 2-CdA seen in WSU-CLL cells following 48-72 h exposure to bryostatin 1. It may raise questions as to the importance of the bi-directional transporters in determining the resistance or sensitivity of CLL cells to 2-CdA or other nucleoside analogues.

Topics: Aged; Antineoplastic Agents; Biological Transport, Active; Bryostatins; Carrier Proteins; Cladribine; Deoxycytidine Kinase; Dipyridamole; Down-Regulation; Drug Resistance, Neoplasm; Humans; Lactones; Leukemia, Lymphocytic, Chronic, B-Cell; Macrolides; Male; Membrane Proteins; Nucleoside Transport Proteins; Phosphorylation; Thioinosine; Tumor Cells, Cultured; Vidarabine

2-Chlorodeoxyadenosine (2-CdA) is an important agent in the treatment of hairy cell leukemia and chronic lymphocytic leukemia (CLL). Others have reported that levels of 2-CdA phosphates present in human leukemia cells decline rapidly when the cells are in 2-CdA-free medium (Santana et al. J Clin Oncol 1991; 9: 416-422). In the present study, time-courses of 2-CdA loss from CLL cells were biexponential: the mean half-life of the initial phase was 0.30 +/- 0.18 h; the presence of 0.5 microM nitrobenzylthioinosine (NBMPR, a classical inhibitor of nucleoside transport) in the suspending medium, significantly decreased the initial rate of 2-CdA efflux (mean half-life, 0.43 +/- 0.22 h). As a consequence, AUCs (areas under time-course plots) were significantly higher in the NBMPR-treated cells (4.56 +/- 2.01 pmol.h/10(6) cells, n = 19) than in untreated control cells (3.83 +/- 1.74 pmol.h/10(6) cells; n = 19). 2-CdA was the principal efflux product released into the medium from 2-CdA-loaded CLL cells. We conclude that nucleoside transport processes contribute to the efflux of 2-CdA from CLL cells and that NBMPR may be useful as a retentive agent.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Biological Transport; Cladribine; Female; Half-Life; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Thioinosine