Arabinosylguanine-induced apoptosis of T-lymphoblastic cells: incorporation into DNA is a necessary step.
9-Beta-D-Arabinosylguanine (ara-G) is a recently introduced and effective treatment for T-cell acute lymphoblastic leukemia, but how ara-G and ara-G triphosphate (ara-GTP) kill cells is not known. We hypothesized that, in cycling T-lymphoblastoid cells, ara-G may act directly by incorporation into DNA, which may lead to apoptosis. Hence, blocking the incorporation of ara-G monophosphate (ara-GMP) into DNA may prevent apoptosis. To test this hypothesis, we performed experiments in a T-lymphoblastic leukemia cell line (CCRF-CEM) after synchronization with a double aphidicolin block. Intracellular accumulation of ara-GTP was neither cell cycle dependent nor affected by aphidicolin (53 +/- 5 microM/h without aphidicolin, 50 +/- 5 microM/h with aphidicolin). Cells at the G1-S boundary accumulated 75 +/- 7 microM ara-GTP with minimal incorporation into DNA (5 +/- 2 pmol ara-GMP/mg DNA) and had little biochemical or morphological evidence of apoptosis. In marked contrast, cells in S phase had significantly more ara-G incorporated into DNA (24 +/- 4 pmol ara-GMP/mg DNA), although the cytosolic concentration of ara-GTP (85 +/- 7 microM) was similar to that in the G1-enriched population. In the S-phase cells, there was a corresponding increase in apoptosis (measured as high molecular weight DNA fragmentation and morphological changes), and the incorporation of ara-GTP into DNA resulted in a >95% inhibition of DNA synthesis. There was a direct linear relationship between the number of cells in S phase and both the total number of ara-GMP molecules in DNA and the inhibition of DNA synthesis. Blocking of ara-GTP incorporation into S-phase DNA abolished biochemical and morphological features of apoptosis, even in the presence of cytotoxic level of intracellular ara-GTP. Taken together, these data demonstrate that the incorporation of ara-GTP into DNA is the critical event that mediates the induction of apoptosis in CCRF-CEM cells.
Rodriguez
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Department of Clinical Investigation, The University of Texas MD Anderson Cancer Center, and The Graduate School of Biomedical Sciences, Houston 77030, USA.
Gandhi
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D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000633:toxicity; D016590:Aphidicolin / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001087:Arabinonucleosides / Q000493:pharmacokinetics* / Q000633:toxicity*; D002453:Cell Cycle / Q000187:drug effects; D053938:DNA Fragmentation; D004273:DNA, Neoplasm / Q000096:biosynthesis*; D016193:G1 Phase; D006801:Humans; D007700:Kinetics; D015459:Leukemia-Lymphoma, Adult T-Cell; D016196:S Phase; D013601:T-Lymphocytes / Q000187:drug effects*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D001087:Arabinonucleosides; D004273:DNA, Neoplasm; C028771:9-arabinofuranosylguanine; D016590:Aphidicolin