Clinical Cancer Research 2005-09-15

Mechanisms of cell death of chronic lymphocytic leukemia lymphocytes by RNA-directed agent, 8-NH2-adenosine.

Kumudha Balakrishnan, William G Wierda, Michael J Keating, Varsha Gandhi

Index: Clin. Cancer Res. 11(18) , 6745-52, (2005)

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Abstract

To determine if RNA-directed nucleoside analogue, 8-NH(2)-adenosine, induces cell death and if that is accompanied with transcription inhibition of the key survival factors of chronic lymphocytic leukemia (CLL) cells.Primary lymphocytes from CLL patients were incubated with 10 micromol/L 8-NH(2)-adenosine for 2, 4, and 6 or 8 hours. The accumulation of analogue triphosphate and the decline in endogenous ATP pool were analyzed by high-performance liquid chromatography. Inhibition of global RNA and protein synthesis was measured and correlated with specific decline in transcript and protein levels of MCL-1, XIAP, and BCL-2, the key survival factors of CLL. These biochemical and molecular end points were related to cell death of these quiescent lymphocytes.In vitro incubations of CLL lymphocytes with 8-NH(2)-adenosine resulted in rapid but heterogeneous accumulation of 8-NH(2)-ATP (390-680 micromol/L), with a concomitant decline in endogenous ATP (median, >50% by 4 hour). Global RNA synthesis was decreased in all samples and was associated with a decline in MCL-1, XIAP, and BCL-2 transcripts. There was a parallel decrease in the protein level of MCL-1 and XIAP but not BCL-2. These biochemical changes were accompanied by apoptosis.The evidence of CLL cell death with complementary changes in the expression of survival proteins provides a molecular rationale for using 8-NH(2)-adenosine as a therapeutic agent for this indolent leukemia.