2'-Deoxyadenosine causes apoptotic cell death in a human colon carcinoma cell line

The combination of 2'-deoxyadenosine and 2'-deoxycoformycin is toxic for the human colon carcinoma cell line LoVo. In this study we investigated the mode of action of the two compounds and have found that they promote apoptosis. The examination by fluorescence microscopy of the cells treated with the combination revealed the characteristic morphology associated with apoptosis, such as chromatin condensation and nuclear fragmentation. The occurrence of apoptosis was also confirmed by the release of cytochrome c and the proteolytic processing of procaspase-3 in cells subjected to the treatment. To exert its triggering action on the apoptotic process, 2'-deoxyadenosine enters the cells through an equilibrative nitrobenzyl-thioinosine-insensitive carrier, and must be phosphorylated by intracellular kinases. Indeed, in the present work we demonstrate by analysis of the intracellular metabolic derivatives of 2'-deoxyadenosine that, as suggested by our previous findings, in the incubation performed with 2'-deoxyadenosine and 2'-deoxycoformycin, an appreciable amount of dATP was formed. Conversely, when also an inhibitor of adenosine kinase was added to the incubation mixture, dATP was not formed, and the toxic and apoptotic effect of the combination was completely reverted.