Adenosine and adenosine analogues are more toxic to chronic lymphocytic leukemia than to normal lymphocytes

We compared the effect of adenosine and adenosine analogues on the phytohemagglutinin-induced proliferative response of blood lymphocytes from normal subjects and patients with chronic lymphocytic leukemia. As measured by the inhibition of thymidine or leucine incorporation, adenosine was more toxic to chronic lymphocytic leukemia (CLL) than to normal lymphocytes. This difference was not affected by the removal of adherent cells. The patients' B lymphocytes were more susceptible to adenosine toxicity than normal B lymphocytes. Similar responses were noted in T lymphocytes from both sources. Differential susceptibility was also observed with deoxyadenosine and adenosine analogues, including 5′deoxyadenosine. Uridine rescue from adenosine toxicity was observed for normal and CLL lymphocytes. In the presence of uridine, there was no difference in the residual inhibition of CLL as compared to normal lymphocytes. Intact CLL lymphocytes metabolized 14C-adenosine at a much lower rate than normal lymphocytes. While it appears that the greater toxicity of adenosine to CLL lymphocytes reflects the impaired catabolism of this nucleoside by these cells, evidence is presented that this is not the only mechanism underlying the differential susceptibility. These results may serve as the basis for further pharmacologic investigations of adenosine and adenosine deaminase inhibitors in chronic lymphocytic leukemia.