Two approaches that increase the activity of analogs of adenine nucleosides in animal cells.

Deamination of many analogs of adenine nucleosides results in the loss of their chemotherapeutic efficacy. Two approaches have been used in this study to overcome this problem. First, some adenine nucleotides, which are resistant to mammalian adenosine deaminase, are more toxic to animal cells than are the respective nucleosides. For toxic to animal cells than are the respective nucleosides. For example, 9-beta-D-arabinofuranosyladenine 5'-phosphate, a molecule that penetrates the cell without degradation, has a more sustained toxicity against mouse fibroblasts (L-cells) than does 9-beta-D-arabinofuranosyladenine (ara-A). Furthermore, L-cells treated with 2',3'-dideoxyadenosine 5'-phosphate are extensively killed after 48 hr, whereas 2',3'-dideoxyadenosine is almost nontoxic to L-cells. Specific inhibition of adenosine deaminase by nontoxic concentrations of erythro-9-(2-hydroxy-3-nonyl)adenine greatly potentiates the biological activity of both ara-A and 3'-deoxyadenosine (cordycepin). Simultaneous administration of cytostatic concentrations of ara-A and the inhibitor of adenosine deaminase to L-cells killed greater than 99.9 percent of cells in 36 hr. A similar concentration of ara-A plus the deaminase inhibitor also markedly extended the mean survival of mice bearing Ehrlich ascites carcinoma as compared to ara-A alone. A cytostatic concentration of cordycepin 1 x 10-4 M), administered in the presence of deaminase inhibitor, killed greater than 99.9 percent of cultured L-cells in only 8 hr. During the latter incubation, accumulation of uridine in acid-insoluble material reached a maximum after 30 min, and incorporation of thymidine into acid-insoluble material was almost totally arrested after 2 hr.