Analysis of adenosine-mediated pyrimidine starvation using cultured wild-type and mutant mouse T-lymphoma cells

Using the S49 T-cell lymphoma system for the study of immunodeficiency diseases, we characterized several variants in purine salvage and transport pathways and studied their responses to the cytotoxic action of adenosine (5-20 μM) in the presence of adenosine deaminase (ADA) inhibitors. Both an adenosine transport deficient mutant and a mutant lacking adenosine (ado) kinase activity are resistant to the cytotoxic effects of adenosine up to 15 μM. Variants lacking hypoxanthine-guanine phosphoribosyl transferase or adenine phosphoribosyltransferase are sensitive to the killing action of adenosine. We monitored the intracellular concentrations of purine and pyrimidine nucleotides, orotate, and PPribose P in mutant and wild-type cells following the addition of adenosine and an ADA inhibitor. We conclude that at low concentrations, adenosine must be phosphorylated to deplete the cell of pyrimidine nucleotides and PPribose P and to promote the accumulation of orotate. These alterations account for one mechanism of adenosine toxicity.