The toxicity of adenine and of purine-analogs to 2,6-diamino-purine-sensitive and -resistant L-strain mouse cells.

Abstract

The toxicity of adenine, hypoxanthine, and several purine-analogs to 2,6-diaminopurine (DAP)-resistant (DAP-r) and -sensitive (DAP-s) murine L cells has been tested in tissue culture. Resistance of DAP-r cells to DAP and 8-azaadenine was found to be stable over a period of about 5 years. DAP-r cells were cross-resistant to 8-azaadenine, less sensitive than DAP-s cells to 6-thioguanine and hypoxanthine, and more sensitive than DAP-s cells to 6-mercaptopurine and 8-azaxanthine.The concentration of adenine required to inhibit cell multiplication by 50% was 1.37 times greater for DAP-r cells than for DAP-s cells, although DAP-r cells lack, or have very low levels of, adenine phosphoribosyltransferase, which catalyzes adenosine 5′-monophosphate formation from adenine. Adenine toxicity to DAP-r and DAP-s cells could not be prevented by 4-amino-5-imidazolecarboxamide, guanine, hypoxanthine, xanthine, purine ribonucleosides, including adenosine, pyrimidine ribonucleosides, or thymidine. Purine and pyrimidine deoxyribonucleosides, amino acids, and vitamins were supplied in the cell culture medium. Increased concentrations of thiamine, calcium pantothenate, or p-aminobenzoic acid also did not prevent adenine toxicity.It is concluded that the toxicity of adenine to DAP-r and DAP-s L cells likely occurs by the same mechanism in both types of cell. This mechanism does not include the formation of adenosine 5′-monophosphate as an activation step, and does not involve the synthesis of thiamine, pantothenate, amino acids, purines, or pyrimidines which has been involved in other cases of adenine toxicity to bacterial and mammalian cells. A hitherto unknown mechanism seems to be operative.