Cyclic nucleotide analogs as carcinostatic agents

Three cylcic nucleotide analogs, cyclic 3′,5′-arabinosyladenine monophosphate, cyclic 3′,5′-ribofuranosyl-6-mercaptopurine monophosphate and cyclic 3′,5′-ribofuranosyl-6-methylmercaptopurine monophosphate were tested for ability to penetrate murine tumor cells and human lymphocytes. Tests based on either tumor inhibition or inhibition of DNA synthesis in human lymphocytes undergoing blastogenesis, or both, indicated that these agents penetrated intact cells. It was demonstrated in one case (cAraMP) that the cells could convert the cyclic 3′,5′ nucleoside to 5′-nucleotide and that this had to occur intracellularly.