Antitumour imidazotetrazines-X. Effect of 8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4-(3H)-one (CCRG 81045; M & B 39831; NSC 362856) on DNA methylation during induction of haemoglobin synthesis in human leukaemia cell line K562.

Treatment of K562 human erythroleukaemia cells with 8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4-(3H)-one (CCRG 81045) caused a concentration-dependent increase in the number of cells producing haemoglobin after 3 days of treatment. The ethyl analogue (CCRG 82019) was inactive in the induction of erythroid characteristics. The concentration of 5-methyl-cytosine in the DNA of CCRG 81045 treated cells decreased 3 days after treatment, and was directly proportional to the number of benzidine-positive cells in the cultures, suggesting a direct correlation between hypomethylation of DNA and the induction of haemoglobin synthesis. Although the mechanism of this drug-induced hypomethylation of DNA is not known, the methyl analogue (CCRG 81045) also appeared to reduce template activity of isolated DNA to a greater extent than the ethyl analogue, suggesting that the extent or position of alkylation of DNA bases be important in inhibiting DNA-recognition enzymes.