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

Abstract

Treatment of K562 human erythroleukaemia cells with 8-carbamoyl-3-methylimidazo[5,1-d]-l,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 druginduced 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.