tokens: To test the validity of the hypothesis that hypomethylation of DNA plays an important role in the initiation of carcinogenic process , 5 - azacytidine ( 5 - AzC ) ( 10 mg / kg ) , an inhibitor of DNA methylation , was given to rats during the phase of repair synthesis induced by the three carcinogens , benzo [ a ] - pyrene ( 200 mg / kg ) , N - methyl - N - nitrosourea ( 60 mg / kg ) and 1 , 2 - dimethylhydrazine ( 1 , 2 - DMH ) ( 100 mg / kg ) .