[3] NOC are alkylating agents formed by the reaction of nitrite or other nitrogen oxides with secondary amines and N-alkylamides, yielding N-alkylnitrosamines and N-alkylnitrosamides.

[2] NOC are found in some foods (bacon, sausages, cheese) and tobacco smoke, and are formed in the gastrointestinal tract, especially after consumption of red meat.

[2] In addition, endogenous nitric oxide levels were found to be enhanced under chronic inflammatory conditions, and this could favor NOC formation in the large intestine.

In 1985 Yarosh summarized the early work that established 6-O-methylguanine as the alkylated base in DNA that was the most mutagenic and carcinogenic.

[9] These effects are due to interaction of the DNA mismatch repair pathway with 6-O-methylguanine, and also depend on signaling network activation, led by early ATM, H2AX, CHK1 and p53 phosphorylation.