N'-Nitrosonornicotine

N'-Nitrosonornicotine (NNN) is a carcinogenic tobacco-specific nitrosamine present in both unburned tobacco and cigarette smoke. It forms DNA adducts and induces tumors in the respiratory and upper digestive tracts of rodents, with urinary levels in smokers correlating to esophageal cancer risk. This compound is used in research models for studying carcinogenesis and DNA damage mechanisms.