Breakage of human cell DNA after exposure to 3-methylcholanthrene-11,12-oxide

Damage to and repair of DNA isolated from human neonatal and fetal skin cells were measured by alkaline sucrose gradient analysis. 3-Methylcholanthrene did not induce single-strand breaks in DNA of the cells in culture, whereas the 11,12-oxide of 3-methylcholanthrene was very effective in this regard. The cis-1,2-dihydroxy, trans-11,12-dihydroxy, and cis-11,12-dihydroxy derivatives of 3-methylcholanthrene exerted little effect. The breaks in DNA caused by 3-methylcholanthrene oxide occurred during a 60-min incubation period and were repaired during the following 60 min. Methylmethane sulfonate also induced breaks in the DNA within 60 min.