Use of an indicator sequence of human DNA to study DNA damage by methylbis(2-chloroethyl)amine.

A highly reiterated sequence of human DNA was used to determine the sites of modification of DNA caused by the anti-tumor drug methylbis(2-chloroethyl)amine (HN2, mechlorethamine, nitrogen mustard) upon treatment of cells in culture and of purified DNA. The lengths of the breakage products of the DNA treated with HN2 were compared to the lengths of DNA scission products produced by chemical reactions used for DNA sequence determination. HN2 was found to create alkali-labile lesions at positions of guanine. The distribution of the guanine modifications was the same for DNA extracted from cells treated with HN2 and for purified DNA treated with HN2. However, the extent of damage was at least 2-fold greater when purified DNA was used as the substrate. Several nitrogen mustard analogues also produced alkali-labile lesions at positions of guanine.