Reactions of N,N-bis(2-chloroethyl)-p-aminophenylbutyric acid (chlorambucil) with 2'-deoxyguanosine

N,N-Bis(2-chloroethyl)-p-aminophenylbutyric acid (chlorambucil, 1) was allowed to react in the presence of 2'-deoxyguanosine (16 mM) at physiological pH (cacodylic acid, 50% base), and the reactions were followed by HPLC/MS/MS techniques. Although the predominant reaction observed was chlorambucil hydrolysis, ca. 24% of 1 reacted with different heteroatoms of the nucleoside. As expected, the principal site of 2'-deoxyguanosine alkylation was N7. Alkylation of N7 caused spontaneous depurination, and N-(7-guaninylethyl)-N-hydroxyethyl-p-aminophenylbutyric acid (5) and the corresponding N7,N7-bis-adduct (6) were the major stable dGuo derivatives. Also several other adducts were detected and tentatively identified by means of MS/MS and UV. From them, the O(6-), N1-, N(2-), and O5'-derivatives can be biologically significant. Our results shed new light on DNA modifications caused by chlorambucil, which is an important chemotherapeutic drug and a known carcinogen.