DNA SEQUENCE-SPECIFIC ADENINE ALKYLATION BY THE NOVEL ANTITUMOR DRUG TALLIMUSTINE (FCE-24517), A BENZOYL NITROGEN-MUSTARD DERIVATIVE OF DISTAMYCIN

FCE 24517, a novel distamycin derivative possessing potent antitumor a ctivity, is under initial clinical investigation in Europe. Tn spite o f the presence of a benzoyl nitrogen mustard group this compound fails to alkylate the N7 position of guanine, the major site of alkylation by conventional nitrogen mustards. Characterisation of DNA-drug adduct s revealed only a very low level of adenine adduct formation. Using a modified Maxam-Gilbert sequencing method the consensus sequence for FC E 24517-adenine adduct formation was found to be 5'-TTTTGA-3'. A singl e base modification in the hexamer completely abolishes the alkylation of adenine. Using a Tag polymerase stop assay alkylations were confir med at the A present in the hexamer TTTTGA and, in addition, in one ou t of three TTTTAA sequences present in the plasmid utilized. The seque nce specificity of alkylation by FCE 24517 is therefore the most strik ing yet observed for an alkylating agent of small molecular weight.