P-32 POST-LABELING ANALYSIS OF NUCLEOBASES INVOLVED IN THE FORMATION OF DNA-ADDUCTS BY ANTITUMOR 1-NITROACRIDINES

Adducts generated in vitro by the reaction of 1-nitroacridines with po ly(dN)s in the presence of dithiothreitol were used to identify a kind of nucleic base involved in the formation of individual adducts. The patterns of chromatographic spots corresponding to modified nucleotide s obtained by P-32-post-labelling assay for synthetic homopolymers of four deoxyribonucleotides were compared with the fingerprints detected -in the case of calf thymus DNA reacted with 1-nitroacridines under co nditions in which the formation of identical DNA adducts as in cellula r models was demonstrated in earlier investigations. Both compounds st udied (Ledakrin and C-857) turned out to bind covalently only with pur ine nucleotides. Ledakrin formed with dG four and C-857 five different adducts. All of them were also detected in ctDNA. The incubation with poly(dA) resulted in four Ledakrin-dA species, two of which were foun d in ctDNA, and in two C-857-dA adducts that were not, however, observ ed in DNA containing samples. Modification of purines accounted for al l adducts observed in ctDNA. For both compounds studied, the level of total binding to poly(dA) was about one order of magnitude lower than to poly(dG) for which it was comparable with the extent of ctDNA modif ication. This indicates that dG represents a preferential site of cova lent binding of 1-nitroacridines to DNA. (C) 1997 Elsevier Science Ire land Ltd.