ACMA (9-amino-6-chloro-2-methoxy acridine) forms three complexes in the presence of DNA

The interaction of ACMA (9-amino-6-chloro-2-methoxy acridine) (D) with DNA (P) has been studied by absorbance, fluorescence, circular dichroism, spectrophotometry, viscometry and unwinding electrophoresis. A T-jump kinetic study has also been undertaken. The experimental data show that, totally unlike other drugs, ACMA is able to form with DNA three complexes (PDI, PDII, PDIII) that differ from each other by the characteristics and extent of the binding process. The main features of PDI fulfil the classical intercalation pattern and the formation/dissociation kinetics have been elucidated by T-jump techniques. PDII and PDIII are also intercalated species but, in addition to the dye units lodged between base pairs, they also bear dye molecules externally bound, more in PDIII relative to PDII. A reaction mechanism is put forward here. Comparison between absorbance, fluorescence and kinetic experiments has enabled us to determine the binding constants of the three complexes, namely (6.5 +/- 1.1) x 10(4) M-1 (PDI), (5.5 +/- 1.5) x 10(4) M-1 (PDII) and (5.7 +/- 0.03) x 10(4) M-1 (PDIII). The Comet assay reveals that the ACMA binding to DNA brings about genotoxic properties. The mutagenic potential studied by the Ames test reveals that ACMA can produce frameshift and transversion/transition mutations. ACMA also is able to produce base-pair substitution in the presence of S9 mix. Moreover, the MTT assays have revealed cytotoxicity. The biological effects observed have been rationalized in light of these features.