Spectroscopic studies of the interaction of aspirin and its important metabolite, salicylate ion, with DNA, A·T and G·C rich sequences

Among different biological effects of acetylsalicylic acid (ASA), its anticancer property is controversial. Since ASA hydrolyzes rapidly to salicylic acid (SA), especially in the blood, interaction of both ASA and SA (as the small molecules) with ctDNA, oligo(dA·dT) ₁₅ and oligo(dG·dC) ₁₅, as a possible mechanism of their action, is investigated here. The results show that the rate of ASA hydrolysis in the absence and presence of ctDNA is similar. The spectrophotometric results indicate that both ASA and SA cooperatively bind to ctDNA. The binding constants ( K) are (1.7 ± 0.7) × 10 ³ M ^-1 and (6.7 ± 0.2) × 10 ³ M ^-1 for ASA and SA, respectively. Both ligands quench the fluorescence emission of ethidium bromide (Et)-ctDNA complex. The Scatchard plots indicate the non-displacement based quenching (non-intercalative binding). The circular dichroism (CD) spectra of ASA- or SA-ctDsNA complexes show the minor distortion of ctDNA structure, with no characteristic peaks for intercalation of ligands. T_m of ctDNA is decreased up to 3 °C upon ASA binding. The CD results also indicate more distortions on oligo(dG·dC) ₁₅ structure due to the binding of both ASA and SA in comparison with oligo(dA·dT) ₁₅. All data indicate the more affinity for SA binding with DNA minor groove in comparison with ASA which has more hydrophobic character.