The interaction of three chosen non-steroidal anti-inflammatory drugs (NSAID), indomethacin, sulindac and tolmetin with calf thymus DNA has been investigated by fluorescence with the use of fluorescence probes, ethidium bromide (EB) and neutral red (NR). When bound to DNA, sulindac and indomethacin could quench the fluorescence of EB at low concentration by exchanging with the EB probe, and attained saturation quickly. But sulindac and indomethacin continuously quenched the fluorescence emission and resonance light scattering spectra of NR in the presence of DNA until rather high concentration. These spectral characteristics supported the intercalation of NSAID into DNA as well as electrostatic assembly on the surface of DNA double strands.

Key words: non-steroidal anti-inflammatory drug, calf thymus DNA, fluorescence, resonance light scattering spectra, probe