DNA-drug interaction measurements using surface plasmon resonance

The interactions of the drugs 2,7-bis[(diethylamino)-ethoxy]-fluoren-9-one dihydrochloride (<(Tilorone)under bar>), 2,7-bis[(dipropylamino)-acetamido]-fluoren-9-one dihydrochloride (<(FA-2)under bar>), 2'-(4-hydroxyphenyl)-5-(4-methyl-1-piperazinyl)-2,5'-bi-1H-benzimidazole trihydrochloride (<(Hoechst 33258)under bar>), and hematoporphyrin IX derivative (<(HPD)under bar>) with synthetic self-complementary DNA (36-b.p.; 5'-biotin-spacer-[d(CGCTATATAGCG)](3)-3') were studied by SPR (Surface Plasmon Resonance). Monolayers of biotinylated DNA were immobilized on a streptavidin-dextran-gold triple-layer. Small portions of the drugs (approximately 30 pmol/ml) were injected in continuous flow. The mass corresponded to the amount of the bound molecules. Injections of 50 mM sodium hydroxide pulses separated the DNA double strands, releasing the effector molecules. Subsequent treatments with the effecters gave reproducible results. The maximum interaction between drug and DNA was observed in the case of Tilorone. 41 molecules could bind to the 36-b.p. DNA duplex. To investigate the microscopic behavior in condensed nucleic acid phases, SFM (Scanning Force Microscopy)-imaging and polarizing microscopic observations of DNA-effector complexes were carried out. Supplementary UV-absorption thermal denaturation curves of DNA with the above-mentioned effecters in dilute solutions were measured. As an additional aid to understand the geometries of DNA-drug interactions, computer simulations were performed and compared with the experimental data.