Assessment of amsacrine binding with DNA using UV-visible, circular dichroism and Raman spectroscopic techniques

An ultrasensitive label-free assay of 8-hydroxy-2'-deoxyguanosine based on the conformational switching of aptamer

We developed a highly sensitive label-free assay of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using 8-OHdG-aptamer (Apt) as the recognition element. The Apt was adsorbed onto the surface of gold nanoparticles (AuNPs), which prevents them from aggregating under high-salt conditions. Upon addition of 8-OHdG, the conformation of the Apt changes to form a G-quadruplex structure, which leads to the aggregation of the AuNPs along with the increase of the resonance light scattering intensity. The mechanism of 8-OHdG that induces Apt to form G-quadruplexes structure was studied by circular dichroism. The response signals linearly correlated with the concentration of 8-OHdG ranging from 90.8pM to 14.1nM with a detection limit of 27.3pM, which is much lower than that obtained by other methods. This method does not need any label steps and sophisticated equipment. The application for detection of 8-OHdG in real samples further demonstrated its reliability. This strategy would be helpful for developing a universal analytical method by simply replacing corresponding aptamers for various target molecules.

Synthesis, DNA binding and topoisomerase I inhibition activity of thiazacridine and imidazacridine derivatives

Thiazacridine and imidazacridine derivatives have shown promising results as tumors suppressors in some cancer cell lines. For a better understanding of the mechanism of action of these compounds, binding studies of 5-acridin-9-ylmethylidene-3-amino-2-thioxo-thiazolidin-4-one, 5-acridin-9-ylmethylidene-2-thioxo-thiazolidin-4-one, 5-acridin-9-ylmethylidene-2-thioxo-imidazolidin-4-one and 3-acridin-9-ylmethyl-thiazolidin-2,4-dione with calf thymus DNA (ctDNA) by electronic absorption and fluorescence spectroscopy and circular dichroism spectroscopy were performed. The binding constants ranged from 1.46 × 10⁴ to 6.01 × 10⁴ M⁻¹. UV-Vis, fluorescence and circular dichroism measurements indicated that the compounds interact effectively with ctDNA, both by intercalation or external binding. They demonstrated inhibitory activities to human topoisomerase I, except for 5-acridin-9-ylmethylidene-2-thioxo-1,3-thiazolidin-4-one. These results provide insight into the DNA binding mechanism of imidazacridines and thiazacridines.

Spectroscopic studies of the effects of anticancer drug mitoxantrone interaction with calf-thymus DNA

Mitoxantrone (MTX) (1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9,10-anthracenedione) is a synthetic antineoplastic drug, widely used as a potent chemotherapeutic agent in the treatment of various types of cancer. It is structurally similar to classical anthracyclines. Widespread interest in the anticancer agent mitoxantrone has arisen because of its apparent lower risk of cardio-toxic effects compared to the naturally occurring anthracyclines. In the present work, we investigated the interaction of mitoxantrone with DNA in the buffer solution at physiological pH using Fourier transform infrared (FTIR), UV-Visible absorption and circular dichroism spectroscopic techniques. FTIR analysis revealed the intercalation of mitoxantrone between the DNA base pairs along with its external binding with phosphate-sugar backbone. The binding constant calculated for mitoxantrone-DNA association was found to be 3.88×10(5)M(-1) indicating high affinity of drug with DNA double helix. Circular dichroism spectroscopic results suggest that there are no major conformational changes in DNA upon interaction with drug except some perturbations in native B-DNA at local level. The present work shows the capability of spectroscopic analysis to characterize the nature of drug-biomolecule complex and the effects of such interaction on the structure of biomolecule.