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

Abstract

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 × 10(4) to 6.01 × 10(4) 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.

Scheme 1

Synthesis of thiazacridine and imidazacridine derivatives.

Figure 1

Chemical structure of 3-acridin-9-ylmethylthiazolidine-2,4-dione (7).

Figure 2

Absorption spectra of derivative 6 (25 µM) with increasing concentrations of ctDNA. [DNA] = 0 (black), 10 (red), 20 (green), 40 (yellow), 60 (blue), 80 (pink) µM. Arrows (↓) and (→) refer to hypochromic and bathchromic effects, respectively. Inset: corresponding to the plot of [DNA]/(ε_a − ε_f) as function of DNA concentration as determined from the absorption spectral data.

Figure 3

Absorption spectra of derivative 5 (50 µM) with increasing concentrations of ctDNA. [DNA] = 0 (black), 10 (red), 20 (green), 40 (yellow), 60 (blue), 80 (pink) µM. Arrow (↑) refers to hyperchromic effect. Inset: corresponding to the plot of [DNA]/(ε_a − ε_f) as function of DNA concentration as determined from the absorption spectral data.

Figure 4

Fluorescence spectra of derivative 5 (10 µM) with increasing concentrations of ctDNA. [DNA] = 0 (black), 20 (red), 40 (green), 80 (yellow) e 120 (blue) µM. Insert: corresponding the fluorescence intensity of bound derivative to ctDNA (I)/fluorescence intensity of free derivative (I₀).

Figure 5

Circular dichroism spectra of ctDNA (100 µM) in 10 mM Tris HCl buffer pH 7.6, in the presence of 4 (red), 5 (green), 6 (yellow) and 7 (blue) derivatives.

Figure 6

Quantitative analysis of the thiazacridine and imidazacridine derivatives effects on the relaxation of pUC19 DNA plasmid by human topoisomerase 1.