Structural insights into the anti-cancer activity of quercetin on G-tetrad, mixed G-tetrad, and G-quadruplex DNA using quantum chemical and molecular dynamics simulations

Human telomerase referred as 'terminal transferase' is a nucleoprotein enzyme which inhibits the disintegration of telomere length and act as a drug target for the anticancer therapy. The tandem repeating structure of telomere sequence forms the guanine-rich quadruplex structures that stabilize stacked tetrads. In our present work, we have investigated the interaction of quercetin with DNA tetrads using DFT. Geometrical analysis revealed that the influence of quercetin drug induces the structural changes into the DNA tetrads. Among DNA tetrads, the quercetin stacked with GCGC tetrad has the highest interaction energy of -88.08 kcal/mol. The binding mode and the structural stability are verified by the absorption spectroscopy method. The longer wavelength was found at 380 nm and it exhibits bathochromic shift. The findings help us to understand the binding nature of quercetin drug with DNA tetrads and it also inhibits the telomerase activity. Further, the quercetin drug interacted with G-quadruplex DNA by using molecular dynamics (MD) simulation studies for 100 ns simulation at different temperatures and different pH levels (T = 298 K, 320 K and pH = 7.4, 5.4). The structural stability of the quercetin with G-quadruplex structure is confirmed by RMSD. For the acidic condition (pH = 5.4), the binding affinity is higher toward G-quadruplex DNA, this result resembles that the quercetin drug is well interacted with G-quadruplex DNA at acidic condition (pH = 7.4) than the neutral condition. The obtained results show that quercetin drug stabilizes the G-quadruplex DNA, which regulates telomerase enzyme and it potentially acts as a novel anti-cancer agent. Communicated by Ramaswamy H. Sarma