Recognition of human telomeric G-quadruplex DNA by 1,5-disubstituted diethyl-amido anthraquinone derivative in different ion environments causing thermal stabilization and apoptosis

Abstract

Ligand binding to G-quadruplex (G4) structures at human telomeric DNA ends promotes thermal stabilization, disrupting the interaction of the telomerase enzyme, which is found active in 80–85% of cancers and serves as a molecular marker. Anthraquinone compounds are well-known G-quadruplex (G4) binders that inhibit telomerase and induce apoptosis in cancer cells. Our current investigation is based on 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione, a derivative of anthraquinone and its binding characterization with two different human telomeric DNA structures, wHTel26 and HTel22, in the effect of K⁺ and Na⁺ by using an array of biophysical, calorimetry, molecular docking and cell viability assay techniques. Binding constants (K_b) in the range of ∼10⁵–10⁷ M⁻¹ and stoichiometries of 1:1, 2:1 & 4:1 were obtained from the absorbance, fluorescence, and circular dichroism study. Remarkable hypochromism (55, 97%) and ∼17 nm shift in absorbance, fluorescence quenching (95, 97%), the unaltered value of fluorescence lifetime, restoration of Circular Dichroism bands, absence of ICD band, indicated the external groove binding/binding somewhere at loops. This is also evident in molecular docking results, the ligand binds to groove forming base (G4, G5, G24, T25) and in the vicinity to TTA loop (G14, G15, T17) bases of wHTel26 and HTel22, respectively. Thermal stabilization induced by ligand was found greater in Na⁺ ion (27.5 °C) than (19.1 °C) in K⁺ ion. Ligand caused cell toxicity in MCF-7 cancer cell lines with an IC₅₀ value of ∼8.4 µM. The above findings suggest the ligand, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione could be a potent anticancer drug candidate and has great therapeutic implications.

Binding of disubstituted amido anthraquinone derivative, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione to human telomere HTel22 antiparallel conformation induced thermal stabilization.

Communicated by Ramaswamy H. Sarma

Keywords:

• Anthraquinone derivative
• anticancer activity
• differential scanning calorimetry
• fluorescence quenching
• G-quadruplex (G4)
• human telomeric DNA
• hypochromism
• molecular docking
• spectroscopy
• thermal stabilization

Authors’ contribution

R.B. conceptualized the idea; A.K., K.P. and R.B. designed the methodology. Synthesis of ligand molecule was carried out by A.K. under the supervision of R.K.P. Data mining and curation and biophysical experiments were performed by A.K. Cell-based MTT assay and thermal melting were performed by K.P. Fund was raised by R.B., M.N. & R.K.P. Original draft was written by A.K. and reviewed by R.K.P. and R.B.

Disclosure statement

There are no conflicts of interest to declare.

Additional information

Funding

The author A.K. would like to thank the University of Grant Commission, Government of India, for the JRF/SRF Fellowship (Grant no-319638). R.B. would like to thank the Department of Biotechnology (DBT), Government of India, for providing financial support in the form of a research project grant (Reference: BT/PR/14187/BRB/10/1413/2015). R.K.P & R.B. would like to thank the special grant provided by the Indian Institute of Technology Roorkee in the form of research assistance (Grant name/code OH-31-22-104-412).