BIOPHYSICAL STUDIES OF DIAMIDO ANTHRAQUINONE LIGAND-G-QUADRUPLEX DNA INTERACTIONS

Abstract

Anthraquinones (9,10-dioxoanthracenes) represent a significant category of natural and synthetic compounds with broad uses. In addition to being employed as dyes, anthraquinone variants have been utilized for ages in medical implications, such as for laxative purposes, as well as for their antimicrobial and anti-inflammatory properties. Current applications of anthraquinone include arthritis, multiple sclerosis, and cancer. For centuries, anthraquinones have served as a privileged chemical structure having anthraquinone moiety, which work as a central framework for various anti-cancer drugs. Nevertheless, the appearance of drug-resistant cancers necessitates the innovation of fresh anticancer ligands/drugs. In recent years, there has been a rapid escalation in research efforts aimed at generating novel anthraquinone-derived compounds. These compounds serve as fundamental chemical blueprints, enabling structural modifications that lead to the creation of innovative anthraquinone based compounds with substantial potential as effective anticancer agents. In terms of mechanism, the majority of the compounds derived from anthraquinone hinder the advancement of cancer by focusing on crucial cellular proteins. Initially, anthraquinone ligands worked on inhibiting topoisomerases, closed circular DNA, duplex DNA, and triplex DNA but the current research attention centered on human telomeric sequences containing G-quadruplex Structures. G-quadruplex structure formation is associated with telomerase dysfunction and Telomerase enzyme is found active in 85% of cancer cells, and consequently it became an attractive target of anticancer therapeutics. Several types of anthraquinone derivatives have been synthesized and applied to several types of cancer such as leukemia, lymphoma, breast cancer, ovarian cancer and many more for more than two decades, to minimize the cytotoxicity of anthraquinone-based ligands/drugs. The researchers employed substitution methods to make new derivatives of anthraquinone bearing covalently linked different side chains at different positions (2-6, 2-7, 1-4, 1-5, 1-8) with some specific groups to enhance selectivity and specificity towards G-quadruplex DNA. Phillip J. Perry, Stephen Neidle and Huang et al, made a library of such compounds, in which some ligands scored high in anticancer therapeutics. The first anthraquinone derivative 2,6-amido anthraquinone documented, to successfully inhibit telomerase activity with IC50 = 23 μM (Telomerase assay) in cancer cells, was BSU-1051. It shows thermal stabilization (ΔTm) of the DNA by ~20 ⁰C stabilized the G-quadruplex DNA. The successful implication of such anthraquinone derivatives as anticancer drugs motivates us to work on these compounds. We synthesized 1,5-diamido anthraquinone derivatives and investigated through various spectroscopy techniques, UV-absorption, Fluorescence (steady state & lifetime), Circular Dichroism, thermal melting by using CD and Difference Scanning Calorimetry along with molecular modelling and biological assay (MTT) on breast cancer cell lines. Such a comprehensive study of these compounds was not reported earlier with two different G-quadruplex sequences HTel22 and wHTel26 in the presence of Na+ and K+ ions, respectively. We investigated the binding characteristics of a 1,5-diamide anthraquinone derivative against human telomere sequence d-[AGGG(TTAGGG)3] and with -TT- overhang at 5’ and 3’ terminals. The core DNA sequence d-[AGGG(TTAGGG)3] (HTel22) attains anti-parallel (basket) conformation in the presence of Na+ ions, whereas d-[AGGG(TTAGGG)3] with -TT-overhang (wHTel26) attains hybrid conformation (3+1) in presence of K+ ions. We got substantial results with these compounds which can work as anticancer agents in anticancer therapeutics.