GW-2974 and SCH-442416 modulators of tyrosine-kinase and adenosine receptors can also stabilize human telomeric G-quadruplex DNA: Insights into their anticancer effect

Abstract GW-2974 is a potent inhibitor for the tyrosine kinase receptor. It inhibits EGFR and ErbB-2 in tumor cells with high selectivity towards malignant over normal cells. SCH-442416 is a potent antagonist for adenosine receptor with high selectivity towards human A2a receptor over other adenosine receptors. The two compounds were reported to possess antitumor properties. In this work, we studied the stabilization of human telomeric G-quadruplex DNA by GW-2974 and SCH-442416, as a probable underlying mechanism for their anticancer effects. Interactions of human telomeric G-quadruplex DNA - sequence AG3(TTAGGG)3 – with both compounds were studied using UV-Vis, fluorescence quenching, melting temperature, circular dichroism and molecular docking techniques. Results obtained from absorption, fluorescence and CD indicated that GW2974 and SCH-442416 interacted with G-quadruplex through intercalation binding modes on two types of dependent binding sites. Binding affinities of 1.3x108 - 1.72x106 M-1 and of 1.55x107 - 3.74x105 M-1 were respectively obtained for GW-2974 for SCH-442416. An average number of binding sites between 1 and 2 was obtained for both compounds. The melting temperature curves indicated that complexations of both compounds to G-quadruplex DNA have respectively stabilized it by ΔTm = 9.9 oC and 9.6 oC, relative non-complexed G-quadruplex DNA. Increasing the molar ratios of GW-2974 or SCH-442416 relative to G-quadruplex DNA over 1:1 has shown to destabilized G-quadruplex DNA. Our selectivity experiment indicated 4.7- and 4.0-folds better selectivity for GW-2974 and SCH-442516 towards G-quadruplex DNA over ds-DNA, respectively. The two compounds have also proved to selectively bind and stabilize G-quadruplex DNA over calf thymus duplex ct-DNA. In silico molecular docking indicated exothermic intercalation bindings on two sites of the G-quadruplex DNA These results supported our hypothesis that both GW-2974 and SCH-442416 strongly stabilize human telomeric G-quadruplex DNA in additions to modulating tyrosine-kinase and adenosine receptors. Consequently, stabilizing G-quadruplex DNA could contribute to the mechanism of their anticancer activity.