The binding modes of carbazole derivatives with telomere G-quadruplex

It is reported that carbazole derivatives can stabilize G-quadruplex DNA structure formed by human telomeric sequence, and therefore, they have the potential to serve as anti-cancer agents. In this present study, in order to further explore the binding mode between carbazole derivatives and G-quadruplex formed by human telomeric sequence, two carbazole iodides (BMVEC, MVEC) molecules were synthesized and used to investigate the interaction with the human telomeric parallel and antiparallel G-quadruplex structures by NMR, CD and molecular modeling study. Interestingly, it is the pivotal the cationic charge pendant groups of pyridinium rings of carbazole that plays an essential role in the stabilizing and binding mode of the human telomeric sequences G-quadruplex structure. It was found that BMVEC with two cationic charge pendant groups of pyridinium rings of 9-ethylcarbazole cannot only stabilize parallel G-quadruple of Hum6 by groove binding and G-tetrad stacking modes and antiparallel G-quadruplex of Hum22 by groove binding, but also induce the formation of mixed G-quadruplex of Hum22. While MVEC with one cationic charge pendant groups of pyridinium ring only can bind with the parallel G-quadruplex of Hum6 by the stacking onto the G4 G-tetrad and could not interact with the G-quadruplex of Hum22.