A promising anticancer therapeutic
strategy is the stabilization
of telomeric G-quadruplexes using G-quadruplex-binding small molecules.
Although many G-quadruplex-specific ligands have been developed, their
low potency and selectivity to G-quadruplexes over duplex remains
unsolved. Recently, a crystal structure of a telomeric 3′ quadruplex–duplex
hybrid was reported and the quadruplex–duplex interface was
suggested to a good target to address the issues. However, there are
no high-resolution complex structures reported for G-quadruplex ligands
except for a docked BSU6037. In this study, molecular dynamic (MD)
binding simulations with a free ligand were used to study binding
poses and dynamics of four representative ligands: telomestatin, TMPyP4,
BSU6037, and BRACO19. The MD data showed that BSU6037 was able to
fully intercalate into the interface whereas TMPyP4 and BRACO19 could
only maintain partial intercalation into the interface and telomestatin
only binds at the quadruplex and duplex ends. Both linear ligands,
BSU6037 and BRACO19, were able to interact with the interface, yet
they were not selective over duplex DNA. The DNA geometry, binding
modes, and binding pathways were systematically characterized, and
the binding energy was calculated and compared for each system. The
interaction of the ligands to the interface was by the means of an
induced-fit binding mechanism rather than a lock–key mechanism,
consisting of the DNA unfolding at the interface to allow entrance
of the drug and then the refolding and repacking of the DNA and the
ligand to further stabilize the G-quadruplex. On the basis of the
findings in this study, modifications were suggested to optimize the
interface binding for TMPyp4 and telomestatin.