Tetraphenylethene Derivatives Modulate the RNA Hairpin-G-Quadruplex Conformational Equilibria in Proto-oncogenes

RNA G-quadruplex (GQs) sequences in 5'-UTRs of certain proto-oncogenes co-localize with hairpin (Hp) forming sequences resulting in intramolecular Hp-GQ conformational equilibria, which is suggested to regulate cancer development and progression. Thus, regulation of Hp-GQ equilibria with small molecules is an attractive but less explored therapeutic approach. Herein, two tetraphenylethene (TPE) derivatives, TPE-Py and TPE-MePy, were synthesized and their effect on Hp-GQ equilibrium was explored. FRET, CD and molecular docking experiments suggest that cationic TPE-MePy shifts the Hp-GQ equilibrium significantly towards the GQ conformer mainly through π-π stacking and van der Waals interactions. In the presence of TPE-MePy, the observed rate constant values for first and second folding steps were increased up to 14.6 and 2.6-fold, respectively. The FRET melting assay showed a strong stabilizing ability of TPE-MePy (ΔTm=4.36 °C). Notably, the unmethylated derivative TPE-Py did not alter the Hp-GQ equilibrium. Subsequently, luciferase assay analysis demonstrated that the TPE-MePy derivatives suppressed the translation efficiency by ∼5.7-fold by shifting the Hp-GQ equilibrium toward GQ conformers in the 5'-UTR of TRF2. Our data suggests that HpGQ equilibria could be selectively targeted with small molecules to modulate translation for therapy.