Tetraphenylethene Derivatives Modulate the RNA Hairpin-G-quadruplex Conformational Equilibria in Proto-Oncogenes

RNA G-quadruplexes (GQs) sequence in 5' UTRs of certain proto-oncogenes colocalize with hairpin (Hp) forming sequence 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 tetraphenylethenes (TPE) derivatives TPE-Py and TPE-MePy were synthesized and their effect on Hp-GQ equilibrium was explored. The FRET, CD and molecular docking experiments suggested that cationic TPE-MePy shifts the Hp-GQ equilibrium significantly towards the GQ conformer mainly through - stacking and van der waals interaction. In presence of TPE-MePy the observed rate constant values for first and second folding step was increased up to 14.6 and 2.6-fold respectively. The FRET melting assay showed a strong stabilizing ability of TPE-MePy (Tm = 4.36 C). Notably, the unmethylated derivative TPE-Py did not alter the Hp-GQ equilibrium. Subsequently, the luciferase assay demonstrated that the TPE-MePy derivatives suppressed the translation efficiency by 5.7-fold by shifting the Hp-GQ equilibrium toward GQ conformers in 5’ UTR of TRF2. Our data suggest that HpGQ equilibria could be selectively targeted with small molecules to modulate translation for therapy.