Diverse tools, including small molecules, peptides, aptamers, antibodies, and derived combinatorial tools, are used to target rG4s and regulate rG4-mediated gene expression. (A) Representative small molecules with different scaffolds for rG4 targeting, such as cationic porphyrins (TmPyP4), quinoline derivatives (cPDS), polyaromatic compounds (RGB-1), and guanine-clamp analogs (PhpC). (B) De novo peptides specifically target G4 structures selected by G4-mRNA display-seq. An mRNA library was linked to puromycin linker and translated in vitro to create the mRNA-peptide fusion library, followed by reverse-transcription and screening against an rG4 target to isolate functional sequences. The tandem and cyclic version of peptide showed enhanced binding to rG4 and downregulated rG4-mediated gene expression. (C) L-RNA aptamers bind to rG4, leading to disruption of rG4–protein interaction and inhibition of gene expression. (D) Antibody BG4 binding to rG4 for rG4 imaging in cells via confocal microscopy. Icon adapted from “confocal-scanning-laser-microscope-CSLM” by DBCLS (https://togotv.dbcls.jp/en/pics.html) is licensed under CC-BY 4.0 Unported (https://creativecommons.org/licenses/by/4.0/). (E) Antisense oligonucleotides composed of γPNA oligomers potently invade and destabilize rG4, resulted in formation of γPNA–RNA duplex. (F) Dual binding of an rG4 ligand cPDS and an antibody BG4 to TERRA rG4 in a two-stage manner. cPDS initially binds competitively to TERRA rG4, followed by a slow conformational rearrangement of ternary complex with BG4. (G) A bifunctional guanine-RHAU23 peptide conjugate (GRPC) for G-vacancy-bearing G-quadruplexes (GVBQs) targeting. The guanine group fills into the G-vacancy in a GVBQ, facilitating the binding of RHAU23 to the GVBQs.
