Mechanism studies on anti-HepG2 cell proliferation of phenanthroline derivatives as G-quadruplex DNA stabilizers

4,5-Diazafluorene N-glycopyranosyl hydrazones as scaffolds for potential bioactive metallo-organic compounds: Synthesis, structural study and cytotoxic activity

A series of novel N¹-(4,5-diazafluoren-9-yliden)-N²-glycopyranosyl hydrazines was prepared in synthetically useful yields by treatment of 9H-4,5-diazafluoren-9-hydrazone with different unprotected monosaccharides. The reactions with the monosaccharides tested afforded stereoselectively, and exclusively, cyclic derivatives, whose structures correspond to N-β-glycopyranosyl hydrazones except for the d-arabinose derivative that agrees with the α-anomer. Several copper(II) complexes having a 2:1 ligand to metal mole ratio were also prepared. The metal complexes can bind DNA sequences and preferentially stabilize G-quadruplex DNA structures over dsDNA. The fucose, rhamnose and deoxyglucose copper(II) complexes exhibited a cytotoxic activity against cultured HeLa and PC3 tumor cells comparable to other metal complexes normally used for chemotherapeutic purposes, such as cisplatin.

Arylsulfanyl groups - Suitable side chains for 5-substituted 1,10-phenanthroline and nickel complexes as G4 ligands and telomerase inhibitors

Guanine-rich DNA sequences can undergo self-assembly into unique G-quadruplex structures that interfere with the binding of proteins to the same DNA region. The formation of DNA G-quadruplexes requires monovalent cations (Na⁺ and K⁺) or small molecules known as G-quadruplex (G4) ligands. Phenanthroline is a type of G4 ligand scaffold known for its coordination with metal ions to form complexes with a large aromatic surface area, which aptly stack with G-quartets. In this report, we have investigated the side chain effect on G-quadruplex recognition by evaluating a series of 5-substituted phenanthroline-based metal complexes (Phen-Ni) binding to telomeric G-quadruplex DNA. Results from biophysical methods including fluorescence and circular dichroism (CD) thermal denaturation, CD titration, and the fluorescent intercalator displacement (FID) assay suggest that several Phen-Ni complexes bind to G-quadruplex DNA with submicromolar ^G4DC₅₀ values. Arylsulfanyl groups at the 5 position of 1,10-phenanthroline are the best side chains regarding binding affinity and selectivity towards G-quadruplex DNA. Most of the G-quadruplex binding Phen-Ni complexes can inhibit telomerase activity in vitro as indicated by the telomeric repeat amplification protocol (TRAP) assay and such inhibition is clearly concentration dependent. Our results here provide a guidance of utilizing 5-substituted phenanthroline derivatives as a viable and facile approach to design novel G4 ligands.