Molecular dynamics simulations and quantum mechanics/molecular mechanics calculations provided a mechanism for G-quadruplex binding of three transition metal complexes.

With the aim of exploiting the use of organometallic species for the efficient modification of proteins through C‐atom transfer, the gold‐mediated cysteine arylation through a reductive elimination process occurring from the reaction of cyclometalated Au III C^N complexes with a zinc finger peptide (Cys 2 His 2 type) is here reported. Among the four selected Au III cyclometalated compounds, the [Au(C CO N)Cl 2 ] complex featuring the 2‐benzoylpyridine (C CO N) scaffold was identified as the most prone to reductive elimination and Cys arylation in buffered aqueous solution (pH 7.4) at 37 °C by high‐resolution LC electrospray ionization mass spectrometry. DFT and quantum mechanics/molecular mechanics (QM/MM) studies permitted to propose a mechanism for the title reaction that is in line with the experimental results. Overall, the results provide new insights into the reactivity of cytotoxic organogold compounds with biologically important zinc finger domains and identify initial structure–activity relationships to enable Au III ‐catalyzed reductive elimination in aqueous media.

The binding modes and free-energy landscape of two Au /N-heterocyclic carbene complexes interacting with G-quadruplexes, namely a human telomeric (hTelo) and a promoter sequence (C-KIT1), are studied here for the first time by metadynamics. The theoretical results are validated by FRET DNA melting assays and provide an accurate estimate of the absolute gold complex/DNA binding free energy. This advanced in silico approach is valuable to achieve rational drug design of selective G4 binders.

We present a thorough characterization of the interaction of novel nickel(II) (1), copper(II) (2) and zinc(II) (3) Schiff base complexes with native calf thymus DNA (ct-DNA), in buffered aqueous solution at pH 7.5. UV-vis absorption, circular dichroism (CD) and viscometry titrations provided clear evidence of the intercalative mechanism of the three square-planar metal complexes, allowing us to determine the intrinsic DNA-binding constants (K(b)), equal to 1.3 × 10(7), 2.9 × 10(6), and 6.2 × 10(5) M(-1) for 1, 2 and 3, respectively. Preferential affinity, of one order of magnitude, toward AT compared to GC base pair sequences was detected by UV-vis absorption titrations of 1 with [poly(dG-dC)]2 and [poly(dA-dT)]2. Structural details of the intercalation site of the three metal complexes within [dodeca(dA-dT)]2 were obtained by molecular dynamics (MD) simulations followed by density functional theory/molecular mechanics (DFT/MM) calculations. The calculations revealed that three major intermolecular interactions contribute to the strong affinity between DNA and the three metal complexes: (1) the electrostatic attraction between the two positively charged triethylammoniummethyl groups of the metal complexes and the negatively charged phosphate groups of the DNA backbone; (2) the intercalation of the naphthalene moiety within the four nitrogen bases of the intercalation site; (3) the metal coordination by exocyclic donor atoms of the bases, specifically the carbonyl oxygen and amine nitrogen atoms. Remarkably, the Gibbs formation free energy calculated for the intercalation complexes of 1, 2 and 3 with [dodeca(dA-dT)]2 in the implicit water solution is in agreement with the experimental Gibbs free energy values obtained from the DNA-binding constants as ΔG° = -RT ln(K(b)). In particular, the DNA-binding affinity trend, 1 > 2 > 3, is reproduced. Finally, the first shell coordination distances calculated for the intercalation complex 3/[dodeca(dA-dT)]2 are in excellent agreement with the experimental distances extracted from the extended X-ray absorption fine structure (EXAFS) spectrum of the corresponding 3/ct-DNA solutions. The latter results provided the first evidence of metal ion coordination by native DNA in aqueous solution.

The organometallic AuI bis‐N‐heterocyclic carbene complex [Au(9‐methylcaffeine‐8‐ylidene)2]+ (AuTMX2) was previously shown to selectively and potently stabilise telomeric DNA G‐quadruplex (G4) structures. This study sheds light on the molecular reactivity and mode of action of AuTMX2 in the cellular context using mass spectrometry‐based methods, including shotgun proteomics in A2780 ovarian cancer cells. In contrast to other metal‐based anticancer agents, this organogold compound is less prone to form coordinative bonds with biological nucleophiles and is expected to exert its drug effects mainly by non‐covalent interactions. Global protein expression changes of treated cancer cells revealed a multimodal mode of action of AuTMX2 by alterations in the nucleolus, telomeres, actin stress‐fibres and stress‐responses, which were further supported by pharmacological assays, fluorescence microscopy and cellular accumulation experiments. Proteomic data are available via ProteomeXchange with identifier PXD020560.