Dinuclear nickel(ii) supramolecular helicates down-regulate gene expression in human cells by stabilizing DNA G-quadruplexes formed in the promoter regions

Abstract

We investigated the interaction of the M- and P-enantiomers of the dinuclear nickel(II) tetracationic supramolecular helicate ([Ni2L3]4+, L = C25H20N4) with a series of four DNA G4s (hTelo, c-myc, c-kit1,...

Asymmetric triplex metallohelices stabilise DNA G-quadruplexes in promoter oncogene sequences and efficiently reduce their expression in cancer cells

“…The highest SI values of 12.8 and 13 were recorded for the binding of Λ-1 and Λ-2 towards k-ras G4 at 80 mM K + , respectively, but generally, good binding selectivity of both metallohelices towards k-ras and c-myc G4s was observed with SIs starting from 9.5 and 5.7, respectively. These values are lower than those recorded for some of the previously studied symmetric metallohelices 26 , but on the other hand, they are higher than SIs of Ni(II) cylinders 25 that were still able to downregulate the expression of the c-MYC oncogene in human cells. Data also demonstrate that 2 is a stronger and more selective binder to k-ras and c-myc G4s than 1 .…”

“…Noticeably, the Λ-enantiomers of 1 and 2 exhibited markedly higher binding affinities towards c-myc and k-ras G4s than the Δ-enantiomers, and at the same time, both enantiomers of 2 were more potent displacers of TO from all G4s than their 1 analogs. The binding selectivities of 1 and 2 towards G4s over duplex DNA were dependent on the ionic strength as it was observed for previously studied symmetric metallohelices 26 and Ni(II) cylinders 25 . The values of selectivity indexes (SIs) raised markedly when the concentration of K + was doubled from 40 to 80 mM and then slightly declined when the concentration of K + was further increased to 160 mM.…”

“…In the case of the most stable G4s c-myc and c-kit2 , with the T m s values of 77.6 and 68.5 °C in 10 mM K + and 87.4 and 77.4 °C in 40 mM K + , respectively, it can be observed that 2 provided lower stabilisation than 1 which is not in agreement with the results from the FID assays and for c-myc in 40 mM K + both enantiomers of 2 completely lost their capacity to stabilise this structure. The inconsistencies between the results obtained by FID assays and FRET melting assays when assessing the binding affinity of metallo-supramolecular helices towards DNA G4s were already observed in our previous publications 25 , 26 . The discrepancy may result from different experimental conditions but also from different binding modes of the ligands.…”

“…We have recently reported that the binding affinities of metallohelices to G4 and duplex DNA depend on the ionic strength and that as the ionic strength increases the interaction of metallohelices with duplex DNA is generally weakened more than that with G4 DNA 25 , 26 . This effect is manifested by an enhancement of the selectivity indexes (SIs) calculated as the ratio of DC 50 values for duplex and G4 DNA.…”

“…We have recently reported that some metallo-supramolecular helical assemblies with size, shape and charge similar to short cationic α-helical peptides 23 , 24 can target and stabilise G4s in vitro and downregulate the expression of G4-regulated genes in human cells 25 , 26 . While α-helices are inherently asymmetric, being formed from directional oligopeptide strands, the above-mentioned chiral metallohelical structures are of high symmetry due to synthetic feasibility and the use of symmetric strands AB-BA.…”