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

Some metallo-supramolecular helical assemblies with size, shape, charge and amphipathic architectures similar to short cationic α-helical peptides have been shown to target and stabilise DNA G-quadruplexes (G4s) in vitro and downregulate the expression of G4-regulated genes in human cells. To expand the library of metallohelical structures that can act as efficient DNA G4 binders and downregulate genes containing G4-forming sequences in their promoter regions, we investigated the interaction of the two enantiomeric pairs of asymmetric Fe(II) triplex metallohelices with a series of five different DNA G4s formed by the human telomeric sequence (hTelo) and in the promoter regions of c-MYC, c-KIT, and k-RAS oncogenes. The metallohelices display preferential binding to G4s over duplex DNA in all investigated G4-forming sequences and induced arrest of DNA polymerase on template strands containing G4-forming sequences. Moreover, the investigated metallohelices suppressed the expression of c-MYC and k-RAS genes at mRNA and protein levels in HCT116 human cancer cells, as revealed by RT-qPCR analysis and western blotting.

Shape-Selective Targeting on RNA Bulges by Peptidomimetic Metallohelices.

RNA bulges represent one of the most common motifs in the RNA secondary structure and serve in a variety of biological functions. Compounds stabilizing RNA bulges are important for probing RNA structure and function and for therapy of some diseases. Here, the ability of a series of enantiomeric pairs of optically pure bimetallic metallohelices with different flexible linkers to target various RNA bulges is investigated. The results show that binding affinities of the metallohelices to bulged RNA differ and strongly depend on the size of the bulge and the base composition of the bulge loop. Notably, the shorter, more compact, and less flexible metallohelices bind to RNA bulges most efficiently and selectively. Interestingly, the ability of the metallohelices to bind to RNA bulges correlates with their previously reported antimicrobial activity, which suggests that the selective recognition of bulged regions in RNA by the metallohelices might also contribute to their biological activity.

Cationic FeII Triplex-Forming Metallohelices as DNA Bulge Binders.

Bulges are essential structural elements in nucleic acids. The detection and targeting of bulged DNA sequences are highly important. Small molecules capable of targeting DNA bulges have attracted considerable attention because they cannot only be used as reagents for bulge recognition, but also as potential therapeutic drugs. Herein, the interactions of DNA duplexes, containing bulges of various sizes and base compositions, with a series of FeII triplex-forming metallohelices are reported. The results obtained, with the aid of molecular biophysics methods, show that the investigated metallohelices prefer to bind to bulged DNA, rather than double-stranded DNA, and that their binding affinities towards bulges differ among individual metallohelices. Moreover, their binding affinities towards bulges strongly depend on the bulge size and the base composition of the bulge loop. The investigated metallohelices can enter eukaryotic cells and accumulate in the cell nucleus, allowing them to interact with nucleic acids. Hence, it is reasonable to suggest that the interaction of metallohelices with nucleic acid bulges might contribute to the mechanism of their biological activity.

Glycoconjugated Metallohelices have Improved Nuclear Delivery and Suppress Tumour Growth In Vivo.

Monosaccharides are added to the hydrophilic face of a self-assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water-stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+ ) with respect to the non-cancerous ARPE-19 cell line. While the most selective compound is a glucose-appended enantiomer, its cellular entry is not mainly glucose transporter-mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5-fold, and a non-destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects.