Photoactivatable platinum(II) terpyridine derivatives for G-quadruplex DNA double anchoring

Mustards-Derived Terpyridine-Platinum Complexes as Anticancer Agents: DNA Alkylation vs Coordination

The development of bifunctional platinum complexes with the ability to interact with DNA via different binding modes is of interest in anticancer metallodrug research. Therefore, we report platinum(II) terpyridine complexes to target DNA by coordination and/or through a tethered alkylating moiety. The platinum complexes were evaluated for their in vitro antiproliferative properties against the human cancer cell lines HCT116 (colorectal), SW480 (colon), NCI-H460 (non-small cell lung), and SiHa (cervix) and generally exhibited potent antiproliferative activity although lower than their respective terpyridine ligands. ¹H NMR spectroscopy and/or ESI-MS studies on the aqueous stability and reactivity with various small biomolecules, acting as protein and DNA model compounds, were used to establish potential modes of action for these complexes. These investigations indicated rapid binding of complex PtL3 to the biomolecules through coordination to the Pt center, while PtL4 in addition alkylated 9-ethylguanine. PtL3 was investigated for its reactivity to the model protein hen egg white lysozyme (HEWL) by protein crystallography which allowed identification of the N^δ1 atom of His15 as the binding site.

Teaching photosensitizers a new trick: red light-triggered G-quadruplex alkylation by ligand co-localization

We propose a bimolecular approach for G-quadruplex alkylation, using a pro-reactive furan-containing ligand, activated by red-light irradiation of a proximate G4-binding photosensitizer. G4- over dsDNA alkylation can be achieved selectively and proves high-yielding at low ligand excess. HPLC and modelling studies allowed identifying potential residues involved in the alkylation.

New derivatives of 4'-phenyl-2,2':6',2″-terpyridine as promising anticancer agents

Terpyridine derivatives are known from their broad application including anticancer properties. In this work we present the newly synthesized 4'-phenyl-2,2':6',2″-terpyridine group with high antiproliferative activity. We suggest that these compounds influence cellular redox homeostasis. Cancer cells are particularly susceptible to any changes in the redox balance because of their handicapped and inefficient antioxidant cellular systems. The antiproliferative activity of the studied compounds was tested on five different cell lines that represent several types of tumours; glioblastoma, leukemia, breast, pancreatic and colon. Additionally, we also tested their selectivity towards normal cells. We performed molecular biology studies in order to detect the response of a cell to its treatment with the compounds that were tested. We looked at the in-depth changes in the proteins and cellular pathways that lead to cell cycle inhibition (G0/G1 and S), and consequently, death on the apoptosis and autophagy pathways. We proved that the studied compounds targeted DNA as well. Special attention was paid to the targets connected with ROS generation.

A study of Pt(II)-phenanthroline complex interactions with double-stranded and G-quadruplex DNA by ESI-MS, circular dichroism, and computational docking

The binding interactions of a series of square-planar platinum(II)-phenanthroline complexes of the type [Pt(P_L)(A_L)]²⁺ [where P_L = variously methyl-substituted 1,10-phenanthroline (phen) and A_L = ethane-1,2-diamine (en)] were assessed with a G-quadruplex DNA (5'-TTG GGG GT-3', G4DNA) and a double-stranded DNA (5'-CGC GAA TTC GCG-3', dsDNA) sequence by ESI-MS. The results indicate a strong correlation between G4DNA affinity and increasing phenanthroline methyl substitution. Circular dichroism (CD) spectroscopy and molecular docking studies also support the finding that increased substitution of the phenanthroline ligand increased selectivity for G4DNA. ESI-MS was used to probe the interaction of a range of square-planar Pt(II)-phenanthroline complexes with double-stranded and G-quadruplex DNA.

Selectivity of Terpyridine Platinum Anticancer Drugs for G-quadruplex DNA

Guanine-rich DNA can form four-stranded structures called G-quadruplexes (G4s) that can regulate many biological processes. Metal complexes have shown high affinity and selectivity toward the quadruplex structure. Here, we report the comparison of a panel of platinum (II) complexes for quadruplex DNA selective recognition by exploring the aromatic core around terpyridine derivatives. Their affinity and selectivity towards G4 structures of various topologies have been evaluated by FRET-melting (Fluorescence Resonance Energy Transfert-melting) and Fluorescent Intercalator Displacement (FID) assays, the latter performed by using three different fluorescent probes (Thiazole Orange (TO), TO-PRO-3, and PhenDV). Their ability to bind covalently to the c-myc G4 structure in vitro and their cytotoxicity potential in two ovarian cancerous cell lines were established. Our results show that the aromatic surface of the metallic ligands governs, in vitro, their affinity, their selectivity for the G4 over the duplex structures, and platination efficiency. However, the structural modifications do not allow significant discrimination among the different G4 topologies. Moreover, all compounds were tested on ovarian cancer cell lines and normal cell lines and were all able to overcome cisplatin resistance highlighting their interest as new anticancer drugs.

Probing of G-Quadruplex Structures via Ligand-Sensitized Photochemical Reactions in BrU-Substituted DNA

We studied photochemical reactions of ^BrU-substituted G-quadruplex (G4) DNA substrates with two pyrene-substituted polyazamacrocyclic ligands, M-1PY and M-2PY. Both ligands bind to and stabilize G4-DNA structures without altering their folding topology, as demonstrated by FRET-melting experiments, fluorimetric titrations and CD spectroscopy. Notably, the bis-pyrene derivative (M-2PY) behaves as a significantly more affine and selective G4 ligand, compared with its mono-pyrene counterpart (M-1PY) and control compounds. Upon short UVA irradiation (365 nm) both ligands, in particular M-2PY, efficiently sensitize photoreactions at ^BrU residues incorporated in G4 structures and give rise to two kinds of photoproducts, namely DNA strand cleavage and covalent ligand-DNA photoadducts. Remarkably, the photoinduced strand cleavage is observed exclusively with G4 structures presenting ^BrU residues in lateral or diagonal loops, but not with parallel G4-DNA structures presenting only propeller loops. In contrast, the formation of fluorescent photoadducts is observed with all ^BrU-substituted G4-DNA substrates, with M-2PY giving significantly higher yields (up to 27%) than M-1PY. Both ligand-sensitized photoreactions are specific to ^BrU-modified G4-DNA structures with respect to double-stranded or stem-loop substrates. Thus, ligand-sensitized photoreactions with ^BrU-substituted G4-DNA may be exploited (i) as a photochemical probe, allowing "photofootprinting" of G4 folding topologies in vitro and (ii) for covalent trapping of G4 structures as photoadducts with pyrene-substituted ligands.

Alkylating probes for the G-quadruplex structure and evaluation of the properties of the alkylated G-quadruplex DNA

The G-quadruplex structure has been found in biologically significant regions of the genomic DNA, including the telomere and promoter regions, and is known to play an important role in a number of biological processes. In this paper, we report the development of alkylating probes for the G-quadruplex structure and evaluation of the properties of the modified G-quadruplex structure.

How to obtain Pt(iv) complexes suitable for conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]. Dalton Trans 2018;46:10246-10254. [PMID: 28737785 DOI: 10.1039/c7dt01706e]

Oxidation of [Pt^(II)Cl(terpy)]⁺ (terpy = 2,2':6',2''-terpyridine) has been attempted with several oxidizing agents and under different experimental conditions in order to obtain a Pt(iv) complex suitable for the conjugation to nanovectors to be used in drug delivery targeting for anticancer therapy. The best compromise in terms of yield and purity of the final complex was obtained by microwave-assisted reaction at 70 °C in 50% aqueous H₂O₂ for 2 h. Under these conditions the quantitative formation of [Pt^(IV)Cl(OH)₂(terpy)]⁺ was observed. The subsequent synthetic steps were, (i) functionalization of [Pt^(IV)Cl(OH)₂(terpy)]⁺ in the axial position with succinic anhydride to obtain [Pt^(IV)Cl(OH)(succinato)(terpy)]⁺ and (ii) reaction of the latter with nonporous silica nanoparticles (SNPs) with an external shell containing primary amino groups to obtain a nanovector able to transport the Pt(iv) antitumor prodrug in the form of a conjugate Pt-SNP. Finally, the antiproliferative activity and cell accumulation of [Pt^(II)Cl(terpy)]⁺, [Pt^(IV)Cl(OH)₂(terpy)]⁺, and the Pt-SNP conjugate were measured on three cancer cell lines. Despite highly effective accumulation of Pt-SNP in cells, a modest increase in activity was observed with respect to the molecular species. Further experiments showed that the Pt-SNP conjugate can release [Pt^(II)Cl(terpy)]⁺ upon reduction, but this metabolite may undergo hydrolysis, and the resulting aquo complex could coordinate once again the free amino groups of the SNPs. In the resulting tetraamine form, the Pt(ii) complex conjugated to the SNPs cannot completely perform its antiproliferative activity.

Dual functional dinuclear platinum complex with selective reactivity towards c-myc G-quadruplex

G-quadruplexes (GQ) folded by the oncogenic G-rich sequences are the promising targets for developing anticancer therapeutic molecules. However, the current drug development mainly focused on non-covalent dynamic binders to stabilize GQ structures, while the covalent targeting from inorganic complexes via chelating principles, as a potent therapeutic strategy was surprisingly lack of exploration. Herein, a series of dinuclear platinum complexes, [(Pt(Dip)Cl)₂(μ-diamine)](NO₃)₂ (Dip: 4,7-diphenyl-1,10-phenanthroline), were designed to contain two dual-functional Pt cores connected by an alkyl linkage. Pt3 with nonanediamine linkage optimized the specific binding towards c-myc G-quadruplex via dual functional clamp on GQ as 1) non-covalently π-stacking of aromatic ligands, and 2) two Pt(II) cores covalently chelated to guanines at both 3'- and 5'-ends.

Spectroscopy, electrochemistry and antiproliferative properties of Au(iii), Pt(ii) and Cu(ii) complexes bearing modified 2,2′:6′,2′′-terpyridine ligands

Impact of the metal centre and the substituent incorporated into a terpy framework.