Quadruplex Nucleic Acids as Novel Therapeutic Targets

Quadruplex-forming sequences are widely prevalent in human and other genomes, including bacterial ones. These sequences are over-represented in eukaryotic telomeres, promoters and 5' untranslated regions. They can form quadruplex structures, which may be transient in many situations in normal cells since they can be effectively resolved by helicase action. Mutated helicases in cancer cells are unable to unwind quadruplexes, which are impediments to transcription, translation or replication, depending on their location within a particular gene. Small molecules that can stabilise quadruplex structures augment these effects and produce cell and proliferation growth inhibition. This article surveys the chemical biology of quadruplexes and critically examines the major classes of quadruplex-binding small molecules that have been developed to date, and the various approaches to discovering selective agents. The challenges of requiring (and achieving) small-molecule targeted selectivity for a particular quadruplex are discussed in relation to the potential of these small molecules as potentially clinically-useful therapeutic agents

Antiproliferative properties and g-quadruplex-binding of symmetrical naphtho[1,2-b:8,7-b’]dithiophene derivatives

Background: G-quadruplex (G4) forming sequences are recurrent in telomeres and promoter regions of several protooncogenes. In normal cells, the transient arrangements of DNA in G-tetrads may regulate replication, transcription, and translation processes. Tumors are characterized by uncontrolled cell growth and tissue invasiveness and some of them are possibly mediated by gene expression involving G-quadruplexes. The stabilization of G-quadruplex sequences with small molecules is considered a promising strategy in anticancer targeted therapy. Methods: Molecular virtual screening allowed us identifying novel symmetric bifunctionalized naphtho[1,2-b:8,7-b’]dithiophene ligands as interesting candidates targeting h-Telo and c-MYC G-quadruplexes. A set of unexplored naphtho-dithiophene derivatives has been synthesized and biologically tested through in vitro antiproliferative assays and spectroscopic experiments in solution. Results: The analysis of biological and spectroscopic data highlighted noteworthy cytotoxic effects on HeLa cancer cell line (GI(50) in the low μM range), but weak interactions with G-quadruplex c-MYC promoter. Conclusions: The new series of naphtho[1,2-b:8,7-b’]dithiophene derivatives, bearing the pharmacophoric assumptions necessary to stabilize G-quadruplexes, have been designed and successfully synthesized. The interesting antiproliferative results supported by computer aided rational approaches suggest that these studies are a significant starting point for a lead optimization process and the isolation of a more efficacious set of G-quadruplexes stabilizers

Anticancer Activity, Reduction Mechanism and G-Quadruplex DNA Binding of a Redox-Activated Platinum(IV)–Salphen Complex

Aiming at reducing the unselective cytotoxicity of Pt(II) chemotherapeutics, a great deal of effort has been concentrated into the design of metal‐containing drugs with different anticancer mechanisms of action. Inert Pt(IV) prodrugs have been proposed to be a valid alternative as they are activated by reduction directly into the cell releasing active Pt(II) species. On the other hand, a promising strategy for designing metallodrugs is to explore new potential biological targets rather than canonical B‐DNA. G‐quadruplex nucleic acid, obtained by self‐assembly of guanine‐rich nucleic acid sequences, has recently been considered an attractive target for anticancer drug design. Therefore, compounds capable of binding and stabilizing this type of DNA structure would be greatly beneficial in anticancer therapy. Here, computational analysis reports the mechanism of action of a recently synthesized Pt(IV)–salphen complex conjugating the inertness of Pt(IV) prodrugs with the ability to bind G‐quadruplexes of the corresponding Pt(II) complex. The reduction mechanism of the Pt(IV) complex with a biological reducing agent was investigated in depth by means of DFT, whereas classical MD simulations were carried out to shed light into the binding mechanism of the released Pt(II) complex. The results show that the Pt(IV) prodrug may be reduced by both inner‐ and outer‐sphere mechanisms, and the active Pt(II) complex, as a function of its protonation state, stabilizes the G‐quadruplex DNA prevalently, either establishing π‐stacking nteractions with the terminal G‐tetrad or through electrostatic interactions along with H‐bonds formation

Identifying and validating the presence of guanine-quadruplexes (G4) within the blood fluke parasite schistosoma mansoni

Schistosomiasis is a neglected tropical disease that currently affects over 250 million individ-uals worldwide. In the absence of an immunoprophylactic vaccine and the recognition that mono-chemotherapeutic control of schistosomiasis by praziquantel has limitations, new strategies for managing disease burden are urgently needed. A better understanding of schistosome biology could identify previously undocumented areas suitable for the development of novel interventions. Here, for the first time, we detail the presence of G-quadru-plexes (G4) and putative quadruplex forming sequences (PQS) within the Schistosoma mansoni genome. We find that G4 are present in both intragenic and intergenic regions of the seven autosomes as well as the sex-defining allosome pair. Amongst intragenic regions, G4 are particularly enriched in 3´ UTR regions. Gene Ontology (GO) term analysis evi-denced significant G4 enrichment in the wnt signalling pathway (p<0.05) and PQS oligonu-cleotides synthetically derived from wnt-related genes resolve into parallel and anti-parallel G4 motifs as elucidated by circular dichroism (CD) spectroscopy. Finally, utilising a single chain anti-G4 antibody called BG4, we confirm the in situ presence of G4 within both adult female and male worm nuclei. These results collectively suggest that G4-targeted compounds could be tested as novel anthelmintic agents and highlights the possibility that G4-stabilizing molecules could be progressed as candidates for the treatment of schistosomiasis

Identifying and validating the presence of Guanine-Quadruplexes (G4) within the blood fluke parasite Schistosoma mansoni

Schistosomiasis is a neglected tropical disease that currently affects over 250 million individuals worldwide. In the absence of an immunoprophylactic vaccine and the recognition that mono-chemotherapeutic control of schistosomiasis by praziquantel has limitations, new strategies for managing disease burden are urgently needed. A better understanding of schistosome biology could identify previously undocumented areas suitable for the development of novel interventions. Here, for the first time, we detail the presence of G-quadruplexes (G4) and putative quadruplex forming sequences (PQS) within the Schistosoma mansoni genome. We find that G4 are present in both intragenic and intergenic regions of the seven autosomes as well as the sex-defining allosome pair. Amongst intragenic regions, G4 are particularly enriched in 3´ UTR regions. Gene Ontology (GO) term analysis evidenced significant G4 enrichment in the wnt signalling pathway (p<0.05) and PQS oligonucleotides synthetically derived from wnt-related genes resolve into parallel and anti-parallel G4 motifs as elucidated by circular dichroism (CD) spectroscopy. Finally, utilising a single chain anti-G4 antibody called BG4, we confirm the in situ presence of G4 within both adult female and male worm nuclei. These results collectively suggest that G4-targeted compounds could be tested as novel anthelmintic agents and highlights the possibility that G4-stabilizing molecules could be progressed as candidates for the treatment of schistosomiasi

DNA and the chromosome – varied targets for chemotherapy

The nucleus of the cell serves to maintain, regulate, and replicate the critical genetic information encoded by the genome. Genomic DNA is highly associated with proteins that enable simple nuclear structures such as nucleosomes to form higher-order organisation such as chromatin fibres. The temporal association of regulatory proteins with DNA creates a dynamic environment capable of quickly responding to cellular requirements and distress. The response is often mediated through alterations in the chromatin structure, resulting in changed accessibility of specific DNA sequences that are then recognized by specific proteins. Anti-cancer drugs that target cellular DNA have been used clinically for over four decades, but it is only recently that nuclease specific drugs have been developed to not only target the DNA but also other components of the nuclear structure and its regulation. In this review, we discuss some of the new drugs aimed at primary DNA sequences, DNA secondary structures, and associated proteins, keeping in mind that these agents are not only important from a clinical perspective but also as tools for understanding the nuclear environment in normal and cancer cells