Targeting Oncogene Promoters and Ribosomal RNA Biogenesis by G-Quadruplex Binding Ligands Translate to Anticancer Activity

Abstract

G-Quadruplex (GQ) nucleic acids are promising therapeutic targets in anticancer research due to their structural robustness, polymorphism, and gene-regulatory functions. Here, we presented the structure−activity relationship of carbazole-based monocyanine ligands using region-specific functionalization with benzothiazole (TCA and TCZ), lepidine (LCA and LCZ), and quinaldine (QCA and QCZ) acceptor moieties and evaluated their binding profiles with different oncogenic GQs. Their differential turnon fluorescence emission upon GQ binding confirmed the GQ-toduplex selectivity of all carbazole ligands, while the isothermal titration calorimetry results showed selective interactions of TCZ and TCA to c-MYC and BCL-2 GQs, respectively. The aldehyde group in TCA favors stacking interactions with the tetrad of BCL-2 GQ, whereas TCZ provides selective groove interactions with c-MYC GQ. Dualluciferase assay and chromatin immunoprecipitation (ChIP) showed that these molecules interfere with the recruitment of specific transcription factors at c-MYC and BCL-2 promoters and stabilize the promoter GQ structures to inhibit their constitutive transcription in cancer cells. Their intrinsic turn-on fluorescence response with longer lifetimes upon GQ binding allowed real-time visualization of GQ structures at subcellular compartments. Confocal microscopy revealed the uptake of these ligands in the nucleoli, resulting in nucleolar stress. ChIP studies further confirmed the inhibition of Nucleolin occupancy at multiple GQ-enriched regions of ribosomal DNA (rDNA) promoters, which arrested rRNA biogenesis. Therefore, carbazole ligands act as the "double-edged swords" to arrest c-MYC and BCL-2 overexpression as well as rRNA biogenesis, triggering synergistic inhibition of multiple oncogenic pathways and apoptosis in cancer cells.

Synthesis and Characterizations of Bioactive Glass Nanoparticle-Incorporated Triblock Copolymeric Injectable Hydrogel for Bone Tissue Engineering

“…Here, it may be noted that cyclic polymers have drawn much attention due to their exceptional properties like small hydrodynamic volume and lower intrinsic viscosity. , From the scientific and industrial points of view, carbazole-based polymers have attracted more attention due to their hole transport, high charge-carrier mobility, and electroluminescent properties. , Among carbazole polymers, pNVC is much more familiar due to its easy synthesis procedure and solubility in most organic solvents. , They are used as biosensors, cellular markers, protective agents against radiation, and antimicrobial coatings. ,,− The non-toxic nature of pNVC was also tested against NIH 3T3 mammalian fibroblast cells. The results demonstrated that pNVC-based material was nontoxic to fibroblast cells, meaning that this material is appropriate for tissue engineering applications .…”

Development and Characterization of Benzoselenazole Derivatives as Potent and Selective c-MYC Transcription Inhibitors

“…31 A recent study also showed that several benzothiazole−carbazole hybrids had the potential to be selective c-MYC G-quadruplex ligands. 37 In view of these, we therefore employed carbazole to extend the aromatic system of benzoazoles. The other modification direction we took was to increase the binding of benzoazole to the groove and loop regions of the c-MYC G-quadruplex by introducing an appropriate side chain.…”

“…Benzoazoles are a class of benzene-fused heterocyclic compounds including benzothiazole, benzoxazole, benzoselenazole, and so forth. Among them, the benzothiazole scaffold has been widely used in the design of fluorescent probes and medicinal agents for G-quadruplexes. − However, compared to the extensive attention devoted to benzothiazole, there are relatively few studies on its analogues benzoxazole and benzoselenazole. Especially for benzoselenazole, there is considerable evidence that incorporating selenium into heterocycles may improve their pharmacological activities .…”

“…We have successfully used carbazole as a substituent to improve the selectivity of the aryl-substituted imidazoles for the c-MYC G-quadruplex . A recent study also showed that several benzothiazole–carbazole hybrids had the potential to be selective c-MYC G-quadruplex ligands . In view of these, we therefore employed carbazole to extend the aromatic system of benzoazoles.…”

Self-reporting styrylthiazolium photopharmaceuticals: mitochondrial localisation as well as SAR drive biological activity

“…26 Neither StyBtz nor StyTz have been tested as E ⇄ Z -photoisomerisable photopharmaceuticals, not even in cell-free assays. However, (1) StyBtz photochemistry has been studied: they E ⇄ Z -photoisomerise reversibly in organic and aqueous media, 27 and have fluorescence emission around 500 nm 28 (note the similarity of push–pull StyBtz to truncated Cy dyes); and (2) some E -StyBtz, though structurally distant, have been reported to have general antiproliferative activity against eukaryotic cells 29–32 (and further reports of E -StyBtz for cell-free or bacterial applications have also been made 33 ). Therefore, while applications to live-cell protein control in eukaryotes, based on in-cell photoswitchability, have remained untested until now, these were indications that suitable E ⇄ Z -photoisomerisable designs could be applicable.…”