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G-quadruplexes (G4s) are guanine-rich non-canonical secondary structures of nucleic acids that were identified in vitro almost half a century ago. Starting from the early 1980s, these structures were also observed in eukaryotic cells, first at the telomeric level and later in regulatory regions of cancer-related genes, in regulatory RNAs and within specific cell compartments such as lysosomes, mitochondria, and ribosomes. Because of the involvement of these structures in a large number of biological processes and in the pathogenesis of several diseases, including cancer, the interest in G4 targeting has exponentially increased in the last few years, and a great number of novel G4 ligands have been developed. Notably, G4 ligands represent a large family of heterogeneous molecules that can exert their functions by recognizing, binding, and stabilizing G4 structures in multiple ways. Regarding anti-cancer activity, the efficacy of G4 ligands was originally attributed to the capability of these molecules to inhibit the activity of telomerase, an enzyme that elongates telomeres and promotes endless replication in cancer cells. Thereafter, novel mechanisms through which G4 ligands exert their antitumoral activities have been defined, including the induction of DNA damage, control of gene expression, and regulation of metabolic pathways, among others. Here, we provided a perspective on the structure and function of G4 ligands with particular emphasis on their potential role as antitumoral agents. In particular, we critically examined the problems associated with the clinical translation of these molecules, trying to highlight the main aspects that should be taken into account during the phases of drug design and development. Indeed, taking advantage of the successes and failures, and the more recent technological progresses in the field, it would be possible to hypothesize the development of these molecules in the future that would represent a valid option for those cancers still missing effective therapies. [ABSTRACT FROM AUTHOR]

TERF2/TRF2 is a pleiotropic telomeric protein that plays a crucial role in tumor formation and progression through several telomere-dependent and -independent mechanisms. Here, we uncovered a novel function for this protein in regulating the macroautophagic/autophagic process upon different stimuli. By using both biochemical and cell biology approaches, we found that TERF2 binds to the non-histone chromatin-associated protein HMGB1, and this interaction is functional to the nuclear/cytoplasmic protein localization. Specifically, silencing of TERF2 alters the redox status of the cells, further exacerbated upon EBSS nutrient starvation, promoting the cytosolic translocation and the autophagic activity of HMGB1. Conversely, overexpression of wild-type TERF2, but not the mutant unable to bind HMGB1, negatively affects the cytosolic translocation of HMGB1, counteracting the stimulatory effect of EBSS starvation. Moreover, genetic depletion of HMGB1 or treatment with inflachromene, a specific inhibitor of its cytosolic translocation, completely abolished the pro-autophagic activity of TERF2 silencing. In conclusion, our data highlighted a novel mechanism through which TERF2 modulates the autophagic process, thus demonstrating the key role of the telomeric protein in regulating a process that is fundamental, under both physiological and pathological conditions, in defining the fate of the cells. Abbreviations: ALs: autolysosomes; ALT: alternative lengthening of telomeres; ATG: autophagy related; ATM: ATM serine/threonine kinase; CQ: Chloroquine; DCFDA: 2',7'-dichlorofluorescein diacetate; DDR: DNA damage response; DHE: dihydroethidium; EBSS: Earle's balanced salt solution; FACS: fluorescence-activated cell sorting; GFP: green fluorescent protein; EGFP: enhanced green fluorescent protein; GSH: reduced glutathione; GSSG: oxidized glutathione; HMGB1: high mobility group box 1; ICM: inflachromene; IF: immunofluorescence; IP: immunoprecipitation; NAC: N-acetyl-L-cysteine; NHEJ: non-homologous end joining; PLA: proximity ligation assay; RFP: red fluorescent protein; ROS: reactive oxygen species; TIF: telomere-induced foci; TERF2/TRF2: telomeric repeat binding factor 2. [ABSTRACT FROM AUTHOR]

The telomeric repeat‐binding factor 2 (TRF2) is a telomere‐capping protein that plays a key role in the maintenance of telomere structure and function. It is highly expressed in different cancer types, and it contributes to cancer progression. To date, anti‐cancer strategies to target TRF2 remain a challenge. Here, we developed a miRNA‐based approach to reduce TRF2 expression. By performing a high‐throughput luciferase screening of 54 candidate miRNAs, we identified miR‐182‐3p as a specific and efficient post‐transcriptional regulator of TRF2. Ectopic expression of miR‐182‐3p drastically reduced TRF2 protein levels in a panel of telomerase‐ or alternative lengthening of telomeres (ALT)‐positive cancer cell lines. Moreover, miR‐182‐3p induced DNA damage at telomeric and pericentromeric sites, eventually leading to strong apoptosis activation. We also observed that treatment with lipid nanoparticles (LNPs) containing miR‐182‐3p impaired tumor growth in triple‐negative breast cancer (TNBC) models, including patient‐derived tumor xenografts (PDTXs), without affecting mouse survival or tissue function. Finally, LNPs‐miR‐182‐3p were able to cross the blood–brain barrier and reduce intracranial tumors representing a possible therapeutic option for metastatic brain lesions. Synopsis: A miRNA‐based strategy to inhibit the telomeric protein TRF2 was developed, which led to efficient decrease of triple negative breast cancer growth. miR‐182‐3p was identified as an efficient regulator of TRF2 expression in human cancer through high‐throughput miRNA luciferase screening.TRF2 inhibition by miR‐182‐3p induced DNA damage at telomeric and pericentromeric sites and consequent genomic instability.miR‐182‐3p limited the growth of Triple Negative Breast Cancer (TNBC) models by activating apoptosis.Lipid nanoparticles (LNPs) containing miR‐182‐3p reduced tumor volume in vivo in various TNBC models, including Olaparib‐resistant patient‐derived tumor xenografts.LNPs‐miR‐182‐3p crossed the blood brain barrier, showing therapeutic potential against brain metastasis. [ABSTRACT FROM AUTHOR]

The activation of endothelin-A receptor ([ET.sub.A]R) by endothelin-1 (ET-1) has a critical role in ovarian tumorigenesis and progression. To define the molecular mechanism in ET-1-induced tumor invasion and metastasis, we focused on [beta]-arrestins as scaffold and signaling proteins of G protein-coupled receptors. Here, we demonstrate that, in ovarian cancer cells, [beta]-arrestin is recruited to [ET.sub.A]R to form two trimeric complexes: one through the interaction with Src leading to epithelial growth factor receptor (EGFR) transactivation and [beta]-catenin Tyr phosphorylation, and the second through the physical association with axin, contributing to release and inactivation of glycogen synthase kinase (GSK)-3[beta] and [beta]-catenin stabilization. The engagement of [beta]-arrestin in these two signaling complexes concurs to activate [beta]-catenin signaling pathways, We then demonstrate that silencing of both [beta]-arrestin-1 and [beta]-arrestin-2 inhibits ETAR-driven signaling, causing suppression of Src, mitogen-activated protein kinase (MAPK), AKT activation, as well as EGFR transactivation and a complete inhibition of ET-1-induced [beta]-catenin/TCF transcriptional activity and cell invasion. [ET.sub.A]R blockade with the specific [ET.sub.A]R antagonist ZD4054 abrogates the engagement of [beta]-arrestin in the interplay between [ET.sub.A]R and the [beta]-catenin pathway in the invasive program. Finally, [ET.sub.A]R is expressed in 85% of human ovarian cancers and is preferentially co-expressed with [beta]-arrestin-1 in the advanced tumors. In a xenograft model of ovarian metastasis, HEY cancer cells expressing [beta]-arrestin-1 mutant metastasize at a reduced rate, highlighting the importance of this molecule in promoting metastases. ZD4054 treatment significantly inhibits metastases, suggesting that specific [ET.sub.A]R antagonists, by disabling multiple signaling activated by [ET.sub.A]R/[beta]-arrestin, may represent new therapeutic opportunities for ovarian cancer. beta-arrestin | beta-catenin | endothelin A receptor | metastasis | ovarian cancer

Functional telomeres are required for the replicability of cancer cells. The G-rich strand of telomeric DNA can fold into a 4-stranded structure known as the G-quadruplex (G4), whose stabilization alters [...]