Targeting BRCA1 and BRCA2 Deficiencies with G-Quadruplex-Interacting Compounds

“Alkaline Single-Cell Gel Electrophoresis Comet Assay Thecometassaywasperformedaspreviouslydescribed (Singh et al., 1988).”

“Genomic instability is a hallmark of cancer caused by failure of normal DNA replication and/or repair mechanisms (Halazonetis Mo et al., 2008; Negrini et al., 2010).”

“G4 structures have been subsequently detected with several other structure-specific antibodies (Biffi et al., 2013; Henderson et al., 2014; Schaffitzel et al., 2001) and interacting small molecules (Lam et al., 2013; Müller et al., 2010; Rodriguez et al., 2012).”

“RPA accumulation on the chromatin, together with elevated frequency of origin firing and reduced replication rates, represents signatures of replicative stress (Zeman and Cimprich, 2014).”

“Importantly, telomeric G-rich DNA sequences have a high propensity to adopt G4 configurations (Parkinson et al., 2002).”

“A conundrum posed by this quantificationwas that PDS induced approximately fifteen DSBs per metaphase in cells lacking RAD51, yet in silico predictions suggested thatmore than 300,000 genomic sites can adopt G4 configurations (Huppert and Balasubramanian, 2005).”

“…Zimmer, Eliana M.C. Tacconi, Cecilia Folio, ..., Annamaria Biroccio, Julian E. Sale, Madalena Tarsounas Correspondence madalena.tarsounas@oncology.ox.ac.uk In Brief Zimmer et al. discovered that homologous recombination activities of BRCA1 and BRCA2…”

“The ability of G-rich DNA to adopt G4 secondary structures in vitro was reported over 50 years ago (Gellert et al., 1962).”

“HR factors act to stabilize stalled replication forks by preventing their nucleolytic degradation (Hashimoto et al., 2010; Schlacher et al., 2011) to restart arrested forks (Lambert et al., 2010) and to repair double-strand breaks (DSBs) arising from disintegrated forks (Aze et al., 2013).”

“For example, small molecule G4-ligands that bind and stabilize G4 structures can induce genomic instability at sequences with high potential for G4 formation, such as the human minisatellite CEB1 (9) and telomeric DNA (10, 11).”

“Their prevalence in highly transcribed and replication-stressed genomic regions has positioned G4s as compelling therapeutic targets, particularly in cancers with defective DNA damage response (DDR) pathways [ 2–6 ].”

“Cells with defects in pathways important for replication stress, DNA repair, and G4 resolution show increased PDS sensitivity [17, 18].”

“Both agents disrupt rRNA synthesis and induce nucleolar stress across a range of can - cer types (Drygin et al. 2011; Zimmer et al. 2016; Xu et al. 2017; Ferreira et al. 2020).”

“…considered as therapeutic agents to target telomeres in BRCA1 and BRCA2-mutant cancer cells that are defective in homology-directed repair (HDR) (Zimmer et al , 2016; Groelly et al , 2022; Keahi et al , 2025) and clinical trials with G-stabilizers for HDR-deficient tumors have been launched…”

“The connection of G4s and BRCA2 may also be important in other settings of BRCA1/2 deficiency, as the stabilization by PDS leads to cell death in BRCA1/2 deficient cells (Zimmer et al. 2016) and in patient derived xenografts (Groelly et al. 2022).”

“For example, BRCA2 prevents R-loop accumulation [33, 34] and maintains the integrity of telomeres [35] and G-quadruplex-forming sites [36].”

“…analyzed RPA32 Ser33 phosphorylation (pS33) by immunofluorescence analysis, a marker of ssDNA accumulation at replication-associated lesions [ 74 , 75 ], in HU-treated PEO1 cells with or without stable STN1 overexpression, as well as in HeLa cells following BRCA2 depletion, with and without…”

“Consistent with this idea, multiple studies report that PhenDC3 and CX-5461 exhibit selective toxicity in tumors lacking homologous recombination and non-homologous end-joining pathways (Zimmer et al. 2016; Xu et al. 2017; Bruno et al. 2020; Hilton et al. 2022; Jin et al. 2023).”

“These observations are reminiscent of the fi ndings that G4 ligands are toxic to BRCA2-de fi cient cells throughinducingreplication-associatedDNAdamage 18,19 .”

“SsDNA gaps can arise from stalling of DNA polymerases or uncoupling of leading and lagging strand synthesis during persistent replication stress, Okazaki fragment maturation defects, PrimPol-mediated repriming downstream of DNA lesions, impaired chromatin assembly during replication stress, and…”

“Pemeriksaan fisik dilakukan secara sistematis dengan penilaian stadium perkembangan pubertas (Tanner staging) (Taylor et al., 2019).”

“These compounds stabilize G4 structures and may exert anti-cancer effect either by inducing DNA damage selectively in cancer cells or by modulating the expression of oncogenes [11–14].”

“HSV1-TK is a promiscuous kinase that can phosphorylate a broad array of nucleosides including cytidine [38,40].”

“While some ligands have shown binding affinity towards G quadruplex structures for treatment of cancer specific cells and transcriptional alteration (14), binding of other ligands that stabilize G4 lead to multiple DNA damage (14), micronuclei formation, delayed replication fork progression (15), and telomeric defects…”

“Naphtalene diimmides G-quadruplex DDR activation Ionizing radiations Glioma Pancreatic cancer [109][110] [111][112] [113] Pyridostatin G-quadruplex i-motifs DDR activation BRCA1/2 mut Colon cancer Renal cancer [114][53]”

“Importantly, G4-stabilizers are particularly toxic to BRCA-defective cells acquiring PARP inhibitor resistance [5], indicating pharmacological application exploiting G4 stabilization as a new therapeutic”

“Then, we asked whether G4 ligand-induced DNA cleavage was repaired by homologous recombination mechanisms, under our experimental conditions, as reported by other previously (Zimmer et al., 2016).”