NSC746364, a G-Quadruplex-Stabilizing Agent, Suppresses Cell Growth of A549 Human Lung Cancer Cells Through Activation of the ATR/Chk1-Dependent Pathway

New horizons in lung cancer management through ATR/CHK1 pathway modulation

Lung cancer is the leading cause of cancer-related deaths worldwide. Molecular profiling has contributed to a new classification of lung cancer, driving advancements in research and therapy. The ataxia telangiectasia and rad3/checkpoint kinase 1 (ATR/CHK1) pathway plays a crucial role in maintaining genomic stability, and its activation has been linked to the development of lung cancer, drug resistance and poor prognosis. Clinical and preclinical studies have demonstrated promising results in targeting this pathway. ATR and CHK1 are proteins that collaborate to repair DNA damage caused by radiation or chemotherapy. ATR/CHK1 inhibitors are currently under investigation in preclinical and clinical trials. This article explores the ATR/CHK1 pathway and its potential for treating lung cancer.

The Relevance of G-Quadruplexes for DNA Repair

DNA molecules can adopt a variety of alternative structures. Among these structures are G-quadruplex DNA structures (G4s), which support cellular function by affecting transcription, translation, and telomere maintenance. These structures can also induce genome instability by stalling replication, increasing DNA damage, and recombination events. G-quadruplex-driven genome instability is connected to tumorigenesis and other genetic disorders. In recent years, the connection between genome stability, DNA repair and G4 formation was further underlined by the identification of multiple DNA repair proteins and ligands which bind and stabilize said G4 structures to block specific DNA repair pathways. The relevance of G4s for different DNA repair pathways is complex and depends on the repair pathway itself. G4 structures can induce DNA damage and block efficient DNA repair, but they can also support the activity and function of certain repair pathways. In this review, we highlight the roles and consequences of G4 DNA structures for DNA repair initiation, processing, and the efficiency of various DNA repair pathways.

Combined treatment with emodin and a telomerase inhibitor induces significant telomere damage/dysfunction and cell death

G-quadruplex telomeric secondary structures represent natural replication fork barriers and must be resolved to permit efficient replication. Stabilization of telomeric G4 leads to telomere dysfunctions demonstrated by telomere shortening or damage, resulting in genome instability and apoptosis. Chemical compounds targeting G4 structures have been reported to induce telomere disturbance and tumor suppression. Here, virtual screening was performed in a natural compound library using PyRx to identify novel G4 ligands. Emodin was identified as one of the best candidates, showing a great G4-binding potential. Subsequently, we confirmed that emodin could stabilize G4 structures in vitro and trigger telomere dysfunctions including fragile telomeres, telomere loss, and telomeric DNA damage. However, this telomere disturbance could be rescued by subsequent elevation of telomerase activity; in contrast, when we treated the cells with the telomerase inhibitor BIBR1532 upon emodin treatment, permanent telomere disturbance and obvious growth inhibition of 4T1-cell xenograft tumors were observed in mice. Taken together, our results show for the first time that emodin-induced telomeric DNA damage can upregulate telomerase activity, which may weaken its anticancer effect. The combined use of emodin and the telomerase inhibitor synergistically induced telomere dysfunction and inhibited tumor generation.

G-quadruplex ligand-induced DNA damage response coupled with telomere dysfunction and replication stress in glioma stem cells

Glioblastoma (GBM) is an invariably fatal brain tumor in which a small subpopulation of self-renewable glioma stem cells (GSCs) contributes to tumor propagation and relapse. Targeting GSCs could therefore have a significant clinical impact for GBM. Telomestatin is a naturally-occurring compound that preferentially impairs GSC growth by perturbing transcription and inducing a DNA damage response. Telomestatin stabilizes G-quadruplexes (G4s), which are guanine-rich four-strand nucleic acid structures observed in vitro and in vivo. However, the mechanism underlying the GSC-selective nature of the DNA damage response remains unknown. Here we demonstrate that GSCs are more susceptible to telomestatin-induced telomere dysfunction and replication stress when compared with GSC-derived non-stem glioma cells (NSGCs). Telomestatin induced dissociation of the telomere-capping protein TRF2 from telomeres, leading to telomeric DNA damage in GSCs-but not in NSGCs. BIBR1532, a telomerase catalytic inhibitor, did not preferentially inhibit GSC growth, suggesting that telomestatin promotes telomere dysfunction in a telomerase-independent manner. GSCs and NSGCs had comparable levels of G4s in their nuclei, and both responded to telomestatin with phosphorylation of RPA2 at Ser33-a hallmark of replication stress. However, activation of the checkpoint kinase Chk1, induction of a DNA damage response, and subsequent growth inhibition occurred only in telomestatin-treated GSCs. These observations suggest that telomestatin impairs GSC growth through removal of TRF2 from telomeres and potent activation of the replication stress response pathway. Therefore, a novel G4-directed therapeutic strategy could specifically target cancer stem cells in GBM.

Designing a New Class of Bases for Nucleic Acid Quadruplexes and Quadruplex-Active Ligands

A new class of quadruplex nucleobases, derived from 3-deazaguanine, has been designed for various applications as smart quadruplex ligands as well as quadruplex-based aptamers, receptors, and sensors. An efficient strategy for modifying the guanine quadruplex core has been developed and tested by using quantum chemistry methods. Several potential guanine derivatives modified at the 3- or 8-position or both are analyzed, and the results compared to reference systems containing natural guanine. Analysis of the formation energies (BLYP-D3(BJ)/def2-TZVPP level of theory, in combination with the COSMO model for water) in model systems consisting of two and three stacked tetrads with Na(+) /K(+) ion(s) inside the internal channel indicates that the formation of structures with 3-halo-3-deazaguanine bases leads to a substantial gain in energy, as compared to the corresponding reference guanine complexes. The results cast light on changes in the noncovalent interactions (hydrogen bonding, stacking, and ion coordination) in a quadruplex stem upon modification of the guanine core. In particular, the enhanced stability of the modified quadruplexes was shown to originate mainly from increased π-π stacking. Our study suggests the 3-halo-3-deazaguanine skeleton as a potential building unit for quadruplex systems and smart G-quadruplex ligands.