G-quadruplex ligands as potent regulators of lysosomes

Promising G-Quadruplex-Targeted Dibenzoquinoxaline Type-1 Photosensitizer Triggers DNA Damage in Triple-Negative Breast Cancer Cells

G-quadruplexes (G4s) are potential drug targets in cancer treatment. However, the G4-targeted ligands seem to lack sufficient selectivity between tumors and normal tissues, appealing for a new modified anticancer strategy on the basis of them. Type-1 photodynamic therapy (PDT) is a promising strategy possessing excellent spatiotemporal precision for solid tumors with a hypoxic microenvironment. However, type-1 photosensitizers that target G4s and induce in situ photodamage have never been previously reported. In this study, we reported a promising type-1 photosensitizer based on a G4-targeted, high-contrast fluorescent ligand (TR2). The subsequent studies demonstrated that TR2 could transfer from lysosomes to nuclei and induce elevated G4 formation as well as DNA damage upon irradiation. Notably, it was observed that TR2 may not activate DNA damage repair machinery upon irradiation, suggesting a durable, strong effect on inducing DNA damage. Consequently, light-irradiated TR2 exhibited excellent photocytotoxicity on triple-negative breast cancer cell proliferation (at nanomolar concentration) and showed obvious inhibition on the growth of three-dimensional (3D) tumor spheroids. Finally, RNA-seq analysis demonstrated that TR2-mediated PDT may have a negative impact on enhancing the DNA damage repair machinery and may activate the antitumor immunity pathways. Overall, this study provided a promising chemical tool for image-guided PDT.

G-quadruplexes in MTOR and induction of autophagy

G-quadruplex (G4) structures have emerged as singular therapeutic targets for cancer and neurodegeneration. Autophagy, a crucial homeostatic mechanism of the cell, is often dysregulated in neurodegenerative diseases and cancers. We used QGRS mapper to identify 470 G4 sequences in MTOR, a key negative regulator of autophagy. We sought to identify a functional context by leveraging the effect of G4-targeting ligands on MTOR G4 sequences. The effect of Bis-4,3, a G4 selective dimeric carbocyanine dye, was compared with the known G4-stabilizing activity of the porphyrin, TMPyP4 in HeLa and SHSY-5Y cells. Our results show that treatment with G4-selective ligands downregulates MTOR RNA and mTOR protein expression levels. This is the first report describing G4 motifs in MTOR. This study indicates a possible role of G4 stabilizing ligands in induction of autophagy by downregulation of mTOR levels, albeit not precluding MTOR independent pathways.

Harnessing G-quadruplex ligands for lung cancer treatment: A comprehensive overview

Lung cancer (LC) remains a leading cause of mortality worldwide, and new therapeutic strategies are urgently needed. One such approach revolves around the utilization of four-stranded nucleic acid secondary structures, known as G-quadruplexes (G4), which are formed by G-rich sequences. Ligands that bind selectively to G4 structures present a promising strategy for regulating crucial cellular processes involved in the progression of LC, rendering them potent agents for lung cancer treatment. In this review, we offer a summary of recent advancements in the development of G4 ligands capable of targeting specific genes associated with the development and progression of lung cancer.

G-quadruplexes and associated proteins in aging and Alzheimer's disease

Aging is a prominent risk factor for many neurodegenerative disorders, such as Alzheimer's disease (AD). Alzheimer's disease is characterized by progressive cognitive decline, memory loss, and neuropsychiatric and behavioral symptoms, accounting for most of the reported dementia cases. This disease is now becoming a major challenge and burden on modern society, especially with the aging population. Over the last few decades, a significant understanding of the pathophysiology of AD has been gained by studying amyloid deposition, hyperphosphorylated tau, synaptic dysfunction, oxidative stress, calcium dysregulation, and neuroinflammation. This review focuses on the role of non-canonical secondary structures of DNA/RNA G-quadruplexes (G4s, G4-DNA, and G4-RNA), G4-binding proteins (G4BPs), and helicases, and their roles in aging and AD. Being critically important for cellular function, G4s are involved in the regulation of DNA and RNA processes, such as replication, transcription, translation, RNA localization, and degradation. Recent studies have also highlighted G4-DNA's roles in inducing DNA double-strand breaks that cause genomic instability and G4-RNA's participation in regulating stress granule formation. This review emphasizes the significance of G4s in aging processes and how their homeostatic imbalance may contribute to the pathophysiology of AD.