Discovery of a triphenylamine-based ligand that targets mitochondrial DNA G-quadruplexes and activates the cGAS-STING immunomodulatory pathway

G-quadruplex in cancer energy metabolism: A potential therapeutic target

In recent years, energy metabolism in cancer has received increasing attention as an important component of tumor biology, and the functions of transcription factors, mitochondria, reactive oxygen species (ROS) and the autophagy-lysosome system in which have been elucidated. G-quadruplex (G4) is a molecular switch that regulates gene transcription or translation. As an anticancer target, the effect of G4 on cancer cell proliferation, apoptosis, cycle and autophagy has been recognized. The energy metabolism system is a unified whole composed of transcription factors, metabolic regulators, metabolites and signaling pathways that run through the entire cancer process. However, the role of G4 in this complex metabolic network has not been systematically elucidated. In this review, we analyze the close correlation between G4 and transcription factors, mitochondria, ROS and the autophagy-lysosome system and suggest that G4 can exert a marked effect on cancer energy metabolism by regulating the above mentioned key regulatory elements. The anticancer effects of some G4 ligands through regulation of energy metabolism have also been summarized, confirming the clear involvement of G4 in energy metabolism. Although much more research is needed, we propose that G4 may play a critical role in the complex energy metabolism system of cancer, which is a promising target for anticancer strategies focusing on energy metabolism.

A mitochondria-targeting and G-quadruplex structure-binding ligand inducing calcium overload and ferroptosis in human cancer cells

BACKGROUND AND PURPOSE

Regulation of mitochondrial calcium overload and ferroptosis with mitochondria-targeting ligands is an attractive anticancer strategy but it remains a challenge. The aim of the present study was to demonstrate that a mitochondria-targeting and mtDNA G-quadruplex-binding ligand, BYB, induced mitochondrial calcium overload and ferroptosis in HeLa cells and showed potent in vitro and in vivo anticancer activity.

EXPERIMENTAL APPROACH

Cellular functions and molecular mechanism were studied using cell viability assay, live-cell imaging, western blotting, immunofluorescence, cell uptake, cell cycle arrest and apoptosis analysis, mitochondrial metabolism analysis, Comet assay, and wound-healing analysis. Pharmacokinetic studies were conducted in rat. In vivo antitumor activity was studied in a cervical cancer HeLa cell xenograft mouse model.

KEY RESULTS

Cellular results showed that BYB induced mitochondrial calcium overload, attributed to ligand-induced mitochondrial dysfunction via the mechanism of inhibiting mitochondrial DNA replication and transcription. The expression of respiratory chain complexes was markedly downregulated in BYB-treated HeLa cells. The respiratory chain function was also dysregulated. Mitophagy and mitochondrial calcium overload were induced in BYB-treated HeLa cells. Mitochondrial calcium overload markedly induced mtROS production. The induced mtDNA stress activated cGAS-STING pathway, leading to autophagy-dependent ferroptosis. The antitumour efficacy of BYB, evaluated in a HeLa tumour xenograft mouse model, achieved over 60% tumour weight reduction.

CONCLUSION AND IMPLICATIONS

BYB, via targeting mitochondria and mtDNA G-quadruplexes, induced mitochondrial calcium overload and ferroptosis, exhibited high in vivo antitumour efficacy and low toxicity. It shows high potential to be a mitochondria-targeting lead compound for chemical biology and drug discovery.

Mitochondrial DNA-targeted triphenylamine-thiophene (TPATP)-derived ligands boost type-I/II photodynamic therapy for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is aggressive with poor prognosis. Current strategies include chemotherapy, surgery, and radiotherapy, but face challenges like suboptimal outcomes, low survival, and drug resistance. Thus, novel TNBC therapies are crucial. Activity-based photodynamic therapy (PDT) is a highly regarded cancer treatment strategy known for its spatiotemporal precision, making it a promising option for the treatment of TNBC. In this study, we designed and synthesized three triphenylamine-thiophene (TPATP)-derived ligands binding to mitochondrial DNA G4 (mtG4), which were able to label mitochondria in TNBC cells under red-light excitation, and demonstrated significant phototoxicity through type-I/II process under white-light irradiation, hinting at dual-functional potential for PDT and imaging. The optimal ligand, TP2, was demonstrated to disrupt mitochondrial functions under white-light irradiation, leading to MMP loss, ATP reduction, ROS increase, which further triggered significant apoptosis in TNBC cells.

G-Quadruplexes in Tumor Immune Regulation: Molecular Mechanisms and Therapeutic Prospects in Gastrointestinal Cancers

G-quadruplex (G4) is a noncanonical nucleic acid secondary structure self-assembled by guanine-rich sequences. Recent studies have not only revealed the key role of G4 in gene regulation, DNA replication, and telomere maintenance but also showed that it plays a core role in regulating the tumor immune microenvironment. G4 participates in tumor immune escape and the inhibition of immune response by regulating immune checkpoint molecules, cytokine expression, immune cell function, and their interaction network, thus significantly affecting the effect of tumor immunotherapy. This article systematically reviews the molecular mechanism of G4 in tumor immune regulation, especially gastrointestinal tumors, and explores the potential and application prospects of G4-targeted drug strategies in improving anti-tumor immunotherapy.

The G-quadruplex ligand CX-5461: an innovative candidate for disease treatment

The ribosomal DNA (rDNA) plays a vital role in regulating protein synthesis by ribosome biogenesis, essential for maintaining cellular growth, metabolism, and more. Cancer cells show a high dependence on ribosome biogenesis and exhibit elevated rDNA transcriptional activity. CX-5461, also known as Pidnarulex, is a First-in-Class anticancer drug that has received 'Fast Track Designation' approval from the FDA. Initially reported to inhibit Pol I-driven rDNA transcription, CX-5461 was recently identified as a G-quadruplex structure (G4) stabilizer and is currently completed or undergoing multiple Phase I clinical trials in patients with breast and ovarian cancers harboring BRCA1/2, PALB2, or other DNA repair deficiencies. Additionally, preclinical studies have confirmed that CX-5461 demonstrates promising therapeutic effects against multifarious non-cancer diseases, including viral infections, and autoimmune diseases. This review summarizes the mechanisms of CX-5461, including its transcriptional inhibition of rDNA, binding to G4, and toxicity towards topoisomerase, along with its research status and therapeutic effects across various diseases. Lastly, this review highlights the targeted therapy strategy of CX-5461 based on nanomedicine delivery, particularly the drug delivery utilizing the nucleic acid aptamer AS1411, which contains a G4 motif to specifically target the highly expressed nucleolin on the surface of tumor cell membranes; It also anticipates the strategy of coupling CX-5461 with peptide nucleic acids and locked nucleic acids to achieve dual targeting, thereby realizing individualized G4-targeting by CX-5461. This review aims to provide a general overview of the progress of CX-5461 in recent years and suggest potential strategies for disease treatment involving ribosomal RNA synthesis, G4, and topoisomerase.

Recent Progress and Potential of G4 Ligands in Cancer Immunotherapy

G-quadruplex (G4) structures are non-canonical nucleic acid conformations that play crucial roles in gene regulation, DNA replication, and telomere maintenance. Recent studies have highlighted G4 ligands as promising anticancer agents due to their ability to modulate oncogene expression and induce DNA damage. By stabilizing G4 structures, these ligands affect tumor progression. Additionally, they have been implicated in tumor immunity modulation, particularly through the activation and immunogenic cell death induction of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway. Moreover, their disruption of telomere maintenance and regulation of key oncogenes, such as c-MYC and KRAS, position them as candidates for immune-based therapeutic interventions. Despite their therapeutic potential, challenges remain in optimizing their clinical applications, particularly in patient stratification and elucidating their immunomodulatory effects. This review provides a comprehensive overview of the mechanisms through which G4 ligands influence tumor progression and immune regulation, highlighting their potential role in future cancer immunotherapy strategies.

Diphenylaminothiophen-derived fluorescent ligands targeting mitochondrial DNA G-quadruplexes potentially for triple-negative breast cancer therapy

Mitochondrial DNA G-quadruplexes (mtG4s) are thought to play crucial roles in mitochondrial metabolism and may also represent a potential target for anticancer drugs. However, mtG4s remain understudied, necessitating the development of more promising fluorescent ligands specifically targeted to them. In this study, we designed and synthesized a targeted library of diphenylaminothiophen (DPAT)-derived compounds, and subsequently evaluated their optical properties and binding affinities towards mtG4s. From this library, we identified SF3 as the most promising ligand for further investigation. Our findings revealed that SF3 was an exceptional mtG4-targeted near-infrared (NIR) fluorescent ligand, of which the fluorescence could be switched on through the G4-mediated disassembly of its H-aggregates into monomers with restricted conformation, featuring DBIE mechanism. Notably, SF3 significantly inhibited the transcription and replication of mtDNA, disrupted mitochondrial metabolism, induced cell cycle arrest, triggered apoptosis, and demonstrated robust anticancer activity against triple-negative breast cancer (TNBC) either in vitro or in vivo. Collectively, SF3 can serve as a practical chemical tool for investigating mtG4s and holds potential for further development into an innovative anticancer agent.

Cellular Discrepancy of Platinum Complexes in Interfering with Mitochondrial DNA

Mitochondria are associated with cellular energy metabolism, proliferation, and mode of death. Damage to mitochondrial DNA (mtDNA) greatly affects mitochondrial function by interfering with energy production and the signaling pathway. Monofunctional trinuclear platinum complex MTPC demonstrates different actions on the mtDNA of cancerous and normal cells. It severely impairs the integrity and function of mitochondria in the human lung cancer A549 cells, such as dissipating mitochondrial membrane potential, decreasing the copy number of mtDNA, interfering in nucleoid proteins and polymerase gamma gene, reducing adenosine triphosphate (ATP), and inducing mitophagy, whereas it barely affects the mtDNA of the human kidney 2 (HK-2) cells. Moreover, MTPC promotes the release of mtDNA into the cytosol and stimulates the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, thus showing the potential to trigger antitumor immunity. MTPC displays significant cytotoxicity against A549 cells, while it exhibits weak toxicity toward HK-2 cells, therefore displaying great advantage to overcome the lingering nephrotoxicity of platinum anticancer drugs. Discrepant effects of a metal complex on mitochondria of different cells mean that targeting mitochondria has special significance in cancer therapy.

Stimuli-responsive benzothiazole-phenothiazine derivatives: mechanochromism, AIE, acid sensing, and anticancer efficacy in benzo[a]pyrene-induced cancer models

Mechanofluorochromic (MFC) materials are emerging as a versatile candidate for optoelectronic and biomedical applications. In the present work, we designed and synthesized four MFC materials, namely BT-PTZ-1, BT-PTZ-2, BT-PTZO-1, and BT-PTZO-2, using Suzuki cross-coupling reaction. These materials possess benzothiazole (BT) as an acceptor moiety and different donors, including phenothiazine (PTZ) and triphenylamine (TPA), with variations in their spacer units. The photophysical properties of these derivatives have been explored, revealing solvatochromism, aggregation-induced emission (AIE), acid sensing, and mechanochromic behaviour. Single crystal X-ray analysis of BT-PTZO-2 provides crucial structural insights, revealing the twisted conformation of the TPA donor and the bent structure of the PTZ oxide spacer. The biological studies of these BT derivatives reveal the therapeutic potential against benzo[a]pyrene (B[a]P)-induced carcinogenesis in A549 (lung) and HEK293 (kidney) cells. Treatment with BT-PTZ-2 reflects anti-cancerous properties, with significant up-regulation of p53 and down-regulation of β-catenin and pNF-κB. Additionally, downregulation of mitochondrial fission protein (DRP1) and oxidative stress through DCFDA staining in lung cells are observed with BT-PTZ-2 treatment. These findings strongly suggest that BT-PTZ-2 can inhibit lung cancer cell proliferation and survival, suggesting it to be a promising anti-cancer agent. This comprehensive study of these MFC materials provides insights into their design, synthesis, and properties, in addition to their potential applications in various optoelectronic and biomedical fields.

Mitochondrial DNA-activated cGAS-STING pathway in cancer: Mechanisms and therapeutic implications

Mitochondrial DNA (mtDNA), a circular double-stranded DNA located within mitochondria, plays a pivotal role in mitochondrial-induced innate immunity, particularly via the cyclic GMP-AMP synthase (cGAS)-STING pathway, which recognizes double-stranded DNA and is crucial for pathogen resistance. Recent studies elucidate the interplay among mtDNA, the cGAS-STING pathway, and neutrophil extracellular traps (NETs) in the context of cancer. mtDNA uptake by recipient cells activates the cGAS-STING pathway, while mtDNA leakage reciprocally regulates NET release, amplifying inflammation and promoting NETosis, a mechanism of tumor cell death. Autophagy modulates these processes by clearing damaged mitochondria and degrading cGAS, thus preventing mtDNA recognition. Tumor microenvironmental factors, such as metabolic reprogramming and lipid accumulation, induce mitochondrial stress, ROS production, and further mtDNA leakage. This review explores strategies in cancer drug development that leverage mtDNA leakage to activate the cGAS-STING pathway, potentially converting 'cold tumors' into 'hot tumors,' while discussing advancements in targeted therapies and proposing new research methodologies.

PDE4D inhibitors: Opening a new era of PET diagnostics for Alzheimer's disease

As the incidence of Alzheimer's disease (AD) continues to rise, the need for an effective PET radiotracer to facilitate early diagnosis has become more pressing than ever before in modern medicine. Phosphodiesterase (PDE) is closely related to cognitive impairment and neuroinflammatory processes in AD. Current research progress shows that specific PDE4D inhibitors radioligands can bind specifically to the PDE4D enzyme in the brain, thereby showing pathology-related signal enhancement in AD animal models, indicating the potential of these ligands as effective radiotracers. At the same time, we need to pay attention to the important role computer aided drug design (CADD) plays in advancing AD drug design and PET imaging. Future research will verify the potential of these ligands in clinical applications through computer simulation techniques, providing patients with timely intervention and treatment, which is of great significance.

Discovery of a mitochondrial G-quadruplex targeted fluorescent ligand via a slight variation on the near-infrared heptamethine cyanine scaffold

The heptamethine cyanine dyes are one kind of promising near-infrared (NIR) compounds, holding great potential in both diagnostic and therapeutic regions. Remolding such structures to realize detection of unclarified biotargets or interfering with them seems to be important in the field of chemical biology. In this study, we developed a fluorescent ligand (IR1) targeting mitochondrial G-quadruplexes (mitoG4s) by a slight variation on the typical NIR scaffold (IR780). This ligand could be applied for sensing mitoG4s by fluorescence, making it different from the unmodified dye whose fluorescence was quenched by mitoG4s. Then, IR1 was demonstrated to accumulate in the mitochondria through a mitochondrial membrane potential (MMP) dependent manner. Some of IR1 then bound to mitoG4s, causing mtDNA loss and mitochondrial dysfunction, which thereby triggered PANoptosis, including apoptosis, autophagy and pyroptosis. To the best of our knowledge, IR1 was the first NIR fluorescent ligand with emission centered at above 800 nm for mitoG4s, and the first example causing PANoptosis among the reported mitoG4-targeted ligands.

Development of a fluorescent ligand that can illuminate nuclear G-quadruplexes and modulate oncogene expression

In this study, we developed a promising dual-function fluorescent ligand termed KS-1 by a slight structural modification on a reported carbazole-based scaffold. KS-1 was then found to mainly bind and illuminate the nuclear DNA G-quadruplexes (G4s) in a sandwich-like interacting mode, and also effectively modulate the oncogene expression through a G4-mediated manner. Furthermore, KS-1 was proved to inhibit cancer cell growth either in 2D monolayer cells or 3D multicellular tumor spheroids. To be noted, this ligand could overcome the shortcomings of other reported dual-function ligands that appeared to accumulate in the lysosomes or mitochondria, and may be used as a theranostic agent in the future.