Novel quinoxaline analogs as telomeric G-quadruplex ligands exert antitumor effects related to enhanced immunomodulation

Site-selective structural modification of toosendanin enables one-step synthesis of 12-hydroxyamoorastatin: A natural tautomeric antitumor lead with low toxicity

Natural limonoid triterpenoids toosendanin (1) and 12-hydroxyamoorastatin (5) have been reported to possess broad-spectrum antitumor activity. However, development of antitumor drugs for the treatment of 1 has reached an impasse, due to its severe hepatotoxicity. Notably, compound 5 is a C-12 deacetylated product of 1, but scholars have studied and exploited 5 much less than 1 especially on antitumor activity and toxicity, of which the resource scarcity and structural ambiguity of 5 may be great hindrances. To address these concerns, a site-selective modification of 1 was developed, in which C-12 deacetylation with LiHMDS enabled the one-step synthesis of 5 from 1, solving its insufficient resources. We then revised the 5/7-tautomerization to C-12/C-29-tautomerization of HAR (5) by extensive NMR, LC-MS, DFT-calculations, and X-ray analyses, and determined the relative content of the tautomers in solution phase. Moreover, the biological evaluation of the synthesized derivatives prompted identification of 5 as a natural lead with better antitumor activities in vitro/in vivo. Namely, 5 exhibited antitumor activity through multiple mechanisms, including inhibition of DDR repair, down-regulation of the DNA damage stress-associated transcription factor HSF-1 and its downstream HSPs, promotion of synthetic lethality, disruption of the BAX/BCL2 homeostasis, and elicitation of cellular autophagy. Crucially, 5 achieved 62 % TGI (vs. 17 % for 1) in the JIMT-1 xenograft tumor models without exhibiting hepatotoxicity, providing a solid support to the development of natural limonoid antitumor lead.

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.

Adamantane-Quinoxalone Hybrids: Precision Chemotypes and Their Molecular Mechanisms in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive blood cancer with a poor prognosis, especially when diagnosed late. Around 10-15% of cases involve the specific chromosomal abnormality t(8;21), which drives uncontrolled myeloid cell proliferation and contributes to disease onset. Despite advances in AML research and treatment protocols, outcomes for t(8;21) AML remain stagnant, as patients receive standard, nonspecific chemotherapies. This one-size-fits-all approach targets both cancerous and healthy cells, leading to unwanted toxicity and highlighting the urgent need for targeted therapies. In this study, we present a precision chemotype based on a quinoxalone-tethered adamantane framework developed via a metal- and light-free protocol. The compound selectively inhibits t(8;21) AML cell proliferation and induces cell death by disrupting growth and metabolic pathways, as demonstrated through bioassays, RNA sequencing, and proteomic analysis. Notably, it spares other leukemic and solid cancer cells, underscoring its specificity and potential as a targeted therapy for t(8;21) AML.

Repurposing FDA-approved drugs to target G-quadruplexes in breast cancer

Breast cancer, a leading cause of cancer-related mortality in women, is characterized by genomic instability and aberrant gene expression, often influenced by noncanonical nucleic acid structures such as G-quadruplexes (G4s). These structures, commonly found in the promoter regions and 5'-untranslated RNA sequences of several oncogenes, play crucial roles in regulating transcription and translation. Stabilizing these G4 structures offers a promising therapeutic strategy for targeting key oncogenic pathways. In this study, we employed a drug repurposing approach to identify FDA-approved drugs capable of binding and stabilizing G4s in breast cancer-related genes. Using ligand-based virtual screening and biophysical methods, we identified several promising compounds, such as azelastine, belotecan, and irinotecan, as effective G4 binders, with significant antiproliferative effects in breast cancer cell lines. Notably, belotecan and irinotecan exhibited a synergistic mechanism, combining G4 stabilization with their established topoisomerase I inhibition activity to enhance cytotoxicity in cancer cells. Our findings support the therapeutic potential of G4 stabilization in breast cancer, validate drug repurposing as an efficient strategy to identify G4-targeting drugs, and highlight how combining G4 stabilization with other established drug activities may improve anticancer efficacy.

Discovery of a tribenzophenazine analog for binding to the KRAS mRNA G-quadruplex structures in the cisplatin-resistant non-small cell lung cancer

Lung cancer is the malignant tumor with the highest morbidity and mortality rate worldwide, of which non-small cell lung cancer (NSCLC) accounts for approximately 85%. KRAS mutations are one of the significant mechanisms underlying the occurrence, development, immune escape, and chemotherapy resistance of NSCLC. Two KRAS inhibitors are approved by Food and Drug Administration for the treatment of NSCLC in the past 3 years. However, they are only effective to KRAS G12C mutant, and moreover, innate and acquired drug resistance is already reported, leaving an urgent need to block KRAS pathways through novel targets. In this study, we focused on the discovery of ligands targeting the RNA G-quadruplexes in 5'-UTR of KRAS mRNA, and a novel tribenzophenazine analog (MBD) was identified as the lead compound. Further mechanisms were discussed in A549/DDP cells, a cisplatin-resistant and KRAS-mutant NSCLC cell line. Antitumor efficacy was verified both in vitro in A549/DDP cells, and in vivo in a nude mouse xenograft model implanted with A549/DDP cells. To sum up, our results suggest the potential of MBD as a prominent anti-KRAS-driven NSCLC agent and propose a new idea for the development of small molecule ligands targeting KRAS RNA G-quadruplexes.

Kanamycin and G-Quadruplexes: An Exploration of Binding Interactions

G-quadruplexes (G4s) are distinctive four-stranded nucleic acid structures formed by guanine-rich sequences, making them attractive targets for drug repurposing efforts. Modulating their stability and function holds promise for treating diseases like cancer. To identify potential drug candidates capable of interacting with these complex DNA formations, docking studies and molecular dynamics (MDs) simulations were conducted. Our analysis revealed kanamycin's ability to bind to various G4 structures, offering valuable insights into its potential as a modulator of G4 activity. Kanamycin exhibited favorable interactions with both parallel and hybrid G4 topologies in human structures, suggesting a broader mechanism of action for aminoglycosides. These findings may also shed light on aminoglycoside-associated toxicities, indicating that their effects might extend to binding non-ribosomal RNA structures. In summary, this research highlights kanamycin's potential as a promising tool for influencing G4 dynamics, paving the way for innovative therapeutic strategies targeting G4-related pathways.

A Phenotypic Approach to the Discovery of Potent G-Quadruplex Targeted Drugs

G-quadruplex (G4) sequences, which can fold into higher-order G4 structures, are abundant in the human genome and are over-represented in the promoter regions of many genes involved in human cancer initiation, progression, and metastasis. They are plausible targets for G4-binding small molecules, which would, in the case of promoter G4s, result in the transcriptional downregulation of these genes. However, structural information is currently available on only a very small number of G4s and their ligand complexes. This limitation, coupled with the currently restricted information on the G4-containing genes involved in most complex human cancers, has led to the development of a phenotypic-led approach to G4 ligand drug discovery. This approach was illustrated by the discovery of several generations of tri- and tetra-substituted naphthalene diimide (ND) ligands that were found to show potent growth inhibition in pancreatic cancer cell lines and are active in in vivo models for this hard-to-treat disease. The cycles of discovery have culminated in a highly potent tetra-substituted ND derivative, QN-302, which is currently being evaluated in a Phase 1 clinical trial. The major genes whose expression has been down-regulated by QN-302 are presented here: all contain G4 propensity and have been found to be up-regulated in human pancreatic cancer. Some of these genes are also upregulated in other human cancers, supporting the hypothesis that QN-302 is a pan-G4 drug of potential utility beyond pancreatic cancer.