Rational design of small-molecules to recognize G-quadruplexes of c-MYC promoter and telomere and the evaluation of their in vivo antitumor activity against breast cancer

Development of a fluorescent ligand that specifically binds to the c-MYC G-quadruplex by migrating the benzene group on a carbazole-benzothiazolium scaffold

c-MYC is one of the most important oncogenes, which is overexpressed in many cancers, and is highly related to development, metastasis, and drug resistance of cancers. The G4 structure in the promoter of c-MYC oncogene contributes a lot to the gene transcriptional mechanism. Small-molecule ligands binding to the c-MYC G4 appear to be a new class of anticancer agents. However, selective ligands for the c-MYC G4 over other G4s have been rarely reported. In this study, we reported a novel fluorescent ligand by migrating the benzene group on a carbazole-benzothiazolium scaffold, which was demonstrated to exhibit considerable specificity to the c-MYC G4, which was distinguished from other small-molecule ligands. The further cellular experiments suggested that this ligand may indeed target the promoter G4 and cause apparent transcriptional inhibition of the c-MYC oncogene instead of other G4-mediated oncogenes, which thereby resulted in cancer cell growth inhibition. Collectively, this study provided a good example for developing specific c-MYC G4 ligands, which may further develop into an effective anticancer agent that inhibit the c-MYC expression.

Targeting hTERT Promoter G-Quadruplex DNA Structures with Small-Molecule Ligand to Downregulate hTERT Expression for Triple-Negative Breast Cancer Therapy

Human telomerase reverse transcriptase (hTERT) may have noncanonical functions in transcriptional regulation and metabolic reprogramming in cancer cells, but it is a challenging target. We thus developed small-molecule ligands targeting hTERT promoter G-quadruplex DNA structures (hTERT G4) to downregulate hTERT expression. Ligand 5 showed high affinity toward hTERT G4 (Kd = 1.1 μM) and potent activity against triple-negative breast cancer cells (MDA-MB-231, IC50 = 1 μM). In cell-based assays, 5 not only exerts markedly inhibitory activity on classical telomere functions including decreased telomerase activity, shortened telomere length, and cellular senescence but also induces DNA damage, acute cellular senescence, and apoptosis. This study reveals that hTERT G4-targeting ligand may cause mitochondrial dysfunction, disrupt iron metabolism and activate ferroptosis in cancer cells. The in vivo antitumor efficacy of 5 was also evaluated in an MDA-MB-231 xenograft mouse model and approximately 78.7% tumor weight reduction was achieved. No observable toxicity against the major organs was observed.

Immunoglobulin class-switch recombination: Mechanism, regulation, and related diseases

Maturation of the secondary antibody repertoire requires class-switch recombination (CSR), which switches IgM to other immunoglobulins (Igs), and somatic hypermutation, which promotes the production of high-affinity antibodies. Following immune response or infection within the body, activation of T cell-dependent and T cell-independent antigens triggers the activation of activation-induced cytidine deaminase, initiating the CSR process. CSR has the capacity to modify the functional properties of antibodies, thereby contributing to the adaptive immune response in the organism. Ig CSR defects, characterized by an abnormal relative frequency of Ig isotypes, represent a rare form of primary immunodeficiency. Elucidating the molecular basis of Ig diversification is essential for a better understanding of diseases related to Ig CSR defects and could provide clues for clinical diagnosis and therapeutic approaches. Here, we review the most recent insights on the diversification of five Ig isotypes and choose several classic diseases, including hyper-IgM syndrome, Waldenström macroglobulinemia, hyper-IgD syndrome, selective IgA deficiency, hyper-IgE syndrome, multiple myeloma, and Burkitt lymphoma, to illustrate the mechanism of Ig CSR deficiency. The investigation into the underlying mechanism of Ig CSR holds significant potential for the advancement of increasingly precise diagnostic and therapeutic approaches.

A non-B DNA binding peptidomimetic channel alters cellular functions

DNA binding transcription factors possess the ability to interact with lipid membranes to construct ion-permeable pathways. Herein, we present a thiazole-based DNA binding peptide mimic TBP2, which forms transmembrane ion channels, impacting cellular ion concentration and consequently stabilizing G-quadruplex DNA structures. TBP2 self-assembles into nanostructures, e.g., vesicles and nanofibers and facilitates the transportation of Na+ and K+ across lipid membranes with high conductance (~0.6 nS). Moreover, TBP2 exhibits increased fluorescence when incorporated into the membrane or in cellular nuclei. Monomeric TBP2 can enter the lipid membrane and localize to the nuclei of cancer cells. The coordinated process of time-dependent membrane or nuclear localization of TBP2, combined with elevated intracellular cation levels and direct G-quadruplex (G4) interaction, synergistically promotes formation and stability of G4 structures, triggering cancer cell death. This study introduces a platform to mimic and control intricate biological functions, leading to the discovery of innovative therapeutic approaches.

Rational Design of NIR-II G-Quadruplex Fluorescent Probes for Accurate In Vivo Tumor Metastasis Imaging

Accurate in vivo imaging of G-quadruplexes (G4) is critical for understanding the emergence and progression of G4-associated diseases like cancer. However, existing in vivo G4 fluorescent probes primarily operate within the near-infrared region (NIR-I), which limits their application accuracy due to the short emission wavelength. The transition to second near-infrared (NIR-II) fluorescent imaging has been of significant interest, as it offers reduced autofluorescence and deeper tissue penetration, thereby facilitating more accurate in vivo imaging. Nonetheless, the advancement of NIR-II G4 probes has been impeded by the absence of effective probe design strategies. Herein, through a "step-by-step" rational design approach, we have successfully developed NIRG-2, the first small-molecule fluorescent probe with NIR-II emission tailored for in vivo G4 detection. Molecular docking calculations reveal that NIRG-2 forms stable hydrogen bonds and strong π-π interactions with G4 structures, which effectively inhibit twisted intramolecular charge transfer (TICT) and, thereby, selectively illuminate G4 structures. Due to its NIR-II emission (940 nm), large Stokes shift (90 nm), and high selectivity, NIRG-2 offers up to 47-fold fluorescence enhancement and a tissue imaging depth of 5 mm for in vivo G4 detection, significantly outperforming existing G4 probes. Utilizing NIRG-2, we have, for the first time, achieved high-contrast visualization of tumor metastasis through lymph nodes and precise tumor resection. Furthermore, NIRG-2 proves to be highly effective and reliable in evaluating surgical and drug treatment efficacy in cancer lymphatic metastasis models. We are optimistic that this study not only provides a crucial molecular tool for an in-depth understanding of G4-related diseases in vivo but also marks a promising strategy for the development of clinical NIR-II G4-activated probes.

Mitochondria-Selective Dicationic Small-Molecule Ligand Targeting G-Quadruplex Structures for Human Colorectal Cancer Therapy

Mitochondria are important drug targets for anticancer and other disease therapies. Certain human mitochondrial DNA sequences capable of forming G-quadruplex structures (G4s) are emerging drug targets of small molecules. Despite some mitochondria-selective ligands being reported for drug delivery against cancers, the ligand design is mostly limited to the triphenylphosphonium scaffold. The ligand designed with lipophilic small-sized scaffolds bearing multipositive charges targeting the unique feature of high mitochondrial membrane potential (MMP) is lacking and most mitochondria-selective ligands are not G4-targeting. Herein, we report a new small-sized dicationic lipophilic ligand to target MMP and mitochondrial DNA G4s to enhance drug delivery for anticancer. The ligand showed marked alteration of mitochondrial gene expression and substantial induction of ROS production, mitochondrial dysfunction, DNA damage, cellular senescence, and apoptosis. The ligand also exhibited high anticancer activity against HCT116 cancer cells (IC50, 3.4 μM) and high antitumor efficacy in the HCT116 tumor xenograft mouse model (∼70% tumor weight reduction).

Constructing triazole-modified quinazoline derivatives as selective c-MYC G-quadruplex ligands and potent anticancer agents through click chemistry

c-MYC is a hallmark of various cancers, playing a critical role in promoting tumorigenesis. The formation of G-quadruplex (G4) in the c-MYC promoter region significantly suppresses its expression. Therefore, developing small-molecule ligands to stabilize c-MYC G4 formation and subsequentially suppress c-MYC expression is an attractive topic for c-MYC-driven cancer therapy. However, achieving selective ligands for c-MYC G4 poses challenges. In this study, we developed a series of triazole-modified quinazoline (TMQ) derivatives as potential c-MYC G4 ligands and c-MYC transcription inhibitors from 4-anilinoquinazoline lead 7a using click chemistry. Importantly, the c-MYC G4 stabilizing ability and antiproliferation activity were well correlated among these new derivatives, particularly in the c-MYC highly expressed colorectal cancer cell line HCT116. Among them, compound A6 exhibited good selectivity in stabilizing c-MYC G4 and in suppressing c-MYC transcription better than 7a. This compound induced G4 formation, selectively inhibited G4-related c-MYC transcription and suppressed the progression of HCT116 cells. These findings identify a new c-MYC transcription inhibitor and provide new insights for optimizing c-MYC G4-targeting ligands.

Discovery of a near-infrared fluorescent probe for G-quadruplexes by exploiting the concept of unfolding-intramolecular-aggregation-induced emission

In the very recent years, the concept of disaggregation-induced emission (DIE) has been applied to design G4 probes, thereby rendering several fluorophores that may suffer from aggregation-induced quenching (ACQ) to develop into desirable G4-selective probes. However, the design idea based on DIE was often limited by the instability and irreversibility of the "intermolecular" aggregation/disaggregation process. In this study, a self-folded, near-infrared fluorescent probe for selectively illuminating G4s was engineered. This probe restored its fluorescence via unfolding of its intramolecular aggregation (UIA) mediated by distinctive G4 binding, which may display more controllable background emission as well as more promising ability to track G4 forming dynamics as compared to the reported DIE probes. Altogether, this study provided insights into the development of new types of applicable G4 selective fluorescent probes.

Advances and challenges in identifying and characterizing G-quadruplex-protein interactions

G-quadruplexes (G4s) are peculiar nucleic acid secondary structures formed by DNA or RNA and are considered as fundamental features of the genome. Many proteins can specifically bind to G4 structures. There is increasing evidence that G4-protein interactions involve in the regulation of important cellular processes, such as DNA replication, transcription, RNA splicing, and translation. Additionally, G4-protein interactions have been demonstrated to be potential targets for disease treatment. In order to unravel the detailed regulatory mechanisms of G4-binding proteins (G4BPs), biochemical methods for detecting G4-protein interactions with high specificity and sensitivity are highly demanded. Here, we review recent advances in screening and validation of new G4BPs and highlight both their features and limitations.

Oxidation-responsive G-quadruplex ligand for selective inhibition of the proliferation of tumour cells

Tumour cells show a higher level of reactive oxygen species (ROS) than normal cells. On the basis of this difference, we designed an oxidation-responsive G-quadruplex proligand PDS-B by installing borolanylbenzyls on a well-known pyridostatin (PDS) ligand PDS-S to response high level ROS in tumour cells. The rapid oxidative degradation of the proligand to its active form PDS-S in the presence of H2O2 confirms the oxidation-responsive design. According to Förster resonance energy transfer (FRET) assays, circular dichroism (CD) spectra and confocal fluorescence imaging, PDS-B stabilizes telomeric G4 structures after oxidation with H2O2 or intracellular ROS. Apoptosis assays and cell cycle assays showed significant selectivity of PDS-B in inhibiting the proliferation of tumour cells over normal cells through responses to a high level of ROS in the formers. Further assays confirmed higher level of relative Caspase-3 activity in tumour cells than normal cells, consequently the enhanced apoptosis of the tumour cells induced by PDS-B. In summary, the results demonstrate a modification approach to solve the poor selectivity of the G4 ligand in tumour cells and cytotoxicity in normal cells.

Expanding the Toolbox of Target Directed Bio-Orthogonal Synthesis: In Situ Direct Macrocyclization by DNA Templates

Herein, we demonstrate for the first time that noncanonical DNA can direct macrocyclization-like challenging reactions to synthesize gene modulators. The planar G-quartets present in DNA G-quadruplexes (G4s) provide a size complementary reaction platform for the bio-orthogonal macrocyclization of bifunctional azide and alkyne fragments over oligo- and polymerization. G4s immobilized on gold-coated magnetic nanoparticles have been used as target templates to enable easy identification of a selective peptidomimetic macrocycle. Structurally similar macrocycles have been synthesized to understand their functional role in the modulation of gene function. The innate fluorescence of the in situ formed macrocycle has been utilized to monitor its cellular localization using a G4 antibody and its in cell formation from the corresponding azide and alkyne fragments. The successful execution of in situ macrocyclization in vitro and in cells would open up a new dimension for target-directed therapeutic applications.

Structurally diverse G-quadruplexes as the noncanonical nucleic acid drug target for live cell imaging and antibacterial study

The formation of G-quadruplex structures (G4s) in vitro from guanine (G)-rich nucleic acid sequences of DNA and RNA stabilized with monovalent cations, typically K⁺ and Na⁺, under physiological conditions, has been verified experimentally and some of them have high-resolution NMR or X-ray crystal structures; however, the biofunction of these special noncanonical secondary structures of nucleic acids has not been fully understood and their existence in vivo is still controversial at present. It is generally believed that the folding and unfolding of G4s in vivo is a transient process. Accumulating evidence has shown that G4s may play a role in the regulation of certain important cellular functions including telomere maintenance, replication, transcription and translation. Therefore, both DNA and RNA G4s of human cancer hallmark genes are recognized as the potential anticancer drug target for the investigation in cancer biology, chemical biology and drug discovery. The relationship between the sequence, structure and stability of G4s, the interaction of G4s with small molecules, and insights into the rational design of G4-selective binding ligands have been intensively studied over the decade. At present, some G4-ligands have achieved a new milestone and successfully entered the human clinical trials for anticancer therapy. Over the past few decades, numerous efforts have been devoted to anticancer therapy; however, G4s for molecular recognition and live cell imaging and for application as antibacterial agents and antibiofilms against antibiotic resistance have been obviously underexplored. The recent advances in G4-ligands in these areas are thus selected and discussed concentratedly in this article in order to shed light on the emerging role of G4s in chemical biology and therapeutic prospects against bacterial infections. In addition, the recently published molecular scaffolds for designing small ligands selectively targeting G4s in live cell imaging, bacterial biofilm imaging, and antibacterial studies are discussed. Furthermore, a number of underexplored G4-targets from the cytoplasmic membrane-associated DNA, the conserved promoter region of K. pneumoniae genomes, the RNA G4-sites in the transcriptome of E. coli and P. aeruginosa, and the mRNA G4-sites in the sequence for coding the vital bacterial FtsZ protein are highlighted to further explore in G4-drug development against human diseases.

Roles of G4-DNA and G4-RNA in Class Switch Recombination and Additional Regulations in B-Lymphocytes

Mature B cells notably diversify immunoglobulin (Ig) production through class switch recombination (CSR), allowing the junction of distant "switch" (S) regions. CSR is initiated by activation-induced deaminase (AID), which targets cytosines adequately exposed within single-stranded DNA of transcribed targeted S regions, with a specific affinity for WRCY motifs. In mammals, G-rich sequences are additionally present in S regions, forming canonical G-quadruplexes (G4s) DNA structures, which favor CSR. Small molecules interacting with G4-DNA (G4 ligands), proved able to regulate CSR in B lymphocytes, either positively (such as for nucleoside diphosphate kinase isoforms) or negatively (such as for RHPS4). G4-DNA is also implicated in the control of transcription, and due to their impact on both CSR and transcriptional regulation, G4-rich sequences likely play a role in the natural history of B cell malignancies. Since G4-DNA stands at multiple locations in the genome, notably within oncogene promoters, it remains to be clarified how it can more specifically promote legitimate CSR in physiology, rather than pathogenic translocation. The specific regulatory role of G4 structures in transcribed DNA and/or in corresponding transcripts and recombination hereby appears as a major issue for understanding immune responses and lymphomagenesis.

Novel Chiral Ru(II) Complexes as Potential c-myc G-quadruplex DNA Stabilizers Inducing DNA Damage to Suppress Triple-Negative Breast Cancer Progression

Currently, effective drugs for triple-negative breast cancer (TNBC) are lacking in clinics. c-myc is one of the core members during TNBC tumorigenesis, and G-rich sequences in the promoter region can form a G-quadruplex conformation, indicating that the c-myc inhibitor is a possible strategy to fight cancer. Herein, a series of chiral ruthenium(II) complexes ([Ru(bpy)₂(DPPZ-R)](ClO₄)₂, Λ/Δ-1: R = -H, Λ/Δ-2: R = -Br, Λ/Δ-3: R = -C≡C(C₆H₄)NH₂) were researched based on their interaction with c-myc G-quadruplex DNA. Λ-3 and Δ-3 show high affinity and stability to decrease their replication. Additional studies showed that Λ-3 and Δ-3 exhibit higher inhibition against different tumor cells than other molecules. Δ-3 decreases the viability of MDA-MB-231 cells with an IC₅₀ of 25.51 μM, which is comparable with that of cisplatin, with an IC₅₀ of 25.9 μM. Moreover, Δ-3 exhibits acceptable cytotoxic activity against MDA-MB-231 cells in a zebrafish xenograft breast cancer model. Further studies suggested that Δ-3 decreases the viability of MDA-MB-231 cells predominantly through DNA-damage-mediated apoptosis, which may be because Δ-3 can induce DNA damage. In summary, the results indicate that Ru(II) complexes containing alkinyl groups can be developed as c-myc G-quadruplex DNA binders to block TNBC progression.

Recent Developments in G-Quadruplex Binding Ligands and Specific Beacons on Smart Fluorescent Sensor for Targeting Metal Ions and Biological Analytes

The G-quadruplex structure is crucial in several biological processes, including DNA replication, transcription, and genomic maintenance. G-quadruplex-based fluorescent probes have recently gained popularity because of their ease of use, low cost, excellent selectivity, and sensitivity. This review summarizes the latest applications of G-quadruplex structures as detectors of genome-wide, enantioselective catalysts, disease therapeutics, promising drug targets, and smart fluorescence probes. In every section, sensing of G-quadruplex and employing G4 for the detection of other analytes were introduced, respectively. Since the discovery of the G-quadruplex structure, several studies have been conducted to investigate its conformations, biological potential, stability, reactivity, selectivity for chemical modification, and optical properties. The formation mechanism and advancements for detecting different metal ions (Na⁺, K⁺, Ag⁺, Tl⁺, Cu⁺/Cu²⁺, Hg²⁺, and Pb²⁺) and biomolecules (AMP, ATP, DNA/RNA, microRNA, thrombin, T4 PNK, RNase H, ALP, CEA, lipocalin 1, and UDG) using fluorescent sensors based on G-quadruplex modification, such as dye labels, artificial nucleobase moieties, dye complexes, intercalating dyes, and bioconjugated nanomaterials (AgNCs, GO, QDs, CDs, and MOF) is described herein. To investigate these extremely efficient responsive agents for diagnostic and therapeutic applications in medicine, fluorescence sensors based on G-quadruplexes have also been employed as a quantitative visualization technique.

Design, Synthesis, and Evaluation of New Sugar-Substituted Imidazole Derivatives as Selective c-MYC Transcription Repressors Targeting the Promoter G-Quadruplex

c-MYC is a key driver of tumorigenesis. Repressing the transcription of c-MYC by stabilizing the G-quadruplex (G4) structure with small molecules is a potential strategy for cancer therapy. Herein, we designed and synthesized 49 new derivatives by introducing carbohydrates to our previously developed c-MYC G4 ligand 1. Among these compounds, 19a coupled with a d-glucose 1,2-orthoester displayed better c-MYC G4 binding, stabilization, and protein binding disruption abilities than 1. Our further evaluation indicated that 19a blocked c-MYC transcription by targeting the promoter G4, leading to c-MYC-dependent cancer cell death in triple-negative breast cancer cell MDA-MB-231. Also, 19a significantly inhibited tumor growth in the MDA-MB-231 mouse xenograft model accompanied by c-MYC downregulation. Notably, the safety of 19a was dramatically improved compared to 1. Our findings indicated that 19a could become a promising anticancer candidate, which suggested that introducing carbohydrates to improve the G4-targeting and antitumor activity is a feasible option.

Adipose tissue-to-breast cancer crosstalk: Comprehensive insights

The review focuses on mechanistic evidence for the link between obesity and breast cancer. According to the IARC study, there is sufficient evidence that obesity is closely related to a variety of cancers. Among them, breast cancer is particularly disturbed by adipose tissue due to the unique histological structure of the breast. The review introduces the relationship between obesity and breast cancer from two aspects, including factors that promote tumorigenesis or metastasis. We summarize alterations in adipokines and metabolic pathways that contribute to breast cancer development. Breast cancer metastasis is closely related to obesity-induced pro-inflammatory microenvironment, adipose stem cells, and miRNAs. Based on the mechanism by which obesity causes breast cancer, we list possible therapeutic directions, including reducing the risk of breast cancer and inhibiting the progression of breast cancer. We also discussed the risk of autologous breast remodeling and fat transplantation. Finally, the causes of the obesity paradox and the function of enhancing immunity are discussed. Evaluating the balance between obesity-induced inflammation and enhanced immunity warrants further study.

Combination of dl922-947 Oncolytic Adenovirus and G-Quadruplex Binders Uncovers Improved Antitumor Activity in Breast Cancer

G-quadruplexes (G4s) are nucleic secondary structures characterized by G-tetrads. G4 motif stabilization induces DNA damage and cancer cell death; therefore, G4-targeting small molecules are the focus of clinical investigation. DNA destabilization induced by G4 ligands might potentiate the anticancer activity of agents targeting DNA or inhibiting its repair such as oncolytic viruses. This study represents the first approach combining G4 ligands, BRACO-19 (B19), pyridostatin (PDS), and the adenovirus dl922-947 in breast cancer cells. We demonstrated that G4 binders and dl922-947 induce cytotoxicity in breast cancer cells (MDA-MB-231 and MCF-7) and at higher doses in other neoplastic cell lines of thyroid (BHT-101 cells) and prostate (PC3 cells). G4 binders induce G4 motifs distributed in the S and G2/M phases in MCF-7 cells. G4 binder/dl922-947 combination increases cell cytotoxicity and the accumulation in subG0/G1. Indeed, G4 binders favor viral entry and replication with no effect on coxsackie and adenovirus receptor. Notably, dl922-947 induces G4 motifs and its combination with PDS potentiates this effect in MCF-7 cells. The agents alone or in combination similarly enhanced cell senescence. Additionally, PDS/dl922-947 combination inactivates STING signaling in MDA-MB-231 cells. Our results suggest that G4 binder/virotherapy combination may represent a novel therapeutic anticancer approach.

RNA Modification in Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by damage to the intestinal mucosa, which is caused by a combination of factors. These include genetic and epigenetic alterations, environmental influence, microorganism interactions, and immune conditions. Some populations with IBD show a cancer-prone phenotype. Recent studies have provided insight into the involvement of RNA modifications in the specific pathogenesis of IBD through regulation of RNA biology in epithelial and immune cells. Studies of several RNA modification-targeting reagents have shown preferable outcomes in patients with colitis. Here, we note a new awareness of RNA modification in the targeting of IBD and related diseases, which will contribute to early diagnosis, disease monitoring, and possible control by innovative therapeutic approaches.

Discriminating between Parallel, Anti-Parallel and Hybrid G-Quadruplexes: Mechanistic Details on Their Binding to Small Molecules

G-quadruplexes (G4) are now extensively recognised as a peculiar non-canonical DNA geometry that plays a prime importance role in processes of biological relevance whose number is increasing continuously. The same is true for the less-studied RNA G4 counterpart. G4s are stable structures; however, their geometrical parameters may be finely tuned not only by the presence of particular sequences of nucleotides but also by the salt content of the medium or by a small molecule that may act as a peculiar topology inducer. As far as the interest in G4s increases and our knowledge of these species deepens, researchers do not only verify the G4s binding by small molecules and the subsequent G4 stabilisation. The most innovative studies now aim to elucidate the mechanistic details of the interaction and the ability of a target species (drug) to bind only to a peculiar G4 geometry. In this focused review, we survey the advances in the studies of the binding of small molecules of medical interest to G4s, with particular attention to the ability of these species to bind differently (intercalation, lateral binding or sitting atop) to different G4 topologies (parallel, anti-parallel or hybrid structures). Some species, given the very high affinity with some peculiar G4 topology, can first bind to a less favourable geometry and then induce its conversion. This aspect is also considered.

DPA-Substituted Carbazole Derivative as a Fluorescent Ligand for G4 DNA

Herein a conjugated dipicolylamine/carbazole (Car-DPA) molecule was designed and synthesized to enhance the performance for the application as a G4 fluorescent ligand. This ligand has been found to display distinct and specific fluorescence enhancements in the presence of various G4 DNA structures, but limited with ssDNA or dsDNAs. The detail binding characteristics of the ligand with c-MYC G4 DNA were investigated by fluorescence, UV/VIS absorption, CD spectroscopy, and molecular docking. The present study demonstrated that Car-DPA bound to c-MYC G4s with a two-step complex formation, in which the binding mode appeared to be end-stacking. Confocal fluorescence images indicated that ligand Car-DPA could locate in nucleus, which is quite prominent from the cellular internalization studies.

Design and synthesis of quinolinium-based derivatives targeting FtsZ for antibacterial evaluation and mechanistic study

The discovery of small molecular inhibitors targeting essential and conserved bacterial drug targets such as FtsZ protein is a promising approach to fight against multi-drug resistant bacteria. In the present study, two new series of FtsZ inhibitors based on a 1-methylquinolinium scaffold were synthesized. The inhibitors possess a variety of substituent groups including the cyclic or linear amine skeleton at the 2- and 4-position of the quinolinium ring for structure-activity relationship study. In general, the inhibitors bearing a cyclic amine substituent at the 4-position of the quinolinium ring showed better antibacterial activity (MIC down to 0.25 μg/mL) than that at the 2-position, especially against Gram-positive bacteria. Among the twenty FtsZ inhibitors examined in various assays, A3 was identified to exhibit excellent antibacterial activity against S. aureus (MIC = 0.5-1 μg/mL), S. epidermidis (MIC = 0.25 μg/mL) and E. faecium (MIC = 1-8 μg/mL). More importantly, A3 showed low hemolytic toxicity (IC₅ = 64 μg/mL) and was found not readily to induce drug resistance. A3 at 2-8 μg/mL promoted the polymerization of FtsZ and interrupted the bacterial division. Furthermore, the ligand-FtsZ interaction study conducted with circular dichroism and molecular docking revealed that A3 induced secondary structure changes of FtsZ protein upon binding to the interdomain cleft of the protein. A3 is thus a potent inhibitor of FtsZ and shows potential to be used as a new antibacterial agent against drug-resistant bacteria.