Modular Synthetic Routes to Fluorine-Containing Halogenated Phenazine and Acridine Agents That Induce Rapid Iron Starvation in Methicillin-Resistant Staphylococcus aureus Biofilms

CuOTf(Tol)1/2-Catalyzed O-Trifluoroethylation of Alcohols with 2,2,2-Trifluorodiazoethane

Trifluoroethyl groups are important in medicinal chemistry since they can impart desirable properties, such as enhanced lipophilicity, metabolic stability, or binding affinity. A practical and scalable protocol has been developed for O-trifluoroethylation of alcohols with 2,2,2-trifluorodiazoethane using Cu(OTf)(Tol)1/2 catalyst under mild conditions. This novel approach demonstrated high reactivity and broad substrate scope toward a diverse range of alcohols, ranging from fused and bridged ring systems, linear alcohols, to even sugar motifs, which makes the protocol valuable for medicinal chemistry, material science, and other areas where the introduction of trifluoroethyl groups would be beneficial.

Identification of 6,8-ditrifluoromethyl halogenated phenazine as a potent bacterial biofilm-eradicating agent

Bacterial biofilms are surface-attached communities consisting of non-replicating persister cells encased within an extracellular matrix of biomolecules. Unlike bacteria that have acquired resistance to antibiotics, persister cells enable biofilms to demonstrate innate tolerance toward all classes of conventional antibiotic therapies. It is estimated that 50-80% of bacterial infections are biofilm associated, which is considered the underlying cause of chronic and recurring infections. Herein, we report a modular three-step synthetic route to new halogenated phenazine (HP) analogues from diverse aniline and nitroarene building blocks. The HPs were evaluated for antibacterial and biofilm-killing properties against a panel of lab strains and multidrug-resistant clinical isolates. Several HPs demonstrated potent antibacterial (MIC ≤ 0.39 μM) and biofilm-eradicating activities (MBEC < 10 μM) with 6,8-ditrifluoromethyl-HP 15 demonstrated remarkable biofilm-killing potencies (MBEC = 0.15-1.17 μM) against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus clinical isolates. Confocal microscopy showed HP 15 induced significant losses in the polysaccharide matrix in MRSA biofilms. In addition, HP 15 showed increased antibacterial activities against dormant Mycobacterium tuberculosis (Mtb, MIC = 1.35 μM) when compared to replicating Mtb (MIC = 3.69 μM). Overall, this new modular route has enabled rapid access to an interesting series of potent halogenated phenazine analogues to explore their unique antibacterial and biofilm-killing properties.

Piezoelectric Biomaterial with Advanced Design for Tissue Infection Repair

Bacterial infection has become the most dangerous factor in tissue repair, which strongly affects the tissue regeneration efficiency and wellness of patients. Piezoelectric materials exhibit the outstanding advantage of producing electrons without external power supply. The ability of electron enrichment and reactive oxygen species generation through noninvasive stimulations enables piezoelectric materials the potential applications of antibacterial. Many studies have proved the feasibility of piezoelectric materials as a functional addition in antibacterial biomaterial. In fact, numerous piezoelectric materials with ingenious designs are reported to be effective in antibacterial processes. This review summarizes the antibacterial mechanisms of piezoelectric, illuminating their potential in combating bacteria. Recent advancement in the design and construction of piezoelectric biomaterial including defect engineering, heterojunction, synergy with metal and the composite scaffold configuration are thoroughly reviewed. Moreover, the applications and therapeutic effects of piezoelectric materials in common tissues with antibacterial requirements are introduced, such as orthopedics, dental, and wound healing. Finally, the development prospects and points deserving further exploration are listed. This review is expected to provide valuable insight into the relationship between antibacterial processes and piezoelectric materials, further inspiring constructive development in this emerging scientific discipline.

In vitro detection of cancer cells using a novel fluorescent choline derivative

INTRODUCTION

The treatment of preinvasive lesions is more effective than treating invasive disease, hence detecting cancer at its early stages is crucial. However, currently, available screening methods show various limitations in terms of sensitivity, specificity, and practicality, thus novel markers complementing traditional cyto/histopathological assessments are needed. Alteration in choline metabolism is a hallmark of many malignancies, including cervical and breast cancers. Choline radiotracers are widely used for imaging purposes, even though many risks are associated with their radioactivity. Therefore, this work aimed to synthesise and characterise a non-radioactive choline tracer based on a fluorinated acridine scaffold (CFA) for the in vitro detection of cervical and breast cancer cells by fluorescence imaging.

METHODS

CFA was fully characterised and tested for its cytotoxicity on breast (MCF-7), cervical (HeLa), glioblastoma (U-87 MG) and hepatoblastoma (HepG2) cancer cell lines and in normal cell lines (epithelial, HEK-293 and human dermal fibroblasts, HDFs). The cellular uptake of CFA was investigated by a confocal microscope and its accumulation was quantified over time. The specificity of CFA over mesenchymal origin cells (HDFs), as a model of cancer-associated fibroblasts was investigated by fluorescence microscopy.

RESULTS

CFA was toxic at much higher concentrations (HeLa IC50 = 200 ± 18 µM and MCF-7 IC50 = 105 ± 3 µM) than needed for its detection in cancer cells (5 µM). CFA was not toxic in the other cell lines tested. The intensity of CFA in breast and cervical cancer cells was not significantly different at any time point, yet it was greater than HepG2 and U-87 MG (p ≤ 0.01 and p ≤ 0.0001, respectively) after 24 h incubation. A very weak signal intensity was recorded in HEK-293 and HDFs (p ≤ 0.001 and p ≤ 0.0001, respectively). A selective ability of CFA to accumulate in HeLa and MCF-7 was recorded upon co-culture with fibroblasts.

CONCLUSIONS

The results showed that CFA preferentially accumulated in cancer cells rather than in normal cells. These findings suggest that CFA may be a potential diagnostic probe for discriminating healthy tissues from malignant tissues due to its specific and highly sensitive features; CFA may also represent a useful tool for in vitro/ex vivo investigations of choline metabolism in patients with cervical and breast cancers.

Tailoring Biomaterials Ameliorate Inflammatory Bone Loss

Inflammatory diseases, such as rheumatoid arthritis, periodontitis, chronic obstructive pulmonary disease, and celiac disease, disrupt the delicate balance between bone resorption and formation, leading to inflammatory bone loss. Conventional approaches to tackle this issue encompass pharmaceutical interventions and surgical procedures. Nevertheless, pharmaceutical interventions exhibit limited efficacy, while surgical treatments impose trauma and significant financial burden upon patients. Biomaterials show outstanding spatiotemporal controllability, possess a remarkable specific surface area, and demonstrate exceptional reactivity. In the present era, the advancement of emerging biomaterials has bestowed upon more efficacious solutions for combatting the detrimental consequences of inflammatory bone loss. In this review, the advances of biomaterials for ameliorating inflammatory bone loss are listed. Additionally, the advantages and disadvantages of various biomaterials-mediated strategies are summarized. Finally, the challenges and perspectives of biomaterials are analyzed. This review aims to provide new possibilities for developing more advanced biomaterials toward inflammatory bone loss.

Copper(II)-infused porphyrin MOF: maximum scavenging GSH for enhanced photodynamic disruption of bacterial biofilm

Bacterial biofilm infection is a serious obstacle to clinical therapeutics. Photodynamic therapy (PDT) plays a dynamic role in combating biofilm infection by utilizing reactive oxygen species (ROS)-induced bacterial oxidation injury, showing advantages of mild side effects, spatiotemporal controllability and little drug resistance. However, superfluous glutathione (GSH) present in biofilm and bacteria corporately reduces ROS levels and seriously affects PDT efficiency. Herein, we have constructed a Cu2+-infused porphyrin metal-organic framework (MOF@Cu2+) for the enhanced photodynamic combating of biofilm infection by the maximum depletion of GSH. Our results show that the released Cu2+ from porphyrin MOF@Cu2+ could not only oxidize GSH in biofilm but also consume GSH leaked from ROS-destroyed bacteria, thus greatly weakening the antioxidant system in biofilm and bacteria and dramatically improving the ROS levels. As expected, our dual-enhanced PDT nanoplatform exhibits a strong biofilm eradication ability both in vitro and in an in vivo biofilm-infected mouse model. In addition, Cu2+ can promote biofilm-infected wound closing by provoking cell immigration, collagen sediment and angiogenesis. Besides, no apparent toxicity was detected after treatment with MOF@Cu2+. Overall, our design offers a new paradigm for photodynamic combating biofilm infection.

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

Type I Photosensitizer Targeting Glycans: Overcoming Biofilm Resistance by Inhibiting the Two-Component System, Quorum Sensing, and Multidrug Efflux

Stubborn biofilm infections pose serious threats to human health due to the persistence, recurrence, and dramatically magnified antibiotic resistance. Photodynamic therapy has emerged as a promising approach to combat biofilm. Nevertheless, how to inhibit the bacterial signal transduction system and the efflux pump to conquer biofilm recurrence and resistance remains a challenging and unaddressed issue. Herein, a boric acid-functionalized lipophilic cationic type I photosensitizer, ACR-DMP, is developed, which efficiently generates •OH to overcome the hypoxic microenvironment and photodynamically eradicates methicillin-resistant Staphylococcus aureus (MRSA) and biofilms. Furthermore, it not only alters membrane potential homeostasis and osmotic pressure balance due to its strong binding ability with plasma membrane but also inhibits quorum sensing and the two-component system, reduces virulence factors, and regulates the activity of the drug efflux pump attributed to the glycan-targeting ability, helping to prevent biofilm recurrence and conquer biofilm resistance. In vivo, ACR-DMP successfully obliterates MRSA biofilms attached to implanted medical catheters, alleviates inflammation, and promotes vascularization, thereby combating infections and accelerating wound healing. This work not only provides an efficient strategy to combat stubborn biofilm infections and bacterial multidrug resistance but also offers systematic guidance for the rational design of next-generation advanced antimicrobial materials.

Synthesis and Staphylococcus aureus biofilm inhibitory activity of indolenine-substituted pyrazole and pyrimido[1,2-b]indazole derivatives

Staphylococcus aureus is a highly adaptable opportunistic pathogen that can form biofilms and generate persister cells, leading to life-threatening infections that are difficult to treat with antibiotics alone. Therefore, there is a need for an effective S. aureus biofilm inhibitor to combat this public health threat. In this study, a small library of indolenine-substituted pyrazoles and pyrimido[1,2-b]indazole derivatives were synthesised, of which the hit compound exhibited promising antibiofilm activities against methicillin-susceptible S. aureus (MSSA ATCC 29213) and methicillin-resistant S. aureus (MRSA ATCC 33591) at concentrations significantly lower than the planktonic growth inhibition. The hit compound could prevent biofilm formation and eradicate mature biofilms of MSSA and MRSA, with a minimum biofilm inhibitory concentration (MBIC50) value as low as 1.56 µg/mL and a minimum biofilm eradication concentration (MBEC50) value as low as 6.25 µg/mL. The minimum inhibitory concentration (MIC) values of the hit compound against MSSA and MRSA were 50 µg/mL and 25 µg/mL, respectively, while the minimum bactericidal concentration (MBC) values against MSSA and MRSA were > 100 µg/mL. Preliminary structure-activity relationship analysis reveals that the fused benzene ring and COOH group of the hit compound are crucial for the antibiofilm activity. Additionally, the compound was not cytotoxic to human alveolar A549 cells, thus highlighting its potential as a suitable candidate for further development as a S. aureus biofilm inhibitor.

Design, synthesis and evaluation of halogenated phenazine antibacterial prodrugs targeting nitroreductase enzymes for activation

It is of great importance to develop new strategies to combat antibiotic resistance. Our lab has discovered halogenated phenazine (HP) analogues that are highly active against multidrug-resistant bacterial pathogens. Here, we report the design, synthesis, and study of a new series of nitroarene-based HP prodrugs that leverage intracellular nitroreductase (NTR) enzymes for activation and subsequent release of active HP agents. Our goals of developing HP prodrugs are to (1) mitigate off-target metal chelation (potential toxicity), (2) possess motifs to facilitate intracellular, bacterial-specific HP release, (3) improve water solubility, and (4) prevent undesirable metabolism (e.g., glucuronidation of HP's phenol). Following the synthesis of HP-nitroarene prodrugs bearing a sulfonate ester linker, NTR-promoted release experiments demonstrated prodrug HP-1-N released 70.1% of parent HP-1 after 16 hours (with only 6.8% HP-1 release without NTR). In analogous in vitro experiments, no HP release was observed for control sulfonate ester compounds lacking the critical nitro group. When compared to parent HP compounds, nitroarene prodrugs evaluated during these studies demonstrate similar antibacterial activities in MIC and zone of inhibition assays (against lab strains and clinical isolates). In conclusion, HP-nitroarene prodrugs could provide a future avenue to develop potent agents that target antibiotic resistant bacteria.

Design, Synthesis, and Evaluation of Carbonate-Linked Halogenated Phenazine-Quinone Prodrugs with Improved Water-Solubility and Potent Antibacterial Profiles

Pathogenic bacteria have devastating impacts on human health as a result of acquired antibiotic resistance and innate tolerance. Every class of our current antibiotic arsenal was initially discovered as growth-inhibiting agents that target actively replicating (individual, free-floating) planktonic bacteria. Bacteria are notorious for utilizing a diversity of resistance mechanisms to overcome the action of conventional antibiotic therapies and forming surface-attached biofilm communities enriched in (non-replicating) persister cells. To address problems associated with pathogenic bacteria, our group is developing halogenated phenazine (HP) molecules that demonstrate potent antibacterial and biofilm-eradicating activities through a unique iron starvation mode of action. In this study, we designed, synthesized, and investigated a focused collection of carbonate-linked HP prodrugs bearing a quinone trigger to target the reductive cytoplasm of bacteria for bioactivation and subsequent HP release. The quinone moiety also contains a polyethylene glycol group, which dramatically enhances the water-solubility properties of the HP-quinone prodrugs reported herein. We found carbonate-linked HP-quinone prodrugs 11, 21-23 to demonstrate good linker stability, rapid release of the active HP warhead following dithiothreitol (reductive) treatment, and potent antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis, and Enterococcus faecalis. In addition, HP-quinone prodrug 21 induced rapid iron starvation in MRSA and S. epidermidis biofilms, illustrating prodrug action within these surface-attached communities. Overall, we are highly encouraged by these findings and believe that HP prodrugs have the potential to address antibiotic resistant and tolerant bacterial infections.

Transcript Profiling of Nitroxoline-Treated Biofilms Shows Rapid Up-regulation of Iron Acquisition Gene Clusters

Bacterial biofilms are surface-attached communities of slow- or non-replicating cells embedded within a protective matrix of biomolecules. Unlike free-floating planktonic bacteria, biofilms are innately tolerant to conventional antibiotics and are prevalent in recurring and chronic infections. Nitroxoline, a broad-spectrum biofilm-eradicating agent, was used to probe biofilm viability. Transcript profiling (RNA-seq) showed that 452 of 2594 genes (17.4%) in methicillin-resistant Staphylococcus aureus (MRSA) biofilms were differentially expressed after a 2 h treatment of nitroxoline. WoPPER analysis and time-course validation (RT-qPCR) revealed that gene clusters involved in iron acquisition (sbn, isd, MW2101, MW0695, fhu, and feo) were rapidly up-regulated following nitroxoline treatment, which is indicative of iron starvation in MRSA biofilms. In addition, genes related to oligopeptide transporters and riboflavin biosynthesis were found to be up-regulated, while genes related to carotenoid biosynthesis and nitrate assimilation were down-regulated. RT-qPCR experiments revealed that iron uptake transcripts were also up-regulated in established Staphylococcus epidermidis and Acinetobacter baumannii biofilms following nitroxoline treatment. Overall, we show RNA-seq to be an ideal platform to define cellular pathways critical for biofilm survival, in addition to demonstrating the need these bacterial communities have for iron.