Napthalimide-based nuclease inhibitor: A multifunctional therapeutic material to bolster MRSA uptake by macrophage-like cells and mitigate pathogen adhesion on orthopaedic implant

The healthcare burden rendered by methicillin-resistant Staphylococcus aureus (MRSA) warrants the development of therapeutics that offer a distinct benefit in the clinics as compared to conventional antibiotics. The present study describes the potential of napthalimide-based synthetic ligands (C1-C3) as inhibitors of the staphylococcal nuclease known as micrococcal nuclease (MNase), a key virulence factor of the pathogen. Amongst the ligands, the most potent MNase inhibitor C1 rendered non-competitive inhibition, reduced MNase turnover number (Kcat) and catalytic efficiency (Kcat/Km) with an IC50 value of ~950 nM. CD spectroscopy suggested distortion of MNase conformation in presence of C1. Flow cytometry and confocal microscopy indicated that C1 restored the ability of activated THP-1 cells to engulf DNA-entrapped MRSA cells. Interestingly, C1 could inhibit MRSA adhesion onto collagen. For potential application, C1-loaded pluronic F-127 micellar nanocarrier (C1-PMC) was generated, wherein the anti-adhesion activity of the pluronic carrier (PMC) and C1 was harnessed in tandem to deter MRSA cell adhesion onto collagen. MRSA biofilm formation was hindered on C1-PMC-coated titanium (Ti) wire, while eluates from C1-PMC-coated Ti wires were non-toxic to HEK 293, MG-63 and THP-1 cells. The multifunctional C1 provides a blueprint for designing therapeutic materials that hold translational potential for mitigation of MRSA infections.

Targeted mesoporous silica nanoparticles for improved inhibition of disinfectant resistant Listeria monocytogenes and lower environmental pollution

Benzalkonium chloride (BAC) is a common ingredient of disinfectants used for industrial, medical, food safety and domestic applications. It is a common pollutant detected in surface and wastewaters to induce adverse effects on Human health as well as aquatic and terrestrial life forms. Since disinfectant use is essential in combatting against microorganisms, the best approach to reduce ecotoxicity level is to restrict BAC use. We report here that encapsulation of BAC in mesoporous silica nanoparticles can provide an efficient strategy for inhibition of microbial activity with lower than usual concentrations of disinfectants. As a proof-of-concept, Listeria monocytogenes was evaluated for minimum inhibitory concentration (MIC) of nanomaterial encapsulated BAC. Aptamer molecular gate structures provided a specific targeting of the disinfectant to Listeria cells, leading to high BAC concentrations around bacterial cells, but significantly reduced amounts in total. This strategy allowed to inhibition of BAC resistant Listeria strains with 8 times less the usual disinfectant dose. BAC encapsulated and aptamer functionalized silica nanoparticles (AptBACNP) effectively killed only target bacteria L. monocytogenes, but not the non-target cells, Staphylococcus aureus or Escherichia coli. AptBACNP was not cytotoxic to Human cells as determined by in vitro viability assays.

A highly substituted and fluorescent aromatic-fused imidazole derivative that shows enhanced antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)

A novel highly substituted and fluorescent aromatic-fused imidazole derivative has been synthesized by rational design. This novel fluorescent material acts as an alternative antibacterial agent against Gram positive bacteria strains. It shows superior antibacterial activity (with MIC value of 8 μg/mL) against methicillin-resistant Staphylococcus aureus (MRSA) when compared with standard antibiotic drugs Ampicillin (with MIC value of 128 μg/mL) and Kanamycin (with MIC value of >512 μg/mL). The interaction of this novel compound with the bacterial cell and genomic DNA has also been studied to elucidate antibacterial mode of action. Fluorescence spectroscopy and microscopy studies have proved the intracellular uptake of this special compound. Likewise, UV-vis and fluorescence spectroscopy studies have revealed a significant decrease in the absorption and emission bands of the compound upon its interaction with plasmid and genomic DNA, which is likely due to its DNA intercalation property. Furthermore, these findings have been supported by gel electrophoresis of genomic DNA of S. aureus cells treated with the compound. The results indicate that this novel compound exerts its antibacterial activity by causing DNA damage, suggesting the potential utility of fluorescent probes for real-time diagnosis and treatment of bacterial infections.

Ionic Liquid-Functionalized Multiwalled Carbon Nanotube-Based Hydrophobic Coatings for Robust Antibacterial Applications

In recent years, the biomimetic superhydrophobic coatings have received tremendous attention, owing to their potential in fabricating self-cleaning surfaces, in environmental applications. Consequently, extensive research has been devoted to create a superhydrophobic surface using the oxidized derivatives of CNTs and graphene. Thus, the design and development of a self-cleaning/superhydrophobic surface with good biocompatibility are an effective approach to deal with the bacterial infections related to biomedical devices used in hospitals. In this context, herein, we have developed the material based on ionic liquid (IL)-functionalized multiwalled carbon nanotubes (MWCNTs) for hydrophobic coatings, which was fully characterized with various techniques such as Fourier transform infrared, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. We have evaluated the synthesized ILs for their antibacterial potential against the pathogenic bacterial strains such as Gram-positive (Staphylococcus aureus and methicillin-resistant S. aureus) and Gram-negative (Escherichia coli) bacterial strains. Further, atomic force and scanning electron microscopic studies have been performed to investigate the morphological changes to unravel the mechanism of action, whereas DNA binding study indicates the binding of IL-1d@MWCNT with DNA (K_a = 2.390 × 10⁴ M^-1). Furthermore, the developed material (IL-1d@MWCNT) is coated onto the surface of polyvinyl chloride (PVC) and evaluated for hydrophobicity through water contact angle measurements and possesses long-term antibacterial efficiency against both under-investigating pathogenic strains. For the biocompatibility assay, the obtained coated PVC material has also been evaluated for its cytotoxicity, and results reveal no toxicity against viable cells. These all results are taken together, indicating that by coating with the developed material IL-1d@MWCNT, a robust self-sterilizing surface has achieved, which helps in maintaining a bacteria-free surface.

Interplay between Supramolecular and Coordination Interactions in Synthetic Amphiphiles: Triggering Metal Starvation and Anchorage onto MRSA Cell Surface

The present work highlights the implications of supramolecular interaction and metal coordination on the self-assembly behavior and bactericidal potential of salicaldehyde-(C1) and napthaldehyde-based (C2) amphiphiles against methicillin-resistant Staphylococcus aureus (MRSA). LB trough and atomic force microscope (AFM) analysis indicated the propensity of the amphiphiles to form a monolayer as well as spherical aggregates, with the critical micelle concentration (CMC) for C2 (7.0 μM) being lower than C1 (18.5 μM) in water. Formation of an amphiphile-metal complex was evidenced by ESI-MS, FTIR, FETEM-EDX, and ITC analysis. Growth of S. aureus MRSA 100 cells was remarkably impaired in the presence of 5.0 μM C1 or 20 μM C2 as compared to free cells or cells grown in the presence of equivalent levels of amphiphile-metal complexes, suggesting that the amphiphiles perhaps sequester metal and induce metal starvation in MRSA. C1 and C2 rendered superior membrane damage in MRSA and were less toxic to human embryonic kidney (HEK 293) cells as compared to their metal complexes. C1 and C2 rendered a dose-dependent inhibition of S. aureus biofilm formation, while revival of biofilm upon Zn(II) addition suggested that zinc starvation rendered by the amphiphiles may induce biofilm inhibition. C1 imposed a concentration-dependent metal starvation response in MRSA as there was an upregulation of the cntL gene and downregulation of cntA gene, which are involved in synthesis of the zincophore staphylopine (Stp) and transport of the Stp-Zn complex, respectively. ITC analysis revealed that binding of C1 and C2 to staphylococcal lipoteichoic acid (LTA) was stronger than the corresponding Zn(II) complexes, which perhaps accounted for the higher bactericidal potency of the amphiphiles. The study provides a fundamental understanding on how the chemistry-driven multimodal interaction of the amphiphile translates into growth inhibition and metal starvation in MRSA and advances the idea of combating drug resistance in pathogenic bacteria through amphiphiles, which are pluri-active.

Emerging antibacterial nanomedicine for enhanced antibiotic therapy

This review highlights the different mechanisms of current nano-antibiotic systems for combatting serious antibiotic resistance of bacteria.

Bioconjugation with Maleimides: A Useful Tool for Chemical Biology

Maleimide chemistry stands out in the bioconjugation toolbox by virtue of its synthetic accessibility, excellent reactivity, and practicability. The second-generation of clinically approved antibody-drug conjugates (ADC) and much of the current ADC pipeline in clinical trials contain the maleimide linkage. However, thiosuccinimide linkages are now known to be less robust than once thought, and ergo, are correlated with suboptimal pharmacodynamics, pharmacokinetics, and safety profiles in some ADC constructs. Rational design of novel generations of maleimides and maleimide-type reagents have been reported to address the shortcomings of classical maleimides, allowing for the formation of robust bioconjugate linkages. This review highlights the main strategies for rational reagent design that have allowed irreversible bioconjugations in cysteines, reversible labelling strategies and disulfide re-bridging.

Micellar chemotherapeutic platform based on a bifunctional salicaldehyde amphiphile delivers a "combo-effect" for heightened killing of MRSA

The devastating infections caused by methicillin-resistant Staphylococcus aureus (MRSA) coupled with its high resistance towards antibiotics underscores the need for an effective anti-MRSA therapeutic. The present study illustrates the use of a salicylaldehyde based bactericidal amphiphile (C1) in generating a micellar carrier that renders delivery of therapeutic antibiotics. The inherent membrane-targeting activity of C1 present in the micelle could be leveraged to counter the resistance of MRSA and enhance cellular uptake of the released antibiotics, resulting in effective elimination of the pathogen. The inherent bactericidal and antibiofilm activity of C1 was captured in FESEM analysis, solution-based assays and fluorescence microscopy. ANS-based fluorescence spectroscopy indicated that the critical micelle concentration (CMC) for C1 was 18.5 μM in water. DLS studies and FESEM analysis indicated that the average particle size for micelles based on C1 (C1_M) and rifampicin-loaded C1_M (C1_M- R) was smaller than vancomycin-loaded C1_M (C1_M- V). C1_M- R and C1_M- V rendered sustained release of the antibiotics in physiologically relevant fluids. Notably, following interaction with MRSA for 3 h, the relative anti-MRSA activity of C1_M- R and C1_M- V was nearly 12-fold and 8-fold higher, respectively, as compared to the free antibiotics at equivalent concentration, highlighting the merit of leveraging the activity of C1 and the antibiotic concurrently in the micellar system. The relative cell-free antibiotic was also manifold lower in the case of C1_M- R and C1_M- V treated MRSA as against treatment with free antibiotics, suggesting that the amphiphilic warhead breached the membrane barrier and enhanced cellular uptake of the released antibiotics. Interestingly, C1_M- R and C1_M- V exhibited a high therapeutic index, being non-toxic to HEK 293 cells at concentrations higher than their minimum inhibitory concentration (MIC) against MRSA and they could be employed as an antibacterial coating to prevent MRSA biofilm formation on surgical silk sutures. The antibiotic-replete biocompatible micelles based on a self-assembling membrane-targeting amphiphile described herein represent a promising framework to integrate multiple warheads and generate a potent anti-MRSA therapeutic material.

Fabrication of Nontoxic Reduced Graphene Oxide Protein Nanoframework as Sustained Antimicrobial Coating for Biomedical Application

Bacterial colonization on medical devices is a major concern in the healthcare industry. In the present study, we report synthesis of environmental sustainable reduced graphene oxide (rGO) on the large scale through biosynthetic route and its potential application for antibacterial coating on medical devices. HRTEM image depicts formation of graphene nanosheet, while DLS and ζ potential studies reveal that in aqueous medium the average hydrodynamic size and surface charge of rGO are 4410 ± 116 nm and -25.2 ± 3.2 mV, respectively. The Raman, FTIR, and XPS data suggest in situ conjugation of protein with rGO. The as-synthesized rGO protein nanoframework exhibits dose-dependent antibacterial activity and potential of killing of 94% of Escherichia coli when treated with 80 μg/mL of rGO for 4 h. The hemolytic and cytotoxicity studies demonstrate that rGO protein nanoframework is highly biocompatible at the same concentration showing significant antimicrobial properties. The rGO coated on the glass surface obtained through covalent bonding exhibits potent antibacterial activity. Antibacterial mechanism further demonstrates that rGO-protein nanoframework in dispersed state (rGO solution) exerts bactericidal effect through physical disruption accompanied by ROS-mediated biochemical responses. The rGO subsequently entering into the cytoplasm through the damaged membrane causes metabolic imbalance in the cells. In sharp contrast, physical damage of the cell membrane is the dominant antibacterial mechanism of rGO in the immobilized state (rGO coated glass). The obtained results help indepth understanding of the antibacterial mechanism of the biosynthesized rGO and a novel way to develop nontoxic antibacterial coating on medical devices to prevent bacterial infection.

Hydra amphiphiles: Using three heads and one tail to influence aggregate formation and to kill pathogenic bacteria

Hydra amphiphiles mimic the morphology of the mythical multi-headed creatures for which they are named. Likewise, when faced with a pathogenic bacterium, some hydra derivatives are as destructive as their fabled counterparts were to their adversaries. This report focuses on eight new tricephalic (triple-headed), single-tailed amphiphiles. Each amphiphile has a mesitylene (1,3,5-trimethylbenzene) core, two benzylic trimethylammonium groups and one dimethylalkylammonium group with a linear hydrophobe ranging from short (C₈H₁₇) to ultralong (C₂₂H₄₅). The logarithm of the critical aggregation concentration, log(CAC), decreases linearly with increasing tail length, but with a smaller dependence than that of ionic amphiphiles with fewer head groups. Tail length also affects antibacterial activity; amphiphiles with a linear 18 or 20 carbon atom hydrophobic chain are more effective at killing bacteria than those with shorter or longer chains. Comparison to a recently reported amphiphilic series with three heads and two tails allows for the development of an understanding of the relationship between number of tails and both colloidal and antibacterial properties.

Quaternary Ammonium Compounds: An Antimicrobial Mainstay and Platform for Innovation to Address Bacterial Resistance

Quaternary ammonium compounds (QACs) have represented one of the most visible and effective classes of disinfectants for nearly a century. With simple preparation, wide structural variety, and versatile incorporation into consumer products, there have been manifold developments and applications of these structures. Generally operating via disruption of one of the most fundamental structures in bacteria-the cell membrane-leading to cell lysis and bacterial death, the QACs were once thought to be impervious to resistance. Developments over the past decades, however, have shown this to be far from the truth. It is now known that a large family of bacterial genes (generally termed qac genes) encode efflux pumps capable of expelling many QAC structures from bacterial cells, leading to a decrease in susceptibility to QACs; methods of regulation of qac transcription are also understood. Importantly, qac genes can be horizontally transferred via plasmids to other bacteria and are often transmitted alongside other antibiotic-resistant genes; this dual threat represents a significant danger to human health. In this review, both QAC development and QAC resistance are documented, and possible strategies for addressing and overcoming QAC-resistant bacteria are discussed.

A plug-and-play approach to antibody-based therapeutics via a chemoselective dual click strategy

Although recent methods for the engineering of antibody–drug conjugates (ADCs) have gone some way to addressing the challenging issues of ADC construction, significant hurdles still remain. There is clear demand for the construction of novel ADC platforms that offer greater stability, homogeneity and flexibility. Here we describe a significant step towards a platform for next-generation antibody-based therapeutics by providing constructs that combine site-specific modification, exceptional versatility and high stability, with retention of antibody binding and structure post-modification. The relevance of the work in a biological context is also demonstrated in a cytotoxicity assay and a cell internalization study with HER2-positive and -negative breast cancer cell lines.

Antibody–drug conjugates are a class of therapeutic combining the directing ability of antibodies with the cell-killing ability of cytotoxic drugs. Here the authors describe an approach based on click chemistry that enables the rapid assembly of dual-modified antibodies with potential for new therapeutic modalities.

Antimicrobial polymeric materials with quaternary ammonium and phosphonium salts

Polymeric materials containing quaternary ammonium and/or phosphonium salts have been extensively studied and applied to a variety of antimicrobial-relevant areas. With various architectures, polymeric quaternary ammonium/phosphonium salts were prepared using different approaches, exhibiting different antimicrobial activities and potential applications. This review focuses on the state of the art of antimicrobial polymers with quaternary ammonium/phosphonium salts. In particular, it discusses the structure and synthesis method, mechanisms of antimicrobial action, and the comparison of antimicrobial performance between these two kinds of polymers.

A zinc complex of a neutral pyridine-based amphiphile: a highly efficient and potentially therapeutic bactericidal material

The complexation of Zn(ii) with a neutral pyridine-based amphiphile generates a potent bactericidal material for potential antibacterial and antibiofilm therapy.

Biocompatible nanocarrier fortified with a dipyridinium-based amphiphile for eradication of biofilm

Annihilation of bacterial biofilms is challenging owing to their formidable resistance to therapeutic antibiotics and thus there is a constant demand for development of potent antibiofilm agents that can abolish established biofilms. In the present study, the activity of a dipyridinium-based cationic amphiphile (compound 1) against established bacterial biofilms and the subsequent development of a compound 1-loaded nanocarrier for potential antibiofilm therapy are highlighted. Solution-based assays and microscopic analysis revealed the antagonistic effect of compound 1 on biofilms formed by Staphylococcus aureus MTCC 96 and Pseudomonas aeruginosa MTCC 2488. In combination studies, compound 1 could efficiently potentiate the action of tobramycin and gentamicin on P. aeruginosa and S. aureus biofilm, respectively. A human serum albumin (HSA)-based nanocarrier loaded with compound 1 was generated, which exhibited sustained release of compound 1 at physiological pH. The compound 1-loaded HSA nanocarrier (C1-HNC) displayed the signature membrane-directed activity of the amphiphile on target bacteria, efficiently eliminated established bacterial biofilms, and was observed to be nontoxic to a model human cell line. Interestingly, compound 1 as well as the amphiphile-loaded HSA nanocarrier could eradicate established S. aureus biofilm from the surface of a Foley's urinary catheter. On the basis of its biocompatibility and high antibiofilm activity, it is conceived that the amphiphile-loaded nanocarrier may hold potential in antibiofilm therapy.