Cationic amphiphilic dendrons with effective antibacterial performance

Rapid and accurate identification of yeast subspecies by MALDI-MS combined with a cell membrane disruption reagent

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been widely used for microbial analysis. However, due to the impenetrable shell of fungi the direct identification of fungi remains challenges. Targeting on this problem, the yeast Saccharomyces cerevisiae (S. cerevisiae) was selected as a model fungus, and a new fungal cell membrane disruption reagent C18-G1 was used before MALDI-MS detection. As a result, much more intensive peaks which distributed in wider m/z range of S. cerevisiae have been identified in comparison with the use of traditional fungal pretreatment methods. Furthermore, a differential peak at m/z 4993 between two subspecies of S. cerevisiae has been identified. The corresponding protein with exclusive sequence of the specific peak was obtained based on MS/MS fragments and database searching. In addition, the method was successfully applied for the discrimination of four commercial yeasts.

Dendritic systems for bacterial outer membrane disruption as a method of overcoming bacterial multidrug resistance

The alarming rise of multi-drug resistant microorganisms has increased the need for new approaches through the development of innovative agents that are capable of attaching to the outer layers of bacteria and causing permanent damage by penetrating the bacterial outer membrane. The permeability (disruption) of the outer membrane of Gram-negative bacteria is now considered to be one of the main ways to overcome multidrug resistance in bacteria. Natural and synthetic permeabilizers such as AMPs and dendritic systems seem promising. However, due to their advantages in terms of biocompatibility, antimicrobial capacity, and wide possibilities for modification and synthesis, highly branched polymers and dendritic systems have gained much more interest in recent years. Various forms of arrangement, and structure of the skeleton, give dendritic systems versatile applications, especially the possibility of attaching other ligands to their surface. This review will focus on the mechanisms used by different types of dendritic polymers, and their complexes with macromolecules to enhance their antimicrobial effect, and to permeabilize the bacterial outer membrane. In addition, future challenges and potential prospects are illustrated in the hope of accelerating the advancement of nanomedicine in the fight against resistant pathogens.

Amphiphilic dendrimers against antibiotic resistance: light at the end of the tunnel?

With the alarming and prevailing antimicrobial resistance (AMR) comes an urgent need for novel antimicrobial agents that are not only effective and robust but also do not induce resistance development. Amphiphilic dendrimers are emerging as a promising new paradigm to combat bacterial AMR. They can mimic antimicrobial peptides to produce potent antibacterial activity yet with a low likelihood of generating resistance. In addition, they are stable against enzymatic degradation thanks to their unique dendritic architecture. Importantly, these amphiphilic dendrimers are composed of distinct hydrophobic and hydrophilic entities bearing dendritic structures, which can be precisely designed and synthesized to optimize the hydrophobic-hydrophilic balance yielding potent antibacterial activity while minimizing adverse effects and drug resistance. In this short review, we present the challenges and current state of research in developing amphiphilic dendrimers as new antibiotic substitutes. We start with a brief overview of the advantages and opportunities associated with using amphiphilic dendrimers to combat bacterial AMR. We then outline the specific considerations and the mechanisms underlying the antibacterial activity of amphiphilic dendrimers. We focus on the importance of the amphiphilic nature of a dendrimer that balances hydrophobicity and hydrophilicity via gauging the hydrophobic entity and the dendrimer generation, branching unit, terminal group and charge to allow high antibacterial potency and selectivity while minimizing toxicity. Finally, we present the future challenges and perspectives for amphiphilic dendrimers as antibacterial candidates for combating AMR.

Ru(II) Complexes with Enaminone Structures for Rapid Sterilization of Staphylococcus aureus and MRSA with Little Accumulation of Drug Resistance

Drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose a serious threat to human life. Therefore, there is urgent need to develop antibiotics with new chemical structures and antibacterial mechanisms, especially those that elicit little drug resistance after long-term use. Herein we synthesized three novel ruthenium complexes (Ru1-Ru3) containing the enaminone structures for the first time. At a concentration of 5 μM, Ru1-Ru3 can lead to a CFU reduction of about 5 log units towards S. aureus and MRSA. Interestingly, Ru3 displayed rapid bactericidal effects and could decrease the CFU numbers of both pathogens by 5 log units within 40 min. The control compounds (Ru4 and Ru5) without the enaminone structures displayed very poor antibacterial activity under the same conditions. Moreover, S. aureus did not show apparent drug resistance towards Ru3 after 20 passages incubation with a sublethal concentration. These results highlight the critical role of enaminone structures for antibacterial applications.

Guanidinium-Perfunctionalized Polyhedral Oligomeric Silsesquioxanes as Highly Potent Antimicrobials against Planktonic Microbes, Biofilms, and Coronavirus

Supramolecules have been drawing increasing attention recently in addressing healthcare challenges caused by infectious pathogens. We herein report a novel class of guanidinium-perfunctionalized polyhedral oligomeric silsesquioxane (Gua-POSS) supramolecules with highly potent antimicrobial activities. The modular structure of Gua-POSS Tm-Cn consists of an inorganic T10 or T8 core (m = 10 or 8), flexible linear linkers of varying lengths (n = 1 or 3), and peripherally aligned cationic guanidinium groups as the membrane-binding units. Such Gua-POSS supramolecules with spherically arrayed guanidinium cations display high antimicrobial potency against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, as well as fungus (Candida albicans), with the best showing excellently low minimal inhibitory concentrations (MICs) of 1.7-6.8 μM in media, yet with negligible hemolytic activity and low in vitro cytotoxicity to mammalian cells. More significantly, they can inhibit biofilm formation at around their MICs and near-completely break down preestablished difficult-to-break biofilms at 250 μg mL^-1 (∼50 μM). Their strong antiviral efficacy was also experimentally demonstrated against the enveloped murine hepatitis coronavirus as a surrogate of the SARS-CoV species. Overall, this study provides a new design approach to novel classes of sphere-shaped organic-inorganic hybrid supramolecular materials, especially for potent antimicrobial, anti-biofilm, and antiviral applications.

Self-Assembled Cationic Nanoparticles Combined with Curcumin against Multidrug-Resistant Bacteria

The overuse of antibiotics exacerbates the development of antibiotic-resistant bacteria, threatening global public health, while most traditional antibiotics act on specific targets and sterilize through chemical modes. Therefore, it is a desperate need to design novel therapeutics or extraordinary strategies to overcome resistant bacteria. Herein, we report a positively charged nanocomposite PNs-Cur with a hydrodynamic diameter of 289.6 nm, which was fabricated by ring-opening polymerization of ε-caprolactone and Z-Lys-N-carboxyanhydrides (NCAs), and then natural curcumin was loaded onto the PCL core of PNs with a nanostructure through self-assembly, identified through UV-vis, and characterized by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Especially, the self-assembly dynamics of PNs was simulated through molecular modeling to confirm the formation of a core-shell nanostructure. Biological assays revealed that PNs-Cur possessed broad-spectrum and efficient antibacterial activities against both Gram-positive and Gram-negative bacteria, including drug-resistant clinical bacteria and fungus, with MIC values in the range of 8-32 μg/mL. Also, in vivo evaluation showed that PNs-Cur exhibited strong antibacterial activities in infected mice. Importantly, the nanocomposite did not indeed induce the emergence of drug-resistant bacterial strains even after 21 passages, especially showing low toxicity regardless of in vivo or in vitro. The study of the antibacterial mechanism indicated that PNs-Cur could indeed destruct membrane potential, change the membrane potential, and cause the leakage of the cytoplasm. Concurrently, the released curcumin further plays a bactericidal role, eventually leading to bacterial irreversible apoptosis. This unique bacterial mode that PNs-Cur possesses may be the reason why it is not easy to make the bacteria susceptible to easily produce drug resistance. Overall, the constructed PNs-Cur is a promising antibacterial material, which provides a novel strategy to develop efficient antibacterial materials and combat increasingly prevalent bacterial infections.

Photosensitizer-Polypeptide Conjugate for Effective Elimination of Candida albicans Biofilm

Persistent fungal infections caused by biofilms seriously endanger human health. In this study, a photosensitizer-polypeptide conjugate (PPa-cP) comprising a photosensitizer, pyropheophorbide a (PPa), and a cationic polypeptide (cP) is readily synthesized for effective antifungal and antibiofilm treatment. Compared with free PPa, the cationic PPa-cP shows enhanced binding ability to the negatively charged surface of Candida albicans (C. albicans) through electrostatic interactions. As a result, PPa-cP exhibits effective antifungal efficiency against both C. albicans and fluconazole-resistant C. albicans in vitro under light irradiation. The minimum inhibitory concentration (MIC) of PPa-cP for both C. albicans and fluconazole-resistant C. albicans is 1 µm. In addition, PPa-cP also shows improved penetration in a C. albicans biofilm, thus effectively eliminating the C. albicans biofilm by photodynamic effects. More importantly, PPa-cP demonstrats significantly enhanced therapeutic effects in a fluconazole-resistant C. albicans-infected rat model with minimal side effects. In conclusion, the current work presents an effective strategy to combat biofilm infections associated with biomedical equipment.

Dynamic self-assembling supramolecular dendrimer nanosystems as potent antibacterial candidates against drug-resistant bacteria and biofilms

The alarming and prevailing antibiotic resistance crisis urgently calls for innovative "outside of the box" antibacterial agents, which can differ substantially from conventional antibiotics. In this context, we have established antibacterial candidates based on dynamic supramolecular dendrimer nanosystems self-assembled with amphiphilic dendrimers composed of a long hydrophobic alkyl chain and a small hydrophilic poly(amidoamine) dendron bearing distinct terminal functionalities. Remarkably, the amphiphilic dendrimer with amine terminals exhibited strong antibacterial activity against both Gram-positive and Gram-negative as well as drug-resistant bacteria, and prevented biofilm formation. Multidisciplinary studies combining experimental approaches and computer modelling together demonstrate that the dendrimer interacts and binds via electrostatic interactions with the bacterial membrane, where it becomes enriched and then dynamically self-assembles into supramolecular nanoassemblies for stronger and multivalent interactions. These, in turn, rapidly promote the insertion of the hydrophobic dendrimer tail into the bacterial membrane thereby inducing bacterial cell lysis and constituting powerful antibacterial activity. Our study presents a novel concept for creating nanotechnology-based antibacterial candidates via dynamic self-assembly and offers a new perspective for combatting recalcitrant bacterial infection.

A cationic BODIPY photosensitizer decorated with quaternary ammonium for high-efficiency photodynamic inhibition of bacterial growth

On account of the constant evolution of antibiotic-resistant bacteria, the effects of existing antibacterial materials are being gradually weakened, and the difficulty in curing infectious diseases is increasing. Therefore, more novel antibacterial materials or methods are eagerly required to combat microbial infections. Recently, the advantages of photodynamic therapy in the antibacterial field have gradually been validated. Herein, a trimethylamine (TMA) salt-modified 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) photosensitizer (BODIPY-TMA) was synthesized for antibacterial applications. Due to the positive charge of the TMA group, enhanced interactions were observed between the prepared BODIPY-TMA nanoparticles (BODIPY-TMA NPs) and negatively-charged bacterial membranes. The BODIPY-TMA NPs showed much better antibacterial effect toward both S. aureus and E. coli compared with their BODIPY-Br NPs counterpart without a positive charge. Moreover, the BODIPY-TMA NPs efficiently prevented the formation of biofilms and destroyed pre-established biofilms. Thus, such positively-charged photosensitizers may pave the way for the exploration of highly effective antibacterial agents.

Cationic Amphiphilic Dendrons with Anticancer Activity

Cancer has become the leading cause of human death worldwide, and there is an urgent need to design and develop new oncology drugs. In this study, we report series of cationic amphiphilic dendrons with different hydrophobic alkyl chains (C_n) and different generations (G_x) and demonstrate their use for anticancer applications. The results revealed that lower-generation dendrons (G₁) with a longer hydrophobic alkyl chain (C₁₂ and C₁₈) have stronger antitumor activity. Among these dendrons, a lead candidate C₁₂-G₁ was identified that demonstrated excellent broad-spectrum antitumor activity in 7 cancer cell lines including highly metastatic tumor cells, while simultaneously, hemolysis was negligible. Mechanistic studies showed that C₁₂-G₁ could lead to cytoplasmic leakage and induce cancer cell necrosis through membrane disruption. In addition, C₁₂-G₁ showed potent inhibition of tumor growth in a B16-F10 melanoma model. In conclusion, these findings demonstrate that the cationic amphiphilic dendron might be a promising agent for anticancer application.

Photosensitizer-Polypeptides Conjugate with Synergistic Antibacterial Efficacy

Recently, continuous emergence of resistant bacteria has appeared as one of the most serious threats to human health. Therefore, systematic exploration of new antibacterial materials is of guiding significance. In this study, a series of photosensitizer-polypeptides conjugate (PPa-cP) was readily synthesized through the simple ring-opening reactions to realize the synergistic antibacterial effects toward Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) under light irradiation. Compared with free PPa, the cationic PPa-cP showed enhanced binding ability with the negative surface of S. aureus through electrostatic interaction, exhibiting effective antibacterial activity against both S. aureus and MRSA in vitro under light irradiation. Among the synthesized PPa-cP, PPa-cP5 with the degree of polymerization of 37 and modified with 1-methylimidazole side group exhibited the best antibacterial activity with a minimum inhibitory concentration (MIC) value of 2 μM without light irradiation and 0.25 μM with light irradiation. Moreover, PPa-cP5 showed good hemocompatibility. The above-mentioned results elucidate that the positively charged PPa-cP5 could significantly increase the efficiency of photodynamic therapy and effectively eradicate S. aureus biofilm due to its potent penetration ability into S. aureus biofilms. Overall, the present study establishes an efficient strategy for treatment of S. aureus and S. aureus biofilm infections. This article is protected by copyright. All rights reserved.