Melbourne Dental School - Research Publications
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ItemStar-Peptide Polymers are Multi-Drug-Resistant Gram-Positive Bacteria Killers(AMER CHEMICAL SOC, 2022-06-08)Antibiotic resistance in bacteria, especially Gram-positive bacteria like Staphylococcus aureus, is gaining considerable momentum worldwide and unless checked will pose a global health crisis. With few new antibiotics coming on the market, there is a need for novel antimicrobial materials that target and kill multi-drug-resistant (MDR) Gram-positive pathogens like methicillin-resistant Staphylococcus aureus (MRSA). In this study, using a novel mixed-bacteria antimicrobial assay, we show that the star-peptide polymers preferentially target and kill Gram-positive pathogens including MRSA. A major effect on the activity of the star-peptide polymer was structure, with an eight-armed structure inducing the greatest bactericidal activity. The different star-peptide polymer structures were found to induce different mechanisms of bacterial death both in vitro and in vivo. These results highlight the potential utility of peptide/polymers to fabricate materials for therapeutic development against MDR Gram-positive bacterial infections.
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ItemSystematic comparison of activity and mechanism of antimicrobial peptides against nosocomial pathogens(ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER, 2022-03-05)The World Health Organisation has deemed several multi-drug resistant (MDR) nosocomial bacterial pathogens to be of significant threat to human health. A stark increase in morbidity, mortality and the burden to healthcare systems around the world can be attributed to the development of resistance in these bacteria. Accordingly, alternative antimicrobial agents have been sought as an attractive means to combat MDR pathogens, with one such example being antimicrobial peptides (AMPs). Given the reported activity of AMPs, including Pardaxin, MSI-78, dermaseptin-PC (DMPC) and Cecropin B, it is important to understand their activities and modes of action against bacteria for further AMP design. In this study, we compared these AMPs against a panel of nosocomial bacterial pathogens, followed by detailed mechanistic studies. It was found that Pardaxin (1-22) and MSI-78 (4-20) displayed the most pronounced antimicrobial activity against the tested bacteria. The mechanistic studies by membrane permeability and molecular dynamics simulation further confirmed the strong membrane interaction and structure of Pardaxin (1-22) and MSI-78 (4-20), which contributed to their potent activity. This study demonstrated a structure and activity guidance for further design of Pardaxin (1-22) and MSI-78 (4-20) as therapeutics against MDR pathogens. The different effects of DMPC (1-19) and Cecropin B (1-21) on membrane integrity and phospholipid membrane interactions provided critical information for the rational design of next-generation analogues with specificity against either Gram-negative or Gram-positive bacteria.
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ItemNo Preview AvailableDevelopment and application of Diels-Alder adducts displaying AIE properties(CELL PRESS, 2022-02-16)
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ItemThe Potential of Calcium Phosphate Nanoparticles as Adjuvants and Vaccine Delivery Vehicles(FRONTIERS MEDIA SA, 2021-12-22)Vaccination is one of the most efficacious and cost-effective ways to protect people from infectious diseases and potentially cancer. The shift in vaccine design from disrupted whole pathogens to subunit antigens has brought attention on to vaccine delivery materials. For the last two decades, nanotechnology-based vaccines have attracted considerable attention as delivery vehicles and adjuvants to enhance immunogenicity, exemplified with the current COVID vaccines. The nanoparticle vaccines display unique features in protecting antigens from degradation, controlled antigen release and longer persisting immune response. Due to their size, shape and surface charge, they can be outstanding adjuvants to achieve various immunological effects. With the safety and biodegradable benefit of calcium phosphate nanoparticles (CaP NPs), they are an efficient carrier for vaccine design and adjuvants. Several research groups have studied CaP NPs in the field of vaccination with great advances. Although there are several reports on the overview of CaP NPs, they are limited to the application in biomedicine, drug delivery, bone regeneration and the methodologies of CaP NPs synthesis. Hence, we summarised the basic properties of CaP NPs and the recent vaccine development of CaP NPs in this review.
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ItemC-terminus amidation influences biological activity and membrane interaction of maculatin 1.1(SPRINGER WIEN, 2021-05)Cationic antimicrobial peptides have been investigated for their potential use in combating infections by targeting the cell membrane of microbes. Their unique chemical structure has been investigated to understand their mode of action and optimize their dose-response by rationale design. One common feature among cationic AMPs is an amidated C-terminus that provides greater stability against in vivo degradation. This chemical modification also likely modulates the interaction with the cell membrane of bacteria yet few studies have been performed comparing the effect of the capping groups. We used maculatin 1.1 (Mac1) to assess the role of the capping groups in modulating the peptide bacterial efficiency, stability and interactions with lipid membranes. Circular dichroism results showed that C-terminus amidation maintains the structural stability of the peptide (α-helix) in contact with micelles. Dye leakage experiments revealed that amidation of the C-terminus resulted in higher membrane disruptive ability while bacteria and cell viability assays revealed that the amidated form displayed higher antibacterial ability and cytotoxicity compared to the acidic form of Mac1. Furthermore, 31P and 2H solid-state NMR showed that C-terminus amidation played a greater role in disturbance of the phospholipid headgroup but had little effect on the lipid tails. This study paves the way to better understand how membrane-active AMPs act in live bacteria.
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ItemEvaluation of Potential DnaK Modulating Proline-Rich Antimicrobial Peptides Identified by Computational Screening(FRONTIERS MEDIA SA, 2022-04-13)The day is rapidly approaching where current antibiotic therapies will no longer be effective due to the development of multi-drug resistant bacteria. Antimicrobial peptides (AMPs) are a promising class of therapeutic agents which have the potential to help address this burgeoning problem. Proline-rich AMPs (PrAMPs) are a sub-class of AMPs, that have multiple modes of action including modulation of the bacterial protein folding chaperone, DnaK. They are highly effective against Gram-negative bacteria and have low toxicity to mammalian cells. Previously we used an in silico approach to identify new potential PrAMPs from the DRAMP database. Four of these peptides, antibacterial napin, attacin-C, P9, and PP30, were each chemically assembled and characterized. Together with synthetic oncocin as a reference, each peptide was then assessed for antibacterial activity against Gram-negative/Gram-positive bacteria and for in vitro DnaK modulation activity. We observed that these peptides directly modulate DnaK activity independently of eliciting or otherwise an antibiotic effect. Based on our findings, we propose a change to our previously established PrAMP definition to remove the requirement for antimicrobial activity in isolation, leaving the following classifiers: >25% proline, modulation of DnaK AND/OR the 70S ribosome, net charge of +1 or more, produced in response to bacterial infection AND/OR with pronounced antimicrobial activity.
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ItemThe Potential of Modified and Multimeric Antimicrobial Peptide Materials as Superbug Killers(FRONTIERS MEDIA SA, 2022-01-10)Antimicrobial peptides (AMPs) are found in nearly all living organisms, show broad spectrum antibacterial activity, and can modulate the immune system. Furthermore, they have a very low level of resistance induction in bacteria, which makes them an ideal target for drug development and for targeting multi-drug resistant bacteria 'Superbugs'. Despite this promise, AMP therapeutic use is hampered as typically they are toxic to mammalian cells, less active under physiological conditions and are susceptible to proteolytic degradation. Research has focused on addressing these limitations by modifying natural AMP sequences by including e.g., d-amino acids and N-terminal and amino acid side chain modifications to alter structure, hydrophobicity, amphipathicity, and charge of the AMP to improve antimicrobial activity and specificity and at the same time reduce mammalian cell toxicity. Recently, multimerisation (dimers, oligomer conjugates, dendrimers, polymers and self-assembly) of natural and modified AMPs has further been used to address these limitations and has created compounds that have improved activity and biocompatibility compared to their linear counterparts. This review investigates how modifying and multimerising AMPs impacts their activity against bacteria in planktonic and biofilm states of growth.
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ItemEnhancing proline-rich antimicrobial peptide action by homodimerization: influence of bifunctional linker(ROYAL SOC CHEMISTRY, 2022-02-23)Antimicrobial peptides (AMPs) are host defense peptides, and unlike conventional antibiotics, they possess potent broad spectrum activities and, induce little or no antimicrobial resistance. They are attractive lead molecules for rational development to improve their therapeutic index. Our current studies examined dimerization of the de novo designed proline-rich AMP (PrAMP), Chex1-Arg20 hydrazide, via C-terminal thiol addition to a series of bifunctional benzene or phenyl tethers to determine the effect of orientation of the peptides and linker length on antimicrobial activity. Antibacterial assays confirmed that dimerization per se significantly enhances Chex1-Arg20 hydrazide action. Greatest advantage was conferred using perfluoroaromatic linkers (tetrafluorobenzene and octofluorobiphenyl) with the resulting dimeric peptides 6 and 7 exhibiting potent action against Gram-negative bacteria, especially the World Health Organization's critical priority-listed multidrug-resistant (MDR)/extensively drug-resistant (XDR) Acinetobacter baumannii as well as preformed biofilms. Mode of action studies indicated these lead PrAMPs can interact with both outer and inner bacterial membranes to affect the membrane potential and stress response. Additionally, 6 and 7 possess potent immunomodulatory activity and neutralise inflammation via nitric oxide production in macrophages. Molecular dynamics simulations of adsorption and permeation mechanisms of the PrAMP on a mixed lipid membrane bilayer showed that a rigid, planar tethered dimer orientation, together with the presence of fluorine atoms that provide increased bacterial membrane interaction, is critical for enhanced dimer activity. These findings highlight the advantages of use of such bifunctional tethers to produce first-in-class, potent PrAMP dimers against MDR/XDR bacterial infections.
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ItemTumor Associated Macrophages: Origin, Recruitment, Phenotypic Diversity, and Targeting(FRONTIERS MEDIA SA, 2021-12-20)The tumor microenvironment (TME) is known to have a strong influence on tumorigenesis, with various components being involved in tumor suppression and tumor growth. A protumorigenic TME is characterized by an increased infiltration of tumor associated macrophages (TAMs), where their presence is strongly associated with tumor progression, therapy resistance, and poor survival rates. This association between the increased TAMs and poor therapeutic outcomes are stemming an increasing interest in investigating TAMs as a potential therapeutic target in cancer treatment. Prominent mechanisms in targeting TAMs include: blocking recruitment, stimulating repolarization, and depletion methods. For enhancing targeting specificity multiple nanomaterials are currently being explored for the precise delivery of chemotherapeutic cargo, including the conjugation with TAM-targeting peptides. In this paper, we provide a focused literature review of macrophage biology in relation to their role in tumorigenesis. First, we discuss the origin, recruitment mechanisms, and phenotypic diversity of TAMs based on recent investigations in the literature. Then the paper provides a detailed review on the current methods of targeting TAMs, including the use of nanomaterials as novel cancer therapeutics.
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Item(Re)Defining the Proline-Rich Antimicrobial Peptide Family and the Identification of Putative New Members(FRONTIERS MEDIA SA, 2020-12-01)As we rapidly approach a post-antibiotic era in which multi-drug resistant bacteria are ever-pervasive, antimicrobial peptides (AMPs) represent a promising class of compounds to help address this global issue. AMPs are best-known for their membrane-disruptive mode of action leading to bacteria cell lysis and death. However, many AMPs are also known to be non-lytic and have intracellular modes of action. Proline-rich AMPs (PrAMPs) are one such class, that are generally membrane permeable and inhibit protein synthesis leading to a bactericidal outcome. PrAMPs are highly effective against Gram-negative bacteria and yet show very low toxicity against eukaryotic cells. Here, we review both the PrAMP family and the past and current definitions for this class of peptides. Computational analysis of known AMPs within the DRAMP database (http://dramp.cpu-bioinfor.org/) and assessment of their PrAMP-like properties have led us to develop a revised definition of the PrAMP class. As a result, we subsequently identified a number of unknown and unclassified peptides containing motifs of striking similarity to known PrAMP-based DnaK inhibitors and propose a series of new sequences for experimental evaluation and subsequent addition to the PrAMP family.