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Australian Journal of Chemistry Australian Journal of Chemistry Society
An international journal for chemical science
RESEARCH ARTICLE (Open Access)

Directed chemical dimerisation enhances the antibacterial activity of the antimicrobial peptide MSI-78(4–20)

Rong Li A B # , Thomas N.G. Handley A # , Wenyi Li https://orcid.org/0000-0003-3584-0301 C * , Neil M. O’Brien-Simpson D , Mohammed Akhter Hossain A E and John D. Wade https://orcid.org/0000-0002-1352-6568 A E *
+ Author Affiliations
- Author Affiliations

A Florey Institute of Neuroscience and Mental Health, University of Melbourne, Vic. 3010, Australia.

B Department of Biochemistry and Pharmacology, University of Melbourne, Vic. 3010, Australia.

C Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Vic. 3086, Australia.

D ATCV (Antimicrobial and Cancer Therapeutics and Vaccines) Research Group, Division of Basic and Clinical Oral Sciences, The Melbourne Dental School, Royal Dental Hospital, University of Melbourne, Carlton, Vic. 3053, Australia.

E School of Chemistry, University of Melbourne, Vic. 3010, Australia.

# These authors contributed equally to this paper

Handling Editor: Mibel Aguilar

Australian Journal of Chemistry 76(8) 455-464 https://doi.org/10.1071/CH23022
Submitted: 31 January 2023  Accepted: 20 March 2023   Published: 31 May 2023

© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Antimicrobial resistance (AMR) is on the rise, leading to 700 000 deaths worldwide in 2020. Antimicrobial peptides (AMPs) are antibiotic agents that are active against multi-drug resistant pathogens and also have a reduced risk of AMR development. Previous studies have shown that dimerisation of the proline-rich antibacterial peptide (PrAMP) Chex1–Arg20 can enhance its antimicrobial activity while also reducing its toxicity. To determine if dimerisation via a simple disulfide bond can similarly improve other classes of AMPs, the α-helical cationic peptide MSI-78(4–20) was used as a model. The monomer alone, an S-carboxamidomethyl-capped N-terminal Cys–MSI-78(4–20) analogue and the disulfide-linked dimer were successfully synthesised and their antimicrobial activity and toxicity were determined. It was shown that dimerisation enhanced antimicrobial activity against the Gram-positive opportunistic pathogen Staphylococcus aureus ATCC 29213, the Gram-negative bacteria Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 47615. The peptides showed no significant haemolytic activity with red blood cells and only induced 50% lactate dehydrogenase (LDH) release in mammalian cells at the highest tested concentration, 15 µM. The MSI-78(4–20) dimer was less cytotoxic than the monomer and S-alkyl monomer. Together, the data support the strategy of AMP chemically directed dimerisation as a means of producing potentially more therapeutically useful antimicrobial agents.

Keywords: antimicrobial peptide, antimicrobial resistance, chemical modification, dimer, disulfide dimerisation, infections, membrane active, solid-phase peptide synthesis.


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