P003 Synthetic antifungal peptide mimic kills Candida albicans by targeting protein glycosylation and synergistically prevents infection

Abstract

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PMFungal infections represent a serious burden on human health. Increasing numbers of susceptible hosts, a limited set of approved antifungal drugs which frequently trigger undesired side effects, and the emergence of resistant strains highlight the urgent demand for novel antifungal drug formulations. However, the biological similarity of human and fungal cells hampers the development of new antifungals which do not also harm humans. In nature, organisms in almost all domains of life produce antimicrobial peptides to combat microbial pathogens. Those peptides share certain characteristics, such as being short, amphiphilic molecules with a positive net charge.1 We designed synthetic polyacrylamides which mimic the properties of naturally occurring antifungal peptides. These positively charged, amphiphilic polymers are advantageous over peptides because of their easy synthesis and stability against proteases. Initial structure-activity relationship studies revealed an optimal cLogP (the calculated hydrophobicity of a molecule) around 1.5 to ensure activity against C. albicans and simultaneous biocompatibility with host cells.2 Additionally, shorter polymers with a length of 20 subunits were more effective than their longer versions.2 In terms of their therapeutic index, certain compositions outperformed the broad-spectrum antifungal amphotericin B and were even effective against drug-resistant clinical isolates of C. albicans.2 Candida albicans strains with known antifungal drug-resistance mutations were not affected in their susceptibility to the polymers. Therefore, investigations were carried out to elucidate the mode of action of the polymers. The transcriptome of C. albicans cells treated with subinhibitory concentrations of the polymers revealed an increased expression of genes involved in general stress response and upregulation in protein processing in the endoplasmic reticulum, particularly glycosylation and degradation. These findings, together with electron microscopy observations, indicated damage to the mannoproteins in the cell wall of the fungus. Membrane damage was also observed utilizing a C. albicans strain expressing GFP intracellularly. The in vitro therapeutic potential of the most promising polymer was tested in a human epithelial cell (HEC) model simulating C. albicans infection. The polymer alone was not able to prevent C. albicans infection of HECs. However, the combination of polymer with caspofungin or fluconazole showed very strong synergistic effects at otherwise non-inhibitory concentrations of the individual antifungals, successfully stopping fungal infection in vitro without damaging the HECs. These results underline the potential of synthetic polymers as an alternative treatment for fungal infections with low toxicity to human cells and a novel mode of action.Sources1. Fernández de Ullivarri, M., Arbulu, S., Garcia-Gutierrez, E. and Cotter, P.D. Antifungal peptides as therapeutic agents. Front Cell Infect Microbiol 10, 00 105 (2020).2. Schaefer, S. et al. Rational design of an antifungal polyacrylamide library with reduced host-cell toxicity. ACS Appl Mater Interfaces 13, 27430-27444 (2021).