The widespread distribution of fungal infections, with their high morbidity and mortality rate, is a global public health problem. The increase in the population of immunocompromised patients combined with the selectivity of currents treatments and the emergence of drug-resistant fungal strains are among the most imperative reasons to develop novel antifungal formulations. Antimicrobial β-peptides are peptidomimetics of natural antimicrobial peptides (AMPs), which have been proposed as developmental platforms to enhance the AMPs selectivity and biostability. Their tunability allows the design of sequences with remarkable activity against a wide spectrum of microorganisms such as the human pathogenic Candida spp., both in planktonic and biofilm morphology. However, the β-peptide’s effect on surrounding host cells remains greatly understudied. Assessments have mainly relied on the extent of hemolysis that a candidate peptide is able to cause. This work investigated the in vitro cytotoxicity of various β-peptides in the Caco-2 and HepG2 mammalian cell lines. Results indicated that the cytotoxic effect of the β-peptides was influenced by cell type and was also correlated to structural features of the peptide such as hydrophobicity. We found that the selectivity of the most hydrophobic β-peptide was 2–3 times higher than that of the least hydrophobic one, for both cell types according to the selectivity index parameter (IC50/MIC). The IC50 of Caco-2 and HepG2 increased with hydrophobicity, which indicates the importance of testing putative therapeutics on different cell types. We report evidence of peptide-cell membrane interactions in Caco-2 and HepG2 using a widely studied β-peptide against C. albicans.

Fungal infections are a pressing concern for human health worldwide, particularly for immunocompromised individuals. Current challenges such as the elevated toxicity of common antifungal drugs and the emerging resistance towards these could be overcome by multidrug therapy. Natural antimicrobial peptides, AMPs, in combination with other antifungal agents are a promising avenue to address the prevailing challenges. However, they possess limited biostability and susceptibility to proteases, which has significantly hampered their development as antifungal therapies. β-peptides are synthetic materials designed to mimic AMPs while allowing high tunability and increased biostability. In this work, we report for the first time the inhibition achieved in Candida albicans when treated with a mixture of a β-peptide model and fluconazole or ketoconazole. This combination treatment enhanced the biological activity of these azoles in planktonic and biofilm Candida, and also in a fluconazole-resistant strain. Furthermore, the in vitro cytotoxicity of the dual treatment was evaluated towards the human hepatoma cell line, HepG2, a widely used model derived from liver tissue, which is primarily affected by azoles. Analyses based on the LA-based method and the mass-action law principle, using a microtiter checkerboard approach, revealed synergism of the combination treatment in the inhibition of planktonic C. albicans. The dual treatment proved to be fungicidal at 48 and 72 h. Interestingly, it was also found that the viability of HepG2 was not significantly affected by the dual treatments. Finally, a remarkable enhancement in the inhibition of the highly azole-resistant biofilms and fluconazole resistant C. albicans strain was obtained.

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