Synthetic Antimicrobial Peptides. V. Histidine-containing Antifungal Peptides with a "Linear" Type of Amphipathicity

Objective: In this work, in order to optimize the structure of histidine-containing antifungal peptides with a "linear" type of amphipathicity (LTA), we carried out the synthesis and comparative screening of the anti-fungal activity of a series of histidine-containing SAMPs (F2H7, F2H10, F2H13, F2H16, H10, H10F2) with a "linear" type of amphipathicity that we constructed de novo. We also aimed to study their hemolytic properties, to assess their therapeutic index, and to compare the obtained results with similar data for the antifungal histidine-rich 12-mer peptide P113 (AKRHHGYKRKFH), a drug candidate known as PAC-113, one of the shortest and most active analogues of the natural antifungal histidine-rich peptide Hst 5. Methods: Peptides were synthesized by a solid phase method using a Fmoc-based strategy. To determine the antifungal activity of the peptides, we used the opportunistic fungus strainCandida albicans EMTK 34. The number of microorganisms (titer) in the suspension was determined by optical density at a wavelength of 595 nm. To determine the antifungal activity of the peptides, cell cultures were co-incubated with the studied peptides in 96-well plates. The cells were incubated with the drug for 24 h at 37 degrees C. To assess the antifungal activity of the studied peptides, their minimum inhibitory concentrations (MIC50) were determined, i.e. such peptide concentration at which the growth of microorganisms was suppressed by 50%. To assess the toxicity of the peptides, their hemolytic activity was determined, which was tested against fresh human erythrocytes using a photometric method. To assess the selectivity of the action of peptides, the values of the minimum hemolytic concentration (MHC) of the peptides were determined and the values of their therapeutic index (TI) were calculated as the ratio of the minimum hemolytic concentration (MHC) to the MIC50 value. Results and Discussion: It was shown that the antifungal activity of the studied SAMP-LTA increases with an increase in the number of histidine residues in their composition, reaching the maximum value for the histidine-containing peptide F2H16 (MIC50 = 1.0 mu M). It has been shown that as the chain length of peptides increases, their hemolytic toxicity also increases. The TI values for these peptides were 233, 247, 79, and 60, respec-tively. It has been shown that, against C. albicans, histidine-containing SAMP-LTA derivatives with phenylalanine residues at the N-terminus of the peptide (F2H10) are less effective compared to similar peptides (H10F2) containing phenylalanine residues at the C-terminus. Among the studied peptides, the most active was the H10 peptide (MIC50 = 0.7 mu M), which does not contain phenylalanine residues, which in its antifungal activity is not only more effective than all other histidine-containing peptides, including the F2H16 peptide with 16 histidine residues, but also 4-5 times more effective than the antifungal peptide P113 (MIC50 = 3.4 mu M), a short active fragment of natural Hst 5, well known from the literature. Among all the studied peptides, H10 and P113 have minimal (almost zero) values of hemolytic activity. However, due to its higher antifungal activity, the selectivity of the H10 peptide (TI > 1400) exceeds the selectivity of the P113 peptide (TI > 340) by more than 4 times. Conclusions: Thus, peptide H10, due to its high antifungal activity, low hemolytic toxicity and, accordingly, high therapeutic significance, can be used as a promising antifungal peptide drug.