Cc-CATH2

As the most common fungal pathogen of humans, severe drug resistance has emerged in the clinically isolated Candida albicans, which lead to the urgency to develop novel antifungal agents. Here, four our previously characterized cathelicidins (cathelicidin-BF, Pc-CATH1, Cc-CATH2, Cc-CATH3) were selected and their antifungal activities against C. albicans were evaluated in vitro and in vivo using amphotericin B and LL-37 as control. Results showed that all four cathelicidins could eradicate standard and clinically isolated C. albicans strains with most MIC values ranging from 1 to 16 μg/ml, in less than 0.5 h revealed by time-kill kinetic assay. Four peptides only exhibited slight hemolytic activity with most HC50 > 200 μg/ml, and retained potent anti-C. albicans activity at salt concentrations below and beyond physiological level. In animal experiment, 50 mg/kg administration of the four cathelicidins could significantly reduce the fungal counts in a murine oral candidiasis model induced by clinically isolated C. albicans. The antibiofilm activity of cathelicidin-BF, the most potent among the five peptides was evaluated, and result showed that cathelicidin-BF strongly inhibited C. albicans biofilm formation at 20 μg/ml. Furthermore, cathelicidin-BF also exhibited potent anti-C. albicans activity in established biofilms as measured by metabolic and fluorescent viability assays. Structure-function analyses suggest that they mainly adopt an α-helical conformations, which enable them to act as a membrane-active molecule. Altogether, the four cathelicidins display great potential for antifungal agent development against candidiasis.

Cathelicidins comprise a family of antimicrobial peptides sharing a highly conserved cathelin domain, which play a central role in the early innate host defense against infection. In the present study, we report three novel avian cathelicidin orthologs cloned from a constructed spleen cDNA library of Coturnix coturnix, using a nested-PCR-based cloning strategy. Three coding sequences containing ORFs of 447, 465 and 456 bp encode three mature antimicrobial peptides (named Cc-CATH1, 2 and 3) of 26, 32 and 29 amino acid residues, respectively. Phylogenetic analysis indicated that precursors of Cc-CATHs are significantly conserved with known avian cathelicidins. Synthetic Cc-CATH2 and 3 displayed broad and potent antimicrobial activity against most of the 41 strains of bacteria and fungi tested, especially the clinically isolated drug-resistant strains, with minimum inhibitory concentration values in the range 0.3-2.5 μm for most strains with or without the presence of 100 mm NaCl. Cc-CATH2 and 3 showed considerable reduction of cytotoxic activity compared to other avian cathelicidins, with average IC(50) values of 20.18 and 17.16 μm, respectively. They also exerted a negligible hemolytic activity against human erythrocytes, lysing only 3.6% of erythrocytes at a dose up to 100 μg·mL(-1) . As expected, the recombinant Cc-CATH2 (rCc-CATH2) also showed potent bactericidal activity. All these features of Cc-CATHs encourage further studies aiming to estimate their therapeutic potential as drug leads, as well as coping with current widespread antibiotic resistance, especially the new prevalent and dangerous 'superbug' that is resistant to almost all antibiotics.