Proline-Modified RWn Peptides: Enhanced Antifungal Efficacy and Synergy with Conventional Antibiotics for Combating Resistant Fungal Infections

<i>Candida albicans</i> (Ca) and <i>Cryptococcus neoformans</i> (Cn) infections pose a growing threat due to rising antifungal resistance. This study explores a new class of antifungal agents, the RWn series (n = 4, 6, 8) peptides. These synthetic peptides were evaluated for their ability to inhibit Ca and Cn growth. All peptides except RW₄ displayed antifungal activity, with RW₆ exhibiting exceptional potency against Cn. Importantly, the incorporation of a proline residue significantly reduced cytotoxicity while maintaining antifungal activity against Cn for all RWnP peptides. Notably, RW₆P demonstrated broad-spectrum activity against both Ca and Cn with low minimum inhibitory concentrations (MICs) and minimal toxicity. Furthermore, combining RW6P with trace amounts of traditional antibiotics (penicillin, vancomycin, and ampicillin) achieved synergistic effects, significantly reducing MICs against both fungi. These findings suggest that RWnP peptides, particularly RW6P, have promising potential as novel antifungal agents due to their high potency, broad-spectrum activity, and ability to resensitize fungi to existing antibiotics.