PROJECT SUMMARY / ABSTRACT Invasive candidiasis is a disease associated with significant morbidity and mortality, with only 3 classes of antifungals available for treatment. While Candida albicans remains the most common species associated with this disease, other non-albicans Candida species are emerging or growing in prevalence. The global emergence of Candida auris, a species with a high rate of multi-drug resistance capable of nosocomial transmission, and reports of Candida glabrata infections resistant to both azoles and echinocandins, highlight the critical need for new classes of antifungal drugs that can combat resistance and treat invasive fungal diseases. AimMax Therapeutics is developing a novel class of promising antifungal peptides that are differentiated from other antimicrobial peptides in development. Peptides have been considered as promising therapeutics because of their novel mechanisms of action, rapid cidality, low propensity for resistance development and low potential for drug-drug interactions. However, there are certain liabilities associated with historical antimicrobial peptides as systemic therapeutics, including propensity for lysis of human cell membranes causing toxicity and degradation by circulating proteases and peptidases. Our preliminary studies have shown that: 1) several of the AimMax peptides have antifungal activity across Candida species, including activity against resistant strains, 2) this activity is rapidly fungicidal in nature, 3) there is no cell lysis or intracellular cytotoxicity against human cells and they are well-tolerated following repeat dosing in vivo, 4) they are salt tolerant and retain activity under physiological conditions, and 5) they can be modified to increase stability against proteolytic degradation and demonstrate good plasma exposure in vivo. The objective of this proposal is to optimize the peptides by enhancing antifungal activity and microbiological profile, while maintaining safety (no toxicity) and minimizing proteolytic instability and undesirable physicochemical properties. These studies are essential to select potent antifungal peptides to combat resistance and ensure that they are “druggable” for further development. The objectives of the proposal will be achieved by rational peptide design and structure-activity relationship analysis using data from a series of in vitro and in vivo screening assessments. Peptides selected based on pre-determined criteria will undergo expanded evaluations. Together, these studies will form the basis of candidate selection for further development and IND-enabling work in a Phase 2 SBIR application. The ultimate goal of this program is to develop a broad- spectrum antifungal drug that will address the rising threat of drug resistance in Candida species and provide an alternative treatment option for life-threatening invasive candidiasis.