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Discovery and Characterization of a Rapidly Fungicidal and Minimally Toxic Peptoid against Cryptococcus neoformans
R Madison Green1, Kevin L Bicker1
1Department of Chemistry, Middle Tennessee State University, 1301 E. Main St., Murfreesboro, Tennessee 37132, United States.
Abstract:
A limited number of antifungals are available to treat infections caused by fungal pathogens such as Cryptococcus neoformans and Candida albicans. Current clinical antifungals are generally toxic, and increasing resistance to these therapies is being observed, necessitating new, effective, and safe antifungals. Peptoids, or N-substituted glycines, have shown promise as antimicrobial agents against bacteria, fungi, and parasites. Herein we report the discovery and characterization of an antifungal peptoid termed RMG8-8. This compound was originally discovered from a combinatorial peptoid library using the Peptoid Library Agar Diffusion assay to screen against C. albicans. Though the efficacy of RMG8-8 against C. albicans was modest (25 μg/mL), the efficacy against C. neoformans was excellent (1.56 μg/mL). Cytotoxicity against a panel of cell lines proved RMG8-8 to be minimally toxic, with selectivity ratios ranging from 34 to 121. Additional studies were carried out to determine the pharmacological importance of each peptoid monomer in RMG8-8, characterize the killing kinetics of this compound against C. neoformans (t 1/2 = 6.5 min), and evaluate plasma protein binding and proteolytic stability. Finally, a liposomal lysis assay suggested that RMG8-8 likely exerts fungal killing through membrane permeabilization, the generally accepted mechanism of action for most antimicrobial peptides and peptoids.
Insights
A novel antifungal peptoid, RMG8-8, shows potent activity against Cryptococcus neoformans and minimal toxicity. This discovery offers a promising new avenue for treating challenging fungal infections.
Area of Science:
- Medicinal Chemistry
- Antimicrobial Research
- Drug Discovery
Background:
- Limited antifungal options exist, with increasing resistance and toxicity issues.
- Peptoids (N-substituted glycines) show potential as broad-spectrum antimicrobial agents.
- Development of new, safe, and effective antifungals is urgently needed.
Purpose of the Study:
- To discover and characterize a novel antifungal peptoid.
- To evaluate the efficacy and safety of the identified peptoid against key fungal pathogens.
- To elucidate the mechanism of action and pharmacokinetic properties of the antifungal peptoid.
Main Methods:
- Screening of a combinatorial peptoid library using the Peptoid Library Agar Diffusion assay against Candida albicans.
- Antifungal efficacy testing against Candida albicans and Cryptococcus neoformans.
- Cytotoxicity assays on various cell lines, pharmacokinetic profiling, and liposomal lysis assays.
Main Results:
- The peptoid RMG8-8 demonstrated excellent efficacy against Cryptococcus neoformans (1.56 μg/mL) and modest efficacy against Candida albicans (25 μg/mL).
- RMG8-8 exhibited minimal toxicity, with selectivity ratios ranging from 34 to 121.
- Pharmacological studies indicated rapid killing kinetics (t 1/2 = 6.5 min) and likely membrane permeabilization as the mechanism of action.
Conclusions:
- RMG8-8 is a promising novel antifungal agent with potent activity against Cryptococcus neoformans and a favorable safety profile.
- The findings support peptoids as a viable class of compounds for developing new antifungal therapies.
- Further investigation into RMG8-8 and related peptoids could lead to effective treatments for invasive fungal infections.
