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Published on: February 14, 2018
Antifungal activity of eumelanin-inspired indoylenepheyleneethynylene against Cryptococcus neoformans
Brittney N Conn1, Jacob A Lieberman1, Priscilla Chatman1
1Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK, United States.
Abstract:
Cryptococcus neoformans is an opportunistic fungal pathogen that causes meningitis in >152,000 immunocompromised individuals annually, leading to 112,000 yearly deaths. The four classes of existing antifungal agents target plasma membrane sterols (ergosterol), nucleic acid synthesis, and cell wall synthesis. Existing drugs are not highly effective against Cryptococcus, and antifungal drug resistance is an increasing problem. A novel antimicrobial compound, a eumelanin-inspired indoylenepheyleneethynylene, EIPE-1, was synthesized and has antimicrobial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MSRA), but not towards Gram-negative organisms. Based on EIPE-1's antibacterial activity, we hypothesized that EIPE-1 could have antifungal activity. For these studies, we tested EIPE-1 against C. neoformans strain H99 and 6 additional cryptococcal clinical isolates. We examined antifungal activity, cytotoxicity, effects on fungal gene expression, and mechanism of action of EIPE-1. Results showed that EIPE-1 has fungicidal effects on seven cryptococcal strains with MICs ranging from 1.56 to 3.125 μg/mL depending on the strain, and it is non-toxic to mammalian cells. We conducted scanning and transmission electron microscopy on the exposed cells to examine structural changes to the organism following EIPE-1 treatment. Cells exposed displayed structural changes to their cell wall and membranes, with internal contents leaking out of the cells. To understand the effect of EIPE-1 on fungal gene expression, RNA sequencing was conducted. Results showed that EIPE-1 affects several processes involved stress response, ergosterol biosynthesis, capsule biosynthesis, and cell wall attachment and remodeling. Therefore, our studies demonstrate that EIPE-1 has antifungal activity against C. neoformans, which affects both cellular structure and gene expression of multiple fungal pathways involved in cell membrane stability and viability.
Insights
A novel compound, EIPE-1, shows potent antifungal activity against Cryptococcus neoformans, a major cause of fungal meningitis. This compound is non-toxic to human cells and disrupts fungal cell structure and gene expression.
Area of Science:
- Mycology
- Antimicrobial drug discovery
- Medical mycology
Background:
- Cryptococcus neoformans causes life-threatening meningitis in immunocompromised individuals.
- Existing antifungal drugs have limited efficacy and face increasing resistance.
- Novel therapeutic strategies are urgently needed to combat cryptococcal infections.
Purpose of the Study:
- To evaluate the antifungal activity of a novel eumelanin-inspired compound, EIPE-1, against Cryptococcus neoformans.
- To determine the mechanism of action and cytotoxicity of EIPE-1.
- To assess the impact of EIPE-1 on fungal gene expression.
Main Methods:
- Antifungal susceptibility testing (MIC determination) against multiple C. neoformans strains.
- Cytotoxicity assays using mammalian cells.
- Scanning and transmission electron microscopy to observe cellular structural changes.
- RNA sequencing to analyze gene expression alterations.
Main Results:
- EIPE-1 demonstrated potent fungicidal activity against seven C. neoformans strains, with MICs between 1.56-3.125 μg/mL.
- EIPE-1 exhibited no toxicity to mammalian cells.
- Microscopy revealed structural damage to the fungal cell wall and membrane, leading to leakage of cellular contents.
- RNA sequencing indicated that EIPE-1 affects stress response, ergosterol and capsule biosynthesis, and cell wall remodeling pathways.
Conclusions:
- EIPE-1 is a promising antifungal agent with a novel mechanism of action against Cryptococcus neoformans.
- Its non-toxicity and disruption of key fungal pathways suggest potential for developing new treatments for cryptococcal meningitis.
