Discovery and development of novel antifungal agents for the treatment of Candida auris infections

dc.contributor.authorElgammal, Yehia Abdallahen
dc.contributor.committeechairSeleem, Mohamed Naguieben
dc.contributor.committeememberCaswell, Clayton Christopheren
dc.contributor.committeememberBandara, Aloka BPAen
dc.contributor.committeememberSriranganathan, Nammalwaren
dc.contributor.departmentBiomedical and Veterinary Sciencesen
dc.date.accessioned2025-01-09T09:00:11Zen
dc.date.available2025-01-09T09:00:11Zen
dc.date.issued2025-01-08en
dc.description.abstractFungal infections are one of the leading causes of death in humans, causing infections that range from mild superficial infections to severe, and life-threatening invasive infections that affect the bloodstream and vital organs. Invasive fungal infections have a high mortality rate, leading to approximately 1.5 million deaths annually. The most common pathogens responsible for these infections are Candida, Cryptococcus, and Aspergillus. Currently, treatment options for invasive fungal infections are limited to three main classes of antifungal drugs: azoles, polyenes, and echinocandins. The emergence of new fungal species, such as Candida auris, which displays high resistance and mortality rates (30-60%), has further complicated treatment efforts. Thus, there is a critical need for new therapeutic strategies to combat these life-threatening pathogens. C. auris isolates have demonstrated significant resistance, especially to azoles (fluconazole) and polyenes (amphotericin B, AmB). To address this, we screened approximately 2,600 FDA-approved drugs and clinical compounds to identify agents capable of inhibiting C. auris growth and enhancing or restoring the antifungal activity of existing antifungals. This screening revealed that HIV protease inhibitors, such as lopinavir, atazanavir, saquinavir and ritonavir, significantly enhanced the antifungal activity of azoles (fluconazole, voriconazole, itraconazole, and posaconazole) and polyene (AmB). Mechanistic studies showed that the HIV protease inhibitors inhibited the fungal efflux pump, and interfered with glucose utilization, leading to reduced ATP levels in C. auris. Moreover, HIV protease inhibitors, in combination with AmB, were able to inhibit the virulence factors of Candida species. Furthermore, HIV protease inhibitors, in combination with itraconazole or posaconazole, resulted in a significant reduction of the C. auris burden in mice kidneys. Two additional drugs, darapladib and rilapladib, phospholipase A2 inhibitors, were identified as potent inhibitors of C. auris. Darapladib and rilapladib demonstrated superior killing kinetics compared to itraconazole. Interestingly, C. auris did not develop any detectable resistance to both drugs at sub-inhibitory concentration over 16-passages. Mechanistic studies revealed that darapladib increased the plasma membrane permeability and caused DNA leakage, likely due to a direct interaction with ergosterol, as suggested by competition assays with exogenous ergosterol. We further validated the broad-spectrum, fungicidal, and potent activity of darapladib in combination with AmB, showing significant synergy against multidrug-resistant fungal pathogens, including C. auris, Aspergillus fumigatus and mucormycosis-associated species. Additionally, darapladib demonstrated a superior safety profile compared to AmB, exhibiting lower affinity for cholesterol, and no toxicity in combination with AmB to kidney cells. Finally, rilapladib (at 2× MIC) inhibited the C. auris burden by 1.5 Log10, whereas darapladib (at 2× MIC) achieved complete eradication of the C. auris burden in an in vivo C. elegans model.en
dc.description.abstractgeneralFungi are a group of living organisms that are neither plants nor animals. While Some fungi are beneficial, others can cause serious diseases in humans. Candida auris is a human fungal pathogen that causes serious infections with mortality rate up to 60%. It has become a growing threat to global public health. This pathogen is particularly concerning due to its high virulence, resistance to multiple antifungal drugs, and ability to rapidly spread, often leading to hospital outbreaks. In our current research, we have identified several compounds that either inhibit the growth of C. auris and/or enhance the efficacy of existing antifungals, such as azoles and amphotericin B. We have identified HIV protease inhibitors (lopinavir, atazanavir, saquinavir, and ritonavir) that were able to enhance the antifungal activities of both azoles (fluconazole, itraconazole, voriconazole, and posaconazole) and polyene (amphotericin B) against multidrug-resistant C. auris. The combination of HIV protease inhibitors with amphotericin B inhibited the virulence factors of Candida species, including biofilm and hyphae formation. Two drugs darapladib and rilapladib were found to not only inhibit the growth of C. auris alone but also enhance the antifungal activity of amphotericin B against all medically important fungal pathogens tested. Additionally, we have explored the mechanisms by which these compounds act on the pathogen. Finally, we have confirmed the effectiveness of these drugs in live models, including mice and worms.en
dc.description.degreeDoctor of Philosophyen
dc.format.mediumETDen
dc.identifier.othervt_gsexam:41843en
dc.identifier.urihttps://hdl.handle.net/10919/123974en
dc.language.isoenen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectDrug repurposingen
dc.subjectCandida aurisen
dc.subjectvirulence factorsen
dc.subjectbiofilm formationen
dc.subjectcombination therapyen
dc.subjectantifungal resistanceen
dc.subjectC. elegansen
dc.subjectmouse model of C. auris infectionen
dc.titleDiscovery and development of novel antifungal agents for the treatment of Candida auris infectionsen
dc.typeDissertationen
thesis.degree.disciplineBiomedical and Veterinary Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.nameDoctor of Philosophyen

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