Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

Delivering fluconazole to cryptococcus neoformans in style using pH-responsive lipid nanoparticles (82646)

Sarigama Rajesh 1 , Sheeana Gangadoo 1 , Han Nguyen 1 , Jiali Zhai 1 , Chaitali Dekiwadia 1 , Calum Drummond 1 , James Chapman 1 , Vi Khanh Truong 2 , Nhiem Tran 1
  1. School of Science, RMIT University, Melbourne, VIC, Australia
  2. College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia

Antimicrobial resistance (AMR) is an increasing threat to global health and development, with AMR infections leading to higher morbidity and mortality rates as well as huge burdens on economic and health care systems [1,2]. AMR can occur in life-threatening pathogens such as Cryptococcus neoformans, a yeast-like fungus that causes fatal disease Cryptococcal Meningitis, with numerous reports demonstrating the increased resistance of this fungus against many antifungal treatments such as fluconazole [3].

This work presents a novel approach to improve the delivery of an antifungal agent and increase the drug’s targetability and availability to the infection site. C. neoformans possesses an acidic mucopolysaccharide capsule in its cell wall whereby the fungal cell’s metabolic activity decreases the pH of the surrounding infected site. Exploiting this acidic pH property, we have developed a pH-responsive lipid nanoparticle (LNP) encapsulating fluconazole to inhibit the growth of pathogenic fungi.

The LNP-fluconazole delivery system consists of a neutral lipid monoolein (MO) and a novel ionisable lipid 2-morpholinoethyl oleate (O2ME), where its hexasome structure and negative charge in a neutral pH environment transition to a cubic structure and positive charge in acidic pH. Results showed treatment with the LNP system significantly reduce MIC50 compared to free fluconazole at an acidic pH. Additionally in the acidic environment, the LNP system successfully achieved MIC90, while free fluconazole failed to reduce fungal populations by 90%. The antifungal effects of the LNP system were supported by the confocal laser scanning and scanning electron microscopies, where cells were shrivelled with reduced membrane integrity and cell contents leaking out in acidic pH. Derivatisation and PCA analysis of spectroscopic infrared data suggest a possible mechanism of action of the enhanced antifungal LNP system, which could be due to the disruption and blocking of aromatic amino acid biosynthesis [4]. This current study represents a significant advancement in the delivery of targeted antifungal therapy to combat fungal antimicrobial resistance.

  1. World Health Organization. Antimicrobial resistance; 2020. https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistanceDOI: https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance.
  2. Dadgostar, P. Antimicrobial resistance: implications and costs. Infection and drug resistance 2019, 12, 3903.
  3. Rajasingham, R.; Smith, R. M.; Park, B. J.; Jarvis, J. N.; Govender, N. P.; Chiller, T. M.; Denning, D. W.; Loyse, A.; Boulware, D. R. Global burden of disease of HIV-associated cryptococcal meningitis: an updated analysis. The Lancet infectious diseases 2017, 17 (8), 873-881.
  4. Fernandes, J. D. S.; Martho, K.; Tofik, V.; Vallim, M. A.; Pascon, R. C. The role of amino acid permeases and tryptophan biosynthesis in Cryptococcus neoformans survival. PloS one 2015, 10 (7), e0132369.