Enhanced efficacy of pH-sensitive nystatin liposomes against Cryptococcus neoformans in murine model

OBJECTIVES: To evaluate the efficacy of pH-sensitive liposomes of nystatin against Cryptococcus neoformans infection in a murine model. METHODS: In the present study, we investigated the antifungal activity of nystatin entrapped in pH-sensitive liposomes in a murine model. Mice infected with C. neoformans were treated with nystatin in neutral egg phosphatidylcholine (egg-PC) liposomes, as well as pH-sensitive nystatin liposomes. The anticryptococcal efficacy of liposomal formulations of nystatin was assessed by continued survival and colony-forming units (cfu) in liver and brain of the treated mice. RESULTS: pH-sensitive liposomes of nystatin showed better efficacy compared with its free or egg-PC liposome form against C. neoformans infection in BALB/c mice. Mice treated with pH-sensitive nystatin liposomes showed 80% survival with less fungal burden in liver and brain of treated mice. However, there was only 40% survival in the group of animals treated with egg-PC liposome-intercalated nystatin, whereas its free form had poor efficacy with 20% survival. CONCLUSIONS: The enhanced anticryptococcal efficacy of the pH-sensitive nystatin liposomes can be attributed to the pH-dependent release of the drug in the low pH environment of lysosomes. The destabilization of the pH-sensitive liposomes in the acidic environment of macrophages results in the site-specific targeting of nystatin that improves its intracellular antifungal activity.