A Plumieridine-Rich Fraction FromAllamanda polyanthaInhibits Chitinolytic Activity and Exhibits Antifungal Properties AgainstCryptococcus neoformans

Cryptococcosis is a fungal infection caused mainly by the pathogenic yeastsCryptococcus neoformansandCryptococcus gattii. The infection initiates with the inhalation of propagules that are then deposited in the lungs. If not properly treated, cryptococci cells can disseminate and reach the central nervous system. The current recommended treatment for cryptococcosis employs a three-stage regimen, with the administration of amphotericin B, flucytosine and fluconazole. Although effective, these drugs are often unavailable worldwide, can lead to resistance development, and may display toxic effects on the patients. Thus, new drugs for cryptococcosis treatment are needed. Recently, an iridoid named plumieridine was found inAllamanda polyanthaseed extract; it exhibited antifungal activity againstC. neoformanswith a MIC of 250 mu g/mL. To address the mode of action of plumieridine, severalin silicoandin vitroexperiments were performed. Through a ligand-based a virtual screening approach, chitinases were identified as potential targets. Confirmatoryin vitroassays showed thatC. neoformanscell-free supernatant incubated with plumieridine displayed reduced chitinase activity, while chitinolytic activity was not inhibited in the insoluble cell fraction. Additionally, confocal microscopy revealed changes in the distribution of chitooligomers in the cryptococcal cell wall, from a polarized to a diffuse cell pattern state. Remarkably, further assays have shown that plumieridine can also inhibit the chitinolytic activity from the supernatant and cell-free extracts of bacteria, insect and mouse-derived macrophage cells (J774.A1). Together, our results suggest that plumieridine can be a broad-spectrum chitinase inhibitor.