Miltefosine exhibits fungicidal activity through oxidative stress generation and Aif1 activation in Candida albicans

Invasive candidiasis is the most common and serious fungal disease worldwide, and the development of antifungal drug resistance in Candida spp. is an emerging problem. Miltefosine, approved as an orphan drug for the therapy of invasive candida infections by the US Food and Drug Administration, has broad-spectrum antifungal activity, but its mechanism of action is unclear. This study evaluated the antifungal drug susceptibility of azole-resistant Candida spp. isolates and found that miltefosine showed good activity, with a geometric mean value of 2 µg/mL. Miltefosine was found to increase production of intracellular reactive oxygen species (ROS) and induce apoptosis in Candida albicans. RNA sequencing (RNA-Seq) analysis and iTRAQ-labelling-based quantitative proteomic mass spectrometry analysis were undertaken. Aif1 and the oxidative stress pathway involved in miltefosine-mediated apoptosis were identified using global transcriptomic and proteomic combined screening. Miltefosine increased mRNA and protein expressions of Aif1. The localization of Aif1 was examined using confocal microscopy, and the GFP-Aif1 fusion protein was found to be translocated from the mitochondria to the nucleus when sensing miltefosine. Next, the pex8 Δ/Δ strain was constructed, and the minimum inhibitory concentration of miltefosine was found to decrease four-fold (from 2 to 0.5 µg/mL) and the intracellular ROS increased significantly after knocking out the PEX8 gene. Moreover, miltefosine was found to trigger Hog1 phosphorylation. These findings indicate that Aif1 activation and the Pex8-mediated oxidative stress pathway are the mechanisms of action of miltefosine on C. albicans. The results help to aid understanding of the mechanisms by which miltefosine acts on fungi.