Screening of chemical libraries for new antifungal drugs against Aspergillus fumigatus reveals sphingolipids are involved in the potential mechanism of action of miltefosine

Aspergillus fumigatus is an important fungal
pathogen and the main etiological agent of aspergillosis, a disease
characterized by a noninvasive process that can evolve to a more severe clinical
manifestation called invasive pulmonary aspergillosis (IPA) in
immunocompromised patients. The antifungal arsenal to threat aspergillosis is
very restricted. Azoles are the main therapeutic approach to control IPA, but
the emergence of azole-resistant A.
fumigatus isolates has significantly increased over the last decades.
Therefore, new strategies are necessary to combat aspergillosis and drug
repurposing has emerged as an efficient and alternative approach for
identifying new antifungal drugs. Here, we used a screening approach to analyze
A. fumigatus in vitro susceptibility
to 1,127 compounds. A. fumigatus was susceptible
to 10 compounds, including miltefosine, a drug that displayed fungicidal
activity against A. fumigatus. By
screening an A. fumigatus
transcription factor null library, we identified a single mutant, which has the
smiA (sensitivity to miltefosine)
gene deleted, conferring a phenotype of susceptibility to miltefosine. The
transcriptional profiling (RNA-seq) of the wild-type and the ΔsmiA strains and the
Chromatin Immunoprecipitation coupled to next generation sequencing (ChIP-Seq)
of a SmiA-tagged strain exposed to miltefosine revealed genes of the
sphingolipids pathway that are directly or indirectly regulated by SmiA.
Sphingolipids analysis demonstrated that the mutant has overall decreased
levels of sphingolipids when growing in the presence of miltefosine. The
identification of SmiA represents the first genetic element described and
characterized which plays a direct role in miltefosine response in fungi.