Background: Anti-aspergillus efficacy of existing antifungal agents for invasive pulmonary aspergillosis (IPA) is still insufficient. Aiming to identify a new anti-aspergillus compound from our natural product library, we discovered ASP2397 (ASP) which is a novel antibiotic isolated from the fungus Acremonium sp. MF-347833. Here we report on its mechanism of action and the antifungal activity of ASP as a potential clinical candidate against IPA. Methods: Susceptibility of medically important Aspergillus spp. to ASP was determined in human serum and RPMI in accordance with CLSI M38-A2 as broth media. Fungicidal activity was examined for growth from germinated conidia by in vitro time-kill assay and kinetic imaging for living cells. The mechanism of action was investigated using UV-induced A. fumigatus resistant mutant (RSV-1) and wild-type gene transfer to RSV-1. Uptake of ASP into germinated conidia was measured by LC/MS/MS. Results: ASP had antifungal activities against A. fumigatus, azole-resistant A. fumigatus, A. terreus, A. flavus, and A. nidulans with an MIC range of 1 to 4 μg/mL in human serum. The in vitro antifungal activity of ASP against the most prevalent Aspergilus spp., A. fumigatus was examined. ASP showed a more rapid onset of inhibition of hyphal elongation from germinated conidia of A. fumigatus than voriconazole (VRCZ). ASP had steep time-kill curves against A. fumigatus with over 1 log10 CFU reduction compared with VRCZ. RSV-1 had a point mutation in a membrane transporter gene which is absent from mammalian cells. Introduction of the wild-type transporter gene into RSV-1 recovered sensitivity for ASP. In an uptake assay, ASP was actively and rapidly incorporated into wild-type A. fumigatus strains. Conclusions: ASP was effective in vitro against a range of frequently occurring Aspergillus spp including azole-resistant A. fumigatus and was actively transported into A. fumigatus hyphae through a transporter. Furthermore, ASP showed a more rapid onset and potent fungicidal effect against A. fumigatus than VRCZ. These results suggest ASP is a potential candidate for anti-aspegillus therapy.
Full conference title:
54th Interscience Conference of Antimicrobial Agents and Chemotherapy
- ICAAC 54th (2014)