ASP2397: A Novel Natural Product with Potent Fungicidal Activity against Aspergillus spp. (1)-A New Mode of Action and In Vitro Activity

I. Nakamura, K. Ohsumi, K. Yoshikawa, R. Kanasaki, T. Masaki, S. Takase, M. Hashimoto, A. Fujie, T. Nakai, S. Matsumoto, S. Takeda, S. Akamatsu, S. Uchida, K. Maki; Astellas pharma. Inc., Tsukuba, Japan


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.

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Full conference title: 

54th Interscience Conference of Antimicrobial Agents and Chemotherapy
    • ICAAC 54th (2014)