Natural products are the major source of currently available drugs. However, screening natural product presents several challenges, including the time-consuming and labor-intensive steps required for the isolation of a drug from crude extracts as well as the differences between the activities of compounds in vitro and in vivo. To address these challenges, we used silkworm larvae infected with Aspergillus fumigatus to screen a natural products library for potent drugs to treat invasive aspergillosis. A rationally designed library was constructed using numerous, geographically diverse fungal species and then screened to collect extracts of microorganisms that had detectable anti-Aspergillus activity. We evaluated this library using cultures of A. fumigatus and a silkworm model system of A. fumigatus infection. With this model, we identified the novel antifungal compound ASP2397 that not only cured infected silkworm larvae but also increased the rates of survival of mice infected with A. fumigatus. These findings strongly support the utility of the silkworm screening system for the simple and rapid isolation of antibiotics from natural products libraries.

Novel antifungal lipopeptides, FR227673 and FR190293, were isolated from the fermentation broths of fungal strains Chalara sp. No. 22210 and Tolypocladium parasiticum No. 16616, respectively. These compounds have the same cyclic peptide nuclear structure as FR901379, with different side chains, and showed antifungal activity against Aspergillus fumigatus and Candida albicans attributed to inhibition of 1,3-b-glucan synthesis.

Novel antifungal lipopeptides, FR220897 and FR220899, were isolated from the fermentation broth of a fungal strain No. 14573. This strain was identified as Coleophoma empetri No. 14573 from morphological and physiological characteristics. FR220897 and FR220899 showed antifungal activities against Aspergillus fumigatus and Candida albicans attributed to inhibition of 1,3-bglucan synthesis. Furthermore, FR220897 was effective in a murine model of systemic candidiasis.

An antifungal antibiotic, FR207944, was isolated from the culture broth of a fungal strain Chaetomium sp. no. 217. FR207944 is a triterpene glucoside with antifungal activity against Aspergillus fumigatus and Candida albicans. Specifically, FR207944 exhibits in vitro and in vivo antifungal activity against A. fumigatus. The effects of FR207944 on the morphology of A. fumigatus were shown to be similar to those of FR901379, a known 1,3-beta-glucan synthase inhibitor. The MECs of FR207944 against A. fumigatus FP1305 and C. albicans FP633 in micro-broth dilution test were 0.039 and 1.6 mug/ml respectively. FR207944 showed good potency by subcutaneous injection and oral administration against A. fumigatus in a murine systemic infection model, with ED(50)s of 5.7 and 17 mg/kg respectively.

Novel antifungal lipopeptides, FR209602, FR209603 and FR209604, were isolated from the fermentation broth of a fungal strain No. 738 which was identified as Coleophoma crateriformis from morphological and physiological characteristics. The antibiotics were purified by solvent extraction, HP-20, YMC-ODS and silica gel column chromatography and lyophilization. These compounds were structurally similar to FR901379 previously reported by ourselves which had a sulfate residue in the cyclic peptide portion.