Session: Poster Session: New Anti-Fungal Agents
Sunday, October 26, 2008: 12:00 AM
Room: Hall C
Background: AN2718 is a member of a new class of antifungals, benzoxaboroles, which inhibit fungal growth by blocking protein synthesis. AN2718 is being developed for the topical treatment of tinea pedis including the hard to treat mocassin-type, which at present is only treatable with oral antifungals. Methods: MICs were determined according to CLSI guidelines. The Candida albicans and Aspergilus fumigatus cytoplasmic leucyl-tRNA synethetases (LeuRS) were over-expressed in E. coli as N-terminal six-histidine-tagged proteins and purified by standard techniques using a nickel column. Enzyme inhibition was determined by the inhibition of leucine incorporation into crude baker’s yeast tRNA measured by TCA precipitation. To obtain a crystal structure for the C. albicans cytoplasmic leucyl-tRNA synthetase we over-expressed the C-terminal six-histidine-tagged editing domain. Results: AN2718 has a broad-spectrum of antifungal activity with MIC90 of 1 μg/mL, 0.25 μg/mL, 1 μg/mL, 0.5 μg/mL for C. albicans (n=100), C. glabrata (n=100), Trichophyton mentagrophytes (n=100) and T. rubrum respectively (n=100). We show that AN2718 inhibits cytoplasmic LeuRS from molds, A. fumigatus, and from yeasts, C. albicans, with an IC50 of 2 μM and 4.2 μM, respectively. An analogue of AN2718, AN3018, was shown by co-crystal structure determination to bind to the editing active site as an adduct with AMP, a surrogate for the terminal ribonucleotide of tRNA. The boron in AN3018 was bound to the cis-diol on the ribose of AMP in the active site. Conclusions: AN2718 Inhibits LeuRS by the OBORT mechanism of trapping tRNALEU in the editing site of LeuRS. AN2718 has good MIC90 activity against the dermatophytes, T. rubrum and T. mentagrophytes, which supports its use as a topical agent to treat tinea pedis.
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