Identification of Anziaic Acid, a Lichen Depside from Hypotrachyna sp., as a New Topoisomerase Poison Inhibitor

Topoisomerase inhibitors are effective for antibacterial and anticancer therapy because they can lead to the accumulation of the intermediate DNA cleavage complex formed by the topoisomerase enzymes, which trigger cell death. Here we report the application of a novel enzyme-based high-throughput screening assay to identify natural product extracts that can lead to increased accumulation of the DNA cleavage complex formed by recombinant Yersinia pestistopoisomerase I as part of a larger effort to identify new antibacterial compounds. Further characterization and fractionation of the screening positives from the primary assay led to the discovery of a depside, anziaic acid, from the lichen Hypotrachyna sp. as an inhibitor for both Y. pestis and Escherichia colitopoisomerase I. In in vitro assays, anziaic acid exhibits antibacterial activity against Bacillus subtilis and a membrane permeable strain of E. coli. Anziaic acid was also found to act as an inhibitor of human topoisomerase II but had little effect on human topoisomerase I. This is the first report of a depside with activity as a topoisomerase poison inhibitor and demonstrates the potential of this class of natural products as a source for new antibacterial and anticancer compounds.

Antibacterial Activity of Extracellular Products from Cyanobacteria.

Cyanobacteria are photosynthetic prokaryotes that can be found in freshwater and marine environments as well as in soil. These organisms produce a variety of different biologically active compounds exhibiting anti-bacterial, anti-fungal and anti-cancer properties among others. In this study, cyanobacterial isolates were screened for their ability to produce extracellular antibacterial products. Cyanobacteria were isolated from fresh water and soil samples collected in the Pembroke Pines, FL area. Twenty- seven strains of cyanobacteria were isolated belonging to the following genera: Limnothrix, Nostoc, Fischerella, Anabaena, Pseudoanabaena, Lyngbya, Leptolyngbya, Tychonema, and Calothrix. Individual strains were grown in liquid culture in laboratory conditions. Following 14-day cultivation, the culture liquid was filtered and tested for activity against the following bacteria: Escherichia coli, Bacillus megatarium, Staphylococcus aureus, and Micrococcus luteus. Among all genera of cyanobacterial strains tested, Fischerella exhibited the greatest inhibitory activity. An attempt was made to isolate the active compound from the culture liquid of the active strains. Lipophilic extracts from culture liquid were obtained from three selected Fischerella strains. The extracts proved to have varying levels of activity against the tested bacteria. Inhibitory activity from all three Fischerella strains was detected against B. megatarium and M luteus. The only strain that was active against S. aureus was Fischerella sp. 114-12 while none of the extracts showed activity against E. coli. This kind of screening has potential pharmaceutical and agricultural benefits, including possible discovery of novel antibiotics.