Lichens: a promising source of antibiotic and anticancer drugs
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Lichens: a promising source of antibiotic and anticancer drugs Gajendra Shrestha • Larry L. St. Clair
Received: 29 August 2012 / Accepted: 21 March 2013 / Published online: 28 March 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract Lichens are symbiotic associations between fungi and a photosynthetic alga and/or cyanobacteria. Lichenized fungi have been found to produce a wide array of secondary metabolites, most of which are unique to the lichenized condition. These secondary metabolites have shown an impressive range of biological activities including antibiotics, antifungal, anti-HIV, anticancer, anti-protozoan, etc. This review focuses primarily on the antibiotic and anticancer properties of lichen secondary chemicals. We have reviewed various publications related to antibiotic and anticancer drug therapies emphasizing results about specific lichens and/or lichen compounds, which microbes or cancer cells were involved and the main findings of each study. We found that crude lichen extracts and various isolated lichen compounds often demonstrate significant inhibitory activity against various pathogenic bacteria and cancer cell lines at very low concentrations. There were no studies examining the specific mechanism of action against pathogenic bacteria; however, we did find a limited number of studies where the mechanism of action against cancer cell lines had been explored. The molecular mechanism of cell death by lichen compounds includes cell cycle arrest, apoptosis, necrosis,
G. Shrestha (&) L. L. St. Clair Department of Biology and the M. L. Bean Life Science Museum, Brigham Young University, Provo, UT 84602, USA e-mail: [email protected]
and inhibition of angiogenesis. Although lichens are a reservoir for various biologically active compounds, only a limited number have been tested for their biological significance. There is clearly an urgent need for expanding research in this area of study, including in depth studies of those compounds which have shown promising results as well as a strong focus on identifying specific mechanisms of action and extensive clinical trials using the most promising lichen based drug therapies followed by large scale production of the best of those compounds. Keywords Lichens Biological role Natural products Secondary metabolites Anti-bacteria Anti-cancer
Introduction Lichens are obligate symbiotic systems consisting of a filamentous fungus and a photosynthetic partner (eukaryotic algae and/or cyanobacterium), and in some cases non-photosynthetic bacteria (Hodkinson and Lutzoni 2009; Selbmann et al. 2010). Lichens are ecologically diverse and are distributed from the tropics to the polar regions (Brodo et al. 2001). The worldwide lichen flora is estimated to include approximately 18,500 species (Boustie and Grube 2005; Feuerer and Hawksworth 2007) and cover about 8 % of the earth’s land surface (Ahmadjian 1995). Lichens are one of the slowest growing symbiotic associations
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and according to Coley (1988) slow growing organisms occupying lo
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