Biosynthesis and diversification of polyene antifungals with improved properties using tailoring enzymes Saadia Nasr Mirza, Alberto Carella, Wei Li Thong, Katherine J. Robins, Jason Micklefield University of Manchester, UK Polyene macrolides are a class of natural products of Streptomyces origin which include vital clinically relevant antifungal therapeutics. The prominent polyene family members include amphotericin B, nystatin and pimaricin, which are all WHO essential medicines. However, despite high potency and rare occurrence of resistance, their use is limited by dose dependent toxicity in the mammalian cells, mainly due to non-specific binding to cholesterol present in human cell membranes and poor serum solubility. New derivatives with improved therapeutic index are therefore highly desirable. Although synthetic derivatives have previously been designed to improve selectivity for ergosterol over cholesterol and reduced toxicity, this involves extensive multi-step synthesis which is too expensive for antimicrobial drug development. We have designed bio-based methods of derivatizing improved analogues of WHO essential medicines. This involves the use of regio- and stereo-specific enzymes to introduce targeted amidation and glycosylation in polyenes. Engineering microbial host cells with desired enzymes has enabled the production of improved polyenes via inexpensive and scalable single-step fermentation process . Interestingly based on MIC values, the new polyene derivatives were found to have improved activity against clinically resistant fungal strains. Cytotoxicity testing of these compounds is underway.
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