Engineering microbial cell factories for production of improved polyene antifungal agents

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Fungal infections are an escalating global threat to human health. The fewantifungal agents currently available are becoming increasingly ineffective due to emergingmultidrug resistant pathogens (e.g. Aspergillus fumigatus, Candida albicans & Candida auris).Despite the acute need for alternative treatments, very few new drug candidates have emerged inrecent years, and we remain reliant on a few established antifungals, particularly polyenesincluding WHO essential medicines amphotericin B (AmB), nystatin (Nys) and pimaricin (Pim).Polyenes are complex cyclic polyketide macrolides produced by Actinobacteria. Given polyeneshave potent broad-spectrum activity and the incidence of resistance to them is relatively low, theyremain the most effective and widely used antifungal agents. AmB, which is produced byStreptomyces nodosus, is the frontline treatment for many common systemic fungal infections.Recently, AmB was used to combat the outbreak of COVID-19 associated mucormycosis (blackfungus). AmB is also an essential treatment of the parasitic disease leishmaniasis which causeshigh mortality in the developing world. Despite their medical importance, polyenes exhibitsevere toxicity, and there is an urgent need for safer, less toxic alternatives. SAR shows that anexocyclic C16-carboxylate in AmB, which is also present in the majority of the otherpolyenes, is a key determinant of toxicity. AmB derivatives lacking this moiety are significantly lesstoxic and chemical modification of the C16-carboxylate also affords derivatives with loweredtoxicity.In addition to C16-modification, conjugation of polyenes with sugars and other moieties that improve solubility and reduce aggregation can also reduce toxicity. However,chemical synthesis of complex polyenes is very challenging, requiring multiple steps, deleteriousreagents and extensive use of protecting groups, which is expensive, unsustainable and difficult toscale-up. In this project we aim to engineer microbial cell factories, that can deliver safer polyenevariants with improved activity and lower toxicity via a sustainable single-step fermentationapproach.