Novel 5-Flucytosine Based Antifungal Therapeutics

Current estimates suggest more than 1.7 billion people are annually affected by fungal diseases. A significant proportion of individuals suffer from invasive infections resulting in >1.5 million deaths per year. Of these, around one third result from invasive and chronic mold infections, predominantly caused by the major human mold pathogen Aspergillus fumigatus (AFU). Due to the close evolutionary similarity between human and fungi, the development of novel antifungal medicines is associated with difficulties. Therefore, the current therapeutic arsenal for the treatment of invasive fungal infections comprises only four classes of antifungal agents - triazoles, polyenes, echinocandins and nucleobase-analogs. Over the past 30 years, triazole based drugs have been the cornerstone of antifungal therapy. Worryingly, resistance to this drug class, particularly in the major human mold pathogen AFU is emerging rapidly and raises the question if this class of antifungals can be retained in clinical usage. The clinical use of 5-flucytosine (5FC), the only member of the antifungal nucleobase-analog class, for the treatment of Aspergillus diseases is limited and according to the Infectious Diseases Society of America currently not included in the practice guidelines for the management of aspergillosis. The overall goal of this project involves the investigation of intrinsic 5FC resistance and 5FC activity determinants in AFU in order to use the acquired knowledge for the optimization of current therapies as well as for the development of novel treatment strategies. One approach will combine fungal molecular genetics, antifungal activity testing as well as drug treatment analysis using a mammalian host organism (mouse) to elucidate major genetic determinants of 5FC activity. Concomitantly, genetic factors responsible for resistance to 5FC will be identified. The second, mainly translational aspect of the proposed project aims to develop novel therapeutic strategies, involving the conjugation of 5FC and its antifungal acting metabolites to carrier molecules that promote and specify cellular uptake into the fungal cell. This so-called Trojan horse approach involves siderophores, small molecules the fungus excretes to sequester the essential trace element iron from the environment, as well as cell penetrating peptides as carriers for the delivery of inhibitory molecules into the fungus. Additionally, we aim to identify small RNA molecules and small compounds that act synergistically in combination with 5FC. Taken together, employing a variety of so far unexplored therapeutic strategies exploiting the 5FC metabolic pathway, outcomes of this work are going to form the fundament of a novel field in antifungal therapy.