Modified Siderophores for "Theranostics" of Aspergillosis

Background: Invasive fungal diseases (with an incidence of 70000 cases/year in the EU), mainly caused by Aspergillus fumigatus (AFU), are a major cause of morbidity and mortality in patients with reduced immune defense. Such infections are very difficult to detect and therefore treating patients at risk without definite diagnosis has entered clinical practice causing unnecessary side effects and raising resistance. For the development of novel specific diagnostic and therapeutic methods fungal infection specific biomarkers are required. The iron acquisition system represents one of the few fundamental differences between fungal and human cells. Iron is essential for fungi, which therefore specific iron transporting molecules, siderophores that tightly bind iron and allow its uptake. We have shown that fungi activate this siderophore system during infection and we could use radioactive Gallium replacing Iron to follow siderophores, which are taken up by fungi allowing specific imaging of the infection by positron emission tomography (PET). This Trojan Horse mechanism will be used in this project by developing novel synthetic siderophores for diagnosis by attaching fluorescent and radioactive markers and therapy by attaching antifungal agents. Methods: Staring from Fusarinine C, a fungus specific siderophore, derivatives with fluorescent makers and three different types of antifungal residues will be prepared. They will be radiolabeled with a Gallium isotope (68Ga), having the same binding properties as iron. The new compounds will be investigated in fungal cultures to determine their recognition and impact on growth of AFU. Using novel imaging technologies (PET and optical imaging) will allow to investigate and establish accumulation and therapeutic activity in fungal infections. Novelty: The development of these synthetic siderophores opens a novel approach for the management of fungal diseases. The combination of imaging with treatment (Theranostics) is so far not available and can bring a great benefit for fighting this dangerous infectious disease. Using the essential iron transport mechanism of the microorganisms we hope to be able to earlier detect the disease and treating it with less side effects and lower risk of resistance.

From Diagnosis to Theranostics: Modified Siderophores for Imaging and treatment of Aspergillosis Background: Invasive fungal diseases (with an incidence of 70.000 cases/year in the EU), mainly caused by Aspergillus fumigatus (AFU), are a major cause of serious illness and mortality in patients with reduced immune defense. Such infections are very difficult to detect and therefore treating patients at risk without definite diagnosis has entered clinical practice causing unnecessary side effects and raising resistance. For the development of novel specific diagnostic and therapeutic methods, fungal infection-specific biomarkers are required. The iron acquisition system represents one of the few fundamental differences between fungal and human cells. For uptake of the essential iron, fungi secrete specific iron transporting molecules, termed "siderophores", that tightly bind iron to allow its uptake. We had shown that fungi activate this siderophore system during infection and that replacement of iron by radioactive gallium allows to follow the route of siderophores, which are taken up by fungi allowing specific imaging of the infection by positron emission tomography (PET). This "Trojan Horse" mechanism was in the core of this project to develop novel siderophore derivatives for diagnosis by attaching fluorescent and radioactive markers and for therapy by attaching antifungal agents. Results: Starting from fusarinine C (FSC), a fungus-specific siderophore, derivatives with fluorescent makers and various types of antifungal residues were prepared. Fluorescent markers allowed to visualize fungal uptake mechanism via the specific siderophore transporter MirB and to use them to combine molecular imaging via PET with optical imaging generating so called hybrid probes. By connecting antifungal compounds to FSC specific delivery to the fungal cell could be achieved with a variety of compounds. Not all of them exhibited overall antifungal activity, in particular peptide-based compounds showed low activity, but with small molecules antifungal properties could be achieved. Siderophores are known to bind a variety of metals and we could show that in particular siderophore complexes with gallium and cobalt have high antifungal activities. Finally, new approaches using platinum-based compounds or molecules with photoreactive residues were investigated. Novelty: The development of modified siderophores opened a novel approach for the management of fungal diseases. The combination of imaging with treatment ("theranostics") is so far not available and can bring a great benefit for fighting these dangerous infectious diseases. We could show that by targeting the essential iron transport mechanism of the microorganisms novel antifungal compounds based on FSC can be prepared, that hold the potential for earlier detection and treatment with less side effects and lower risk of resistance.