FwF Projekt Nr. L 676-B18 (English Version)

Introduction: Invasive Aspergillosis (IA) is a major cause of death in immunocompromised patients and has increased tremendously over the last years. Early diagnosis of IA could be live saving, but is difficult to achieve. Currently used diagnostic methods lack specificity and sensitivity, even though considerably research efforts have been made to develop suitable diagnostic agents. In the pathophysiology of Aspergillus fumigatus (A.f.) iron plays an essential role during infection. A.f. employs a specific and highly efficient iron transporter mechanism based on iron binding siderophores, that are upregulated in A.f. and essential for A.f. during infection. In this project we aimed to develop novel diagnostic agents for Positron Emission Tomography (PET), a highly sensitive imaging technique using radionuclides, by using siderophores labelled with 68Ga, a short lived radionuclide, as a substitution of iron-siderophores, and to evaluate these agents for their ability to image IA.

Results: Initial studies compared a number of different siderophores for their ability to bind 68Ga and to determine their properties in vitro regarding stability and uptake by A.f. cultures. In particular two siderophores Triacetylfusarenine C (TAFC) and Ferrioxamine E (FOXE) showed excellent radiolabelling properties resulting in highly pure compounds, but also very high uptake by Aspergillus, which was in particular highly dependent on iron supply. Other siderophores either showed inferior radiolabelling properties, low stability or low uptake by A.f. These two compounds also showed high metabolic stability in vivo and most favourable distribution properties with rapid excretion via the kidneys, which is required to clear unbound agents rapidly from circulation to allow detection of specific uptake in infection. A rat-model of IA was established and it could be shown that both compounds were retained in infected lungs dependent on severity of infection with so far unreported high uptake values in infected lung tissue. Using a novel micro-PET technique we were able to image the development of disease and the extension of infection in lung tissue as well as to determine optimal imaging time points in cooperation with Radboud University Nijmegen Medical Centre, Netherlands. For clinical imaging applications not only the ability to detect A.f. infections is a challenge, but also whether a novel agent is specific for Aspergillosis. We therefore compared the uptake of 68Ga-labelled TAFC and FOXE also in different microorganisms, whereby TAFC showed advantages in being more specific especially regarding bacterial infections. It also could be shown that a high iron load, which often occurs in the clinical setting of immunocompromised patients, did not significantly reduce the uptake of these new compounds in infected tissue.

Overall Outcome: Within this project we could successfully translate the knowledge from basic investigations on the role of iron in IA towards the use for a specific and sensitive novel technology to image IA, potentially allowing early detection of this disease. Our results form the basis to bring this new technique into clinical application.

Publications:

Petrik M, Haas H, Dobrozemsky G, Lass-Flörl C, Helbok A, Blatzer M, Dietrich H, Decristoforo C. 68Ga-siderophores for PET imaging of invasive pulmonary aspergillosis: proof of principle. J Nucl Med. 2010 Apr;51(4):639-45.

Link: http://jnm.snmjournals.org/content/51/4/639.long

 

Petrik M, Haas H, Schrettl M, Helbok A, Blatzer M, Decristoforo C. In vitro and in vivo evaluation of selected (68)Ga-siderophores for infection imaging. Nucl Med Biol. 2012 Apr;39(3):361-9. Epub 2011 Dec 14.

Link: http://www.sciencedirect.com/science/article/pii/S096980511100237X