Drug delivery systems for macrophage- and organelle-specific targeting

The treatment of intracellularly residing pathogens is a challenge of modern medicine. These pathogens are able to hide from the host immune system by residing intracellularly in different types of endosomes or the cytoplasm thereby interfering with the immune response of phagocytic cells. Aspergillus fumigatus is a clinically important fungal pathogen that causes severe systemic infections. Conidia of this fungus are able to survive inside macrophages for some time. In order to treat this pathogen, we have developed a strategy using drug delivery systems to overcome the cell membrane and phagosomal membrane to reach conidia residing in phagolysosomes of macrophages. Here, we provide evidence that targeting of intracellular conidia is possible with polymeric particles of 800 nm size. These particles were fluorescently labeled and their uptake by infected macrophages was studied. Particle delivery to conidia-containing phagolysosomes was confirmed by different microscopic methods and the generation of transfected cell lines. Targeting occurs by fusion of phagolysosomes containing conidia with phagolysosomes containing the particle, as it was demonstrated by presence of phagolysosomal markers on phagosomes containing both conidia and particles. In order to enhance the fusion frequency, several compounds were tested that affected the lipid composition of the phago(lyso)some and its maturation. Based on these proof-of-concept results, smart drug delivery systems carrying antifungal activity were developed. In a first step, macromolecules such as polymer-caspofungin conjugates were generated. They showed antifungal activity as macromolecule, although the drug was not released. By comparison, drug release was demonstrated with a polymer-voriconazole conjugate, linked by a cathepsin B-sensitive peptide. Taken together, this thesis demonstrates the potential of drug delivery systems to target intracellularly residing pathogens in macrophages with antibiotics.