Surfactant protein A - mediated biogenic targeting of alveolar macrophages using surface-modified nanoparticles for treatment of pulmonary tuberculosis
Final Report Abstract
Recent data suggest that pulmonary surfactant assimilates the uptake of differently modified nanoparticles in macrophages. Conversely, hitherto existing targeting strategies using functionalized nanoparticles might be questioned, as elaborated surface modifications with specialized targeting ligands might be shielded by adsorbed biomolecules from pulmonary surfactant. This may lead to a significant loss of the targeting specifity. Instead, a solution to this problem could be a 'biogenic' targeting concept, in which the targeting ligand is already present in the biological fluid primarily encountered by the nanoparticle, and which binds the particle with high affinity once it contacts these fluids. Such a strategy would diminish inactivating effects caused by adsorption of other biomolecule species, and could be an advantage over conventional targeting strategies. Interesting candidates for such endogenous targeting ligands could be any kind of protein capable of mediating or inducing an endocytotic mechanism, e.g. phagocytosis, or dathrin-mediated endocytosis. One such relevant candidate is surfactant protein A (SP-A), the most abundant protein associated with pulmonary surfactant. Pulmonary surfactant is a complex surface-active lipo-protein matrix located at the air-liquid interface, which prevents the alveoli of the lungs from collapsing and is thus required for proper lung function. Due to its position at the air-liquid interface, SP-A can act as opsonin by binding to foreign materials that deposit in the deep lungs and thus contact pulmonary surfactant. The Inevitable interaction with SP-A and opsonization leads to enhanced recognition by cells of the host defense system, such as alveolar macrophages. Once bound to the foreign structure, SP-A triggers an immune response that results in an overall more efficient removal of pathogens or particulates from the lungs. However, there are some pathogens that exploit this very kind of interaction in order to invade host cells as a biological niche. For instance, it is known that both SP-A and surfactant protein receptors play an important role in the invasion of Mycobacterium tuberculosis (Mtb) in alveolar macrophages. Thus, an interesting approach here would be a system that mimics Mtb and follows the pathway by which the pathogen is internalized in order to end up in close intracellular proximity. In this project, a mannosylated poly(lactide)-block-poly(ethylene glycol) (PLA-PEG) co-polymer was synthesized and used to prepare nanoparticles that are capable to selectively adsorb SP-A. The obtained nanoparticles featured a core-shell structure with surface-immobilized mannose-residues that were shown to biologically interact with mannose-binding proteins such as Concanavalin A or SP-A. In vitro experiments in THP-1 monocyte derived macrophages demonstrated the preferential uptake of mannosylated nanoparticles in presence of SP-A compared to absence of the protein. These in vitro results were confirmed in a preliminary in vivo study in mice, where SP-A-coated PLA-PEG-Mannose nanopartides showed significantly higher uptake in isolated alveolar macrophages compared to nanoparticles without SP-A-coating. Overall, it could be demonstrated that SP-A can mediate the cellular uptake of mannosylated nanoparticles, and thus could be exploited as an endogenous ligand for macrophage targeting in the lungs. Hence, by the choice of the right material, it is possible to follow such a biomimetic approach and to selectively trigger bionano interactions, leading to an intended biological response. Here, SP-A was chosen as one possible and exemplary candidate for the concept of biogenic targeting. Thus, approaches using surface-functionalized nanoparticles that mimic the uptake pathway of other intracellular bacteria may be one way towards more effective treatinents of intracellular infections. The essential starting point in such approaches, however, is the choice of the right material, as well as a proper prediction and understanding of how this material will interad with biomolecules in relevant fluids of the body. Understanding the entity of the ongoing bio-nano interactions and infiuencing their outcome may path the way for new therapy forms that exploit the concept of biogenic targeting.
Publications
- (2013). Adsorption of pulmonary surfactant proteins to nanoscale drug carriers: implications for targeting alveolar macrophages. ISAM Conference 2013, Chapel Hill. NC, USA
Ruge C.A., Canadas O., Schaefer U.F., Casals C., Lehr C.-M.
- (2013). Pulmonary drug delivery: from generating aerosols to overcoming biological barriers - therapeutic possibilities and technological challenges. The Lancet Respiratory Medicine, 1(5), pp 402
Ruge, C. A., Kirch, J., Lehr, C.-M.
(See online at https://doi.org/10.1016/S2213-2600(13)70072-9) - (2014). Preparation of Nanoscale Pulmonary Drug Delivery Formulations by Spray Drying. Advances in Experimental Medicine and Biology, 811, pp 183
Bohr A., Ruge C.A., Beck-Broichsitter M.
(See online at https://doi.org/10.1007/978-94-017-8739-0_10) - (2014). Surfactant protein A - mediated biogenic targeting of macrophages using surface-modified NP for treatment of pulmonary tuberculosis. PBP World Meeting, Lisbon. Portugal
Ruge C.A., Hillaireau H., Beck-Broichsitter M., Tsapis N., Nicolas J., Fattal E.
