Rüger et al., accepted in J Control Release

article accepted in J Control Release

In vivo near-infrared fluorescence imaging of FAP-expressing tumors with activatable FAP-targeted, single-chain Fv-Immunoliposomes.

Rüger R ¹, Tansi FL ², Rabenhold M ³, Steiniger F ⁴, Kontermann RE ⁵, Fahr A ⁶, Hilger I ⁷

¹Department of Pharmaceutical Technology, Friedrich-Schiller-University Jena, Lessingstrasse 8, 07743 Jena, Germany.
²Dept. of Experimental Radiology, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Erlanger Allee 101, 07747 Jena, Germany.
³Department of Pharmaceutical Technology, Friedrich-Schiller-University Jena, Lessingstrasse 8, 07743 Jena, Germany.
⁴Center for Electron microscopy, Jena University Hospital - Friedrich Schiller University Jena, Ziegelmuehlenweg 1, 07743 Jena, Germany.
⁵Institute of Cell Biology and Immunology, University Stuttgart, Allmandring 31, 70569 Stuttgart, Germany.
⁶Department of Pharmaceutical Technology, Friedrich-Schiller-University Jena, Lessingstrasse 8, 07743 Jena, Germany.
⁷Dept. of Experimental Radiology, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Erlanger Allee 101, 07747 Jena, Germany.

Abstract:

Molecular and cellular changes that precede the invasive growth of solid tumors include the release of proteolytic enzymes and peptides in the tumor stroma, the recruitment of phagocytic and lymphoid infiltrates and alteration of the extracellular matrix. The reactive tumor stroma consists of a large number of myofibroblasts, characterized by high expression of fibroblast activation protein alpha (FAP). FAP, a type-II transmembrane sialoglycoprotein is an attractive target in diagnosis and therapy of several pathologic disorders especially cancer. In the underlying work, a fluorescence-activatable liposome (fluorescence-quenched during circulation and fluorescence activation upon cellular uptake), bearing specific single-chain Fv fragments directed against FAP (scFv'FAP) was developed, and its potential for use in fluorescence diagnostic imaging of FAP-expressing tumor cells was evaluated by whole body fluorescence imaging. The liposomes termed anti-FAP-IL were prepared via post-insertion of ligand-phospholipid-conjugates into preformed DY-676-COOH-containing liposomes. The anti-FAP-IL revealed a homogeneous size distribution and showed specific interaction and binding with FAP-expressing cells in vitro. The high level of fluorescence quenching of the near-infrared fluorescent dye sequestered in the aqueous interior of the liposomes, enable fluorescence imaging exclusively upon uptake and degradation by cells, which results in fluorescence activation. Only FAP-expressing cells were able to take up and activate fluorescence of anti-FAP-IL in vitro. Furthermore, anti-FAP-IL accumulated selectively in FAP-expressing xenograft models in vivo, as demonstrated by blocking experiments using free scFv'FAP. The local tumor fluorescence intensities were in agreement with the intrinsic degree of FAP-expression in different xenograft models. Thus, anti-FAP-IL can serve as a suitable in vivo diagnostic tool for pathological disorders accompanied by high FAP-expression.