Developing an antibody-binding protein cage as a molecular recognition drug modular nanoplatform.

We genetically introduced the Fc-binding peptide (FcBP) into the loop of a self-assembled protein cage, ferritin, constituting four-fold symmetry at the surface to use it as a modular delivery nanoplatform. FcBP-presenting ferritin (FcBP-ferritin) formed very stable non-covalent complexes with both human and rabbit IgGs through the simple molecular recognition between the Fc region of the antibodies and the Fc-binding peptide clusters inserted onto the surface of FcBP-ferritin. This approach realized orientation-controlled display of antibodies on the surfaces of the protein cages simply by mixing without any complicated chemical conjugation. Using trastuzumab, a human anti-HER2 antibody used to treat patients with breast cancer, and a rabbit antibody to folate receptor, along with fluorescently labeled FcBP-ferritin, we demonstrated the specific binding of these complexes to breast cancer cells and folate receptor over-expressing cells, respectively, by fluorescent cell imaging. FcBP-ferritin may be potentially used as modular nanoplatforms for active targeted delivery vehicles or molecular imaging probes with a series of antibodies on demand.