Oral delivery of protein drugs: driver for personalized medicine

The pathogenesis of common diseases, such as metabolic diseases, is caused by the complex and individual interplay of many susceptibility genes, which necessitates both personalized diagnosis and therapy. Small-molecule drugs which adequately address the multiple tissue-specific target proteins affected probably will not become available in near future. In contrast, therapeutic proteins, such as growth factors and antibodies, specifically replacing or inactivating the corresponding susceptibility gene products, are currently being identified with increasing efficacy. However, the failure to be administered by the oral route and to reach the cytoplasm of the diseased cells typically prevents their therapeutic use. Recent developments suggest that these limitations may be overcome by encapsulation of therapeutic proteins into nanoparticles or their covalent modification with glycolipid (glycosylphosphatidylinositol, GPI) structures. These act as membrane anchors for so-called GPI-anchored proteins and direct certain attached passenger proteins from lipid raft areas of the plasma membrane via cytoplasmic lipid droplets into small vesicles. These leave the donor cells and transfer the GPI-anchored proteins into the cytoplasm of acceptor cells. This pathway may enable the transport of therapeutic proteins across the intestinal barrier into the circulation and eventually across the plasma membrane of the diseased target cells. For therapy, a number of challenges remains to be tackled, in particular, control of release from the GPI anchor which determines the pharmacokinetic and pharmacodynamic profiles. Together these findings nourish the hope that oral path finding to drug targets by encapsulation and covalent modification of therapeutic proteins may enable personalized therapy of common diseases.