Impact of degradation in subcutaneous tissue and lymphatic fluid on absorption of Fc-fusion proteins following subcutaneous administration

Subcutaneous administration is widely used as a clinical administration route for Fc-fusion proteins. However, predicting bioavailability (BA) in humans after subcutaneous administration is challenging due to multiple factors involved in the absorption process. This study aimed to elucidate the impact of degradation on the BA of Fc-fusion proteins. We established two measurement methods for each Fc-fusion protein: the Fc/Fc method, which recognizes the Fc region; and the Protein/Fc method, which recognizes both protein and Fc region. BA of dulaglutide and romiplostim in rats were 80.1 % and 99.4 % by the Fc/Fc method, and 35.0 % and 55.5 % by the Protein/Fc method, respectively. The lower BA with the Protein/Fc method indicates that the protein region undergoes degradation during the absorption process. In stability studies with rat skin homogenates and lymphatic fluid, degradation of the protein region for both dulaglutide and romiplostim was confirmed, which was inhibited by protease inhibitors. In contrast, abatacept and etanercept were stable in skin homogenates and lymphatic fluid, and their BA in rats were comparable between the Fc/Fc and Protein/Fc methods. This study indicates that the presence or absence of protease-mediated degradation during the absorption process is one of the factors affecting the BA of Fc-fusion proteins.