Development of an ex vivo porcine skin model for the preclinical evaluation of subcutaneously injected biomacromolecules.

Subcutaneous administration is used to deliver systemically-acting biotherapeutics, e.g. antibodies, and locally-acting biomacromolecules, e.g. hyaluronic acid. However, few preclinical models are available to evaluate post-injection behaviour in the tissue microenvironment. In vivo animal studies are costly, time-consuming, and raise obvious ethical concerns. In vitro models are cost-efficient, high-throughput solutions, but cannot simulate complex skin structure and biological function. An ex vivo model (containing hypodermis) with an extended culture period that enabled longitudinal studies would be of great interest for both the pharmaceutical and cosmeceutical industries. We describe the development of one such ex vivo model, using viable full-thickness porcine skin. Structural integrity was evaluated using a histological scoring system: spongiosis and epidermal detachment were identified as discriminating parameters. Ki67 and Claudin-1 expression reported on epidermal cell proliferation and barrier function, respectively and their expression decreased as a function of incubation time. After optimization, the system was used to investigate the fate/impact of subcutaneously administered hyaluronic acid (HA) formulations. The results showed that HA was localized at the injection site and adjacent adipocytes were well preserved during 5 days' incubation and confirmed that the full-thickness ex vivo porcine skin model could provide a platform for preclinical evaluation of subcutaneously injected biomacromolecules.