Vehiculation and functional delivery of lipophilic therapeutics and antibiotics via pulmonary surfactant in a lung-on-chip model.

Pulmonary surfactant forms a dynamic proteolipid thin-film at the alveolar air-liquid interface. It is both a barrier to a "last mile" carrier for inhaled particulate matter to the distal lung. Its importance in pulmonary delivery of inhaled particles and therapeutics is poorly understood in part because existing vehiculation models are entirely acellular. Here we report methodological innovations that implement vehiculation in a human lung-on-chip (LoC) model by adapting a thin-film bridge (TFB) method used in acellular models to deliver functionally-effective cargo to the epithelial layer. We find that breathing-like stretch is essential for vehiculation. Vehiculated cargos are retained and strongly co-localize with surfactant lipids in the epithelial layer. In LoCs reconstituted with in vitro-differentiated alveolar-like macrophages, both cargo and lipid are predominantly taken up by these cells, mimicking in vivo physiology. In contrast, delivery of cargos in surfactant formulations in liquid (a protocol typically used in vitro) leads to an unphysiological high uptake in alveolar epithelial cells, poor uptake in macrophages even in LoCs with alveolar-like macrophages and rapid separation of lipid and cargo. We demonstrate that surfactant formulations containing bedaquiline can be effectively vehiculated in both acellular and the human LoC models. TFB-vehiculated bedaquiline effectively suppressed subsequent growth of Mycobacterium tuberculosis in a prophylactic manner. Overall, our work demonstrates an approach for studying drug vehiculation in models of the alveolar interface in vitro, and the feasibility of surfactant-containing therapeutic formulations for direct and effective pulmonary delivery.