A primary cell-based fluidic co-culture model to investigate drug transport across the human placenta.

Although women often need to take medication during pregnancy, reliable human-based models mimicking the maternal-fetal interface and allowing predictions on drug transport across the human placenta are scarce. In this study, we developed a novel microfluidic Transwell-based co-culture model consisting exclusively of primary cells (trophoblasts/endothelial cells) for assessing maternal-fetal drug transfer. We aimed to (1) investigate the effects of fluidic flow on drug transfer patterns, (2) evaluate barrier integrity and different transfer processes (diffusion, active transport) across the combined trophoblast/endothelial monolayers and (3) determine the expression and functional activity of main placental drug efflux transporters (ABCB1 and ABCG2). After applying different flow rates (50/150 µl/min), our system maintained cellular integrity and barrier function while enhancing syncytialization markers such as hCG. Our model effectively mimics key features of the placental microenvironment, including polarized expression and functional activity of both efflux transporters. Using fluorescent substrates and specific inhibitors (ABCB1: Rhodamine 123/Cyclosporin A; ABCG2: Bodipy-FL-Prazosin/Ko123), we confirmed that both transporters are not only expressed in the primary co-cultures, but also actively restrict the passage of compounds in the mother-to-fetus direction. Importantly, our system also captured passive diffusion dynamics of reference compounds (antipyrine/caffeine), with transport rates increasing under higher flow, mirroring in vivo behaviour. While our model does not yet replicate the full complexity of the placenta, our findings provide strong evidence that dynamic flow systems can recapitulate key placental transport phenomena and offer a valuable in vitro model to study human-based transplacental transport processes. KEY POINTS: Medication use during pregnancy is an essential aspect of obstetrical care, it remains a major concern due to potential risks to fetal and placental development. Current in vitro models for assessing maternal-fetal drug transfer mostly consist of immortalized cell lines and/or lack critical components of the placental microenvironment, such as stromal cells or dynamic fluid flow. We developed a dynamic Transwell-based co-culture model , composed exclusively of primary trophoblast and endothelial cells. The model effectively mimics key features of the placental barrier properties, including polarized expression and functional activity of major placental drug efflux transporters. The dynamic primary cell based flow systems offer a physiologically relevant human in vitro model to investigate and predict transplacental drug transfer.