Design and Application of a μSiM Outer Blood-Retinal Barrier (OBRB) Model as a Drug Development Tool
The outer blood-retinal barrier (OBRB) is the primary interface through which systemically circulating drugs reach the retina. A tool that measures delivery across this barrier would support the development of targeted therapies as alternatives to repeated intravitreal injection, and the screening of drugs that reach the retina as an off-target toxicity. Such a tool should deliver drugs fluidically through a vascular compartment, measure transport across the retinal pigment epithelium (RPE), and display disease phenotypes relevant to efficacy. Here we adapt the SiM platform, which places epithelium and endothelium in direct juxtaposition across a permeable, optically transparent silicon nitride nanomembrane. ARPE-19 and human umbilical vein endothelial cells (HUVECs) were used as development cell sources. ARPE-19 monocultures reached a transepithelial electrical resistance of 68 {+/-} 26 {Omega} cm2 by 28 days, and ARPE-19 + HUVEC co-cultures reached a small-molecule permeability of 6.34 {+/-} 1.3 x 10-4 cm min-1 within 14 days, a state reported elsewhere only after longer culture. The barriers developed an intervening basement membrane. Drugs perfused through the basal vascular channel crossed into an open apical well, where sampling and mass spectrometry showed transport correlating with lipophilicity, as reported in vivo. The device also displayed two clinically relevant phenotypes. Digoxin at a clinically toxic concentration reduced viability in the co-barrier by about half and doubled permeability. In a vascularized configuration, VEGF drove endothelial invasion of the RPE layer, as seen in neovascular AMD. The SiM-OBRB therefore satisfies basic design criteria for measurement of drug bioavailability, toxicity, and efficacy.