Abstract
Numerous approaches have been employed to improve the efficacy of drug and gene delivery systems, but their strategic development is hindered by a lack of mechanistic understanding and assessment of drug transport and action. Optimizing the efficiency of a drug delivery system requires a detailed understanding of the pharmacokinetics, transendothelial transport, distribution at the tumor site, and uptake in target cells. Elucidating transport kinetics and rate-limiting steps in animal models can be extremely challenging, while in vitro platforms often fail to recapitulate the complexities of drug transport in vivo. To recapitulate the critical aspects of delivery of anticancer agents, we have developed a 3D tissue-engineered microvessel model of the tumor microenvironment. Our model consists of single MDA-MB-231 breast cancer cells embedded within a collagen matrix that surrounds a perfusable cylindrical microvessel lined with human endothelial cells. Here we compare transport and action of free doxorubicin and Doxil, a liposomal formulation of doxorubicin. We show that the mode of drug delivery influences uptake in the vessel endothelium and tumor cells. Through quantification of endothelial and tumor cell proliferation, apoptosis, and motility, we profile the kinetics of drug action with mechanisms of drug transport across the vessel lumen and into the surrounding matrix. Our model can be customized to mimic specific tumor microenvironments and disease states within a physiologically relevant microfluidic platform and provides a basis for characterizing and optimizing drug delivery systems.