Investigation of Intercellular Adhesion Molecule-1 Targeted Drug Transport Across the Gastrointestinal Epithelium
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Contrary to systemic injection of therapeutics, oral formulations represent clear advantages to patients, healthcare systems, and pharmaceutical companies including safety, low cost and patient compliance. However, oral delivery remains a major obstacle due to (1) drug instability in the harsh environment of the gastrointestinal (GI) tract owing to low gastric pH and enzymatic hydrolysis; (2) low permeability through the mucus layer and subsequent adhesion to the GI epithelium; and (3) suboptimal transport into or across the GI epithelium- the cell barrier responsible for selective absorption of substances into the circulation, for local or systemic delivery. While encapsulation methods have been developed to overcome barriers to stability and adhesion to the GI epithelium, safe and effective transport into and across this lining has not yet been achieved for several drugs, especially biotherapeutics. Hence, our goal is to overcome these challenges for delivery of therapeutics (including biotherapeutics) via the oral route. For this purpose, we targeted drugs to intercellular adhesion molecule-1 (ICAM-1), a protein expressed on the GI epithelium and other cell types. We previously demonstrated, that polymer nanocarriers (NCs) coated with antibodies to bind multiple copies of ICAM-1 (multimeric targeting) triggered uptake and transport across cultured GI epithelial cells, enabling intracellular and transcellular drug delivery. To implement this strategy in vivo, we successfully encapsulated antibody-coated NCs in chitosan-alginate microspheres for gastric protection of labile targeting antibodies, site-specific release in the intestinal environment (the site of drug absorption) and retention of targeting ability following release in vitro, in cell culture, and in vivo. Furthermore, to expand the utility of the ICAM-1 targeting approach, we explored a novel drug delivery system that binds only one to two molecules of ICAM-1 (monomeric targeting), which provides distinct advantages for oral drug delivery compared with multimeric strategies. In order to elucidate the advantages offered by this monomeric targeting approach, we compared the uptake and intracellular trafficking of ICAM-1 targeted monomeric antibodies vs. multimeric antibody-coated NCs in cultured endothelial cells, a commonly used cellular model to study ICAM-1 transport. We then revealed that the distinct itinerary of transport offered by monomeric ICAM-1 targeted antibodies led to enhanced uptake and transport across cultured GI epithelial cells, showing promise for oral delivery. Finally, in order to exploit this transport pathway for oral drug delivery, we conjugated a model drug cargo to monomeric ICAM-1 targeted antibodies, which was shown to endow drug targeting and delivery into and across cultured GI epithelial cells, while preserving the functional activity of the drug cargo. These findings demonstrate that monomeric vehicles serve as a viable alternative to multimeric strategies, expanding the range of oral delivery applications afforded by ICAM-1 targeting. Taken together, the work performed in this dissertation advocates the potential of ICAM-1 targeting strategies for improving oral absorption of therapeutics, and provides a foundation for studying these strategies in vivo.