The colon as a possible target for orally administered peptide and protein drugs

Oral administration offers a potential portal to the superficial layers of the gastrointestinal (GI) tract (local delivery) and to the blood and lymphatics (systemic delivery). The harsh hydrolytic environment of the GI tract and the epithelial barriers to absorption, however, pose major challenges to the success of this mode of drug delivery for peptide and protein drugs. One approach to minimizing enzymatic degradation in the GI tract is to target drugs to the apparently less proteolytically active colon. In this review, the evidence supporting the colon as an attractive site for peptide and protein drug delivery will be discussed. The discussion will be confined to specific examples of delivery systems bearing both peptides and proteins that have been tested in the colonic context.