(315g) Award Submission: Rational Selection of Intestinal Permeation Enhancers for Oral Macromolecular Drug Delivery

Oral delivery of proteins remains a pressing, unmet need in the field of drug delivery, primarily due to poor transport across the intestinal epithelium. A common approach to achieve transepithelial transport is the use of materials called permeation enhancers that manipulate the epithelial cell monolayer. Unfortunately, the clinical translation of permeation enhancers has been limited. Although many reported enhancers increase drug permeability across commonly-used Caco-2 cell monolayers, their efficacy rarely extends to studies in mice or rats. Poor translation from in vitro to in vivo systems can be partially attributed to inadequate understanding of the physical limits of intestinal permeation enhancement in cell culture and in animals. This study systematically determined how three mechanistically distinct permeation enhancers affect the in vitro and in vivo permeability of macromolecules with varied size, surface charge, and conformation. This newfound knowledge will enable rational selection of permeation enhancers when developing delivery systems for therapeutic proteins.

Five proteins (insulin, 5.7 kDa; cytochrome C, 12 kDa; ovalbumin, 44 kDa; bovine serum albumin, 66 kDa; and mouse IgG, 150 kDa) and five dextrans with corresponding molecular weights were fluorescently labeled and characterized for hydrodynamic diameter, molecular weight, and surface charge. Permeability was measured in vitro using Caco-2 monolayers and in mice by intestinal injection. Solutions of one marker mixed with one of three enhancers (1-phenylpiperazine, silica nanoparticles, or sodium deoxycholate) were administered to cells or mice, and fluorescence measurements quantified permeation from media or blood samples.

The three permeation enhancers operated via different mechanisms in Caco-2 monolayers, and the effect of macromolecular size on permeation varied significantly with enhancer type. In Caco-2 monolayers, silica nanoparticles were efficacious for markers less than 40 kDa, while low concentrations of 1-phenylpiperazine increased permeability of all markers. Translation to mice was challenging in that effective in vitro enhancer concentrations were not reflective of required concentrations in vivo. However, with optimization of enhancer doses, significant permeability increases were observed in mice. For 4 kDa dextran, silica nanoparticles more than doubled the permeability and 1-phenylpiperazine achieved a remarkable 17-fold increase in permeability.

This study improves our understanding of how permeation enhancers aid intestinal absorption of macromolecular drugs by thoroughly examining the performance of three mechanistically distinct permeation enhancers. Ultimately, compatibility between enhancer mechanism and the properties of the macromolecules dictated permeation enhancer performance in mice.