Biocompatible Polymers Modified with d-Octaarginine as an Absorption Enhancer for Nasal Peptide Delivery

Peptide and protein drugs, which are categorized as biologics, exhibit poor membrane permeability. This pharmacokinetic disadvantage has largely restricted the development of noninvasive dosage forms of biologics that deliver into systemic circulation. We have been investigating the potential use of cell-penetrating peptide-linked polymers as a novel absorption enhancer to overcome this challenge. Since our previous study revealed that biocompatible poly( N-vinylacetamide- co-acrylic acid) modified with d-octaarginine, a typical cell-penetrating peptide, enhanced in vitro permeation of biomolecules such as plasmid DNA and bovine serum albumin through cell membranes, the present study evaluated whether the polymers enhanced in vivo absorption of biologics applied on the mucosa. Mouse experiments demonstrated that d-octaarginine-linked polymers drastically enhanced nasal absorption of exendin-4, whose injection is clinically used. The mean bioavailability was 20% relative to subcutaneous administration, even though it fell short of 1% when exendin-4 alone was administered nasally. The absorption-enhancing function of the polymers was superior to that of sodium caprate and sodium N-(8-(2-hydroxybenzoyl)amino) caprylate, which have been used for humans as an absorption enhancer. In vitro experiments using several biologics with different characteristics revealed that biologics interacted with d-octaarginine-linked polymers and were taken up into cells when incubated with the polymers. The interaction and cellular uptake were enhanced as molecular weights of the biologics increased; however, their charge-dependent in vitro performance was not clearly observed. The current data suggested that biologics formulated with our polymers became an alternative to their conventional invasive parenteral formulations.