Design and Testing of Efficient Mucus-Penetrating Nanogels-Pitfalls of Preclinical Testing and Lessons Learned

Mucosal surfaces pose a challenging environment for efficient drug delivery. Various delivery strategies such as nanoparticles have been employed so far; yet, still yielding limited success. To address the need of efficient transmucosal drug delivery, this report presents the synthesis of novel disulfide-containing dendritic polyglycerol (dPG)-based nanogels and their preclinical testing. A bifunctional disulfide-containing linker is coupled to dPG to act as a macromolecular crosslinker for poly-N-isopropylacrylamide (PNIPAM) and poly-N-isopropylmethacrylamide (PNIPMAM) in a precipitation polymerization process. A systematic analysis of the polymerization reveals the importance of a careful polymer choice to yield mucus-degradable nanogels with diameters between 100 and 200 nm, low polydispersity, and intact disulfide linkers. Absorption studies in porcine intestinal tissue and human bronchial epithelial models demonstrate that disulfide-containing nanogels are highly efficient in overcoming mucosal barriers. The nanogels efficiently degrade and deliver the anti-inflammatory biomacromolecule etanercept into epithelial tissues yielding local anti-inflammatory effects. Over the course of this work, several problems are encountered due to a limited availability of valid test systems for mucosal drug-delivery systems. Hence, this study also emphasizes how critical a combined and multifaceted approach is for the preclinical testing of mucosal drug-delivery systems, discusses potential pitfalls, and provides suggestions for solutions.