(626e) Design of pH-Responsive Hydrogels for Oral Delivery of High Isoelectric Point Therapeutic Proteins

Protein therapeutics represent a rapidly growing pharmacological sector, with over 200 FDA-approved products. However, due to poor stability and large molecular weight, protein administration is almost exclusively limited to injection. These frequent injections can be very painful and are often associated with fear and major side effects at the injection site – nearly one-third of patients or caregivers admit to intentionally skipping doses. Achieving oral delivery is ideal and would almost certainly improve patient compliance but is fraught with challenges. Efforts to develop delivery platforms have been limited by the conditions in the gastrointestinal tract: the highly acidic pH of the stomach, the proteolytic enzymes present through the gastrointestinal tract, and the mucous-lined epithelium of the small intestine, which tightly regulates the passage of large molecules but is where most drugs are absorbed. These barriers greatly reduce the activity of the proteins, and thus, their bioavailability is negligible if delivered in an unprotected state. Environmentally responsive polymer carriers have been explored for the development of an oral delivery platform for protein drugs. These pH-responsive carriers rely on charge interactions for the complexation behavior that facilitates protein loading and release. This characteristic presents a difficulty with proteins that exhibit a high isoelectric point, as the protein is likely to remain bound to the anionic hydrogel carrier at the pH of the small intestine instead of being repelled. This interaction must be overcome to allow protein release and thus, therapeutic efficacy. The aims of our work were to explore strategies for increasing the bioavailability of therapeutic proteins delivered via the oral route.

Copolymeric nanoparticle systems containing itaconic acid (poly(itaconic acid-grafted-poly(ethylene glycol)) and poly(itaconic acid-co-N-vinylpyrrolidone)) and crosslinked with tetraethylene glycol dimethacrylate were synthesized via UV-initiated free radical emulsion polymerization. Following purification, the composition of the resulting particles was confirmed with Fourier-transform infrared spectroscopy, nuclear magnetic resonance, potentiometric titration, and differential scanning calorimetry. The surface morphology of the nanogels was evaluated using electron microscopy. Nanogel swelling was characterized with dynamic light scattering and the zeta potential was measured with electrophoretic light scattering. Loading and release studies of high pI proteins were conducted in physiologically relevant buffers and quantified with a microBCA assay. The nanogels were confirmed to have the expected conformation, morphology, and properties. The itaconic acid-based platforms exhibited a greater degree of swelling than the methacrylic acid-based systems. Both platforms successfully loaded high pI protein from solution before collapse was induced by reducing the pH to simulate gastric conditions. Upon raising the pH to simulate intestinal conditions, a larger fraction of protein was released from the itaconic acid-based particles than the methacrylic acid-based system.

This work was supported in part by NIH grant number R01 EB022025 and an NSF GRF.