Category: Preclinical Development
Purpose: 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, such as those that respond to changes in pH, have been explored for the development of an oral delivery platform for protein drugs. These pH-responsive carriers, shown in Figure 1, 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.
Methods: 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 via ionomer collapse and dialysis for eight water changes, 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.
Results: With dynamic light scattering, it was confirmed that the synthesized nanogels exhibit the expected swelling behavior with increasing pH values, as shown in Figure 2. The particles with grafted PEG chains were generally smaller and more monodisperse than the particles copolymerized with N-vinylpyrrolidone. At pH 2, the particles precipitated from solution. Electrophoretic light scattering demonstrated that both formulations exhibit a negative zeta potential, with the value becoming more negative with increasing pH values. FTIR analysis of these gels showed the expected characteristic peaks, but no difference was observed between the two formulations, so NMR was used to confirm the expected structure.
Conclusion: Itaconic acid-based nanoscale pH-responsive hydrogels were successfully synthesized and characterized. These formulations will continue to be characterized and the ability to load and release high isoelectric point proteins in solution will be evaluated. If the systems show potential as an oral delivery platform for these proteins, they will be evaluated in in vitro and in vivo systems to determine their potential for clinical application.