(181d) Towards Oral Protein Delivery with Poly(acrylamide-co-itaconic acid) Nanoscale Complexation Hydrogels

Protein therapeutics represent a rapidly growing pharmacological sector, with over 200 FDA-approved products¹. 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, which greatly reduce the activity of the proteins, and thus, their bioavailability is negligible if delivered in an unprotected state². Environmentally responsive polymer carriers, such as those that swell and collapse in response to changes in pH, 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 release³. 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 high isoelectric point therapeutic proteins delivered via the oral route.

Copolymeric nanoparticle systems containing acrylamide and itaconic acid and crosslinked with N,N’-methylenebisacrylamide were synthesized via inverse emulsion polymerization, a protocol adapted from Zhong et al⁴. Following purification with ethanol and dialysis against an ethanol:water gradient, the composition of the resulting particles was confirmed with Fourier-transform infrared spectroscopy and potentiometric titration. Nanogel swelling was characterized with dynamic light scattering and the zeta potential was measured with electrophoretic light scattering. With dynamic light scattering, it was confirmed that the synthesized nanogels exhibit the expected swelling behavior with increasing pH values, swelling from a hydrodynamic diameter of approximately 60 nm at pH 3 to 120 nm at pH 9. 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 and potentiometric titration suggested that particles with increasing incorporation of itaconic acid required higher volumes of hydrochloric acid to decrease the pH, indicating the presence of more carboxylic acid groups. The synthesized nanogels show promise for oral protein delivery applications. Protein loading and release in simulated gastric and intestinal conditions was evaluated using cytochrome C, which exhibits an isoelectric point of 10. Further testing is needed, such as the design and implementation of strategies to enhance protein transport across the intestinal epithelium.

This work was supported in part by NIH grant number R01 EB022025 and the Cockrell Family Regents Chair in Engineering (UT Austin). H.F.O. was supported by the National Science Foundation Graduate Research Fellowship and the Archie W. Straiton Endowed Graduate Fellowship in Engineering #2 (UT Austin).

References

1. Fosgerau, K. & Hoffmann, T. Drug Discovery Today 20, 122–128 (2015).
2. Gupta, S. et al. Drug Delivery 20, 237–246 (2013).
3. Brannon-Peppas, L. & Peppas, N.A Journal of Controlled Release 16, 319–329 (1991).
4. Zhong, J.X., et al.J Biomed Mater Res Part A 106A, 1677– 1686 (2018).