Compatibility between Proteins and Polysaccharide Excipients in Oral Delivery Tablets

The development of oral protein biopharmaceuticals has gradually become a hot area of research. Currently, most of the added excipients are oral excipients used in traditional small molecule drugs, such as starch and lactose. However, the interaction between proteins and oral excipients has not received much attention. For example, the interaction may have an effect on protein stability, efficacy, etc. Herein, we observed a strong interaction between protein and sodium carboxymethyl starch (CMS), a common disintegrator in oral formulations of small molecule drugs. CMS can cause the complete disappearance of a free soluble protein in trastuzumab (TRA) tablets after reconstituted, as detected by size-exclusion high-performance liquid chromatography. While the other two polysaccharides with similar structures, hydroxyethyl starch and methylcellulose, exhibited no effect on the soluble TRA concentration. CMS produces an electrostatic interaction with TRA in a certain pH range, which affects the soluble protein monomer concentration and solution turbidity, increases the hydrophobicity of the TRA-CMS complex, and reduces the thermal stability of TRA, without changing its biological activity detected by an enzyme-linked immunosorbent assay. Thus, the CMS and TRA electrostatic binding is reversible, and CMS has a potential application in sustained release in oral monoclonal antibody (mAb) and protein delivery tablets. Mixed solutions of infliximab and etanercept (a fusion protein) with CMS at different pH were also studied by SE-HPLC. The results showed that the concentration of the free soluble protein detected by SE-HPLC was significantly and universally reduced when pH was below the isoelectric point, where the positively charged protein forms a strong electrostatic interaction with the negatively charged CMS. The structural characteristics of the protein (such as surface charge, surface hydrophobicity, etc.) should be fully considered in selecting the appropriate excipients for protein biopharmaceutical tablets.