Pharmaceutical Analysis of Protein–Peptide Coformulations and the Influence of Polysorbates

Coformulation is an approach to formulating multiple biopharmaceutical therapeutics in a single formulation, promising the benefits of both therapies in one dose. However, as molecular stability is a key consideration in traditional biopharmaceutical formulations, stability of coformulations will require extensive investigation. This study evaluated the effects of traditional formulation stabilizers, specifically surfactants, at different grades, namely, regular grade (RG) Tween 20 and Tween 80 and Super-refined Polysorbate 20 and 80. Their effects were assessed through their interactions with human serum albumin (HSA) and a glucagon-like peptide-1 (GLP-1) receptor agonist (MEDI7219). Isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) were implemented to determine the strength of the binding interactions and thermal stability of the tertiary system. ITC confirmed that upon titration of MEDI7219 into a solution of HSA and RG, Tween 20 the binding affinity of the peptide was reduced, resulting in negatively cooperative binding. However, when the peptide was titrated into a solution of HSA and both grades of Tween 80, the binding affinity increased with positive cooperative binding. DSC established that MEDI7219 increased the thermal stability of HSA to a similar extent to the polysorbates. Combining peptide and polysorbate did not further increase the thermal stability of HSA; however, it did reduce the unfolding of HSA molecules in the absence of heat. Overall, the unique findings in this study have demonstrated that the order of addition in a ternary coformulation affects the final composition which is an important consideration for pharmaceutical development.