Role of Cosolute-Protein Interactions in the Dissociation of Monoclonal Antibody Clusters

The solution thermodynamics and interactions of a reversibly self-associating monoclonal IgG1 antibody (mAb1) have been investigated as a function of cosolute type (NaCl, NaSCN, Arginine-HCl) and cosolute concentration over a wide range of protein concentrations (1-275 mg/mL) using static light scattering. Within the framework of multicomponent solution thermodynamic theory, the preferential interactions of cosolutes with mAb1 were evaluated in the concentration limit of the system. The overall interactions of cosolutes with mAb1 relative to the bulk solutions appear to be very weak, but preferential interactions alone are insufficient to account for the cosolutes' dissociation of mAb1 clusters. As a complementary approach to understanding cosolute interactions at high concentrations, mAb1 concentration dependent light scattering was also analyzed with models of interacting hard spheres (IHS). Evaluating the cosolute concentration dependence of association constants and states as specific binding interactions to dissociate mAb1 oligomers, numerical estimates of cosolute molecules required to dissociate oligomers were obtained. A descending order of cosolute binding number per mAb oligomer was found: arginine-Cl (similar to 17) > NaSCN (similar to 12) > NaCl (similar to 8). Differences in the cosolute effectiveness in reducing mAb1 equilibrium oligomer formation (self-association) are in part attributable to ion binding and salt identity (Hofmeister series) effects that reduce the attractive electrostatic interactions of mAb1. However, only Arg-Cl effectively disrupts mAb1 dimer formation, likely through interactions with the hydrophobic surface features on mAb1. Results indicate that localized cosolute-protein binding interactions have an important role in modulating nonspecific protein self- or heteroassociations at high concentrations.