(734h) Viscosity Increase in Concentrated Mab Solutions Due to Large Transient Clusters
This work addresses a fundamental challenge in controlling properties and stability in concentrated protein solutions, which is both of basic scientific interest and industrial importance. Proteins in densely packed environments are abundant in our bodies and in commercially produced biopharmaceutical products. In addition to product stability during lyophilization and long-term storage, successful drug product formulation is essential for the processing and drug delivery stages of a product’s life cycle. In particular, an increase in a therapeutic’s viscosity could introduce challenges to material handling, such as during filling, and also adversely limit the variety of available drug delivery methods. Recent reports on monoclonal antibodies (mAbs) have highlighted their tendency to form small, strongly bound, reversible clusters, which produce an undesirable significant increase in viscosity at elevated concentrations (Biophys. J. 105:720, 2013). Clusters in fluids are important structural features formed by the balance of different interaction potential features that are especially prominent in concentrated protein solutions. Several types of short-range attractive interactions contribute to effective inter-protein interactions that may serve as the origin of clustering. While previous studies have discussed clustering in mAb solutions via electrostatic driven interactions, here we highlight a more hydrophobic mAb where the addition of salt induces the formation of large transient clusters. Cluster formation becomes more extensive with increasing salt concentration and reduced temperature. At the lowest temperatures studied, signs of slow kinetic arrest are present. However, despite the formation of a gel, the local dynamics of individual proteins in these transient clusters measured by neutron spin echo are surprisingly found to be very fast. This is dramatically different from that of globular proteins and previously studied mAb systems. Despite the fast motion of these mAbs, the short range interaction is still strong enough to produce a very large weakly linked protein network causing the increase of solution viscosity or gelation. These results highlight the difference between transient and strongly bound dynamic clusters and the sensitivity of mAb therapeutic material properties to the origin of inter-protein interactions and the purity of product formulation.