Submicron Aggregation of Chemically Denatured Monoclonal Antibody.

Isothermal chemical denaturation (ICD) has been widely used to evaluate the conformational stability of therapeutic proteins such as monoclonal antibodies. However, the chemical unfolding pathway and the subsequent aggregation of antibodies are not yet well-understood. In the present work, we conducted a systematic study on an ICD-induced aggregation of a pharmaceutical monoclonal antibody. Using dynamic light scattering, we monitored formation and growth of submicron aggregates in various buffers. Our experiments revealed a nucleation-controlled submicron aggregation of the antibody in the presence of chemical denaturant. After the unfolded protein reached a steady state, we reduced the denaturant concentration by dilution or dialysis to trigger further aggregation after ICD. In this way, we studied the pH effect on aggregation of the stressed protein after removal of denaturant. The ICD-dilution experiment provides a practical means for studying the propensity of unfolded proteins to form aggregates under various formulation conditions. This unique method allows us to control the degree of protein unfolding and the initiation of post-ICD aggregation.

Metastability Gap in the Phase Diagram of Monoclonal IgG Antibody.

Crystallization of IgG antibodies has important applications in the fields of structural biology, biotechnology, and biopharmaceutics. However, a rational approach to crystallize antibodies is still lacking. In this work, we report a method to estimate the solubility of antibodies at various temperatures. We experimentally determined the full phase diagram of an IgG antibody. Using the full diagram, we examined the metastability gaps, i.e., the distance between the crystal solubility line and the liquid-liquid coexistence curve, of IgG antibodies. By comparing our results to the partial phase diagrams of other IgGs reported in literature, we found that IgG antibodies have similar metastability gaps. Thereby, we present an equation with two phenomenological parameters to predict the approximate location of the solubility line of IgG antibodies with respect to their liquid-liquid coexistence curves. We have previously shown that the coexistence curve of an antibody solution can be readily determined by the polyethylene glycol-induced liquid-liquid phase separation method. Combining the polyethylene glycol-induced liquid-liquid phase separation measurements and the phenomenological equation in this article, we provide a general and practical means to predict the thermodynamic conditions for crystallizing IgG antibodies in the solution environments of interest.