Monitoring protein aggregation kinetics with simultaneous multiple sample light scattering.

A simultaneous multiple sample light scattering (SMSLS) prototype instrument was built to simultaneously measure light scattering from many independent monoclonal antibody (mAb) solutions in order to monitor their time-dependent aggregation behavior and to characterize, via absolute Rayleigh scattering ratios, their molecular masses and second, third, and fourth virial coefficients under non-aggregating conditions at concentrations up to 190mg/ml. One stable mAb and another prone to aggregation were studied. Early phase aggregation rates spanned six orders of magnitude over temperatures 30 to 83°C for both mAbs and divided into "Arrhenius" and "Stochastic" regimes. The Arrhenius regimes comprise two thermal regimes whose breakpoint occurs near the first thermal unfolding temperature of the mAb domain structure. The Stochastic regime occurs for T⩽40°C. Rates yielded activation energies and temperature and concentration crossovers among rate-limiting regimes. Virial coefficients were closely related to aggregation kinetics. Hydrodynamic diameter relationship to virial coefficients provided further insight into stability. SMSLS detected as few as three dimerization events among 1000 monomeric proteins. Although early phase aggregation is linear in time and reproducible, aggregation becomes chaotic in later phases. SMSLS dramatically increases protein monitoring throughput, providing continuous monitoring for hours, weeks, and longer. New samples can be changed in and out without affecting other sample measurements in progress.