Therapeutic proteins represent a fast growing class of drugs in the pharmaceutical market. Achieving a better understanding of the mechanisms responsible for protein aggregation is crucial for successful commercialization of protein drugs. In this work, we investigate the aggregation stability of several mAbs in conditions relevant for downstream processing. The time evolution of the aggregates is analyzed by a combination of dynamic light scattering, size exclusion chromatography and field flow fractionation. Secondary structure changes are monitored by circular dichroism and thioflavin binding.
The results get insights into the intricate combined effect of pH, salt, kind of salt, temperature and antibody class on aggregation stability. Depending on operating conditions either reversible oligomerization or aggregation into insoluble, high molecular weight aggregates may occur. The experimental results are rationalized by providing a mechanistic description of both processes which connects the aggregation kinetics to the protein conformational stability and colloidal stability.
Particularly, an anion specific effect in inducing aggregation is observed according to a ranking which follows the Hofmeister series with the exception of the sulphate anion. An explanation of the observed anion effect at the molecular level is proposed, which could also be extent to the stabilizing/de-stabilizing effect of co-solutes on protein stability.
P. Arosio, G. Barolo, T. Müller-Spath, H. Wu, and M. Morbidelli, Pharmaceutical Research; 2011, in press
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