Relationship between native-state solubility and non-native aggregation of recombinant human granulocyte colony stimulating factor: practical implications for protein therapeutic development.

Abstract

Prescreening methods are needed in the biotechnology industry for rapid selection of protein therapeutic candidates and formulations of low aggregation propensity. In recent reports solubility measurements have shown promise as one such method, although the connection between protein solubility and non-native aggregation is not well understood. In the present investigation, recombinant human granulocyte colony stimulating factor (rhGCSF) was used to explore this relationship since it was previously shown to rapidly undergo non-native aggregation/precipitation under physiological conditions in a reaction attenuated by the addition of sucrose [Krishnan, S.; et al. Biochemistry 2002, 41, 6422-6431]. Strong correlations were found between rhGCSF non-native aggregation and both solubility and thermal stability as a function of sucrose concentration. We believe these results make sense in the context of an rhGCSF aggregation mechanism where loss of monomer to insoluble aggregate is limited by association to an observable dimer from a less soluble (and aggregation competent) intermediate species that exists in a temperature sensitive pre-equilibrium with the native monomer. Both solubility and measures of conformational stability report on the position of this equilibrium and therefore the concentration of reactive intermediate. Interestingly, aggregation also correlated with rhGCSF solubility as a function of salting-in concentrations of phosphate since both are dependent on the colloidal stability of the reactive intermediate but not with conformational stability. In lieu of a complete understanding of the aggregation processes that limit protein therapeutic shelf life, these results highlight the potential of using simple solubility measurements as an additional tool in the biotechnology prescreening repertoire.