Selective domain stabilization as a strategy to reduce human serum albumin-human granulocyte colony stimulating factor aggregation rate

Therapeutic proteins must be generally formulated to reduce unwanted aggregation. Fusion proteins, which comprise domains assembled from separate proteins, may require unique formulation strategies in order to maximize their stability. A fusion protein of human serum albumin (HSA) and human granulocyte colony stimulating factor (GCSF; HSA-GCSF) was used as a model to test the hypothesis that formulations that increase the thermodynamic conformational stability of the least stable domain of a fusion protein will stabilize the entire fusion protein against aggregation. Conformational stability of HSA-GCSF was modulated by addition of octanoic acid, which was previously shown to increase the conformational stability of HSA, the least stable domain. Contrary to our hypothesis, increased conformational stability of the HSA domain did not result in increased resistance to aggregation of HSA-GCSF. These results for HSA-GCSF were also compared with similar studies conducted previously on a therapeutic protein formed by the fusion of HSA and human growth hormone (hGH; HSA-hGH).