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October 01, 2010 (Vol. 30, No. 17)

Enhancing Stabilization of Protein Products

Recombinant Albumin Characterization as a Robust Formulation Pharmaceutical Excipient

  • Protein therapeutics can be susceptible to a range of stresses during manufacturing and storage that can trigger protein instability and degradation. Protein degradation can take the form of aggregation, denaturation, or absorption and can arise as a result of changes in temperature, shear stresses, and lyophilization.

    Oxidation of the protein during processing and storage is also common. With the potential to increase immunogenicity and decrease efficiency and shelf life of the protein drug product, protein stability is a key issue.

    Protein therapeutics are formulated to protect against degradation and provide a suitable shelf life for transportation and storage. Human serum albumin (HSA) has been commonly used as an excipient in therapeutic protein formulations. As the most abundant protein in human plasma, the potential for HSA to elicit an immunogenic response is minimal.

    Formulation scientists, however, have moved away from its use due to concerns that blood-borne contaminants such as prions or viruses that may contaminate the final drug product.

  • rAlbumin's Stabilization Effect

    Click Image To Enlarge +
    Figure 1. Suppression of MSP-2 protein aggregation in the presence of rAlbumin, glycine, polysorbate 80, or PEG over time

    Aggregation can cause numerous issues during the therapeutic protein manufacturing process. This association of mis-folded proteins can result in significant product losses, potentially increasing the immunogenicity of the drug product. Aggregation can occur as a consequence of process operations like refolding, purification, mixing, freeze-thawing, freeze drying, and reconstitution as well as during transportation and storage.

    In a study conducted at Novozymes Biopharma, recombinant albumin was evaluated for its ability to suppress amyloid-fibril formation by the merozoite surface protein, MSP-2 protein, after a single freeze–thaw cycle.

    A range of rAlbumin concentrations was evaluated for their ability to suppress aggregation, where fibril formation was measured by the effect on light scattering at 320 nm.

    rAlbumin at various concentrations was dissolved in a solution of PBS buffer; the MSP-2 protein (3.5 mg/mL) was then added to all samples followed by a single freeze-thaw cycle. Samples were then aliquoted into 96-well plates and stored at 2–8ºC. Absorbance readings were taken at multiple time intervals over a five-day period.

    Excipients, which are widely applied across the industry to enhance protein stability, were also assessed against rAlbumin for their ability to reduce protein aggregation. rAlbumin (15 mg/mL), glycine (20 mg/mL), PEG 400 (1 mg/mL), polysorbate 80 (0.82 mg/mL), or polysorbate 80 (8.2 mg/mL) were tested in the same model as described above.

    Aggregation was suppressed by 50% at a 1:1 molar ratio of the antigen to rAlbumin and reduced by 80% in the presence of the highest concentration of rAlbumin. rAlbumin also suppressed aggregation of the MSP-2 antigen to a greater extent compared to other commercially available excipients (Figure 1).

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