Substantially Improved Stability of Biological Agents in Dried Form The Role of Glassy Dynamics in Preservation of Biopharmaceuticals

Recent advances in the field of biotechnology have led to products containing enzymes, antibodies, and many other biological agents suitable for use as pharmaceuticals, veterinarian preparations, and foods. Often, economic and ease-of-use considerations dictate that proteins be stabilized in a dry format. Well over a decade ago it became clear that carbohydrate glasses play a central role in anhydrous preservation of biological agents in nature (1, 2). Currently, simple sugars and sugar alcohols are often used as the primary preservation medium for biological agents (3–6). Unfortunately, formulation of such dried preparations can be a very complex process. Consideration must be made for processing the aqueous formulation and for both the physical and biochemical stability of the final dried product. Dried biopharmaceuticals are typically prepared in a glassy matrix by spray drying or lyophilization. When the glassformer is a simple sugar, physical properties of the dried products are often not robust. For example, even small amounts of residual moisture can cause the lyophilate to shrink and collapse or cause the spray-dried powder to fuse and cake up. In either case, the product does not redissolve readily. Polymer glasses have the advantage of yielding products with good physical characteristics, but when used alone, they seem to be less effective than small-molecule glassformers at preserving biological agents (7–11). Formulations that combine smallmolecule sugars with polymers (12–15) or amino acids (16–19) seem to yield products with both good physical characteristics and good biopreservation. Amino acids are used in freeze-drying for their propensity to crystallize and form a continuous crystalline network throughout the product, giving it structural support. The drawback to this approach is that proteins are not stabilized in the crystalline phase (20, 21), and sometimes loss of product occurs in these formulations (22). Polymers also provide structural support to the product, but they do so by virtue of their ability to form physical networks, and crystallization is not necessarily involved. The advantage of product being nominally 100% amorphous must be weighed against the fact that such formulations often also have higher viscosity in the aqueous phase and may thus be more difficult to handle. Stability concerns. If liquid handling and physical properties of the dried product were the only concerns, formulation of biopharmaceuticals would be greatly simplified. Obviously, biochemical stability is also of utmost importance. As an added complication, the factors governing stability of biological structures or biomacromolecules in a dried format are only poorly understood. These factors may be broadly categorized as either related to dynamics or thermodynamics. Spectroscopic (23) and phenomenological (24–26) Substantially Improved Stability of Biological Agents in Dried Form The Role of Glassy Dynamics in Preservation of Biopharmaceuticals