Downstream processing - Pharmaceutical Biotechnology: Concepts and Aapplications - page 166

6.9.2 Stabilizing excipients used in fi nal product formulations

A range of various substances may be added to a purifi ed therapeutic protein in order to stabilize
that product ( Table 6.7). Such agents can stabilize proteins in a number of different ways, and
some specifi c examples are outlined below.
Serum albumin addition has been shown to stabilize various different polypeptides ( Table 6.8).
HSA is often employed in the case of biopharmaceuticals destined for parenteral administration
to humans. In many cases, it is used in combination with additional stabilizers, including amino
acids (mainly glycine) and carbohydrates. Serum albumin itself is quite a s table molecule, capable
of withstanding conditions of low pH or elevated temperature (it is s table for over 10 h at 60 C). It

also displays excellent solubility characteristics. It is postulated that albumin stabilizers exert their
stabilizing infl uences by both direct and indirect means. Certainly, it helps decrease the level of
surface adsorption of the active biopharmaceutical to the internal walls of fi nal product contain-
ers. It also could act as an alternative target, for example, for traces of proteases or other agents
that could be deleterious to the product. It may also function to stabilize the native conformation
of many proteins directly. It has been shown to be an effective cryoprotectant for several biophar-
maceuticals (e.g. IL-2, tPA and various interferon preparations), helping to minimize potentially
detrimental effects of the freeze-drying process on the product.
However, the use of HSA in now discouraged due to the possibility of accidental transmission
of blood-borne pathogens. The use of recombinant HSA would overcome such fears.
Various amino acids are also used as stabilizing agents for some biopharmaceutical products
( Table 6.9). Glycine is most often employed, and it (as well as other amino acids) has been found
to help stabilize various interferon preparations, as well as EPO, factor VIII, urokinase and ar-
ginase. Amino acids are generally added to fi nal product at concentrations ranging from 0.5 per
cent to 5 per cent. They appear to exert their stabilizing infl uence by various means, including
reducing surface adsorption of product, inhibiting aggregate formation, and directly stabilizing

Table 6.7 Some major excipient groups that may be added to protein-based
biopharmaceuticals in order to stabilize the biological activity of the fi nished product

Serum albumin
Various individual amino acids
Various carbohydrates
Alcohols and polyols
Surfactants

Table 6.8 Various biopharmaceutical preparations for which HSA has
been described as a potential stabilizer

IFN-α and -β interferons tPA

IFN-γ Tumor necrosis factor

IL-2 Monoclonal antibody preparations

Urokinase γ-Globulin preparations

EPO Hepatitis B surface antigen