Product analysis - Pharmaceutical Biotechnology: Concepts and Aapplications - page 176

Table 7.1 The range and medical signifi cance of potential impurities present in biopharmaceutical
products destined for parenteral administration

Impurity Medical consequence

Microorganisms Potential establishment of a severe microbial infection - septicaemia

Viral particles Potential establishment of a severe viral infection

Pyrogenic substances Fever response that, in serious cases, culminates in death

DNA Signifi cance is unclear - could bring about an immunological response

Contaminating proteins Immunological reactions. Potential adverse effects if the contaminant

exhibits an unwanted biological activity

endonuleases to the cell homogenate to degrade the large quantity of DNA liberated upon cellular
disruption. (DNA promotes increased solution viscosity, rendering processing diffi cult. Viscosity,
being a function of the DNA's molecular mass, is reduced upon nuclease treatment.)
Minor amounts of protein could also potentially enter the product stream from additional
sources, e.g. protein shed from production personnel. Implementation of good manufacturing
practice (GMP), however, should minimize contamination from such sources.
The clinical signifi cance of protein-based impurities relates to (a) their potential biological
activities and (b) their antigenicity. Whereas some contaminants may display no undesirable bio-
logical activity, others may exhibit activities deleterious to either the product itself (e.g. proteases
that could modify/degrade the product) or the recipient patient (e.g. the presence of contaminating
toxins).
Their inherent immunogenicity also renders likely and immunological reaction against protein-
based impurities upon product administration to the recipient patient. This is particularly true in
the case of products produced in microbial or other recombinant systems (i.e. most biopharmaceu-
ticals). Although the product itself is likely to be non-immunogenic (usually being coded for by a
human gene), contaminant proteins will be endogenous to the host cell, and hence foreign to the
human body. Administration of the product can elicit an immune response against the contaminant.
This is particularly likely if a requirement exists for ongoing, repeat product administration (e.g. ad-
ministration of recombinant insulin). Immunological activation of this type could also potentially
(and more seriously) have a sensitizing effect on the recipient against the actual protein product.
In addition to distinct gene products, modifi ed forms of the protein of interest are also consid-
ered impurities, rendering desirable their removal from the product stream. Although some such
modifi ed forms may be innocuous, others may not. Modifi ed product 'impurities' may compro-
mise the product in a number of ways, e.g.:

• biologically inactive forms of the product will reduce overall product potency;

• some modifi ed product forms remain biologically active, but exhibit modifi ed pharmacokinetic

characteristics (i.e. timing and duration of drug action);

• modifi ed product forms may be immunogenic.

Altered forms of the protein of interest can be generated in a number of ways by covalent and non-
covalent modifi cations (e.g. see Table 6.5).