Sources and upstream processing - Pharmaceutical Biotechnology: Concepts and Aapplications - page 111

Table 5.4 Proteins of actual or potential therapeutic use that are
glycosylated when produced naturally in the body (or by hydridoma
technology in the case of monoclonal antibodies). These proteins are
discussed in detail in various subsequent chapters. See also Table 2.9
Most interleukins (IL-1 being an important exception)
IFN-β and -γ (most IFN-αs are unglycosylated)
CSFs
TNFs
Gonadotrophins (FSH, luteinizing hormone and hCG)
Blood factors (e.g. Factor VII, VIII and IX)
EPO
Thrombopoietin
tPA
α 1 -Antitrypsin
Intact monoclonal antibodies
An alternative means of reducing/potentially eliminating inclusion body accumulation entails
the high-level co-expression of molecular chaperones along with the protein of interest. Chaper-
ones are themselves proteins that promote proper and full folding of other proteins into their bio-
logically active, native three-dimensional shape. They usually achieve this by transiently binding
to the target protein during the early stages of its folding and guiding further folding by prevent-
ing/correcting the occurrence of improper hydrophobic associations.
The inability of prokaryotes such as E. coli to carry out post-translational modifi cations (par-
ticularly glycosylation) can limit their usefulness as production systems for some therapeuti-
cally useful proteins. Many such proteins, when produced naturally in the body, are glycosylated
(Table 5.4). However, the lack of the carbohydrate component of some glycoproteins has little, if
any, negative infl uence upon their biological activity. The unglycosylated form of IL-2, for exam-
ple, displays essentially identical biological activity to that of the native glycosylated molecule. In
such cases, E. coli can serve as a satisfactory production system.
Another concern with regard to the use of E. coli is the presence on its surface of LPS molecules.
The pyrogenic nature of LPS (Chapter 7) renders essential its removal from the product stream.
Fortunately, several commonly employed downstream processing procedures achieve such a
separation without any great diffi culty.
5.2.2 Expression of recombinant proteins in animal cell culture systems
Technical advances facilitating genetic manipulation of animal cells now allow routine production
of therapeutic proteins in such systems. The major advantage of these systems is their ability to
carry out post-translational modifi cation of the protein product. As a result, many biopharmaceu-
ticals that are naturally glycosylated are now produced in animal cell lines. CHO and BHK cells
have become particularly popular in this regard.
Although their ability to carry out post-translational modifi cations renders their use desira-
ble/essential for producing many biopharmaceuticals, animal cell-based systems do suffer from
a number of disadvantages. When compared with E. coli , animal cells display a very complex