MONOMERIC Fc-FUSION PROTEINS - Fusion Protein Technologies for Biopharmaceuticals: Applications and Challenges - page 114

dynamics of disulfide bond formation inside the cells.
Therefore, there can be significant variations in the percent-
age of monomer Fc fusion among individual cell lines and it
is often necessary to establish methods for selecting cell
lines that not only express high level of monomer Fc fusions
but also higher percentage of monomer Fc-fusion proteins. It
should be noted that fusion with Fc fragment often improves
the expression level [100] and the monomer Fc fusion
expression level is comparable to and often higher than
that of effector protein alone. In addition to expression,
challenges can also be encountered during purification
process in separation of Fc fusion monomer from Fc fusion
homodimer and Fc dimer, especially when the effector
protein is small in size and has similar charge and hydro-
phobicity to Fc fragment.

FSH- a fusedtoonearmofFcandFSH- b fused to the
other. FSHFc heterodimer has improved in vivo half-life
while maintaining FSH bioactivity. Thus the Fc fusion
technology has the potential to be applied to a wide range
of monomeric as well as heterodimeric peptides and
proteins in order to improve biological properties, provide
the potential for less frequent dosing and less invasive
routes of administration.

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7.6 CONCLUSIONS AND FUTURE
PERSPECTIVES

Protein therapeutics are a major source of drug development
initiatives in modern medicine. However, one of the most
challenging issues can be their short half-life in vivo.
Significant efforts have been made to develop approaches
to prolong the half-life of protein or peptide drugs. Fc fusion
technology, by which the Fc fragment of IgG is fused to a
protein or peptide drug to extend its in vivo half-life by
means of the FcRn recycling mechanism, is one of the
successful examples. Well-known and validated traditional
Fc-fusion drugs, such as etanercept for the treatment of
rheumatoid arthritis and the VEGF-trap for the treatment
of macular degeneration, consist of two copies of protein or
peptide molecules linked to the Fc region to improve PKs,
solubility, and production efficiency. This new class of Fc-
fusion proteins, Fc monomeric fusion, that links a single
copy of effector protein or peptide drug to the Fc region has
demonstrated improved biological properties, including fur-
ther extended half-life and increased bioavailability, com-
pared to traditional Fc fusion dimer. These fusion proteins
include EpoFc, IFN- b Fc, and IFN- a Fc that could be used
for the potential treatment of anemia, MS, and hepatitis C,
respectively. Additionally, blood coagulation factors-Fc
fusions (rFVIIIFc and rFIXFc) have also been generated
with this technology to create long-lasting clotting factors
for the treatment of hemophilia A and hemophilia B. Both
rFVIIIFc and rFIXFc have been shown to have increased
systemic half-lives in preclinical models and Phase I clinical
trials and are currently being evaluated in global pivotal
clinical trials.
In addition to monomeric and dimeric Fc-fusion pro-
teins, heterodimeric Fc-fusion proteins have also been
generated and shown to have improved biological propert-
ies. For example, FSH which is a heterodimer of a and b
subunits has been developed into an Fc heterodimer with

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