Biomedical Engineering Reference
In-Depth Information
both teplizumab (MGA031), an anti-CD3 mAb, and
LY2189265, a GLP-1-Fc fusion, containing the same
Ala
234
and Ala
235
mutations, are in late clinical studies for
type 1 diabetes [105,106]. Recently, Davis et al. reported that
serine substitutions of cysteines at positions 130, 136, and 139
and proline at position 148 in the Fc domain eliminated both
CDC and ADCC activities of abatacept, a CTLA4-Ig fusion
drug [74]. Other approaches have been developed based on
the low level of IgG2 binding to Fc
g
Rs [59] and on the
inability of IgG4 to activate the complement cascade [60],
such as the IgG2/IgG4 hybrid constant region approach used
for eculizumab [78] and the recent approach developed by
Strohl, in which several IgG4 amino acids on the CH2 domain
were introduced into IgG2 at the same position [61].
cleavage and improvement of their physicochemical propert-
ies and advances in production which lower costs; peptide-
based therapeutics have become one of the fastest growing
classes of new drugs in the last few decades. However,
peptides currently account for only 2%of drugs on the market
and none of them become blockbusters comparable to some
recombinant protein therapeutics. The main limitation of
peptides is their short half-lives due to rapid clearance
in vivo. Several techniques, such as PEGylation and HSA
fusion, show promise in prolonging the serum half-life for a
variety of peptides. However, Fc fusion is still the most
advanced strategy in drug development for this purpose.
Withmultiple drugs on the market andmanymore exciting
newmolecules in the pipeline for treating a variety of different
diseases, Fc-fusion proteins, which couple the desirable
biophysical and pharmacokinetic properties of antibodies
with the bioactivity of peptides or proteins fusion partners,
have proven to be an important part of the protein therapeutic
family. Several peptide-Fc-fusion techniques, including pep-
tibody and MIMETIBODY platforms along with other pep-
tide-Fc-fusion approaches discussed in this chapter,
demonstrate the potential for successfully displaying and
prolonging the circulating half-lives of bioactive peptides
and thus represent valuable approaches for engineering pep-
tide therapeutics. For a peptide-Fc-fusion protein to become a
successful therapeutic, it is often necessary to optimize its
biological, biophysical, and pharmacological properties, such
as activity, stability, solubility, heterogeneity, and PK profiles.
Rational protein engineering methods that rely on structural,
computational, or biochemical information about the ligand-
receptor systemof interest are still themost useful approaches
for this purpose, in particular for engineering efforts to
improve protein agonist activities. The development of com-
binatorial engineering technologies to identify protein var-
iants with improved biological and biophysical properties,
rather than just binding affinity, will be the key to future
success of Fc-fusion protein therapeutics.
8.6.8 Reducing Immunogenicity
Although therapeutic proteins are generally safe and non-
toxic, the potential of inducing immune responses is always
a concern. Antidrug antibody (ADA) responses were
observed in patients treated with a variety of human proteins
including insulin, factor VIII, IFN, and erythropoietin (Epo)
[62,63]. ADAs are of particular concern in that they might
decrease the efficacy of the drugs by neutralizing or reducing
the circulating half-life of drugs and might also be associated
with serious safety issues by cross-neutralizing antibodies to
endogenous proteins. Owing to a lack of reliable in vitro
assays and in vivo animal models to predict the immune
responses in humans, a few successful examples exist to
illustrate successful protein engineering efforts for reducing
the immunogenicity of protein therapeutics except for the
humanization of murine antibodies. Nevertheless, several
factors should be considered in the design and engineering
of a therapeutic protein. (1) Since the immune response is
generally more severe for nonhuman proteins, efforts should
be made to avoid extensive modification of human
sequences. (2) Since physical properties such as solubility,
stability, and physical state (oligomers or aggregates) of a
therapeutic protein as well as the administration dosage,
frequency and route of administration can be important
factors in the induction of human immune responses, it is
well worth the efforts to engineer a therapeutic protein to
have better physical, chemical, biological, and pharmaco-
logical properties. (3) Since T-cell epitopes are important for
T-cell-dependent immune responses, it is worthwhile to
remove in silico predicted T-cell epitopes from nonhuman
protein sequences as long as it does not significantly affect
other properties of the protein.
ACKNOWLEDGMENT
The authors would like to thank Lu Lu and Tracy Spinka-
Doms for their technical assistance.
REFERENCES
1. Leader B, Baca QJ, Golan DE. (2008) Protein therapeutics: a
summary and pharmacological classification. Nat. Rev. Drug
Discov. 7, 21-39.
2. Lawrence S. (2007) Pipelines turn to biotech. Nat. Biotechnol.
25, 1342-1342.
3. Huggett B, Hodgson J, Lahteenmaki R. (2011) Public biotech
2010-the numbers. Nature Biotechnology 29, 585-591.
8.7 CONCLUSIONS
Thanks to advances in technologies including chemical mod-
ification of peptides to enhance their resistance to protease
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