| Monoclonal
antibodies (mAbs) are the biotech bandwagon of the
moment. The massive success of Genentech’s
blockbuster mAbs (Rituxan sales alone peaked at more
than $1 billion last year) is heating up the race to
deliver the next “magic bullet.” Vast resources
are being poured into developing more effective,
safer, and less expensive mAbs through in-house
R&D efforts and via acquisitions or
collaborations. More than 50 companies are developing
mAbs, and according to ClinicalTrials.gov,
more than 400 clinical trials with such compounds are
ongoing. |
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MIGHTY
MAB
Xencor’s XmAb suite reengineers FC-domains. |
The
field is raging hot. Analysts at Datamonitor
reportedly expect the mAb market to triple by 2010,
reaching more than $30 billion. Meanwhile, the past
year has witnessed a number of big-money acquisitions:
Merck acquired GlycoFi for $400 million,
GlaxoSmithKline bought Corixa for $300 million, and
Roche acquired GlycArt Biotechnology for $180 million.
“I
think people are realizing that putting the same old
antibodies into the clinic as we have been the past
seven or eight years probably isn’t going to cut the
mustard,” states Bassil Dahiyat, CEO of Xencor. The
company’s PDA (Protein Design Automation) platform
combines proprietary computational software for
protein sequence design with protein expression
screening capability. It uses structure-based
information and rational algorithms to sift through
enormous numbers of possible protein sequences (up to
1040) for an engineered protein. “This
provides a short list of the possible changes you can
make to the protein sequence to improve that property.
Smaller numbers allow you to do much better assays,”
adds Dahiyat.
The
primary applications have been designed to improve
mAbs — a suite called XmAb. By reengineering the
FC-domain of antibodies, via adding new amino acid
sequences, the company has been able to greatly
improve the interaction of the FC region with the
immune system. The new, redesigned region can be used
in many different antibodies.
The
company is developing its own drug candidates and
hopes to have its first potential agent (a cancer
therapeutic for Hodgkin’s lymphoma) in Phase I
trials next year. “We think we’re going to have a
much [more] cytotoxic antibody to kill tumor cells as
a result of our FC domain that greatly enhances immune
activation,” Dahiyat says.
Shifting
Sugars
“Glycosylation can either facilitate or inhibit
interactions between the IgG and its functional
receptor and/or targeted antigen,” says Grace Chu, a
senior scientist at Amgen. “To develop the most
efficacious and stable mAb, detailed characterization
of each of the components that comprises the overall
heterogeneous mAb mixture is important,” she adds.
Shu’s
group has developed a method to analyze heterogeneous
mAbs with additional glycosylation in the Fab domain.
The researchers isolated each isoform from a complex
mixture and characterized its biophysical and
biochemical properties. The glycoforms presented
different stability behavior when formulated at the
same pH but stored at different temperatures. This
research is being used to understand the role of
glycosylation in protein stability and its
applicability towards future mAb development.
Altering
enzymes that affect glycosylation is one way
researchers are improving the ADCC (antibody-dependent
cellular cytotoxicity) response (enhances ability of
antibodies to kill tumor cells). Several companies
have technologies to alter glycosylation patterns.
Swiss-based GlycArt Biotechnology engineers antibody
production cell lines by adding a gene that suppresses
a sugar enzyme. This results in better binding to
antibody receptors. The company has several antibodies
in preclinical stages. Another company, BioWa, also
modifies glycosylation, but uses a different approach.
Their proprietary technology, Potelligent, creates 100
percent fucose-free mAbs, which the company says
increases potency up to 100-fold.
Instead
of using the recognition site of an antibody to
develop therapeutics, CovX Technologies is taking a
different approach. “We’ve created a system where
we can use the same antibody multiple times and attack
different therapeutic targets by changing the
programming agent,” explains Rodney Lappe, CSO. This
agent is a pharmacophore that incorporates one of the
company’s selective linker systems. The linker (a
small organic piece with an active recognition site
for the antibody) forms a covalent bond with a unique
reactive lysine. This makes it 1,000-fold more
reactive than a normal lysine on the surface of a
peptide or protein.
“The
technology allows you to balance the potency and
pharmacokinetics of the ‘CovX-Body’ by how you
adjust the linker — changing its length and location
on the peptide alters how it’s displayed, its
potency and half-life,” says Lappe. There are
currently two CovX-Bodies in preclinical development
targeting inhibition of angiogenesis, with the first
molecule to go to IND at the end of this year. A third
molecule is in late-stage discovery for metabolic
disease.
Researchers
at The Scripps Research Institute have recently
reported success using small-molecule targeting agents
to selectively direct the same antibody to various
sites for the treatment of metastatic breast cancer.
Studies in animal models showed the new compound
remained in circulation for a week versus only a few
minutes for the unaltered molecule. Mice treated with
the new agent developed significantly fewer metastases
than those treated with antibody alone or similar
compounds. This discovery, says lead researcher
Subhash Sinha, could have broad applications in the
treatment of other cancers and potentially increase
the efficacy of existing or underdeveloped
small-molecule therapies.
It’s
About the Cell Line
Most
companies agree on the importance of having a robust
cell line to produce sufficient antibodies in a
consistent way. “If you change the manufacturing
site of your monoclonal, you have to prove to the FDA
that this change did not change the quality of the
product,” explains Thomas Porter, director,
department of characterization and analytical
development, at Wyeth BioPharma. “They require
in-depth protein structural analysis of the new
material made at the new manufacturing site compared
to the original site — it’s called
comparability.”
Jeff
Hutchins, director of mAb development for Inhibitex,
says there is pressure for mAbs to conform to the same
sort of paradigm as well-characterized small
molecules. “CDER is looking for in-process
characterization — very tight reproducibility. The
standards are higher now. For small companies like us,
it ups the ante — we have to do Big Pharma diligence
on our molecules.” In response, his company is
trying to incorporate new technologies to characterize
molecules faster and select a cell line that is robust
and stable early on.
The
technologies Inhibitex are using include: ClonePix
(Genetics — UK), which identifies healthy,
antibody-producing cell colonies using a fluorescent
dye; PhyTip Columns (PhyNexus), which purify target
proteins from micro-volume samples (1 mL or less)
using micro-columns at the end of standard pipette
tips; and Guava ViaCount (Guava Technologies) — a
reagent that incorporates a DNA dye to quickly
determine cell viability, apoptotic fraction, and
total cell count for cultured cell lines.
Engineered
yeast provides a faster and cheaper way versus
mammalian cells to produce antibodies, says Tillman
Gerngross, CSO of GlycoFi. Their proprietary
technology has been used to develop a library of yeast
strains that modify glycosylation on a protein, making
it more human. By adding different glycoforms,
Gerngross says in some cases they are able to enhance
therapeutic activity of an antibody by more than
100-fold.
Whole
Antibodies
Although
there are several companies that are developing
antibody fragments (e.g., CellTech, Xoma), Alder
Pharmaceuticals has developed a proprietary yeast
expression system to make fully functional whole
antibodies. “We saw a need to improve on the
therapeutic properties of whole antibodies and fulfill
some unmet medical needs,” says Randy Schatzman,
CEO. The platform, called Mab Xpress, works by making
alpha-glycosylated antibodies that don’t rely on
ADCC — but have intrinsic function activity built
in. “ADCC brings a lot of safety issues that
complicate the therapeutic spectra for patients — it
causes cytokine release and activates the whole immune
system,” he explains. Another advantage to these
antibodies is that they are homogeneous proteins,
which makes them easier to validate. “We believe
this is the direction the industry is going in — to
make ADCC-free antibodies with much cleaner
profiles,” Schatzman summarizes.
As
more technologies develop, mAbs will continue to
evolve and treat a wider range of diseases. Perhaps a
new platform will enable companies to make monoclonals
less expensive (a year of Herceptin costs up to
$50,000 per patient). There’s little doubt that with
all the research and development going on in this
field, the next few years will deliver more than one
new magic bullet.
HOT
LINKS: In CovX-Bodies a pharmacophore is
connected to the binding site of a specially designed
antibody via specialized linkers.
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