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Proteins are widely used as drugs—insulin
for diabetics is the best known example—and as reagents in research
laboratories, but they react poorly to fluctuations in temperature and are
known to degrade in storage.
Because of this instability, proteins must
be shipped and stored at regulated temperatures, resulting in increased costs,
and sometimes must be discarded because their “active” properties
have been lost. Manufacturers of protein drugs will generally add substances
known as excipients, like polyethylene glycol, to the proteins to prolong their
activity.
In a new study published in the Journal of the American Society of Chemistry,
investigators from the University of California, Los
Angeles (UCLA) Department of Chemistry and
Biochemistry and the California NanoSystems Institute at UCLA (CNSI) describe
how they synthesized polymers to attach to proteins in order to stabilize them
during shipping, storage, and other activities. The study findings suggest that
these polymers could be useful in stabilizing protein formulations.
The polymers consist of a polystyrene
backbone and side chains of trehalose, a disaccharide found various plants and
animals that can live for long periods with very little or no water. An example
many people will recognize is Sea-Monkeys—the ‘novelty aquarium pet’ introduced
in 1962. Sea–Monkeys can be purchased as kits that contain a white powder; when
water is added, the powder becomes small shrimp whose long tails are said to
resemble those of monkeys.
Trehalose is known to stabilize proteins
when water is removed, and as a result, it is an additive in several protein
drug formulations approved by the Food and Drug Administration (FDA) to treat
cancer and other conditions.
“Our polymers were synthesized by a
controlled radical polymerization technique called reversible
addition-fragmentation chain transfer (RAFT) polymerization in order to have
end groups that can attach to proteins to form what is called a protein-polymer
conjugate,” said Heather Maynard, a UCLA associate professor of chemistry
and biochemistry and a member of the CNSI. “We found that the polymers
significantly stabilized the protein we used—lysozyme—better to lyophilization
(freeze-drying, in which water is removed from the protein) and to heat than
did the protein with no additives.”
The research team found that attaching the
polymer covalently to the protein—that is, forming a protein-polymer conjugate—stabilized
the protein to lyophilization better than adding the non-conjugated polymer at
the same concentration.
The team also found that the polymers
stabilized lysozyme significantly better than the currently used excipients
trehalose and polyethylene glycol, depending on the stress and conditions used.
The Maynard research group is currently
exploring the use of their polymer as a stabilizer by attaching it or adding it
to FDA–approved protein therapeutics. In addition, they are investigating the
mechanism of how the polymer stabilizes proteins.
