TSRI scientists discover new method for harnessing venomsfor therapeutic use

There are lessons to be learned from venoms. Scorpions, snakes,
snails, frogs and other creatures are thought to produce tens
or even hundreds of millions of distinct venoms. These venoms
have been honed to strike specific targets in the body.

Chemists at The Scripps Research Institute have developed
a new method to isolate and analyze toxins produced by frogs,
snakes, scorpions and other creatures, opening the door to a
vast array of possible therapeutics. (Illustration used with
permission of Angewandte Chemie.)

For victims of a scorpion’s sting, that spells doom. For
scientists, however, the potent molecules in venoms hold the
potential to be adapted into medicines. But venoms are
difficult to isolate and analyze using traditional methods, so
only a handful have been turned into drugs.

Now a team led by scientists at The Scripps Research Institute
(TSRI) has invented a method for rapidly identifying venoms
that strike a specific target in the body—and optimizing such
venoms for therapeutic use.

The researchers demonstrated the new method by using it to
identify venoms that block a certain protein on T cells—a
protein implicated in multiple sclerosis, rheumatoid arthritis
and other inflammatory disorders. The researchers then used
their method to find an optimized, long-acting variant of a
venom that blocks this protein and showed that the new molecule
powerfully reduces inflammation in mice.

“Until now we haven’t had a way to seriously harness venoms’
vast therapeutic potential,” said principal investigator
Richard A. Lerner, Lita Annenberg Hazen Professor of
Immunochemistry at TSRI.

The report on the advance by Lerner and his colleagues was
selected as a “Hot Paper” and cover story by the journal
Angewandte Chemie.

Choose Your Poison

The use of venoms as therapies may seem paradoxical, since
these molecules generally evolved to harm and kill other
organisms. But a low dose delivered to the right place can
sometimes have highly beneficial effects. The pain-killing drug
ziconotide (Prialt®), for example, is derived from
one of the venoms used by cone-snails to immobilize their fishy
prey. Venoms also are attractive from a drug development
perspective because they tend to hit their targets on cells
with very high potency and selectivity.

Drug companies would have adapted far more venoms into
therapies by now, but the traditional method of determining the
biological target of a venom is slow, difficult and expensive.
It involves the extraction of relatively large quantities of
venom from the animal species in question, followed by
purification of the molecules and laborious lab-dish tests to
see how they affect cells.

The new method is geared for speed and involves the extraction
only of information—with little direct involvement of venomous
creatures. To start, the TSRI-led team, including first author
Hongkai Zhang, a senior scientist in the Lerner laboratory,
consulted animal toxin databases and assembled a list of 589
venoms whose protein sequences have features of interest. They
then synthesized the venoms’ genes and inserted them into
special viruses that deliver genes into cells.

The aim in this initial, proof-of-principle project was to find
venoms that block a potassium ion-channel protein known as
Kv1.3. Ion channels allow charged molecules to flow in and out
of cells, and are involved in a variety of essential biological
functions—which makes them common targets of venoms. Kv1.3 is
of special interest to the pharmaceutical industry because it
appears to facilitate the proliferation and migration of
T-cells that drive inflammatory disorders such as multiple
sclerosis. Drugs that block Kv1.3 are already under
development.

To screen their library of venoms for those that block Kv1.3,
the researchers, including a team of collaborating biologists
at the Institute for Advanced Immunochemical Studies at
ShanghaiTech University, used a cell-based selection system of
a type developed by Lerner, Zhang and colleagues in 2012. They
created a culture of special Kv1.3-containing test cells in
which a strong interaction between a venom and a Kv1.3 ion
channel would switch on a red fluorescence gene. The
researchers distributed the venom-gene-carrying viruses among
the cells and used a fast, automated system to select the cells
that showed strong fluorescence. Standard molecular biology
techniques were then used to identify and quantify the venom
genes these cells contained. The researchers repeated this
selection process for three rounds to see which venom genes
became most abundant in the cells.

In this way, the team soon identified 27 likely Kv1.3-blocking
venoms. All but two turned out to be known blockers of the ion
channel. Another had been reported in the literature as a
suspected potassium-channel blocker, and the last, an
uncharacterized scorpion venom called CllTx1, proved in
subsequent traditional-method testing—using actual venom
extracted from a scorpion—to be a potent Kv1.3 blocker.

Optimal Pharmaceutical Properties

The team realized that their selection system could be useful
not only for screening libraries of natural venoms but also for
screening artificial variants or “analogs” of a given venom to
find those with optimal pharmaceutical properties. To
demonstrate, they generated about a million analogs of a
long-acting protein based on ShK, a sea anemone toxin that
blocks Kv1.3, and put the analogs through three rounds of
selection to find the best one. The resulting candidate, S1-2,
showed a strong effect not only for blocking Kv1.3 but also for
reducing inflammation in a standard rodent model.

“This analog appears to be very potent against Kv1.3 and has no
off-target effects on closely related ion channels,” said
Zhang.

Zhang, Lerner and their colleagues now plan to use their method
with much larger venom datasets to find more drug candidates.
“We’re particularly interested in finding venoms that block
sodium ion channels involved in pain,” Lerner said.

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