It's an eye-catching angle in the story of an experimental treatment
for Ebola: The drug comes from tobacco plants that were turned into
living pharmaceutical factories.
Using plants this way, sometimes
called "pharming" can produce complex and valuable proteins for
medicines. That approach, studied for about 20 years, hasn't caught on
widely in the pharmaceutical industry.
But some companies and
academic labs are pursuing it to create medicines and vaccines against
such targets as HIV, cancer, the deadly Marburg virus and norovirus,
known for causing outbreaks of stomach bug on cruise ships, as well as
Ebola.
While most of the work in this area uses a tobacco plant, it's just a relative of the plant used to make cigarettes.
"It's
definitely not something you smoke", said Jean-Luc Martre, a
spokesperson for Medicago, a Canadian company that's testing flu
vaccines made with tobacco plants.
Medicago has a new production
facility in Research Triangle Park, North Carolina. Once approved by
federal authorities, it's expected to be able to make 30 million doses
of seasonal flu vaccine a year, or 120 million vaccine doses to fight a
major outbreak of "pandemic" flu if the government requests it.
Scientists
favor tobacco plants because they grow quickly and their biology is
well understood, said Ben Locwin, a pharmaceutical biotech consultant in
Portsmouth, New Hampshire, who is considered an expert on
plant-produced medicines by the American association of pharmaceutical
scientists.
Zmapp
The North Carolina
operation can handle as many as 90 000 plants. Under the whir of fans,
rows of young seedlings grow for about a month, until they are about a
foot tall.
Then they are taken by robots to another section of the
facility, turned upside down and dipped in a tank to be "infiltrated"
with whatever proteins they wish to grow.
There are a number of
Ebola treatments and vaccine in development and one comes from tobacco
plants grown in specialized greenhouses at another operation, Kentucky
BioProcessing, in Owensboro, Kentucky.
That experimental
treatment, called ZMapp, uses proteins called antibodies, and is
designed to inactivate the Ebola virus and help the body kill infected
cells.
It hasn't been tested in people but had shown promise in
animal tests, so it was tried in three people sickened by Ebola in West
Africa, two US aid workers and a Spanish missionary priest, who later
died.
The last few doses available are in Liberia. Kentucky
BioProcessing, which produces it for the San Diego-based Mapp
Biopharmaceutical, said it would take several months to make more, but
it is working to increase production.
In general, the idea behind
pharming is to slip the genetic blueprints for a particular protein into
a plant and let the plant's protein-making machinery go to work.
Then
the protein can be extracted from plant tissues. While tobacco plants
are a mainstay of such work, proteins also have been produced in other
plants, such as safflower and potato.
In fact, the only medicine
made this way that the federal government has approved for general use
in people is made in a laboratory from cells of carrot plants. It treats
a genetic illness called Gaucher's disease.
Bacteria
The drug was approved in 2012 by the Food and Drug Administration.
A
plant-made vaccine for a chicken disease gained approval from the
department of agriculture in 2006 but was never brought to market.
Another plant-produced product to fight germs that cause tooth decay has
been approved for use in Europe.
The lack of any stronger track
record for approved drugs in the United States is a key reason why the
plant-based technology hasn't been embraced more fully, Locwin said.
That's
despite the fact that it offers benefits like lower cost than the
standard approach of using vats of cells from mammals to churn out
complex proteins, Locwin said.
Some companies use cells from
bacteria instead, but they can't always produce the complicated proteins
that drug companies need, he said.
The plant-based approach "has a
tremendous amount of promise, but it doesn't yet have the FDA blessing
across the board to be able to say this is successful" and a proven way
to get a drug to market, he said.
And it would cost companies money to change over to the new technology, he said.
Plant-based
drugs have attracted the attention and funding of the federal
government, however, as a fast and cheap approach to make a lot of
vaccine material in case of terrorist attacks, said Daniel Tuse, a
consultant and managing director of Intrusept Biomedicine, which also
works with tobacco plants in Owensboro.
If a new germ appears,
genetic material from it can be quickly inserted into plants, and large
numbers of the plants can churn out supplies of material for vaccines or
treatments, he said.
The plant-based experimental Ebola treatment was developed with government support.
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