Solving a Traditional Chinese Medicine Mystery:
Discovery of Molecular Mechanism Reveals Antitumor Possibilities
ScienceDaily (Mar. 7, 2011) — Researchers at the Johns Hopkins School
of Medicine have discovered that a natural product isolated from a traditional Chinese
medicinal plant commonly known as thunder god vine, or lei gong teng, and used for hundreds
of years to treat many conditions including rheumatoid arthritis works by blocking gene control
machinery in the cell. The report, published as a cover story of the March issue of Nature
Chemical Biology, suggests that the natural product could be a starting point for developing
new anticancer drugs.
"Extracts of this medicinal plant have been used to treat a whole host of conditions and have been
highly lauded for anti-inflammatory, immunosuppressive, contraceptive and antitumor activities," says Jun
O. Liu, Ph.D., a professor of pharmacology and molecular sciences at Johns Hopkins. "We've known about
the active compound, triptolide, and that it stops cell growth, since 1972, but only now have we
figured out what it does."
Triptolide, the active ingredient purified from the plant Tripterygium wilfordii Hook F, has been shown
in animal models to be effective against cancer, arthritis and skin graft rejection. In fact, says Liu,
triptolide has been shown to block the growth of all 60 U.S. National Cancer Institute cell lines at very
low doses, and even causes some of those cell lines to die. Other experiments have suggested that
triptolide interferes with proteins known to activate genes, which gives Liu and colleagues an entry
point into their research.
The team systematically tested triptolide's effect on different proteins involved with gene control by
looking at how much new DNA, RNA and protein is made in cells. They treated HeLa cells with triptolide for
one hour, compared treated to untreated cells and found that triptolide took much longer to have an effect
on the levels of newly made proteins and DNA, yet almost immediately blocked manufacture of new RNA. The
researchers then looked more closely at the three groups of enzymes that make RNA and found that low
doses of triptolide blocked only one, RNAPII.
But the RNAPII enzyme complex actually requires the assistance of several smaller clusters of proteins,
according to Liu, which required more investigative narrowing down. Using a small gene fragment in a test
tube, the researchers mixed in RNAPII components and in some tubes included triptolide and some not to see
which combinations resulted in manufacture of new RNA. Every combination of proteins that included a
cluster called TFIIH stopped working in the presence of triptolide.
But again, TFIIH is made of 10 individual proteins, many of which, according to Liu, have distinct and
testable activities. Using information already known about these proteins and testing the rest to see if
triptolide would alter their behaviors, the research team finally found that triptolide directly binds to
and blocks the enzymatic activity of one of the 10, the XPB protein.
"We were fairly certain it was XPB because other researchers had found triptolide to bind to an unknown
protein of the same size, but they weren't able to identify it," says Liu. "
To convince themselves that the interaction between triplotide and XPB is what stops cells from growing,
the researchers made 12 chemicals related to triplotide with a wide range of activity and treated HeLa
cells with each of the 12 chemicals at several different doses. By both counting cells and testing XPB
activity levels, the team found that the two correlate; chemicals that were better at decreasing XPB
activity were also better at stopping cell growth and vice versa.
"Triptolide's general ability to stop RNAPII activity explains its anti-inflammatory and anticancer
effects," says Liu. "And its behavior has important additional implications for circumventing the
resistance that some cancer cells develop to certain anticancer drugs. We're eager to study it further
to see what it can do for future cancer therapy."
This research was supported in part by discretionary funds from the Johns Hopkins Department of
Pharmacology and the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins.
Authors on the paper include Denis Titov, Qing-Li He, Shridhar Bhat, Woon-Kai Low, Yongjun Dang, Michael
Smeaton and Jun O. Liu of Johns Hopkins; Benjamin Gilman, Jennifer Kugel and James Goodrich of the
University of Colorado, Boulder; and Arnold Demain of Drew University, Madison, N.J.
Johns Hopkins Medical Institutions. "Solving a traditional Chinese medicine mystery: Discovery of
molecular mechanism reveals antitumor possibilities." ScienceDaily 7 March 2011. 14 March