| Low Levels of Common Enzyme Key to Resistance
in Ewing’s Sarcoma
A study from scientists at the University of Freiburg, Germany,
and their collaborators at the National Cancer Institute (NCI),
part of the National Institutes of Health, has pinpointed a potential
mechanism for resistance of Ewing’s sarcoma, a type of bone cancer, to
a protein that may be useful in fighting cancer — and a possible
method for overcoming this resistance. The results appear
online May 23, 2007, in the Journal of Pathology.
The protein, called TRAIL (tumor necrosis factor apoptosis-inducing
ligand),has generated tremendous interest among scientists looking
for new therapies that target cancer cells but spare normal dividing
cells. TRAIL binds to receptors on the surface of cancer cells
and sets off a series of signals that cause the cells to commit
suicide. Almost all normal cells are unaffected by TRAIL. The cells
of many solid tumors, including Ewing’s sarcoma, have shown extreme
sensitivity to TRAIL in laboratory experiments, and investigators
have started testing the protein in early clinical trials.
Ewing’s sarcoma is the second most common bone tumor in children
and adolescents. For children who have metastatic or relapsed disease,
their prognosis is poor. More effective treatments are needed for
The scientists who conducted the study, led by Udo Kontny, M.D.
from the University of Freiburg, showed that Ewing’s sarcoma cells
that express low levels of an enzyme called caspase-8, which plays
a role in cell suicide (apoptosis), are resistant to TRAIL-induced
killing. However, the addition of interferon-gamma, a protein produced
by cells of the immune system, to treatment with TRAIL caused the
resistant cells to produce more caspase-8, making them once again
sensitive to TRAIL-induced death.
“This study is an excellent example of how modern molecular biology
can help us unlock the detailed mechanisms driving the new, targeted
therapies for cancer,” said NCI Director John E. Niederhuber, M.D. “If
a targeted treatment that shows promise in the laboratory does
not work as expected in clinical trials, we need to go back and
understand what properties of the cancer cells might be driving
“When you look in the test tube, it’s really quite remarkable
how quickly and dramatically Ewing’s sarcoma is killed by TRAIL,” explained
Crystal Mackall, M.D., from NCI’s Center for Cancer Research (CCR),
whose laboratory headed the NCI portion of the investigation. “But
the initial results in animal studies were just not as effective
as we would have expected. So we ended up thinking that, however
this tumor is becoming resistant, it must be really important,
and we’re going to need to add something to improve the effectiveness
of TRAIL treatment in the clinic.”
The scientists focused on caspase-8 because lack of the protein
had been linked in laboratory studies to TRAIL resistance in Ewing’s
sarcoma cells and the cells of other tumors. To see if caspase-8
expression is also limited in tumor tissues acquired from patients,
the researchers measured the expression of caspase-8 in 54 tissue
samples taken from 47 patients with Ewing’s sarcoma. They found
that, while 50 out of the 54 samples expressed caspase-8, the number
of cells within each sample that expressed the protein varied considerably.
In 76 percent of the samples, caspase-8 expression was detected
in 60 to 100 percent of the cells. In the other 24 percent of the
samples, caspase-8 expression was detected in only 0 to 50 percent
of the cells. Therefore, within any individual Ewing’’s sarcoma
tumor, cells that lack caspase-8 could cause resistance to TRAIL.
The investigators next tested whether interferon-gamma, which
has been shown in the laboratory to increase caspase-8 expression
in cells, could sensitize Ewings’s sarcoma cells with low expression
of caspase-8 to treatment with TRAIL. They found that doses of
interferon-gamma, within the range easily tolerated by patients,
increased caspase-8 expression in caspase-8-deficient cells. When
the interferon-gamma-treated cells were treated with TRAIL, they
underwent cell death, indicating restored sensitivity to TRAIL.
Because most patients with Ewing’s sarcoma undergo chemotherapy,
the investigators also looked at whether chemotherapy alters the
levels of caspase-8 in Ewing’s sarcoma tumors. Using samples from
the same 47 patients, they compared the number of tumor cells expressing
caspase-8 between tumor samples collected before and after chemotherapy.
They did not find any significant difference between the samples,
suggesting that chemotherapy does not select for tumor cells that
lack caspase-8, which would make subsequent treatment with TRAIL
less effective. Data indicated that caspase-8 does not influence
the sensitivity of Ewing’s sarcoma tumors to chemotherapy.
The investigators confirmed these results in the laboratory. When
cells with different levels of caspase-8 expression were treated
with the chemotherapy drug doxorubicin, no differences in sensitivity
to the drug were seen. Changing the levels of caspase-8 expressed
by the cells, genetically or by adding interferon-gamma, did not
alter their sensitivity to chemotherapy, indicating “that the combination
of TRAIL and interferon-gamma with standard chemotherapeutics in
Ewing’s sarcoma could be feasible,” stated the authors.
“I’d like to see a clinical trial in humans of interferon-gamma
and TRAIL or an agent that interacts with the TRAIL receptor, because
I do believe that adding interferon-gamma will make cells more
susceptible to TRAIL-induced killing,” said Dr. Mackall. An early
phase study will be particularly important, she explained, because
it is possible that adding interferon-gamma to treatment with TRAIL
might also increase the incidence of side effects.
Lissat A, Vraetz T, Tsokos M, Klein R, Braun M, Koutelia N, Fisch
P, Romero ME, Long L, Noellke P, Mackall CL, Niemeyer CM, Kontny
U. Interferon-gamma sensitizes resistant Ewing’s sarcoma cells
to TRAIL-induced apoptosis by upregulation of caspase-8 without
altering chemosensitivity. J Pathol. Published online
May 23, 2007.
Researchers are from the Division of Pediatric Hematology and
Oncology and the Institute of Pathology, University of Freiburg,
Germany; and the Pediatric Oncology Branch and Laboratory of Pathology,
CCR, NCI, Bethesda, Md.
For more information on NCI's Laboratory of Pathology, visit http://ccr.cancer.gov/labs/lab.asp?labid=106.
For more information about cancer, please visit the NCI Web site
at http://www.cancer.gov, or
call NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237).
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