What is prostate
cancer’s secret weapon? What allows it to survive an onslaught of
the most lethal chemotherapy drugs known to science? Why, if such drugs
are akin to amini-nuclear blast, do a few cells manage to stagger out
of the mushroom cloud, and start growing again?
This is called “therapeutic resistance, ”and it’s one
of the biggest challenges facing men with advanced prostate cancer, and
the doctors working to treat it. Prostate cancer succeeds, in large part,
by sheer diversity, Its cells are notoriously heterogeneous — which
means that each cell can respond differently to the same type of therapy.
This differential response is the ultimate culprit that causes cancer
to turn aggressive, as the milder cancer cells are killed, and the tougher
ones — the ones resistant to further therapy — survive.
|The most lethal drugs are like amini-nuclear
blast to cancer. And yet,a few cells manage to stagger out of the
mushroom cloud,and start growing again.
Jun Luo, Ph.D., assistant professor ofu rology, wants to figure out what’s
in the hardiest cells’ survival kits. What do they need, or what
do they do, so they can survive in the cytotoxic environment created by
the cell-killing drugs? As a basic scientist, he is particularly interested
in how cancer cells sense the danger, make last-minute adjustments, repopulate,
and thrive. With funding help from The Peter Jay Sharp Foundation, he
is focusing on a particular part of the cell, called the endoplamic reticulum
(ER), which is responsible for the folding and maturation of proteins
that will eventually be secreted outside the cell.
“The ER is very sensitive to environmental changes,” Luo
explains, “and may be the sensor that determines the survivability
ofthe cancer cells.” Like a military bunker in wartime, the ER is
chock-full of sensors, and functions to keep the cell alive even when
it’s under attack. “Characterizing the key molecular sensors
will give us new targets for advanced therapeutics that can disrupt the
adaptive strategies that cancer cells use to survive treatment.”
Luo believes that these sensors may be moving targets — that, like
emergency batteries, they switch on and off, and probably provide just
the immediate and transient relief that cancer cells need to survive the
therapy. His challenge now is to catch them in the act.
Working on a molecular level, Luo is using cutting-edge technologies
such as microarray to investigate the machinery that enables cancer cells
to respond and adapt to stress. His results are promising: Already, Luo
has found a molecule, named AGR2, that is massively over-produced in cancer
cells subjected to the toxic stress that happens in chemotherapy. This
molecule is quickly sensed by the ER. Luo has also found that this molecule
is over-produced in human prostate cancer tissues.
Luo’s work, says Patrick C. Walsh, M.D., University Distinguished
Professor of Urology, “proves that cancer cells have acquired the
readiness to respond and adapt to stress conditions caused by the therapeutic
drugs.While there is much work to do to follow this important lead, the
basic concept is starting to bear fruit.” The next step is to design
with this “secret weapon” in mind — to target and disable
the adaptive response pathway that cancer cells use to evade primary therapy.