I am lying on a gurney being wheeled into an outpatient operating room, in part because of
Stanley Lada, a coal miner who died in 1944, three years before I was born. This procedure is no
big deal, I keep telling myself. No. Big. Deal. Really. And honestly it isn't. Nonetheless, during
the intake procedure the nurse raises her eyebrows at my blood pressure. "You're a little
nervous, aren't you?" she notes. And, because of Stanley Lada, the honest answer is "Uh-hunh."
The orderly pushes the gurney down a long corridor, then through double doors into a
brightly lit room, where a doctor and two nurses in surgical scrubs await. We introduce
ourselves, engage in a minute or two of small talk, and then it's down to business. I turn on my
side, and the nurse injects a liquid into the IV shunt in my wrist. It feels like cold water splashing
on top of my hand. And then . . . without skipping a beat it seems to me, the doctor shows me a
color photo of the insides of a pink vacuum-cleaner hose.
"Some of my patients actually frame these as souvenirs," he says as he hands me the
photo.
I feel a little woozy, not from any drug that's been administered but from the out-of-body
experience of looking deep within my own body. The pink vacuum-cleaner hose is, in fact, the
interior of my own large intestine, my colon.
"We found two small polyps and took care of them," my gastroenterologist says. "You'll
get a pathology report in the mail. But I wouldn't worry; they looked fine." And when the report
comes a few days later that's exactly what it says. Stanley Lada, however, wasn't so lucky. I am
acutely aware that my grandfather died from colon cancer at precisely my age, and therefore of
my need to be screened regularly for the disease since I may be at slightly higher risk.
This is my second colonoscopy, a procedure in which a tiny hollow tube with a light and
video camera has been snaked up my internal plumbing, allowing a doctor to visually inspect my
innards for polyps, small nodules that for unknown reasons sometimes form and sometimes
become cancerous. I feel absolutely no discomfort afterward, even though the doctor has snipped
off two polyps with tiny clippers attached to the scope. As promised, the IV sedative induced a
blip of amnesia that erased any recollection of a procedure which lasted less than an hour. All I
experienced of the colonoscopy was the cold splash of the IV and the doctor handing me the
photo. That's it. No big deal, just like I said.
Colon cancer, however, is a big deal. After lung cancer, it is the second-leading cause of
cancer deaths in the United States. More than 130,000 new cases are diagnosed annually, while
the disease claims 56,000 lives a year. Among them are the rich and the famous, like Charles
Schulz, creator of the Peanuts comic strip, former Israeli foreign minister Moshe Dayan, Jackie
Gleason and Audrey Hepburn, as well as the poor and unknown like Stanley Lada. By all rights,
however, the death toll shouldn't be nearly so high, since colon cancer is among the most
treatable and curable cancers if caught early enough. And there's the catch. Most fatal cases are
not discovered early.
Which brings us back to colonoscopies and other screening methods. Typically colon
cancer forms first in a polyp that, if it is cancer-prone, takes from five to 15 years to morph to a
cancerous state, giving ample opportunity to interrupt the process through surgery, radiation
and/or chemotherapy. Since the disease rarely strikes before 50, doctors recommend screening
begin at that age.
With its 94 percent success rate in detecting cancer and ability to remove suspect polyps,
the colonoscopy remains the gold standard of screening tests over such methods as the fecal
occult blood test, which detects telltale traces of blood in the stool; the barium enema, used to
make an X-ray image of the colon; and the sigmoidoscopy, which is similar to a colonoscopy but
examines only the lower colon and rectum.
Arguably, colonoscopy remains even superior to such recent advances as the new DNA
test for colon cancer and the virtual colonoscopy, which employs a CT or MRI scan of the colon.
The DNA test is about 30 percent less accurate than conventional colonoscopy, while virtual
colonoscopy can miss small polyps -- although smaller polyps rarely are cancerous -- and it
cannot take tissue samples or remove polyps.
Nonetheless, while colonoscopy may be the current gold standard, it is not the ideal
screening test. Like anything gold, it's expensive. Colonoscopies, which are covered to some
extent by Medicare and most insurance plans, can cost anywhere from $800 to $1,600, and
obviously are costly in terms of time and skilled-labor. Beyond that, although extremely rare,
there is a remote chance of complication. Finally, notwithstanding my testimonial, many people
are squeamish because the procedure is invasive and requires clearing your digestive tract.
The bottom line is that for all the above reasons and more, the number of people getting
screened is not as high as it should be. And so the race is on among colon-cancer researchers to
find a superior replacement, something that is fast, accurate, simple and cheap.
Of mice and men
Some unusual mice from Notre Dame's Walther Cancer Research Center, a unit of the Notre
Dame Cancer Institute, give Rudy Navari and Mary Prorok hope that just maybe they are on to
something.
Navari is director of the Notre Dame Cancer Institute as well as assistant dean and
director of the Indiana University School of Medicine at South Bend. If that weren't enough, the
M.D., who also holds a Ph.D. in chemical engineering, is actively invovled in several research
programs, including one looking for the "magic bullet" colon-cancer biomarker that might
become the basis of a fast, accurate, simple and cheap blood or urine test for the disease. A
biomarker is a certain protein associated with a particular cancer. For various reasons tumors
may secrete some proteins, so if you can detect the marker protein in blood or urine you should
have an early warning of the cancer. That's the theory.
"Finding a biomarker is kind of a needle-in-the-haystack thing; you have to be a little
lucky," says Prorok, a Walther Center protein chemist whom Navari enlisted to oversee the
project. To find that needle, the Notre Dame research team has employed a sophisticated
technique known as transcriptional profiling. This allows them to genetically compare diseased
tissue with normal tissue, sorting out which genes are turned on, or "up-regulated," in the disease
state versus the healthy state.
Every cell has the same DNA blueprint in its genes. What makes one type of cell
different from another -- skin from bone, say -- is which genes get "up-regulated,"causing a
specific protein to be produced. RNA is the key compound in this process. "So we're looking for
RNAs in cancer cells that are either 'up' or 'down,'" Prorok explains. "That would indicate
either the presence of a marker or the absence of something."
Transcriptional profiling allows researchers to scan thousands of gene interactions at a
time. In fact, so great is the number that a mathematician is part of the team charged with
statistically interpreting which are the dependable "up" and "down" regulated signals.
Initially, the researchers started their biomarker quest by analyzing cancer patients' urine
for telltale proteins. "That turned out to be a mess," Prorok recalls, "because the patients were on
a variety of different medicines and so we had a difficult time sorting out what was showing up
in the urine."
After that false start the team decided to switch to a simpler, more easily controlled
system, namely some special Walther Center mice that have a genetic defect which causes them
to spontaneously develop polyps and colon cancer at about 60 days of age. "It's a fairly decent
model of the human condition," Prorok says.
Soon after the switch good things began to happen. The biochemists found several genes
that were "very much up-regulated" in the diseased mice. One protein in particular, called
cathepsin E, caught their attention. While little is known about its normal function, it doesn't
appear essential for life. A strain of mice genetically engineered without the gene shows signs of
dermatitis and a few minor problems but otherwise survives quite well.
What excited Navari, Prorok and their colleagues about cathepsin E is that while it is
almost imperceptible in healthy mouse colon tissue, in diseased mice the levels are "absolutely
explosive" and it's always there. A red chemical stain that binds with cathepsin E showed red-stained cells, indicating the protein in every slide of mouse colon-cancer tissue -- a phenomenal
100 percent hit rate.
"Whether this particular protein is a cause of the cancer -- which I don't think it is -- or
whether it is a consequence is almost immaterial," Prorok says. "The fact that it is so strongly
linked to the disease makes it an excellent candidate for a screening test."
But staining a mouse tissue sample 100 percent of the time for cancer is one thing,
serving as an accurate screening test in a person is quite another. When it moves to the human
realm, cathepsin E proves to be "promising" but not quite as phenomenally predictive as with
mice. In human tumor samples the protein pops up about 50 percent of the time. The ND
researchers aren't sure exactly why the disparity, but Porok points out, "All of our mice get the
same cancer in the same way; they all have the same genetic defect. In humans there may be
many genetic reasons, environmental triggers, all sorts of unknown things that could cause the
cancer."
Still, cathepsin E is promising enough to warrant the next step, looking for signs of the
protein in mouse blood or urine. That task is daunting since a mouse supplies only about 3/100
of an ounce of blood, and getting a urine sample from the rodent obviously is tricky. Prorok and
her colleagues have been up to the challenge, however, and were encouraged to find a fragment
of cathepsin E in some preliminary analyses of mice pee.
"We're hopeful that maybe we have a handle on something here," she says. "The goal is
a biomarker that is 95 percent reliable, so we're not there yet. But this is a start, a validation of
the approach."
A further benefit of the biomarker work is that a genetic fingerprint of the disease begins
to emerge. "We're already seeing clusters of genes that seem to go awry in both the human and
mice samples," Prorok notes.
Navari says in the future Notre Dame researchers hope to look for an overlap between the
colon-cancer genetic profile in mice and humans. "And then, eventually, working with Notre
Dame Keck Center for Transgene Research, we can see if we might be able to knock out these
genes and possibly prevent colon cancer," he says.
The future of cancer treatment lies in such targeted therapy, the Notre Dame Cancer
Institute director continues. "We know, for instance, that some families develop colon cancer
between 25 and 35 years of age because of a certain folding of a protein. But if you could
somehow alter that amino-acid sequence without causing other damage, then maybe you could
prevent that from ever developing, from being expressed in that person's life."
Short of the ultimate goal of eradicating colon cancer outright, researchers continue to
hunt for more effective drugs to combat the disease and improve survival. Sometimes that search
leads in exotic directions.
Harvesting sea slugs
Unless you're a World War II history buff versed in arcane details of the conflict, like where the
legendary Indiana war correspondent Ernie Pyle lost his life, you've probably never heard of Ie
Jima. John Kane '03Ph.D. certainly hadn't. However, several summers ago, the Notre Dame
chemistry grad student found himself on a flight to the tiny South Pacific volcanic island near
Okinawa, dispatched there by his adviser, Professor Paul Helquist, to gather as many specimens
as possible of the sea slug Eudistoma cf. rigida, which lives on coral reefs around the island.
When he got there, Kane enlisted local divers to harvest the slugs, which look like lumps
of tar. He spent the remainder of his time slicing and dicing the creatures they brought him,
treating them with a variety of solvents, filtering and purifying the liquid. From 45 pounds of
slugs he returned to Notre Dame with 1/3,000 of an ounce of a curious chemical brew of four
related compounds known collectively as iejimalides (pronounced ee-ay-jeema-lides), after the
island.
The rare substances are part of a broad category of naturally occurring compounds known
as macrolides, which have been a source of antibiotics and anti-cancer drugs. The iejimalides
were discovered in the late 1980s by a Japanese chemist who had worked out their gross
chemical structure and reported the compounds' potency against a few cancer-cell lines. There
had been little follow-up until Helquist, who has had a research interest in macrolides for years,
decided to investigate them more closely.
With the rare samples safely back at Notre Dame, work began in earnest to understand
the intricacies of the compounds' chemical structure and whether they might be a potential anti-cancer drug. Testing the compounds against various cancer cell lines, researchers found them
incredibly potent, with just one-billionth of an ounce enough to stop cell growth. "Cells don't
aggregate any more when they come in contact with iejimalides; they just float freely and stop
growing and dividing," Helquist notes. Within dose ranges typically used for cancer drugs, he
adds, the compounds have not been toxic to mice.
Still more positive news: The sea-slug compounds have shown some level of activity
against more than 60 different cancer-cell lines, but for some reason seem most potent against
colon-cancer cells. On that score, one of the leading cancer drug researchers in the country,
Professor George Pettit of Arizona State University, after examining a sample provided by
Helquist, wrote the Notre Dame biochemist and said, "Good news. This compound is a winner."
As encouraging as that assessment may be, the compounds still remain a long way from
becoming a drug, if ever. Many more studies are needed to thoroughly characterize the
compounds: Do they work in an organism as well as a cell culture? What dose is required? What
happens when the compound gets into the organism? How is it broken down and excreted? Once
those questions are answered for mice, they need to be replicated in other organisms, working up
the ladder to humans.
The main thing hampering progress on the iejimalides at this point, however, is their
rarity. Researchers can't get their hands on enough of the stuff. As a result of the Notre Dame
work, for instance, the National Cancer Institute became interested in the compounds and
requested larger quantities for its own studies. Remedying the dearth in supply is now a focus of
the Helquist lab on two fronts.
After years of work, especially by Kane and researcher Dirk Schweitzer, the Notre Dame
group is on the verge of completing the first total synthesis of the substance. That should do a lot
to alleviate the shortage. Meanwhile, attacking the same problem from a different direction,
members of the lab returned this past summer to gather iejima slugs a fifth time. They were not
interested in the slugs themselves but any microrganism that may co-exist with them and may be
the actual source of the active compound.
"The real source may not be the slug," Helquist says. "There are many cases where very
potent compounds actually are produced by a symbiotic creature -- something that co-exists with
the main organism, perhaps a bacterial species, fungus or algae. So if there is some
microorganism responsible and we can isolate it and grow it back here in the lab, we could have
an ongoing supply of the active compound." Scientific progress often requires chasing down such
"ifs."
Meanwhile, a vote of confidence and a hopeful sign: This past May, three drug companies
inquired into the Helquist lab's iejimalide work. Could a sea slug actually become a weapon
against colon cancer? Maybe, just maybe.
John Monczunski is an associate editor of this magazine.
(July 2006)
