TIME: Almanac 1993/TIME Almanac 1993.iso/time/091790/0917350.000

Text File | 1992-08-28 | 3.8 KB | 84 lines

                                                                                MEDICINE, Page 79

Giving Up on The Mice


Scientists searching for cancer cures try a new tactic


    It was time to give the mice a rest and try something else.
For 35 years scientists laboring in the National Cancer
Institute's screening program have injected more than 400,000
chemicals into leukemic mice, hoping to find chemotherapies
that would help solve the riddles of cancer. All that
frustrating work has produced only 36 licensed drugs. Most of
them, while dramatically effective against leukemia, have shown
only modest value in other forms of cancer. "Maybe," says David
Korn, chairman of the National Cancer Institute's advisory
board, "we've been using the wrong system as the screening
device."

    Maybe so. In a radical departure from the traditional
methods, researchers have swapped their mice for a procedure
that they hope will detect a drug's potency not only against
leukemia but also in scores of different types of cancer cells.
The new effort, which is being employed at the Developmental
Therapeutics Program in Frederick, Md., uses an arsenal of
automated devices and computers to test potential
cancer-fighting drugs on real human cancer cells, grown in
laboratories, rather than on mice. This enables scientists to
test more than 300 chemicals a week. Many of these drugs had
failed in the past when tested on mice, but the researchers
hope their more sophisticated approach will produce fresh
leads. Says Michael Boyd, founder and director of the program:
"It's a high-risk venture, but this is a gamble worth taking."

    At one time, the assumption was that cancer cells shared
common characteristics and that therefore a drug effective
against leukemia would kill, say, cancerous lung cells as well.
With mouse screening, that technique brought solid advances in
leukemia chemotherapy but yielded mixed results in other forms
of cancer.

    The theory behind the new program is that cancers from
different organs share certain "family" characteristics. For
example, brain cells that turn cancerous might share qualities
with other brain cancers but differ dramatically from colon
cancers or leukemias. To look for common weaknesses among
different types of cancer, the automation process tests
chemical compounds directly against a range of 60 lines of
living tumor cells grown in Petri dishes and representing seven
leading cancer killers: colon, lung, melanoma, kidney, ovarian,
brain and blood.

    Half the compounds are manufactured by chemical and
pharmaceutical companies; the rest are provided by botanists
and ethnobiologists who collect folk medicines and exotic
living materials like the bark of the Pacific yew tree, from
which scientists extract Taxol, shown to be effective against
ovarian cancer cells. The researchers are looking for "natural"
cell killers harvested from such remote locations as the
Brazilian rain forest and Australia's Great Barrier Reef. Even
ground-up seashells, sponges and coral starfish are studied for
chemicals that might show some ability to fight cancer.

    Some critics are concerned that the new $4 million-per-year
program will fail to spot drugs that are enhanced naturally by
the body's metabolism or immune system, and that the old mouse
screens were better in that respect. In any case, new agents
discovered by the automated screening may require years of
additional testing in the lab -- and then on animals -- before
any newly discovered therapies can be tried on human cancer
patients. "All it will take," says NCI adviser Korn, dean of
the Stanford University School of Medicine, "is one smashing
winner. Then everyone will say it was worth it."


By Dick Thompson/Washington.