NEW DRUGS HIT CANCER CELLS SEARCH-AND-DESTROY STYLE.

Byline: Bob LaMendola Knight-Ridder Tribune News Wire

In the war on cancer, South Florida researchers are perfecting a new weapon: drugs that seek out tumors like guided missiles.

The new protein-based drugs hunt down cancer cells, attach themselves to the skin of the tumor and deliver a tiny radioactive payload that can signal the location of hidden cancer.

In an advance with major potential, scientists are refining ways to arm the protein missiles with radioactive or toxic substances that kill the tumor - creating the equivalent of cancer smart bombs.

``This has many, many exciting possibilities,'' said Dr. Aldo Serafini, a University of Miami nuclear medicine specialist who is leading several studies. ``It homes in on its target and goes right to it.''

The techniques promise better success in finding and treating cancers in the prostate, breast, colon, skin, blood and various organs, among others.

The new attacks spring from a growing knowledge that cancer is caused by defects in genes, the chemical blueprints of life. Tumors, which are cells growing out of control, result when defects cripple the genes that are supposed to abort such cells.

The realization opened the door for scientists to start figuring out the mechanics of cancer - killer of 1.4 million Americans a year - and possible ways to outsmart it.

At least a half-dozen studies are under way in South Florida to test new compounds that detect tiny hidden tumors that otherwise would grow to serious proportion.

In October, doctors at North Ridge Medical Center in Oakland Park, Fla., tested an experimental cancer-detector on the first two patients in the nation.

Radiologist Claudio Smuclovisky injected the compound into a man with a melanoma tumor visible on his chest. Scanner pictures showed the tumor as a bright yellow blob. But doctors were surprised to see a second yellow spot: Another tumor was growing below the skin near the man's armpit, in the lymphatic system.

``We had no idea that tumor was there,'' Smuclovisky said. ``If you can see where the cancer is spreading, it makes a tremendous difference in catching it early and treating it the right way.''

Surgeons now may be able to save the man. Early detection is crucial with melanoma, a relentless killer. Almost 95 percent of patients survive five years if it's caught while only on the skin. But if it spreads, the survival rate drops to 16 percent, and no treatment can defeat it.

Smuclovisky's test also caught a small melanoma inside the neck of Pompano Beach, Fla., butcher Charles Dick. He had already had surgery to remove an initial skin tumor, which had developed after 35 years of avid fishing.

``This nuclear scan is a blessing,'' said Dick, 69.

At Memorial Regional Hospital in Hollywood, Fla., surgeon Robert Donoway used a similar test to unearth a small melanoma in a woman. It had spread to a cluster of lymph nodes where tumors normally do not appear. Conventional tests, such as CAT scans, had missed it.

``She would have been completely missed,'' Donoway said.

The new type of tests, called radio-labeling, capitalizes on a decade of research.

First, biochemists identified ``receptor'' proteins posted on the surface of tumorlike sentries. Then, they isolated proteins and antibodies that seek and bind to the receptors.

Now, scientists can load those missiles with tiny grains of radioactive material that are too short-lived and weak to pose much health danger. If enough of the missiles stick to the tumor, doctors with scanners can see the radiation signal like a lighthouse.

Until now, no method has reliably detected secondary tumors at early, treatable stages.

The first of the new tumor detectors was federally approved for use about three years ago, and others have come out since. More and more cancer doctors are starting to use them. Last month, University of Miami doctors christened a newly approved colorectal detector they had tested.

``We're just now learning to use these agents,'' Serafini said. ``The second and third generations will be significantly improved upon.''

The detectors have no real side effects, but they have a flaw: Some of the missiles may miss the tumor and stick to normal cells. So, doctors must still verify the results by conventional means.

The latest versions have been improved to be 90 percent accurate, Donoway said.

The newest aspect of the research uses the tumor detectors as treatments, by attaching anti-cancer chemicals or radioactive atoms. Serafini's team in Miami soon will start testing one such experimental weapon on patients with Hodgkin's disease, a lymphatic cancer.

The missile - in this case, an antibody - delivers a small but intense dose of radiation to the tumor. The rays penetrate only about an inch, killing far fewer normal cells than standard radiation or chemotherapy does, Serafini said.

Initial tests of the experimental treatment were encouraging: 40 percent to 50 percent of end-stage Hodgkin's patients had at least partial remissions, compared to zero of the patients who received conventional therapies, Serafini said.

But there are problems. Doctors still must perfect the dosage, so that the missiles deliver the right amount of radiation to kill all the cancer without hurting other cells.

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