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    WASHINGTON (AP) _ Starting with twigs from a Malaysian gum tree, researchers in 1991 isolated a compound that blocked the spread of the AIDS virus in human immune cells.

    The team sent biologists racing back to Malaysia for more samples from the tree. But when they got to the swamp, the tree was gone. And no tree found since has produced the same compound.

    The frustrating saga was revealed in a confidential paper made public Thursday by Rep. Gerry Studds, D-Mass.

    ″We’ve jokingly called it, ’Medicine Man for Real,‴ said Dr. John Cardellina II, a co-author of the paper. He was referring to the Sean Connery movie in which a doctor tramps through the jungle after finding, and then losing, a cure for cancer.

    To be sure, the real-life team was a long way from finding a cure for AIDS. Tests using human immune system cells were conducted in a laboratory. No tests were conducted on humans.

    ″We have very good data. It’s very promising,″ Cardellina said. ″To say it’s definitely going to be a cure is jumping way ahead of the game.″

    But Cardellina said the initial testing indicated that the newly discovered compound could more than just control the disease. ″The emphasis is on eradicating the virus in the patient,″ he said.

    The tree that showed promise was a member of the guttiferae family of gum- producing trees. The particular type, known as calophyllum lanigerum, was found in a swamp in the Malaysian island province of Sarawak in Southeast Asia. Researchers collected about two pounds of twigs, bark and fruit from the tree - enough to conduct a few experiments.

    The scientists collected the sample as part of a broader effort to find medicinal substances in tropical trees.

    Back at the National Cancer Institute’s research center in Maryland, scientists reduced sap-like material found in the tree down to a new compound, ″calanolide A.″ They tested it against the HIV-1 virus - the most common virus form in known AIDS cases.

    Human cells placed in a test container would normally be killed by the virus within days, according to Cardellina. The team found the new compound was ″100 percent effective″ in blocking that process. They said it ″completely inhibits the virus’ pathological effects on human immune system cells, without causing damage to the human cells.″

    Results of the study were published last year after peer review by the Journal of Medicinal Chemistry.

    In the paper released by Studds, the authors said that when their team returned to Malaysia in 1991 for more raw material, they found that the tree had been cut down shortly after the first sample had been taken in 1987.

    No identical trees were found in the immediate area and samples from the same tree species found elsewhere did not yield the calanolide A compound.

    Word that the source of the compound had been cut down did not surface until Thursday when Studds released a copy of the tropical plant paper marked ″confidential.″

    Cardellina said one reason the researchers were cautious about broadcasting the source of calanolide A was the fear that AIDS sufferers would scour rain forests looking for the tree, posing risks both to themselves and the forests.

    Some of the lookalike trees contain materials toxic to humans, he said.

    Dr. Djaja Soejarto of the University of Illinois at Chicago, the team member mainly responsible for collecting test samples from the rain forest, said that even if another tree can be found, several tons of plant material would be needed for testing on a clinical scale.

    ″If the compound achieves new drug status, then truly massive amounts of the source plant material may be needed,″ the team wrote. Because of the diversity of rain forest environments, trees rarely grow in solid stands.

    ″This example vividly illustrates many of the unique problems and challenges which must be faced and solved for successful drug development following such a discovery, before the true medicinal potential of tropical rain forest plants can be realized,″ the team wrote.

    The paper on the ″Industrial Utilization of Tropical Plants,″ was presented at a scientific symposium in Enugu, Nigeria, in February by Soejarto and four scientists from the National Cancer Institute’s research center in Frederick, Md.