NEW YORK _ Something in a pregnant woman's urine can wipe out tumors of Kaposi's sarcoma, an AIDS-related cancer, and suppress HIV itself. But what is it?
After a false start, scientists say they're on the trail to finding out.
It all began with a chance observation a few years ago in a study of Kaposi's, a potentially lethal disorder that causes disfiguring skin lesions in people with AIDS. Researchers were creating Kaposi's in mice for study, and they noticed they couldn't get the disease to develop in pregnant females.
Apparently, something related to pregnancy was quashing the disease. A hormone called human chorionic gonadotropin, or hCG, is produced early in human pregnancies, so it seemed like a good candidate. Researchers reported in 1995 that doses of commercial hCG preparations killed Kaposi's cells in the laboratory and shrank Kaposi's tumors in mice.
The following year, scientists reported that injecting commercial hCG preparations into tumors could often make them disappear in human patients. In addition, in studies where patients got the preparations injected in their bloodstreams, they sometimes showed a decline in the amount of HIV in their blood.
But almost from the time of the first mouse study, researchers became suspicious about whether hCG itself was really doing all this. Commercial preparations are derived from pregnant women's urine and contain many contaminants, so one or more of these impurities might really be responsible.
Some recent studies have pointed to a contaminant, though nobody has actually identified it. The latest chapter of the story appears in the April issue of the journal Nature Medicine.
Scientists present evidence that an unidentified substance they call HAF is responsible, and that hCG is just a red herring. HAF can be found in hCG preparations and in urine from pregnant women, they reported.
HAF may be two proteins, but more likely it's two forms of the same protein, said Dr. Robert Gallo of the University of Maryland's Institute of Human Virology, who did the work with colleagues. Once it is purified and analyzed, it might become a new treatment for Kaposi's and HIV infection, he said.
HAF also showed signs of being able to promote growth of bone marrow cells, suggesting it might help protect people from marrow damage caused by cancer treatments with radiation or chemotherapy.
HAF stands for hCG-associated factor. The new paper shows it sharply inhibited growth of Kaposi's sarcoma tumors in mice and suppressed HIV in the test tube. It also promoted the growth of bone marrow cells in the test tube.
In contrast, purified hCG showed none of these effects in the new study.
David Adams of the University of Leeds in England, who has also reported that something other than hCG is responsible for the effect against Kaposi's sarcoma, said he hasn't yet identified the substance his group implicated. It might be similar to HAF or even HAF itself, he said.
In any case, the search for the active ingredient in hCG preparations may be nearing an end.
"We're now starting to get closer to whatever it is," Adams said.