The American team explored the drug's anti-angiogenic potential using in vivo and in vitro methods. They demonstrated that the drug suppressed growth of tumors in mice implanted with cells from inflammatory breast cancer. In addition, they found that the drug prevented formation of tumors in mice bred to develop breast cancer. With use of cultures of rat arterial cells bathed in human breast cancer cells, they found that the drug blocked angiogenesis. Furthermore, they proved with the in vitro work that the drug suppressed release of a key signaling molecule known to stimulate angiogenesis.

"Taken together, these results support the initial findings of the clinical trials that have been done with tetrathiomolybdate and indicate that copper reduction can inhibit tumor angiogenesis with minimal adverse effects," says senior author Sofia D. Merajver, M.D., Ph.D. She notes that the copper reduction achieved with drug use is far greater that what can be achieved through diet alone.

Merajver has helped lead clinical and laboratory investigations of the drug for oncology use for several years, including a current Phase II trial for advanced breast cancer patients. The drug is also being tried at multiple centers for patients with prostate cancer, breast cancer, head and neck cancer, multiple myeloma, liver cancer, mesothelioma, and other malignancies.

Tetrathiomolybdate, which is made up of sulfur and molybdenum, was originally developed as a treatment for Wilson's disease, which is characterized by excessive levels of copper. After the drug bonds to copper and albumin, the chelated complex is eliminated from the body. At the same time in the 1990s that scientists realized the drug was successful in treating Wilson's disease, researchers found that copper was important to the activity of various growth factors required for angiogenesis.

The research group decided to collaborate on studies investigating tetrathiomolybdate and angiogenesis; results from a Phase I trial with a group of late-stage cancer patients were published in the January 2000 issue of the journal Clinical Cancer Research. The goal was to test the drug's safety and effectiveness to lower copper levels in cancer patients. However, in an unexpected finding the researchers saw evidence of tumor stabilization in a handful of patients whose copper levels were reduced to 20 percent of their original levels for three months or longer.

Meanwhile, Merajver and her team have continued basic research. In the current study, the team used two animal models of breast cancer -- one in which mice received human inflammatory breast cancer cells and one using mice that are likely to develop cancer in their first year. The mice with cancer xenografts that received drug treatment had tumor size suppressed by 69 percent compared with mice that did not receive treatment. As for the mice genetically modified for breast cancer, no mice that received preventive drug treatment developed tumors. This statistically significant effect ended when the drug was discontinued -- all mice developed tumors within two weeks.

In one of the in vitro experiments, researchers inserted breast cancer cells whose nuclei carried a genetic sequence that could only be transcribed by the NFkB transcription factor and a DNA label that produced a telltale glowing molecule whenever transcription occurred. NFkB activity was 2.5 times greater in the cancer cell culture than it was in a normal breast cell culture. However, when tetrathiomolybdate was added, NFkB activity was decreased almost 2.0 times as much in cancer cells as it was in normal cells.

When the researchers looked at the genes encoding the proteins that make up the NFkB molecule, they found that drug treatment cut production of those proteins significantly. When they looked at the interleukin and growth factor molecules whose transcription is also usually controlled by NFkB, production was also lower in the presence of tetrathiomolybdate.

"It appears that tetrathiomolybdate exerts its anti-angiogenic action at least in part by restricting the release of factors that promote angiogenesis, and by suppressing NFkB activity," says Merajver. "This is potentially exciting from a clinical perspective because NFkB is involved in cancer's resistance to chemotherapy and radiation therapy. And, the suppressive effect we've seen suggests a promising role for tetrathiomolybdate as a chemopreventive agent in people who carry alterations in genes that make them susceptible to cancer."