The compounds, called synthetic migrastatin analogues, prevented 91 to 99 percent of metastatic breast cancer cells in mice, and are the first to target only metastatic cells.
"They're unbelievably effective, and in vitro study suggests they'll work just as well at inhibiting the migration of prostate and colon cancer cells," said senior researcher Dr. Xin-Yun Huang, Professor of Physiology and Biophysics at Weill Cornell Medical College in New York City.
The findings have just been published in Proceedings of the National Academy of Sciences.
For decades, doctors have fought cancer by using surgery, chemotherapy, or radiation to excise or shrink the primary tumor.
"However, in too many cases it's simply impossible to completely remove the tumor," Dr. Huang explained. "So recently the idea of targeting cell migration -- metastasis -- has become an alternative strategy that's gained a lot of interest among researchers."
If compounds could be found that slowed or halted cancer spread, doctors could gain valuable time in shrinking the primary tumor. "If we had the luxury of time, we could treat that primary tumor at lower doses, too, with fewer side effects for the patient," Dr. Huang said.
Until now, agents that specifically target metastatic cells have remained elusive. However, a new avenue of research opened up when Dr. Huang's team noticed that the Streptomyces bacterium -- the bug that gives us the antibiotic streptomycin -- also produces a natural compound called migrastatin, which appears to inhibit cell migration.
Natural migrastatin's effect is relatively weak, but Dr. Huang suspected the molecule might be manipulated in to something more potent. In collaboration with the laboratory of Dr. Samuel Danishefsky at the Memorial Sloan-Kettering Cancer Center, the team went to work creating what's called a "synthetic analogue."
"Starting with the basic migrastatin molecule, we cut a piece there, add a piece here," he explained, "and what we ended up with were two compounds -- core macroketone and core macrolactam -- that are about 1,000 times more powerful at inhibiting cancer cell migration."
In fact, in a mouse model, the analogues were between 91 to 99 percent effective in stopping the spread of breast cancer cells, the researchers report. Cell culture studies suggest they can reproduce that success in a wide range of other cancers, too.
"What's unique about these analogues is that they do all this without affecting primary tumor cells, or their blood supply," Dr. Huang said. "To our knowledge, that's a real first."
Exact mechanisms remain unclear.
"Obviously, these compounds are targeting some step in the cell-migration process," Dr. Huang said. The activity of a migration-linked protein called Rac appears to be much reduced in cancer cells affected by the analogues, and the researchers also noticed that malignant cells failed to grow tiny "antennas," called lamellipodia, another crucial step in the migration process.
"Therefore, the migrastatin analogues must be working on something upstream of those two important steps," Dr. Huang said.
Dr. HuangÕs next important step is moving these analogues into clinical trials.
"We're trying right now to get a company interested in this, especially because the mice used in our trial seemed to experience minimal toxicity -- a good sign that patients might tolerate these compounds, too," Dr. Huang said.
"It's all very exciting," he said. "Metastatic disease is such a tough problem, and these compounds could provide patients with a brand new kind of hope."
The research was funded by grants from the National Institutes of Health.
Co-researchers included Ms. Dandan Shan (first author), Mr. Lin Chen, and Dr. Xiaojing Ma, of Weill Cornell Medical College; and Dr. Jon T. Njardarson, Dr. Christoph Gaul, and Dr. Samuel Danishefsky, of Memorial Sloan-Kettering Cancer Center, New York.