Washington, Oct 15 : A Chinese herb - more than 2,000-year-old - eaten as salad in many countries has been given a new twist to develop a compound to combat cancer.
According to researchers at the University of Washington, the new compound is more than 1,200 times more specific in killing certain kinds of cancer cells than currently available drugs, and paves the way for more effective chemotherapy drug with minimal side effects. The compound is based on the common anti-malarial drug artemisinin, which is derived from the sweet wormwood plant (Artemisia annua L). The scientists attached a chemical homing device to artemisinin that targets the drug selectively to cancer cells, sparing healthy cells, they report in the recent issue of the journal Cancer Letters.
The artemisinin compound takes advantage of cancer cell's high iron levels. "The compound is like a special agent planting a bomb inside the cell," said Tomikazu Sasaki, chemistry professor at UW and senior author of the study.
For the study, the researchers tested their artemisinin-based compound on human leukemia cells, and found it to be highly selective at killing the cancer cells.
Sasaki said that the researchers also have preliminary results showing that the compound is similarly selective and effective for human breast and prostate cancer cells, and that it effectively and safely kills breast cancer in rats.
He added that most available chemotherapies to treat cancer are very toxic, destroying one normal cell for every five to 10 cancer cells killed.
"Side effects are a major limitation to current chemotherapies. Some patients even die from them," said Sasaki.
The new compound, however, kills 12,000 cancer cells for every healthy cell, i.e. it could be turned into a drug with minimal side effects, which in turn would be more effective than currently available drugs, since it could be safely taken in higher amounts.
Artemisinin alone is fairly effective at killing cancer cells- it kills approximately 100 cancer cells for every healthy cell, about ten times better than current chemotherapies. For improving the effectiveness further, the researchers added a small chemical tag to artemisinin that sticks to the "iron needed here" protein signal.
Unaware of the toxic compound lurking on its surface, the cancer cell waits for the protein machinery to deliver iron molecules and engulfs everything - iron, proteins and toxic compound. After entering the cell, the iron reacts with artemisinin to release poisonous molecules called free radicals, which on accumulation kills the cell.
"The compound is like a little bomb-carrying monkey riding on the back of a Trojan horse," said Henry Lai, UW bioengineering professor and co-author of the study.
The compound is so selective for cancer cells partly due to their rapid multiplication, which requires high amounts of iron, and partly because cancer cells are not as good as healthy cells at cleaning up free-floating iron.
"Cancer cells get sloppy at maintaining free iron, so they are more sensitive to artemisinin," said Sasaki.
"Most currently available drugs are targeted to specific cancers. This compound works on a general property of cancer cells, their high iron content," said Lai.