【B1】 [br] 【B4】 [originaltext] Scientists have developed a new cancer drug. So

Scientists have developed a new cancer drug. So far, they have tested it only on laboratory animals. The drag is designed to invade and kill cancer cells but not healthy ceils.
   First, the drag enters the cancer and destroys the supply of blood. Then it releases poison to destroy the cancer cells.
   Researchers at the Massachusetts Institute of Technology in Cambridge carried out the study. The results appeared in Nature magazine. A school news release called the drug an "anti-cancer smart bomb."
   Ram Sasisekharan is a professor at M.I.T. He says his team had to solve three problems. They had to find a way to destroy the blood vessels, then to prevent the growth of new ones. But they also needed the blood vessels to supply chemicals to destroy the cancer.
   So, the researchers designed a two-part "nanocell". The cell is measured in nanometers, or one thousand millionth of a meter.The particle used was two hundred nanometers--much, much smaller than a human hair.
   The scientists say it was small enough to pass through the blood vessels of the cancer, but it was too big to enter normal blood vessels. The surface of the nanocells also helped them to avoid natural defenses.
   The scientists designed the cell as a balloon inside a balloon. They loaded the outer part with a drug that caused the blood vessels to fall in on themselves. That cut off the blood supply and trapped the nanocell inside the cancer. Then, the nanocell slowly released chemotherapy drags to kill the cancer cells.
   The team says the treatment shrank the cancer and avoided healthy cells better than other treatments.