Bacteria speeds drug to tumors.

• Position: Use of Clostridium acetobutylicum enzyme to activate cancer drug CB 1954 - Special Newsletter Edition: Your Health

Think of the rod-shaped bacteria as tiny submarines cruising through a cancer patient's blood-stream, unlesashing a chemother-apeutic cargo only where it is needed. Researchers at Stanford University have genetically engineered the bacterium Clostridium acetobutylicum to produce an enzyme that activates a cancer drug. This bacterium can germinate only in low-oxygen environments--and tumors are the sole oxygen-starved sites in the body. Thus, the scientists expect it to produce the enzyme only in tumors, even though the injected microbes might spread throughout the patient's body.

Though the Clostridium bacterium, which normally lives in the soil and causes no human disease, has been studied for decades because of its innate ability to proliferate in solid tumors, this is the first time researchers have altered it to activate an anticancer drug, indicates graduate student Marilyn Lemmon, who is working on the project. Its specially engineered cargo is a gene that is transferred from another bacterium, coding for the enzyme nitroreductase, which transforms the cancer drug CB 1954 from a relatively benign state into a potent killer of cells. "With this system, the drug would only get converted into the nasty stuff in the tumors because that's the only place where the enzyme produced by the bacteria would be present," she explains. By specifically targeting tumor cells, the experimental system by passes one of the pitfalls of cell-killing chemotherapy--cancer drugs typically...