BALTIMORE (Map, News) - Some cancers are too sensitive to proteins that stimulate their growth, Johns Hopkins researchers say in a study that could lead to safer, more effective therapies that block that growth.

Cancers with two active genes for a hormone become addicted to that protein, according to an article appearing this week in the online edition of the Proceedings of the National Academies of Sciences. The Hopkins research team demonstrated that blocking this “addiction” in mice can prevent cancer growth.

That raises hopes that doctors will eventually be able to target such cells directly instead of relying on drugs that kill everything in their path.

“If this is translatable to people, it could be really exciting,” said Dr. Andrew Feinberg, professor of medicine, oncology and molecular biology and genetics and director of the Epigenetics Center at Hopkins. “It means we might be able to do something about at-risk cells before cancer develops.”

Most people inherit two genes for the growth factor, called “insulin like growth factor two,” or IGF-II, but normally, the copy from your father is turned on and the one from your mother is turned off, the study found. Activation of the maternal copy has been associated with a five-fold increase in intestinal tumors in people.

In the Hopkins study, mice with colon cancer were given a drug that specifically blocks IGF-II. These mice developed 70 percent fewer precancerous lesions than those without treatment.

Normal mouse cells responded to normal doses of growth factor and recovered within 90 minutes. But researchers found cells with two active copies of the gene were stimulated by the smallest doses and remained active for more than two hours.

“It’s like they were on a hair trigger, which was totally counterintuitive,” study co-director Andre Levchenko said in a statement. “You would expect ... that it would take higher doses to activate the cell.”

khille@baltimoreexaminer.com