( more likely to become cancerous becaus...)Reactivated gene shrinks tumors

In this study, the researchers used engineered mice that had the gene for p53 turned off. But, they also included a genetic "switch" that allowed the researchers to turn p53 back on after tumors developed.

Once the switch was activated, p53 appeared in the tumor cells and the majority of the tumors shrank between 40 and 100 percent.

The researchers looked at two different types of cancer-lymphomas and sarcomas. In lymphomas, or cancers of the white blood cells, the cancer cells underwent apoptosis within 1 or 2 days of the p53 reactivation.

In contrast, sarcomas (which affect connective tissues) did not undergo apoptosis but went into a state of senescence, or no growth. Those tumors took longer to shrink but the senescent tumor cells were eventually cleared away.

The researchers are not sure why these two cancers are affected in different ways, but they have started trying to figure it out by identifying the other genes that are activated in each type of tumor when p53 turns back on.

The study also revealed that turning on p53 has no damaging effects in normal cells. The researchers had worried that p53 would kill normal cells because it had never been expressed in those cells.

"This means you can design drugs that restore p53 and you don't have to worry too much about toxic side effects," said Ventura.

Possible therapeutic approaches to turn on p53 in human cancer cells include small molecules that restore mutated p53 proteins to a functional state, as well as gene therapy techniques that introduce a new copy of the p53 gene into tumor cells. One class of potential drugs now under investigation, known as nutlins, acts by interfering with MDM2, an enzyme that keeps p53 levels low.

In follow-up studies, the MIT researchers are looking at other types of cancer, such as epithelial
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Source:Massachusetts Institute of Technology