Engineered E. coli may lead to new drugs

Hormones must be present in specific amounts to maintain health. For example, sufficient levels of the hormone estrogen are necessary for bone formation and reproduction, but too much of it has been implicated in premature puberty as well as the development of breast cancer and heart disease. The Princeton engineers hope that the bacteria can shed light on the way hormone-like compounds affect the body and eventually guide the development of drugs that can regulate hormone levels.

David Wood, an assistant professor of chemical engineering at Princeton, and Georgios Skretas, who earned his Ph.D. at Princeton in 2006 and is now at the University of Texas-Austin, designed the bacteria by linking the proteins that bind to estrogen, called estrogen receptors, with a protein required for growth in E. coli. This design allows the researchers to distinguish between compounds that stimulate the receptors and those that block them simply by observing bacterial cell growth. Since the bacteria respond quickly -- results are typically seen in about 15 hours under simple growth conditions -- they should be able to rapidly screen thousands of compounds that affect estrogen's activity, making an important contribution to the drug discovery process, Wood said.

When used to screen a small library of potential antioxidants, the bacteria identified two novel estrogen-mimicking compounds. Based upon bacterial growth in the presence of the mimics, the researchers predicted that one of the compounds would behave like estrogen in human cells, while the other would inhibit estrogen-related activity. The researchers confirmed their predictions with subsequent tests in human cells.

Although neither of the compounds turned out to be potent enough to make a good drug, the fact that the bacteria responded appropriately to the substances has made the researchers optimistic.

'Though these compounds themselves aren't likely to have pharmaceutical applications, the results prove that the system can work for drug-like compounds," Wood said. "Our system is also very good at detecting weakly binding substances, which is essential for the identification of hormone-like pollutants, which are found in many substances, including plastics and cosmetics."

In future work, the researchers plan to design bacteria that detect and respond to additional hormone-like compounds, including those that mimic or block the activity of testosterone, the stress hormone cortisol and thyroid hormone. This may advance the search for a nonsurgical treatment for Graves' disease, which is caused by the overabundance of thyroid hormone.-Princeton University