The company has tested the drug on hundreds of rodents and recently moved to studies in pigs that don't produce enough insulin--models that may more closely resemble the diabetic environment in humans. In the experiments, the researchers injected the drug into diabetic animals and followed up with injections of sugar to simulate a meal. They tracked blood-sugar concentrations with continuous glucose monitors and also noted the amount of insulin released in response to increased glucose. So far, Zion's team has observed that the drug is able to sense and adapt to fluctuating glucose levels and deliver insulin as needed, keeping concentrations stable while avoiding insulin overdoses that may lead to hypoglycemia. The group plans to compare the technology with existing insulin-delivery devices in the future.

"The idea of having insulin that responds to glucose, and having an injection once every day, or every three or four days, would be a wonderful advance for diabetics," says Michael Sefton, a professor of chemical engineering and applied chemistry at the University of Toronto. "This could enable them to control blood sugar better and match delivery of insulin to their need for insulin." While the initial data seems promising, Sefton says, it's not yet clear whether the drug works fast enough to be effective in humans.

Zion aims to begin clinical trials within the next two years. Last week, SmartCells received $1 million to fund safety and efficacy studies in preclinical animal trials as part of a partnership with the Juvenile Diabetes Research Foundation.

Before starting clinical trials, the researchers will have to make sure that the drug is, in essence, foolproof--that is, that there aren't any molecular signals other than glucose that could unnecessarily release insulin into the bloodstream, says Frederick Schoen, a professor of pathology and health sciences and technology at Harvard Medical School. "You have to avoid bursts of insulin, which can be dangerous," says Schoen. "It's an exciting concept, and should be pursued, but lots of questions should be answered along the way."