Utah's Kopeckova says there has been heated discussion for a decade "about the size of the carrier of the drug, and I think this paper will bring lots of details which were missing." She'll use the new information in her work on a carrier for an ovarian cancer drug that finds tumors by recognizing markers on their cells.

Chilkoti has already begun applying the results to his work on a synthetic protein drug carrier that becomes insoluble in the blood at 42 degrees Celsius (five degrees above normal body temperature). Technologies have already been developed to heat tumors from the outside, using ultrasound and microwaves, and Chilkoti's drug carrier would piggyback on these techniques. "The idea is when you turn on the heat, these things become insoluble, they form particles inside the tumor. So it's like implanting little tablets of drug," he says. "Then when you turn the heat off, they dissolve from this very high concentration and penetrate throughout the tumor." Chilkoti says this therapy would work well with breast cancer.

But Chilkoti also stresses that his group's study of the detailed mechanisms of drug carriers is only a starting point. "You would use this information to design and select your carrier, and then you would want to go into clinical trials and see if it works," he says.