There’s no shortage these days of drugs that can kill cancer cells. The problem is delivering them effectively, because these same drugs often poison healthy tissue as well, forcing doctors to limit the concentrations they can safely administer.

Now, thanks to recent innovations at Duke University, an improved drug-delivery system may soon be in sight for cancer patients, one that targets individual tumors through heat and delivers cancer-fighting drugs in higher concentrations than conventional carriers.

Working on an idea first proposed in 1978, Duke researchers have developed a heat-activated liposome, or biological sac, formed from a membrane that only becomes permeable at certain temperatures. At normal body temperatures, the new liposome prevents the anti-cancer drug it carries from spreading into the system. But when the liposome enters a heat zone, such as a tumor that has been heated to 39° C or higher, the walls of the sac “melt”-undergo a gel-liquid phase transition-releasing the drug inside the tumor.

When the liposome exits the heated tumor, it reseals, minimizing the amount of drug released into the surrounding tissue.

The therapeutic benefit of using the new liposome for controlled drug release comes from the ability to deliver very high concentrations of anti-cancer drugs to precisely targeted tumor sites.

Last December, Duke researchers reported that the new liposome took only seconds to release doxorubicin, a potent chemotherapy drug, into cancerous tumors in mice-compared with hours using conventional liposomes. As a result, the drug concentration in the tumors was 30 to 50 times higher than that attained with conventional carriers, cutting tumor growth rate in half and eventually eradicating the tumors in two-thirds of the mice treated.

Columbia, MD-based Celsion Corporation is now working to couple the new liposome with microwave heat technology developed at MIT to target prostate, liver and ovarian cancers. “This liposome has potential for encapsulating many different cancer drugs,” said Augustine Cheung, Celsion’s chairman and chief scientific officer.

Celsion is producing an initial batch of liposomes containing doxorubicin for use in several large animal toxicity studies, which should be completed by the end of the year, Cheung said.

A first-phase clinical feasibility study with up to 30 patients will follow, perhaps a year or more away.