A new nanodelivery system is able to sneak cancer treatments past the defenses of drug-resistant tumor cells—offering hope to many cancer patients who benefit little from existing drug treatments.

Researchers at the University of Tokyo designed small soapy clusters of molecules, called micelles, to carry drugs into tumor cells and release their cargo inside. The molecules harness the cell’s internal transport system to get close to their target—the cell’s DNA.

Releasing the drug close to a cancer cell’s nucleus appears to protect it from the cell’s self-defense mechanism. The approach slowed the growth of tumors in mice—even tumors that were completely resistant to the drug when it was administered normally. The work was published yesterday in the journal Science Translational Medicine.

“This addresses a key hurdle in cancer treatment by overcoming the limitations faced by free drugs—that is, development of resistance by cells,” says Samir Mitragotri, professor of chemical engineering at the University of California, Santa Barbara, who was not involved with the research.

Micelles were tested as a delivery system for the colorectal cancer drug oxaliplatin in mice with drug-resistant human colon cancer.

Ordinarily, oxaliplatin is injected into a patient’s bloodstream, and from there it enters the cytoplasm of tumor cells by way of small gaps or channels in the cell membrane. Only about 5 to 10 percent of the drug particles make it to the cell’s nucleus, but those that do attach themselves to the DNA and disrupt its function, eventually killing the cancer cell. Once colorectal cancer has begun to metastasize, however, within nine months it develops defense proteins in its cytoplasm that inactivate oxaliplatin.