Sugar-coating nanoparticles to tempt cancer cells brings dual benefits

An iron-centered nanoparticle (left) has a coating of the sugar dextran, whose tendrils prevent groups of the particles from clumping. When tumor cells ingest them (right), the particles still congregate closely enough to share heat, killing the cells. White arrow indicates a red blood cell (Image: NIST)

Researchers believe nanoparticles hold the promise of battling cancer without the damaging side effects of chemotherapy or radiation treatment. They have discovered that coating minuscule balls of iron oxide with sugar molecules not only makes them particularly attractive to resource-hungry cancer cells, it also makes them more effective by allowing them to get close to each other, but not too close to render treatment ineffective.

Once the sugar-coated particles are injected into the patient's body, cancer cells ingest them, allowing doctors to then apply an alternating magnetic field that causes the iron oxide centers to heat, killing the cancer but leaving surrounding tissue unharmed. A research team at the National Institute of Standards and Technology (NIST) studying the potential for sugar-coated nanoparticles as a possible cancer therapy uncovered a delicate balancing act that makes the particles more effective than conventional thinking says they should be.

The particles, which are about 100 nanometers wide, were revealed to be potent cancer killers because they interacted with one another in ways that smaller nanoparticles did not. The interactions, thought by many bioengineers to be undesirable, actually helped the larger particles heat up better when subjected to an alternating magnetic field.

This finding went against conventional wisdom that says because larger particles are more strongly magnetic they tend to clump together, which makes them large enough to attract the body’s defense systems before they can reach a tumor. Coating the particles with sugar molecules overcomes this problem because the sugar coating has fibers extending out that push against one another when two particles get too close together, making them spring apart and maintain an antibody-defying distance rather than clumping.

Moreover, when the particles do get close, the iron oxide centers all rotate together under the influence of a magnetic field, both generating more heat and depositing this heat locally. All these factors helped the nanoparticles destroy breast tumors in three out of four mice after one treatment, with no regrowth.

“The push-pull is part of a tug of war that fixes the distance between nanoparticles,” says NIST materials scientist Cindi Dennis. “This suggests we can stabilize interacting particles in ways that potentially pay off in the clinic.”

The research was carried out by the NIST team in collaboration with colleagues at The Johns Hopkins University, Dartmouth College, the University of Manitoba and two biopharmaceutical companies.

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