Tiny Metallic Nanoflowers Will Target the Most Difficult to Reach Cancers

A team of National Institute of Health-funded researchers has unveiled a new approach to a long-sought method of cancer treatment: hyperthermia, or using heat to kill cancer cells. Their weapon is a tiny magnetic nanoflower that can potentially be deployed with enough precision to scorch difficult-to-reach cancer cells while leaving healthy tissues intact.

The Dartmouth-based team describes their work in the current issue of the Applied Physics Letters.

The general goal is to perfect a method for clinical hyperthermia. As heat is known to damage or destroy cancer cells, it should be possible to target those cells by raising the patient's body temperature. The catch, however, is clear enough: raising the body's temperature high enough to damage cancer cells risks damaging the body.

Currently, hyperthermia is used as an "adjuvant" to more traditional therapies like radiation and chemotherapy, and then only carefully targeted and locally. For now, targeted hyperthermia is considered to be part of the "fourth leg" of cancer treatment (along radiation, chemo, and surgery), while full-body hyperthermia therapy remains a highly experimental procedure. In order for the treatment to work, the heat must be precise and sustained.

There are currently several methods being used or investigated for therapeutic hyperthermia. They range from microwaves (which is more reasonable than it might at first sound) to "infrared saunas," to the most basic: wrapping a patient in hot blankets or introducing hot liquids into their system. The Dartmouth researchers have a (potentially) better strategy by injecting the patient with tiny metallic nanoparticles that can be activated and heated using sound, light, or alternating magnetic waves.

That last method has a lot of promise but again comes with the caveat that heating the particles with magnetic waves risks overheating and damaging healthy tissue as well. "To date, most commercially available particles designed for the application of hyperthermia heat very well in a relatively high frequency, strong magnetic field," notes Fridon Shubitidze, a Dartmouth associate professor of engineering, in a statement. "However, there is a limit to the frequency and strength that can be applied."

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So, the goal becomes developing nanoparticles that can be heated with relatively low-energy magnetic fields. It's not an unreasonable target. "When shrunken down to nano size, these materials can heat in a few different ways that don't occur on a larger scale," Shubitidze explains. "Some involve motion, with the particles physically rotating and/or moving under the influence of the field, while others are entirely non-mechanical and only involve changes in the direction in which the particles are magnetized."

It's possible to optimize the nanoparticles in such a system using factors such as size, shape, and composition. And this is where we get our magnetic nanoflowers, which are, as one would expect, tiny nanoparticles sorta shaped like flowers, e.g. with thin petal-like appendages that, in the presence of a high-frequency alternating magnetic field, start acting as tiny propellers. When these particles get to spinning, they generate heat through friction or, more specifically, friction as it relates to the viscosity of their surroundings.

The trick is a phenomenon known as hysteresis, in which the application and subsequent removal of a magnetic field leaves the target magnetized. So, the particles keep spinning even after the field has been removed. It's sort of like they have a memories.

"This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets," Shubitidze and company write in the current study, "potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue."

The Dartmouth nanoflowers are, of course, hardly alone on the leading-edge of nanomedicine, with a variety of nanomachines, nanovolcanoes, and nanobots ready to handle tasks ranging from diagnostics to drug delivery to immune system manipulation. The future of medicine is invisible to the naked eye and closing in quickly.