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Precision cancer treatment using magnet-guided, heat-activated nanoparticles

Traditionally, radiation, chemotherapy, and surgery have been the most common ways to remove and destroy malignant cells. However, because these treatments can also damage healthy cells, they often have significant side effects. Today, more precise and targeted therapies are emerging, designed to attack cancer cells while sparing normal tissues.

Professor Eijiro Miyako and his research team at the Japan Advanced Institute of Science and Technology (JAIST) are pioneering such innovative approaches to cancer treatment. Previously, his team developed tumor-targeting bacteria that trigger the immune system to attack tumor cells.

In their study in the journal Small Science on March 3, 2025, Prof. Miyako and his team have developed nanoparticles that can be magnetically directed to tumor cells and then heated up with a laser to destroy tumor cells.

This treatment is based on photothermal therapy, which involves attaching photothermal nanoparticles—particles that absorb light and convert it into heat—to selectively destroy cancer cells. When exposed to near-infrared (NIR) laser light, the nanoparticles generate heat, destroying the tumor.

The team used biocompatible carbon nanohorns (CNHs) as the photothermal agents. CNHs are spherical graphene-based nanostructures that have been previously employed for drug delivery and bioimaging. However, a key challenge in using CNHs is ensuring that the nanoparticles accumulate effectively in tumors.

To address this, the team modified the CNHs by adding magnetic ionic liquid 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl₄]) to their surface. Ionic liquids have anticancer properties and impart magnetic properties to the nanoparticles, allowing them to be guided to tumor sites using an external magnet. However, CNHs are naturally insoluble in water, and [Bmim][FeCl₄] is hydrophobic (water-repellent), posing a challenge for use in the body.

To improve the dispersibility of the particles in the body, the researchers added a coating of polyethylene glycol to improve the particle's water solubility and dispersibility. They also incorporated a fluorescent dye, indocyanine green, into the nanoparticles to act as a visual tracker, enabling real-time monitoring of the nanoparticles.

"This study's innovative approach to nanocomplex design allows us to apply magnetic ionic liquids to cancer treatment for the first time," explains Professor Miyako. "This represents a significant advancement, offering a new avenue for cancer theranostics."

The nanoparticles, just 120 nanometers in size, had a photothermal conversion efficiency of 63%, outperforming many conventional photothermal agents, and were sufficient to kill cancer cells. In laboratory tests, when added to mouse-derived colon carcinoma (Colon26) cells, the nanoparticles effectively induced cell death upon exposure to an 808 nm NIR laser at 0.7 W (~35.6 mW mm^−2) for 5 minutes.

When injected into mice with Colon26 tumors, the nanoparticles were directed to the tumor using a magnet. These accumulated nanoparticles heated the tumors to 56°C, a temperature high enough to destroy cancer cells.

The results were promising: mice treated with the magnet-guided nanoparticles showed complete tumor elimination after six laser treatments, with no recurrence over the following 20 days. In contrast, when the nanoparticles were not guided by magnets, the tumors regrew after the laser treatment was stopped, indicating that insufficient nanoparticles had accumulated to fully eradicate the cancer cells.

This innovative treatment combines three powerful mechanisms: heat-based destruction of cancer cells, the tumor-targeting chemotherapeutic effect of the ionic liquid, and magnetic guidance. This multimodal approach offers a more effective alternative to conventional therapies, which typically rely on a single mode of action. Moreover, the study highlights the potential of magnetic ionic liquids in cancer treatment, paving the way for new therapeutic strategies.

"This simple yet highly effective nanoplatform, which leverages multiple tumor-killing mechanisms, has significant potential for future clinical applications in cancer diagnosis and treatment," says Prof. Miyako. "However, further safety testing and the development of an efficient endoscopic laser system will be necessary for treating deeper tumors."