Gold nanoparticle imaging boosts cancer treatment

Traditional imaging methods often involve tracers like fluorescent dyes and radioisotopes, which give limited visualisation and inaccurate results due to detachment from AuNPs.

Now, researchers from Waseda University in Japan have introduced a new imaging technique that uses neutron activation to transform stable gold into a radioisotope of gold that enables long-term tracking of the AuNPs within the body.

The study was led by Nanase Koshikawa, a PhD student in the Graduate School of Advanced Science and Engineering at Waseda University, and Jun Kataoka, a Professor in the Faculty of Science and Engineering at Waseda University, in collaboration with Osaka University and Kyoto University. The findings of this study are published in Applied Physics Letters.

“Traditional imaging methods involve external tracers, which may detach during circulation,” Koshikawa said in a statement. “To overcome this limitation, we directly altered the AuNPs, making them detectable via X-rays and gamma rays without the use of external tracers.”

For activation of the AuNPs, the researchers irradiated the stable gold nanoparticles with neutrons, converting the stable (197Au) to radioactive (198Au). The radioactive 198Au emits gamma rays, which are detectable from outside the body.

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Prof. Kataoka said: “Activation of atoms through particle irradiation is a technique that directly alters the material. The altered elements are sometimes unstable and emit X-rays and gamma rays that make the material visible from outside the body. This does not change the atomic number, and thus the chemical properties of the element are preserved.”

The researchers further confirmed the tracking of these radioactive AuNPs by injecting them into tumour-bearing mice and visualising them using a special imaging system.

Additionally, the study demonstrated this imaging technique for drug delivery of 211At, a radio-therapeutic drug used in targeted cancer therapy. The 211At emits alpha particles and X-rays, which are detectable for a shorter duration due to a shorter half-life.

The researchers labelled the 211At with the radioactive AuNPs, forming 211At-labeled (198Au) AuNPs. This approach provided long-term imaging of the drug due to the longer half-life (2.7 days) of 198Au, overcoming the limitations of the short half-life of 211At.

“211At has a half-life of 7.2 hours, and hence its emitted X-rays disappear within two days, but with the (198Au) AuNPs labelling, we were able to track the drug’s distribution for up to five days using gamma rays from ¹⁹⁸Au, which has a longer half-life of 2.7 days,” said co-author Atsushi Toyoshima from the Institute for Radiation Sciences, Osaka University.

According to the team, the direct tracking of AuNPs inside the body could lead to more effective cancer treatments with precise monitoring of drug distribution. The study could also open new possibilities for real-time pharmacokinetic studies, ensuring improved drug safety and efficacy.

Co-author Yuichiro Kadonaga, an Assistant Professor from the Institute for Radiation Sciences, Osaka University, said: “We plan to enhance the imaging resolution and extend this technique to various nanoparticle-based systems. By further refining neutron activation imaging, we aim to make drug monitoring a clinical reality.”