A Nanowerk article by Carl Walkey from the integrated nanotechnology and biomedical sciences laboratory at the University of Toronto reports that Chinese researchers have shown that nanoparticles smaller than 10 nm in diameter accumulate more efficiently and penetrate more deeply in tumors than larger nanoparticles.
Most nanomaterials approved for clinical use are approximately 100 nm in diameter, according to Walkey. However, this large size prevents them from diffusing effectively within the tumor. Remaining near the vessel wall, they can reach only the first few layers of tumor cells. Consequently, current nanomaterials used for medical therapeutic applications do not destroy tumor cells that lie far from blood vessels.
The Chinese team, headed by Xing-Jie Liang at the National Centre for Nanoscience and Nanotechnology (Beijing), synthesized 2-, 6-, and 15-nm gold nanoparticles stabilized with the thiolated molecule tiopronin. Introducing these nanoparticles into a 3-D breast cancer tumor model, they discovered that the 2-nm particles accumulated over 10 times more efficiently and penetrated more deeply than the 15-nm particles.
Importantly, the ability of the ultrasmall nanoparticles to penetrate more deeply than larger particles enables them to penetrate to the subcellular level. In contrast to the 15-nm nanoparticles, the 2- and 6-nm nanoparticles diffused throughout the cytoplasm and even entered the cell nucleus. This is significant because stopping the growth of cancer cells often requires access to their DNA.
Walkey notes that while the ability of ultrasmall nanoparticles to diffuse deep into the tumor may foster the design of better therapeutic nanoparticles, the gold nanoparticles used in Liang's study are not suitable for clinical applications. To be effective in the battle against cancer, future nanoparticles will have to dispense with gold cores. Nevertheless, the ability of minuscule nanoparticles to penetrate deeply into tumor cells will influence the design of future cancer-fighting nanomaterials.