Nanotech News

September 2007

PET Scanning Tracks Injected Quantum Dots

A wide variety of experiments have shown that nanoscale quantum dots have the potential to detect early-stage cancer and even monitor the progress of anticancer therapies. But a new study from a team of investigators at the Center for Cancer Nanotechnology Excellence Focused (CCNE) on Therapy Response suggests that quantum dots as they currently exist may not remain in the body long enough to prove useful in human clinical applications.

Sanjiv Gambhir, M.D., Ph.D., principal investigator of the Stanford University-based CCNE, along with fellow CCNE investigators Anna Wu, Ph.D., and Xiaoyuan Chen, Ph.D., used positron emission tomography (PET) to track the fate of radioactively labeled quantum dots labeled after injection into mice. After injection, PET imaging revealed that as much as a half of the quantum dots were removed from the blood stream by the liver and spleen and that the entire dose was removed from circulation within 10 minutes of injection. Quantum dots coated with poly(ethylene glycol) (PEG), a biocompatible polymer used to extend the circulating lifetime of many types of nanoparticles, fared little better. The size of the quantum dots also had little effect on blood clearance rates.

The researchers note that while this study raises important biodistribution issues that must be solved if quantum dots are to become a useful clinical tool, it also demonstrates that PET monitoring of radiolabelled nanoparticles can provide rapid, quantitative data on nanoparticle biodistribution. In addition, the real-time nature of PET monitoring allowed the investigators to identify differences in pharmacokinetic properties between PEG-coated and native quantum dots. These differences would not have been spotted using traditional pharmacokinetic assays.

This work, which was supported by the National Cancer Institute's Alliance for Nanotechnology in Cancer, is detailed in the paper, "MicroPET-based biodistribution of quantum dots in living mice." Investigators from the University of California, Los Angeles, School of Medicine also participated in this study. An abstract of this paper is available through PubMed.
View abstract.