February 27, 2006
Bismuth Nanoparticles Yield Promising X-ray Imaging Agent
A major focus of research in cancer nanotechnology aims to develop nanoparticles that can improve the ability of various imaging techniques to spot tumors at a very early stage. While these efforts have focused almost exclusively on developing so-called “contrast agents” for use with magnetic resonance and ultrasound imaging, one group of investigators has now developed a polymer-coated bismuth nanoparticle that holds promise for improving the tumor-detecting capabilities of computed tomography X-ray imaging, or CT.
Reporting its work in the journal Nature Materials, a team of researchers led by Ralph Weissleder, M.D., Ph.D., at Massachusetts General Hospital and Harvard Medical School, began their work by refining a method for growing bismuth sulphide nanocrystals to produce flat, rectangular particles of reproducible size and shape. They then coated the resulting nanocrystal with the biocompatible polymer poly(vinylpyrrolidone), or PVP, to create nanoparticles that would be inert in the body, absorb X-rays efficiently, and remain long enough to accumulate in the tumor, and thus, be more visible in a CT image. The researchers note that the PVP coating should also enable them to add tumor-targeting molecules to the particles to increase their ability to image small tumors.
Tests in animals showed that these bismuth nanoparticles remained in the bloodstream far longer than commercially available iodine-based CT contrast agents, and could be used at lower doses. More importantly, when the researchers injected the bismuth nanoparticles into mice, they were able to clearly image regional lymph nodes and blood vessels, which the researchers noted was a promising result. Initial toxicity tests showed that the bismuth nanoparticles were also less toxic than the contrast agents now in clinical use.
This work, funded in part by the National Cancer Institute, is detailed in a paper titled, “An X-ray computed tomography imaging agent based on long-circulating bismuth sulphide nanoparticles.” Weissleder is the co-director of the MIT/Harvard Center for Cancer Nanotechnology Excellence. An abstract of this paper is available through PubMed.
These two CT images of a live mouse before (left) and after (right) injection of polymer-coated bismuth sulphide nanoparticles show how the nanoparticles readily delineate the vasculature, heart and other organs. Image courtesy of Ralph Weissleder.