Posted: August 28, 2006

Quantum dots enable rapid tumor typing using clinical tissue samples

(Nanowerk News) Measuring gene expression in clinical tissue samples may one day provide a powerful method for typing tumors and determining the optimal course of therapy for individual patients. Today, however, obtaining accurate results from gene expression arrays requires using fresh-frozen tissue samples, which is not practical for routine clinical analysis. A new method that uses multiple quantum dot imaging, developed by an international team of investigators, appears to solve this practical problem.
Richard Byers, M.D., of the University of Manchester, in the United Kingdom, led the team that developed the new assay technology, the details of which were published in the journal Biochemical and Biophysical Research Communications ("Imaging of multiple mRNA targets using quantum dot based in situ hybridization and spectral deconvolution in clinical biopsies."). This assay system relies on using multiple quantum dots, each of which radiates fluorescent light of a specific color, and a technique known as spectral imaging, to obtain a gene expression profile for tissue samples fixed in paraffin. Paraffin-fixing is a standard technique for preserving tissue samples.
The investigators first created nucleic acid probes capable of binding to specific messenger RNA (mRNA) molecules; mRNA contains the information cells used to translate genetic information encoded in genes into proteins, and thus are a reflection of gene expression. Each probe consists of a quantum dot linked to a stretch of RNA complimentary to an mRNA of interest. Each mRNA probe contains a quantum dot with a unique color profile.
After applying a mixture of probes to a tissue sample, the researchers recorded the entire spectral image from each pixel in a fluorescence microscope viewing field. They then used a computational method called signal deconvolution to analyze the light emitted from each pixel and separate the light emitted by each color of quantum dot from the large amount of fluorescent light given off the tissue fixed in paraffin. From this analysis, the investigators were able to identify the specific mRNAs present in the tissue samples.
Source: National Cancer Institute