Isotope Coded Affinity Tags (ICAT)

Principal Investigator:  Ruedi Aebersold
Organization: University of Washington (now with Institute of Molecular Systems Biology, ETH Zurich)
Years of Grant(s): 2000-2002

  • What is it?
    • Using an instrument called a mass spectrometer, special chemical labels (isotope-coded affinity tags, or ICAT reagents) are added to proteins taken from cancer cells. ICAT was a totally new way to find proteins linked with cancers, allowing researchers to detect and measure many different proteins at the same time and whether cancer followed from significant changes in how many of these proteins were found in cells. Proteins might serve as signs for identifying cancer or maybe as a way to develop new drugs to treat it.
  • How does IMAT intend to change research/solutions in cancer?
    • ICAT technology has given researchers an easier and more accurate way to look more broadly within a sample of cancer cells for many different proteins simultaneously. Not only was this technology successful and useful, but it also served to motivate many follow-on technologies that have further expanded our ability to explore the complicated mixture of proteins and their activity in cellular biology.
  • How is this important for the patient?
    • As was true at the time and is still true today, researchers struggle to identify and treat most cancers before they have grown to the point where the patient cannot be cured. This technology has brought researchers a step closer to studying the population of individual actors in cancer cells that might be unique to one specific cancer. Finding one protein that is either unusually plentiful or oddly absent might provide some understanding as to how that cancer grows and becomes dangerous. It also might serve as a useful direction for developing a way of treating that cancer.
  • Example(s) of success:
    • One example of how ICAT technology was used to make an important discovery is in showing a number of proteins involved in chronic pancreatitis were also uniquely involved in pancreatic cancer, and contributed understanding to the basic mechanisms controlling the development of this deadly condition (Chen et al, Molecular & Cellular Proteomics, 2007)


Additional Information about ICAT:

  • Taken from the 2008 IMAT Evaluation (conducted by SAIC)

Understanding the associations made by proteins within cells that let them perform their different functions is a major goal of proteomics research (i.e., the study of all expressed proteins in an organism). In the past, this painstaking research involved studying one protein at a time. The ICAT technology made it possible to identify and quantitatively analyze many proteins at the same time in biological samples, such as cell and tissue extracts and biological fluids, using mass spectrometry. This method may be used for both large-scale analysis of complex samples, including whole proteomes, and small-scale analysis of subproteomes.

Dr. Rudolf Aebersold and colleagues first described the initial proof-of-principle test of the ICAT™ technology to quantitate protein mixtures in Nature Biotechnology in 1999. This technology has since been widely applied, and this seminal publication has been cited 3,346 times to date . Dr. Aebersold further developed the technology through IMAT award R33CA084698. The aim of the IMAT R33 award was to design a new approach for measuring quantitative protein profiles in complex biological mixtures. The project’s goals included developing the ICAT™ reagents, liquid chromatography/mass spectrometry (LC/MS) tools, data processing tools, and technology protocols.

The success of the research funded by the IMAT award is evident in the patent applications and commercialization of the technology. Dr. Aebersold and colleagues have filed seven patent applications based on this research. All of these applications cite the IMAT award, and one patent has been granted as a result of these applications (Methods for Isolation and Labeling of Sample Molecules, Patent 7,183,116).

Applied Biosystems made the ICAT™ reagent kit commercially available in April 2001 and a second generation of ICAT reagents in 2002. The technology for ICAT™ applications incorporates the informatics tools developed by the major MS instrument manufacturers, and the Applied Biosystems commercialized for the Pro ICAT™ software for processing data from ICAT™ LC/MS applications.

Both the Institute for Systems Biology and Applied Biosystems have continued their research on this technology beyond the grant funding period to broaden the detection of proteins, including proteins modified after translation. Additional work has gone into enhancements of the LC/MS tools, techniques, and software.

ICAT™ is usually used to find and identify differences in the complex expression patterns of different samples (protein profiling). But ICAT™ has also been used with quantitative MS to find proteins with specific properties in a complex background of other proteins that lack these properties.

In addition, the technology has been used and applied in a new way to fission yeast. This model organism has growth mechanisms similar to those in humans. This research, led by Dr. Mark Flory in the laboratory of ICAT™ creator Dr. Aebersold, used ICAT™ and quantitative mass spectrometry to find proteins associated with centrosomes (protein structures) that accumulate in abnormal ways in cancer cells and tumors. The investigators have since developed strategies to identify related proteins in human cancer cell lines, which potentially serve as diagnostic biomarkers or targets for therapeutic intervention.