Absolute quantitation of cancer-related proteins using an MS-based peptide chip

New technologies are needed that can diagnose cancer more rapidly and accurately. These technologies must also have the ability to identify the particular cellular abnormalities contributing to the malignancy, thus directing the appropriate treatments. Such technologies should permit absolute quantitation of specific tumor biomarkers and their level of posttranslational modifications. Quantitative molecular profiling of cancer signaling networks would provide a more detailed understanding of the contribution of protein expression and posttranslational modification levels to tumorigenesis. We have developed a unique approach for absolute quantitation of protein expression that integrates affinity capture of proteolytic peptides with mass spectrometry and thus provides detection, identification, and quantitation of their cognate proteins. We have previously shown the high sensitivity and specificity of this approach. Here we demonstrate the absolute quantitation of a model peptide using our technology. We have used this approach to capture epitope-containing peptides from proteolytically digested target proteins, including p53, epidermal growth factor receptor (EGFR), and prostate-specific antigen (PSA). Our technology can easily be extended to the absolute quantitation of protein modification levels, in addition to the determination of protein expression levels, and can be readily adapted for use in a microarray format. This method offers an improved approach to protein chip technology that should prove useful for clinical diagnosis and drug development applications.