Abstract 4810: Multiplexed immunoprecipitation-liquid chromatography-multiple reaction monitoring mass spectrometry quantification of protein expression and phosphorylation for breast cancer biomarkers

Abstract

Abstract Introduction: Estrogen receptor alpha (ER alpha), progesterone receptor B (PR B), and the receptor tyrosine kinase, Her2, are tumor markers classified by the American Society of Clinical Oncology (ASCO) as level of evidence I in breast cancer. The quantitative evaluation of protein expression and phosphorylation status of these targets in tumor tissues will enable subtype classification and support clinical decision-making and selection of targeted therapy in breast cancer. Experimental Procedures: Breast cancer cell lines were used to develop peptide-based quantitative assays for protein expression and phosphorylation using immunoprecipitation (IP) and liquid chromatography-multiple reaction monitoring mass spectrometry (LC-MRM). Stable isotope-labeled standard peptides were synthesized and developed as internal standards. Multiplexed IP for ER alpha, PR B, and HER2 will be developed to enable the enrichment of the proteins to enable quantification of the expression and phosphorylation of these biomarkers in the same sample. The sensitivity of each assay will be tested using serial dilutions of cell lysate to evaluate requirements for analysis of clinical specimens. Data Summary: LC-MRM assays for both unmodified and phosphorylated peptides have been developed and characterized for each protein. Recovery using multiplexed IP for these proteins is similar to recovery of individual IP. Data have been generated for cell line models of stimulation and treatment. For example, LC-MRM quantification of HER2 in cell line models stimulated with EGF or Heregulin shows that protein expression is unchanged, but phosphorylation increases; on the other hand, LC-MRM shows clearly that phosphorylation of Her2 is inhibited with Lapatinib. Conclusions: The ability to examine the protein expression as well as the phosphorylation status in these biomarkers with quantitative mass spectrometry will produce improved understanding of their role in the development and progression of breast cancer and has the potential to improve the selection of targeted therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4810. doi:1538-7445.AM2012-4810