Identification of ovarian cancer-associated proteins in symptomatic women: A novel method for semi-quantitative plasma proteomics.

To evaluate the utility of an enhanced biomarker discovery approach in order to identify potential biomarkers relevant to ovarian cancer detection. We combined immuno-depletion, liquid-phase IEF, 1D-DIGE, MALDI-TOF/MS and LC-MS/MS to identify differentially expressed proteins in the plasma of symptomatic ovarian cancer patients, stratified by stage, compared to samples obtained from normal subjects. We demonstrate that this approach is a practical alternative to traditional 2D gel techniques and that it has some advantages, most notably increased protein capacity. Proteins were identified in all 76 bands excised from the gels in this project and confirmed the cancer-associated expression of several well-established biomarkers of ovarian cancer. These included C-reactive protein (CRP), haptoglobin, alpha-2 macroglobulin and A1A2. We also identified new ovarian cancer candidate biomarkers, Protein S100-A9 (S100A9) and multimerin-2. The cancer-associated differential expression of CRP and S100A9 was further confirmed by Western blot and ELISA. The methods developed in this study allow for the increased loading of plasma proteins into the analytical stream when compared to traditional 2D-DIGE. This increased protein identification sensitivity allowed us to identify new putative ovarian cancer biomarkers.