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Methods for Identification of CA125 from Ovarian Cancer Ascites by High Resolution Mass Spectrometry
Adelaide Proteomics Centre, School of Molecular and Biomedical Science, University of Adelaide, Adelaide 5005, Australia
Research Centre for Reproductive Health, Robinson Institute, University of Adelaide, Adelaide 5005, Australia
These authors contributed equally to this work.
* Author to whom correspondence should be addressed.
Received: 15 May 2012; in revised form: 11 July 2012 / Accepted: 24 July 2012 / Published: 9 August 2012
Abstract: CA125 is the most widely used tumour marker in ovarian cancer with unsatisfactory sensitivity and specificity especially at early stage. It is quantified by antibody-based immunoassays; however different molecular weight isoforms have been described in the literature which have never been validated by mass spectrometry, potentially affecting the diagnostic accuracy and clinical reliability of the test. In this study, CA125 was detected by Western blot and its identity confirmed by mass spectrometry. Two-dimensional (2D) gel electrophoresis in combination with mass spectrometry revealed that positive Western blot signals up to 500 kDa are most likely false-positive interactions of M11-like and OC125-like antibodies. Fibronectin, identified as one of these false-positive interaction partners, increased the reading for CA125 in a first generation ELISA significantly (p = 0.02). The existence of low-molecular weight isoforms of CA125 is therefore questionable and is most likely reflecting cross-reactivity of the antibodies with other proteins. This would explain the conflicting reports on the molecular structure of CA125 and also the inconsistency of CA125 levels by different ELISAs. Our results are also the first steps towards a mass spectrometric assay for CA125 quantification, which would improve sensitivity and reliability.
Keywords: CA125; mucin 16; mass spectrometry; ovarian cancer; antibody; false-positives
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Weiland, F.; Fritz, K.; Oehler, M.K.; Hoffmann, P. Methods for Identification of CA125 from Ovarian Cancer Ascites by High Resolution Mass Spectrometry. Int. J. Mol. Sci. 2012, 13, 9942-9958.
Weiland F, Fritz K, Oehler MK, Hoffmann P. Methods for Identification of CA125 from Ovarian Cancer Ascites by High Resolution Mass Spectrometry. International Journal of Molecular Sciences. 2012; 13(8):9942-9958.
Weiland, Florian; Fritz, Katarina; Oehler, Martin K.; Hoffmann, Peter. 2012. "Methods for Identification of CA125 from Ovarian Cancer Ascites by High Resolution Mass Spectrometry." Int. J. Mol. Sci. 13, no. 8: 9942-9958.