Abstract LB-247: Circulating proteolytic products of tumor-resident enzyme as potential biomarkers for early detection of breast cancer

Abstract

Abstract In theory, any or all of tumor-secreted proteins can serve as cancer biomarkers. However, the reality is challenging to monitor because of the large degree of fluctuation in abundance and localization of these tumor-secreted proteins, especially in the early stage of tumor development and/or metastasis. As such, it seems feasible that we might take advantage of the fact that secreted proteases/peptidases in the tumor microenvironment generate proteolytic products, also referred to as “circulating peptides”, which are detectable in bloodstream and provide ample information about the body, “coded” in the patterns and quantity of these peptides. Herein we clearly link the catalytic activity of Carboxypeptidase N (CPN) to its proteolytic products during breast tumor progression in mouse model and clinical samples. CPN plays important roles in regulating vasoactive peptide hormones, growth factors, and cytokines by specifically cleaving their C-terminal basic residues. Circulating fragment profiling, by an approach combining nanopore fractionation and mass spectrometry, revealed the nature and extent of cleavage by CPN. These results correlated with the level of CPN-catalyzed peptides in blood taken from the tumor-bearing mice, healthy women and breast cancer patients. We showed that generation of C3f_R1310-L1319 specifically correlated with the CPN expression level. In both mouse and clinical patient samples, the amount of CPN was increased in tumor tissues compared to that seen in normal breast tissue, while its counterpart in blood remained constant. The amount of 6 CPN-catalyzed peptides predominantly increased in sera taken from both the mice at 2 weeks after orthotropic implantation and the patients’ plasma as early as the first pathologic stage of breast cancer. In conclusion, the circulating level of the selected 6 CPN-catalyzed proteolytic products reflects the extent of this enzyme's activity in tumors, and our results clearly indicate their strong potential as biomarkers for non-invasive early diagnosis of breast cancer. Citation Format: Ye Hu. Circulating proteolytic products of tumor-resident enzyme as potential biomarkers for early detection of breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-247. doi:10.1158/1538-7445.AM2014-LB-247