Fluorescence Detection of Colonic Neoplasia Using a Novel Peptide

Abstract

Background. Overexpression of AnnexinA2 (ANXA2) has been reported in several epithelial cancers, including colorectal cancers (CRC) (Cancer Letters, 2007). Increasing expression of gastrin gene, and hence progastrin (PG), has also been reported in CRCs. We recently discovered that ANXA2 serves as a non-conventional receptor for PG (Oncogene, 2007). We additionally reported that binding of PGwith extracellular, membrane associated, ANXA2 results in endocytosis and co-localization of PG/ANXA2 intracellularly (Gastro, 2010), and that ANXA2 is required for mediating mitogenic and anti-apoptotic effects of PG on colon cancer cells. ANXA2 is normally involved with intracellular trafficking. During the course of our studies we discovered that ANXA2 is also present on outer membranes of CRC cells, bound to a 29KDa transmembrane protein, and also released into the medium. To further understand physiological significance of these unexpected findings, we examined if ANXA2 is present in serum of patients positive for colorectal growth and if ANXA2 co-localizes with PG in tumor sections, in relation to disease status. Methods, Results and Conclusions. Secretion of ANXA2 (10-50ng/106 cells) was confirmed in conditioned medium (CM) of CRC cells using quantitative Western Blot assay using standard curve with rhANXA2; nontransformed cells were negative. Serum from CRC tumor bearing mice were positive for ANXA2, while control mice were negative. Next, serum samples were obtained from consented patients at time of endoscopy or as discarded samples from CRC patients on day of surgery, as per our IRB protocols. Serum from patients, negative for colonic growths (Normal, N) had low levels of ANXA2 (<1ng/ml), while serum from patients with hyperproliferative growths (Hp), Adenomas (Ad) and adenocarcinomas (AdCA) were on an average positive for 42, 80, and 490 ngs/ml, respectively, suggesting elevation of serum ANXA2 in relation to disease status. Paraffin blocks of Hp, Ads, AdCAs and adjoining N mucosa were obtained as discarded specimens from Department of Pathology and stained immunofluorescently for PG/ANXA2. Hp, Ads and AdCAs were increasingly positive for ANXA2 and PG expression compared to N specimens; ~ 10, 25 and 60 % of respective specimens were positive for intracellular co-localization of PG/ANXA2, suggesting presence of functional PG/ANXA2 axis, confirmed by progressive elevation of nuclear β-catenin and stem cell markers (DCAMKL+1, Lgr5) in relation to disease status. It remains to be determined if, 1) presence of co-localized PG/ANXA2 intracellularly represents a prognostic marker for predicting treatment/recurrence, and 2) if serum ANXA2 levels can be used as a non-invasive diagnostic marker for predicting presence of colorectal growths, stage of disease and/or relapse. Supported by NCI grants CA97959 and CA114264 to PS.