Abstract 4446: Evaluation of the sensitivity and specificity of a fluorescent nanobeacon for imaging colorectal cancer

Abstract

Abstract Purpose: One of the potential molecular biomarkers associated with the development and progress of colon cancer is the Thomsen-Friedenreich (TF) antigen (Galα1,3GalNacα-O-Ser/Thr). Yet while the TF antigen is overexpressed in colon cancer, it is rarely expressed in normal colon tissue. For example, it has been shown that TF-associated cancer is a marker for poor prognosis in patients with colon cancer and for cancer risk in people with ulcerative colitis. Therefore, it is plausible that TF antigens are unique and can be used as a target for colon cancer imaging. The ubiquitous association of the TF antigen with tumors is an ideal in vivo antigen for early detection. Methods: In this work, we developed and validated the sensitivity and specificity of a novel nanobeacon for the detection of colon cancer using human cell lines and specimens. The nanobeacon is comprised of a submicron-sized polystyrene nanosphere encapsulated with a hydrophobic fluorescent dye, coumarin6. The surface was modified with the peanut agglutinin (PNA) and poly(N-vinylacetamide) (PNVA) moieties. Of note, the former binds to the cancer-specific carbohydrate antigen, Gal-α(1-3)GalNAc, with high affinity, while the latter enhances the specificity of PNA for the carbohydrates. Thus, the nanobeacon can detect colorectal tumors by recognizing the tumor-specific TF antigen through the surface-immobilized PNA with minimal background signal. Imaging is made via the fluorescence signal obtained from the coumarin 6 encapsulated in the nanosphere's core. We used optical imaging, a cell-sorting method and qPCR to quantify the level of expression of TF and compared with immunohistochemistry data. Results: The nanobeacon is specific for TF-associated cancer as the study was performed in colon cancer cells and human specimens. The cell-sorting analysis revealed that the biorecognition ability of the nanobeacon was superior to the antibody method. For human cancer tissue study, we observed that the nanobeacon's binding specificity to the tissues was corroborated with the immunohistochemistry data, not only in space, but also through signal intensity. The probe can detect different levels of TF antigen expression in cancer tissue. To confirm further the dynamic activity of the probe, we depleted the TF expression on human colon cancer tissue by treating the tissue with O-glycanase, thereby abolishing the fluorescence signal. Since the probe is designed to avoid systemic distribution that may cause subsequent toxicity, we performed a biodistribution study and found that the compound was not absorbed through the intestine. As a result, the nanobeacon was not distributed to the major organs including liver, kidneys and serum. Conclusion: These data suggest that the nanobeacon is capable of detecting TF-associated colon cancer. Moreover, in conjunction with colonoscopy, the nanobeacon is suitable for us as topical contrasting agent. 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 4446. doi:1538-7445.AM2012-4446