Abstract 2585: Targeting extra-cellular Annexin2 on epithelial cancer cells with labeled ligands for diagnosis/treatment of cancers
Authors: Singh Pomila , Sarkar Shubhashish 
Published: February 2011

Abstract
Extracellular membrane receptors for peptide hormones are used for diagnosing and treating cancers. Annexin2 (Anx2) was identified by proteomic methods as being over-expressed by epithelial tumors. Importantly, extracellular Anx2 is not expressed by non-dividing cells, such as normal hepatocytes. Membrane-associated Anx2 functions as a high-affinity receptor for many ligands. We recently discovered that progastrin (PG) represents a novel ligand which specifically binds Anx2. We additionally discovered that bound Anx2/PG rapidly internalize and co-localize within endosomes. Thus Anx2 represents a novel and unique molecule which can be used for diagnostic/therapeutic purposes of epithelial tumors, without collateral damage to normal tissues, especially liver. In the current studies we investigated the usefulness of labeled PG for diagnosing epithelial tumors, in vivo. Fluorescent-PG peptide fragments were used for diagnosing the size and metastatic spread of epithelial cancer xenografts in nude mice. Retention of endocytosed labeled PG by tumor lesions was imaged with either in vivo high resolution optical microscopy or micro-CT/spect imaging. PG26 was biologically active, and FITC-PG26 demonstrated equivalent binding affinity for Anx2 as the full length 80AA PG peptide. Endocytotic internalization of FITC-PG26 in PG responsive cells demonstrated strong peri-nuclear co-localization of FITC-PG26 with Anx2 within 15min of labeling The homing potential of FITC-PG26 to Anx2 over-expressing tumors, growing as xenografts in nude mice, was examined. FITC-PG26 specifically homed to the site of a colon cancer xenograft, growing either sub-dermally or as a metastatic lesion in the liver. FITC-PG26, injected intra-tumorally retained fluorescence for &gt;30 mins (without demonstrating any spread of the dye) confirming tumor specific retention of endocytosed FITC-PG26. FITC-PG26 successfully homed to the tumor site after i.v. injection through the tail vein, within 5 min of injection, and was retained in the tumor for ∼60min. Even small tumor lesions were detected with FITC-PG26 after tail vein injection. FITC-control peptide was not detected in the tumor after injecting into the tail vein, confirming specificity of FITC-PG26 peptide for homing to tumors in situ. No other organ was labeled; excretion of FITC from kidneys and bladder was observed. Results from these experiments provide critical information required for further developing PG peptides/mimetics as diagnostic/treatment tools for negating growth of epithelial cancers (lung, renal, pancreatic, colon, ovarian, breast), which over-express Anx2 by several fold, without collateral damage to liver and other normal tissues.
Supported by NIH grants to PS (2R01 CA097959; 1 R01 CA114264) and a Sealy Smith Cancer Center grant to PS.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2585.