Abstract 5250: Optimization of an orthotopic mouse model for in vivo fluorescent uPA imaging in breast cancer

Abstract

Abstract The urokinase plasminogen activator (uPA) system is one of the serine protease systems involved in extracellular matrix degradation, which will facilitate tumor cell invasion and intravasation. Recently, the Medicinal Chemistry group of the University of Antwerp (UAMC) developed some very selective covalently binding uPA inhibitors. Besides its function as possible therapeutic target, uPA and its endogenous inhibitor PAI-1 are described as prognostic biomarkers for breast cancer with the highest level of evidence. Commercial ELISA and PCR kits are available for the screening of uPA in breast tumors. These ex vivo assays measure or predict the total uPA content (active and inactive). We present here a more advanced technique, which will be able to monitor the actual enzymatic uPA activity in a non-invasive manner. The technology is based on the modification of the UAMC inhibitors towards activity based probes containing a fluorescent label. Currently, we are evaluating these probes as imaging tools for uPA monitoring. The developed imaging probes will be profoundly tested in an orthotopic model of human MDA-MB-231 and MCF7 breast cancer cells since these cell lines show a high and low uPA expression respectively. We will use these models to study the potential beneficial characteristics of activity based probes in the field of bio-imaging applications targeted to uPA as a validated biomarker. The current protocol, which is still under evaluation, can be described as followed: Cell suspensions (2.106 cells/100μl) of each cell line were implanted in the mammary fat pads at both flanks of 7 mice, alternatively with and without Matrigel. Tumor size was monitored using bioluminescent imaging (BLI) and caliper measurements. When the tumor volume reached 200 - 400mm3, the rhodamine labeled uPA-inhibitor (uPA-probe) was administered (0.3 mg / kg i.v.). Fluorescent images were taken at 1, 2, 4, 6, 8, 12, 24 and 48 hours after injection. At 48 hours, the mice were sacrificed and the tumor, liver and lung were excised for ex vivo bioluminescent or fluorescent imaging and stored for histological examination. In this presentation, we describe the evaluation of the model and the first promising results. Considering the role of uPA in migration and invasion, the uPA-probe will also be tested in the future for the detection of micrometastases. 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 5250. doi:1538-7445.AM2012-5250