[1727] Expression Pattern of Argininosuccinate-Synthetase (ASS) in Normal and Tumor Tissue as a Marker for Susceptibility to Arginine-Deiminase (ADI) Therapy

A Jungbluth, J Tassello, D Frosina, N Hanson, G Ritter, BW Wu, LJ Old. Ludwig Institute for Cancer Research, New York, NY; Polaris Pharmaceuticals, San Diego, CA

Background: Enzymatically induced amino acid deprivation of malignant tumors (e.g.asparaginase in acute leukemia) lacking particularly enzymes is a well established therapeutic concept for malignant disease. Arginine-Deiminase (ADI) treatment of tumors is based on a similar concept. Tumor cells lacking argininosuccinate synthetase (ASS) are arginine-auxotrophic and depend on extracellular arginine uptake. ADI treatment lowers blood arginine levels and tumor cell death is potentially induced by amino acid deprivation. However, little is know about the presence of ASS in normal and tumor tissues on the actual protein level.
Design: A monoclonal antibody (mAb) to ASS was generated employing ASS fusion protein and classical hybridoma technology. The novel reagent, mAb 195-21-1 was tested for specificity and its suitability in IHC. Subsequently, panels of normal organs and tumors were analyzed by IHC for presence of ASS.
Results: MAb 195-21-1 worked well in paraffin embedded tissue using heat-based antigen retrieval techniques. In normal tissues, ASS was widely distributed and present in most normal organs such as kidney, liver, lung, gastro-intestinal tract and others. endothelial cells were positive in vessels of all analyzed tissues. Interestingly, particular cells remained negative such as pancreatic islets, melanocytes, as well as adrenal medulla. In most analyzed tumors such as carcinomas of the lung, GIT, kidney and breast, as well as various sarcomas ASS was expressed ranging from 25%-100% ASS-positive tumor cells, though single tumors showed only focal ASS expression. However, in melanoma, neuroendocrine carcinomas and SCLC only ASS-expression was absent or present in only focal tumors cells.
Conclusions: ADI induces efficient lowering of peripheral arginine levels and tumor cells lacking ASS are potentially susceptible to ADI administration. In normal organs, ASS is widely distributed showing expression in most tissues. Its presence in tumors parallels its expression in normal tissue with colorectal, kidney and breast cancer being mostly ASS-positive though occasional neoplasms show little ASS expression. However, SCLC, melanomas, and neuroendocrine carcinomas show little to none ASS expression. Our study indicates that melanoma, small cell lung cancer, and neuroendocrine carcinomas are potential candidates for ADI-based cancer therapy.
Category: Pathobiology

Wednesday, March 24, 2010 9:30 AM

Poster Session V # 226, Wednesday Morning


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