Abstract 1692: Expression of argininosuccinate synthetase protein and correlation with response to the novel therapeutic pegylated arginine deiminase (ADI-PEG20) in osteosarcoma

Abstract

Abstract The amino acid arginine is involved in protein synthesis and tumor metabolism and is essential for the growth of human cancer cells. Pegylated arginine deiminase (ADI-PEG20) is a novel therapy that lowers extracellular arginine levels and has shown evidence of clinical response and low toxicity in patients with tumors lacking argininosuccinate synthetase (ASS1) protein expression, including melanoma and hepatocellular carcinoma. Recently it has been shown that ASS1 expression was deficient in 63% (39/62) of Japanese osteosarcoma patient samples, and reduced ASS1 was associated with pulmonary metastases. In addition, they showed that ASS1 deficient, but not ASS1 expressing, osteosarcoma cells lines did not grow in arginine-deficient media, and recommended evaluation of arginine depletion with ADI-PEG20 in osteosarcoma. Because ADI-PEG20 efficacy appears to correlate with ASS1 protein expression, a cohort of osteosarcoma tissue sections (n=171) was stained immunohistochemically to determine the presence or absence of ASS1 protein. Sixty-four percent (n=109) indicated negligible or no staining for ASS1 protein suggesting further that osteosarcoma might be a candidate for ADI-PEG20 sensitivity. Western blots were performed on patient-derived osteosarcoma cell lines (n=18) to determine levels of ASS1 protein expression prior to treatment with ADI-PEG20. Of the 18 cell lines studied, four cell lines had noticeably diminished ASS1 protein expression. The remaining 13 cell lines exhibited varying amounts of ASS1 protein expression with five of these cell lines appearing strongly positive indicating possible overexpression of ASS1 protein. Cytotoxicity assays were performed on a subset of cell lines representing both elevated and decreased ASS1 protein expression to determine the in vitro effectiveness of ADI-PEG20 in patient-derived osteosarcoma cell lines and its correlation with ASS1 protein expression. Some of the ASS1 deficient cell lines showed decreased cell viability in response to arginine depletion with ADI-PEG 20. These findings suggest that arginine depletion with ADI-PEG 20 may be a potential targeted treatment for osteosarcoma patients deficient in ASS1 expression. In addition, further preclinical studies are ongoing, including xenograft models, to understand better the mechanism of this agent in osteosarcoma. 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 1692. doi:1538-7445.AM2012-1692