Abstract 4137: L-asparagine synthetase in solid tumors: Screening and implication in pancreatic cancer

Abstract

Abstract L-Asparaginase (L-Asp) depletes L-Asn in the plasma and is commonly used in the treatment of acute lymphoblastic leukemia (ALL) for over 40 years. Its indication is motivated by the fact that L-asparagine synthetase deficient leukemic cells are unable to synthesize L-Asn to meet metabolic demands and therefore depend on circulating L-asparagine (L-Asn) to survive and to proliferate. Unfortunately, its use in patients with solid tumours failed due to high toxicity. L-Asp entrapped inside red blood cells (GRASPA®) significantly improves its therapeutic index, thus allowing its use with acceptable tolerance in patients with solid tumors. There is strong rational for plasmatic L-Asn depletion in patients with negative or low-expressing L-asparagine synthetase (ASNS) cancers. Indeed ASNS catalyzes the biosynthesis of L-Asn from L-Aspartate and L-Glutamine and its overexpression appears to be crucial in L-Asp resistance in an ALL cell line model (Aslanian, 2001). In the same way, an inverse causal relationship was observed between ASNS expression (at the protein level) and L-Asp activity in a panel of human ovarian cancer cell lines, and a weak expression of ASNS by immunohistochemistry for 15% of the 55 ovarian cancers tested (Lorenzi, 2006). To demonstrate the implication of ASNS in solid tumors, we performed a large screening of ASNS expression by tissue microarray in several cancer types (bladder, brain, breast, colon, head & neck, kidney, liver, lung, lymphoma, melanoma, myeloma, ovary, pancreas and prostate). We first focused on pancreatic tumors and studied ASNS expression on 4 different tissue microarrays (n=172) and on a large series of standard pancreatic tumors slides (n=124). By this indirect immunohistochemistry method, we determine the proportion of low-expressing tumors in a representative subset of human pancreatic ductal adenocarcinomas. In parallel, we evaluate the IC50 of L-Asp in SW1990 (low ASNS expression), PANC-1 and MIA-PaCa-2 (ASNS positive) pancreatic cancer cell lines. Our results indicate that: - ASNS expression was strongly decreased in human ductal adenocarcinoma (percentage of negative or low-positive tumors > 65%) as compared to the high-expressing adjacent healthy pancreas tissue (< 10%); - In vitro, The ASNS low-expressing cell line SW1990 was more sensitive to L-Asp than the PANC-1 and MIA-PaCa-2 ASNS positive cell lines (IC50 (IU/mL L-Asp): 0.07±0.04 versus 0.18±0.05 and 0.24±0.06, respectively). In conclusion, we demonstrate that ASNS expression is strongly down-regulated in human pancreatic cancer. We also highlight in vitro causality between ASNS status and sensitivity to L-Asp in 3 pancreatic cancer cell lines. According to these results, ASNS was identified as a candidate biomarker to screen patients in solid tumors, especially for pancreatic carcinoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4137. doi:10.1158/1538-7445.AM2011-4137