Abstract 5629: Arginine depravation therapy with arginine deiminase and autophagy inhibition is a novel therapeutic approach for the treatment of metastatic sarcomas that lack argininosuccinate synthetase expression

Abstract

While sarcomas are a rare group of tumors, the poor response to current clinical regimens represents an important unmet need in oncology. A better therapeutic understanding of the biology and metabolism of sarcoma growth is necessary to develop novel therapies to treat patients with this group of tumors. Argininosuccinate synthase 1 (ASS1) is the rate-limiting enzyme in the conversion of citrulline to arginine. When ASS1 is not expressed arginine becomes an essential amino acid to a cancer cell that must be delivered from the diet. Immunohistochemical analysis of 701 patient specimens representing 45 subtypes of sarcoma demonstrates that ASS1 is not expressed in over 85% of sarcomas (619 of 701 patient samples). This suggests that sarcomas may be sensitive to the arginine deprivation therapy using pegylated arginine deiminase (ADI-PEG20). Treatment of a panel of leiomyosarcoma, osteosarcoma, alveolar soft part sarcoma, malignant peripheral nerve sheath tumor and Ewing's sarcoma cell lines with ADI-PEG20 resulted in cell cycle arrest but not apoptosis when ASS1 expression was low, whereas the ASS1 high osteosarcoma cell line MG63 continued to divide. Response in sarcoma cell lines is dependent on ASS1 expression, as bone sarcomas, soft tissue sarcomas, complex cytogenetic sarcomas and translocation dependent sarcomas all demonstrate cell cycle inhibition upon treatment with ADI-PEG20. The IC50 for treated cell lines treated with ADI-PEG20 ranged from 0.02-0.1ug/mL in ASS1 low sensitive cell lines. Treatment of sarcomas that lack ASS1 with ADI-PEG20 induces autophagy. Depletion of arginine by ADI-PEG20 in ASS1 negative sarcomas when combined with chloroquine, an inhibitor of autophagy, induces cell death as measured by Annexin V. Xenograft of the ASS1 low expressing osteosarcoma cell line MNNG into nude mice followed by treatment with ADI-PEG20 demonstrated a significantly slower tumor growth rate as compared to PBS treated controls. Experiments are now ongoing in mice using the combination of chloroquine and ADI-PEG20. Successful control of tumor burden by using arginine deprivation therapy and autophagy inhibition in our preclinical studies will help to justify and orient future clinical trials for this innovative treatment for patients with sarcoma that lack ASS1 expression. 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 5629. doi:1538-7445.AM2012-5629