Abstract 5512: Preclinical evaluation of the recombinant human arginase PEG-BCT-100 leading to arginine deprivation in sarcomas

Background: Arginine deprivation is a novel approach to limit arginine-dependent tumour growth. The presence of enzymes involved in the de novo synthesis of arginine from citrulline, argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL) and ornithine transcarbamylase (OTC), can influence the sensitivity of tumour to arginine depletion. We studied the preclinical efficacy of PEG-BCT-100 (also known as rhArg1peg5000), a PEGylated recombinant human arginase 1 on sarcoma cell lines. In this study, ASS, ASL and OTC expression were established in sarcoma cell lines and the sensitivity of each cell line to PEG-BCT-100 treatment was determined in order to establish their suitability as predictive markers to determine responsiveness to PEG-BCT-100 treatment. Methods: Cells from 5 representative soft-tissue sarcoma (STS) cell lines (RD, GCT, HT-1080, SW872, SW982) and 1 osteosarcoma cell line (SJSA-1), either incubated in full culture medium (control), arginine free medium or PEG-BCT-100 (1U/ml) treated medium. They were monitored by live cell imaging for 72 hours. Their corresponding IC50 were determined by cell viability assay. The expression of ASS, ASL and OTC were determined by Western blotting. Results: All sarcoma cell lines were sensitive to PEG-BCT-100 and demonstrated significant cell proliferation inhibition. Their IC50, as determined by cell viability assay were 0.023 U/ml, 0.028 U/ml, 0.023 U/ml, 0.026 U/ml, 0.20 U/ml, 0.053 U/ml, and 0.03 U/ml for GCT, HT-1080, RD, SJSA-1, SW872 and SW982 respectively. Western blot analysis confirmed strong basal protein expression of ASL and low OTC expression in all sarcoma cell lines, suggesting sensitivity to PEG-BCT-100 is not determined by ASL but rather, OTC. On the contrary, low ASS basal protein expression was revealed in all sarcoma cell lines except for RD. A strongly expressed ASS was observed in RD despite of its sensitivity to PEG-BCT-100, implying that ASS might be less important in the response towards PEG-BCT-100. Conclusion: Arginine deprivation by PEG-BCT-100 is effective in suppressing STS cell growth in vitro, suggesting arginine auxotrophism in STSs. Moreover, arginase treatment can be an effective strategy against STS. Low expression of OTC, instead of ASS and ASL, may be a more important predictive biomarker for response to treatment. Further in-vivo and clinical studies are warranted. Citation Format: Chi Tung Choy, Hio Teng Cheong, Kin Pong U, Chi Hang Wong, Herbert Ho Fung Loong. Preclinical evaluation of the recombinant human arginase PEG-BCT-100 leading to arginine deprivation in sarcomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5512. doi:10.1158/1538-7445.AM2015-5512