Abstract 4445: Pegylated arginine deiminase induces mitochondrial apoptosis and synergizes with cisplatin in ASS1-negative malignant pleural mesothelioma

Abstract

Abstract We have explored the role of pegylated arginine deiminase (ADI-PEG20), an arginine catabolizing enzyme, in argininosuccinate synthetase 1 (ASS1)-negative malignant pleural mesothelioma (MPM). MPM is a chemorefractory disease, increasing worldwide, with a median survival of less than 1 year. Novel treatments are urgently required. MPM tumors, lacking ASS1, are auxotrophic for arginine and therefore sensitive to arginine depletion driven by ADI-PEG20. First we assessed the impact of ADI-PEG20 on global gene expression to identify novel interacting pathways in the ASS1-negative MPM cell line, JU77, using the human genome U133 Plus 2.0 Array from Affymetrix combined with bioinformatic analysis. Next, three ASS1-negative MPM cell lines (MSTO-211H, 2591 and JU77) were treated in triplicate with different fixed ratios of ADI-PEG20 and cisplatin. Cellular viability was determined 6 days post-treatment by MTS colorimetric assay. Apoptosis protein induction by ADI-PEG20 and platinum, alone and in combination, was measured by western blot after mitochondrial and cytosolic fractionation. Drug interactions were analyzed using the isobologram method of Chou and Talalay. ADI-PEG20 modulated several thousand genes involved in cell cycle, DNA damage, immune, and inflammatory pathways in the ASS1-negative JU77 MPM cell line by 24hrs of drug treatment. In contrast, stable transfection of ASS1 cDNA in ASS1-negative MPM cell lines resulted in resistance to ADI-PEG20 with minimal evidence of gene modulation by 24hr of drug treatment as assessed in the JU77 MPM cell line. ADI-PEG20 triggered mitochondria-dependent apoptosis as evidenced by Smac release from mitochondria into the cytosol of ASS1-negative MPM cell lines. We confirmed that arginine depletion by ADI-PEG20 altered the mTOR/p70S6K signaling pathway and led to dephosphorylation of the translation regulation proteins S6K and E4-BP1. The expression of cell cycle regulating proteins p21 and cyclin D1 was decreased by arginine depletion, alone and in combination with cisplatin. The enhancement of cisplatin cytotoxicity by ADI-PEG20 with loss of ASS1-negative MPM cell viability as early as 24hr post treatment, supports the demonstrated strong synergy between the two drugs. In summary, the antitumor effect of platinum was potentiated markedly using ADI-PEG20, suggesting that combining arginine depletion with the current standard of care, platinum and antifolates, may offer an improvement over doublet chemotherapy alone. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4445.