Abstract 1206: Cisplatin resistant non small cell lung cancer is sensitive to arginine deprivation therapy
Authors: Wangpaichitr Medhi , Wu Chunjing , Nguyen Dao M. , You Min , Li Ying Ying , Chen Shumei , Feun Lynn G. , Savaraj Niramol 
Published: August 2015

Abstract
Drug resistance is a major obstacle to cancer chemotherapy. Despite early positive response to platinum-based chemotherapy, the majority of non small cell lung cancer (NSCLC) develops resistance. We have previously shown that all cisplatin resistant (CR) cell lines exhibit high levels of reactive oxygen species (ROS) production which leads to alteration in tumor metabolism. We and others have shown that CR cells have low or no expression of argininosuccinate synthetase (ASS) when compared to their parental cells. Since ASS is a key enzyme to synthesize arginine from citrulline, lack of ASS expression will make arginine an essential amino acid for these CR tumors. Certain NSCLC cell lines/tumor samples also express very low levels of ASS; however, it is unclear how this expression will be affected by cisplatin treatment. In this report, we investigate the underlying mechanism using 6 pairs of NSCLC cell lines and their CR variants: H460/H460CR, F/FCR, S/SCR, A549/A549CR, H1299/H1299CR, and H23/H23CR. Note that H460, F, S are ASS(+) and A549, H1299, H23 are ASS(-). No ASS expression due to hypermethylation was found in H1299, while in A549 and H23, it is most likely due to transcription regulation which governs ASS expression, as we have been previously reported in melanoma. All these CR cells possess at least 7 fold resistances to cisplatin and express 3-5 fold increase in ROS levels when compared to parental cell counterparts. CR cells, derived from parental cells that possess high ASS expression, exhibited significantly lower levels of ASS once they became resistant to cisplatin. These CR cells were also hypersensitive to arginine deprivation using ADI-PEG20 (provided by Polaris Inc) which degrades arginine to citrulline. Importantly, the addition of 50ng/ml of ADI-PEG20 restored cisplatin sensitivity to CR cells. With the combination of cisplatin and ADI-PEG20, the ID50 dosage of cisplatin decreased (5-7 fold) to the original levels as their parental counterparts. When compared with cisplatin alone treatment, the percentage of cells with caspase activation increased from 5% (2ug/ml of cisplatin) to 70% (combination with ADI-PEG20). However, in three pairs of CR cells derived from ASS(-) cells, the ASS remains negative in H1299CR while in A549CR and H23CR the ASS expression showed 1-1.5 fold increase both at mRNA and protein levels. Nevertheless, the addition of ADI-PEG20 still can sensitize these CR cells to cisplatin treatment. To further verify the role of ASS in cisplatin resistance, we have overexpressed ASS into SCR cell line and determine the sensitivity to cisplatin. This transfectant became resistant to ADI-PEG20, but maintains similar levels of cisplatin resistance. These data suggest that silencing ASS in these CR cells is most likely a consequence of other biochemical changes occurring in CR cells. These metabolic alterations can be used to target CR lung cancer. Supported by Department of Veterans Affairs, CDA2 award (1K2BX001289).
Citation Format: Medhi Wangpaichitr, Chunjing Wu, Dao M. Nguyen, Min You, Ying Ying Li, Shumei Chen, Lynn G. Feun, Niramol Savaraj. Cisplatin resistant non small cell lung cancer is sensitive to arginine deprivation therapy. [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 1206. doi:10.1158/1538-7445.AM2015-1206