Abstract 4847: Arginine deprivation by PEG-ADI induces autophagic cell death and enhances the tumor suppression effect of gemcitabine in pancreatic cancer

Metabolic stress has been recently recognized to induce autophagic cell death; we have recently shown that nearly 80% of pancreatic adenocarcinoma tumor specimens are auxotrophic for the semi-essential amino acid arginine due to transcriptional suppression of argininosuccinate synthase (ASS). We hypothesized that selective arginine deprivation would induce autophagy and furthermore, by targeting alternative death pathways would increase the cytotoxic response to the chemotherapy gemcitabine. Methods: The human pancreatic cell line MIA-PaCa-2 was shown to be deficient in ASS by western blot. Arginine deprivation was achieved by treatment of cells and xenografts with PEG-ADI, which shuttles arginine to citrulline. Cells were treated with either PEG-ADI, gemcitabine or both. Cell death was measured by MTT and FACS. Western blot was used to measure autophagy by LC3 processing and apoptosis by caspase-3 cleavage. RRM2 expression was measured by western blot in cells treated with PEG-ADI. ASS expression was measured by western blot in cells treated with gemcitabine. To test the in vivo effect arginine deprivation a mice xenograft model was created by subcutaneously injecting Mia-PaCa2 cells into the flanks of 28 mice (two tumors per mice). Tumors were allowed to mature at which time the mice were assigned to one of four treatment groups: PBS control (once weekly), ADI-PEG20 (5 IU once weekly), Gemcitabine (125mg/kg twice weekly), or Gemcitabine and ADI-PEG20. All treatments were administered via intraperitoneal injection and tumors were measured twice a week. Results: 1. MIA-PaCa-2 lacks ASS and is auxotrophic for arginine. 2. PEG-ADI induces autophagy and cell death 3. Gemcitabine has little in vitro cytotoxicity 4. The combination of gemcitabine and PEG-ADI is at least additive in vitro and in vivo. 5. PEG-ADI does not regulate RRM2 expression and gemcitabine does not regulate ASS expression. Conclusions: Therapy targeting autophagy may provide increased efficacy for traditional genotoxic chemotherapies in pancreatic cancer. PEG-ADI in combination with gemcitabine is a novel combination to be pursued in clinical trials 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 4847.