Figure 3.

ADI-PEG20 treatment inhibits tumor growth until ASS1 re-expression confers resistance. (a) Flow cytometry analysis of cell death induction, as measured by percentage of cells staining positive for PI, upon treatment with ADI-PEG20. As a single agent, ADI-PEG20 does not induce cell death in these sarcoma cell lines. (N=3). Data represented as mean±S.D. (b) Tumor growth of ASS1^low SK-LMS-1 cells xenografted into nude mice with or without ADI-PEG20 treatment. Significant tumor growth inhibition was observed when mice were treated with ADI-PEG20 as compared with tumor growth in PBS-treated mice. Shown below is a western blot of five tumor lysates from five mice after ADI-PEG20 treatment showing re-expression of ASS1 in tumors, which had gained resistance to ADI-PEG20 mediated growth inhibition. (N=5 mice per arm). Data represented as mean tumor volume±S.E.M. (c) Re-expression of ASS1 in SK-LMS-1 cells after treatment with 1 μg/ml ADI-PEG20, 5 μM 5-aza-dC or both, as compared with untreated cells. After 48 h of combination treatment, ASS1 expression levels have significantly increased above wild-type conditions, as well as either drug individually. (N=3)