Analysis of mechanism underlying the metabolic effects of ADI-PEG20 at gene expression level. The hypothesis tested in the present study was that ASS1-deficient breast cancer cells would be arginine-auxotrophs and would therefore be sensitive to arginine starvation. Results provide important information of the response of ASS1-deficient breast cancer cells to ADI-PEG20-treatment, such as the suppression of mRNAs encoding mitochondrial respiratory chain proteins. Total RNA obtained from ADI-treated, or ADI- and L-arginine-treated 231 cells compared to untreated cells.