GPX1 and breast carcinoma: The immortalized lymphocyte cell line GM10832 and breast cancer-derived cell line MDA-MB-231 were each exposed to cytostatic doses of imatinib (300 nm and 500 nM, respectively) for 7 days and no significant change in either GPx activity or GPx-1 protein levels were observed (Figs. 3A and 3B).