monstrated that elevated levels of ROS can be exploited in vitro and in vivo to specifically target cancer cells while sparing normal cells. Because our data showed that NSC130362 treatment caused both dose-dependent accumulation of ROS and peroxidation of the mitochondrial lipid CL in MDA-MB-435 cells but not in human hepatocytes, we propose that NSC130362 could specifically induce cell death in cancer cells. To test if combining NSC130362 with different oxidative stress inducers could be a potent and cancer cell-specific treatment, we analyzed various breast, pancreatic, prostate, and lung carcinoma cell lines, along with melanoma MDA-MB-435 and AML cells from patients. To confirm tumor selectivity, we also treated human primary hepatocytes. To induce oxidative stress, we employed three oxidative stress inducers, ATO, BSO, and Myr. Our results convincingly demonstrated that induction of oxidative stress selectively potentiated the cytotoxic activity of NSC130362 in cancer cells without any notable effect on the viability of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19709857 human primary hepatocytes. Mammalian cells have two electron donor systems, the thioredoxin system and the GSH system that regulate cell metabolism, motility, viability, and reproduction. The stress inducer ATO and the naturally occurring flavonol Myr irreversibly inhibit Trx reductase, thereby inactivating the Trx system, while the stress inducer BSO is an inhibitor of GSH synthesis through the irreversible inactivation of gamma-glutamylcysteine synthetase. Based on our cytotoxicity data, we posit that the strategy to inhibit both cellular redox systems is an 
PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19713490 efficient approach to selectively target cancer cells. The potent and safe to primary hepatocytes combined treatments of NSC130362 and oxidative stress inducers against a variety of cancer cells as well as the effect of NSC130362 on the TRAIL pathway undoubtedly warranted additional studies using mouse models. The short half-life of NSC130362 in the mouse bloodstream greatly diminished the possibility of obtaining any noticeable effect of its combination with also short-lived TRAIL on tumor growth in mice. For these reasons we decided not to test the combination efficacy of TRAIL and NSC130362 in animal xenograft tumor model as it was shown, for example, for wogonin and TRAIL. Recently, we identified several NSC130362 analogs that have LY-411575 anti-tumor activity and safety to hepatocytes comparable to those of NSC130362. Their pharmacokinetic profile is currently under investigation. As soon as we identify stable NSC130362 analogs, we will test them in combination with TRAIL in vivo. In the current studies, we selected ATO as an agent that could substitute TRAIL in in vivo studies and confirm the anti-tumor activity and safety to normal cells of NSC130362 in mice. In agreement with the cell-based assays, combination of ATO and NSC130362 retarded growth of MIA PaCa-2 xenografts. Importantly, this combined treatment was not toxic to normal tissue as was evidenced by the H&E staining of liver and heart tissue sections, which are the most sensitive to oxidative stress. In summary, we have demonstrated that phenotypic TRAIL-based HTS and in silico methods can be employed to identify chemical compounds that specifically induce cytotoxicity in cancer cells while sparing normal cells. In our study we identified a specific inhibitor of GSR activity, which, when combined with other oxidative stress inducers, may provide the basis for a potent and non-toxic cancer therapy. Our