Abstract 4480: Evaluation of anti-tumor enone-based bioactive compounds as specific thioredoxin reductase inhibitors
Authors: Kaminska Kamila K. , Low Joanne Jia-An , Chua Wan-Ying , Woon Esther , Chew Eng-Hui 
Published: August 2015

The thioredoxin system is a promising anti-cancer therapeutic target. It is one of the main cellular thiol antioxidant systems and comprises of thioredoxin, thioredoxin reductase and NADPH. In particular, thioredoxin reductase is an attractive target with susceptibility to inhibition by electrophilic compounds due to its nucleophilic selenocysteine residue in the C-terminal active center. In our laboratory, a series of enone-based compounds were synthesized and evaluated for their possible selectivity to inhibit thioredoxin reductase. To this end, the compounds were first screened for their in vitro thioredoxin reductase and glutathione reductase inhibitory activities, and their anti-proliferative activities were assessed by the MTT cell viability assay. The effects of selected analogs on the activities of thioredoxin reductase, thioredoxin and glutathione reductase were next studied. Finally, the molecular events linking thioredoxin reductase inhibition to apoptosis induction were elucidated. A number of the enone-based structural analogs were identified to posses anti-proliferative activities against HCT116 colorectal and MCF7 breast carcinoma cells at GI50 values in the low micromolar range, as well as inhibit activity of rat thioredoxin reductase with half-maximal inhibitory concentrations in the nanomolar range. Furthermore, these compounds displayed relatively weaker in vitro glutathione reductase inhibitory activities with half-maximal inhibitory concentrations in the micromolar range. In corroboration with results obtained from the in vitro enzyme activity assays, the identified lead analogs exhibited significant dose-dependent cellular thioredoxin reductase inhibition accompanied by a near negligible lack of effect on cellular thioredoxin and glutathione reductase activity. Conversely, the parent compound was found to not only inhibit cellular thioredoxin reductase activity, but also caused an inhibition of cellular thioredoxin and glutathione reductase activities. Finally, at a molecular level, the identified lead analogs that exhibited selective inhibition against thioredoxin reductase were found to induce apoptosis through activation of JNK and p38 MAPK pathways. In conclusion, this study had evaluated and identified enone-based bioactive compounds that display selective and dose-dependent inhibition of thioredoxin reductase activity in susceptible cell lines, which led to activation of p38 and JNK MAPK signaling pathways that at least in part triggered the apoptotic cascade. Taken together, the findings have indicated the potential of designing and developing these compounds that exert their anti-tumor effects through selective inhibition of thioredoxin reductase.

Citation Format: Kamila K. Kaminska, Joanne Jia-An Low, Wan-Ying Chua, Esther Woon, Eng-Hui Chew. Evaluation of anti-tumor enone-based bioactive compounds as specific thioredoxin reductase inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4480. doi:10.1158/1538-7445.AM2015-4480