Oridonin Induces Oxidative Stress-mediated Cancer Cells Apoptosis Targeting Thioredoxin Reductase.

Background: Thioredoxin reductase (TrxR) plays vital role in regulating cellular redox balance as well as redox-mediated signal transduction. Accumulating evidence supports that overactivation of TrxR is closely related to tumorigenesis and that targeting TrxR ablation reverses the growth of numerous malignant tumors, making TrxR a promising target for cancer chemotherapy. Thus, the discovery and development of molecules as promising anticancer agents that target TrxR is of great significance. Oridonin was shown to inhibit TrxR activity, but the detailed cellular mechanism is largely unknown.

Objective: The study investigated the mechanism of action and underlying inhibitory properties of oridonin on TrxR in HeLa cells.

Methods: A covalent docking was performed to reveal the possible interaction between oridonin and TrxR by Schrödinger Software Suite. TrxR activity was determined by 5,5'-dithiobis-2- nitrobenzoic acid reduction assay and endpoint insulin reduction assay. Sulforhodamine B and colony formation assay were employed to assess the viability and growth of cells. Reactive oxygen species level was measured by probe 2', 7'-dichlorfluorescein diacetate, and dihydroethidium. Hoechst 33342 staining, caspase 3 activation, and fluorescein-5-isothiocyanate-conjugated Annexin V and propidium iodide double staining were used to evaluate apoptosis.

Results: Here, we reported the oridonin as a potent inhibitor of TrxR. Inhibition of TrxR results in a decrease of thiols content and total glutathione, elevates reactive oxygen species levels, and finally promotes oxidative stress-mediated apoptosis of cancer cells.

Conclusion: Targeting TrxR by oridonin discloses a novel molecular mechanism underlying the biological action of oridonin and sheds light on developing oridonin as a potential tumor therapeutic agent.