Inhibitory Mechanism And Anti-tumor Activities Of Natural Small Molecule Compounds Targeting TXNRD1

Thioredoxin system is closely related to the occurrence and development of various diseases by maintaining cellular redox homeostasis and modulating signaling cascade.Thioredoxin reductase（TXNRD）reduces physiological substrate thioredoxin（TXN）,TXN reduces downstream proteins subsequently to maintain redox balance.Based on TXNRD’s important physiological functions,TXNRD is emerged as a promising vulnerability in cancer therapy,and a series of in vitro and in vivo studies showed that TXNRD-targeting antitumor drugs contains selectively lethality to cancer cell.However,the development of TXNRD inhibitors is still limited and the inhibition mechanism is unclear at present.Therefore,it is of great value to investigate the interaction between small-molecule inhibitors and TXNRD,which is helpful in the further development and application of TXNRD-targeting antitumor drugs.This thesis elucidated the interaction between some natural small molecules and TXNRD1,and then revealed its anti-tumor activity through inhibiting TXNRD1 activities.The results are shown as follows:Piperlongumine irreversibly inhibited TXNRD1 activity by modifying the key amino acid residue Sec⁴⁹⁸ through 1,4-Michael addition reaction and further converts TXNRD1 from an antioxidant enzyme to a pro-oxidant enzyme was demonstrated,thereby boosting ROS-dependent cancer cell death.Piperlongumine did not work as a ferroptosis inducer.The combination of piperlongumine and erastin significantly decreased cellular GSH contents and increased the production of lipid peroxides,which forces cancer cell ferroptosis.What’s more,two terpenoid lactone compounds,ergolide and eupalinolide K,were found to be effective inhibitors of TXNRD1.Eupalinolide K and ergolide inhibited TXNRD1 activity and suppressed cancer growth and proliferation by inducing apoptosis,which could be alleviated by antioxidant NAC,suggesting a ROS-dependent apoptosis stimulation.Six terpenoid lactone compounds containingα,βunsaturated carbonyl group were evaluated.In addition to andrographolide,five lactone compounds,including ergolide,eupalinolide K,parthenolide,costunolide and alantolactone,targeted and modified the Sec⁴⁹⁸ residue of TXNRD1 to inhibit its activity.Among them,ergolide and parthenolide showed stronger inhibitory effects compared with other lactone compounds.Taken together,this study revealed the inhibitory mechanism of piperlongumine on TXNRD1,and provided a new strategy based on TXNRD1 inhibition and ferroptosis inducers to sensitize cancer cells to ferroptosis.In addition,ergolide and eupalinolide K are two natural plant-derived inhibitors of TXNRD1 with better antitumor activity than other lactone compounds,which extends the inhibitor library of TXNRD and is beneficial for developing effective inhibitors targeting TXNRD1.