Targeting thioredoxin reductase by plumbagin contributes to inducing apoptosis of HL-60 cells

Plumbagin (PLB), a natural naphthoquinone from the traditional folk medicines Plumbago zeylanica, Dionaea muscipula, or Nepenthes gracilis, has been documented possessing a wide variety of pharmacological activities. Although PLB demonstrates anticancer activity in multiple types of malignant cells, the cellular targets of PLB have not been well defined and remained only partially understood. We reported here that PLB selectively inhibits TrxR and elicits reactive oxygen species in human promyelocytic leukemia HL-60 cells, which leads to elevation of GSSG/GSH ratio and decrease of cellular thiol pool. As a consequence, PLB disturbs the cellular redox homeostasis, induces oxidative stress-mediated apoptosis and eventually selectively kills HL-60 cells. Inhibition of TrxR by PLB thus discloses an unprecedented mechanism underlying the anticancer efficacy of PLB, and sheds light in considering the usage of PLB as a promising cancer therapeutic agent.