β-Lapachone suppresses radiation-induced activation of nuclear factor-κB

Anticancer effects of β-lapachone (β-lap) are due to generation of ROS and metabolic catastrophes as a result of NAD(P)H:quinone oxidoreductase (NQO1)-mediated futile cycling between the oxidized and reduced forms of β-lap. It has been shown that NQO1 is also essential for the TNF-induced activation of NF-κB and that β-lap suppresses the TNF-induced NF-κB activation. We investigated whether or not NQO1 is involved and β-lap suppresses the radiation-induced NF-κB activation using A549 human lung cancer cells and NQO1-knock down A549 cells (shNQO1 A549 cells). Irradiation with 4 Gy markedly increased the DNA binding activity of NF-κB in A549 cells, but not in the shNQO1 A549 cells, thus demonstrating that NQO1 plays a pivotal role in irradiation-induced NF-κB activation. Treatment with 10 µM β-lap for 4 h almost completely abrogated the radiation-induced increase in NF-κB activation and the transcription of NF-κB target genes such as bcl2 , gadd45β and cyclinD1 . Moreover, β-lap markedly suppressed the activation of IκB kinase γ (IKKγ) and the subsequent phosphorylation of IκBα, thereby inhibiting NF-κB activation. It is concluded that β-lap suppresses the radiation-induced activation of NF-κB by interrupting the involvement of NQO1 in the activation of NF-κB, thereby inhibiting the transcription of survival signals. The radiosensitization caused by β-lap may, in part, be attributed to β-lap-induced suppression of NF-κB activation.