NQO1 and lung cancer: In order to determine whether NQO1 was a key regulator in β-lapachone-mediated lung cancer cell death, cells were incubated for 6 h with 10 μM dicoumarol, a specific NQO1 inhibitor, and this resulted in about a 67% and 77% reduction in NQO1 activity in CL1-1 and CL1-5 cells, respectively (Figure S3A).