NQO1 and Patent ductus arteriosus: In contrast, normal human IMR-90 embryonic lung fibroblasts that express low levels of NQO1 remained resistant to β-lap, with or without FK866 pretreatment (Figure 1c), suggesting that toxicity to normal cells was not increased by FK866 pretreatment.9 As with MiaPaca2 cells, the survival of other PDA cells showed similar hypersensitivity to β-lap+FK866 compared with either drug alone (Figure 1d).