NQO1 and cancer: Analyzing both the potency of IPI-504, the hydroquinone/quinone (HQ/Q) ratio of this drug and NQO1 enzyme abundance in 30 cancer cell lines, levels of NQO1 expression were found to be correlated with the intracellular HQ/Q ratio of IPI-504 in only a subset of these cell lines and were, overall, poorly correlated with the growth inhibitory effects of IPI-504 [37].