ML171 is a potent and selective inhibitor of NOX1, with an IC50 of 129–156 nM in cell-based assays. ML171 is not cytotoxic, and is selective among NOX family members NOX2, NOX3, and NOX4, as well as against xanthine oxidase, another cellular source of ROS. In addition, ML171 is highly effective in inhibiting the cellular production of invadopodia in a human colon cancer cell line. It strongly blocks ROS generation in HT29 cells (IC50HT29 = 0.129 μM). ML171 does not inhibit mitochondrial ROS production.