HHQ induced intracellular ROS production in human breast cancer cells, MDA-MB-231 [A] and MCF-7 [C]. The breast cancer cells were treated with 12.5 μM and 25 μM of HHQ for 48 h at 37 °C, intracellular ROS was detected by a fluorescent microscope. Quantitation of the ROS signals in MDA-MB-231 and MCF-7 is shown in [B] and [D], respectively. Significant increase in ROS level was observed in HHQ treated cells. Data are representative of three independent experiments done in triplicates and expressed as mean ± S.E.M. Increase in ROS generation in HHQ treated groups with 12.5 μM and 25 μM were statistically significant (*P<0.05).