A mitochondria-targeted fluorescent probe for revealing H2O2 elevation modulated by basal HClO in HeLa and A549 cells

Hydrogen peroxide, which is mainly produced in mitochondria, plays deleterious and beneficial roles in cells depending on its localized concentration. Tumor cells have been observed to have increased H2O2 levels due to enhanced metabolic activity. Moderately high levels of H2O2 are crucial for the growth and survival of tumor cells. Monitoring mitochondrial H2O2 is essential for revealing the factors that affect cellular redox balance. In the present work, we have developed a fast responsive fluorescent probe for the detection of H2O2 in mitochondria. Hcy-S shows high selectivity, sensitivity and a fast response to H2O2, enabling imaging of basal levels of mitochondrial H2O2 in tumor cells in 1 min. Hcy-S has been applied to the study of the impact of HOCl on H2O2 level. The results revealed that endogenous HOCl raises the levels of H2O2 by inactivating catalase and glutathione peroxidase in HeLa and A549 cells. We also found out that inhibiting myeloperoxidase activity can suppress tumor cell proliferation. This study offers a novel insight into the redox balance in tumor cells.