A superoxide anion generator, pyrogallol, inhibits the growth of HeLa cells via cell cycle arrest and apoptosis

We investigated the in vitro effects of pyrogallol on cell growth, cell cycle regulation, and apoptosis in HeLa cells. Pyrogallol inhibited the growth of HeLa cells with an IC₅₀ of approximately 45 μM. Pyrogallol induced arrest during all phases of the cell cycle and also very efficiently resulted in apoptosis in HeLa cells, as evidenced by flow cytometric detection of sub-G1 DNA content, annexin V binding assay, and DAPI staining. This apoptotic process was accompanied by the loss of mitochondrial transmembrane potential (ΔΨ_m), Bcl-2 decrease, caspase-3 activation, and PARP cleavage. Pan-caspase inhibitor (Z-VAD) could rescue some HeLa cells from pyrogallol-induced cell death, while caspase-8 and -9 inhibitors unexpectedly enhanced the apoptosis. When we examined the changes of the ROS, H ₂O₂ or O₂^.- in pyrogallol-treated cells, H₂O₂ was slightly increased and O₂ ^.- significantly was increased. In addition, we detected a decreased GSH content in pyrogallol-treated cells. Only pan-caspase inhibitor showing recovery of GSH depletion and reduced intracellular O₂^.- level decreased PI staining in pyrogallol-treated HeLa cells, which indicates dead cells. In summary, we have demonstrated that pyrogallol as a generator of ROS, especially O₂^.-, potently inhibited the growth of HeLa cells through arrests during all phases of the cell cycle and apoptosis.