Ovatodiolide isolated from Anisomeles indica induces cell cycle G2/M arrest and apoptosis via a ROS-dependent ATM/ATR signaling pathways

Ovatodiolide was isolated from the traditional Chinese medicinal herb Anisomeles indica, possesses anti-bacterial and anti-inflammatory properties; however, the anti-cancer activity and its mechanisms have been limitedly reported. This study aimed to examine the effect and molecular action of ovatodiolide in lung cancer cells. Cell cycle distribution and reactive oxygen species (ROS) generation were measured by flow cytometry. Apoptosis was detected by propidium iodide/annexin V staining and TUNEL assay. DNA damage was investigated by comet assay and γ-H2AX staining. Caspase activity was determined using caspase fluorometric kits. Moreover, protein levels were examined by western blot. Ovatodiolide provoked reactive oxygen species generation and DNA damage, as well as inhibited cell growth and induced apoptosis in human lung cancer A549 and H1299 cell lines. DNA damage-related molecules, ATM/ATR and CHK1/CHK2 were activated by ovatodiolide. Moreover, ovatodiolide-mediated G2/M arrest was associated with the decrease of Cyclin B1 and CDC25C levels, and increase of p21WAF1/CIP1 expression. Additionally, ovatodiolide-triggered apoptosis was through both intrinsic and extrinsic pathways characterized by the elevating PUMA, Bax, and DR5 proteins, decreasing Bcl-2 and Mcl-1, and activating caspase-8, caspase-9 and caspase-3. Caffeine, an ATM/ATR inhibitor, rescued ovatodiolide-mediated cell cycle arrest and apoptosis, but not reactive oxygen species generation. Nevertheless, antioxidant N-acetyl-cysteine completely blocked ovatodiolide-mediated molecular events, G2/M arrest, and apoptosis. These observations suggest that ovatodiolide stimulates reactive oxygen species generation, causes oxidative stress and DNA damage; subsequently, provokes DNA damage signaling pathways, eventually leads to block cell cycle at G2/M phase and trigger apoptosis in lung cancer A549 and H1299 cells.