2-Aminophenoxazine-3-one (Phx-3)-induced apoptosis was investigated. Phx-3 suppressed the viability of human lung adenocarcinoma cell line A549 and induced cellular apoptosis 6 h after treatment. Prior to these events, intracellular pH (pHi) was rapidly decreased from pH 7.65 to 7.10 within 30 min when A549 cells were treated with 7 µM Phx-3. This intracellular acidification continued for 3 h in the cells. Augmented production of reactive oxygen species (ROS) was obseved 1 h after treatment of A549 cells with 7 µM Phx-3, and cell cycle arrest at G1 was indicated 3 h after treatment. The translocation of NF-κB from the cytosol to the nucleus was clearly indicated 1 h after the administration of Phx-3 to A549 cells, while it was significantly suppressed when Nac, a scavenger of ROS, was added to the cells with Phx-3. The Phx-3-induced apoptosis in A549 cells was significantly suppressed when Nac was administered to the cells. These results suggest that a decrease of pHi, caused by depolarization of the mitochondria, may trigger the dysfunction of mitochondria causing ROS production; therefore, both the translocation of NF-κB from the cytoplasm to the nucleus and apoptosis induction were promoted in A549 cells. Microscopic examination of the cellular localization of Phx-3 in A549 cells revealed that Phx-3 was mainly localized in the cytoplasm and the mitochondria, but not in the nucleus. The present results indicate that Phx-3 might be a strong anticancer drug against lung cancer, which is intractable to chemotherapy, by causing various early events, including the decrease of pHi and ROS production, and finally inducing cellular apoptosis.

Related Articles