Novel anti-leukemia activities of pipoxolan operate via the mitochondria-related pathway in human leukemia U937 cells and attenuate U937 cell growth in an animal model

Pipoxolan HCl (5,5-diphenyl-2-(2'-piperidino-ethyl)-1,3-dioxolane-4-one hydrochloride) is a compound containing a dioxolan moiety that was reported to induce apoptosis in cancer cells. In this study, we investigated the anti-leukemia effects of pipoxolan on U937 leukemia cells both in vivo and in vitro. Cell viability, reactive oxygen species (ROS) production, mitochondrial membrane potential, apoptosis and caspases-9 and -3 activity were examined following treatment of U937 leukemia cells with 10 µM pipoxolan by flow cytometry and caspase-activity assay. The apoptosis-associated Bcl-2 family proteins, Bax, Bcl-2 and Bcl-xL, were examined by Western blotting. We found that pipoxolan inhibited U937 cell proliferation in a dose- and time-dependent manner. Morphological assessment and cell cycle analysis indicated that pipoxolan induced the apoptosis of the U937 cells. Pipoxolan (10 µM) increased ROS production and decreased mitochondrial membrane potential 1 h after pipoxolan treatment. Pre-treatment of pipoxolan-treated cells with N-acetyl-L-cysteine (a ROS chelator) inhibited the increase in ROS production. After treatment with 10 µM pipoxolan for 24 h, there was an increase in pro-apoptotic Bax and a decrease in anti-apoptotic Bcl-2 and Bcl-xL proteins. In vivo, we found that pipoxolan significantly suppressed tumor growth in BALB/cnu-/nu- mice inoculated with U937 cells. Taken together, the data from our studies indicate that pipoxolan possesses potent anti-leukemia activity and is a potential novel alternative cancer therapeutic agent for human leukemia.