Pipoxolan Exhibits Antitumor Activity Toward Oral Squamous Cell Carcinoma Through Reactive Oxygen Species-mediated Apoptosis

Abstract

Pipoxolan is frequently prescribed as a smooth muscle relaxant. Pipoxolan has also been shown to have anticancer activity. Our study investigated whether pipoxolan induced apoptosis in oral squamous cell carcinoma (OSCC). Cell cytotoxicity was evaluated by the MTT assay. Cell apoptosis and cell-cycle distribution were measured by annexin V/propidium iodide (PI) double staining and flow cytometry, respectively. Apoptotic-related proteins were assessed by western blotting. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Following exposure of TW206 OSCC cells to pipoxolan, a time-dependently decrease in MMP and an increase in ROS were observed. However, these effects were significantly abrogated by the free radical scavenger N-acetyl-L-cysteine. Since high levels of ROS were produced early in the treatment, intracellular ROS seemed to play a key role in pipoxolan-induced apoptosis. In HSC-3 OSCC cells, our results demonstrated that pipoxolan treatment caused a time-dependent increase of protein expression of active caspase-3 and -9, cytosolic cytochrome c, cleavage of poly (ADP-ribose) polymerase, and B-cell lymphoma 2 (BCL2)-like protein 4 (BAX). However, expression of BCL2 itself was reduced. Clearly, such an increase in BAX/BCL2 ratio would be associated with apoptosis. In addition, pipoxolan markedly suppressed the protein expression of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) and phosphorylation of protein kinase B (AKT). These data suggest that pipoxolan acts against HSC-3 in vitro via intrinsic apoptotic signaling pathways, and inhibition of PI3K/AKT signaling.

Keywords: OSCC; Pipoxolan; apoptosis; caspase-3; reactive oxygen species.