Cantharidin, a potent and selective PP2A inhibitor, induces an oxidative stress-independent growth inhibition of pancreatic cancer cells through G2/M cell-cycle arrest and apoptosis.
Cantharidin is an active constituent of mylabris, a traditional Chinese medicine. It is a potent and selective inhibitor of protein phosphatase 2A (PP2A) that plays an important role in control of cell cycle, apoptosis, and cell-fate determination. Owing to its antitumor activity, cantharidin has been frequently used in clinical practice. In the present study, we investigated the therapeutic potential of cantharidin in pancreatic cancer. Cantharidin efficiently inhibited the growth of pancreatic cancer cells, but presented a much lighter toxicity effect against normal pancreatic duct cells. It caused G2/M cell-cycle arrest that was accompanied by the down-regulation of cyclin-dependent kinase 1 (CDK1) and up-regulation of p21 expression. It induced apoptosis and elevated the expressions of pro-apoptotic factors tumor necrosis factor-alpha (TNF-alpha), TNF-related apoptosis inducing receptor 1 (TRAILR1), TRAILR2, Bad, Bak, and Bid, and decreased the expression of anti-apoptotic Bcl-2. Activation of caspase-8 and caspase-9 suggested that both extrinsic and intrinsic pathways are involved in the induction of apoptosis. Interestingly, unlike previous studies on other cancer cells, we found that the inhibitory role of cantharidin is independent of oxidative stress in pancreatic cancer cells. Mitogen-activated protein kinases (MAPKs), including ERK, JNK, and p38, were activated after treatment with cantharidin. Inhibition of JNK, but not ERK or p38, alleviated the cytotoxity effect of cantharidin, suggesting cantharidin exerted its anticancer effect through the JNK-dependent way. Hence, in addition to being an attractive candidate compound with therapeutic potential, cantharidin also highlighted the possibility of using PP2A as a therapeutic target for pancreatic cancer treatment.