Plumbagin, Isolated from Plumbago zeylanica, Induces Cell Death through Apoptosis in Human Pancreatic Cancer Cells

Background and Aims: Pancreatic cancer is one of the most resistant malignancies. Several studies have indicated that piumbagin isolated from Plumbagozeylanica possesses anticancer activity. However, its antitumor effects against pancreatic cancer have not been explored. Methods: We investigated the effect of piumbagin on the growth of human pancreatic carcinoma cells and its possible underlying mechanisms. Results: Plumbagin inhibited the growth of Panc-1 and Bxpc-3 cells in a dose-dependent and time-dependent manner. Liu's staining and transmission electron microscopy demonstrated morphological changes resembling apoptosis in Panc-1 ceils treated with piumbagin. The degree of apoptosis was assessed by measuring the proportions of sub-G1, annexin V+/propidium iodide-, and terminal-deoxynucleotidyl-transferase-mediated-nick-end labeling (TUNEL)+ cells, and a significant increment in apoptotic cells was observed. Exposure to piumbagin caused theupregulation of Bax, a rapid decline in mitochondrial transmembrane potential, apoptosis-inducing factor overexpression in cytosol, and the cleavage of procaspase-9 and poly ADP-ribose polymerase. Activation of caspase-3, but not caspase-8, was evidenced by fluorometric substrate assay. Pretreatment with caspase inhibitors did not block plumbagin-induced apoptosis. Alternatively, it is possible that piumbagin down-regulated phosphoinositide3-kinase activity through a negative feedback mechanism. In an orthotopic pancreatic tumor model, piumbagin markedly inhibited the growth of Panc-1 xenografts without any significant effect on leukocyte counts or body weight. Conclusion: Piumbagin may induce apoptosis in human pancreatic cancer cells primarily through the mitochondria-related pathway followed by both caspase-dependent and caspase-independent cascades. It indicates that piumbagin can be potentially developed as a novel therapeutic agent against pancreatic cancer.