Re: Autophagic Cell Death of Human Pancreatic Tumor Cells Mediated by Oleandrin

[Guest guest]

Peiying Yang, PhD

Department of Experimental Therapeutics

Lipid-soluble cardiac glycosides such as bufalin, oleandrin, and digitoxin have

been suggested as potent agents that might be useful as anticancer agents. Past

research with oleandrin, a principle cardiac glycoside in Nerium oleander L.

(Apocynaceae), has been shown to induce cell death through induction of

apoptosis. In PANC-1 cells, a human pancreatic cancer cell line, cell death

occurs not through apoptosis but rather through autophagy. Oleandrin at low

nanomolar concentrations potently inhibited cell proliferation associated with

induction of a profound G2/M cell cycle arrest. Inhibition of cell cycle was not

accompanied by any significant sub G1 accumulation of cells, suggesting a

nonapoptotic mechanism. Oleandrin-treated cells exhibited time- and

concentration-dependent staining with acridine orange, a lysosomal stain.

Subcellular changes within PANC-1 cells included mitochondrial condensation and

translocation to a perinuclear position accompanied

by vacuoles. Use of a fluorescent oleandrin analog (BODIPY-oleandrin) revealed

co-localization of the drug within cell mitochondria. Damaged mitochondria were

found within autophagosome structures. Formation of autophagosomes was confirmed

through electron microscopy and detection of green fluorescent protein—labeled

light chain 3 association with autophagosome membranes. Also observed was a

drug-mediated inhibition of pAkt formation and up-regulation of pERK.

Transfection of Akt into PANC-1 cells or inhibition of pERK activation by MAPK

inhibitor abrogated oleandrin-mediated inhibition of cell growth, suggesting

that the reduction of pAkt and increased pERK are important to oleandrin's

ability to inhibit tumor cell proliferation. The data provide insight into the

mechanisms and role of a potent, lipid-soluble cardiac glycoside (oleandrin) in

control of human pancreatic cancer proliferation