Plumbagin induces G2-M arrest and autophagy by inhibiting the AKT/mammalian target of rapamycin pathway in breast cancer cells.

Abstract

This study is the first to investigate the anticancer effect of plumbagin in human breast cancer cells. Plumbagin exhibited cell proliferation inhibition by inducing cells to undergo G2-M arrest and autophagic cell death. Blockade of the cell cycle was associated with increased p21/WAF1 expression and Chk2 activation, and reduced amounts of cyclin B1, cyclin A, Cdc2, and Cdc25C. Plumbagin also reduced Cdc2 function by increasing the association of p21/WAF1/Cdc2 complex and the levels of inactivated phospho-Cdc2 and phospho-Cdc25C by Chk2 activation. Plumbagin triggered autophagic cell death but not predominantly apoptosis. Pretreatment of cells with autophagy inhibitor bafilomycin suppressed plumbagin-mediated cell death. We also found that plumbagin inhibited survival signaling through the phosphatidylinositol 3-kinase/AKT signaling pathway by blocking the activation of AKT and downstream targets, including the mammalian target of rapamycin, forkhead transcription factors, and glycogen synthase kinase 3beta. Phosphorylation of both of mammalian target of rapamycin downstream targets, p70 ribosomal protein S6 kinase and 4E-BP1, was also diminished. Overexpression of AKT by AKT cDNA transfection decreased plumbagin-mediated autophagic cell death, whereas reduction of AKT expression by small interfering RNA potentiated the effect of plumbagin, supporting the inhibition of AKT being beneficial to autophagy. Furthermore, suppression of AKT by plumbagin enhanced the activation of Chk2, resulting in increased inactive phosphorylation of Cdc25C and Cdc2. Further investigation revealed that plumbagin inhibition of cell growth was also evident in a nude mouse model. Taken together, these results imply a critical role for AKT inhibition in plumbagin-induced G2-M arrest and autophagy of human breast cancer cells.

• Authors: Po-Lin Kuo, Ya-Ling Hsu, Chien-Yu Cho
• Journal: Molecular cancer therapeutics (Mol Cancer Ther) Vol. 5 Issue 12 Pg. 3209-21 (Dec 2006) ISSN: 1535-7163 [Print] United States
• PMID: 17172425 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents, Phytogenic
• Naphthoquinones
• Phosphoinositide-3 Kinase Inhibitors
• RNA, Small Interfering
• Protein Kinases
• MTOR protein, human
• mTOR protein, mouse
• Proto-Oncogene Proteins c-akt
• TOR Serine-Threonine Kinases
• Sirolimus
• plumbagin

Topics

• Animals
• Antineoplastic Agents, Phytogenic (pharmacology)
• Apoptosis (drug effects)
• Autophagy (drug effects)
• Breast Neoplasms (drug therapy, genetics, metabolism, pathology)
• Cell Division (drug effects)
• Cell Growth Processes (drug effects)
• Cell Line, Tumor
• Female
• G2 Phase (drug effects)
• Humans
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Naphthoquinones (pharmacology)
• Phosphatidylinositol 3-Kinases (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Protein Kinases (metabolism)
• Proto-Oncogene Proteins c-akt (antagonists & inhibitors, genetics, metabolism)
• RNA, Small Interfering (genetics)
• Sirolimus (immunology)
• TOR Serine-Threonine Kinases