title: Synergistic anticancer effects of combined γ-tocotrienol and oridonin treatment is associated with the induction of autophagy.
abstract: γ-Tocotrienol and oridonin are natural phytochemicals that display potent anticancer activity. Studies showed that combined treatment with subeffective doses of γ-tocotrienol with oridonin resulted in synergistic autophagic and apoptotic effects in malignant +SA, but not normal CL-S1 mouse mammary epithelial cells in vitro. Specifically, combined treatment with low doses of γ-tocotrienol (8 µM) and oridonin (2 µM) for 24 h resulted in synergistic inhibition of +SA mammary cancer cells viability. This combination significantly enhanced the expression of autophagy cellular markers including the conversion of LC3B-I to LC3B-II, beclin-1, Atg3, Atg7, Atg5-Atg12, LAMP-1 and cathepsin-D, and pretreatment with the autophagy inhibitors 3-methyladenine (3-MA) or bafilomycin A1 (Baf1) blocked these effects. Furthermore, blockade of γ-tocotrienol and oridonin-induced autophagy with 3-MA or Baf1 induced a modest, but significant reduction in cytotoxicity resulting from the combined treatment of these phytochemicals. The anticancer effects of combination treatment was also associated with a large suppression in Akt/mTOR mitogenic signaling and corresponding increase in the levels of apoptotic cellular marker including cleaved caspase-3 and PARP, and Bax/Bcl-2 ratio in these tumor cells. These effects were also found to be selective against cancer cells, since similar combined treatment with γ-tocotrienol and oridonin did not induce autophagy or reduce viability of normal mouse CL-S1 mammary epithelial cells. These findings indicate that combined γ-tocotrienol and oridonin-induced autophagy plays a role in mediating the synergistic anticancer effects of these phytochemicals.
authors.affiliation: School of Pharmacy, University of Louisiana at Monroe, 700 University Avenue, Monroe, LA, 71209, USA.
authors.forename: Roshan V
authors.initials: RV
authors.lastname: Tiwari
authors.affiliation: School of Pharmacy, University of Louisiana at Monroe, 700 University Avenue, Monroe, LA, 71209, USA.
authors.forename: Parash
authors.initials: P
authors.lastname: Parajuli
authors.affiliation: School of Pharmacy, University of Louisiana at Monroe, 700 University Avenue, Monroe, LA, 71209, USA. sylvester@ulm.edu.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Sylvester
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols; D001343:Autophagy / Q000187:drug effects; D015415:Biomarkers / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002839:Chromans / Q000494:pharmacology*; D045786:Diterpenes, Kaurane / Q000494:pharmacology*; D004357:Drug Synergism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D051379:Mice; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D015415:Biomarkers; D002839:Chromans; D045786:Diterpenes, Kaurane; C011959:oridonin; D014810:Vitamin E; C013649:plastochromanol 8
keywords: Autophagy; Beclin-1; Breast cancer; Cathepsin-D; LAMP-1; γ-Tocotrienol