title: Podophyllotoxin acetate enhances γ-ionizing radiation-induced apoptotic cell death by stimulating the ROS/p38/caspase pathway.
abstract: To develop a new radiosensitizer against non-small cell lung cancer cells, we screened a natural product library for growth-inhibitory compounds. PA was found to be cytotoxic toward NCI-H460 cells, and its IC₅₀ value was determined. The radiosensitizer effects of PA were tested at its IC₅₀ value in clonogenic and cell-counting assays. The intracellular mechanism underlying this effect was determined by immunoblotting and by measuring propidium iodide uptake and ROS generation. The radiosensitizer activity of PA in vivo was tested in nude mice by treating with PA and IR, and measuring tumor volume and assessing apoptosis. PA, tested at its experimentally determined IC₅₀ value (12 nM), enhanced IR-induced death of NCI-H460 cells by increasing apoptosis, yielding a mean calculated dose-enhancement ratio of 1.67. Combination with PA and IR also increased the production of ROS, which subsequently induced phosphorylation of p38, suppressed phosphorylation of ERK, and activated caspase-3, -8, and -9. Notably, inhibition of ROS production prevented p38 phosphorylation, and inhibition of ROS production or p38 activation blocked caspase activation and apoptosis. In a xenograft assay, combination with PA and IR delayed tumor growth by 11.4 days compared with controls, yielding an enhancement factor of 1.48. Collectively, these results indicate that PA functions as a radiosensitizer by enhancing apoptosis through activation of a ROS/p38/caspase pathway and suppression of ERK.
authors.affiliation: Department of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, Korea; Department of Food and Microbial Technology, College of Natural Sciences, Seoul Women's University, Seoul, Korea.
authors.forename: Jae Yeon
authors.initials: JY
authors.lastname: Choi
authors.affiliation: Department of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Hyun-Ji
authors.initials: HJ
authors.lastname: Cho
authors.affiliation: Department of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Sang-Gu
authors.initials: SG
authors.lastname: Hwang
authors.affiliation: Department of Urology, College of Medicine, Chungbuk National University, Chungbuk, Korea.
authors.forename: Wun-Jae
authors.initials: WJ
authors.lastname: Kim
authors.affiliation: Department of Food and Microbial Technology, College of Natural Sciences, Seoul Women's University, Seoul, Korea.
authors.forename: Jong-Il
authors.initials: JI
authors.lastname: Kim
authors.affiliation: Department of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, Korea. Electronic address: hdum@kirams.re.kr.
authors.forename: Hong-Duck
authors.initials: HD
authors.lastname: Um
authors.affiliation: Department of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, Korea. Electronic address: jkpark@kirams.re.kr.
authors.forename: Jong Kuk
authors.initials: JK
authors.lastname: Park
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D002289:Carcinoma, Non-Small-Cell Lung; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D005720:Gamma Rays; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D015394:Molecular Structure; D011034:Podophyllotoxin / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D017382:Reactive Oxygen Species; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases; D011034:Podophyllotoxin
keywords: Apoptosis; ERK; Podophyllotoxin acetate; Radiosensitizer; Reactive oxygen species; p38