α-Difluoromethylornithine Induction of Apoptosis
A Mechanism Which Reverses Pre-established Cell Proliferation and Cancer Initiation in Esophageal Carcinogenesis in Zinc-deficient Rats1
- Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 [L. Y. Y. F., V. T. N., P. N. M.]; and Department of Cellular and Molecular Physiology, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania 17033 [A. E. P.]
Abstract
α-Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase, the first enzyme in polyamine synthesis. Previous work showed simultaneous administration of DFMO and a zinc-deficient (ZD) diet to weanling rats from the beginning inhibited the onset of zinc-deficiency-induced esophageal cell proliferation by activating apoptosis and reduced the incidence of N-nitrosomethylbenzylamine (NMBA)-induced esophageal cancer. Because esophageal cancer initiation by NMBA is very rapid in ZD rats, this study determined whether DFMO is effective in preventing esophageal carcinogenesis when administered after the establishment of a carcinogenic environment. Weanling rats were given a ZD diet for 5 weeks to establish sustained increased esophageal cell proliferation and then an intragastric dose of NMBA. Thereafter, 20 rats were switched to DFMO-containing water while nine control ZD animals remained on deionized water; all of the animals continued on the ZD diet. Esophagi were collected 15 weeks later. The upper portion was processed for immunohistochemical analysis of cell proliferation, apoptosis, and expression of related genes, and the lower was processed for polyamine content. DFMO substantially reduces the levels of esophageal putrescine and spermidine and esophageal tumor incidence from 89 to 10% in ZD rats. Importantly, DFMO-treated ZD esophagi display increased rate of apoptosis accompanied by intense bax expression and greatly reduced cell proliferation by proliferating cell nuclear antigen expression. In addition, the p16ink4a/retinoblastoma control at G1 to S, deregulated in ZD esophagi, is restored after DFMO treatment. These results demonstrate that DFMO, a highly effective chemopreventive agent in esophageal carcinogenesis, reverses and counteracts esophageal cell proliferation/cancer initiation in ZD animals by way of stimulating apoptosis.
Footnotes
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 Supported by Grant 97B115-REV and 99B045-REN from the American Institute for Cancer Research (to L. Y. Y. F.), and Grant GM-26290 from the National Institute of General Medical Sciences, NIH (to A. E. P.).
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↵2 To whom requests for reprints should be addressed, at Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107. Phone: (215) 503-4763; Fax: (215) 923-7144; E-mail: L_Fong{at}hendrix.JCI.TJU.EDU
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↵3 The abbreviations used are: ODC, ornithine decarboxylase; DFMO, α-difluoromethylornithine; ZD, zinc-deficient; NMBA, N-nitrosomethylbenzylamine; PCNA, proliferating cell nuclear antigen; LI, labeling index; TUNEL, terminal deoxynucleotidyl transferase-mediated nick end labeling; DAB, 3,3′-diaminobenzidine tetrahydrochloride; AI, apoptotic index.
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- Accepted January 5, 1901.
- Received July 12, 1900.
- Revision received December 24, 1900.
