Selenium Modulation of Cell Proliferation and Cell Cycle Biomarkers in Normal and Premalignant Cells of the Rat Mammary Gland 1 Clement Ip, 2 Henry J. Thompson, and Howard E. Ganther Department of Experimental Pathology, Roswell Park Cancer Institute, Buffalo, New York 14263 [C. I.]; Center for Nutrition in the Prevention of Disease, AMC Cancer Research Center, Denver, Colorado 80214 [H. J. T.]; and Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706 [H. E. G.] Abstract The present study was designed to assess the effect of Se- methylselenocysteine or triphenylselenonium chloride treatment on cell proliferation [bromodeoxyuridine (BrdUrd) labeling] and cell cycle biomarkers [proliferating cell nuclear antigen (PCNA), cyclin D 1 , and p27/Kip 1] in the intact mammary gland of rats. Immunohistochemical assays of the above end points were carried out in different morphological structures: (a) terminal end bud cells and alveolar cells of a maturing mammary gland undergoing active differentiation; and (b) premalignant mammary intraductal proliferations (IDPs) identified at 6 weeks after carcinogen dosing. Neither compound was found to affect BrdUrd labeling or the expression of cell cycle biomarkers in the normal terminal-end bud cells and alveolar cells. Se-methylselenocysteine reduced the total number of IDP lesions by 60%. Interestingly, this was not accompanied by decreases in BrdUrd labeling or the proportion of IDP cells expressing PCNA and cyclin D 1 . An enhancement in the fraction of p27/Kip 1-positive IDP cells, however, was detected as a result of Se- methylselenocysteine treatment. Although triphenylselenonium chloride did not reduce the total number of IDPs, there were more of the smaller-sized lesions and fewer of the larger-sized lesions compared with those found in the control group. Triphenylselenonium chloride also significantly decreased the proportion of IDP cells incorporating the BrdUrd label or expressing PCNA and cyclin D 1 . The above findings suggest that early transformed cells are sensitive to selenium intervention, whereas normal proliferating cells are not. It is possible that Se-methylselenocysteine blocks carcinogenesis by a pathway that may not involve cell growth inhibition as a primary response; in contrast, triphenylselenonium chloride is likely to act by a cytostatic mechanism. The data also imply that selenium efficacy testing in intervention trials is possible with the use of biomarkers, provided that the appropriate biomarkers are matched with the selenium compound of interest and that the pathological characteristics of the cell population to be evaluated are taken into consideration. Introduction A variety of selenium-containing compounds with diverse chemical structures are known to inhibit cell proliferation in vitro (1–10). These compounds include inorganic selenium salts, methylselenocyanate, and selenoamino acids as well as benzyl and phenyl selenium derivatives. Animal feeding studies with these same agents have also demonstrated their efficacies in cancer chemoprevention (11). Successful protection against tumorigenesis in most cases can be achieved without any evi- dence of growth depression or change in organ size, suggesting that cell proliferation in various tissues is minimally affected by chronic treatment with these selenium compounds. However, little information is available regarding selenium intake and the measurement of cell proliferation in situ, especially with re- spect to the behavior of normal growing cells versus neoplastic cells in the same target organ site. Over the past decade, our collaborative group has been focusing our attention on two selenium compounds in particu- lar, i.e., Se-methylselenocysteine and triphenylselenonium chloride, and has published a number of reports on their in vivo cancer-protective activities (12–19). Se-methylselenocysteine is a water-soluble prodrug designed to deliver a monomethyl- ated selenium metabolite, which we believe to be a critical intermediate in selenium chemoprevention (11, 20). This sel- enoamino acid is also found naturally in selenium-enriched plants (21–23). Triphenylselenonium chloride is a synthetic compound with a cationic selenium atom bonded directly to three unsubstituted benzene rings; therefore, it is a very stable molecule that is not likely to release bioavailable selenium (19). Despite the lipophilic nature of the benzene rings, triphenylsel- enonium chloride is water soluble because of the positive charge. Previous studies have shown that both Se-methylsel- enocysteine and triphenylselenonium chloride are effective against rat mammary gland carcinogenesis, although their dose responses are quite different (12, 16). When given in the diet, the levels of Se-methylselenocysteine and triphenylselenonium chloride required to attain 50% inhibition of tumor yield are about 2 and 20 ppm selenium, respectively. We also have indirect evidence suggesting that these compounds might exert their chemopreventive effects by different modes of action (18, 24). In the first part of the present study, we compared the effects of Se-methylselenocysteine and triphenylselenonium Received 8/2/99; revised 10/22/99; accepted 11/6/99. 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. 1 Supported by Grants CA 61763 and CA 27706 from the National Cancer Institute, NIH, and Roswell Park Cancer Institute Core Grant CA 16056. 2 To whom requests for reprints should be addressed, at Department of Experi- mental Pathology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buf- falo, NY 14263. Phone: (716) 845-8875; Fax: (716) 845-8100; E-mail: cip@sc3101.med.buffalo.edu. 49 Vol. 9, 49 –54, January 2000 Cancer Epidemiology, Biomarkers & Prevention on June 9, 2016. © 2000 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from