Research Article Proteomic Profiling of Potential Molecular Targets of Methyl-Selenium Compounds in the Transgenic Adenocarcinoma of Mouse Prostate Model Jinhui Zhang 1 , Lei Wang 1 , Lorraine B. Anderson 2 , Bruce Witthuhn 2 , Yanji Xu 3 , and Junxuan Lü 1 Abstract Because the Selenium (Se) and Vitamin E Cancer Prevention Trial (SELECT) failed to show the efficacy of selenomethionine for prostate cancer prevention, there is a critical need to identify safe and efficacious Se forms for future trials. We have recently shown significant preventive benefit of methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) in the transgenic adenocarcinoma mouse prostate (TRAMP) model by oral administration. The present work applied iTRAQ proteomic approach to profile protein changes of the TRAMP prostate and to characterize their modulation by MSeA and MSeC to identify their potential molecular targets. Dorsolateral prostates from wild-type mice at 18 weeks of age and TRAMP mice treated with water (control), MSeA, or MSeC (3 mg Se/kg) from 8 to 18 weeks of age were pooled (9-10 mice per group) and subjected to protein extraction, followed by protein denaturation, reduction, and alkylation. After tryptic digestion, the peptides were labeled with iTRAQ reagents, mixed together, and analyzed by two-dimensional liquid chromatography/tandem mass spectrometry. Of 342 proteins identified with >95% confidence, the expression of 75 proteins was significantly different between TRAMP and wild-type mice. MSeA mainly affected proteins related to prostate functional differentiation, androgen receptor signaling, protein (mis)folding, and endoplasmic reticulum–stress responses, whereas MSeC affected proteins involved in phase II detoxification or cytoprotection, and in stromal cells. Although MSeA and MSeC are presumed precursors of methylselenol and were equally effective against the TRAMP model, their distinct affected protein profiles suggest biological differences in their molecular targets out- weigh similarities. Cancer Prev Res; 3(8); 994–1006. ©2010 AACR. Introduction Chemoprevention of prostate carcinogenesis is a plau- sible and necessary approach to deal with the prostate cancer problem at the root (1). Previous studies have suggested that supplementation of selenium (Se) may modify the risk of and prevent human prostate cancer (2–4). However, the National Cancer Institute stopped the Selenium and Vitamin E Cancer Prevention Trial (SELECT) in October 2008, several years ahead of sched- ule, because of the failure to show an efficacy of seleno- methionine (SeMet) for prostate cancer prevention in North American men (5). Possible reasons for failure to show SeMet efficacy have been reviewed, including dosage, chemical form, and Se status of subjects (6). In hindsight, experiments with preclinical prostate can- cer animal models conducted before (7) and since SELECT was initiated including our study with xenograft models (8, 9) did not support any in vivo anticancer activity of SeMet. In contrast, we have shown that orally administered second-generation selenium compounds (in reference to SeMet and selenium inorganic salts) methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) inhibit the in vivo growth of DU145 and PC-3 human prostate can- cer xenograft in athymic nude mice (9). Our group has also reported recently the in vivo efficacy of daily oral administration of MSeA and MSeC against primary carci- nogenesis in the transgenic adenocarcinoma mouse pros- tate (TRAMP) model (10). We showed that MSeA given to TRAMP mice from 10 or 16 weeks of age increased their survival to 50 weeks of age and delayed the death due to synaptophysin-positive neuroendocrine (NE) car- cinomas and synaptophysin-negative prostate lesions, and seminal vesicle hypertrophy (10). Because of the metabolic and biological differences that have been well documented between SeMet and other Se forms (9, 11), the failure of SeMet in the SELECT study should not be equated to all Se forms as “ineffective” for prostate cancer prevention. We believe that the quest for effective Se agents takes on even greater significance and urgency Authors' Affiliations: 1 The Hormel Institute, University of Minnesota, Austin, Minnesota; and 2 Department of Biochemistry, Molecular Biology and Biophysics and 3 Minnesota SuperComputing Institute, University of Minnesota, Minneapolis, Minnesota Corresponding Author: Junxuan Lü, Hormel Institute, University of Min- nesota, 801 16th Avenue Northeast, Austin, MN 55912. Phone: 507-437- 9680; Fax: 507-437-9606; E-mail: jlu@hi.umn.edu. doi: 10.1158/1940-6207.CAPR-09-0261 ©2010 American Association for Cancer Research. Cancer Prevention Research Cancer Prev Res; 3(8) August 2010 994 Cancer Research. on June 1, 2020. © 2010 American Association for cancerpreventionresearch.aacrjournals.org Downloaded from Published OnlineFirst July 20, 2010; DOI: 10.1158/1940-6207.CAPR-09-0261