Journal of Steroid Biochemistry & Molecular Biology 112 (2008) 13–19 Contents lists available at ScienceDirect Journal of Steroid Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/jsbmb Changes in biomarkers of estrogen receptor and growth factor signaling pathways in MCF-7 tumors after short- and long-term treatment with soy and flaxseed Krista A. Power 1 , Jian Min Chen, Niina M. Saarinen 2 , Lilian U. Thompson ∗ Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S-3E2, Canada article info Article history: Received 5 September 2007 Received in revised form 9 May 2008 Accepted 17 July 2008 Keywords: Flaxseed Soy protein MCF-7 xenografts Biomarkers abstract Previously we have shown that MCF-7 human breast tumor growth is stimulated after prolonged treat- ment with dietary soy protein isolate (SPI). However, the effects are attenuated when SPI is combined with flaxseed (FS). This study determined the changes that occur in tumor growth biomarkers, after both short- and long-term treatment with SPI, FS or their combination, to help identify signaling pathways potentially involved in SPI-stimulated tumor growth. Ovariectomized mice with established MCF-7 tumors were fed basal diet (control), 20%SPI, 10%FS, or SPI + FS for 2 or 25 weeks. After 2 weeks, there were no differences in tumor size, however, compared with control, SPI-treated tumors had higher IGF-IR and cyclin D1 while FS and SPI + FS-fed mice had lower pMAPK expression. After 25 weeks, SPI-treated tumors were larger, had higher proliferation, ER, cyclin D1, IGF-IR, and pMAPK and lower ER and HER2 levels. When com- bined with FS, however, the effects on these tumor biomarkers induced by SPI were attenuated. This study demonstrates that SPI and FS differently modulate tumor biomarkers of estrogen and growth factor sig- naling pathways, after both short- and long-term treatment, which may indicate a role of these pathways in the tumor stimulatory effects of SPI and the tumor inhibitory effects of FS. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction It is well known that MCF-7 human breast tumor xenografts in athymic nude mice require estrogen, acting through the estrogen receptor (ER), to stimulate tumor growth. Once mice are deprived of estrogen, through ovariectomy or administered antiestrogens [1], tumors regress. This model has thus been used to determine the estrogenic/antiestrogenic effects of potential therapeutic agents (pharmaceutical and dietary) on breast cancer growth. We have previously used this model to determine the estrogenic potential of two phytoestrogen-rich diets, soy protein isolate (SPI) and flaxseed (FS), alone and in combination, on tumor growth [2]. We demon- strated in mice that neither SPI nor FS stimulated the growth of established MCF-7 tumors during the first few weeks of estrogen deprivation. However, after prolonged estrogen deprivation, con- tinuous treatment with SPI induced the growth of MCF-7 tumors, ∗ Corresponding author. Tel.: +1 416 978 3523; fax: +1 416 978 5882. E-mail address: lilian.thompson@utoronto.ca (L.U. Thompson). 1 Current address: Guelph Food Research Centre, Agriculture and Agri-food Canada, 93 Stone Road West, Guelph, Ontario N1G 5C9, Canada. 2 Current address: University of Turku, Functional Foods Forum, FI-20014, Univer- sity of Turku, Finland. while treatment with FS did not. Furthermore, when FS and SPI were combined, the tumor stimulatory effect of SPI was negated. These findings indicate that changes in tumor biology may have occurred after prolonged estrogen deprivation which enabled SPI to induce tumor growth, and for this effect to be negated when SPI is combined with FS. Comparing tumor biomarkers at two differ- ent time points, i.e. 2 weeks of treatment (a time point in which the dietary treatments do not stimulate tumor growth) and 25 weeks of treatment (a time point in which SPI diet stimulates tumor growth, and FS negates that effect), may help identify potential signaling pathways involved in these SPI and FS effects. One of the active components of SPI and FS is their phy- toestrogens, specifically the isoflavones and lignans, respectively. Phytoestrogens are compounds structurally similar to estrogen, and thus can potentially bind and activate the ER to induce biological effects. The most studied isoflavone is genistein, which binds to both ER subtypes (ER and ER), however, it has a greater binding preference for ER [3]. The major flaxseed lignan is secoisolari- ciresinol diglycoside (SDG), which upon ingestion, is metabolized by gut microflora to the mammalian lignans, enterolactone and enterodiol. The mammalian lignans have been shown to be more biologically active than their plant precursors and are weak ER ligands, with ER being the preferred ER subtype [4–6]. Thus, dif- ferences in MCF-7 tumor ER and/or ER levels between samples 0960-0760/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsbmb.2008.07.003