Abstract
Estrogen receptors (ER), including ER-α and ER-β, are known to regulate multiple biologic responses in various cell types. The expression of ER-β is lost in various cancers. ER-β agonists were shown to modulate inflammation, cancer cell proliferation, and differentiation. Here, we investigated the cancer chemopreventive properties of Erb-041, an ER-β agonist, using a model of UVB-induced photocarcinogenesis in SKH-1 mice. Erb-041 significantly reduced UVB-induced carcinogenesis. Tumor numbers and volume were reduced by 60% and 84%, respectively, in the Erb-041-treated group as compared with UVB (alone) control. This inhibition in tumorigenesis was accompanied by the decrease in proliferating cell nuclear antigen (PCNA), cyclin D1, VEGF, and CD31, and an increase in apoptosis. The lost ER-β expression in squamous cell carcinomas (SCC) was significantly recovered by Erb-041 treatment. In addition, the UVB-induced inflammatory responses were remarkably reduced. Myeloperoxidase activity, levels of cytokines (interleukin (IL)-1β, IL-6, and IL-10), and expression of p-ERK (extracellular signal-regulated kinase) 1/2, p-p38, p-IκB, iNOS, COX-2, and nuclear NF-κBp65 were diminished. The number of tumor-associated inflammatory cells (GR-1(+)/CD11b(+) and F4/80(+)) was also decreased. Tumors excised from Erb-041-treated animal were less invasive and showed reduced epithelial-mesenchymal transition (EMT). The enhanced expression of E-cadherin with the concomitantly reduced expression of N-cadherin, Snail, Slug, and Twist characterized these lesions. The WNT/β-catenin signaling pathway, which underlies pathogenesis of skin cancer, was found to be downregulated by Erb-041 treatment. Similar but not identical changes in proliferation and EMT regulatory proteins were noticed following treatment of tumor cells with a WNT signaling inhibitor XAV939. Our results show that Erb-041 is a potent skin cancer chemopreventive agent that acts by dampening the WNT/β-catenin signaling pathway.