Calcitriol restores antiestrogen responsiveness in estrogen receptor negative breast cancer cells: A potential new therapeutic approach

Nancy Santos-Martínez,David Ordaz-Rosado,Janice García-Quiroz,Javier Camacho,Fernando Larrea,Euclides Avila,José Esparza-López,Lorenza Díaz,Heriberto Medina-Franco,María J Ibarra-Sánchez,David Barrera,Ali Halhali,Rocío García-Becerra

doi:10.1186/1471-2407-14-230

Abstract

BackgroundApproximately 30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches. Studies are ongoing in order to restore ERα expression in ERα-negative breast cancer. The aim of the present study was to determine if calcitriol induces ERα expression in ER-negative breast cancer cells, thus restoring antiestrogen responses.MethodsCultured cells derived from ERα-negative breast tumors and an ERα-negative breast cancer cell line (SUM-229PE) were treated with calcitriol and ERα expression was assessed by real time PCR and western blots. The ERα functionality was evaluated by prolactin gene expression analysis. In addition, the effects of antiestrogens were assessed by growth assay using the XTT method. Gene expression of cyclin D1 (CCND1), and Ether-à-go-go 1 (EAG1) was also evaluated in cells treated with calcitriol alone or in combination with estradiol or ICI-182,780. Statistical analyses were determined by one-way ANOVA.ResultsCalcitriol was able to induce the expression of a functional ERα in ER-negative breast cancer cells. This effect was mediated through the vitamin D receptor (VDR), since it was abrogated by a VDR antagonist. Interestingly, the calcitriol-induced ERα restored the response to antiestrogens by inhibiting cell proliferation. In addition, calcitriol-treated cells in the presence of ICI-182,780 resulted in a significant reduction of two important cell proliferation regulators CCND1 and EAG1.ConclusionsCalcitriol induced the expression of ERα and restored the response to antiestrogens in ERα-negative breast cancer cells. The combined treatment with calcitriol and antiestrogens could represent a new therapeutic strategy in ERα-negative breast cancer patients.

Highlights

30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches
All cell lines were incubated in the presence of calcitriol (1X10-7 M) during 24 hr and ERα gene expression was assessed by Real time polymerase chain reaction (qPCR)
Calcitriol induced a functional ERα In order to determine the functionality of the ERα induced by calcitriol, we evaluated the effects of E2 and the antiestrogen ICI-182,780 on the expression of PRL, cathepsin D (CTSD) and trefoil factor 1 (TFF1) as examples of estrogen inducible genes [31]

Summary

Introduction

30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches. Tamoxifen is the most common and effective therapy in pre- and postmenopausal patients affected with ER-positive tumors, since a long-term use of this compound increases disease-free survival and reduces tumor recurrence [6,7]. Knockdown of specific microRNAs or inhibition of MAPK activity is followed by restoration of a functional ERα in ER-negative breast cancer cells [9,10]. These findings indicate that the ERα-negative phenotype could be reverted for therapeutic purposes

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