Differential response to α-oxoaldehydes in tamoxifen resistant MCF-7 breast cancer cells.

Norbert Nass,Frank Hirche,Andreas Simm,Aoife Ward,Stefan Wiemann,Roland Hartig,Anne E Lykkesfeldt,Hans-Jürgen Brömme,Thomas Kalinski,Sevil Korkmaz,Albert Roessner,Saadettin Sel,Toshi Shioda

doi:10.1371/journal.pone.0101473

Abstract

Tamoxifen is the standard adjuvant endocrine therapy for estrogen-receptor positive premenopausal breast cancer patients. However, tamoxifen resistance is frequently observed under therapy. A tamoxifen resistant cell line has been generated from the estrogen receptor positive mamma carcinoma cell line MCF-7 and was analyzed for putative differences in the aldehyde defence system and accumulation of advanced glycation end products (AGE). In comparison to wt MCF-7 cells, these tamoxifen resistant cells were more sensitive to the dicarbonyl compounds glyoxal and methylglyoxal and displayed increased caspase activity, p38-MAPK- and IκBα-phosphorylation. However, mRNA accumulation of the aldehyde- and AGE-defence enzymes glyoxalase-1 and -2 (GLO1, GLO2) as well as fructosamine-3-kinase (FN3K) was not significantly altered. Tamoxifen resistant cells contained less free sulfhydryl-groups (glutathione) suggesting that the increased sensitivity towards the dicarbonyls was due to a higher sensitivity towards reactive oxygen species which are associated with dicarbonyl stress. To further analyse, if these data are of more general importance, key experiments were replicated with tamoxifen resistant MCF-7 cell lines from two independent sources. These cell lines were also more sensitive to aldehydes, especially glyoxal, but were different in their cellular signalling responses to the aldehydes. In conclusion, glyoxalases and other aldehyde defence enzymes might represent a promising target for the therapy of tamoxifen resistant breast cancers.

Highlights

Tamoxifen is the most commonly used anti-hormonal drug for adjuvant treatment of estrogen receptor (ER) positive premenopausal breast cancer patients
Toxicity of dicarbonyls was increased in tamoxifen resistant cells To analyse whether the three independently generated tamoxifen resistant cell lines would differ in their respective aldehyde stress response we determined the viability/proliferation of these cells towards methylglyoxal and glyoxal
No difference in toxicity was found for methylglyoxal (EC50 value: 0.860.3 mM for both cell lines, p = 0.8) but tamoxifen resistant MCF-7 cells (TamR)-Hd cells were more sensitive to glyoxal (EC50 value 1.160.3 mM and 2.160.8 mM respectively (p = 7.6*1024)

Summary

Introduction

Tamoxifen is the most commonly used anti-hormonal drug for adjuvant treatment of estrogen receptor (ER) positive premenopausal breast cancer patients. This is hampered by a frequently occurring development of resistance during therapy [1]. Several mechanisms have been proposed to explain the frequent occurrence of tamoxifen resistance in ER positive breast cancers [2]. Among these are increased signalling via the HER receptor system [3], altered expression of ER cofactors [4] or enhanced NFkB activity [5]. We have recently demonstrated the contribution of the alternative G-protein coupled estrogen receptor GPR30 to the tamoxifen resistance phenotype [7,8]

Methods

Results

Conclusion