A new role for tamoxifen in oestrogen receptor-negative breast cancer when it is combined with epigallocatechin gallate

Abstract

We have previously shown that tamoxifen þ epigallocatechin gallate (EGCG) is synergistically cytotoxic towards oestrogen receptor (ER)-negative breast cancer cells. To determine if this response would correlate with significant tumour suppression in vivo, athymic nude female mice were implanted with MDA-MB-231 cells and treated with tamoxifen, EGCG, EGCG þ tamoxifen, or vehicle control for 10 weeks. Tumour volume in EGCG-(25 mg kg À1 ) þ tamoxifen (75 mg kg À1 )-treated mice decreased by 71% as compared with vehicle control (Po0.05), whereas tumour weight was decreased by 80% compared with control (Po0.01). Epigallocatechin gallate treatment did not alter ER protein expression in MDA-MB-231 cells and thus was not a mechanism for the observed tumour suppression. However, western blotting of tumour extracts demonstrated that epidermal growth factor receptor (EGFR; 85% lower than control), pEGFR (78% lower than control), mammalian target of rapamycin (mTOR; 78% lower than control), and CYP1B1 (75% lower than control) were significantly lower after the combination treatment as compared with all other treatments. Nuclear factor-kB (NF-kB), b-Raf, p-MEK, S6K, 4EBP1, Akt, vascular EGFR-1 (VEGFR-1) and VEGF expressions were decreased in control but not in the individual treatments, whereas MEK, phospholipase D 1/2, TGFa, and ERK expressions were not changed after any treatment. The results demonstrate that tamoxifen at realistic doses (75 mg kg À1 ) can suppress the growth of ERnegative breast cancer when combined with EGCG. In addition, the dominant mechanism for tumour suppression is the concomitant decrease in tumour protein expressions of mTOR and the EGFR.

Sex steroid hormones regulate constitutive expression ofCyp2e1in female mouse liver

“…Among these factors, hormones hold a critical role (8,56). Nonetheless, despite intense investigation, the sex differentiation and the role of female sex steroid hormones in constitutive CYP2E1 regulation remain unclear (59).…”

“…The role of testosterone is less clear (49,67). Previous studies in humans and experimental animals presented contradictory findings regarding sex differentiation in CYP2E1 constitutive expression and the role of sex steroid hormones in this regulation (5,11,29,33,34,59). This contradiction is probably due, at least in part, to the complexity of the female hormonal state within the different phases of the estrous cycle.…”

“…The multifactorial differentiation in the biological profile of males and females including drug metabolizing systems, added to the cross-talk between the steroid receptor-linked signaling pathways and those pathways regulating CYP2E1, set the necessity for further investigation of the sex-specific differences and the role of female sex steroid hormones in CYP2E1 regulation (59). Since sex steroid hormones are the basis of the widely used contraceptives and hormonal replacement therapy in menopausal women for the prevention of osteoporosis and cardiovascular events (26,58), this study investigated the role of female sex steroid hormones in hepatic Cyp2e1 regulation, using ovariectomized mice supplemented with 17␤-estradiol and/or progesterone.…”

In vitro mechanism of action for the cytotoxicity elicited by the combination of epigallocatechin gallate and raloxifene in MDA-MB-231 cells

“…Importantly, pharmacological inhibition of EGFR, AKT and mTOR in MDA-MB-231 human breast cancer cells all result in the induction of apoptosis. Furthermore, we have also demonstrated in vivo that the concomitant suppression of mTOR, Akt and EGFR results in a powerful tumor suppression (75% smaller than control) in an MDA-MB-231 xenograft model (20). With this in mind our in vitro data suggest that the combination of EGCG and raloxifene is also likely to elicit a strong tumor suppressive effect in this model.…”

Mechanisms of anti-cancer effects of plant polyphenols II. Suppression on tumor growth

“…Полифенолы могут также увеличить спектр противоопухолевой активности препарата. Так, использование ЭГКГ совместно с тамоксифеном, который не оказывает действия на клетки рака молочной железы, не несущие эстрогеновых рецепторов, оказалось эффективным в отношении этих клеток in vitro и на модели бестимусных мышей [109,110]. Чрезвычайно важна также способность полифенолов преодолевать часто развивающуюся резистентность раковых клеток к противоопухолевым антибиотикам [111,112].…”