The anti-oestrogen ICI 182,780, but not tamoxifen, inhibits the growth of MCF-7 breast cancer cells refractory to long-term oestrogen deprivation through down-regulation of oestrogen receptor and IGF signalling

Abstract

Long-term culture of MCF-7 wild-type (wt) cells in steroid-depleted medium (LTED) results in hypersensitivity to oestradiol (E2) coinciding with elevated levels of ERa and enhanced growth factor signalling. In this study, we aimed to compare the effects of the pure anti-oestrogen ICI 182,780 (ICI) with the competitive anti-oestrogen tamoxifen (TAM) on oestrogen and IGF signalling in these cells. Wt MCF-7 and LTED cells were treated with a log 7 concentration range of E2, TAM or ICI. Effects on cell growth, ERa transactivation, expression of ERa, ERb and components of the IGF pathway were measured with and without insulin. In the presence of insulin, growth of LTED cells was refractory to TAM but inhibited by ICI and E2. In the absence of insulin, LTED cells showed persistent hypersensitivity to E2, and remained inhibited by ICI but were largely unaffected by TAM. ICI but not TAM inhibited ER-mediated gene transcription and treatment with ICI resulted in a dose-dependent reduction in ERa levels whilst having no effect on ERb expression. IGF-I receptor and insulin receptor substrate 2 levels were increased in LTED versus the Wt MCF-7 cells, and ICI but not TAM reduced their expression in a dose-dependent fashion. Thus IGF signalling as well as ERa expression and function are enhanced during LTED. While the resultant cells are resistant to TAM, ICI down-regulates ERa, reducing IGF signalling and cell growth. These results support the use of ICI in women with ER-positive breast cancer who have relapsed on an aromatase inhibitor.

Selective recruitment of breast cancer anti-estrogen resistance genes and relevance for breast cancer progression and tamoxifen therapy response

“…The probability of recovery of a particular gene under different selection conditions may depend on the integration position modulating its level of expression and on the consequences of the particular anti-estrogen on the biology of the ZR-75-1 cells. Our observations that the mechanisms underlying resistance against diverse anti-estrogens differ are in line with previous observations in breast cancer cell models (Soulez & Parker 2001, Faridi et al 2003, Frasor et al 2004, Martin et al 2005, Fan et al 2006, Kuske et al 2006, Scafoglio et al 2006, Shaw et al 2006, Osipo et al 2007. Accordingly, patients with breast tumors failing on tamoxifen have been shown to respond to the pure anti-estrogen fulvestrant (Howell et al 2002, Osborne et al 2002, Howell 2006, indicating subtle differences in the underlying mechanisms of tumor growth control.…”

The HOXB7 protein renders breast cancer cells resistant to tamoxifen through activation of the EGFR pathway

“…MCF-7-LTED, the estrogen-hypersensitive MCF-7 subline, was generated from MCF-7 cells by long-term culture under estrogen-deprived conditions and thus they are called LTED cells (14) (a kind gift from Richard Santen). LTED cells are refractory to tamoxifen but sensitive to fulvestrant (11). MCF-7-TAMLT, long-term tamoxifen-stimulated tumors, were kindly provided by V. Craig Jordan and were developed by retransplanting growing estradiol-dependent MCF-7 tumors into new athymic mice and treating the mice with tamoxifen for >5 y (15).…”

“…A reduced need for estrogen by ER + cells is often linked to their resistance to TAM treatment (11). HOXB7 overexpression in MCF-7 cells resulted in a much reduced dependence on nutrients.…”

ETAR antagonist ZD4054 exhibits additive effects with aromatase inhibitors and fulvestrant in breast cancer therapy, and improves in vivo efficacy of anastrozole

“…However, in vascular endothelium, many studies have demonstrated the inhibition of ET-1 expression by estrogens [46,47], a mechanism that may explain the well-known vasoprotective estrogen effects [47].Fulvestrant in contrast to tamoxifen left gene expression of the ET system unaffected, supporting the perception of fulvestrant as the clinically superior compound. Different from the SERM tamoxifen, fulvestrant is an ER antagonist and ER downregulator without agonistic activity [48]. It is well-known that tamoxifen different from fulvestrant holds a considerable partial agonistic activity (PAA) on the ER [48,49], which easily explains the inducing effect of tamoxifen on the ET system, as the physiological ER agonist E 2 too enhanced gene expression of ET-1,…”

“…Different from the SERM tamoxifen, fulvestrant is an ER antagonist and ER downregulator without agonistic activity [48]. It is well-known that tamoxifen different from fulvestrant holds a considerable partial agonistic activity (PAA) on the ER [48,49], which easily explains the inducing effect of tamoxifen on the ET system, as the physiological ER agonist E 2 too enhanced gene expression of ET-1,…”