RESUMEN
Despite the success of tamoxifen in treating hormone-responsive breast cancer, its use is limited by the development of resistance to the drug. Understanding the pathways involved in the growth of tamoxifen-resistant cells may lead to new ways to treat tamoxifen-resistant breast cancer. Here, we investigate the role of cyclin D1, a mediator of estrogen-dependent proliferation, in growth of tamoxifen-resistant cells using a cell culture model of acquired resistance to tamoxifen. We show that tamoxifen and 4-hydroxytamoxifen (OHT) promoted cell cycle progression of tamoxifen-resistant cells after growth-arrest mediated by the estrogen receptor down-regulator ICI 182,780. Down-regulation of cyclin D1 with small interfering RNA blocked basal cell growth of tamoxifen-resistant cells and induction of cell proliferation by OHT. In addition, pharmacologic inhibition of phosphatidylinositol 3-kinase/Akt or mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 pathways decreased basal cyclin D1 expression and impaired OHT-mediated cyclin D1 induction and cell cycle progression. These findings indicate that cyclin D1 expression is necessary for proliferation of tamoxifen-resistant cells and for tamoxifen-induced cell cycle progression. These results suggest that therapeutic strategies to block cyclin D1 expression or function may inhibit development and growth of tamoxifen-resistant tumors.
Asunto(s)
Ciclo Celular/efectos de los fármacos , Ciclina D1/fisiología , Tamoxifeno/farmacología , Western Blotting , Neoplasias de la Mama/genética , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , Ciclo Celular/fisiología , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Cromonas/farmacología , Ciclina D1/genética , Ciclina D1/metabolismo , Resistencia a Antineoplásicos , Antagonistas de Estrógenos/farmacología , Flavonoides/farmacología , Humanos , Proteínas Quinasas Activadas por Mitógenos/antagonistas & inhibidores , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Morfolinas/farmacología , Fosfatidilinositol 3-Quinasas/metabolismo , Inhibidores de las Quinasa Fosfoinosítidos-3 , Fosforilación/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/metabolismo , Interferencia de ARN , ARN Interferente Pequeño/genética , Fase S/efectos de los fármacos , Fase S/fisiología , Transducción de Señal/genética , Tamoxifeno/análogos & derivados , Factores de TiempoRESUMEN
A common problem in breast cancer therapy is resistance to the antiestrogen tamoxifen. However, tamoxifen-resistant breast tumors can still respond to other hormonal therapies. In animal models of tamoxifen-resistant breast cancer cells, physiological levels of estrogen can induce tumor regression. Recently, the estrogen receptor downregulator fulvestrant was shown to promote tumor growth of tamoxifen-resistant cells when added in combination with physiological levels of estrogen. Here, we show, using a cell culture model, that continuous exposure of tamoxifen-resistant cells to physiological levels of estrogen leads to cell death. Addition of the estrogen receptor downregulator fulvestrant prevents estrogen-induced death in a dose-dependent manner. Our data indicate that endogenous levels of estrogen affect the response of tamoxifen-resistant cells to fulvestrant. These results suggest that failure of fulvestrant to inhibit tumor growth in some tamoxifen-resistant patients may be due to endogenous estrogen levels. Moreover, these studies support short-term treatment with estrogen as a second-line hormonal therapy for tamoxifen-resistant breast cancer.
Asunto(s)
Apoptosis/efectos de los fármacos , Neoplasias de la Mama/tratamiento farmacológico , Resistencia a Antineoplásicos , Estradiol/análogos & derivados , Estrógenos/farmacología , Receptores de Estrógenos/antagonistas & inhibidores , Tamoxifeno/farmacología , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , Proliferación Celular/efectos de los fármacos , Regulación hacia Abajo , Estradiol/farmacología , Antagonistas de Estrógenos/farmacología , Moduladores de los Receptores de Estrógeno/farmacología , Femenino , Fulvestrant , Humanos , Neoplasias Hormono-Dependientes/tratamiento farmacológico , Neoplasias Hormono-Dependientes/metabolismo , Neoplasias Hormono-Dependientes/patología , Receptores de Estrógenos/metabolismo , Células Tumorales CultivadasRESUMEN
The development of resistance to tamoxifen, the most common antiestrogen used in the treatment of breast cancer, is a frequent and severe clinical problem. Tamoxifen-resistant tumors are still capable of responding to other hormonal therapies such as those that downregulate estrogen receptor expression. Mechanisms leading to acquisition of tamoxifen-resistant but hormone-sensitive growth are not completely understood. In tamoxifen-sensitive breast cancer cells, tamoxifen inhibits, whereas estrogen induces, expression of cyclin D1, a key cell cycle regulatory protein. Ectopic expression of cyclin D1 can lead to antiestrogen resistance. Thus, to determine whether cyclin D1 is involved in the growth of tamoxifen-resistant cells, we developed several tamoxifen-resistant variants from MCF-7 cells. These variants grow in the absence of estrogen or in the presence of tamoxifen, but their growth is inhibited by estrogen receptor downregulators. We show here that cyclin D1 expression is maintained at comparable levels in all tamoxifen-resistant variants, whereas pS2, another estrogen-regulated protein, is not. The addition of physiological levels of estrogen further stimulates cyclin D1 expression and proliferation. In contrast, treatment with estrogen receptor downregulators decreases cyclin D1 expression and proliferation. Thus, changes in cyclin D1 expression upon second-line hormonal therapy may predict hormonal sensitivity of tamoxifen-resistant tumors. These studies suggest that estrogen receptor mediates cyclin D1 expression and growth of tamoxifen-resistant tumors.