Estrogen Receptor Expression and Estrogen Receptor‐independent Cytotoxic Effects of Tamoxifen on Malignant Rhabdoid Tumor Cells in vitro

Abstract

Key words: Malignant rhabdoid tumor -Estrogen receptor -Antiestrogen -ApoptosisEstrogens have long been recognized to play important roles in the growth and differentiation of reproductive and non-reproductive tissues.1, 2) It has also become clear that most breast cancers are dependent on estrogens for growth and progression, and this has been the basis for continuing interest in the role of estrogen receptor (ER) in the prognosis of this devastating disease. However, some recent reports have demonstrated that ER expression may have a role in neoplasms other than breast cancer, such as colon cancer, meningioma, prostate cancer, and myeloma. [3][4][5][6] The antiestrogen tamoxifen (TAM) has been widely used in the treatment of breast cancer, 7) and recently against some other cancers as well.8) Antiestrogens can be classified into two major groups: analogs of TAM or its metabolites (type I) that have mixed estrogenic/antiestrogenic actions, and pure antiestrogens (type II) that have no estrogen-like properties in laboratory assays.9) 4-Hydroxytamoxifen (4-OHT) is converted to an active metabolite of TAM, while ICI 182 780 is a pure antiestrogen that is being clinically evaluated as a useful agent following failure of TAM treatment.9-12) It is thought that inhibition of ER by antiestrogens may block the secretion of growth factors, such as epidermal growth factor (EGF) and transforming growth factor alpha (TGF-α). In addition to its cytostatic effects, TAM has also been shown to be cytotoxic against tumor cells, even tumor cells lacking ER. 13,14) Such cytotoxic effects were thought to be mediated by the induction of apoptosis. 15,16) Malignant rhabdoid tumors (MRT) are rare, highly aggressive neoplasms specific to early childhood, and have an extremely poor prognosis due to the high potential for distant metastasis. [17][18][19] While various organs and tissues, including the kidneys, can be the primary site of MRT, [20][21][22][23][24] a characteristic feature of MRT cells is the presence of large eosinophilic inclusions in the cytoplasm. 25)Poor response to treatment results in an extremely poor prognosis.19) Our laboratory has previously reported that expression of insulin-like growth factor receptor 26) and EGF receptor 27) was associated with MRT cell proliferation. However, very little is known of MRT cell growth and differentiation. We believe that further investigation into the mechanisms of MRT cell proliferation may help to improve the poor disease prognosis.ER expression and the effects of antiestrogens on MRT cells are currently unknown. Therefore, we first focussed on MRT cell ER expression through examination of ER mRNA and protein levels in six MRT cell lines. We then studied the effects of antiestrogens 4-OHT, TAM, and ICI 182 780 on the MRT cell lines by analyzing alterations in cell growth. Lastly, we also studied the induction of apoptosis through the use of nuclear morphology and DNA fragmentation assays. MATERIALS AND METHODSCell culture and compound MRT cell lines TM87-16,

Targeting cyclin D1, a downstream effector of INI1/hSNF5, in rhabdoid tumors

“…Consistent with the previous findings, treatment of MON cells with 10 mM or less of 4OH-Tam alone did not drastically inhibit the survival, whereas concentrations above 10 mM resulted in rapid cell death ( Figure 3a) (Koshida et al, 2002). Therefore, we tested the effect of combination of 4-HPR with 10 mM 4OH-Tam for various times of exposure ( Figure 3b).…”

Expression of pericyte, mesangium and muscle markers in malignant rhabdoid tumor cell lines: Differentiation‐induction using 5‐azacytidine

“…The results for these six MRT cell lines was confirmed with both histopathology and electron microscopy. 3,10,[17][18][19][20] Aberration of the hSNF5/INI1 gene was also detected in the six MRT cell lines. 22) 5-Aza-CR was utilized to examine the expression of several muscle markers.…”

“…7,[17][18][19][20][21] Recently, Sugimoto et al 21) reported a smooth muscle phenotype in an MRT cell line. Steahelin et al 25) reported MyoD expression in bone marrow metastasis of extrarenal MRT.…”

“…Previous studies involving STM91-01 cells failed to show expression of any specific gene suggesting a particular phenotype. 3,10,[17][18][19][20] We examined megsin expression in the STM91-01 cell line, which was established from renal MRT, expressing myf-6 and having a possible pericyte phenotype. An important relationship between myf-5 or myf-6 mRNA expression and mesangial cell development was recently reported.…”

“…13) Various cellular origins have been proposed for MRT, including neuroectodermal, 3,9,10) myogenic, 7) histiocytic, 14) neural 15) and epithelial. 16) Various authors have reported MRT as having multiphenotypic characteristics, 3,7,[17][18][19][20][21] but the true origin of this enigmatic tumor remains unknown. Neural phenotypes of some MRTs have been shown by our laboratory.…”