Parisot J P, Hu X F, Sutherland R L, Wakeling A, Zalcberg J R, DeLuise M
Department of Oncology, Heidelberg Hospital, Melbourne, Australia.
Int J Cancer. 1995 Aug 9;62(4):480-4. doi: 10.1002/ijc.2910620420.
Both estrogen receptor-positive (ER+), tamoxifen-sensitive (5-21) and tamoxifen-resistant (5-23) subclones of the parental MCF-7 breast cancer cell line were used in competitive ligand binding studies involving either [3H]ICI 182,780 or 4-OH-[3H]tamoxifen (4OHT) displacement by unlabelled estradiol (E2) or the antiestrogens (AE) 4OHT and ICI 182,780. Neither radioligand was displaced significantly by E2 over a range of concentrations; binding was predominantly inhibited by the corresponding radio-inert ligand. Scatchard analysis of the data revealed that the binding capacities of both cell lines for ICI 182,780 were approximately 7-fold greater than the previously determined number of ER sites per cell, with the affinity being an order of magnitude less than that of E2 for ER. No difference was found between the TAM-sensitive and -resistant cells in their binding of either AE. When cells were preincubated with either E2, TAM or 4OHT at a high, fixed concentration to block the ER or AE binding sites (AEBS), respectively, displaceable binding of [3H]ICI 182,780 was still observed, indicating binding at a site other than the classical ER or previously described AEBS. Our results suggest that there is a specific, saturable and relatively high-affinity binding site for ICI 182,780 in MCF 5-21 and MCF 5-23 breast cancer cells. However, the physiological relevance of this binding site requires further clarification because in cell growth assays, E2 (at 1/10 the dose of ICI 182,780) overcame the inhibitory effect of the antiestrogen in both of the cell lines.
亲代MCF - 7乳腺癌细胞系的雌激素受体阳性（ER +）、他莫昔芬敏感（5 - 21）和他莫昔芬耐药（5 - 23）亚克隆均用于竞争性配体结合研究，该研究涉及用未标记的雌二醇（E2）或抗雌激素（AE）4 - 羟基 - [3H]他莫昔芬（4OHT）和ICI 182,780置换[3H]ICI 182,780或4 - 羟基 - [3H]他莫昔芬（4OHT）。在一系列浓度范围内，E2均未显著置换这两种放射性配体；结合主要被相应的放射性惰性配体抑制。对数据进行Scatchard分析表明，两种细胞系对ICI 182,780的结合能力比先前测定的每个细胞的ER位点数量大约高7倍，其亲和力比E2与ER的亲和力低一个数量级。在对任一AE的结合方面，未发现他莫昔芬敏感和耐药细胞之间存在差异。当细胞分别用高浓度、固定浓度的E2（雌二醇）、他莫昔芬（TAM）或4 - 羟基他莫昔芬（4OHT）预孵育以分别阻断ER或AE结合位点（AEBS）时，仍观察到[3H]ICI 182,780的可置换结合，表明在经典ER或先前描述的AEBS以外的位点存在结合。我们的结果表明，在MCF 5 - 21和MCF 5 - 23乳腺癌细胞中存在一个对ICI 182,780具有特异性、可饱和且相对高亲和力的结合位点。然而，该结合位点的生理相关性需要进一步阐明，因为在细胞生长试验中，E2（剂量为ICI 182,780的1/10）克服了抗雌激素对两种细胞系的抑制作用。
