DIOXIN/EPITHELIAL CELL INTERACTIONS--MECHANISM AND ASSAY

本建议的目的是确定监管机制 2，3，7，8-四氯二苯并对二恶英（TCDD）对雌激素依赖的人的作用 小鼠乳腺癌肿瘤生长。 最终，了解这一点 该机制将提供：1）观察到的耐药性的基础， 用于雌激素依赖性乳腺癌的抗雌激素治疗，2）和方法 用于基于机制的内分泌相关风险评估， 慢性低水平暴露于二恶英类外源性物质，以及3）新型Ah 基因座介导的类固醇依赖性化疗策略 雌激素和雌激素受体的作用， 乳腺癌的病因TCDD抑制17 β-雌二醇（E2）依赖性 MCF-7人乳腺癌细胞体外融合后增殖。 这种效应是通过Ah基因座介导的过程引起的， 与代谢增加导致的E2耗竭同时发生。体内研究 显示了类似的，但短暂的抑制E2依赖的人类 乳腺癌MCF-7肿瘤在免疫抑制的雄性BDF 1小鼠中的生长。那里 是一个为期两周的TCDD敏感期，其中TCDD抑制E2 刺激MCF-7肿瘤生长，随后是TCDD抗性期， 在此期间，肿瘤生长速率与未接受TCDD治疗的 对照这种雌激素效应从TCDD敏感到 TCDD耐药提供了一个独特的机会，以检查人类的变化， 雌激素调节的体内组织，以进一步阐明 TCDD介导的抗雌激素作用机制。还确定 E2耗竭导致MCF-7雌激素受体水平升高。 这 提出了一个假设，即敏感性和随后的阻力， TCDD抑制E2依赖的MCF-7人乳腺癌生长的体内研究 最初是由于TCDD依赖性，Ah基因座介导的雌激素耗竭 在肿瘤中，随后增强肿瘤对E2的敏感性 由雌激素受体水平的代偿性增加引起。的 提出了以下具体目标来检验这一假设：1）确定 如果在宿主或肿瘤中需要Ah基因座功能， 雌激素依赖MCF-7肿瘤对TCDD抑制敏感性和抵抗性 通过使用小鼠和具有各种Ah基因座能力的MCF-7细胞的生长。（二） 确定TCDD对E2依赖性MCF-7肿瘤生长的抑制是否 与通过测量E2诱导代谢引起的E2耗竭相关 和E2代谢。 3)确定是否雌激素受体的状态， 与未接受TCDD治疗的肿瘤相比，TCDD耐药肿瘤发生了改变， 雌激素受体功能、丰度和合成的测量。

The objective of this proposal is to determine the mechanism of regulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) of estrogen dependent human breast cancer tumor growth in mice. Ultimately, knowledge of this mechanism will provide: 1) the basis of the observed drug resistance to antiestrogen therapy for estrogen dependent breast cancer, 2) and approach for mechanism-based endocrine related risk assessment associated with chronic low level exposures to dioxin-like xenobiotics, and 3) novel Ah locus-mediated chemotherapeutic strategy for steroid hormone-dependent cancer and understanding of the role of estrogen and estrogen receptors in breast cancer etiology. TCDD inhibits the 17beta-estradiol (E2)-dependent postconfluent proliferation of MCF-7 human breast cancer cells in vitro. This effect is elicited though an Ah locus-mediated process which is coincident with depletion of E2 by increased metabolism. In vivo studies demonstrated a similar, but transient suppression of E2-dependent human breast cancer MCF-7 tumor growth in immunosuppressed male BDF1 mice. There was a two-week period of TCDD sensitivity, in which TCDD suppresses E2 stimulation of MCF-7 tumor growth, followed by a TCDD-resistant phase, during which the tumor growth rate is similar to that in non TCDD-treated controls. The conversion of this estrogenic effect from TCDD sensitive to TCDD resistant offers a unique opportunity to examine changes in a human estrogen-regulated tissue in vivo, for further elucidation of the mechanism of TCDD mediated antiestrogenicity. It was also determined that E2 depletion results in increased levels of MCF-7 estrogen receptor. This suggests the hypothesis that the sensitivity and subsequent resistance to TCDD suppression of E2-dependent MCF-7 human breast tumor growth in vivo is initially due to TCDD-dependent, Ah locus mediated estrogen depletion in the tumor with subsequent enhancement of tumor sensitivity to E2 resulting from a compensatory increase in estrogen receptor levels. The following specific aims are proposed to test this hypothesis: 1) Determine if there is a requirement for Ah locus function in the host or tumor for sensitivity and resistance to TCDD suppression of E2-dependent MCF-7 tumor growth by use of mice and MCF-7 cells of various Ah locus competency. 2) Determine if the TCDD suppression of E2-dependent MCF-7 tumor growth is associated with E2 depletion by induced metabolism by measurement of E2 and E2 metabolism. 3) Determine if the estrogen receptor status of the TCDD resistant tumor is altered compared to non TCDD-treated tumors by measurement of estrogen receptor function, abundance, and synthesis.