Induction of the Estrogen Specific Mitogenic Response of MCF-7 Cells by Selected Analogues of Estradiol-17β: A 3D QSAR Study

Analogues of estradiol-17β (E2) have been evaluated
for estrogen receptor (ER) binding affinity
and mitogenic potential in the human breast cancer cell line MCF-7.
These 42 compounds
represent subtle modifications of the natural estrogen structure
through the placement of
hydroxyl, amino, nitro, or iodo groups around the ring system in
addition to, or as replacement
of, the 3- and 17β-hydroxyls of E2. The mitogenic
activity of the analogues was found to be
related to ER binding only to a limited extent. In order to
elucidate structural features that
are uniquely responsible for receptor binding affinity or mitogen
potential of estrogens, the
three-dimensional quantitative structure−activity (QSAR) method
Comparative Molecular Field
Analysis (CoMFA) was employed. Separate CoMFA models for receptor
binding and cell growth
stimulation were optimized through the use of various alignment rules
and region step size.
Whereas the CoMFA contour plots did outline the shared structural
requirements for the two
measured biological properties, specific topological features in this
set of estrogens were
delineated that distinguish mitogenic potential from ER binding
ability. In particular, steric
interference zones which affected growth extend in a band from above
the A-ring to position 4
and below, whereas the ER binding steric interference zones are limited
to isolated polyhedra
in the 1,2 and 4 positions and the α face of the B-ring. In
addition, electronegative features
located around the A-, B-, or C-rings contribute to receptor affinity.
However, growth is
dependent only on electronegative and electropositive properties near
the 3-position. In a final
QSAR model for the mitogenic response, the value of ER binding was
included along with
structural features as a descriptor in CoMFA. The resulting
3D-QSAR has the most predictive
potential of the models in this study and can be considered a prototype
model for the general
evaluation of a steroidal estrogen's growth stimulating ability in
MCF-7 cells. For example,
the location of D-ring contours illustrate the model's preference for
17β-hydroxy steroids over
the less mitogenic 17α- and 16α-hydroxy compounds. In
addition, the enhanced mitogenic
effect of steric bulk in the 11α-position is also evident. The
QSAR studies in this report illustrate
the fact that while ER binding may be a required factor of the estrogen
dependent growth
response in MCF-7 cells, particular structural characteristics, in
addition to those responsible
for tight receptor binding, must be present to induce an optimal
mitogenic response. Therefore,
this report demonstrates that the CoMFA QSAR method can be utilized to
characterize
structural features of test compounds that account for different types
of estrogenic responses.

以雌二醇-17β（E2）的类似物为研究对象，对其与雌激素受体（ER）的结合亲和力和在人类乳腺癌细胞系MCF-7中的促增殖潜能进行了评估。这42种化合物通过在环系周围添加羟基、氨基、硝基或碘基，对天然雌激素结构进行了细微的修饰，这些基团或作为E2的3-和17β-羟基的替代品，或与之共存。研究发现，类似物的促增殖活性与ER结合仅在一定程度上相关。为了阐明雌激素受体结合亲和力或促增殖潜能的独特结构特征，采用了三维定量结构-活性（QSAR）方法，即比较分子场分析（CoMFA）。通过运用不同的对齐规则和区域步长，分别优化了受体结合和细胞增殖刺激的CoMFA模型。CoMFA轮廓图概述了两种测量的生物学特性共有的结构要求，并在此雌激素系列中确定了区分促增殖潜能与ER结合能力的特定拓扑特征。特别是，影响生长的立体干扰区域从A环上方延伸至位置4及其下方，而ER结合的立体干扰区域则局限于1、2和4位置孤立的多面体以及B环的α面。此外，位于A、B或C环周围的电负性特征有助于受体亲和力。然而，生长仅依赖于3位置附近的电负性和电正性特性。在最终的QSAR模型中，将ER结合值以及结构特征作为描述符纳入CoMFA。所得的3D-QSAR模型在本研究的模型中具有最高的预测潜力，可以被视为评估甾体雌激素在MCF-7细胞中生长刺激能力的原型模型。例如，D环轮廓的位置说明了模型对17β-羟基甾体的偏好，而相对促增殖能力较弱的17α-和16α-羟基化合物则不受此偏好。此外，11α位置立体体积的增加也增强了促增殖效果。本报告中的QSAR研究说明了虽然ER结合可能是MCF-7细胞中雌激素依赖性生长反应的必要因素，但除了那些负责紧密受体结合的结构特征外，还需要特定的结构特征以诱导最佳的促增殖反应。因此，本报告展示了CoMFA QSAR方法可以用来表征测试化合物中负责不同类型雌激素反应的结构特征。