^99mTc-labeled estradiol as an estrogen receptor probe: Preparation and preclinical evaluation

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• 作者：Xiaotian Xia¹ ; Hongyan Feng¹ ; Chongjiao Li ; Chunxia Qin ; Yiling Song ; Yongxue Zhang ; ^{zhyx1229@163.com" class="auth_mail" title="E-mail the corresponding author} ; Xiaoli Lan ; ^{LXL730724@hotmail.com" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Breast cancer ; Estrogen receptors ; Estradiol ; Single-photon emission-computed tomography
• 刊名：Nuclear Medicine and Biology
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：43
• 期：1
• 页码：89-96
• 全文大小：911 K

文摘

Most breast cancers express estrogen receptors (ERs). Noninvasive imaging of ER expression may be helpful for planning therapy of ER+ tumors. We developed a new ER- binding probe, ^99mTc-labeled estradiol, with diethylenetriaminepentaacetic acid (DTPA) as a chelating ligand, and assessed its targeting ability in vitro and in vivo.

Methods

3-Aminoethyl estradiol was synthesized in two steps from estrone, followed by ^99mTc labeling. Western blotting and immunofluorescence staining were used to detect ER expression in MCF-7 and MDA-MB-231 breast cancer cells. Saturation binding and specific binding were performed by incubating MCF-7 cells with increasing concentrations of ^99mTc-DTPA-estradiol. Cell uptake, efflux, and blocking assays were also performed. To test ^99mTc-DTPA-estradiol in vivo, nude mice bearing either MCF-7- (high ER expression) or MDA-MB-231- derived tumors (low ER expression) were injected with ^99mTc-DTPA-estradiol, and underwent single-photon emission-computed tomography (SPECT). Mice injected with excess unlabeled DTPA-estradiol were used as controls. Ex vivo gamma-counting of tissues from normal and tumor-bearing mice was used to evaluate ^99mTc-DTPA-estradiol biodistribution.

Results

The radiochemical purity of ^99mTc-DTPA-estradiol was 98.3% ± 1.3% with a specific activity of 33.1 ± 1.5 MBq/μmol (n = 3). Western blotting and immunofluorescence staining confirmed extensive expression of ERs by the MCF-7 cells, and less extensive expression by MDA-MB-231 cells. There was high binding affinity of ^99mTc-DTPA-estradiol to MCF-7 cells with a > 45% specific rate of total cell uptake. SPECT images and the biodistribution study results showed significantly higher uptake by MCF-7 tumors (6.06 ± 0.38 %ID/g) than by MDA-MB-231 tumors (1.57 ± 0.28 %ID/g). Pre-injection of MCF-7 tumor-bearing nude mice with excess unlabeled DTPA-estradiol significantly reduced tumor uptake of ^99mTc-DTPA-estradiol (2.24 ± 0.28 %ID/g), suggesting that ^99mTc-DTPA-estradiol specifically targets ERs in tumors.

Conclusions

^99mTc-DTPA-estradiol can be synthesized with satisfactory labeling efficiency and stability. ^99mTc-DTPA-estradiol specifically targeted ERs in vitro and in vivo with favorable pharmacokinetics, allowing ER receptor expression assessment with SPECT imaging.