Functional imaging of estrogen receptors with radiolabeled-GAP-EDL in rabbit endometriosis model

Use of Radionuclide-Based Imaging Methods in Breast Cancer

Breast cancer is one of the most commonly occurring cancers in women globally and is the primary cause of cancer mortality in females. Thus, early and effective breast cancer diagnosis is crucial for enhancing the survival rate. Current standard diagnostic techniques to assess the hormone receptor status in biopsies include immunohistochemistry and fluorescence in situ hybridization. However, in recent years, there has been an increase in research on noninvasive techniques for molecular imaging of hormone receptors. These methods offer many advantages over conventional imaging, as repeated measurements can be used to capture heterogeneous tumor expression throughout the body, as well as transformations in receptor status during disease progression. Thus, the noninvasive method, as an adjunct to conventional imaging, offers the potential to improve patient selection, optimize dose and schedule, and streamline the assessment of response.

New biomarkers in endometriosis

Endometriosis is a benign gynecological disorder which presents significant challenges in terms of diagnosis and management. Despite decades of research, there are no sufficiently sensitive and specific signs and symptoms nor blood tests for the clinical confirmation of endometriosis, which hampers prompt diagnosis and treatment. The huge majority of potential biomarkers has been discarded in research stage and very few have been translated to clinical practice. Serum CA-125 is the most studied and used one, but studies have shown its poor diagnostic performance. Several factors involved in the chronic inflammatory process of endometriosis, such as hormones, cytokines, chemokines, angiogenic factors, oxidative stress markers and others, have been implicated in the disease's pathogenesis and have been extensively studied, but not a single one has successfully been able to accurately identify the disease. MicroRNAs have emerged more recently but their utility to detect endometriosis remains uncertain. The search for a biomarker or a set of biomarkers is still open and may benefit from novel molecular biology and bioinformatics approaches to mine and uncover molecular signatures specifically associated with the disease.

Efficient Synthesis of Glutamate Peptide-Estradiol Conjugate for Imaging Estrogen Receptor-Positive Diseases

Molecular imaging of estrogen receptor-positive (ER+) pathway-activated system serves the basis of ER+ disease management such as cancers and endometriosis. ER+ patients have better response to endocrine therapy and survive twice as long as negative ER patients. However, tumor resistance resulting from clinical used aromatase inhibitors and antiestrogens is unpredictable. Radiolabeled ER+ ligand could quantify ER+ tissue uptake which helps to stage and restage of the cancer as well as endometriosis. The differential diagnosis of ER+ lesions by using a labeled ligand helps to select the patients for optimal response to endocrine therapy and to discontinue the treatment when resistance occurs. In addition, radiolabeled ER+ ligand serves as basis for image-guided response follow-up. Glutamate receptors are cell surface receptors which are overexpressed in inflammation and infection. Using glutamate peptide as a drug carrier helps to target intracellular genes via glutamate receptor-mediated process. Reports have shown that polyglutamate is a drug carrier that could alter drug solubility and enhance estrogen receptor-ligand binding pocket. However, polyglutamate was a blend of mixed polymer with a wide range of molecular weight. Thus, the structural confirmation and purity of the conjugates were not optimized. To overcome this problem, the efficient synthesis of glutamate peptide-estradiol (GAP-EDL) conjugate was achieved with high purity. EDL was conjugated site-specific at the first glutamate of GAP. The average cell uptake of ⁶⁸Ga-GAP-EDL was 5-fold higher than the previous reported synthesis. The efficient synthesis of GAP-EDL has greatly enhanced sensitivity and specificity in cell uptake studies. In vivo PET imaging studies indicated that ⁶⁸Ga-GAP-EDL could image ER (+) tumors in MCF-7 tumor-bearing mice. Therefore, GAP-EDL makes it possible to image ER-enriched endometriosis and cancer.

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

INTRODUCTION

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, (99m)Tc-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 (99m)Tc 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 (99m)Tc-DTPA-estradiol. Cell uptake, efflux, and blocking assays were also performed. To test (99m)Tc-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 (99m)Tc-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 (99m)Tc-DTPA-estradiol biodistribution.

RESULTS

The radiochemical purity of (99m)Tc-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 (99m)Tc-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 (99m)Tc-DTPA-estradiol (2.24±0.28 %ID/g), suggesting that (99m)Tc-DTPA-estradiol specifically targets ERs in tumors.

CONCLUSIONS

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

Molecular imaging of Bcr-Abl phosphokinase in a xenograft model

The purpose of this study was to determine whether the Bcr-Abl tyrosine kinase can be assessed by gamma-imaging using an 111In-labeled anti-phosphotyrosine (APT) antibody, and if the response to treatment with imatinib could be detected using this imaging technique. APT antibody was labeled with 111In using ethylenedicysteine (EC) as a chelator. To determine if 111In-EC-APT could assess a nonreceptor tyrosine kinase, xenografts of the human chronic myelogenous leukemia cell line K562 were used. gamma-Scintigraphy of the tumor-bearing mice, before and after imatinib treatment, was obtained 1, 24, and 48 h after they were given 111In-EC-APT (100 microCi/mouse i.v.). 111In-EC-APT is preferentially taken up by Bcr-Abl-bearing tumor cells when compared with 111In-EC-BSA or 111In-EC-IgG1 controls and comparable with the level of uptake of 111In-EC-Bcr-Abl. Imatinib treatment resulted in decreased expression of phospho-Bcr-Abl by Western blot analysis, which correlated with early (4 days after starting imatinib) kinase down-regulation as assessed by imaging using 111In-EC-APT. The optimal time to imaging was 24 and 48 h after injection of 111In-EC-APT. Although tumor regression was insignificant on day 4 after starting imatinib treatment, it was marked by day 14. 111In-EC-APT can assess intracellular phosphokinase activity, and down-regulation of phosphokinase activity predates tumor regression. This technique may therefore be useful in the clinic to detect the presence of phosphokinase activity and for early prediction of response.

In vivo imaging of molecular targets and their function in endocrinology

Imaging is one of the fastest growing fields of study. New technologies and multimodal approaches are increasing the application of imaging to determine molecular targets and functional processes in vivo. The identification of a specific target, transporter, or biological process using imaging has introduced major breakthroughs to the field of endocrinology primarily utilizing computed tomography, magnetic resonance imaging, ultrasonography, positron emission tomography, single-photon emission computed tomography, and optical imaging. This review provides a general background to the specific developments in imaging that pertains to in vivo function and target identification in endocrine-based diseases.