Synthesis and preliminary evaluation of a 18 F-labeled ethisterone derivative [18 F]EAEF for progesterone receptor targeting

Development of STING probes and visualization of STING in multiple tumor types

PURPOSE

The stimulator of interferon genes (STING) is a critical component of the innate immune system and plays a pivotal role in tumor immunotherapy. Developing non-invasive in vivo diagnostic methods for visualizing STING is highly valuable for STING-related immunotherapy. This work aimed to build a noninvasive imaging platform that can dynamically and quantitatively monitor tumor STING expression.

METHODS

We investigated the in vivo positron emission tomography (PET) imaging of STING-expressing tumors (B16F10, MC38, and Panc02) with STING-targeted radioprobe ([18F]F-CRI1). The expression of STING in tumors was quantified, and correlation analysis was performed between these results and the outcomes of PET imaging. Furthermore, we optimized the structure of [18F]F-CRIn with polyethylene glycol (PEG) to improve the pharmacokinetic characteristics in vivo. A comprehensive comparison of the imaging and biodistribution results obtained with the optimized probes was conducted in the B16F10 tumors.

RESULTS

The PET imaging results showed that the uptake of [18F]F-CRI1 in tumors was positively correlated with the expression of STING in tumors (r = 0.9184, P < 0.001 at 0.5 h). The lipophilicity of the optimized probes was significantly reduced. As a result of employing optimized probes, B16F10 tumor-bearing mice exhibited significantly improved tumor visualization in PET imaging, along with a marked reduction in retention within non-target areas such as the gallbladder and intestines. Biodistribution experiments further validated the efficacy of probe optimization in reducing uptake in non-target areas.

CONCLUSION

In summary, this work demonstrated a promising pathway for the development of STING-targeted radioprobes, advancing in vivo PET imaging capabilities.

Novel Molecular Classification of Breast Cancer with PET Imaging

Breast cancer is a heterogeneous disease characterized by a wide range of biomarker expressions, resulting in varied progression, behavior, and prognosis. While traditional biopsy-based molecular classification is the gold standard, it is invasive and limited in capturing tumor heterogeneity, especially in deep or metastatic lesions. Molecular imaging, particularly positron emission tomography (PET) imaging, offering a non-invasive alternative, potentially plays a crucial role in the classification and management of breast cancer by providing detailed information about tumor location, heterogeneity, and progression. This narrative review, which focuses on both clinical patients and preclinical studies, explores the latest advancements in PET imaging for breast cancer, emphasizing the development of new tracers targeting hormone receptors such as the estrogen alpha receptor, progesterone receptor, androgen receptor, estrogen beta receptor, as well as the ErbB family of receptors, VEGF/VEGFR, PARP1, PD-L1, and markers for indirectly assessing Ki-67. These innovative radiopharmaceuticals have the potential to guide personalized treatment approaches based on the unique tumor profiles of individual patients. Additionally, they may improve the assessment of treatment efficacy, ultimately leading to better outcomes for those diagnosed with breast cancer.

Molecular Imaging of Steroid Receptors in Breast Cancer

ABSTRACT

Steroid receptors regulate gene expression for many important physiologic functions and pathologic processes. Receptors for estrogen, progesterone, and androgen have been extensively studied in breast cancer, and their expression provides prognostic information as well as targets for therapy. Noninvasive imaging utilizing positron emission tomography and radiolabeled ligands targeting these receptors can provide valuable insight into predicting treatment efficacy, staging whole-body disease burden, and identifying heterogeneity in receptor expression across different metastatic sites. This review provides an overview of steroid receptor imaging with a focus on breast cancer and radioligands for estrogen, progesterone, and androgen receptors.

Nuclear Receptor Imaging In Vivo-Clinical and Research Advances

Nuclear receptors are transcription factors that function in normal physiology and play important roles in diseases such as cancer, inflammation, and diabetes. Noninvasive imaging of nuclear receptors can be achieved using radiolabeled ligands and positron emission tomography (PET). This quantitative imaging approach can be viewed as an in vivo equivalent of the classic radioligand binding assay. A main clinical application of nuclear receptor imaging in oncology is to identify metastatic sites expressing nuclear receptors that are targets for approved drug therapies and are capable of binding ligands to improve treatment decision-making. Research applications of nuclear receptor imaging include novel synthetic ligand and drug development by quantifying target drug engagement with the receptor for optimal therapeutic drug dosing and for fundamental research into nuclear receptor function in cells and animal models. This mini-review provides an overview of PET imaging of nuclear receptors with a focus on radioligands for estrogen receptor, progesterone receptor, and androgen receptor and their use in breast and prostate cancer.

Radionuclide-Based Imaging of Breast Cancer: State of the Art

Simple Summary

Breast cancer is one of the most commonly diagnosed malignant tumors, possessing high incidence and mortality rates that threaten women’s health. Thus, early and effective breast cancer diagnosis is crucial for enhancing the survival rate. Radionuclide molecular imaging displays its advantages for detecting breast cancer from a functional perspective. Noninvasive visualization of biological processes with radionuclide-labeled small metabolic compounds helps elucidate the metabolic state of breast cancer, while radionuclide-labeled ligands/antibodies for receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer. This review focuses on the most recent developments of novel radiotracers as promising tools for early breast cancer diagnosis.

Abstract

Breast cancer is a malignant tumor that can affect women worldwide and endanger their health and wellbeing. Early detection of breast cancer can significantly improve the prognosis and survival rate of patients, but with traditional anatomical imagine methods, it is difficult to detect lesions before morphological changes occur. Radionuclide-based molecular imaging based on positron emission tomography (PET) and single-photon emission computed tomography (SPECT) displays its advantages for detecting breast cancer from a functional perspective. Radionuclide labeling of small metabolic compounds can be used for imaging biological processes, while radionuclide labeling of ligands/antibodies can be used for imaging receptors. Noninvasive visualization of biological processes helps elucidate the metabolic state of breast cancer, while receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer, contributing to early diagnosis and better management of cancer patients. The rapid development of radionuclide probes aids the diagnosis of breast cancer in various aspects. These probes target metabolism, amino acid transporters, cell proliferation, hypoxia, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), gastrin-releasing peptide receptor (GRPR) and so on. This article provides an overview of the development of radionuclide molecular imaging techniques present in preclinical or clinical studies, which are used as tools for early breast cancer diagnosis.

Design, Synthesis and Binding Affinity Evaluation of Cytochrome P450 1B1 Targeted Chelators

BACKGROUND

Cytochrome P450 1B1 (CYP1B1) is specifically expressed in a variety of tumors which makes it a promise imaging target of tumor.

OBJECTIVE

We aimed to design and synthesize CYP1B1 targeted chelators for the potential application in positron emission tomography (PET) imaging of tumor.

METHODS

1,4,7-triazacyclononane-1,4-diiacetic acid (NODA) was connected to the CYP1B1 selective inhibitor we developed before through polyethylene glycol (PEG) linkers with different lengths. The inhibitory activities of chelators 6a-c against CYP1 family were evaluated by 7-ethoxyresorufin o-deethylation (EROD) assay. The manual docking between the chelators and the CYP1B1 are conducted subsequently. To determine the binding affinities of 6a-c to CYP1B1 in cells, we further performed a competition study at the cell level.

RESULTS

Among three chelators, 6a with the shortest linker showed the best inhibitory activity against CYP1B1. In the following molecular simulation study, protein-inhibitor complex of 6a showed the nearest F-heme distance which is consistent with the results of enzymatic assay. Finally, the cell based competitive assay proved the binding affinity of 6a-c to CYP1B1 enzyme.

CONCLUSION

We designed and synthesized a series of chelators which can bind to CYP1B1 enzyme in cancer cells.To our knowledge, this work is the first attempt to construct CYP1B1 targeted chelators for radiolabeling and we hope it will prompt the application of CYP1B1 imaging in tumor detection.

Recent Advances in Imaging Steroid Hormone Receptors in Breast Cancer

Estrogen receptor (ER) and progesterone receptor (PR) are important prognostic and predictive biomarkers in breast cancer. PET using ER- and PR-specific radioligands enables a whole-body, noninvasive assessment of receptor expression. Recent investigations of ER imaging with ¹⁸F-fluoroestradiol have focused on diagnosing ER-positive metastatic disease, optimizing ER-targeted drug dosage, and predicting endocrine therapy benefit. Studies of PR imaging with ¹⁸F-fluorofuranyl norprogesterone have investigated how imaging changes in PR expression as a downstream target of ER activation may reflect an early response to ER-targeted therapy. This focused review highlights recent achievements in preclinical and clinical imaging of ER and PR in breast cancer.

18F-labeled ethisterone derivative for progesterone receptor targeted PET imaging of breast cancer

PURPOSE

A novel radiolabeled probe 1‑(17‑[¹⁸F]fluoro‑3,6,9,12,15‑pentaoxaheptadecyl‑1H‑1,2,3‑triazole testosterone ([¹⁸F]FPTT) was synthesized and evaluated for PET imaging of progesterone receptor (PR)-positive breast cancer.

METHODS

The ethinyl group of ethisterone, a PR targeting pharmacophore, was coupled with azide modified PEG-OTs by click chemistry to obtain the labeling precursor. The final [¹⁸F]FPTT was synthesized by a one-step nucleophilic substitution reaction with ¹⁸F. The in vitro stabilities of [¹⁸F]FPTT in saline or rat serum were determined after 2 h incubation. Then the in vitro cell binding, ex vivo biodistribution and in vivo imaging of [¹⁸F]FPTT were further investigated to evaluate the PR targeting ability and feasibility for the diagnosis of PR-positive breast cancer with PET imaging.

RESULTS

[¹⁸F]FPTT was obtained in high decay-corrected radiochemical yield (78 ± 9%) at the end of synthesis. It had high radiochemical purity (>98%) after HPLC purification and good in vitro stability. The molar activity of [¹⁸F]FPTT was calculated as 17 GBq/μmol. The microPET imaging of [¹⁸F]FPTT in tumor-bearing mice showed much higher tumor uptake in PR-positive MCF-7 tumor (3.9 ± 0.20%ID/g) than that of PR-negative MDA-MB-231 tumor (1.3 ± 0.08%ID/g). The high MCF-7 tumor uptake could be specifically inhibited by blocking with ethisterone (1.3 ± 0.11%ID/g) or [¹⁹F]FPTT (2.20 ± 0.17%ID/g), respectively. The biodistribution in estrogen-primed female SD rats of [¹⁸F]FPTT showed high uterus and ovary uptakes (8.31 ± 1.74%ID/g and 3.79 ± 0.82%ID/g at 1 h post-injection). The specific uptakes of uterus and ovary in normal rats were 3.52 ± 0.29%ID/g and 3.22 ± 0.50%ID/g respectively and could be inhibited by co-injecting of ethisterone.

CONCLUSION

A novel [¹⁸F]FPTT probe based on ethisterone modification could be a potential diagnostic agent for PR-positive breast cancer.

Radioiodinated progesterone derivative for progesterone receptor targeting with enhanced nucleus uptake via phenylboronic acid conjugation

A novel ¹³¹ I-radiolabeled probe with aromatic boronate motif (¹³¹ I-EIPBA) was designed to target progesterone receptor (PR)-positive breast cancer with enhanced nucleus uptake. Acetylene progesterone was conjugated with pegylated phenylboronic acid via click reaction and radiolabeled with ¹³¹ I to afford ¹³¹ I-EIPBA. Meanwhile, ¹³¹ I-EIPB without boronate was prepared as control agent. After determination of the lipophilicity and stability of these tracers, in vitro cell uptake studies and in vivo biodistribution in rats were performed to verify the enhanced nucleus uptake and PR targeting ability of ¹³¹ I-EIPBA. ¹³¹ I-EIPBA was obtained with moderate radiochemical yield (40.35 ± 3.52%) and high radiochemical purity (>98%). As expected, the high binding affinity (39.58 nM) of ¹³¹ I-EIPBA for PR was determined by cell binding assay. The internalization ratio of ¹³¹ I-EIPBA was remarkably higher than that of ¹³¹ I-EIPB in PR-positive MCF-7 cells. Furthermore, the enhanced nucleus uptake of ¹³¹ I-EIPBA (0.59 ± 0.02%) was found to be significantly higher than that of ¹³¹ I-EIPB (0.13 ± 0.01%) in MCF-7 cells. A novel ¹³¹ I-EIPBA compound was developed for PR targeting with improved cellular nucleus uptake. Furthermore, the introduction of aromatic boronate motif provides a worthwhile strategy for enhancing the nuclear receptor targeting of tracers.

Enhancement of therapeutic effect in breast cancer with a steroid-conjugated ruthenium complex

A hybrid metallic prodrug for targeting PR-positive breast cancer therapy was prepared, which revealed significantly in vivo antitumor effect.