Longitudinal Molecular Imaging of Progesterone Receptor Reveals Early Differential Response to Endocrine Therapy in Breast Cancer with an Activating ESR1 Mutation

Elevated GRHL2 Imparts Plasticity in ER-Positive Breast Cancer Cells

Estrogen receptor (ER)-positive breast cancer is characterized by late recurrences following initial treatment. The epithelial cell fate transcription factor Grainyhead-like protein 2 (GRHL2) is overexpressed in ER-positive breast cancers and is linked to poorer prognosis as compared to ER-negative breast cancers. To understand how GRHL2 contributes to progression, GRHL2 was overexpressed in ER-positive cells. We demonstrated that elevated GRHL2 imparts plasticity with stem cell- and dormancy-associated traits. RNA sequencing and immunocytochemistry revealed that high GRHL2 not only strengthens the epithelial identity but supports a hybrid epithelial to mesenchymal transition (EMT). Proliferation and tumor studies exhibited a decrease in growth and an upregulation of dormancy markers, such as NR2F1 and CDKN1B. Mammosphere assays and flow cytometry revealed enrichment of stem cell markers CD44 and ALDH1, and increased self-renewal capacity. Cistrome analyses revealed a change in transcription factor motifs near GRHL2 sites from developmental factors to those associated with disease progression. Together, these data support the idea that the plasticity and properties induced by elevated GRHL2 may provide a selective advantage to explain the association between GRHL2 and breast cancer progression.

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.

The Current and Future Roles of Precision Oncology in Advanced Breast Cancer

Breast cancer is a common but heterogeneous disease characterized by several biologic features, including tumor grade, hormone receptor status, human epidermal growth factor receptor 2 status, and gene expression assays. These biologic and genomic features drive treatment decisions. In the advanced disease setting, inter- and intrapatient tumor heterogeneity is increasingly recognized as a challenge for optimizing treatment. Recent evidence and the recent approval of novel radiopharmaceuticals have increased recognition and acceptance of the potential of molecular imaging as a biomarker to impact and guide management decisions for advanced breast cancer.

Comparison between an SGLT2 inhibitor and insulin in tumor-to-tissue contrasts in 18F-FDG PET imaging of diabetic mice

18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) has been widely utilized for tumor diagnosis. Hyperglycemia affects the 18F-FDG uptake and reduces tumor-to-tissue contrasts, however, ideal hypoglycemic drugs are lacking. This study compared the role of insulin with the novel widely used hypoglycemic drug, sodium-glucose cotransporter 2 (SGLT2) inhibitor, on 18F-FDG PET imaging in diabetic conditions. The streptozotocin (STZ)-induced diabetic C57BL/6N mice were inoculated with B16 (mouse melanoma) cells to establish the xenograft tumor model. After the mice had been administrated with dapagliflozin (30 mg/kg, IG) or insulin (0.75 U/kg, IP) for one hour, 9.25 MBq/10 g 18F-FDG was injected. Biodistributions were detected by gamma counting and microPET imaging. The results showed dapagliflozin did not significantly affect the 18F-FDG uptake in tumors but reduced uptake in reference tissues, resulting in a significant increase in the tumor-to-skeletal muscle ratio. Conversely, insulin increased 18F-FDG uptake in tumors without significant reduction in uptake in reference tissues; Although there was an observable improvement in tumor imaging, it did not reach significantly statistical differences. This study suggests that insulin and SGLT2 inhibitor yield comparable effects on the quality of 18F-FDG PET imaging in diabetic patients. Nevertheless, SGLT2 inhibitors would be more suitable when skeletal muscle is used as reference tissue.

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.

PET Imaging of Estrogen Receptors Using 18F-Based Radioligands

In vivo molecular imaging of estrogen receptor alpha (ER) can be performed via positron emission tomography (PET) using ER-specific radioligands, such as 16α-[¹⁸F]fluoro-17β-estradiol (¹⁸F-FES). ¹⁸F-FES is a radiopharmaceutical recently approved by the United States Food and Drug Administration for use with PET imaging to detect ER+ lesions in patients with recurrent or metastatic breast cancer as an adjunct to biopsy. ¹⁸F-FES PET imaging has been used in clinical studies and preclinical research to assess whole-body ER protein expression and ligand binding function across multiple metastatic sites, to demonstrate inter-tumoral and temporal heterogeneity of ER expression, to quantify the pharmacodynamic effects of ER antagonist treatment, and to predict endocrine therapy response. ¹⁸F-FES PET has also been studied for imaging ER in endometrial and ovarian cancer. This chapter details the experimental protocol for ¹⁸F-FES PET imaging of ER in preclinical tumor xenograft models. Consistent adherence to key methodologic details will facilitate obtaining meaningful and reproducible ¹⁸F-FES PET preclinical imaging results, which could yield additional insight for clinical trials regarding imaging biomarkers and oncologic therapy.