PET Imaging Characterization of Sphingosine-1-Phosphate Receptor 2 in a Mouse Model of Esophageal Adenocarcinoma and...

Esophageal adenocarcinoma (EAC) is an aggressive cancer with a rapidly increasing incidence globally. Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that interacts with five G protein-coupled S1P receptor subtypes (S1PR1-5), regulating physiological and cellular processes. Among these receptors, S1PR2 plays a significant role in cancer cell proliferation and metastasis. It was reported that S1PR2 was involved in the invasive growth of EAC cells through conjugated bile acid (CBA)-induced activation of the S1PR2 signaling pathway. This study aims to investigate the role of S1PR2 in promoting EAC development and progression using a potent and selective S1PR2 radiotracer [¹⁸F]TZ9555. Imaging data of the OE33 tumor model and metastatic lymph node (LN) were acquired using the Inveon PET/CT scanner system from 40 to 60 min after tail vein administration of [¹⁸F]TZ9555. The S1PR2 inhibitor JTE013 was used to block S1PR2 activity in OE33 cells for the regulation of their biological function. Western blotting, hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC), immunofluorescence (IF), cell uptake assay, autoradiography, and confocal microscopy analysis were performed for in vitro biological characterization. A biodistribution study of [¹⁸F]TZ9555 was conducted in OE33 tumor-bearing nude mice. Single-cell RNA-sequencing analysis was performed using a data set comprised of human EAC samples and adjacent normal tissues. The PET imaging data showed that [¹⁸F]TZ9555 had average uptake (%ID/g) of 0.58 ± 0.08 and 1.38 ± 0.26 in the OE33 tumor xenograft and metastatic LN, respectively, compared to the uptake of 0.21 ± 0.06 in the corresponding muscle. The average tumor-to-muscle uptake ratio was 2.8-fold, and the average metastatic LN-to-muscle ratio was 7.0-fold. The biodistribution study demonstrated higher EAC tumor uptake. IHC confirmed elevated S1PR2 expression in OE33 tumors and metastatic LN tissues. Autoradiography showed significantly high uptake in OE33 tumors and metastatic LN tissue, which were blocked by JTE013. Single-cell analysis showed a significantly increased S1PR2 expression in fibroblasts within human EAC samples. Treatment with JTE013 decreased tumor cell proliferation and reduced S1PR2 and α-SMA expression in OE33 cells. Together, our study suggested that [¹⁸F]TZ9555 has a substantial preclinical and clinical potential for assessing S1PR2 expression in predicting EAC progression.