PSMA-positive tumor vessels around renal cell carcinoma with high angiogenic potential as therapeutic targets and predictors of tumor recurrence.

561 Background: The expression of prostate-specific membrane antigen (PSMA) protein increases as prostate cancer advances and metastasizes. Recently, 68Ga-labeled PSMA PET has been used in diagnosing prostate cancer. Our previous studies demonstrated that PSMA-positive vesicles secreted by prostate cancer cells enhance the angiogenic activity of vascular endothelial cells, suggesting a role for PSMA in tumor angiogenesis. In this study, we focus on renal cell carcinoma, examining the relationship between PSMA expression in peritumoral blood vessels and clinical outcomes, particularly tumor recurrence, in surgically excised renal cancer specimens. Methods: Immunohistochemical analysis was performed on renal cell carcinoma samples from 45 patients who underwent nephrectomy or partial nephrectomy at our institution between January 2018 and December 2022. The correlation between PSMA expression levels in tumor-associated vessels and the rate of recurrence was evaluated. In addition, PSMA levels in human umbilical vein endothelial cells (HUVECs) treated with conditioned medium (CM) from renal cancer cell lines Caki1 and ACHN were analyzed by Western blotting (WB) and immunofluorescence (IF). Angiogenic activity was measured using a tube formation assay, and RNA sequencing (RNA-seq) was conducted to examine gene expression changes in endothelial cells influenced by vesicles secreted from renal cancer cells. Spatial gene expression analysis was performed to compare differences in gene expression between tumor vessels near and vessels away from the tumor. Results: Immunohistochemical staining for PSMA and CD31 revealed that only peritumoral vessels exhibited PSMA positivity. PSMA expression was categorized into three levels: weak (18 cases), moderate (11 cases), and strong (16 cases), with these levels corresponding to different recurrence rates. When the 10,000 g pellet fraction of CM from renal cancer cell lines was applied to HUVECs, they became PSMA-positive, leading to enhanced tube formation. RNA-seq analysis further demonstrated that HUVECs exposed to CM from renal cancer cells showed upregulation of pathways associated with angiogenesis. Conclusions: Vesicles secreted by renal cancer cells promote PSMA expression in vascular endothelial cells and boost angiogenic activity. Future research will aim to elucidate the mechanism by which PSMA becomes expressed in normal vascular endothelial cells, with the potential to pave the way for new anti-angiogenic therapies.