Sphingosine-1-Phosphate-Receptor 1 as a Marker for Endothelial Cells in Mouse Xenograft Models of Human Cancer

The sphingosine-1-phosphate (S1P) 1 receptor (S1P R) is an important receptor for the modulation of endothelial cell function. We, therefore, wanted to investigate its expression as a blood vessel marker. The expression of the S1P receptor 1 (S1P R) in mouse blood vessel endothelium was investigated immunohistochemically in normal blood vessel endothelium and blood vessel endothelium of xenografted human tumors. The S1P receptor was expressed in the endothelium of most mouse organs. Endothelia of the intestinal tract and of adipose tissue showed the strongest immunoreactivity. However, a difference in staining between larger vessels and fenestrated endothelium was observed, whereas fenestrated endothelium expressed a weaker staining. In addition to normal endothelia, most tumor blood vessel endothelia expressed S1P R. A particularly strong expression in the endothelium was detected in primary pancreatic and prostate cancer xenografts. In both xenograft tumor entities, no significant difference in staining intensities of the endothelium between arteries, veins and capillaries was observed. As S1P R is expressed in most blood vessel endothelia and in the tumor blood vessel endothelia, it is an ideal blood vessel marker.