Localization and characterization of endothelin-1 receptor binding in the blood vessels of human pulmonary tumors

Abstract

We have demonstrated endothelin-1 (ET-1) binding sites in the blood vessels of human pulmonary tumors by in vitro autoradiography. The blood vessels of the tumors were confirmed by immunostaining with von Willebrand factor. Specific [125I]ET-1 binding was identified in the blood vessels of all sizes in both tumor and stromal tissues. Nonspecific binding was observed in squamous cell carcinomas and in carcinoids. The ET-1 binding in blood vessels was specific, saturable, and time-dependent. The binding reached equilibrium at 120 min. Scatchard analysis of [125I]ET-1 binding to sections of blood vessels of squamous cell carcinoma indicated binding to a single class of binding sites, with a dissociation constant (Kd) of 0.16 nM and a maximal density of binding sites (Bmax) of 126 amol/mm2. The binding was competitively inhibited by ET-1 >> VIC > ET-2 > sarafotoxin (SRb) > ET-3 but not by other unrelated peptides. Our results provide evidence that ET-1 binding is localized in the blood vessels of pulmonary tumors and in stromal tissues surrounding the tumor nest. ET may play a role in the angiogenesis of tumor growth.