LUNG ENDOTHELIAL DIPEPTIDYL PEPTIDASE-IV IS AN ADHESION MOLECULE FOR LUNG-METASTATIC RAT BREAST AND PROSTATE CARCINOMA-CELLS

Attachment of circulating tumor cells to endothelial cell adhesion mol ecules restricted to select vascular compartments is thought to be res ponsible for site-specific metastasis. Lung-metastatic rat R3230AC-MET breast and RPC-2 prostate carcinoma cells bound outside-out endotheli al cell membrane vesicles, prepared by perfusion of the rat lung vascu lature with a low-strength formaldehyde solution, in significantly hig her numbers than their nonmetastatic counterparts R3230AC-LR and RPC-L R. In contrast, vesicles derived from the vasculature of a nonmetastas ized organ (e.g., hind leg muscle) showed no binding preference for ei ther of the four tumor cell lines. Lung-derived endothelial vesicles w ere used here to generate mAbs against lung endothelial cell adhesion molecules. The first group of mice were actively immunized against lun g endothelial vesicles, whereas the second group was injected with syn geneic mouse antiserum against leg endothelial vesicles before active immunization with lung endothelial vesicles. 17 hybridoma supernatants obtained from the two fusions bound lung vesicles with at least a 10- fold higher affinity than leg vesicles. Seven (four obtained by a pass ive/active immunization protocol) stained rat capillary endothelia. On e mAb, mAb 8.6A3, inhibited specific adhesion of lung-derived vesicles to lung-metastatic breast and prostate carcinoma cells. Purification of the antigen (endothelial cell adhesion molecule) from rat lung extr acts revealed a protein with a 110-kD mol wt. NH2-terminal sequencing established identity with dipeptidyl peptidase IV which had been repor ted to serve as a fibronectin-binding protein. These results indicate that vesicles obtained from in situ perfused organs are a convenient i mmunogen for the production of antibodies to compartment-specific endo thelial cell surface molecules, and reinforce the concept that endothe lial cell surface components are selectively recognized by circulating cancer cells during metastasis formation.