An isolated perfused vessel model was used to examine the mechanisms underlying the adhesive interactions between
circulating tumor cells and subendothelial matrix in denuded arterioles. Arterioles ranging from 70 to 100 microm in diameter were isolated from rat mesentery, transferred to an isolated vessel chamber, cannulated on both ends with glass micropipettes, and perfused with media containing 10(6) hamster
melanoma (RPMI 1856) cells/ml. In a second group of arterioles, the endothelium was denuded by running 2 ml of air through the vessel lumen. Since the
tumor cells did not adhere to the vessel wall when perfused at physiologically relevant shear rates, perfusate flow was stopped and the
tumor cells were allowed to settle onto the vessel wall for 20 min. After counting the number of
tumor cells that settled onto the arteriolar wall, perfusate flow was re-initiated and unattached cells were washed away. The number of cells remaining adherent were counted and the percentage of adherent cells (relative to the total number of cells that settled on to the vessel wall during the period of no-flow) were calculated and compared among different groups. We observed that
tumor cells are much more adhesive to denuded arterioles than to intact arterioles. To determine the mechanisms responsible for the adhesive interactions that become established and stabilized during the period of flow reduction, denuded arterioles were treated with
fibronectin antiserum or
Arg-Gly-Asp (RGD)
peptides. Both treatments significantly reduced
tumor cell adhesion to denuded arterioles. In subsequent studies,
melanoma cells were treated with a
transglutaminase inhibitor,
monodansylcadaverine (MDC), which reduced the ability of adherent
tumor cells to withstand the anti-adhesive effects of a subsequent increase in perfusate flow rate after the period of no-flow. Our data suggest that
tumor cells adhere to
fibronectin in the subendothelial matrix in denuded arterioles by an RGD-dependent mechanism. Moreover, our observations are consistent with the concept that a
transglutaminase-catalysed reaction acts to stabilize the adhesive interactions between subendothelial matrix components and
melanoma cells during the period of flow stasis such that the cells are able to withstand subsequent substantial increases in wall shear rate and remain adherent.