Effects of the pyrimido-pyrimidine derivative RX-RA 85 on metastatic tumor cell-vascular endothelial cell interactions.

An important step in the metastatic process is the interaction of blood-borne malignant cells with the vascular endothelium. Among the agents that may interfere with this process are pyrimido-pyrimidines, such as RX-RA 85, developed originally as an antiplatelet agent. Using an endothelial cell momolayer attachment assay we have investigated the effects of RX-RA 85 on tumor cell and endothelial cell properties. Exposure of bovine aortic endothelial cells for 3 h to greater than 4 micrograms/ml RX-RA 85 produced toxic effects, resulting in vacuole formation, retraction and finally rounding up of the cells. Endothelial cells derived from different sources behaved dissimilarly; human brain, human meninges, mouse brain, mouse lung and rat lung endothelial cells were less sensitive to drug treatment than bovine aortic endothelial cells. RX-RA 85 treatment of bovine aortic endothelial cells increased B16-F1 melanoma cell adhesion. When B16-F1 cells were exposed to 4-8 micrograms/ml RX-RA 85, increased adhesion to the subendothelial matrix occurred, whereas exposure to higher drug concentrations (8-16 micrograms/ml RX-RA 85) decreased adhesion. Indirect immunofluorescence staining of cytoskeletal structures in B16-F1 cells adhering to and spreading on matrix revealed that the differential effects of RX-RA 85 on the organization of microtubules and microfilaments might explain the dose-dependent differences in adhesion kinetics.