Interactions between cancer cells and the endothelium in metastasis.

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.

Intravital videomicroscopic evidence for regulation of metastasis by the hepatic microvasculature: effects of interleukin-1alpha on metastasis and the location of B16F1 melanoma cell arrest.

There have been few reported visual observations of metastatic cancer cell arrest in vivo. To seek evidence that inducible vascular adhesive properties can regulate hepatic metastasis, groups of 9-14 c57bl/6 mice were given 1.5 microg of interleukin-1alpha (IL-1alpha) 4 h before the injection of 3 x 10(5) B16F1 melanoma cells into a mesenteric vein. After 7 days, these mice had an 11-22-fold greater hepatic tumor burden than controls given i.p. saline. In both groups, small metastases were seen in the portal tract region. Twice as many 125I-labeled UdR-labeled B16F1 cells were detected in the livers of IL-1alpha-treated animals 5 min after injection, and 7 times as many were found after 24 h. Intravital videomicroscopy showed marked differences in the arrest pattern of the B16F1 cells between controls and IL-1alpha-treated mice. In controls, arrest occurred at a median distance of 32 microm beyond the sinusoidal inlet, where the median sinusoidal diameter was 16 microm. However, in IL-1alpha-treated mice, arrest occurred in the presinusoidal portal vein branches, which had a median diameter of 34 microm. Maximum observed tumor cell velocities were 2-fold less in the IL-1alpha-treated mice, although there was no significant difference in the flow rate of RBCs. To look for effects on the adhesive properties of the hepatic microvasculature, 5 x 10(4) B16F1 cells were incubated for 15 min on 5-microm sections of liver from control and IL-1alpha-treated mice. Three-fold more cells adhered to sections of liver from IL-1alpha-treated mice. This phenomenon was blocked by GRGDS peptides and by antibodies to E-selectin, ICAM-1, VCAM-1, and the alpha v integrin subunit. We postulate that pretreatment of mice with IL-1alpha alters a number of adhesive interactions between B16F1 cells and the hepatic microvasculature, contributing to the site of arrest and to the subsequent fate of the arrested cells.