Endothelialization of embolized tumor cells during metastasis formation

Adhesion and spreading of corneal endothelial cells on collagens type I and IV in vitro: a model to study mechanisms of endothelial repair

In vitro assays using endothelial cells (EC, bovine corneal) were performed to study adhesion and spreading on collagen types I and IV. Adhesion was quantitatively analyzed by counting the EC under a light microscope. Spreading was determined by measuring cell area using a scanning electron microscope (SEM). Collagen types I, IV, and IV-F, a mixture of 70, 120, and 140 KD fragments of type IV, all promoted EC adhesion, Types IV and IV-F showed evidence of giving a more marked adhesion than type I. A study of cell area, carried out under identical conditions, such as those in the adhesion assay, showed that types I and IV-F, but not type IV, promoted cell spreading. This provides evidence that cell adhesion and spreading are indeed separate biological phenomena. Furthermore, the ability of fragments of type IV collagen to promote both cell adhesion and spreading may represent an inherent repair mechanism in damaged endothelium.

Organ-preference of metastasis. The role of endothelial cell adhesion molecules

The initial, site-specific colonization of secondary organs by blood-borne cancer cells appears to be mediated by endothelial cell adhesion molecules. These molecules are part of the organ-specific microvascular phenotype and are regulated through complex interactions of the endothelium with the extracellular matrix (e.g., distinct matrix macromolecules and growth factors). They are induced in vitro by growing 'unspecific' (large vessel) endothelial cells on extracts of organ-specific biomatrices. In many respects, these molecules are similar to the various classes of chemically different adhesion molecules that regulate lymphocyte traffic, but are believed to be distinct from the inducible adhesion molecules that govern leukocyte adhesion during acute episodes of inflammation. Biochemical and biophysical data indicate that preference of tumor cell adhesion to organ-specific microvascular endothelium may not require qualitative differences of such homing receptors between endothelia, but may be explained on the basis of quantitative receptor differences as well as differences of receptor avidity. Following adhesion, the metastatic cascade proceeds by the establishment of metabolic conduits between the endothelium and adherent tumor cells. This heterotypic coupling represents an early step in the extravasation of cancer cells from the microvasculature, initiating endothelial cell retraction from its basement membrane and recanalization around the arrested tumor cell. These events, together with local growth promoting effects exerted by the metastasized organ, are believed to provide the basis for Paget's 'seed and soil' hypothesis of metastasis.

Interactions between cancer cells and the microvasculature: a rate-regulator for metastasis

Hematogenous metastasis is a major consideration in the staging, treatment and prognosis of patients with cancer. Key events affecting hematogeneous metastasis occur in the microvasculature. This is a brief, selective review of some interactions involving cancer cells and the microvasculature in pathologic sequence, specifically: (1) intravasation of cancer cells; (2) the arrest of circulating cancer cells in the microvasculature; (3) cancer cell trauma associated with arrest; (4) microvascular trauma; (5) the inflammatory; and (6) the hemostatic coagulative responses associated with arrest, and finally (7) angiogenesis, leading to tumor vascularization. The evidence shows that through a series of complex interactions with cancer cells, the microvasculature acts as a rate-regulator for the metastatic process, in addition to providing routes for cancer cell dissemination and arrest sites for cancer cell emboli.