The role of calcium in the regulation of invasion and angiogenesis.

The complex process of invasion and metastasis is now being dissected at the level of cell-cell and cell-substratum signaling. New tools are being developed to facilitate these studies. These tools include mechanisms for the investigation of cellular actions, such as the identification of agents that can be used to examine the signaling pathways involved in adhesion, proteolysis, motility, and angiogenesis. We have demonstrated that CAI, carboxyamido-triazole, selectively inhibits calcium uptake, stimulated or basal, and thereby modulates the elements involved in invasion and angiogenesis. Through modulation of cellular calcium balance, CAI secondarily inhibits calcium-dependent signaling pathways, such as release of second messengers, protein phosphorylation and gene transcription. We have demonstrated that CAI treatment resulted in inhibition of endothelial cell adhesion, migration, expression of proteolytic enzymes, and vessel formation in vitro and in vivo. The process of endothelial cell adhesion and spreading on extracellular matrix substrata results in an increase in intracellular calcium that can be inhibited by CAI exposure. Furthermore, endothelial cell adhesion and spreading on type IV collagen stimulates the secondary signaling events of tyrosine phosphorylation of focal adhesion kinase (pp125FAK) and autophosphorylation of pp125FAK. CAI treatment of the endothelial cells inhibited cell spreading, and both the induction of pp125FAK phosphorylation and the phosphorylation of exogenous substrates by pp125FAK kinase. These data indicate that regulation of cellular events key in the process of angiogenesis may be modulated by intracellular calcium balance thereby creating a new therapeutic target for anticancer research. CAI is in phase I clinical trial for patients with advanced cancers, yielding plasma concentrations in the in vitro anti-angiogenic range.