The matrix metalloproteinase inhibitor batimastat inhibits angiogenesis inliver metastases of B16F1 melanoma cells

Matrix metalloproteinases (MMPs) have been shown to contribute functionally to tumor metastasis. MMP inhibitors are thus being assessed for clinical u tility as anti-metastatic therapeutics. Batimastat (BB-94) is a synthetic M MP inhibitor that has been shown to inhibit tumor growth and metastasis in mice. Here we assessed the ability of batimastat to inhibit liver metastase s of murine B16F1 cells, after injection of cells in mice via mesenteric ve in to target the liver. We then determined which of the sequential steps in metastasis were affected by batimastat, in order to identify its mechanism of action in vivo. Intravital videomicroscopy was used to assess the effec t on extravasation, and a 'cell accounting' procedure was used to determine the effect on initial survival of cells. Stereological quantification of f unctional blood vessels was used to determine the effect on tumor vasculari ty, thereby avoiding problems associated with immunohistochemical detection of liver sinusoidal endothelial cells. We found that batimastat (50 mg/kg i.p. 5 h prior to and after cell injection, daily thereafter) resulted in a 23% reduction in mean diameter of liver metastases (equivalent to a 54% re duction in tumor volume), while not reducing the number of metastases. Extr avasation of cells from the liver circulation was not affected: at 8, 24 an d 48 h after injection of cells, the same proportion of cells had extravasa ted from treated vs. control mice. Batimastat also did not inhibit early su rvival of cells. However, batimastat-treated mice had a significantly reduc ed percentage vascular volume within liver metastases, indicating inhibitio n of angiogenesis. This study demonstrates in vivo that the mechanism by wh ich batimastat limits growth of B16F1 metastases in liver is not by affecti ng extravasation, but by inhibiting angiogenesis within metastases. This fi nding suggests that MMP inhibitors may be appropriate for use in patients w ith metastatic cells that have already extravasated in secondary sites.