Various antibacterial compounds, antitumor compounds, enzyme inhibitors and recent
signal transduction inhibitors have been discovered from microorganisms and plants.
Therefore, it should be possible to find antimetastatic compounds from these sources, if a
simple assay system is available. We isolated several enzyme inhibitors from nature to
inhibit experimental metastasis. Leupeptin is an old protease inhibitor and inhibited blood-
borne lung metastasis of hepatoma cells in rats. A leupeptin analogue inhibiting urokinase …