Suppression by cathepsin L inhibitors of the invasion of amnion membranes by murine cancer cells

Cysteine proteinases, particularly cathepsins B and L, have been strongly implicated in fostering metastasis in mice. In this work four different inhibitors of cysteine proteinases have been shown to inhibit the invasion of the human amnion by murine melanoma and mammary carcinoma cells in vitro. Two of the inhibitors are synthetic peptides [ZPhePheCHN2 (benzyloxycarbonyl-L-phenylalanyl-L-phenylalanyldiazomethane) and ZPheAlaCH2F [3-(N-benzyloxycarbonylphenylalanylamido)-DL-1-fluoro-2-butanone]] and two are thiol protease inhibitors (TPIn, TPId) isolated from the skeletal muscle of the hind limbs of normal and dystrophic mice, respectively. The inhibitors (ZPhePheCHN2, TPId), with apparent selectivity for cathepsin L, blocked invasion as effectively as inhibitors (ZPheAlaCH2F, TPIn) effective on both cathepsins. The data reveal that in these cell lines the cysteine proteinases contribute significantly to the invasive capacity of the cells, but to a lesser extent than do the metalloproteinases. We suggest that the cysteine proteinases facilitate the action of metalloproteinases (collagenase, gelatinase, and stromelysin), possibly by activating them, by inactivating the tissue inhibitor of metalloproteinases, and/or by making basement membrane matrix more accessible.