We demonstrated previously that the switch from nonmetastatic to highly metastatic phenotype of human
melanoma cells is directly related to secretion of
procathepsin L form. This
cysteine proteinase was identified on the basis of its property to cleave human C3, the third component of
complement. In an attempt to control
procathepsin L secretion, we have recently generated an anti-
cathepsin L single chain variable fragment (ScFv) from an anti-
cathepsin L monoclonal antibody generated against recombinant
cathepsin L. We herein selected clones stably transfected with this anti-
cathepsin L ScFv and analyzed them for changes in
tumor growth and
metastasis. We show that in stably transfected clones, anti-
cathepsin L ScFv strongly inhibited the secretion of
procathepsin L without modifying the intracellular amount or processing pattern of
cathepsin L forms. Confocal analysis demonstrated colocalization of endogenous
cathepsin L and anti-
cathepsin L ScFv. In addition, expression of this ScFv strongly inhibited generation of
tumor and
metastasis by these human
melanoma clones in nude mice. In vivo, the anti-
cathepsin L ScFv-transfected cells produced
tumors with decreased vascularization (angiogenesis) concomitant with increased apoptosis of
tumor cells.
Matrigel assay also demonstrated that
melanoma invasiveness was completely abolished. Thus, this is the first demonstration that anti-
cathepsin L ScFv could be used to inhibit the tumorigenic and metastatic phenotype of human
melanoma, depending on
procathepsin L secretion, and could therefore be used as a molecular tool in a therapeutic cellular approach.