Antisense RNA inhibition of cathepsin L expression reduces tumorigenicity of malignant cells

Several tumour-forming cell lines are known to overproduce the lysosomal cy steine peptidase cathepsin L. We have used an antisense approach to investi gate whether inhibition of cathepsin L overexpression in two malignant cell lines (myeloma SP cells and L cells) reduces their tumorigenic potential. Two different cDNA fragments of murine cathepsin L were inserted in the ant isense direction into the pcDNA3 vector, and SP and L cells were stably tra nsfected with these plasmid constructs. Several of the selected clones expr essing the antisense transcript showed specific reduction of the mRNA level and the intracellular activity of cathepsin L, and a greatly diminished am ount of secreted procathepsin L. When tested in Balb/c nu/nu mice, the cell lines with low cathepsin L activity exhibited a significantly decreased po tential for tumour growth when compared with control cells expressing wild- type levels of cathepsin L activity. This observation suggests that catheps in L is a critical factor in tumour growth. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.