Overexpression of legumain in tumors is significant for invasion/metastasis and a candidate enzymatic target for prodrug therapy

Expression of Legumain, a novel asparaginyl endopeptidase, in tumors was identified from gene expression profiling and tumor tissue array analysis. Legumain was demonstrated in membrane-associated vesicles concentrated at the invadopodia of tumor cells and on cell surfaces where it colocalized with integrins. Legumain was demonstrated to activate progelatinase A. Cells overexpressing Legumain possessed increased migratory and invasive activity in vitro and adopted an invasive and metastatic phenotype in vivo, inferring significance of Legumain in tumor invasion and metastasis. A prodrug strategy incorporating a legumain-cleavable peptide substrate onto doxorubicin was developed. The prototype compound, designated legubicin, exhibited reduced toxicity and was effectively tumoricidal in vivo in a murine colon carcinoma model.