Legumain correlates with neuroblastoma differentiation and can be used in prodrug design

Neuroblastoma (NB) is a highly malignant solid tumor in children. The cysteine endopeptidase legumain is expressed in adult solid tumors, but its expression in NB has not been examined. In this study, we assayed legumain expression in two NB cell lines and in microarrays of tumor tissues collected from 46 children with undifferentiated NB, differentiated NB, and ganglioneuroblastoma. Correlation analyses showed that legumain was expressed in all NB cell lines tested and that expression correlated with the degree of tumor differentiation. The efficacy, specificity, and toxicity of EMC-AANL-DOX, a novel doxorubicin-based legumain-activated prodrug, were then evaluated in mouse model of NB. Compared with DOX, EMC-AANL-DOX showed greater inhibition of tumor growth and a lower toxicity at high doses. Neither leukocyte or platelet counts nor renal function or cardiac anatomy differed significantly between the EMC-AANL-DOX and control groups (p > .05), suggesting that the prodrug caused minimal bone marrow depression and did not induce renal or cardiac damage. The good specificity and efficacy of EMC-AANL-DOX and low toxicity recommend its use in the treatment of NB. Correlation analyses of NB differentiation and legumain expression may reveal a novel anti-tumor-related functions of the drug and a new strategy for the treatment of pediatric solid tumors.