Midkine lacking its last 40 amino acids acts on endothelial and neuroblastoma tumor cells and inhibits tumor development.

Midkine (MDK) is a member of a new family of neurotrophic factors considered as rate-limiting growth and angiogenic factors implicated in the onset, invasion, and metastatic process of neuronal tumors, including neuroblastoma. We showed that all neuroblastoma cell lines highly expressed MDK, indicating that it is a critical player in tumor development, which may henceforth represent an attractive therapeutic target. We showed that the knockdown of MDK expression by siRNA led to a marked and significant decrease in neuroblastoma (IGR-N91 and SH-SY5Y) cell proliferation in vitro. Using a new strategy, we then evaluated the antitumor effect of a truncated MDK protein, lacking the C-terminal 81-121 portion of the molecule (MDKΔ81-121), which may act as a dominant-negative effector for its mitogenic, angiogenic, and tumorigenic activities by heterodimerizing with the wild-type protein. In vitro studies showed that MDKΔ81-121 selectively inhibited MDK-dependent tumor cells and was able to strongly reduce endothelial cell proliferation and migration and to induce ER stress-mediated apoptosis. We then investigated the effects of MDKΔ81-121 in vivo using electrotransfer of a plasmid encoding a secretable form of MDKΔ81-121 into tibialis cranialis muscles of nude mice. We showed that MDKΔ81-121 dramatically inhibited (up to 91%) tumor development and growth. This inhibition was correlated with the detection of the MDKΔ81-121 molecule in plasma and the suppression of intratumor neovascularization. Our findings demonstrate that MDK inhibition is a tractable therapeutic target for this lethal pediatric malignancy.