Inhibition of nuclear factor kappa-B signaling reduces growth in medulloblastoma in vivo

Background: Medulloblastoma is a highly malignant pediatric brain tumor that requires surgery, whole brain and spine irradiation, and intense chemotherapy for treatment. A more sophisticated understanding of the pathophysiology of medulloblastoma is needed to successfully reduce the intensity of treatment and improve outcomes. Nuclear factor kappa-B (NF kappa B) is a signaling pathway that controls transcriptional activation of genes important for tight regulation of many cellular processes and is aberrantly expressed in many types of cancer. Methods: To test the importance of NF kappa B to medulloblastoma cell growth, the effects of multiple drugs that inhibit NF kappa B, pyrrolidine dithiocarbamate, diethyldithiocarbamate, sulfasalazine, curcumin and bortezomib, were studied in medulloblastoma cell lines compared to a malignant glioma cell line and normal neurons. Expression of endogenous NF kappa B was investigated in cultured cells, xenograft flank tumors, and primary human tumor samples. A dominant negative construct for the endogenous inhibitor of NF kappa B, I kappa B, was prepared from medulloblastoma cell lines and flank tumors were established to allow specific pathway inhibition. Results: We report high constitutive activity of the canonical NF kappa B pathway, as seen by Western analysis of the NF kappa B subunit p65, in medulloblastoma tumors compared to normal brain. The p65 subunit of NF kappa B is extremely highly expressed in xenograft tumors from human medulloblastoma cell lines; though, conversely, the same cells in culture have minimal expression without specific stimulation. We demonstrate that pharmacological inhibition of NF kappa B in cell lines halts proliferation and leads to apoptosis. We show by immunohistochemical stain that phosphorylated p65 is found in the majority of primary tumor cells examined. Finally, expression of a dominant negative form of the endogenous inhibitor of NF kappa B, dnI kappa B, resulted in poor xenograft tumor growth, with average tumor volumes 40% smaller than controls. Conclusions: These data collectively demonstrate that NF kappa B signaling is important for medulloblastoma tumor growth, and that inhibition can reduce tumor size and viability in vivo. We discuss the implications of NF kappa B signaling on the approach to managing patients with medulloblastoma in order to improve clinical outcomes.