Abstract 1731: Decreased cyclin B1 expression contributes to mitochondrial apoptosis in medulloblastoma.

Abstract Medulloblastoma, the most common malignant pediatric brain tumor, remains difficult to cure. Previously, we have shown that downregulation of MMP-9 and uPAR induces Chk1-mediated G2/M cell-cycle arrest in medulloblastoma cells. In this study, we observed that downregulation of MMP-9 in nude mice D283 xenografts downregulated the expression of cyclin B1. Increasing evidence indicates that the deregulation of cyclin B1 is involved in neoplastic transformation, suggesting that inhibition of cyclin B1 could be an attractive strategy for anti-tumor therapy. To determine the effect of downregulation of cyclin B1, we treated medulloblastoma cells with nocodazole, which is an anti-neoplastic agent. Nocodazole-treated cells have undergone G2/M cell-cycle arrest because of the mitotic spindle arrest. Prolonged arrest of cells in mitosis due to nocodazole treatment typically results in cell death by apoptosis. Hence, we confirmed the induction of apoptosis in medulloblastoma cells by TUNEL analysis. Immunoblot analysis of cell cycle checkpoint proteins Chk1, Chk2 and cyclin B1 revealed that they were downregulated in combination treatments of shMMP-9 with radiation. Further, apoptotic proteins BAD, BAX and BAK were highly upregulated, which shows the involvement of mitochondria-mediated apoptosis in our treatments. In vivo analysis of BAD molecules in D283 nude mice xenografts confirmed that downregulation of cyclin B1 induces BAD-mediated apoptotic death in medulloblastoma tumors treated with either shMMP-9 alone or in combination with radiation. With this study, we demonstrate that downregulation of cyclin B1 is an effective and specific approach to induce apoptosis for effective anti-tumor therapy against medulloblastoma. Citation Format: Venkata Ramesh Dasari, Swapna Asuthkar, Arun Kumar Nalla, Jasti S. Rao. Decreased cyclin B1 expression contributes to mitochondrial apoptosis in medulloblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1731. doi:10.1158/1538-7445.AM2013-1731