MYCN sensitizes neuroblastoma to the MDM2-p53 antagonists Nutlin-3 and MI-63

MYCN amplification is a major biomarker of poor prognosis, occurring in 25-30% of neuroblastomas. MYCN plays contradictory roles in promoting cell growth and sensitizing cells to apoptosis. We have recently shown that p53 is a direct transcriptional target of MYCN in neuroblastoma and that p53-mediated apoptosis may be an important mechanism of MYCN-induced apoptosis. Although p53 mutations are rare in neuroblastoma at diagnosis, the p53/MDM2/p14(ARF) pathway is often inactivated through MDM2 amplification or p14(ARF) inactivation. We hypothesised that reactivation of p53 by inhibition of its negative regulator MDM2, using the MDM2-p53 antagonists Nutlin-3 and MI-63, will result in p53-mediated growth arrest and apoptosis especially in MYCN amplified cells. Using the SHEP Tet21N MYCN regulatable system, MYCN(−) cells were more resistant to both Nutlin-3 and MI-63 mediated growth inhibition and apoptosis compared to MYCN(+) cells and siRNA mediated knockdown of MYCN in 4 MYCN amplified cell lines resulted in decreased p53 expression and activation, as well as decreased levels of apoptosis following treatment with MDM2-p53 antagonists. In a panel of 18 neuroblastoma cell lines treated with Nutlin-3 and MI-63, the sub-set amplified for MYCN had a significantly lower mean GI(50) value and increased caspase 3/7 activity compared to the non MYCN amplified group of cell lines, but p53 mutant cell lines were resistant to the antagonists regardless of MYCN status. We conclude that amplification or overexpression of MYCN sensitizes neuroblastoma cell lines with wildtype p53 to MDM2-p53 antagonists and that these compounds may therefore be particularly effective in treating high risk MYCN amplified disease.