Effects of n-Myc and c-Myc on the expression of p53 family members and their transcriptional targets in human neuroblastoma cells.

Neuroblastoma (NB) is an embryonic malignancy causing 15 % of pediatric cancer fatalities. Amplification of the MYCN gene is one of the major NB drivers and biomarkers of high-risk NB. MYCN amplification is associated with high p53-coding gene expression and decreased survival rates in patients. Importantly, only 1-2 % of NB cases harbor TP53 mutations. Moreover, both high TP53 and low MYC expression levels are unfavorable prognostic markers for NB patients, which is not typical for most types of tumors. In this study we analyzed the effect of MYCN amplification on the expression of genes coding p53 family members - TP63 and TP73. We show that, unlike TP53, TP63 and TP73 levels are higher in MYCN-amplified samples. Furthermore, high TP63 and TP73 expression is a favorable prognostic marker for NB patients' survival. That MDM2 inhibition contributes to p53 stabilization and augments the cytotoxic activity of doxorubicin in NB cells prompted us to test the cytotoxic effects of three small-molecule inhibitors of MDM2 that differ in their mechanisms: Nutlin-3a, Mel23, and SP-141. Our results showed that despite the same target, MDM2, these compounds displayed different cytotoxic effects and synergy with doxorubicin on two widely used NB cell lines, IMR-32 and SH-SY5Y that vary in the amount of MDM2 expression. Collectively, our results suggest that except Nutlin-3a, the other two inhibitors, Mel23 and SP-141, employ additional Mdm2-independent mechanisms of cytotoxicity in NB cells that warrants further investigation.