We review here these mechanisms for evasion of p53-mediated growth control and conclude that deregulation of the p14(ARF)-MDM2-p53 axis seems to be the principal mode of p53 inactivation in neuroblastoma, opening new perspectives for targeted therapeutic intervention.
These data support the hypothesis that elevated MDM2 levels contribute to MYCN-induced genomic instability through altered regulation of centrosome replication in neuroblastoma.
Our results indicate that MDM2 has a p53-independent role in the regulation of both MYCN mRNA stabilization and its translation, suggesting that MDM2-mediated MYCN expression is one mechanism associated with growth of MYCN-associated neuroblastoma and disease progression.
MDM2 is a key inhibitor of p53 and a positive activator of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) activity with an important role in neuroblastoma pathogenesis.
The present study evaluated the effect of ethanolic extract of <i>Nardostachys jatamansi</i> roots (NJ<sub>et</sub>) on MYCN mediated regulation of expression of MDM2 and p53 proteins in neuroblastoma cell lines, IMR-32 and SK-N-MC.
Importantly, neuroblastoma maintains both an active p53 and an aberrant mTOR signaling.<b>Experimental Design:</b> Using an orthotopic xenograft model and modulating p53 levels, we investigated the antitumor effects of the mTORC1 inhibitor temsirolimus in neuroblastoma expressing normal, decreased, or mutant p53, both as single agent and in combination with first- and second-generation MDM2 inhibitors to reactivate p53.<b>Results:</b> Nongenotoxic p53 activation suppresses mTOR activity.
We previously reported that 3 p53 wild type (wt) MYCN amplified (MNA) neuroblastoma cell lines failed to G1 arrest after DNA damage despite induction of p53, p21(WAF1) and MDM2.
Also, we found that the enforced overexpression of MDM2, or conversely, the inhibition of overexpressed endogenous MDM2, led to either a remarkable increase or decrease in tumor growth, respectively, in MYCN-amplified neuroblastoma (even though no p53 function was involved).
A cohort of 497 NB children, enrolled in the Italian Neuroblastoma Registry between January 1985 and December 2005 and previously investigated for the prognostic role of MDM2 SNP309, was considered for this study.
In summary, our data strongly suggest that MDM2-specific inhibitors like SAR405838 may serve not only as a stand-alone therapy, but also as an effective adjunct to current chemotherapeutic regimens for treating NB with an intact MDM2-p53 axis.
Here we establish the role of these conjugates in activating p53 pathway by phosphorylation at Ser15, 20 and 46 residues and downregulate key oncogenic proteins such as MYCN and Mdm2 in IMR-32 neuroblastoma cells.
The Neuroblastoma New Drug Development Strategy (NDDS) has: 1) established a group with expertise in drug development; 2) prioritised targets and drugs according to tumour biology (target expression, dependency, pre-clinical data; potential combinations; biomarkers), identifying as priority targets ALK, MEK, CDK4/6, MDM2, MYCN (druggable by BET bromodomain, aurora kinase, mTORC1/2) BIRC5 and checkpoint kinase 1; 3) promoted clinical trials with target-prioritised drugs.
To test this hypothesis, p53 expression, location, and functional integrity was examined in neuroblastoma by irradiating 6 neuroblastoma cell lines and studying the effects on p53 transcriptional function, cell cycle arrest, and induction of apoptosis, together with the transcriptional function of p53 after irradiation in three ex vivo primary, untreated neuroblastoma tumors. p53 sequencing showed five neuroblastoma cell lines, two of which were MYCN-amplified, and that all of the tumors were wild-type for p53. p53 was found to be predominantly nuclear before and after irradiation and to up-regulate the p53 responsive genes WAF1 and MDM2 in wild-type p53 cell lines and a poorly-differentiated neuroblastoma, but not a differentiating neuroblastoma or the ganglioneuroblastoma part of a nodular ganglioneuroblastoma in short term culture.
The observed treatment effects without the need of imposing a genotoxic burden suggest that selective MDM2 antagonists might be beneficial for treatment of neuroblastoma patients with and without MYCN amplification.