Neuroblastoma (NB) is a childhood cancer that exhibits either a favorable or an unfavorable phenotype. Twenty percent of NB cases have MYCN amplification, which is strongly associated with older age, advanced stage disease, rapid tumor progression, and the worst disease outcome. However, the significance of MYCN expression in NB has been controversial. We recently demonstrated that NB can be divided into three subgroups based on MYCN expression, MYCN amplification, and patient survival. Group 1 includes those with MYCN amplification and the worst disease outcome. Group 2 and Group 3 are NB lacking MYCN amplification expressing low and high levels of MYCN expression, respectively. Interestingly though, the survival rate of Group 3 is better than that of Group 2. With the forced expression of MYCN in NB cell lines (derived from Group 2) by transfection, there is induced apoptosis and enhanced expression of favorable NB genes. Based on these observations, we hypothesize that high MYCN expression confers the opposite biological consequence in NB depending on whether or not MYCN is amplified. In addition, age-dependent DNA methylation on MYCN binding sites influences how MYCN modulates the behavior of NB. Chemotherapeutic agents that can reduce or enhance MYCN expression in MYCN-amplified or MYCN-non-amplified NB, respectively, would have great impact on therapeutic strategies against these malignant tumors. Specifically, (Aim 1) we will perform comprehensive clinical correlative studies among MYCN expression, tumor stage, patient age, MYCN amplification, 1p and 11q deletion status, and favorable NB gene expression in a large NB cohort by multivariable Cox regression models, and examine the prognostic significance of MYCN expression in subsets of high-risk MYCN-non-amplified NB by Kaplan-Meier analysis and log rank test, (Aim 2) identify MYCN target genes that provide NB with a favorable phenotype (favorable NB gene candidates) by genome wide gene expression profiling and ChIP-on-chip assay, and examine their clinical relevance in NB, (Aim 3) correlate age-dependent DNA methylation patterns and gene expression profiles in four age-based subsets (0- 6, 6-12, 12-18, and >18 months) to gain insight into the "Age Factor" of NB: the younger the patients, the better the outcome, and (Aim 4) examine the efficacy of dexamethasone, a site-specific DNA demethylation inducer in combination with DNA methylation inhibitors (5-Aza-2'- deoxycytidine and RG108) and RAS pathway specific MYCN protein destabilizers in preclinical human NB subcutaneous and metastatic xenograft models.
Future advances in the control of resistant malignant NB cells will be made through modulation of their intrinsic biology. We expect this series of translational research experiments will confirm the critical importance of how MYCN expression could modulate the malignancy of such NB cells. In addition, the results of our experiments will hold promise for the early introduction of favorable NB gene enhancers and MYCN-destabilizers into clinical trials, for example, in the control of minimal residual disease.
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