Abstract PR09: MYCN and is a therapeutic target in neuroblastoma

Neuroblastoma is a childhood cancer of the sympathetic nervous system. Approximately 20% of patients present with an aggressive metastatic disease characterized by amplification of the MYCN locus. However, an additional 30% of patients suffer from an equally aggressive disease, yet there are no unified genetic markers available. To identify potential biomarkers of poor prognosis in neuroblastoma, we conducted unsupervised hierarchical clustering on 649 primary neuroblastoma tumors based on a 51 gene MYC core target signature. This demonstrated strong activation within the MYCN amplified cohort as expected, but surprisingly there was a large subset of MYCN non-amplified patients that exhibited high MYC signaling. High expression of this MYC signature proved to be strongly predictive of poor overall survival, in both the full cohort (Hazard ratio (HR): 47.6, p= 2.7x10-35, n=649) and in MYCN non-amplified patients (HR=32.8, p=1.3x10-13, n=554), suggesting that neuroblastoma can be driven by MYC signaling in the absence of MYCN amplification. To evaluate potential therapeutic targets within this MYC signature, we conducted cox regression analysis on the 51 individual members and identified that SPT16 was a particularly potent predictor of poor outcome in these 649 neuroblastoma patients (HR: 7.2, p=2.7x10-17). SPT16 is a subunit of the FACT histone chaperone complex, which together with its heterodimer partner SSRP1, has previously been shown to function in dynamic regulation of chromatin to drive transcription, DNA replication and DNA repair. Similar to SPT16, high SSRP1 expression was a strong predictor of poor prognosis in 649 neuroblastoma patients (HR: 12.5, p=5.812x10-26) implicating FACT as a mediator of MYC driven neuroblastoma. Next we investigated the biological relationship between FACT and MYCN in neuroblastoma. siRNA experiments showed that FACT and MYCN participate in a positive feedback transcriptional loop that is essential for maintaining mutual high expression. Immunohistochemistry in sympathetic ganglia of pre-tumor TH-MYCN mouse model of neuroblastoma identified that FACT was highly expressed at tumor initiation and chemical inhibition of FACT by CBL0137 markedly reduced tumor initiation and subsequent tumorigenesis in vivo. Next we tested CBL0137 against established neuroblastoma in TH-MYCN mice. CBL0137 was highly cytotoxic to tumors either as a single agent or by synergistically promoting clinically used chemotherapeutics. This was accom