Tumourigenesis in the TH-MYCN transgenic-mouse model of neuroblastoma is characterised by transient repression of p53 stress responses in embryonal ganglionic neuroblasts, causing them to persist postnatally as cancer-prone lesions12. p53 re-activation may be a potential therapeutic strategy for removal of these lesions before they later transform with oncogenic stimuli. One potential target for p53 activation is the FACT heterodimer, which is known to inhibit p53 signalling.
Here we show that high mRNA expression of the two FACT-subunits, SSRP1 and SPT16, is associated with poor patient outcome (p<0.001) in primary neuroblastoma tissues (Kaplan-Meier analysis, n=650) and both SSRP1 and SPT16 have a strong correlation with MYCN expression, particularly in high-risk MYCN-amplified neuroblastoma tissues (p<0.05). Also, MYCN siRNA lowers SSRP1 and SPT16 expression in neuroblastoma cell-lines and a chemical inhibitor of FACT, called Cbl137, is potently and selectively cytopathic in neuroblastoma cell-lines as compared to non-malignant MRC5-fibroblasts (p<0.001).
To examine the role of FACT in MYCN-driven tumourigenesis we evaluated the effect of Cbl137 on tumour-initiation in TH-MYCN mice. Low-micromolar Cbl137 doses effectively restored normal, p53-dependent death responses to primary ganglion cell-cultures deprived of serum from neonatal TH-MYCN mice, while ganglion cultures from wild-type mice were significantly more resistant to Cbl137, with or without serum-deprivation (p<0.001). Most importantly, prophylactic Cbl137 treatment of neonatal TH-MYCN mice had a marked inhibitory effect on postnatal ganglion neuroblast persistence in vivo for both heterozygote and homozygote TH-MYCN mice, as compared to vehicle-only treated animals (p=0.01, p=0.035, respectively).
Taken together, our data for the first time identifies FACT as a novel effector of MYCN-driven neuroblastoma tumourigenesis. Inhibitors of FACT may be a novel treatment for high risk MYCN-amplified neuroblastoma and a potential strategy for neuroblastoma prevention.