Abstract A59: CHAF1A blocks neuroblastoma differentiation and promotes tumor growth via metabolic reprogramming

Neuroblastoma (NB), an embryonal tumor arising in tissues of the sympathetic nervous system, accounts for 13% of all deaths due to childhood malignancies. NB arises from embryonal neural crest secondary to a block in differentiation and long-term survival inversely correlates with the degree of neuronal differentiation. Importantly, treatment with differentiation agents, such as retinoic acid (RA), has modestly improved survival. We have recently demonstrated a novel function for the histone chaperone CHAF1A in promoting tumor progression by blocking NB differentiation. CHAF1A is a MYCN target gene and a subunit of the Chromatin Assembly Factor-1 (CAF1) which regulates H3K9-trimethylation and DNA methylation. Here, in order to define the mechanism for CHAF1A-mediated inhibition of differentiation, we performed transcriptome analyses (Affymetrix U133+2.0 arrays) in NB cells upon CHAF1A silencing. Notably, gene set enrichment analysis (GSEA) revealed repression of oncogenic pathways and enrichment of cell metabolism pathways (valine, leucine, and isoleucine degradation, glutamate metabolism and insulin pathways). Furthermore, Q-PCR confirmed that CHAF1A significantly affects the expression of critical genes regulating glucose uptake. Based on these findings and the fact that cancer cells have defective mitochondria, which forces them to depend on aerobic glycolysis, we then examined the sensitivity of NB cells to different glycolytic inhibitors. We hypothesized that targeting glucose metabolism will decrease NB cell growth and restore sensitivity to RA. The effect of the glycolytic inhibitors metformin, dichloroacetate (DCA), and 2-Deoxy-D- glucose (2-DG) on cell proliferation was determined by MTT-Assay in several NB lines under normoxic and hypoxic conditions (1% O2). 2-DG treatment significantly blocked cell proliferation in all NB lines tested, with enhanced effect under hypoxic conditions. However, metformin and DCA's anti-proliferative effects were dependent on MYCN status and levels of O2 deprivation. Notably, MYCN non-amplified lines showed greater sensitivity to metformin and DCA under normoxia than under hypoxic conditions (IC50 normoxia: 6.25 mM vs. IC50 hypoxia: > 50 mM). In contrast, MYCN-amplified cell lines maintained high proliferation under hypoxia and revealed high sensitivity to metformin and DCA both under normoxic and hypoxic conditions (IC50 normoxia: 25 mM vs. IC50 hypoxia: 22.5 mM). In conclusion, we have shown that: 1) the differenti