Fig. 5. BET inhibition synergizes with Aurora A inhibition and promotes cell death in MYCN expressing GBM cells.

JQ1-sensitive GBM cells showed significantly higher MYCN expression compared to JQ1-resistant cells, with a similar trend observed in the expression of AURKA (a, data downloaded from www.hgcc.se). In a large GBM patient cohort (TCGA) the expression of AURKA positively correlates with MYCN expression (Pearson correlation, n = 153) (b). JQ1-sensitive cells demonstrated significantly (see Table S9) stronger reduction in viability following Aurora A inhibition using small molecule inhibitor MLN8237 compared do JQ1-resistant cells (c). Combined BET and Aurora A inhibition was synergistic in both JQ1-sensitive and resistant GBM cell lines (d). While in JQ1-sensitive cells the dual inhibition resulted in cell cycle arrest and apoptosis, JQ1-resistant cells were predominantly arrested in either G0/G1 or G2 phase (e, see also Supplementary Table S10 for multiple comparison-adjusted p-values). While cellular senescence was induced in both JQ1-sensitive and resistant GBM cells as demonstrated by a decrease in Lamin B1 following JQ1 or dual inhibition, only one of the JQ1-sensitive GBM cell lines demonstrated a significant upregulation of Cleaved Caspase 3, indicating an induction of apoptosis (f). EC₅₀ (JQ1) = 500 nM, EC₅₀ (MLN8237) = 750 nM. CI = combination index (CI < 0.8: synergism; 0.8 < CI < 1.2: addition; CI > 1.2: antagonism). Immunoblotting was normalized to loading control (ACTIN) and untreated sample (DMSO control).