Taken together, our results suggest that IGF1R and the downstream PI3K/AKT/mTOR kinase cascade mediate intrinsic resistance to BET inhibitors in Ewing sarcoma.
These results provide the first insights on the transcriptional regulation of EWS/FLI1, an area that has not been investigated so far, and offer an additional molecular explanation for the known sensitivity of ES cell lines to PI3K inhibition.
Novel somatic mutations were identified in four out of 18 patients with advanced ES and two of 10 patients with advanced DSRCT (six out of 28 (21.4%));KRAS (n = 1), PTPRD (n = 1), GRB10 (n = 2), MET (n = 2) and PIK3CA (n = 1).
Our results indicate that further study on combination of conventional chemotherapies with MEK and PI3K inhibitors may be considered for innovative treatments of Ewing sarcoma patients.
Moreover, PI3K inhibition significantly reduced ET cell proliferation and, in primary ET samples, cyclin D1 expression correlated with expression of activated AKT.