Combinatorial BRD4 and AURKA inhibition is synergistic against preclinical models of Ewing sarcoma

Abstract

AbstractBackgroundEwing sarcoma (ES), a bone cancer affecting children, adolescents, and young adults, is driven by the EWS‐FLI1 fusion protein in the majority of cases, but the mechanisms of tumorigenesis are still being elucidated. Consequentially, therapeutic advances have been limited in the last 25 years. Two therapeutic targets have been recently examined. Aurora kinase A (AURKA) promotes cell cycling and posttranslational stabilization of the oncoprotein MYC, while bromodomain‐containing protein 4 (BRD4) promotes gene expression epigenetically. Studies of AURKA and BRD4 inhibitors showed some impairment of tumorigenesis in ES preclinical models, but this efficacy was limited in single‐agent use. AURKA and BRD4 activate common oncogenic pathways through different mechanisms, so we hypothesized dual inhibition would be synergistic against tumorigenesis.Aims(a) Define the synergistic antineoplastic effects of BRD4 inhibitor I‐BET151 and AURKA inhibitor alisertib against ES cell lines in vitro. (b) Confirm the mechanism of activity of each agent in these cell line models. (c) Define the efficacy of I‐BET 151 and alisertib alone and in combinations with each other, and with the chemotherapeutic drug vincristine against ES tumor xenografts in vivo.Methods and resultsI‐BET151 and alisertib synergistically inhibit viability in ES cell lines SK‐ES, TC71, and ES2 in vitro. Alisertib alone upregulates transcriptional expression of its targets, but combined use of I‐BET151 mitigates that upregulation, likely contributing to the drug synergy and downregulating RNA and protein expression of key oncogenic pathways as shown by RT‐qPCR and western blot. Alisertib and I‐BET151 significantly prolong survival in three ES xenograft models in vivo, and this efficacy is augmented by the addition of vincristine.ConclusionDual targeting of oncogenic drivers in ES epigenetically and posttranslationally, specifically by use of BRD4 and AURKA inhibitors, may have significant clinical efficacy in ES alone and/or in combination with current chemotherapy regimens.