Epigenetic Mechanisms underlying Ewing Sarcoma Pathogenesis

Rationale:
Ewing sarcoma, the second most common pediatric bone cancer, is a highly lethal malignancy. Despite multimodal therapy, recurrence and mortality remain high for metastatic cases. It has been proposed that its refractory nature arises in part from resistance of a cancer stem cell (CSC) subpopulation to chemotherapy. Thus, it is essential that novel therapeutics target this population.
We have found that the epigenetic modifier drug, JQ1, is highly toxic to Ewing sarcoma cells in vitro, and is especially efficacious in targeting the CSC subpopulation. Pilot studies further suggest that JQ1 attenuates tumorigenesis of xenografted Ewing sarcoma cells. JQ1 functions by inhibiting BET proteins, factors that bind to acetylated histones. Microarray and additional analyses reveal that JQ1 rapidly reverses the EWS-FLI1-dependent gene expression, indicating that EWS-FLI1 requires BET proteins for function. The goal of this work is to elucidate the mechanism by which JQ1 and BET proteins regulate EWS-FLI1 activity.

Hypothesis:
We hypothesize that EWS-FLI1 requires BET proteins to induce target genes that control proliferation, survival, and “stemness”.

Specific Aims & Design:
Our goal is to identify the mechanism by which BET proteins/JQ1 modulate EWS-FLI1 activity, which includes determining their actions in the CSC population. Aim 1: identify specific BET family member(s) that are required by EWS-FLI1. Aim 2: identify JQ1-sensitive EWS-FLI target genes essential for proliferation, survival, and “stemness.” of Ewing sarcoma cancer stem cells. These Aims will be achieved through molecular/biochemical characterization of EWS-FLI1 and BET proteins, genome-wide ChIP and transcriptome analysis.

Our work will determine whether JQ1 is an effective treatment for Ewing sarcoma, a cancer for which targeted therapies have remained elusive and mortality rates high. Notably, JQ1 and related compounds are already in clinical trials for the treatment of other malignancies, and thus could be rapidly translated to trials in Ewing sarcoma patients.