EWS::FLI1-DHX9 interaction promotes Ewing sarcoma sensitivity to DNA topoisomerase 1 poisons by altering R-loop...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Drug resistance significantly impacts cancer treatment outcomes.
• Ewing sarcoma (EwS) is a pediatric cancer with high treatment failure rates, driven by EWSR1::ETS gene fusions.
• Understanding gene fusion roles in drug response is crucial for EwS therapy.

Purpose of the Study:

• To elucidate a novel mechanism of sensitivity to DNA topoisomerase 1 poisons in EwS.
• To investigate the role of EWS::FLI1 and DHX9 helicase in drug resistance.
• To explore the clinical implications of DHX9 levels in EwS patient outcomes.

Main Methods:

• Investigated R-loop resolution dynamics in EwS cells treated with topoisomerase 1 inhibitors.
• Analyzed the interaction between EWS::FLI1 and DHX9 helicase.
• Assessed the impact of altered DHX9 or EWS::FLI1 levels on drug sensitivity and cellular phenotypes.

Main Results:

• EWS::FLI1 sequesters DHX9, inhibiting R-loop resolution and causing accumulation of replication stress and genome instability.
• Elevated DHX9 or reduced EWS::FLI1 confers resistance to SN-38 (irinotecan metabolite) independent of proliferation and transcription.
• High DHX9 levels correlate with worse clinical outcomes in EwS patients.

Conclusions:

• A novel mechanism of drug sensitivity involving EWS::FLI1-mediated DHX9 sequestration and R-loop accumulation in EwS is described.
• This mechanism explains SN-38 resistance and highlights DHX9 as a potential predictive biomarker for EwS.
• Targeting this pathway may offer new therapeutic strategies for pediatric cancer.