Strategies to inhibit FGFR4 V550L-driven rhabdomyosarcoma.

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Rhabdomyosarcoma (RMS) is a pediatric cancer often driven by fusion proteins or mutations in signaling molecules like RAS or FGFR4.
• While mutations offer precision medicine opportunities, no targeted treatments are currently available for FGFR4-driven RMS.
• The FGFR4 V550L activating mutation is a key driver in a subset of RMS cases.

Purpose of the Study:

• To evaluate the biological properties and therapeutic targeting strategies for the FGFR4 V550L activating mutation in RMS.
• To identify effective inhibitors and alternative therapeutic pathways for FGFR4 V550L-driven rhabdomyosarcoma.
• To assess the efficacy of targeting FGFR4 V550L in preclinical RMS models.

Main Methods:

• Characterization of FGFR4 V550L signaling and trafficking using confocal microscopy and proteomics.
• Assessment of drug effects on cell proliferation and signaling via live-cell imaging and MTS assays.
• Evaluation of therapeutic strategies in a relevant RMS mouse xenograft model.

Main Results:

• The FGFR4-specific inhibitor FGF401 demonstrated potent inhibition of FGFR4 V550L signaling and proliferation at nanomolar concentrations.
• Other FGFR4 inhibitors (BLU9931, H3B6527) showed limited activity against FGFR4 V550L.
• Phosphoproteomic analysis revealed RAS/MAPK and PI3K/AKT pathways as essential downstream targets, and HSP90 dependency was identified.
• FGF401 effectively inhibited tumor growth in a mouse xenograft model, unlike a pan-FGFR inhibitor.

Conclusions:

• FGFR4 V550L is a druggable target in rhabdomyosarcoma, with FGF401 showing significant preclinical efficacy.
• Targeting downstream pathways like RAS/MAPK, PI3K/AKT, or HSP90 presents alternative therapeutic strategies.
• These findings support the development of precision medicine approaches for FGFR4 V550L-driven RMS.