ID #500 Novel therapeutic targets in drug-resistant BRAFV600E paediatric high-grade glioma

Abstract

The BRAFV600E mutation is a critical oncogenic driver in a subset of paediatric high-grade gliomas (pHGG). Whilst these tumours initially respond well to targeted BRAF and MEK inhibitors, the inevitable emergence of therapeutic resistance leads to disease progression. To address this clinical challenge, our pre-clinical study investigates the molecular mechanisms governing acquired resistance in BRAFV600E pHGG to uncover novel vulnerabilities and more durable therapeutic strategies.

In vitro cytotoxicity assays confirmed the resistant nature of BRAF inhibitor-resistant, MEK inhibitor-resistant and BRAF+MEK inhibitor-resistant BRAFV600E pHGG cultures, derived through chronic exposure of a BRAFV600E patient-derived culture to vemurafenib (BRAFi), trametinib (MEKi) or a combination of both drugs, respectively. This resistance was further validated in vivo, where animals orthotopically xenografted with vemurafenib-resistant cells demonstrated significantly reduced survival following BRAF inhibition (dabrafenib) treatment compared to those bearing matched parental tumours.

All three resistant cell lines spontaneously transformed from a spheroid phenotype to adherent growth; proteomics pathway analysis correspondingly identified enrichment of extracellular matrix and cytoskeletal pathways. Differential expression analysis on RNAseq data revealed enrichment of signalling receptor pathways and receptor tyrosine kinase (RTK) gene sets. This identified potent upregulation of several RTKs in vemurafenib-resistant cells, including FGFR, EGFR and NTRK2, providing promising therapeutic targets. Erdafitinib (FGFRi) displayed potent synergistic activity when combined with vemurafenib against vemurafenib-resistant BRAFV600E pHGG cells and parental cells in vitro, inducing apoptosis and reducing MAPK/ERK and AKT/mTOR pathway activation. Similar, potent synergistic responses were observed with repotrectinib (NTRK2i)/vemurafenib and dacomitinib (EGFRi)/vemurafenib treatment, confirming RTK inhibition as a promising therapeutic option

This study has demonstrated that analysing tumour mechanisms is a powerful tool for identifying effective therapies in treatment-refractory tumours. Using an omics-based approach in BRAFV600E pHGG, we have identified novel drivers of drug resistance, key therapeutic targets and several promising therapeutic strategies.