DDDR-83. Dynamic kinome reprogramming drives resistance to treatments in BRAFV600E pediatric gliomas, revealing actionable therapeutic vulnerabilities

Abstract BACKGROUND Pediatric low- and high-grade gliomas (pL/HGG) harboring a BRAFV600E mutation represent a diverse subset of brain tumors. Current treatment strategies concentrate on blocking BRAF and MEK with dabrafenib (DAB) and trametinib (TRA) to reinforce the inhibition of the main oncogenic driver pathway. Despite encouraging (~47%) objective response rates (ORR) in BRAFV600E pLGG, therapeutic response is inconsistent across patients and treatment discontinuation is frequently followed by rapid tumor rebound, representing a significant clinical challenge. Treatment efficacy is further limited in BRAFV600E pHGG, with <30% ORR and common upfront therapeutic resistance. New approaches are needed to discover which pathways cause treatment failure and to rationally design drug combinations capable of inducing durable, safe therapeutic response. METHODS We applied an innovative functional kinome mapping system to characterize the phospho-signaling circuits that wire patient tumors (n=16; grade 1-to-4, including a set of patient-matched specimen before treatment and after recurrence), mouse tumors (n=7; immunocompetent RCAS model), and cell models (n=14). We compared tissues/cells before and after DAB+TRA treatment. Kinase activity signatures were computationally integrated and propagated through protein/gene networks (i.e., PhosphoAtlas, ReactomeFI) to reveal which (phospho-)signaling cascades/pathways are most significantly associated with response and adaptation to treatment and tumor progression. After additional tissue profiling using single-cell RNAseq, the druggability of top candidates was assessed and further prioritized in combination strategies in cell systems and mouse models. RESULTS We found that BRAF+MEK inhibition causes systematic feedback activation of a particular set of RTKs, i.e., PDGFRA/B, FGFR1/2, EGFR/HER4, which cohesively enforce pathways that orchestrate tumor cell survival and proliferation (e.g., RAF/MAPK, PI3K/AKT, PKC). Using blood-brain barrier penetrant targeted therapies that block these RTKs, we found that such inhibitors can synergize with DAB+/-TRA and effectively augment the killing of glioma cells/tumors. CONCLUSION While we keep investigating mechanisms of compensatory response to therapeutic pressure, our advances reveal valuable treatment opportunities to improve BRAFV600E pL/HGG patients’ outcome.