Transcriptomic analysis (RNA-seq) in bevacizumab-resistant xenograft mouse model

Background: Bevacizumab treatments in recurrent glioblastoma (GBM) patients have shown clinical benefits for prolonged disease-free survival (DFS) but have not improved overall survival (OV) because of the unique resistance mechanism. The initial effect of bevacizumab treatment is often hypothesized as an adaptive phenotypic shift to a more aggressive histology, but its molecular mechanism is not known.Methods: To elucidate the molecular mechanisms of bevacizumab-induced drug resistance in GBM, we performed a longitudinal analysis of multiomics data, including transcriptomic (RNA-seq), LC-MS/MS-based global and phosphoproteomic analyses, using an orthotopic mouse model of GBM.Results: Neuronal differentiation induced by the expression of synapse-related molecules triggered the development of bevacizumab resistance. Biological validation studies strongly support that CTNNB1 (beta-catenin) upregulates the expression of neural cell 33 enriched secreted protein neuregulin (NRG3) and leads to upregulation of synapse 34 related molecules such as MAP2 and synapsin1 to initiate drug resistance by triggering neural phenotypes. Prolonged survival of an orthotopic mouse model of GBM by the combination treatment of bevacizumab and the Wnt/beta-catenin-specific inhibitor PRI-724 proved the functional significance of neural transition during the period of bevacizumab resistance development.Conclusion: These results suggested that drug resistance to bevacizumab treatment is induced by multistep mechanism of subtype change leading to neuronal differentiation and that the CTNNB1/NRG3 pathway triggers the initiation of this process. Our results raised future therapeutic possibilities for the combination of a Wnt inhibitor and bevacizumab in recurrent GBM patients.