DRES-08. DYNAMIC KINOME PROFILING OF GENETICALLY-DEFINED, EGFRvIII-DRIVEN MURINE ASTROCYTE MODELS OF GLIOBLASTOMA REVEALS TARGETS FOR DUAL KINASE INHIBITOR THERAPY

Glioblastoma (GBM) has poor survival and lacks effective treatments. Due to frequent amplification and mutation of epidermal growth factor receptor (EGFR), several EGFR tyrosine kinase inhibitors have been trialed, but none have proven successful. One potential reason for failure is acquired resistance, particularly acute, adaptive responses in the kinome. To study this adaptive resistance mechanism, we used RNA-seq and multiplex inhibitor bead/mass spectrometry (MIB-MS) to analyze transcriptomes and kinomes of genetically-engineered murine astrocytes with genotypes commonly seen in human GBM. We previously showed that 38% (86 of 228) of the expressed kinome varied among a panel of genetically diverse murine astrocytes harboring Cdkn2a deletion (C) plus Pten deletion (CP), wild-type human EGFR (CE) or EGFRvIII (CEv3) overexpression, or both overexpressed EGFRvIII and Pten deletion (CEv3P). Pairwise genotype comparisons revealed multiple differentially activated kinases, including Pdgfrb, Fgfr2, Lyn, Ddr1, and several members of the Ephrin family. We further investigated these potential targets for dual therapy with EGFR TKI by examining the transcriptional response of our cultured astrocyte panel at 4, 24, and 48 hours after 3 μM afatinib. Afatinib induced no kinome changes in C and only 3 kinases (Fn3k, Prkg2, and Syk) were altered in CP astrocytes. Despite similar baseline gene expression profiles, CE astrocytes overexpressing wild-type EGFR responded significantly differently than C astrocytes without. Five kinases (Dclk1, Epha3, Epha7, Fgfr3, and Prkg1) were induced, while 14 were repressed. Six were similarly repressed in CEv3 (Bub1, Nek2, Pask, Plk4, Prkcb, and Vrk1). Whereas the kinase transcriptome response was blunted in C, CP, and CE astrocytes, afatinib induced altered expression of significantly more kinases in CEv3 (82) and CEv3P cells (49). One particularly attractive target in CEv3 astrocytes was Epha4, which afatinib induced >40-fold. Dual inhibition of EGFRvIII and Epha4 kinases may thus provide an opportunity for more effective targeted therapy.