Patient-Specific Screening Using High-Grade Glioma Explants to Determine Potential Radiosensitization by a TGF- β Small Molecule Inhibitor1,2

High-grade glioma (HGG), a deadly primary brainmalignancy, manifests radioresistance mediated by cell-intrinsic and microenvironmental mechanisms. High levels of the cytokine transforming growth factor- beta(TGF-beta) in HGG promote radioresistance by enforcing an effective DNA damage response and supporting glioma stem cell self-renewal. Our analysis of HGG TCGA data and immunohistochemical staining of phosphorylated Smad2, which is the main transducer of canonical TGF beta signaling, indicated variable levels of TGF-beta pathway activation across HGG tumors. These data suggest that evaluating the putative benefit of inhibiting TGF-beta during radiotherapy requires personalized screening. Thus, we used explant cultures of seven HGG specimens as a rapid, patient-specific ex vivo platform to test the hypothesis that LY364947, a small molecule inhibitor of the TGF- beta type I receptor, acts as a radiosensitizer in HGG. Immunofluorescence detection and image analysis of y - H2AX foci, amarker of cellular recognition of radiation-induced DNA damage, and Sox2, a stem cell marker that increases post-radiation, indicated that LY364947 blocked these radiation responses in five of seven specimens. Collectively, our findings suggest that TGF-beta signaling increases radioresistance inmost, but not all, HGGs. We propose that short-term culture of HGG explants provides a flexible and rapid platform for screening context-dependent efficacy of radiosensitizing agents in patient-specific fashion. This time-and cost-effective approach could be used to personalize treatment plans in HGG patients.