OS07.7.A GLIOBLASTOMA HYBRID CELL STATE CONVEYS RESISTANCE TO CONVENTIONAL THERAPIES

Abstract

Abstract BACKGROUND Glioblastoma (GB) is a deadly disease and no therapeutic improvements have been made in the last 20 years. High phenotypic plasticity has been recognized as a major obstacle to the efficient treatment of GB. Single-cell sequencing revealed the coexistence of four different cell states within the same tumor. The transition from one subtype (or state) to another, such as from proneural (PN) to mesenchymal (MES), has been suggested as a mechanism for resistance to therapies. However, there is no prognostic value of the current GB states for patients, meaning that mechanisms of resistance may not lie in hardwire identities but in the transition from one subtype to another. Therefore, we investigated the role of the hybrid cell states in GB resistance to therapy. MATERIAL AND METHODS To dynamically follow spatiotemporal changes in GB plasticity in real time, we transduced patient-derived GB cells (patient-derived cell lines with different mutational and phenotypic landscapes) using two specific GB-subtype fluorescent synthetic genetic tracing cassettes. To follow the hybrid cell state dynamics and features, we functionally and transcriptionally investigated GB cells labeled with activated reporters for both the PN and MES subtypes. Using a combination of cytofluorimetry, live imaging, preclinical models, bulk and single-cell RNA-sequencing, we visualized the single-cell GB plasticity and studied the changes in the hybrid state subpopulation proportion over time and under therapeutic stress. RESULTS We discovered that the PN/MES hybrid state (GB-hybrid) has a definite molecular and phenotypic identity and that it is strongly induced after conventional therapies. The GB-hybrid cell state is highly resistant to therapy and more proliferative. Importantly, when implanted in mice the GB-hybrid cells were more aggressive than the rest of the cells, which is consistent with the marked prognostic power for the GB-hybrid geneset signature when tested in the TCGA database. Mechanistically, we showed that GB-hybrid cells were characterized by broad chromatin remodeling, an important increase in overall mRNA quantity per cell and intensification of the nuclear import/export machinery. CONCLUSION Here, we present a novel GB transition cell state between PN and MES subtypes/states. The GB-hybrid is at the same time highly proliferative and resistant to therapy, making it an interesting target to slow down GB recurrence after therapy.