CSIG-22. A CD133-Akt-Wnt SIGNALING AXIS PROVIDES FUNCTIONAL INSIGHT INTO THE ROLE OF CD133 IN GLIOBLASTOMA BRAIN TUMOR-INITIATING CELLS

Current transcriptional profiles of adult glioblastoma (GBM) recognize the activation of distinct signaling programs. Single-cell sequencing efforts have provided greater resolution of core developmental pathways implicated in disease progression and relapse. Of note, the Wnt pathway is activated in a subset of patients, despite the lack of recurrent activating mutations in human GBM. Given the description of CD133 as a marker of tumor-initiating cells in a number of human cancers associated with activated Wnt signaling, we investigated the role of CD133 in human GBM as a novel Wnt regulator. CD133high GBM lines were found to have greater Wnt levels when compared to CD133low lines. To establish a signaling axis between CD133 and Wnt we investigated the CD133-dependent activation of Akt and the subsequent downstream inhibition of GSK leading to beta-catenin activation. Ectopic expression of CD133 resulted in increased pAKT, pGSK (Ser 9), and beta-catenin. To further describe the context-dependent role for Akt activation of Wnt through GSK inhibition, CD133high lines were treated with the Akt inhibitor, MK-2006, which decreased pAKT, pGSK (Ser 9), and beta-catenin. In order to validate the tumorigenic potential of Wnt-activated cells, a Wnt reporter was used to isolate cells with endogenous Wnt signaling. Wnt-active cells maintained an increased self-renewal and tumor-initiating capacity when compared to Wnt-inactive cells. Xenografts generated from Wnt active cells had a reduced survival advantage as these contained an enhanced expression of stemness genes when compared to Wnt-inactive xenografts. To develop a rationale clinical therapeutic, we used RWO3, a novel humanized antibody directed at CD133. In vivo treatment with RW03 showed a significant reduction in activated Wnt signaling, highlighting the role of CD133 in modulating the Wnt pathway. Our work establishes a CD133-Akt-Wnt signaling axis in GBM through the functional characterization of CD133 and subsequent context-specific Akt-dependent regulation of the canonical Wnt pathway.