Brain tumors represent the leading cause of childhood cancer mortality, of which medulloblastoma (MB) is the most frequent malignant pediatric brain tumor. Current molecular subgroups of MB recognize distinct disease entities of which activated Wnt signaling (monosomy 6, exon 3 mutations in CTNNB1, and Wnt gene signature) is associated with a distinct subgroup and the best overall outcome. In contrast, only non-Wnt MBs are characterized by metastatic disease, increased rate of recurrence, and poor overall survivorship. Given the excellent clinical outcome in patients with Wnt-driven MB, we aimed to convert treatment-resistant MB subgroups into an ostensibly benign tumor through selective targeting by small molecules and transgenic patient-derived lines containing a stabilized beta-catenin mutant. Activated Wnt signaling by way of Wnt agonists in treatment-refractory MBs resulted in decreased in vitro self-renewal and promoted differentiation. Comparative gene expression profiling of control and transgenic lines containing a stabilized beta-catenin mutant demonstrated a reduction in stem cell self-renewal genes following beta-catenin overexpression, including Sox2 and Bmi1. In order to validate the therapy-sensitive nature of Wnt-activated cells, we developed stable patient-derived lines containing a 7XTOPFlash reporter for endogenous Wnt signaling. Rare subclonal Wnt-active cells demonstrated a reduced self-renewal and tumor-initiating capacity through in vivo limiting dilution assays when compared to bulk Wnt-inactive cells. The therapeutic relevance of these findings were demonstrated with an in vivo survival advantage in mice with orthotopic injections of cells containing a stabilized beta-catenin mutant representative of constitutively active Wnt signaling or endogenous Wnt-active cells. Xenografts generated from Wnt-activated tumors were smaller in size, maintained a lower rate of proliferation, and reduction in MB self-renewal genes. To further illustrate the clinical utility of activated Wnt signaling, we modified the Children’s Oncology Group therapy protocol for childhood MB so that xenografts may receive chemo/radiotherapy. Tumors generated from Wnt-active xenografts were much more radiosensitive and displayed a significant reduction in spinal metastasis when compared to mice receiving standard therapy without Wnt activation. To develop a rationale clinical therapeutic, we developed unique agonist antibodies that target the Wnt co-receptor LRP5. Treatment with LRP5 antibodies showed a significant reduction in tumor burden and increase in survival of patient-derived tumors that were otherwise treatment-resistant. Our work establishes for the first time activated Wnt signaling as a novel treatment paradigm in childhood MB, identifies a rationale therapeutic approach for recurrent MB, and provides evidence for the context-specific tumor suppressive function of the canonical Wnt pathway.
Note: This abstract was not presented at the meeting.
Citation Format: Branavan Manoranjan, Chitra Venugopal, Zvezdan Pavlovic, David Bakhshinyan, Michelle Kameda-Smith, Minomi Subapanditha, Sujeivan Mahendram, Jason Moffat, Bradley W. Doble, Sheila Singh. Activated Wnt signaling for the treatment of recurrent medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5831. doi:10.1158/1538-7445.AM2017-5831