Abstract PR03: Myxopapillary spinal ependymomas demonstrate a Warburg phenotype
Authors: Mack Stephen C. , Taylor Michael D. 
Published: May 2016

Introduction: Spinal ependymomas are rare slow-growing tumors found in both children and adults. Myxopapillary ependymomas are a distinct histological variant arising predominantly in the conus medullaris, cauda equina, or filum terminale. Despite an overall favorable prognosis, distant metastases, subarachnoid dissemination, and late recurrences have been reported particularly in the pediatric population. Currently the only effective treatment for myxopapillary ependymoma is gross-total resection. We characterized the genomic and transcriptional landscape of spinal ependymomas in an effort to delineate the genetic basis of this disease and identify new leads for therapy.

Methods: Gene expression profiling was performed on 35 spinal ependymomas (Affymetrix Gene 1.1ST), and copy number profiling on and overlapping cohort of 38 spinal ependymomas. (Affymetrix SNP6.0). GISTIC2.0 was used to identify significant broad and focal copy number events. Consensus hierarchical clustering and non-negative matrix factorization were used to establish subgroup assignments. Pathway analysis was performed using gene set enrichment analysis and visualized with Cytoscape: Enrichment map. Western blot analysis was used to confirm gene expression values. PKM2 expression was assessed in a non-overlapping series of 39 spinal ependymomas using immunohistochemistry. Functional validation experiments were performed on primary tumor lysates consisting of assays measuring pyruvate kinase M activity (PKM), hexokinase activity (HK), and lactate production.

Results: At a gene expression level, we demonstrate that Grade II and myxopapillary spinal ependymomas are molecularly and biologically distinct. These findings are supported by specific copy number alterations occurring in each histological variant. Pathway analysis revealed that myxopapillary ependymoma are characterized by increased cellular metabolism, associated with up-regulation of HIF-1α and its transcriptional targets. These findings were validated by western blot analysis demonstrating increased protein expression of HIF-1α, PKM2, HK2, PDK1, and phosphorylation of PDHE1α. These findings were validated in an independent series of spinal ependymomas, confirming over-expression of PKM2 protein preferentially in myxopapillary tumors. Lastly, functional assays were performed on myxopapillary tumor lysates to demonstrate decreased PKM activity, increased HK activity, and elevated lactate production.

Conclusion: Our findings suggest that myxopapillary ependymoma may be driven by a Warburg metabolic phenotype, mediated by the HIF1α transcriptional network. The key enzymes promoting the Warburg phenotype: HK2, PKM2, and PDK are targetable by next-generation small molecule inhibitors/activators that inhibit aerobic glycolysis, and which should be tested in pre-clinical studies as therapy for myxopapillary ependymoma.

Citation Format: Stephen C. Mack, Michael D. Taylor. Myxopapillary spinal ependymomas demonstrate a Warburg phenotype. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr PR03.