Abstract 415: Differential expression of therapeutic targets across tumor micro-environments and at infiltrative margins in glioblastoma

Glioblastoma (GBM; WHO grade IV) is the most common primary brain tumor and is associated with a poor prognosis. The Cancer Genome Atlas (TCGA) project has revealed discrete molecular classes of GBM, raising the possibility of targeted therapies. Molecular heterogeneity across tumor microenvironments presents a challenge to targeted therapy, since effective therapies will be directed at targets near resection margins rather than those expressed in bulk resected tumor. To this end, we initiated studies to delineate spatial and temporal variations of potential druggable targets in GBM, focusing on potential protein targets at the tumor margin. By utilizing 5-ALA (5-aminolevulinic acid, an oral compound that accumulates in malignant glioma cells and is metabolized to the fluorescent agent, protoporphyrin IX) fluorescence-guided surgery of primary and recurrent GBMs in a Phase II clinical trial, we were able to precisely define perinecrotic, bulk, and marginal regions within the glioma intraoperatively in order to sample tissues for further molecular characterization. Tissues harvested from these 3 tumor regions from 5 patients were analyzed using reverse phase protein array (RPPA) analysis with 218 antibodies (Array-Pro). Relative protein levels were determined and a heatmap was generated as a hierarchical cluster using Pearson Correlation and a center metric. Forty proteins had statistically significant altered expression at the tumor margin compared with bulk and perinecrotic tumor. Among these, STAT1, STAT2, STAT3, PDGFRA, PDGFRB, EGFR, JAK2, MET, PIK3R1, and ERBB2 were upregulated at the margins and are potential druggable targets worthy of further investigation. Also upregulated at the tumor margins were NFKBIA, JUN, ZAP70, GAPDH, and CD28, whereas STAT5A, EFNB2, NTRK1, KDR, FGFR1, PTPRA, IFNGR1, and EFNB1 were downregulated at margins. Our data demonstrate significant variation of druggable targets and signaling networks across tumor microenvironments in GBM. Marginal tumor differs from bulk and perinecrotic tumor by the relative overexpression of STAT proteins, growth factor receptors, and receptor kinases. Directing therapy at networks and targets present at the tumor margin of GBM may be an effective strategy. Citation Format: Myles R. McCrary, David Gutman, William Dunn, Milota Kaluzova, Alexandros Bouros, Merete Williams, Xialong Zhang, Lee AD Cooper, Constantinos G. Hadjipanayis, Daniel J. Brat. Differential expression of therapeutic targets across tumor micro-environments and at infiltrative margins in glioblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 415. doi:10.1158/1538-7445.AM2015-415